Biopsychology

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Department
Psychology
Course
Psychology 2220A/B
Professor
Scott Mac Dougall- Shackleton
Semester
Fall

Description
Brain and Behaviour Textbook notes Chapter 1: Biopsychology as a Neuroscience - What is Biopsychology Anyway?  The human brain is an amazing, intricate network of neurons – cells that receive and transmit electrochemical signals  Neuroscience is the scientific study of the nervous system and may prove to be the brain’s ultimate challenge, understanding itself  Biopsychology is just one discipline of many  The four major themes in this book include thinking clearly and becoming a critical thinker about biopsychology, clinical implications to help diagnosed abnormal disorders, learning the evolutionary perspective by comparative approach with other species and neuroplasticity showing that the brain is flexible 1.1 What is Biopsychology?  Biopsychology is the scientific study of the biology of behaviour – also called psychobiology, behavioural biology, or behavioural neuroscience  Hebb played a key role in its emergence in the 20 century – 1949- as he was the first to release a book with scientific theories for perceptions, emotions, thoughts and memories based on his own research and has ultimately paved the way for psychology 1.2 What is the Relation between Biopsychology and the Other Disciplines of Neuroscience?  Biopsychologists are neuroscientists who bring to their research a knowledge of behaviour and of the methods of behavioural research  The other disciplines that are relevant to biopsych are neuroanatomy, neurochemistry, neuroendocrinology, neuropathology, neural pharmacology and neurophysiology 1.3 What Types of Research Characterize the Biopsychological Approach  Research can involve humans or non human participants, can be pure or applied and formal or non experimental studies - Human and nonhuman subjects  Human subjects have an advantage over others because they can support their subjective feelings, they are cheaper, and they have human brains –which is ultimately what we want to know about  Nonhuman animals are studied because of the evolutionary continuity of the brain and they do have some advantages as well like the fact that they are simpler, so you can more easily learn about brain- behaviour interactions, insights can come from comparative approaches, and you can have more ethical leeway - Experiments and nonexperiments  The experiment is the method used to find out what causes what and as such it is almost single handily responsible for our modern way of life  Conditions need to be set for under which participants will be tested  There can be different groups in each condition called between subjects design or the same group can go through all the conditions called the within subjects design  The difference between the conditions is called the independent variable and the variable measured is assessing the effect of the independent is called the dependent variable  When there is more than one difference that can affect the dependent variable it is called a confounded variable so we must try to eliminate these as much as possible  Lester and Gorzalka demonstrated the Coolidge effect whereby a copulating male who becomes incapable of maintaining sex with one partner can often recommence with another but bottom line, experiments wondered whether it was disinterest or the fact that males tired out more easily. The experiment checked for lordosis – the arching of the back and found that the female would arch more for unfamiliar males  A quasiexperimental study is when there are impediments that make it impossible to assign subjects to particular conditions and the researchers use conditions in the real world to conduct the experiment  There are many more potential confounding variables with these because no random assignment takes place  Case studies are studies that focus on a single case of subjects which provides an in depth picture but their generalizability is never great because we are only looking at one individual - Pure and applied research  Pure research is research motivated primarily by the curiosity of the researcher and is done solely for the purpose of acquiring knowledge  Applied research is research intended to bring about some direct benefit to humankind  Pure research is more vulnerable to vagaries of political regulations because they do not have a direct intention to help out 1.4 What are the divisions of Biopsychology - Physiological psychology  This is the division that studies neural mechanisms of behaviour through the direct manipulation of the brain in controlled experiments like surgery and electrical manipulation  Usually this is on lab animals more  The emphasis is on research that contributes to the development of theories of the neural control of behaviour - Psychopharmacology  It focuses on the manipulation of neural activity and behaviour with drugs – much of which is applied  The main purpose is to develop therapeutic drugs - Neuropsychology  This is the study of psychological effects of brain damage in human patients – dealing almost all of the time with case studies, quasi experiments, etc  The cerebral cortex is most likely to be damaged by accident or surgery which is why it is focused on in this division  It is almost always applied so it facilitates diagnosis and this help the doctor prescribe treatment - Psychophysiology  This studies the relation between physiological activity and psychological processes in human subject  This can be done non invasively with EEGs, eye movement, muscle tension to measure the autonomic NS - Cognitive neuroscience  This is the youngest division which is the study of the neural bases of cognition which is higher intelligence processes  It is non invasively studied in human subject usually with fMRIs - Comparative psychology  The biological of behaviour is studied here by comparing the behaviour of different species in order to understand evolution, genetics and adaptiveness of behaviour  Some do it in the lab while some engage in ethological research – the study of animal behaviour in its natural environment  Two important points that often employ comparative psychology are evolutionary psychology focusing on understanding behaviour based on origins and behavioural genetics which is the study of genetic influences on behaviour 1.5 Converging Operations: How do Biopsychologists Work Together?  Progress is most likely when all of the approaches are used so that their strengths can overcome each other’s weaknesses. This approach is called converging operations  In evaluating biopsychological claims, it is rarely sufficient to consider the results of one study or even of one line of experiments using the same approach 1.6 Scientific Inference: How Do Biopsychologists Study the Unobservable Workings of the Brain  Scientists used empirical methods, their effects are observed but the processes themselves cannot be seen so we inference in scientific inference – measuring the observable to logically infer the nature of events we cannot see  Ex. The eye trick to find that an image’s position on the retina is what allows us to see movement 1.7 Critical Thinking about Biopsychological Claims  There are more case studies to think about – the bull that stopped when an electrode was stimulated – when there are several possible interpretations for a behaviour observation the rule is to give precedence to the simplest one, called Morgan’s Canon  The prefrontal lobotomy is the procedure in which the connections between the prefrontal lobes and the rest of the brain are cut as treatment for mental illness  More variations came through like the transorbital lobotomy which involved going in through the eye socket  The program of psychosurgery – any brain surgery performed for the treatment of mental illness – was based upon observations of chimps Chapter 2: Evolution, Genetics and Experience – Thinking about Biology of Behaviour  Knowledge is ingrained into us by the Zeitgeist, the general intellectual climate of our culture which is why sometimes our ways of thinking are contradictory to the facts 2.1 Thinking about the Biology of Behaviour: From Dichotomies to Relations and Interactions  The tendency to think about behaviour in terms of dichotomies is illustrated by two kinds: is it psychological or physiological? And is it inherited or is it learned? And both of these have proved to be misguided  Physiological or Psychological?  This question can be traced back to the ancient Greeks who started the idea and then it was reborn in the Renaissance where the church was being fought  Descartes suggested that life was composed of two elements: physical matter and the human mind  This Cartesian dualism made the idea that the body and the mind were separate widely accepted so now people still believe that behaviour is one or the other despite evidence that it is dualistic  Is it inherited or is it learned?  This is more commonly known as the nature- nurture debate  Most scientists in north America took after behaviouralist Watson who believed children were a blank slate  Then ethology, the study of animal behaviours in the wild, shed light on instinctive behaviours that were common in every species and therefore must be relatively innate  Problems with thinking about the biology of behaviour in terms of traditional dichotomies - Physiological or psychological dichotomy thinking runs into difficulty  This assumption, that some things are too complex for the human brain to do alone was challenged by evidence  Even the most complex things were shown to be due to the power of the brain through lesion and damaged brain research and the fact that some animals are now showing signs of things that we previously thought were distinctly humans  Self awareness is widely regarded as the hallmark of the human mind and is illustrated in a number of case studies  Oliver Sack’s patient, the man who feel out of bed, has asomatognosia, a deficiency in the awareness of parts of one’s own body due to damage in the right parietal lobe  The second case is Gallup’s research of self awareness in chimps, showing that even non humans who are assumed to have no mind have considerable psychological complexity, in this case, self awareness - Nature or nurture thinking runs into difficulties  The debate is always changing and reborn, for new definitions and understanding  Evidence always pops up for the existence of both nature and nurture so people started asking how much is genetic and how much is experience  At this point it is sufficient to know that neurons are present long before they are active, and the triggered activation is usually a result of experience - A model of the biology of behaviour  This model has been adopted by many and boils down to the premise that all behaviour is the interaction between the organism’s natural endowment, which is a product of evolution, its experience and its perception of the current situation 2.2 Human Evolution  Darwin was the first to suggest that species evolve, undergo gradual orderly change, from pre- existing species  He presented evidence through fossil records of progressively recent layers, he found striking structural similarities among living species which suggests they have evolved from one ancestor and saw the pattern of selective breeding  His main evidence came from direct observations of finches in the Galapogos islands where natural selection was when members of each species varied greatly and that the heritable traits that are associated with high rates of survival and reproduction are the most likely ones to be passed on, which leads to evolution in the survival of the most adaptive  Fitness was the ability of an organism to survive and contribute its genes to the next generation  A scientific theory is an explanation that provides the best current account of some phenomenon based on available evidence  Evolution and Behaviour  Although not as obvious as the ability to find food or defence territory, two important genes to pass on are those of social dominance and courtship display - Social dominance  Most species establish a hierarchy of social dominance through hostility, physical violence or just the threatening aspect  It is so important because dominant males copulate more and thus pass on their genes more  Dominant females are more likely to produce healthy babies which will survive to carry on the gene more readily  These higher up female chimps can maintain access to food storage more readily - Courtship display  These precede copulation in many species so it is important if the genes will get passed along  They also promote the emergence of new species, which are a group of organisms that are reproductively isolated. When a barrier discourages this, new breeding and new species occur and in this case, the barrier is behavioural when the courtship displays are inappropriate for their conspecifics (members of their own species)  Course of Human Evolution - Evolution of vertebrates  Chordates are animals with dorsal nerve cords, and then they had protective bones called vertebrates, the first of which were boney fish - Evolution of amphibians  When the first bony fish started the venture out of the water, it could briefly survive on land where they could escape to new schools for fresh water and new food so natural selection created lungs and legs and the first amphibian was created - Evolution of reptiles  They were covered with dry scales an laid shell covered eggs which reduced their reliance on watery habits so it can live without water or it has that option - Evolution of mammals  The first mammals fed their young from mammary glands, hence their name, in the Jurassic period  Soon they stopped laying eggs, and raised their young in a watery environment until they were mature enough for land. The platypus is the last mammal who lays eggs  Spending the first bit of life in the mom had survival value with long term security and added time for complexities to form  Now there are 14 orders, and we belong to primates - Emergence of humankind  Primates of the family that includes humans are called hominids which has two genera, Australopithecus and homo  Homo has two species – erectus (extinct) and sapiens  The Australopithecus eere upright but small and had small brains. The homo sapiens derived from them, with much larger brain capacities so they could use tools  This developed into the modern human who could walk upright, had large brains and opposable thumbs  Thinking about Human Evolution  Evolution doesn’t proceed in a single line (ex. Dense bush metaphor)  We have little reason to claim evolutionary supremacy  It is not always slow, evolution can be rapid triggered by sudden changes in the environment (palaeontologists still debate whether humans were the result of a quick cooling of the earth or a steady transformation over time)  Only the tips of the branches of the evolutionary tree have survived (fewer than 1%)  Evolution doesn’t progress to perfection – its a tinkerer, and only produce a change that may provide a bit of an advantage to adapt to the environment at the time  Not all existing behaviours are adaptive – there are spandrels, or by product of adaptive things, or things that were adaptive before are no longer because the environment had changed (the appendix)  Not all existing adaptive characteristics evolved to their current function. Some called exaptations evolved to perform one function and later were co-opted to perform another  Similarities between species doesn’t necessarily mean they were from one common ancestor. Things from a common ancestor that have similarities are homologous, and things with similarities without a common origin are analogous  The similarities between analogous features comes from convergent evolution, which is unrelated species of similar solutions to the same environmental demands  Evolution of the human brain  Early research on the brain focused on size in the assumption that brain size and intelligence were interconnected. This was disproved, since larger animals that are not overly intelligent have matched large brains  A more reasonable approach is to compare the evolution of different brain regions like the brain stem separate from the cerebrum  A schematic representation of the relative size of cerebrums and brain stems shows us that the brain has increased in evolution, and most has occurred in the cerebrum, and finally that there is an increased number of convolutions, and increase surface area over the time of evolution in the cerebral cortex  Evolutionary Psychology: Understanding Mate Bonding  Evolutionary psychologists try to understand human behaviours through a consideration of pressures that led to their evolution  Some of the most interesting findings in this field revolve around sex differences in mate bonding  Promiscuity is generally tied with men and such indiscriminate mating is the most common form of copulation  Sometimes males and females do form mating bonds – enduring mating relationships with members of the other sex and most mammals do this  The idea is that female mammals form children in small numbers and of helpless, slow developing young so the mothers need father’s care to promote successful development for the genes to get passed along  The pattern of male bonding that is most common in mammals is polygyny, where one male bonds with many females because females need to make the bigger contribution if she is pregnant  Because each female can only produce so many children, she must be selective with who she passes her genes to and therefore she wants to mate with fit males but males are less selective  Evidence for this comes from studying polyandry, where females are the promiscuous and this never happens in mammals, but may happen in species where the contributions of the male to reproduction are greater than the female’s. An example is the sea horse  Because of the usual selectivity of females, males need to be competitive because they need to pass along their genes  Some are monogamous, where mate bonding is enduring. This happens in humans but usually not in other mammalian species  This goes on the basis that a women can raise more and more fit offspring if she has help  Thinking about Evolutionary Psychology  The forgoing evolutionary theory of mate bonding sparks interest into aspects of human mate bonding including the fact that males value youth and attractiveness, which are both indicators of fertility, while women value power and earning capacity, physical attractiveness will tell whether a women will be with a man of high occupational status, the main courting display for women is improving attractiveness while in men it is highlighting power and resources and men are more likely than women to complete adultery  The study illustrates how evolutionary study can generate insight into complex psychological processes, emphasizes that humans are the products of millions of years of adaptation and stresses that humans are related to other species 2.3 Fundamental Genetics  Darwin didn’t understand how traits are passed along and why conspecifics are different  Mendelian Genetics  He studied the inheritance in pea plants  Dichotomous traits are ones that occur in one form or the other, never in combination  True breeding lines are ones in which interbred members always produce offspring with the same traits generation after generation  He found a dominant trait was one that overpowered the recessive trait, which is why a mix of brown and white seeds would not produce offspring that were half and half  An organisms observable traits is the phenotype, the traits that it can pass on is the genotype  Today we call each inherited factor a gene, and then he proposed that it takes two genes for each dichotomous traits to make an allele  Two identical genes are homozygous for that trait and two different genes are heterozygous for that trait  He also proposed that two kinds of genes for each dichotomous trait dominates the other in heterozygous organisms  Chromosomes: reproduction, Linkage and Recombination  Genes were found to be located on chromosomes, which are in the nucleus of the cell  The two genes that control each trait are located on the same locus, one on each chromosome of a particular pair  The process that creates gametes, or sex cells, is called meiosis when the chromosomes divide and one stays in each cell  Then the gametes meet to create a zygote with a normal two chromosomes, and this cell divides in mitosis in growth development  Meiosis occurs for the diversity in species... every person in the world except for identical twins will have different combinations of chromosomes  The first study of this linkage is conducted by Morgan with fruit flies to conclude that linkage occurs between traits that are encoded on the same chromosome  He then proposed that crossing over provided a solution to the solution of partial linkages and occurs during the first stages of meiosis  As a result of crossing over, parents rarely pass on intact cluster of genes to their children as a result of this genetic recombination so each chromosome is unique and spliced together  This is important because it provides diversity to ensure the survival of the human species and reduce mutations while also is the first means whereby a scientist can study a gene map  Chromosomes: Structure and Replication  Each chromosome is a double stranded molecule of DNA where each strand is a sequence of nucleotide bases attached to a chain of phosphate and deoxyribose, with nucleotide bases of adenine, thymine, guanine and cytosine – the sequence of which is our genetic code  Replication is the process of the DNA molecule to do mitotic division and so they are able to unwind  Sometimes this goes bad and results in a mutation, an accidental alteration in individual genes, sometimes this is lost in the gene pool, sometimes increases or decreases fitness  Sex Chromosomes and Sex-Linked Traits  A typical chromosome with matched pairs is the autosomal chromosomes but the exception is the sex chromosomes which have one pair, and come in X and Y. Traits that are influenced by sex chromosomes are sex linked traits, which are almost always controlled on the X because the Y is so small  Since females are XX they are twice as likely to inherit a dominant gene but men are more at risk with only one X, and are thus more likely to get recessive genes  The Genetic Code and Gene Expression  There are several kinds of genes but usually they are structural genes, which contain information to create a protein which are long chains of amino acids and control activity of all the cells  Operator genes control structural genes to determine whether or not each of its structural genes initiates the synthesis of a protein – whether or not it will be expressed  The control of gene expression by operator genes determines how a cell will develop, and they can be switched on or off  When they are off they are regulated by DNA binding proteins that turn them on – which is the main way genes interact with their environment  First the DNA unravels, providing a template for an RNA short strand, which replaces uracil instead of thymine and has a backbone of ribose instead of deoxyribose  This is now messenger RNA and can carry the genetic code from the nucleus to the ribosomes which can translate the genetic code and read the three letter codons, each of which adds a different amino acid  Transfer RNA is what brings the amino acid to the protein area until it reaches the stop codon whereupon the protein is released (transcription, and translation have taken place)  Mitochondrial DNA  The cell’s mitochondria, which are the energy generating spots in the cell, have their own DNA of which is mostly from the mother, and can have mutations which cause serious disorders as well  These mutations occur at a reasonably consistent rate and can therefore be used as an evolutionary clock and have told us that humans evolved from Africa  Modern Genetics  The human genome project’s purpose was to compile a map of the 3 billion bases that compose the human chromosome, and was completed in 2001  The most surprising result was that we have a small number of protein coding genes in relation to human complexity, suggesting that the current idea of how genes work is incomplete which focused the attention on other lines of research: - Repeal of the one gene – one protein law  It was once believed that each gene has the code for one protein but now that we know about the splicing, we know it’s complex  Alternative splicing is the mechanism by which the information stored in the genes is edited to make it possible for one gene to specify two or more proteins - Discovery of small RNA’s  A new class of RNA’s called small RNA’s have been found and can control DNA, turn off genes, control expression or cleave DNA into segments  These are changing the way scientists think about everything - Activity of pseudogenes  Pseudogenes are those that appear to have been damaged by mutation over the course of evolution. Only evolutionary scientists were interested to place their origins because they were thought to be inactive  Now, there is evidence that they become active over structural genes and seem to encode small RNA’s - The human genome project in perspective  The idea has shifted to understanding the product of the interactions between many genes and how they work with experience 2.4 Behavioural Development: The Interaction of Genetic Factors and Experience  Ontogeny is the development of individuals over their life span  Phylogeny is the evolutionary development of species through the ages  Selective Breeding of Maze Bright and Maze Dull Rats  Tyron argued that behavioural traits can be selectively bred with his experiments on the maze running of lab rats  He trained one group to complete the maze and left one group who would frequently make errors and mated them into offspring that are maze bright and maze dull  He kept selectively breeding them for 21 generations and in the end, the worse of the maze bright still made less errors than the best of the maze dull  He used a cross-fostering control procedure to see if it was the upbringing or the genes and found the nature predominantly mattered  To show that environment mattered to, they did the same experiment but with a rich environment and an impoverished environment and found that the rich environment could help maze dull rates overcome a lot  Phenylketonuria: A Single Gene Metabolic Disorder  This neurological disorder (PKU) showed us that it only takes one abnormal gene to cause a problem  It is diagnosed by high levels of the acid in urine, usually in the mentally retarded  It is a recessive gene which is why it is so rare. When they do have the homozygous disorder it is because they lack the enzyme to break down the acid and it accumulates, also lowering dopamine levels which consequently means abnormal brain development  If infants are found to have this in the blood as newborns they are put on a diet and usually they are okay as long as the treatment is done in the sensitive period for that trait  Development of Birdsong  This song warns off other males but is distinctly different from other species  The ontogenetic development is that the sensory phase a few days after hatching where they form memories of the adult bird songs, and add to their genetic predisposition to sing. They cannot latch on to the song of any other species and if they don’t hear the proper song in this phase, they won’t learn  The next stage is the sensorimotor phase when they twitter sub songs when they are several months old and auditory feedback is necessary  Most of these species are age limited learners where once crystallized the song doesn’t change, while some are open ended learners and can add new songs throughout their lives  The descending motor pathway comes from the high vocal center on each side of the brain to the voice box and it mediates dong production. Then the anterior forebrain pathway mediates song learning  The plasticity of the canary song is remarkable in 4 ways: the left part of the brain plays more of a role (replicating left language dominance in humans), the high vocal center is 4 times larger in male canaries than in females, the song control station doubles in size whenever singing season begins, and the seasonal increase in size results from the growth of new neurons not from increase in size of the existing ones – one of the first documentations of neurogenesis 2.5 The Genetics of Human Psychological Differences  Development of Individuals versus Development of Differences of Individuals  In the development of the individual, the effects of genes and experience are inseparable while in the differences, they are  The man and the panpipe metaphor to show that the variation comes from the man when a group is playing the same type of pipe (now try this with intelligence)  To assess the contributions of genes and experiences to the development of differences of individuals we study people with the same genetics: monozygotic twins who are genetically identical, and fraternal twins, who are like siblings but cuts out cohort effects  When studying twins who have been adopted, we have a good sense of how much genetics versus the environment play a role by comparing their scores with those of their biological parents and their adoptive parents  Minnesota Study of Twins Reared Apart  This study involved 59 pairs of identical twins and 47 pairs of fraternal twins who were reared apart as well as many who were reared together, ages ranging from 19 to 68 years and were tested on personality and intelligence  The results consistently showed that identical twins were more similar than fraternal twins despite being raised separately  The importance of this study is in the fact that it constitutes a particularly thorough confirmation of the results of previous adoption studies, it doesn’t make a point about the relative contributions of genes and experience to intelligence or personality  A heritability estimate is not about individual development, it is an estimate about the proportion of variability that occurred in a particular trait  Another overlooked point is that the genetic differences promote psychological differences by influencing experience by seeking out different environments  When a gene encourages a developing person to select experiences that increase the behavioural effects of the gene, the gene is said to have a multiplier effect Chapter 3: The Anatomy of the Nervous System – The Systems, Structures and Cells that Make Up Your Nervous System 3.1 General Layout of the Nervous System  Divisions of the nervous system  There is the central nervous system located in the skull and spine and the peripheral nervous system that is outside of these areas  The CNS is then divided into the spinal cord and the brain  The PNS is then divided into the somatic nervous system which interacts with the external environment and the autonomic nervous system which regulated the body’s internal environment  The SNS works through afferent nerves carrying signals from the senses to the CNS and efferent nerves carrying information from the CNS to the skeletal muscles  The ANS also has these types of nerves but instead of muscles, the info goes to organs  The autonomic nervous system has two kinds of efferent nerves going to the organs, the sympathetic nerves which are in the lumbar and thoratic regions of the spine while parasympathetic nerves come from the brain and the sacral  All symp and parasymp nerves are two stage neural pathways, projecting from the CNS and go part way to the organ or target before they synapse and then the second stage takes it the rest of the way  The functions tell us that the sympathetic nerves stimulate and mobilize energy sources in threatening situations, that each autonomic target receives a balance of both symp and parasymp inputs and that the symp changes are indicative of psychological arousal and parasymp is relaxation  Most of the nerves in the PNS are the from the spine, but the cranial nerves are from the brain  The functions are these are specific and can tell us a lot about their location  Meninges, ventricles and cerebrospinal fluid  There are three layers of membrane covering the brain and spine called the Meninges, with the outer meninx being the dura mater – tough and rigid, then the arachnoids membrane – spider web like, and under there is the subarachnoid space which has a lot of blood vessels and then there is the innermost meninx called the pia mater which adheres to the surface of the CNS  Also protecting the CNS is the cerebrospinal fluid which fills the subarachnoid space, the central canal of the spinal cord and the ventricles in the brain  The central canal is a small channel that runs the length of the spinal cord and the central ventricles are four large chambers in the brain  The fluid cushions the brain and is continuously produced by the choroid plexuses- networks of capillaries that protrude into the vessels of the pia mater  Excess fluid is absorbed through the dural sinuses which run through the dura mater and drain into large jugular veins in the neck  If this sinus is blocked and the fluid cannot escape it can be a condition called hydrocephalus and is treated by using a shunt  Blood-brain barrier  The brain can be harmed by chemicals so the blood brain barrier ensures that they are filtered due to tightly packed walls that prevent large molecules from getting to the brain  The large molecules that are needed are actively transported, and some small molecules like drugs can get in easily 3.2 Cells of the Nervous System  There are two types of cells in the nervous system called glial cells and neurons  Anatomy of neurons  Neuron cells are specialized for the reception, conduction and transmission of electrochemical signals - Neuron cell membrane  The neuron cell membrane is composed of a lipid bilayer, two layers of fat molecules which is embedded with proteins called channel proteins which passes through certain molecules while others are signal proteins which signal to the inside of the neuron when a molecule binds on the outside - Classes of neurons  A neuron with more than two processes extending from its cell body is classified as a multipolar neurons (most neurons), while some have one process which are called unipolar neurons and with just two processes it’s a bipolar neuron  Neurons with short axons or no axons are interneurons and their function is to integrate the neural activity within a single brain structure  There are two kinds of neural structures in the nervous system, those composed of cell bodies and composed of axons  In the central nervous systems the clusters of cell bodies are called nuclei and in the PNS they are ganglia  In the CNS the bundles of axons are called tracts while in the PNS they are nerves  Glial Cells: The Forgotten Majority  Glial cells are found in the CNS and way out number neurons  There are several kinds, ones with extensions that wrap around the axon are oligodendrocytes, and these extensions are rich in myelin to make a sheath which increases axonal conduction, which is the same as Shwann cells in the PNS  Each Shwann only has one mylien segment whereas myelin has more and Shwann can help with regeneration after damage  Microglia are the third class, and are smaller. They respond to injury or disease by multiplying and triggering inflammatory responses  Astrocytes are the next class, and are the largest. Their extensions cover the outer surface of blood vessels that course through the brain and make contact with neuron cell bodies. Their main function is passing chemicals from blood into CNS neurons and in blocking other chemicals whereas they were considered to be more like cleaners before 3.3 Neuroanatomical Techniques and Directions  Neuroanatomical technique  It is so hard to see the neurons and they are so tightly packed sow e have to prepare the tissue in certain ways - Golgi stain  Silver chromate was found to invade only a few neurons in each slice of tissue and strained them entirely black so that you could see an individual neuron - Nissl stain  The Golgi stain provided no indication of the number of neurons in an area of the nature of their inner structure  This new dye of cresyl violet penetrate all cells but bind to only the structures in neuron cell bodies so we can estimate how many there are - Electron microscopy  This is a technique that provides information about the details of neuronal structure through magnification  The result after using a substance and then shooting the electrons through is the electron micrograph which captures the structure in detail  A scanning electron microscope provides a 3D picture but cannot be as close up - Neuroanatomical tracing techniques  There are two different types: anterograde, forward tracing which is on axons that projects away from cell bodies and retrograde tracing which is backwards when we want to trace the path of axons from the terminal to the axon cell bodies  After either of these is done the brain is removed and sliced, which are then treated to reveal the locations of the injected chemical  Directions in the vertebrate nervous system  There needs to be coordinates in order to understand where to look, and in the body these coordinates are based on location to the spinal cord  Anterior is towards the nose end, posterior is toward the tail end, dorsal is towards the surface of the back or the top of the head and ventral means towards the surface of the chest of the bottom of the head  Medial means towards the midline of the body and lateral is away from the midline and towards the surfaces of the body  Since human heads are different because of the fact that we walk upright, the terms superior and inferior are often used to refer to the top and bottom of the primate head respectively  The brain can be cut on different planes: the horizontal sections, the frontal sections (vertical) and the sagittal sections, which cut the hemisphere in two  A section that cuts the hemispheres in two is a midsagittal section and one cut at a right angle to any long narrow structure like the spinal cord is called a cross section 3.4 The Spinal Cord  The spinal cord comprises two different areas an inner H shaped core of gray matter and a surrounding area of white matter  Gray matter is mostly unmyleinated interneurons and cell bodies whereas white matter is myelinated neurons  The two dorsal arms of the spinal gray matter are called dorsal horns and the two ventral arms are called the ventral horns  Pairs of spinal nerves are attached to the cord, one on the left and one on the right at 31 levels of the spine. There are 62 in total and each one divides as it nears the cord and its axons are joined to the cord via the dorsal root or the central root  All dorsal root axons are sensory, unipolar, afferent neurons with their cell bodies grouped outside the cord to form the dorsal root ganglia  The neurons of the ventral roots are motor, multipolar, efferent neurons with their cell bodies in the central horns  Somatic ones go to the skeletal muscles and the autonomic ones go to ganglia and synapse of neurons that then go to organs 3.5 The Five Major Divisions of the Brain  The first recognizable tissue that develops into the brain are three swellings which turn into the hindbrain, midbrain and forebrain in the neural tube  These then grow into five swellings, the telencephalon, diencephalon, the mesencephalon (midbrain), the metencephalon and the myelencephalon (t is the top, and the rest are in alphabetical order to remember)  The telencephalon is the greatest growth area, and the rest turn into the brain stem, where the myelencephalon is the medulla 3.6 Major Structures of the Brain  Myelencephalon  This is the most posterior part of the brain, and composed of tracts carrying signals between the brain and the body  It includes the reticular formation which is a network of nuclei that occupies the central core of the stem. It plays a big role in arousal as well as sleep, attention, movement, muscle tone and reflexes  Metencephalon  Structures are here creating a buldge called the pons  The other major division here is the cerebellum, which is an important sensorimotor structure for fine motor control  Mesencephalon  This has two divisions, starting with the tectum which has little bumps called colliculi. The posterior pair, inferior colliculi, have auditory function and the anterior pair, superior colliculi, is visual functioning  The tegmentum is tracts of passage and has three more structures: the periaqueductal gray is the gray matter around the cerebral aqueduct, which connects the third and fourth ventricles and mediates pain reducing effects of opiates. The substantia nigra and the red nucleus are important in the sensorimotor area  Diencephalon  It has two main structures starting with the thalamus, which has two lobes, one of which sits on the top of the brain stem and the other of the third ventricle and both are joined by the massa intermedia which runs through the ventricle. On its surface is lamina, myelinated axons  The thalamus has nuclei, some are sensory relay nuclei that receive signals from sensory receptors, process them and then transmit them to appropriate sensory cortex areas. The lateral geniculate nuclei and the medial geniculate nuclei and the ventral posterior nuclei are important relay stations in the visual, auditory and somatosensory systems respectively. They all receive feedback  The hypothalamus is regulating motivated behaviours by controlled the release of hormones from the pituitary gland.  The hypothalamus also contains the optic chiasm where the optic nerves from each eye connect where they decussate (cross over) their fibres which are said to be contralateral (projecting from one side of the body to the other)and the nondecussating fibres are ipsilateral (staying on the same side of the body)  The mammillary bodies are spherical nuclei in the hypothalamus  Telencephalon  The largest part of the brain mediates the most complex functions like voluntary movement, sensory input and cognitive processes like learning, speaking and problem solving - Cerebral cortex  This covers the brain and is deeply convoluted to increase the surface area without increasing the overall size of the brain, but not all mammals have this, most are smoothed brained – lissencephalic  The number and size of the furrows seem to be related to the size of the body since every large mammal has furrows  The large ones are fissures, the small ones are sulci and the ridges between the sulci and fissures are called gyri  The two hemispheres are separated by the biggest fissure called the longitudinal fissure. The hemispheres are only connected by tracts called cerebral commissures, the largest one being the corpus callosum  The two main landmarks on the lateral surface are the central and lateral fissure which divide the brain into four loves: the frontal love, the parietal love, the temporal lobe and the occipital lobe  Among the largest gyri are the precentral gyri, the postcentral gyri, and the superior temporal gyri  The main function of the occipital love is visual input to guide our behaviour  There are two functional areas in the parietal: the postcentral gyrus analyses sensations and the remaining areas play roles in locating things and directing our attention  The cortex of each temporal love has three functional areas: the superior temporal gyrus is hearing and language, the inferior temporal gyrus is involved in identifying visual patterns and the medial portion of the temporal cortex is important in certain kinds of memory  Each frontal lobe has two distinct functional areas: the precentral gyrus and adjacent frontal cortex have motor function while the frontal cortex anterior to motor cortex performs complex cognitive functions like planning response sequences, evaluating outcomes of potential patterns of behaviour and assessing the significance of other’s behaviour  A lot of the cerebral cortex is the neocortex, which is new evolution by product, 6 layers. Characteristics that are important is that there are two types of cortical neurons: pyramidal cells are large multipolar and very long and stellate cells are small interneurons. It is also apparent that the layers differ from one another, plus it is apparent that many long axons and dendrites course vertically through the neocortex which is the basis for the columnar ganization; neurons in a given vertical column of neocortex often form a mini-circuit that performs a single function. There are variations in the thickness of the layers from area to area  The hippocampus is an area of the cortex that is not neocortex- it only has three layers. It folds back on itself to produce a shape that is, in cross section, like a seahorse  The Limbic System and the Basal Ganglia  There are several large subcortical nuclear groups in the area that are either part of the limbic system or the basal ganglia motor system  The limbic system is a circuit of midline structures that circle the thalamus which is involved with regulation of motivated behaviour  It includes the amygdale, the nucleus in the anterior temporal lobe  The cingulated cortex is the large strip of cortex in the cingulated gyrus  The fornix, the major tract of the limbic system , and the septum is a midline nucleus  Several tracts connect the septum and mammillary bodies with the amygdale and hippocampus to complete the circuit  The basal ganglia also contains the amygdale, plus the caudate, which forms a circle structure, with a center connected by fibre bridges called putamen, together known as the striatum  The rest of the basal ganglia is known as the globus pallidus and plays a role all together in the performance of voluntary motor responses  Especially interested in the pathway between the striatum from the substania nigra of the midbrain, as Parkinson’s derives from here  The nucleus accumbens is also of interest here because it is thought to play a role in rewarding effects of addictive drugs Chapter 4: Neural Conduction and Synaptic Transmission – How Neurons Send a Receive Signals 4.1 The Neuron’s Resting Membrane Potential  The membrane potential is the difference in electrical charge between the inside and the outside of a cell  Recording the membrane potential  You need to position the tip of an electrode inside the neuron called the microelectrodes and the tip of another on the outside extracellular fluid  The resting membrane potential  A steady potential of -70mV is recorded indicating that the potential inside the resting neuron is about 70 less than outside and this is the resting potential  With this resting state, it creates a charge across the membrane and it is a polarized neuron  The ionic basis of the resting potential  Charged particles are called ions  Ions are in continual motion and based on the concentration gradient, they tend to move from highly concentrated areas to areas of lower concentration  They are also evenly distributed because of the electrostatic pressure based on an accumulation of charges  Four kinds of ions build up the resting potential: K+, Na+, Cl- and negatively charged particles  Na and Cl are more concentrated inside the cell at rest whereas k is more concentrated on the outside while negative proteins are synthesized inside the cell and for the most part stay there until actively carried out by ion channels  Active involved using energy while passive transportation does not  In resting neurons, K and Cl ions pass readily through the membrane, Na passes with difficulty  Cl has an electrostatic charge of -70, the same as the membrane so the unequal distribution is maintained in balance between the tendency for Cl to move down their concentration gradient into the neuron and 70 mV or electrostatic pressure driving them out  K ions need a charge of 90mV pressure to keep them still  Na ions have 120 mV of pressure on them to make them rest  This means that K is continuously driven out by 20mV of pressure, Na being driven out with 120 mV but there is a mechanism keeping them there counteracting the influx of Na by pumping out Na at fast as they pass out  It is found that ion transport for K into the cell and Na out are not independent processes  The active sodium-potassium pumps continually exchange 3 Na inside for 2 K outside the neuron  Since this discovery, many other classes of transporters have been found 4.2 Generation and conduction of postsynaptic potentials  When neurons fire, they release NT’s which diffuse from synaptic clefts and interact with the next neuron  On the next membrane the NT’s may depolarize the receptive membrane (decrease mV) or hyperpolarize it (increase mV)  Postsynaptic depolarizations are called excitatory postsynaptic potentials (EPSP’s) because they increase the likelihood that the new neuron will fire while postsynaptic hyperpolarizations are called inhibitory postsynaptic potentials (IPSP’s) because they decrease the likelihood it will fire.  Both of these are graded responses, meaning that the amplitudes are proportional to the intensity of the signals that elicit them  They travel passively from their sites of generation at synapses on the dendrites or cell body at great speed and in a decremental fashion, meaning they decrease in amplitude as they travel through the neuron and thus never go very far 4.3 Integration of postsynaptic potentials and generation of action potentials  There are thousands of synapses in a small area and the effect of the neuron firing depends on a net effect, the balance of EPSP’s and IPSP’s  Before, it was believed that the AP’s started at the axon hillock but now we know it is in an adjacent section of the axon  If the sum of the IPSP’s and EPSP’s reaching this point is sufficient to depolarize the membrane to the threshold of excitation (65mV) an AP is generated near the axon hillock  The action potential is a massive but momentary reversal of the membrane potential from - 70mV to +50 mV. These are not graded responses, but are all-or-none responses, meaning they occur to their full extent or do not occur at all  Each multipolar neuron adds together all the graded excitatory and inhibitory potentials and decides to fire or not to fire based on their sum in the process called integration which can happen over space or over time  There are three possible ways of spatial summation, where two EPSP’s get bigger, two IPSP’s get smaller and a EPSP and a IPSP cancel each other out  Temporal summation is how potentials produced in rapid succession at the same synapse sum to form a greater signal by superimposing each other before they dissipate  Because EPSP’s and IPSP’s are transmitted decrementally, synapses near the axon trigger zone have been assumed to have the most influence in the firing of the neuron 4.4 Conduction of Action Potentials  The ionic basis of action potentials  The action of voltage activated ion channels – ion channels that open or close in response to changes in the level of the membrane potential produce and conduct AP  When the membrane is reduced to the threshold of excitation, voltage activated channels open and Na rushes in, driving the membrane potential from -70 to 50mV and the influx of Na stimulates the opening of potassium ion gates and they are driven out by their high internal concentration and by the positive internal charge repelling them  A second later the sodium ion gates close marking the end of the rising phase of the action potential and the beginning of repolarization by the continued influx of K ions  Once repolarization is achieved, the K gates gradually close, but since they don’t close quickly, too many K ions flow out and it is left hyperpolarized for a brief period of time  The AP only involves the small number of ions near the membrane therefore a single AP has little effect on the relative concentrations of various ions inside and outside the neuron, and the resting concentrations next to the membrane are rapidly re-established to resting potential  Refractory periods  There is a brief period 1-2 milliseconds after initiation of an AP during which it is impossible to elicit a second one, this is called the absolute refractory period, followed by the relative refractory period when it is possible for it to fire again  The relative period you would need a little more excitation for it to fire  This period is important because it prevents the charge from moving backwards and it is responsible for the fact that the rate of neural firing is related to the intensity of the stimulation  Axonal conduction of action potentials  The conduction of AP’s along an axon is nondecremental, which means they do not grow weaker and they are conducted more slowly than postsynaptic potentials  The conduction of IPSP’s and EPSP’s is passive along the axon whereas conduction of AP’s is active  Once an AP is generated is passively goes along the axon to sodium channels and opens them to generate a full blown AP and this is repeated over and over  Do not think of it as a wave but a series of discrete events  There is a backward AP when the wave is triggered in the hillock, and it goes back to the cell body and dendrites  The best analogy is the wobbly shelf with the mousetraps because it shows backwards AP, also called antidromic conduction, as well as the refractory period, and how it is nondecremental  Axon conduction in the natural direction from cell body to terminal buttons is orthodromic conduction  Conduction in myelinated axons  Fatty tissue called mylien so the charge goes through the nodes of Ranvier and “jumps” through the areas of mylien  Axonal sodium channels concentrate in the nodes  It travels passively, instantly and decrementally along the first segment of mylien to the new node  The transmission of AP’s in myelinated axons is called salutatory conduction and makes the process a lot quicker, which is why neurodegenerative diseases that damage the nervous system, tend to damage myelin and this causes a lot of issues  The velocity of axonal conduction  The speed of the conduction depends on the diameter of the axon (faster when larger) and when it is myelinated  The maximum in humans is 60 meters per second  Conduction in neurons without axons  Many neurons do not have axons or have very short ones, and many of these do not normally display AP’s  Conduction in these interneurons is typically passive and decremental  The Hodgkin-Huxley model and the changing view of dendritic function  This theory was proposed in the early 50’s  It talks about fundamental characteristics of neural conduction but fails to account for dendrite activity which were assumed to be a passive conductor of potentials  Dendrites have been found to be capable of generating potentials that are actively conducted away from the site of generation in either direction  The other bad findings involved dendritic spines, the nodules of various shapes that are located on the surface of many dendrites and the site of many excitatory synapses  The second finding is that some spines compartmentalize a dendrite that is, keeping chemical changes restricted to immediate areas of the synapse  The third finding is that spines can change rapidly in shape and number in response to neural stimulation 4.5 Synaptic transmission: Chemical transmission of signals from one neuron to another  Structure of synapses  There are axodendritic synapses which are those of the terminal buttons and dendrites  Many excitatory synapses also come from the dendritic spines  Axosomatic synapses are those of the axon terminal buttons on somas  These are the most common but there are others called dendrodendritic synapses which are often capable of transmission in either direction  Axoaxonic synapses are important because they mediate pre-synaptic facilitation and inhibition which allows them to selectively influence one particular synapse rather than the entire presynaptic neuron  There are directed synapses at which the site of NT release and the site of NT reception are in close proximity which is common but there are nondirected synapses too where the site of release is somewhat far from the reception site  In the nondirected, the NT’s are released from varicosities along the axon and its branches, and thus are widely dispersed to surrounding targets. These are called string of beads synapses because of their looks  Synthesis, packaging and transport of neurotransmitter molecules  Large NTs are called neuropeptides which are short amino acid chains with 3-36 amino acids  Small NTs are synthesized in the cytoplasm of the terminal button and packaged in the synaptic vesicles but the button’s Golgi complex  Once the vesicles are filled they are stored in clusters next to the presynaptic membrane while neuropeptides are assembled in the cytoplasm of the cell body on ribosomes and then are packaged in the vesicles and transported by microtubules to the buttons  The vesicles with the neuropeptides are larger and don’t congregate as close to the membrane  Now we think the vesicles may hold more than one NT, a situation called coexistence (usually with one neuropeptide and one small one)  Release of NT molecules  Exocytosis is the process of NT release, and is when vesicles with small NT’s congregate with the membrane that is rich with voltage activated calcium channels, which when stimulated by AP’s open and Ca+ ions enter the button which cause the vesicles to fuse with the membrane and empty contents into the synapse  The small NT’s are released in a pulse each time an AP triggers a momentary influx of ions through the presynaptic membrane while neuropeptides are released more gradually in response to general increases in the level of Ca ions  Activation of receptors by NT molecules  The NTs then bind to receptors in the postsynaptic membrane, and each receptors is a protein that contains binding sites for specific NTs  Any molecule that binds to another is called a ligand  The different types of receptors to which a NT can bind are called the receptor subtypes for that NT and are typically located in different brain areas and respond to the NT in different ways , enabling one NT to transmit different kinds of messages to different parts of the brain  Ionotropic receptors are those associated with ligand-activated ion channels whereas metabotropic receptors which are associated with signal proteins and G proteins  When a NT binds to an ionotropic receptor , the associated ion channel usually opens or closes immediately which induces a postsynaptic potential  When an NT binds to a metabotropic receptors, a subunit of the G protein breaks away and depending on the protein it could move along the inside of the membrane and bind to an ion channel inducing an EPSP or and IPSP or it can trigger then synthesis of a chemical called a second messenger (NTs are the first)  The second messenger diffuses through the cytoplasm and may influence the activities of the neuron in different ways like genetic transmission  Metabotropic receptors are more prevalent and their effects are slower, more longer lasting, more diffuse and more varied  One type of metabotropic receptor is autoreceptors, which have two unconventional characteristics: they bind to their neuron’s own NT and they are located on the presynaptic rather than postsynaptic membrane  They monitory the number of NT’s in the cleft and adjust release accordingly  Smaller NT’s tend to be released into a directed synapse and bind to a receptors that works with ion channels whereas neuropeptides are released and go to mainly metabotropic receptors that act through second messengers  Consequently, neuropeptides = transmission of slow, diffuse, long lasting signals, small NT = transmission of rapid, brief excitatory or inhibitory signals  Reuptake, enzymatic degradation and recycling  Two mechanisms terminate synaptic messages and keep them from staying the synapse and staying active  This is reuptake by transporters and enzymatic degradation  Reuptake is more common, being drawn back into the buttons  Enzymes are the ones that break down the NT’s, the main one being acteylcholinesterase  Once broken down, the NTs are recycled regardless the method of deactivation  Glial function and synaptic transmission  The importance of Glial cells reflect in the greater prevalence of these cells in intelligent organisms  Gap functions  These are narrow spaces between adjacent neurons that are bridged by fine tubular channels that contain cytoplasm, which is continuous so signals and small molecules can pass from one neuron to the next  We now know that they are an integral part of local neural inhibitory circuits and astrocytes have been found to communicate with neurons and other cells through gap functions  They have two advantages – communication is very rapid and they permit communication in either direction  One function seems to be between the dendrites of neurons to synchronize the activity of neighbouring neurons, playing a role in seizures when many neurons fire together 4.6 The neurotransmitters  The following are small NT’s – amino acids, monoamines and acetylcholine but there is also a fourth group called unconventional NT’s because there mechanism is unusual and there is only one class of large NT’s –neuropeptides  NT’s produce either an inhibitory or excitatory response not usually both  Amino acid NT’s  Most NT’s in fast acting areas are amino acids which are the molecule building blocks of protein  The most widely known amino acid NT’s are glutamate, aspartate, glycine and GABA  The first three we consume through proteins while GABA is synthesized from glutamate  Glutamate is the most prevalent excitatory NT in the CNS and GABA is the most prevalent inhibitory but it does have the opposite effects at some synapses  Monoamine NT’s  Each is synthesized from one amino acid and are slightly larger than them, plus their effects are more diffuse  They are usually located in the brain stem and are very branchy with lots of varicosities from which they are diffused  There are four kinds: dopamine, epinephrine, norepinephrine, serotonin, and are divided into subgroups catecholamines (the first three, made from tyrosine, converted to L-dopa, which can then turn into the other two) and indolamines (serotonin made from tryptophan) on the basis of structure  Ones that release norepinephrine are called noradrenergic and those that release epinephrine are adrenergic  Acetylcholine  This is a small NT that is made from an acetyl group mixed with a choline molecule  It is prevalent in junctions, at many synapses in the ANS and is broken down in the synapse by the enzyme acteylcholinesterase and neurons that release it are cholinergic  Unconventional neurotransmitters  These include soluble-gas NT’s including nitric oxide and carbon monoxide  These are produced in the neural cytoplasm and immediately diffuse through the cell membrane into the fluid and nearby cells and easily pass through because they are lipid soluble  Once inside another cell they stimulate the production of a second messenger and then are deactivated by being converted into another molecule – hard to study cause they last a few seconds  Soluble gas NT’s are involved in retrograde transmission which is the process of regulating the activity of presynaptic neurons in the feedback signals to the postsynaptic  The endocannabinoids are ones similar to THC which is the main psychoactive component to weed  This includes anandamide which are produced immediately before they are released and are synthesized from fatty acids and release from dendrites having most effect of the presynaptic neurons, inhibiting subsequent synaptic transmission  Neuropeptides  The action of the neuropeptide depends on the sequence of amino acids that makes it  It is usual to loosely group neuropeptide transmitters into five categories: pituitary peptides – hormones, hypothalamic peptides – hormones form hypothalamus, brain-gut peptides – first found in gut, opioid peptides- similar in structure to opium and miscellaneous peptides – contains all the other neuropeptides 4.7 Pharmacology of Synaptic Transmission and Behaviour  To study the effects of NT’s, researchers administer drugs that have particular effects and then assess the effects of the drugs on behaviour  There are two distinct effects on synaptic transmission: they facilitate it (agonists) or inhibit it (antagonists)  How drugs influence synaptic transmission  The following steps are common amongst most NT’s: 1. Synthesis of NT, 2. Storage in vesicles, 3. Breakdown in cytoplasm of anything leaking from vesicles, 4. Exocytosis, 5. Inhibitory feedback via autoreceptors, 6. Activation of postsynaptic receptors, and 7. Deactivation  Agonist and antagonist drugs affect these processes, for example, some agonists of a NT bind to postsynaptic receptors and activate them, whereas antagonists called receptor blockers, bind to the receptor without activating them and blocking the function of the usual NT  Behavioural pharmacology: three influential lines of research  Each line of research lead to the discovery of an important principle of NT function and illustrates how drugs were used  Wrinkles and darts: discovery of receptor subtypes  It was originally thought that there is one kind of receptor for each NT until acetylcholine was researched which sometimes bind to nicotine or to muscarine (nicotinic and muscarinic receptors)  These two have different modes of action and different behavioural effects  In the PNS, nicotinic is between motor neurons and muscle tissue (ionotropic)whereas muscarinic is in the ANS and is metabotropic  Atropine, which is the main ingredient in belladonna, is a receptor blockers that exerts its effect to muscarinic receptors and blocking effects of acetylcholine and disrupts memory  A curare is a poison and is a receptor blocker at cholinergic synapses but act at nicotinic receptors, blocking transmission to neuromuscular levels and causing paralysis  Botox is a neurotoxin released by a bacterium and is a nicotinic antagonist but it blocks the release of acetylcholine at neuromuscular junctions, which in minute doses in sites it can reduce tremors and reduce wrinkles  Pleasure and pain: discovery of endogenous opioids  Opium has always been used for pleasurable effects and has made morphine which is an effective analgesic  These receptors are generally found in the cerebral aqueduct which connects the third and fourth ventricles called the periaqueductal gray. Small morphine amounts injected into this area creates a strong analgesia  The existence of the opioid receptors in the brain suggests that opioid like chemicals occur naturally in the brain  Several families of endogenous (occurring naturally in the body) opioids were found starting with enkephalins and endorphins – all are neuropeptides and their receptors are metabotropic  Tremors and insanity: discovery of antischizophrenic drugs  Parkinson’s disease played a major role in the discovery of drugs to treat schizophrenia  After 3 weeks, two drugs were found to help schizophrenia, and induce mild Parkinson’s symptoms like tremors  Researchers knew that Parkinson’s is associated with the degeneration of the main dopamine pathway of the brain and that the dopamine agonists –cocaine and amphetamines- produce a temporary schizophrenia  These findings put together show us that schizophrenia is caused by excessive activity at dopamine synapses and thus dopamine antagonists would help Chapter 6: Visual system: How We See  An interesting study is Mrs. Richards and fortification illusions with her headaches 6.1 Light enters the eye and Reaches the Retina  If there is no light, there is no vision  Light is thought of as a photon particles travelling through space or a wave of energy. Light behaves in both ways  The waves are between 380 and 760 nm in length and the human visual system responds to them, some we can see or some we cannot  Wavelgnth and intensity are important properties – the first because it describes colour and the second because it is the perception of brightness  Ex. An intense light is 700 nm in bright red  The Pupil and the Lens  The amount of light reaching the retinas is regulated by the irises which give our eyes their colour  Light enters through the pupil, the hole in the iris, which can adjust to the amount of light they want to let in representing a compromise between sensitivity and acuity  When illumination is high and sensitivity is not a factor, the pupil constricts so the image is sharper and there a greater depth of focus  When the pupil dilates it lets light in but sacrifices acuity  Behind the pupil is the lens which focuses incoming light on the retina such that when our gaze it on something near, the ligaments holding the lens is adjusted by ciliary muscles and the lens assumes a shape that increases the refraction of the light and brings near objects to a focus  The focus on a distant object is when the lens flattens  By moving the lens, we are accommodating  Eye Position and Binocular Disparity  The reason we have two eyes is to see in every direction without moving their heads and sacrifices the ability to see behind as that what is in front can be viewed through two eyes so we can see 3D images and depth  The movement of the eyes is coordinated to converge (turn inward) to see the object in both retinas. This is greatest when looking at things close up  Because the eyes see the world from slightly different perspectives, called binocular disparity, it can create two images which constructs depth 6.2 The Retina and Translation of Light into Neural Signals  The retina is composed of give layers neurons receptors, horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells which all have subtypes as well (amacrine and horizontal specialized for lateral communication which is across major channels of sensory input)  The retina is in a sense inside out: light reaches the first receptor layer only after going through the other four and then once they have been activated, the neural message is transmitted back out through the retinal layers to the retinal ganglion cells whose axon project across the retina before going in a bundle and exiting  The order is: retinal ganglion cells, amacrine cells, bipolar cells, horizontal cells, cone and rods  The inside out arrangement creates the problem of the blind spot and the fact that light entering is distorted by the retinal tissue through which it must pass  The latter problem is minimized by the fovea, a spot on the retina where high acuity seeing occurs because if thinning of retinal ganglion cell layer, reducing the distortion  Completion is the filling in of the visual system in the place of the blind spot, which makes it hardly detectable  This completion is not a response to blind spots but tells us that the visual system takes key information from the object about edges and location in order to perceive the entire object  For instance, the colour and brightness of a large surface are not perceived directly but are filled in a process called surface interpolation  Cone and Rod Vision  There are rod and cone receptors in the retina  From the observation that rod retinas were in the night and cone retinas in day, the duplexity theory emerged that cones and rods mediate different kinds of vision  Photopic visions (cone mediated)predominates in good lighting and provides high acuity coloured perceptions  Scoptopic vision is rod mediated and occurs when there is not enough light to activate cones, however the acuity is a cost as well as colour  The differences occur because of a difference in the way the systems were wired, as they were is a large difference in convergence between the two systems  The output of hundreds of rods can converge onto one retinal cell whereas only a few cones can converge onto a retinal cell  Cones and rods also differ in their distribution on the retina as there are no rods in the fovea and at the boundaries of the fovea there is an increase in rods  The density of rods reaches a maximum at the center of the focea  There are more rods in the nasal hemiretina (retina next to the nose) than in the temporal hemiretina (next to the temples)  Spectral sensitivity  More intense lights appear brighter but wavelength influences this as well because our system is not equally sensitive to wavelengths  There is a intensity represented at different wavelength graph called a spectral sensitivity curve  There are two curves, the photopic spectral sensitivity curve and the scotopic spectral sensitivity curve  They are determined in human through experiments where subjects judge the relative brightness of different wavelengths of light shone on the fovea  Under phototopic conditions, the visual system is sensitive to wavelength of 560 nm so 500 is more intense than 560  Under scotopic conditions, the visual system is max sensitive to 500 nm so a 560 is more intense than 500 nm  This creates the interesting visual effect transition from photopic to scotopic visions called the Purkinjhe effect where yellow and red flowers look bright in the day but at night the blue stood out  Eye movement  Our eyes are continuously scanning the visual field and our perception is the summation of the recent information – and it is because of this
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