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Chapter 3

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University of Toronto Mississauga
Dax Urbszat

Chapter 3 Monday, September 23, 2013 12:32 PM CHAPTER 3: THE BIOLOGICAL BASES OF BEHAVIOUR - Neuropsychology:study of brain - Brain respondswith measurable electrical activity when stimulated Communication in the Nervous System - Behaviour depends on the rapid information processing - Nervous system is a complex communication network in which signals are constantly begin transmitted, received, and integrated - Nervous Tissue: The Basic Hardware - Nervous system is living tissue composed of cells - Cells fall into two major categories: glia and neurons - Neurons are individual cells in the nervous system that receive, integrate, and transmit information ○ Basic link in communication between nervous system ○ Diagram of neurons ○ Soma or cell body, contains the cell nucleus and much of the chemical machinery common to most cells ○ Dendrites are the parts if a neuron that are specialized to receive information ○ Information flows into the cell body and then travels away from the soma along the axon ○ Axon is a long, thin fiber that transmits signals away from the soma to other neurons or to muscles or glands  They may branch to other axon to communicate with each other  Axons are wrapped in cells with high concentration of a white, fatty substance called myelin  Myelin sheath is insulating materials, derived form glial cells, that encases some axons □ Helps speed up the transmission of signals that move along the axon □ Multiple sclerosis is due to a degeneration of myelin sheaths ○ At the end of axon ends are terminal buttons, which are small knobs that secrete chemicals called neurotransmitters  These chemicals serve as messengers that may activate neighboringneurons ○ The point where neurons interconnect is called synapse, which is junction where information is transmitted form one neurons to another - Glia are cells found throughout the nervous system that providevarious types of supportfor neurons ○ Much smaller than neurons ○ Account for 50% of brain volume ○ Glial cells supplynourishmentto neurons, help remove neurons' waste products, and provideinsulation around many axon ○ Research finding states that glial cells paly an important role in memory formation ○ Alzheimer's disease: deterioration of glial tissue ○ Schizophrenia: impaired neural-glial communication The Neural Impulse: Using Energy to send information - Neural impulse: nature of signal - The Neurons at Rest: A Tiny Battery ○ Hodgkins and Huxley learned that neural impulse is a complex electrochemical reaction ○ Both inside and outside the neurons are fluids that contain electrically charged atoms and molecules called ions ○ The cell membrane is semipermeable, permitting movement of some ions ○ +ve charged sodiumand potassium and -ve charged chloride ions flow back and forth across the cell membrane ○ The difference in flow rate leads to a slightly higher concentration of negatively charged ions inside the cells The resulting is a tiny battery, a store of potential energy ○ The resulting is a tiny battery, a store of potential energy ○ The resting potential of a neuron is its stable negative charges when the cells is inactive - The Action potential ○ As long as the voltage of neurons remains constant, then no message is begin sent ○ When stimulated , channels in its cells membrane open, briefly allowing +vely charged sodiumions to rush in ○ An action potential is a very brief shift in neuron's electrical charge that travels along an axon. ○ After the signal in fired, the channels that open to flow of sodiumions. Closes ○ The absolute refractory period is the minimum length of time after another action potentials during which another action potential cannot begin - The All-or-None law ○ The action potential is the same size if a neuron fires or does nor ○ The action potential is all or nothingevent, neurons can convey information about the strength of a stimulus. ○ Various neurons transmit neural impulses at different speeds. The Synapse: Where Neurons Meet - The neural impulse functions as a signal - Successful signal must be transmitted to adjust neuron - Takes place in a junction called synapses - Sending signals: Chemical as Couriers ○ The two neurons do not touch in the synapse ○ They are separated by the synaptic cleft, a microscopic gap between the terminal button of the one neuron and the cell membrane of another neuron ○ The signal sent down the axon needs to cross this gap to permit communication ○ The neuron that send the signal across the gap is called presynaptic neuron and the neuron that receives the signal is called postsynaptic neuron ○ How the message travel through the gap?  The arrival of an action potential at the axon's terminal buttons triggers the release of neurotransmitters  Neurotransmitters are chemicals that transmit information from one neuron to another  In the terminal buttons, these neurotransmitters are stored in synaptic vesicles  The neurotransmitter are released when these vesicles fuses with the membrane of the presynaptic neurons, and the content spills out into the synaptic cleft  Neurotransmitter diffuse across the synaptic cleft to the membrane of the receiving neurons  They may bind with special molecules in the postsynaptic cell membrane at the receptor sites  These sites are specifically tuned to recognize and respond to some neurotransmitters - Receiving signals: Postsynaptic Potentials ○ When a neurotransmitter combines with a receptor site combine, a reaction occurs at the membrane which then causes a postsynaptic potential (PSP), a voltage change at a receptor site on a postsynaptic cell membrane ○ PSP does not follow the all-or-nothing law, but PSP are graded, meaning they vary in size and they increase or decrease the probability of a neural impulse in the receiving cell in proportion to the amount of voltage change. ○ Two types of messages can be sent cell to cell: 1. Excitatory PSP is a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials 2. Inhibitory PSP is a negative voltage shift that decreases the likelihood that a postsynaptic neuron will fire action potential ○ The direction of the voltage shift and the nature of the PSP depends on which receptor sites are activated in the postsynapti c neurons ○ If the neurotransmitter do not bind to a receptor site, they drift way or inactivated by an enzymes ○ Most are reabsorbed into the presynaptic neurons through reuptake, a process in which neurotransmitters are sponged up from the presynaptic membrane ○ Reuptake allows the synapses to recycle their materials - Integrating signals: Neural networks ○ A neuron receives thousandsof signals from other neurons and can fire at thousandsof neurons ○ A neuron must integrate signals arriving at many synapses before it decided whether to fire a neural impulse ○ Most neurons are interlinked in complex chains, pathways, circuits, and networks ○ Our perception, thoughts and actions depend on patterns od neural activity in elaborate neural network ○ These networks consist of interconnected neurons that frequently fire together or sequentially to perform a certain function  The links in these networks are fluid, as new synaptic connection may be made while some old connection wither away  Elimination of old synapses play a bigger role in the sculpting of neural networks than the generation of new synapses  The elimination of old synapses or less active synapses is called synaptic pruning, and it is a key process in the formation of neural network that are crucial for communication through the nervous system Neurotransmitters and Behaviours - Nervous systems rely mostly on chemical to communicate information between neurons - Neurotransmitter are fundamental to behaviour, playingng a key role in everything from muscle movements to moods and mental health - Specific neurotransmitter work at specific kinds of synapses - A neurotransmitter must fit into a receptor site for binding to occur - Specific transmitter delivers signals at certain locations on cell membrane Helps reduce cross talk between densely packed neurons ○ Helps reduce cross talk between densely packed neurons Acetylcholine (Ach) Found through out nervous system - - It is the only transmitter between motor neurons and voluntary muscles - Ach is released by motor neuron to muscles - Ach also appears to contribute to attention, arousal, and memory - An inadequate supply of Ach in certain areas if the brain is associated with the memory loss seen in Alzheimer's disease - Activity of Ach may be influenced by other chemicals in the brain ○ Synaptic receptors sites are sensitive to specific transmitters, sometime they can be fooled by other substances  For example, smoking tobacco, some of the Ach synapses will be stimulated by the nicotine that arrives in your brain □ At the synapses the nicotine acts like Ach, it binds to the receptor sites for Ach, causing postsynaptic potentials (PSP) □ Nicotine is an Ach agonist, is a chemical that mimics the actions of a neurotransmitter ○ Not all chemicals that fool synapses is agonist  Some chemicals will bind to receptors but fail to produce PSP, they temporarily block the action of the natural transmitter by occupying its receptors sites, tendering them unusable □ Therefore they are antagonist, is a chemical that opposes the action of a neurotransmitter □ For example, the drug curare is an Ach antagonist, it blocks action at the Ach synapses, therefore muscles are unable to move Monoamines - Includes 3 neurotransmitter: dopamine, norepinephrine, and serotonin - Neurons used these transmitter to regulate many aspects of everyday behaviour - Dopamine (DA) is used by neurons that control involuntary movements ○ Degeneration of such neurons in a specific area of the brain causes parkinsonism, a disease marked by tremors, muscular rigidity, and reduced control over voluntary movements  The drug used to treat parkinsonism(L-dopa) is converted to dopaminein the brain in partially compensate for diminished dopamineactivity - Serotonin appears to play a prominent role in the regulation to sleep and wakefulness and eating behaviour ○ Evidence suggests that neural circuits using serotonin modulate aggression behaviour in animals and some evidence related to serotonin activity to aggression in humans - Abnormal levels of monoamines in the brain have been related to the development of certain psychological disorders ○ For example, people who suffer from depressive disorders appears to have lowered levels of activation at norepinephrine(NE) and serotonin synapses - Abnormalities in serotonin circuits has also been implicated as a factor for eating disorders and in obsessive-compulsivedisorders - Dopamine hypotheses asserts that abnormalities in activity at dopaminesynapses play a crucial role in the development of schizophrenia ○ therapeutic drug that tame schizophrenia known to be DA antagonists that reduce the neurotransmitter's activity - Temporary alternations at monoamine synapses also appear to account for powerful effects of amphetamines and cocaine ○ Increase activity of dopamine and norepinephrine synapses GABA and Glutamate - Neurotransmitter consists of amino acids: gamma-aminobutyric acid (GABA) and glycine - Only produce inhibitory postsynaptic potentials - GABA receptors are widely spread in the brain ○ Appears to be responsiblefor much of the inhibition in nervous system ○ Studies suggest the GABA is involved in the regulation of anxiety in humans and that disturbances in GABA circuits may contribute to many other anxiety disorders - Glutamate is also widely spread in the brain ○ Only has excitatory effects ○ Known for its contribution in learning and memory ○ Recently noted that disturbance in the glutamate circuit might have contributed to certain features if schizophrenicdisorders Endorphins - Internally produced chemicals that resemble opiates in structure and effects - Contribute to the modulation of pain Organization of the Nervous System - Communication in the nervous system is fundamental to behaviour The peripheral nervous system - Is made up of all those nerves that line outside the brain and the spinal cord. Nerves are bundles if neuron fibres (axons) that are routed together in the peripheral nervous system - Subdivided into: ○ Somatic Nervous System:  Is made up of nerves that connect to voluntary skeletal muscles and to sensory receptors  These nerves carry information from the receptors to skin, muscles, and joints to the central nervous system and that carry commands from CNS to muscle □ Requires two kinds of fibres  Afferent nerves fibres are axon carry information inward to the CNS from periphery of the body Efferent nerves fibres are axons that carry information outward form the CNS to periphery on the body  Efferent nerves fibres are axons that carry information outward form the CNS to periphery on the body  Somatic nerves are "two-way street" with incoming (afferent) and outgoing (efferent) lanes ○ Autonomic Nervous System - Is made up of nerves that connect to the heart, blood vessels, smooth muscles, and glands - Governed by the CNS - Controls automatic, involuntary,visceral functions that people don’t think about - ANS mediates much of the physiological arousal that occurs when people experience emotions - Fight-or-flight response - Can be subdivided into 2 branches □ Sympathetic division is the branch of the ANS that mobilizes the body's resources for emergencies  Activations slows down digestion process, drains blood flow from periphery, lessening breathing if injured  Sympathetic nerves sends signals to adrenal glands, triggering the release of hormones that ready the body for exertion □ Parasympathetic division is the branch of the ANS that generally conserves bodily resources  Active processes that allows the body to same and store energy  Parasympathetic nerves slow heart rate, reduce blood pressure, and promote digestion The Central Nervous System - Is the portion of the NS that lies within the skull and spinal column - It is protected by enclosing sheaths called meninges - CNS is bathed in its own special nutritive fluid called the cerebrospinal fluid (CFS), nourishes the brain and providecushion for it - The hallow cavities in the brain that are filled with CFS are called ventricles Spinal Cord - Connects the brain to the rest of the body through the peripheral nervous system - It is enclosed by the meninges and bathed in CFS - Is an extension of the brain - Spinal cord runs from the base of the brain to just below the waist - Hold bundles of axons that carry the brain's commands to peripheral nerves and that replay sensations from the periphery of the body to the brain - Paralysis occurs due to spinal cord damage The Brain - Is the upper part of the CNS that fills the upper portion of the skull - Integrate information from inside and outside of the body, coordinate body's actions, and enable human begins to talk, think, remember, plan, create, and dream Looking inside the brain: Research Methods Electrical Recordings - Electrical activities can be recorded - In 1929, German psychiatrist named Hans Berger invented a machine that could record broad patterns of the brain electrical activity from intact skull ○ Electrophotography(EEG) is a device that monitors electrical activity of the brain over time by means of recording electrodes attached to the surface of scalp ○ EEG recordings are translated into line tracing, commonly called brain waves ○ Different wave patterns are associated with different mental activity ○ Commonly used in the clinical diagnosis of brain damage and neurological disorders ○ In research application, brain waves can be used to determine specific behaviour or specific emotion Lesioning - Certain misfortunes lead to brain damage, and brain-behaviour-relationship have resulted from observations of behaviouralchanges in people who have suffered from brain injury in certain area of the brain - Famous case study conducted by Brenda Milner ○ Patient H.M, suffered from epilepsy as a child, a result from a bicycle accident ○ Treatment: portion of brain removed, including his medial temporal lobe, involving substantial portions if this hippocampusa nd amygdala ○ After surgery, suffered from amnesia, had good memory for events that occurred before the surgery, but he could not form new long-term memory - To study the relationship between brain and behaviourmore precisely, scientist sometimes observe what happens when specific brain structures in animals are purposely disabled - Lesioning involves destroying a piece of the brain ○ Usually done by inserting an electrode into a brain structure and passing a high-frequency electric current through it to burn the tissue and disable the structure Electrical stimulation of the brain (ESB) - Involves sending a weak electric current into a brain structure to stimulate (activate) it - The current is delivered through an electrode - Does not duplicate normal signals in the brain Transcranial Magnetic Stimulation (TMS) - Is anew technique that permits scientist to temporarily enhance or depress activity in a specific area of the brain - A magnetic coil mounted on a small paddleis held over a specific area of the patient's head, the coil creates a magnetic field that penetrates to a depth of 2cm penetrates to a depth of 2cm - In using TMS to investigate brain function, researchers typically suppress activity in a discrete area of the brain and then put subjects to work on specific type of perceptual or cognitive task to see if the virtual lesion interferes with performance of the task - Limitation is that this technique cannot be used in study of deep areas of the brain Brain-Imaging Procedure - CT ( computerized tomography) scan is a computer-enhanced x-ray of brain structure - Multiple x-ray are shot from many angels, and the computer combines then to create a horizontal slice of the brain - Has helped research uncover an interesting association between schizophrenia disturbance and enlargement of the brain's ventricles - PET (positron emission tomography) examines brain function, mapping actual activity in the brain over time ○ Radioactively chemical are introduced in the brain, they serve as markers for blood flow or metabolic activity in the brain, which can be monitored with x-ray ○ PET scan can provide colour-coded map indicating which areas if the brain becomes active with different activities ○ Can also be used to study activity of specific neurotransmitter - MRI (magnetic resonance imaging) can uses magnetic fields, radio waves, and computerized enhancement to map out brain structure ○ Produces 3D pictures of the brain ○ Helped provide information regarding depressive disorders - Functional magnetic resonance imaging (fMRI) is a new variation in MRI technology that monitors blood flow and oxygen consumption in the brain to identity area of high activity The Brian and Behaviour - Brain is divided into 3 major regions 1. The Hindbrain - Includes the cerebellum and two structures found in the lower part of the brainstem: the medulla and the pons - Medulla is attaches to the spinal cord and is in charge of largely unconscious but vital functions, including circulating blood, breathing, maintaining muscle tone, and regulating reflexes such as sneezing, coughing, and salivations - The pons ("bridge") includes a bridge of fibres that connects the brainstem with the cerebellum □ Consists of several clusters if cell bodies involved with sleep and arousal - Cerebellum ("little brain") is relatively large and deeply folded structure located adjacent to the back surface of the brainstem □ Critical to coordinationof movement and to the sense of equilibrium, or physical balance □ Plays a key role in organizing the sensory information that guides these movements □ Depressed when alcohol is consumed □ Damages can disrupt fine motor skills 2. The midbrain - Is the segment of the brain that lies between the hindbrain and the forebrain - Contains area that is concerned with integrating sensory processes - An important system of dopamine-releasing neurons that projects into various higher brain centres originates in the midbrain ○ Running through both the hindbrainand midbrain is the reticular formation  Contributes to the modulation of muscles reflexes, breathing and pain perception  Most known for sleep and arousal  Activity in the ascending fibres of the reticular formation contributes to arousal 3. The Forebrain - Is the largest and most complex region of the brain, encompassing a variety if structures, including the thalamus, hypothalamus, the limbic system and cerebrum - Thalamus, hypothalamus,and limbic system form the core of forebrain and located near the top of the brainstem - Above them is cerebrum: complex thought - The wrinkled surface of the cerebrum is the cerebral cortex-the outer layer of the brain - The Thalamus: A way station □ Thalamus is a structure in the forebrain though which all sensory information (except smell) must pass to get to the cerebral cortex □ Made up of cluster of cell bodies or somas  Each cluster is concerned with relaying sensory information to a particular part if the cortex □ Also plays an active role in integrating information from various senses - The Hypothalamus:A Regulator of Biological needs □ Hypothalamus is a structure foundnear the base if the forebrain that is involvedin the regulation of basic biological needs □ Lies beneath the thalamus □ Contains clusters of cells that have key functions  Control the ANS □ Serves as a virtual link between the brain and the endocrine system □ Plays a major role in the regulation of basic biological drives related to survival, including the 4 Fs: fighting, fleeing, feeding, and mating □ Contributes to the control of biological processes (hunger, thirst, temp regulation) The Limbic System: The seat of emotion - Limbic system is a loosely connected network of structures located roughly along the border between the cerebral cortex and deeper subcortical areas subcortical areas - Includes parts of the thalamus, hypothalamus,the hippocampus, amygdala, and other structures - Is involved in regulation of emotions, memory, and motivation - There are self-stimulation centers in the brain, many of them lie in the limbic system ○ The heavist concentration appears to be where the medial forebrain bundle passes through the hypothalamus - The cerebrum: the seat of complex thought ○ Cerebrum is the largest and complex part of the brain, includes the brain area that are responsible for complex mental activities ○ Cerebral cortex is the convoluted outer layer of the cerebrum  Cortex is folded and bent ○ Cerebrum is divided into two hemisphere  The cerebral hemisphere: are the right and left of the cerebrum  Hemisphere are separated by a longitudinalfissure that runs form the front to the back of the brain  These fissures descends to a thick band of fibres called the corpus callosum, which is the structure that connects the two cerebral hemispheres  Each hemisphere is divided into 4 parts called lobes, each are dedicated to specific purposes □ Occipital lobe: located at the back if the head, where most visual signals are send and visual processing is begun □ Partial lobe: forward of the occipital lobe, includes the area that registers the senses of touch, called the primary somatosensory cortex  Various section if this area receives signals from different parts of the body  Also involved in integrating visual input and in monitoring the body's position in space □ Temporal lobe: lies below the partial lobe, contains areas devoted to auditory processing called primary auditory cortex  Damages to the left side of the brain can impair the compression of speech and language □ Frontal lobe: the large lobe in the brain, contains the principle areas that control the movements of muscles called the primary motor cortex  When ESB is applied to this area, causes muscles to contract  Cortex is mostly devoted to fine controls rather than large control  The portion of the frontal lobe to the front of the motor cortex is the prefrontal cortex ◊ Accounts for 1/3 of the cerebral cortex ◊ Contributes to working memory, which is temporary buffer that process current information, reasoning about the relationship between objects and events; also types of decision making The plasticity of the brain - Bryan Kolb, neuroscientist, research suggested that the anatomical structure and functional organization if the brain in more "plastic" than assumed ○ Brain plasticity refers "the brain's ability to change structure and function" ○ He suggest that that experience is an important stimulant of brain plasticity and that experience affects dendritic length, synapses formation, and altered metabolic activity - Studies have shown that aspects of experience can sculpt features of the brain structure ○ For example, neuroimaging studies have shown that an area un the somatosensory cortex that receives inputfrom the fingers of the left hand is enlarged in string musicians who constantly use their left hand for stinging - Research have shown that damages to the incoming sensory pathways or the destruction of brain tissue can lead to neural reorganization ○ For example, scientist have amputated the 3rd finger of an owl monkey, the part in its cortex that formerly responded to the 3rd finger gradually became responsive to 2nd and 4th fingers ○ In blind people, areas in the occipital lobe that are normally dedicated to visual processing are "recruited" to help with verbal processing - Neural reorganization has also been seen in response to brain damage as healthy neurons attempt to compensate for the loss of neurons nearby - studies indicate that the adult brain can generate new neurons, process is called neurogenesis, the formation of new neurons ○ Research eventually showed that adult human brain can regenerate new neurons in the olfactory bulb and hippocampus ○ These new neurons migrate to areas in the cortex where they sprout axons and form new synapses with existing neurons - Its has been suggest the neurogenesis might contribute to learning - "stem cells" are unspec
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