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Chapter 3/4

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Psychology 1000

CHAPTER THREE: The Neural Bases of Behaviour - to understand how the brain controls our experience and behaviour, we must understand how its individual cells function and how they communicate with one another Neurons - specialized cells called neurons are the basic building blocks of the nervous system - the nerve cells are linked together in circuits - each neuron has 3 main parts – cell body, dendrites and axon o cell body/soma – contains the biochemical structures needed to keep the neuron alive and carries the genetic info that determines how the cell develops and functions o dendrites –specialized receiving units that are like antennas that collect messages from neighbouring neurons and send them on to the cell body – incoming info is combined and processed o axon – conducts electrical impulses away from the cell body to the other neurons, muscles or glands – the axon branches out at the end to form axon terminals - neurons can vary greatly in size and shape - supported in their function of glial cells – surround the neurons and hold them in place and manufacture nutrient chemicals that neurons need, form the myelin sheath around some axons and absorb toxins and waste materials that might be dangerous - blood-brain barrier prevents many substances including a wide range of toxins from entering the brain Nerve Conduction - neurons do two important things – they generate electricity and they release chemicals - neurons function – own chemical substances is their source of energy, surrounded by a chemical membrane  protects the inner structure and acts as a filter that allows certain particles in body fluid to pass through, surrounded by a salty liquid environment - Action Potentials o AP is a sudden reversal in the neurons membrane voltage o depolarization occurs when the dendrites/cell body of a neuron are stimulated by axons from other neurons, small shifts occur in the cell membrane’s electrical potential o changes are graded potentials are proportional to amount of incoming stimulation o action potential threshold o AP obeys the all-or-none law; it either occurs at maximum intensity or it does not occur at all o graded potentials change membrane potential by acting on ion channels - The Myelin Sheath o a fatty whitish insulation layer derived from glial cells during development o interrupted at regular intervals by Nodes of Ranvier where myelin is thin or absent o creates an increased efficiency of neural transmission that results is partly responsible for the gains that infants exhibit in muscular co-ordination as they grow older o damage to the myelin sheath disrupts the delicate timing of nerve impulses, resulting in jerky, uncoordinated movements Synaptic Transmission - communicate (neurons) at a synapse, a functional (but not physical) connection between a neuron and its target - Neurotransmitters o neurons produce neurotransmitters, chemical substances that carry messages across the synapse to either excite other neurons or inhibit their firing o 5 steps:  synthesis, storage, release, binding and deactivation o in synthesis – chemical molecules are formed inside the neuron o stored – in synaptic vesicles with axon terminals o molecules are released into the fluid filled space o molecules cross the synaptic space and bind to receptor sites - Excitation/Inhibition/Deactivation o excitatory transmitters – this stimulation may exceed AP threshold and cause the post synaptic neurons to fire an action potential o hyperpolarizes – stimulating ion channels making membrane potential more negative  transmitters that create hyperpolarization are inhibitory in their function o every neuron is constantly bombarded with excitatory and inhibitory transmitters from other neurons and the interplay of these influences determines if the cell fires an action potential  Excitatory NT  Depolarizes membrane  increases chance of AP  Inhibitory NT  Hyperpolarizes membrane  decreases chance of AP o once a NT molecule binds to its receptor, it continues to activate/inhibit the neuron until its deactivated o happens two ways:  deactivated by other chemicals located in synaptic spaces that break them down into their chemical composition  re-uptake – transmitter molecules are reabsorbed into the presynaptic axon terminal o psychoactive drugs – target transmitters receptor and bind in place  2 effects – mimic transmitter or have no effect other than blocking - Specialized Transmitter System o acetylcholine (aCh)  excitatory transmitter at the synapses where neurons activate the muscle cell o Dopamine  enhances and inhibits o serotonin  influences mood, eating, sleeping and sexual behaviour o endorphins  reduce pain and increase feelings of well-being The Nervous System - body’s master control centre - 3 major types of neurons – sensory, motor, inter - nervous system can be broken down into 2 parts  central and peripheral Peripheral - all neural structures that lay outside of the brain and spinal cord - 2 major divisions o somatic – sensory neurons – specialized to transmit messages from eyes/ears/other receptors and the motor neurons that send from the brain and spinal cord to the muscles that control voluntary movements o automatic – controls glands/smooth muscles that form the heart, blood vessels, lining of the stomach and intestines involved in respiration, circulation, digestion and aspects of motivation, emotional behaviour and stress response  2 divisions  SNS and PNS  SNS – activation/arousal function and it acts as a total unit (fight or flight)  PNS – slows don’t body processes and maintains a state of tranquility (rest and digest) CNS - spinal cord which connects most parts if the peripheral nervous system with the brain and brain itself - The Spinal Cords o most nerves enter and leave nervous system by way of spinal cord  simple stimulus – response sequences (spinal reflexes), can be triggered at the level of the spinal cords without any involvement of the brain - The Brain o neuropsychological tests – psychologists have developed a variety of neuropsychological tests to measure verbal and non-verbal behaviours that are known to be affected by particular types of brain damage o destruction and stimulation techniques  electrical recording – EEG  brain-imaging – CT, PET, MRI The Hierarchical Brain - The Hindbrain o the brain stem – life support system – medulla is the first structure after leaving the spinal cord  important role in vital body functions – these functions occur automatically o medulla is 2-way through fare for all sensory and motor nerve tracts coming up from the spinal cords and descending from the brain o the pons lie just above the medulla – serves as a bridge carrying nerve impulses between higher and lower levels of the nervous system – cluster of neurons that help regulate sleep and are involved in dreaming and it contains motor neurons that control the muscles and glands of the face and neck and help control vital function - Cerebellum o motor coordination centre o muscular movement and coordination and plays a role in certain types of learning and memory o cerebellum regulates rapidly, complex changing movements that require exquisite timing - The Midbrain o reticular formation o the brain’s gatekeeper o acts as a sentry, both alerting higher centres of the brain that messages are coming and then either blocking them or allowing them to go forward o has an ascending and descending part o central role in sleeping, consciousness and attention o ascending rouses higher centres of the brain, preparing them to receive input from our sense organs o descending serves as a kind of gate through which some inputs are admitted and others are blocked out - The Forebrain o the thalamus  the brains sensory switchboard, the thalamus is an important sensory relay station, sometimes likened to a switchboard that organizes inputs from sense organs and routes them back to appropriate areas of the brain o basal ganglion  movement, surrounds the thalamus, voluntary motor control – especially initiating o hypothalamus  controls biological drives, important connections with endocrine system (hormone-producing glands), controls hormonal secretions that regulate sexual development, metabolism, and reaction to stress - Limbic System o memory and goal-directed behaviour o coordinate behaviours needed to satisfy motivational and emotional urges that arise in the hypothalamus o hippocampus is involved in forming and retrieving memories - The Cerebral Cortex o crown of the brain – not essential for physical survival but for quality of living – each hemisphere is divided into 4 lobes (frontal, parietal, occipital and temporal) o each is associated with specific sensory and motor functions  motor cortex – controls all muscles involved in voluntary movements, each hemisphere governs movement on the opposite side of the body, specific areas are represented in different parts of the motor cortex and the amount of cortex to each area depends on the complexity of the movements that are carried out by the body part  sensory – somatic sensory – receives sensory input that gives rise to out sensations – each hemisphere governs senses on the opposite side of the body certain cells are activated with certain stimulus  speech comprehension – 2 areas which are located in the cortex  Wernicke’s = temporal and comprehension  Broca’s = frontal and production  association cortex - found within all lobes of the cerebral cortex and is critically involved in the highest level of mental functions – “silent areas”  electrically stimulating them does not give rise to any response  frontal lobes – the human difference – prefrontal – executive function  mental abilities involving goal setting, judgement, planning and impulse control that allow people to direct their behaviour in an adaptive fashion  hemispheric lateralization – left and right brains  corpus callosum is a neural bridge that acts as a major communication link between the 2 hemispheres and allows them to function as a single unit  lateralization refers to the relatively greater localization of a function on one hemisphere of the other  the 2 hemispheres differ in cognitive features and functions and also their links with particular types of emotions Plasticity of the Brain - neural plasticity refers to the ability of neurons to change in structure and functions – environmental factors, particularly early in life, have notable effects on brain developments - a person’s ability to recover from brain damage depends on several factors – others things being equal, recovery is greatest early in life and declines with age - when neurons die, surviving neurons can sprout enlarged dendritic networks and extend axons to form new synapses – neurons can also increase the amount of NT substance they release so they are more sensitive to stimulation The Nervous System Interactions with the Endocrine and Immune System - the nervous, endocrine, and immune systems have extensive neural and chemical means of communication, and each is capable of affecting and being affected by the others - the endocrine system secretes hormones into the blood-stream – these chemical messengers affect many body processes – including the activities of the central and autonomic nervous systems – hormonal effects in the womb may produce brain differences in males and females that influence sex differences in ce
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