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Chapter 4

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Queen's University
PSYC 100
Meredith Chivers

Chapter 4: Biology of Behaviour p. 86-125 The Brain and its Components - brain contains 10-100 billion nerve cells - Donald Hebb proposed a theory of the interaction of nerve cells to control behaviour, which was proven by neuroscientists the brain is organized into modules (clusters) of nerve cells that communicate together; individual molecules are connected to other neural circuits, receiving info from, processing, and sending the results to other modules different modules have different speicalized functions Structure of the Nervous System - brain has 3 major functions: controlling behaviour processing/retaining information from environmental stimuli regulating bodys physiological processes - nervous system divides into 2 parts, the CNS and PNS Central Nervous System - communicates with body through nerves - 2 major parts: brain o brain stem- one of the most primitive regions of brain controls physiological functions/automatic behaviour includes medulla, pons, and midbrain o cerebellum- controls posture and coordinates movements o cerebral hemispheres- largest part of brain, most recently evolved, covered by cerebral cortex spinal cord- collection of nerve cells attached to brain o controls simple reflexes (ie. pulls away from hot object) - vertebra: bones encasing spinal cord, consitutes vertebral column - meninges: three-layered set of membrane enclosing brain & spinal cord - cerebrospinal fluid (CSF): liquid filling space between two of the meninges, in which brain & spinal cord float protecting/cushioning them - capillaries (smallest blood vessels) in most of the body have small openings so chemicals can pass from blood into surrounding tissue blood-brain barrier: capillaries in the brain dont have these openings so fewer chemicals can pass from blood to the brain, protecting it - cerebral cortex: covers surface of the cerebral hemispheres, consists of: grey matter- layer of tissue containing nerve cells, abundant in cell bodies of neurons white matter- nerve cells connected to other parts of the brain, abundant in axons cerebral cortex is where perceptions take place, memories are stored, plans are made/executed gyri- bulges in the human cerebral cortex fissures- grooves seperating the gyri Peripheral Nervous System - contains nerves connecting CNS to body: cranial nerves- conveys info from head/neck region to brain and carry info away from the CNS to muscles and glands spinal nerves- conveys info from rest of body to brain and carry info away from CNS to muscles, gland, internal organs - divides into: autonomic nervous system (ANS)- uncontrollable behaviour o sympathetic nervous system- fight/flight response o parasympathetic nervous system- state of calm/digestion skeletal nervous system Cells of the Nervous System - neurons or nerve cells: consists of a cell body with dendrites and an axon whose branches end interminal buttons that synapse with muscle fibres, gland cells, or other neurons elements of the nervous system that receive info from other neurons, process it, and send it to another neuron - glia cells: of the CNS, supports neurons and provides them w. essential chemicals holds nerves cells together forms long fibres to guide developing neurons from its place of birth to its final resting place create chemicals neurons need for their tasks absorb chemicals that interfere with neuron functioning protect nerves by forming a myelin sheath around each nerve fibre - dendrites: branch-like growths attached to nerve cell body transmit electrochemical impulses to the nerve cells neurons in the brain have nerve cells that contain dendritic spines on the surface of dendrites - soma: cell body, largest part of the neuron controls metabolism and maintains the cell in most cells, receives messages from other neurons - axon: part of neuron attached to soma, ends in terminal buttons carries messages away from the nucleus and toward the terminal buttons which then transmit the message through action potential to another nerve cell many axons are insulated with the myelin sheath, increasing action potential in multiple sclerosis (MS), immune system attacks the myelin sheaths, stripping it away causing many axons to no longer function normally - terminal buttons: round swelling at the end of the axon of a neuron releasing chemical called the neurotransmitter - neurotransmitter: chemical released by terminal buttons that causes postsynaptic neuron to be excited or inhibited Action Potential - Helmholtz discovered that the axon transmission is slower than electricity: less than 30m/s - membrane of an axon is electrically charged - resting potential: -70mv (outside charge of axon is positive) - action potential: brief electrochemical event carried by an axon from the soma of the neuron to terminal buttons, causes release of neurotransmitter reversal in the electric charge of axon - the electric charge is caused by unequal distribution of ions in the axon and in the fluid around it - ions: positively/negatively charged particles; produced when substances dissolve in water - ion channel:a special protein molecule located in the membrane of a cell; controls the entry orexit of particular ions can open and close membrane of axon contains Na+ and K+ channels - ion transporter: a special protein molecule in the membrane of a cell; actively transports ionsinto or out of the cell work like pumps need energy of the cell to move ions - action potential is caused when some ion channels open: Na+ ions enter, reversing the membrane potential reversal at this point causes nearby ion channels to open causing another reversal at the new point also, continuing until the terminal buttons action potential is very brief - Na+ channels close, K+ channels open, allowing K+ to exit cell this restores the normal electrical charge eventually ion transporters pump Na+ ions out and K+ ions back in - all-or none law: action potential will either occur if enough stimuli is given or will not occur, once triggered it travels down to the end of the axon - messages not conveyed by a single AP, info is repd by axons rate of firing sensory neurons receive info from sensory organs, sending to brain o strong stimuli trigger high rate of firing in axons of sensory neurons that receive visual information motor neurons: neurons whose terminal buttons from synapses with muscle fibres o high rate of firing in axons of motor neurons causes strong muscular contractions Synapses - synapse: the junction between the terminal button of one neuron and the membrane of a musclefibre, a gland, or another neuron neurons communicate with other cells by means of synapses - presynaptic neuron: neuron whose terminal buttons form synapses with and excite/inhibitanother neuron releases the neurotransmitters - postsynaptic neuron: neuron with which the terminal buttons of another neuron form synapsesand that is excited/inhibited by that neuron receives the message/detects the neurotransmitters - a neuron can be connected with many terminal buttons - the relation between a motor neuron and a muscle when there is an AP in the motor neuron, all the muscle fibres that have synapses with it willcontract a short twitch one muscle has many muscle fibres and so one muscle must be controlled by many motorneurons strength of muscular contraction is proportional to rate of firing of the axons 2 types of synapses: excitatory synapse: makes it more likely that the axons of postsynaptic neurons will fire o if there are many of these, the axon will fire at a high rate inhibitory synapse: makes it less likely that the axons of postsynaptic neurons will fire o if there are many of these, the axon will fire at a low rate or not at all - terminal buttons contain many synaptic vesicles, filled with molecules of the neurotransmitter - neurotransmitter receptor: a special protein molecule located in the membrane of thepostsynaptic neuron that responds to molecules of the neurotransmitter - neurotransmission: when AP reaches terminal button, neurotransmitters are released into the synaptic cleft (fluid-filled space between the presynaptic and postsynaptic membranes; terminal button releases transmitter substance into this space) neurotransmitters attach to the receptor molecules and activate them receptor molecules produce excitatory/inhibitory effects on the postsynaptic neuron by opening ion channels o excite: allow sodium ions to enter- o inhibit: allow potassium ions to leave- - myasthenia gravis: disorder where the immune system attacks neurotransmitter receptors - like the AP, the excitation/inhibition produced by a synapse is brief, they are terminated by reuptake - reuptake: process by which a terminal button retrieves the molecules of transmitter substance that it has just released; terminates the effect of the transmitter substance on the r
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