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Chapter 4

Chapter 4


Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens
Chapter
4

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Kacy Singh
October 12, 2010
1
Chapter 4: Biology of Behaviour
The Brain and Its Components
Structure of the Nervous system
x 3 major functions:
(a) Controlling behaviour
(b) Processing and retaining the information we receive from environments
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x Central nervous system: made up of the brain and spinal cord
o Communicates with rest of body through nerves ± bundles of fibres that transmit
information in and out of the central nervous system
o Peripheral Nervous system: nerves attached to spinal cord and base of brain sensory
information conveyed from sensory organs to brain and spinal cord
o Cranial Nerves: located at base of brain; information from head and neck region
reaches brain through these nerves
o Spinal Nerves: sensory information from the rest of the body reaches the spinal cord
and brain through these nerves
** cranial and spinal nerves also carry information away from the brain as the brain
controls muscles , etc.
x Human brain has three major parts (pg 92, figure 4.2):
(a) The Brain Stem: primarily controls physiological functions and automatic behaviours
(b) The Cerebellum: attached to the back of the brain system, controls and coordinates
movements
(c) The Cerebral Hemispheres: pair constitutes largest part of the human brain; developed
more recently and still have a lot of unknown features
x Brain and spinal cord are protected very well; brain is encased in a skull while the spinal cord
runs through a column of hollow bones known as vertebrae
x Meninges: 3 layer membrane structure which encloses both brain and spinal cord
o Cerebrospinal Fluid (CSF): a liquid that fills the space between the two Meninges,
providing liquid cushioning which surrounds the brain and spinal cord protecting
them from being bruised by the bones that encase them
x Blood ±Brain Barrier: a barrier between the blood and the brain produced by the cells in the
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the brain ± prevents toxic chemicals from entering the brain which could harm the neurons
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October 12, 2010
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x Cerebral Cortex or Grey Matter: covers the surface of the cerebral hemispheres
o Contains billions of nerve cells where perceptions take place, memories are stored
and plans are formulated and executed
o White matter: a set of nerve fibres which connect the Cortex to other parts of the
brain
x Cerebral cortex is very wrinkled; therefore more surface area which enables lots of nerve
cells to be contained there
o Gyri: bulges (fat parts sticking out)
o Fissures: groves (indents)
Cells of the Nervous System
x Neurons: nerve cells which are the elements of the nervous system; bring sensory
information to brain, store memories, reach decisions, and control the activity of the muscles
x Neurons can receive messages through other neurons, process the information and proceed
the information to other neurons
x Glia: assist neurons in their task; help neurons get from place of birth to final resting place,
manufacture chemicals that the neurons need to perform tasks, protect neurons from invading
micro-organisms (LIKE THE NEURONS MOTHER!!)
x Dendrites: tree-like growths attached to the nerve cell, so it can receive messages from other
neurons ± WUDQVPLWLQIRUPDWLRQGRZQWKH³WUXQN´WRFHOOERG\
x Soma: cell body; largest part of the neuron and contains mechanisms that control the
metabolism and maintenance of the cell
x Axon: nerve fibre which carries messages away from soma after it has made a decision to
other neurons for communication purposes ± the messages are called action potentials
o Myelin Sheath: substance which coats the axon
o Prevents axons from colliding with one another and therefore scrambling messages
o Also increases action potential
o Action potential is caused by the opening of some ion channels in the axon membrane
by the end of the axon nearest the soma; charges reverese and cause other ion
channels to open up (domino effect) until the terminal button is reached
x Terminal Buttons: ORFDWHGDWWKHHQGRIWKH³WZLJV´ZKHUHWKH\EUDQFKRII
o Neurotransmitter: chemical secreted by terminal button whenever action potentials
are sent down the axon; affects chemical of the other cells with which the neuron
communicates
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Kacy Singh
October 12, 2010
3
x Synapses: method of communication between neurons; connects terminal button of one
neuron and the membrane of another cell(neuron, muscle cell or gland cell)
o Presynaptic Neuron: neuron that sends messages (terminal button belongs to this)
o Postsynaptic Neuron: neuron that receives messages (detects transmitter substance
from terminal button)
x Two types of Synapses
1) Excitatory Synapses ± when terminal buttons release; the transmitter substance excites
the postsynaptic neurons and they are more likely to fire
2) Inhibitory Synapses ± do the opposite; lower the likelihood that the axons of the
postsynaptic neurons will fire
x When action potential reaches terminal button, causes it to release a small amount of
transmitter substance into the synaptic cleft (fluid filled space between terminal button and
post-synaptic membrane (receiver) ± postsynaptic and terminal button do not touch)
x Neurotransmitter Receptors: special protein molecules embedded in the postsynaptic
membrane which trigger the excited or inhibited reactions coming from the transmitter
substance of the terminal button
x Molecules of Transmitter substance attach to receptors and cause inhibitory or excitatory
actions to occur by opening ion channels; excitatory permit sodium ions to enter the neuron
while inhibitory permit potassium ions from leaving it
x Reuptake: process by which a terminal button retrieves the molecules of transmitter
substance that it has just released; terminates effect of the transmitter substance on the
receptors of the postsynaptic neuron
Drugs and Behaviour
Effects of Drugs on Synaptic Transmission
x Some drugs stimulate terminal buttons to release neurotransmitters continuously even though
axons are not firing
x Others prevent terminal button from releasing neurotransmitters even though the axon is
firing
x Some drugs mimic the effects of a particular neurotransmitter and directly stimulate certain
receptors (using master key to access receptor even though neurotransmitter is no there)
x Some drugs bind with receptors and do not stimulate them; causes a jam and actual
neurotransmitters can no longer access the receptors ± receptors blocked forever
x Some drugs delay process of reuptake; meaning the neurotransmitter will have its effect on
the receptor for a longer time
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