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Chp 4 Textbook Notes

Course Code
Steve Joordens

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Chapter 4:
Biology of Behaviour
human brain = 1.5 kg
contains 10 billion 100 billion nerve cells and about as many helper cells
c nerve cells differ in shape, size, and chemicals they produce
c nerve cells organized into modules (clusters of nerve cells that communicate with each other) that are
connected through neural circuits to other modules that communicate with each other
Peirre Flourens suggested different parts of nervous system were responsible for different functions but
conflicting evidence now some functions more spread out
Donald Hebb (50 years ago) provided better understanding by showing that nerve cells are organized
into larger units functioning could be understood by individual cells and larger networks they comprised
Structure of Nervous System:
brain controls behaviour, processes and retains information we receive from environment, and regulates
body's physiological processes
c receives information from body's sensory receptors and is connected with muscles and glands of body
nervous system consists of two divisions:
c Central Nervous System brain and spinal cord
Spinal cord long, thin collection of nerve cells attached to base of brain and running length of
spinal column
contains circuits of nerve cells that control some simple reflexes (pulling away from hot)
communicates with rest of body through nerves
Nerves bundle of nerve fibres that transmit information between CNS and body's sense
organs, muscles, and glands
c attached to spinal cord and base of brain
c Peripheral nervous system cranial and spinal nerves; that part of the nervous system peripheral to
brain and spinal cord
consists of nerves that connect central nervous system with sense organs, muscles and glands
human brain has 3 major parts: brain stem, cerebellum, cerebral hemisphere
c lower part of cerebellum and brain stem projects beneath left cerebral hemisphere upper part is
normally hidden (see fig. 4.3)
Brain stem most primitive regions of brain, and its functions are basic ones control of physiological
functioning and automatic behaviour (amphibians have brain stem and simple cerebellum)
Cerebral hemispheres constitute large portion of brain
c contains parts of brain that evolved most recently: involved in behaviours of particular interest to
Cerebellum attached to bain of brain, looks like miniature version of cerebral hemispheres
c functions are control and coordination of posture and movement, especially rapid ones
brain is encased in skull and spinal cord runs through middle of hollow bones (vertebra: vertebral column)
both brain and spinal cord are enclosed in 3 layered set of membrane called meninges
float in clear liquid called Cerebrospinal fluid (CSF)
c fills between 2 meninges, providing cushioning
Cerebral cortex outer layer of cerebral hemisphere of brain, approximately 3 mm thick
c often referred to as grey matter contains billions of nerve cells (abundant in nerve cell bodies rather
than axons)
c where perceptions take place, memories are stored, plans are formulated and executed
c nerve cells in cerebral cortex are connected to other parts of brain by layer of nerve fibres called white

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shiny white appearance of substance that coats and insulates axons that travel trough area (axons'
myelin sheath)
c very wrinkled appearance full of bulges separated by grooves
bulges gyri
grooves fissures
they expand amount of surface are of cortex and greatly increase number of nerve cells more
complex the brain, larger cortex
Peripheral nervous system consists of nerves that connect central nervous system with sense organs,
muscles and glands
c nerves carry incoming and outgoing information
c sense organs detect changes in environment and send signals through nerves to central nervous
c brain sends signals through nerves to muscles (causing behaviour) and glands (producing adjustments
in internal physiological processes)
Nerves bundles of many thousands of individual fibres all wrapped in tough, protective membrane (look
like table clothes)
c nerve fibres transmit message through nerve, from sense organ to brain or from brain to muscle/gland
c these make up white matter and other axon tracts
c some attached to spinal cord and others to brain
Spinal nerves bundle of nerve fibres attached to spinal cord; conveys sensory information from
body and carries messages to muscles and glands
Cranial nerves 12 pairs, attached to base of brain; conveys sensory information from face and
head and carries messages to muscles and glands
Cells of Nervous System
Neurons nerve cell; consists of cell body with dentrites and an axon whose branches end in terminal
bittons that synapse to muscle fibres, gland cells, or other neurons
c elements of nervous system that bring sensory information to brain, store memories, reach decisions,
control activity of muscles
c assisted by glia
Glial cells cell of central nervous system that provides support for neurons and supplies them with
essential chemicals
c during development of brain, some types of glial cells form long fibres that guide developing neurons
from place of birth to final resting place
c manufacture chemicals that neurons need to perform tasks and absorb chemicals that might impair
neuron's functioning
c form protective insulating sheaths around nerve fibres
c serve as brain's immune system, protecting it from micro-organisms
Three basic parts of neuron:
c Soma cell body; largest part of neuron
contains mechanisms that control metabolism and maintenance of cell
receives messages from other neurons
c Dentrites treelike part of neuron on which other neurons form synapses
transmit information they receive down trunks to soma
c Axon long, thin part of neuron attached to soma; divides into a few or many branches, ending in a
terminal button
carries message away from soma toward cell with which neuron communicates action potential
(brief changes in electrical charge) also referred to as firing of an axon

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Two complex structures seen in neurons:
c dentritic spines small protuberance on surface of dentrite; appear on neurons in brain
synapse can occur on smooth dentrite or on dentritic spine
c terminal button round swelling at end of axon; releases transmitter substance
connect to dentrites, dentritic spine, soma, and axon on other neuron
secrete transmitter substance/neurotransmitter (chemical that causes postsynaptic neuron to be
excited or inhibited) whenever AP travels down axon
many axons insulated with myelin sheath
c myelin part protein, part fat
produced by glial cells that individually wrap themselves around segments of axon
c insulates axons from each other and prevents scrambling of messages
c increases speed of AP
multiple sclerosis immune system attack protein in myelin and so suffer from various sensory and
motor impairments
The Action Potential
travels less than 100 m/second
membrane of axon is electrically charged at rest is -70 milivolts with respect to outside
action potential brief electrochemical event that is carried by an axon from soma of neuron to its
terminal button; causes release of transmitter signal
c unequal distribution of + or - charge occurs inside axon and in fluid that surrounds it
c axon membrane contains ion channels special protein molecule located on membrane of cell which
controls entry or exit of particular ion
c ion transporters special protein molecule located in membrane of cell that actively transports ions
into or out of cell
use energy resource from cell to actively pump
outside of membrane is + charged and inside is charged
when axon is resting, ion channels are closed
AP is caused by opening of some ion channels in membrane at end of axon near soma opening permits +
charged sodium ions to enter, which reverses membrane potential at that location causing nearby ion
channels to open, producing reversal at that point too process continues all way down to terminal button
as soon as charge reverses, ion channels close and another set opens letting + charged potassium ions out
of axon restores normal charge
ion transporters pump sodium back out of cell and potassium back in
Synapse junction between terminal button of one neuron and membrane of muscle fibre, gland, or other
terminal button belongs to presynaptic neuron and sends out message (neurotransmitter) to postsynaptic
Motor neuron neuron whose terminal button forms synapse with muscle fibres; when AP travels down
its axon, associated muscle fibres with twitch
Two types of synapses:
c excitatory transmitter signal excites postsynaptic neuron increasing chances it will fire too
c inhibitory transmitter signal inhibits postsynaptic neuron decreasing chances it will fire
when AP reaches terminal button, it causes terminal button to release small amount of transmitter
substance into synaptic cleft (fluid-filled gap between pre- and postsynaptic neuron)
reactions are triggered by special sub microscopic protein molecules embedded in postsynaptic membrane
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