NSCI 410 Lecture Notes - Excitatory Postsynaptic Potential, Axon Terminal, Peripheral Nervous System

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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
receives information from body's sensory receptors and is connected with
muscles and glands of body
nervous system consists of two divisions:
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 collumn
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 fibers that transmit information netween
CNS and body's sense organs, muscles, and glands
attached to spinal cord and base of brain
peripheral nervous system – cranial and spinal nerves; that part of the
nervouse 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, cerbral hemisphere
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 (amphibeans
have brain stem and simple cerebellum)
cerebral hemispheres – constitue large portion of brain
contains parts of brain that evolved most recently: involved in behaviours of
particular interest to psychology
cerebellum – attached to bain of brain, looks like miniature version of cerebral
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
float in clear liquid called cerebrospianl fluid (CSF)
fills between 2 meninges, providing cushioning
cerebral cortex – outer layer of cerebral hemisphere of brain, approxiamtely
3 mm thick
often referred to as grey matter – contains billions of nerve cells
(abundant in nerve cell bodies rather than axons)
where perceptions take place,memories are stored, plans are formulated
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and executed
nerve cells in cerebral cortex are connected to other parts of brain by layer
of nerve fibres called white matter
shiny white appearance of substance that coats and insulates axons that
travel trough area (axons' myelin sheath)
very wrinkled appearance – full of bulges seperated 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
nerves carry incoming and outgoing information
sense organs detect changes in environment and send signals
throughnerves to central nervous system
brain sends signals trhough 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)
nerve fibres transmit message through nerve, from sense organ to brain or
from brain to muscle/gland
these make up white matter and other axon tracts
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 mesages to muscles and
cranial nerves – 12 pairs, attached to base of brain; conveys sensory
information from face and head and carries messages to muscles and
Cells of Nervous System
Neurons – nerve cell; consists of cell body with dentrites and an axon whose
branches end in terminal bittons that synaps to muscle fibres, gland cells, or
other neurons
elements of nervous system that bring sensory information to brain, store
memories, reach decisions, control activity of muscles
assisted by glia
Glial cells – cell of central nervous system that provides support for neruons
and supplies them with essential chemicals
during development of brain, some types of glial cells form long fibres that
guide develping neurons from place of birth to final resting place
manufacture chemicals that neurons need to perform tasks and absorb
chemicals that might impair neuron's functioning
form protective insulating sheaths around nerve fibres
serve as brain's immune system, protecting it from micro-organisms
Three basic parts of neruron:
soma – cell body; largest part of neuron
containts mechanisms that control metabolism and maintenance of cell
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receives messages from other neurons
dentrites – treelike part of neuron on which other neurons form synapses
transmit information they receive down trunks to soma
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
Two complex structures seen in neurons:
dentritic spines – small protuberance on surface of dentrite; appear on
neurons in brain
synapse can occur on smooth dentrite or on dentritic spine
terminal button – round swelling at end of axon; releases transmitter
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
myelin – part protein, part fat
produced by glial cells that individually wrap themselves around
segments of axon
insultates axons from each other and prevents scrambling of messages
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
unequal distribution of + or - charge occurs inside axon and in fluid that
surrounds it
axon membrane contains ion channels – special protein molecule located
on membrane of cell which controls entry or exit of particular ion
ion transporters – special protein moelcule located in membran of cell
taht actively transports ions into or out of cell
use energy resource from cell to acituvely 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 – prossess continues all way down to
terminal button
as soon as charge reverses, ion channels close and another set opens letting +
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