PSYC 100 Study Guide - Tonotopy, Nicotine, Color Constancy

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5 Feb 2013
Department
Course
Week 7: Chapter 4: Brain and Behaviour
Nervous System
- structure
central nervous system
o brain and spinal cord
peripheral nervous system
o nerves=bundles of fibres that transmit info between CNS and
the rest of body
o cranial nerves= carries sensory info from head and neck
regions (ex. vision, hearing, eye movements)
o spinal nerves= carries sensory info from rest of body
3 major parts of the brain
o brain stem (most primitive region; incudes medulla, pons,
midbrain)
o cerebellum (attached to back of brain stem; controls and
coordinates movements)
o cerebral hemispheres (largest part of brain; parts of brain the
evolved most recently)
brain and spinal cord protected by meninges
o 3 layered set of membranes
o dura matter, arachnoid membrane, pia matter
brain and spinal cord float in cerebrospinal fluid (CSF)
o fills space between two meninges
o provides a shock-absorbing cushion
brain’s capillaries do not have openings
o blood-brain barrier= prevents some substances from passing
from blood into brain
arteries carry fresh blood to the brain
veins and sinuses carry used blood away from brain
surface of cerebral hemisphere is covered by cerebral cortex
o called grey matter
o contains billions of nerve cells
o perceptions, memories, plans
nerves in cerebral cortex are connected to other parts of the brain by
white matter
o abundant in axons, instead of cell bodies
cerebral cortex is wrinkled to increase surface area
o bulges= gyri
o grooves= sulci, fissures
- cells
neurons
o nerve cells that bring sensory information to brain, store
memories, reach decisions, control activity of muscles
o specialized for receiving, processing and transmitting
information
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o types of neurons: sensory (detects sensory info), motor
(muscle control), interneurons (intergrates info between
sensory and motor neurons)
o parts of a neuron: soma (cell), dendrite (receives messages),
node of Ranvier (jumps from node to node), axon (carries
messages AWAY from soma), terminal button (end of axon;
releases neurotransmitter), myelin sheath (fatty cells that
insulate axons, increase speed of messages)
glial cell
o provides support for neurons and supplies them with essential
chemicals
- action potential
travels down axon to terminal buttons; terminal buttons secrete a
chemical, which is called a neurotransmitter; neurotransmitter affects
activity of other neurons; message is conveyed chemically; action
potential= abrupt, short-lived reversal in the electrical charge of an
axon
steps of an action potential
1. resting state (inside of cell is negatively charged, outside is
positively charged; sodium ion channels closed, potassium ion
channels open)
2. sodium ion channels nearest to cell body open (sodium ions
enter, reversing the membance potential at that location, cell
becomes more positive)
3. reversal causes nearby ion channels to open (produces another
reversal at that point, will only generate if it reaches threshold
of activation=-55 millivolts, continues down towards terminal
buttons with brief depolarizations along the cell membrane)
4. sodium ion channels close & potassium ion channels open (cell
has reached max. positive charge of +40 millivolts, K+ ions
leave restoring membrane potential- repolarization occurs)
5. hyperpolarization occurs (cell becomes temporarily more
negative than resting state at -80 millivolts; called refractory
period)
6. ion transporters pump sodium ions out & potassium ions back
in (restores normal balance at resting state)
all or none law: once an action potential is triggered, it is propogated,
without getting smaller, to the end of the axon
o action potentials are all the same size
o quantitative information is represented by an axon’s rate of
firing
- synapses
neurons communicate with other cells by forming synapses
steps of synapse:
1. axon’s terminal buttons has synaptic vesicles
o little bubble of membrane filled with neurotransmitter
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2. action potential reaches terminal buttons on presynaptic
neuron
3. terminal button releases a small amount of neurotransmitter
into synaptic cleft
4. neurotransmitter diffuses across synaptic cleft to postsynaptic
neuron
5. neurotransmitter attaches to neurotransmitter receptors on
membrane of postsynaptic neuron
o key and lock model- specific match
6. once activated, receptor molecules produce inhibitory or
excitatory effects on postsynaptic neuron
o produce effects by opening ion channels
o excitatory synapses= make it more likely the axon of
postsynaptic neuron will fire (permit sodium ions to
enter neuron)
o inhibitory synapses= lower likelihood that axons of
postsynaptic neuron will fire (permit motassium ions to
leave neuron)
7. inhibition or excitation are short lived- effects are terminated
by reuptake or enzymatic breakdown
o neurotransmitter is quickly taken up again by the
terminal button
o neurotransmitter is converted into a chemical by an
enzyme (enzymatic breakdown)
o the faster neurotransmitter is taken back, the shorter its
effects will be
Drugs and Behaviour
- 2 types of drugs
transmitter agonist: enhances neurotransmitter’s actions
transmitter antagonist: reduces/ block neurotransmitter’s actions
- 3 ways drugs alter synaptic transmission
1. stimulate or inhibit the release of neurotransmitters
o drugs can cause terminal buttons to release neurotransmitter
continuously
o drugs can prevent terminal buttons from releasing their
neurotransmitter
2. stimulate or block postsynaptic receptors
o drugs can turn receptors on, even when the neurotransmitter is
not present (act like “master key”)
o drugs can bind with receptors but not stimulate them, making
them inaccessible (plugs up lock, so key can’t fit)
3. inhibit reuptake
o molecules of neurotransmitter continue to stimulate postsynaptic
neuron for a long time
- 2 most important neurotransmitters
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