PSY100Y5 Chapter Notes - Chapter 3: Myelin, Axon Terminal, Neuroglia
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I. Communication in the Nervous System
A. Nervous Tissue: The Basic Hardware
1. 2 Major Categories for Cells in Nervous System
a. Glia – cells found throughout the nervous system that provide structural
support and insulations for neurons. Help maintain the chemical
environment of the neurons
b. Neurons- the individual cells in the nervous system that receives,
integrates, and transmits info. Permit communication (mostly within
other neurons) – only sensory organs revive signals from outside the
nervous system.
2. Parts of a Neuron:
a. Soma (cell body) – contains the nucleus and much of the chemical
machinery common to most cells.
b. Rest of neuron dedicated to handling info.
c. Dendrites – parts of the neuron that are specialized to receive info.
d. Axon – info travels from dendrites to axon, which is the long thin fiber
that transmits signals away from the soma to other neurons or muscles
and glands.
e. Myelin sheath – many axons wrapped in cells with a high concentration
of myelin. Insulating material, from glial cells, that encases some
neurons. Speeds up transmission of info.
i. Multiple Sclerosis due to deterioration of myelin sheath.
f. Terminal buttons – small knobs that secrete chemicals called
neurotransmitters. At end of axons in clusters.
g. Synapse – point at which neurons connect. Junction where info is
transmitted from one neuron to another.
B. The Neural Impulse: Using Energy to Send Information
1. The Neuron at Rest: A Tiny Battery
a. Neural impulse is a complex electrochemical reaction.
b. The resting potential of a neuron is it’s stable, negative charge when the
cell is inactive. (Potential Energy of a Neuron).
2. The Action Potential – brief shift in a neuron’s electrical charge that travels
along an axon.
a. Absolute Refractory Period – the minimum length of time after an action
potential during which another action potential can not begin (down
time)
3. The All or None Law
a. Either the neuron fires or it doesn’t, and its action potentials are always
the same. i.e. weaker stimuli don’t produce smaller action potentials.
b. However, they can change the rate of action potentials. A stronger
stimulus will make for more rapid action potentials in a shorter period of
time.
C. The Synapse: Where Neurons Meet
1. Sending Messages: Chemicals as Couriers
a. Synaptic Cleft – a microscopic gap between the terminal button of one
neuron and the cell membrane of another neuron.
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b. Presynaptic Neuron – sends the signal, postsynaptic neuron receives the
signal.
c. Neurotransmitters – chemicals that transmit info from one neuron to
another.
2. Receiving Signals: Postsynaptic Potentials
a. Postsynaptic Potential (PSP) – a voltage change at a receptor site on a
postsynaptic cell membrane.
i. Graded – vary in size and increase/decrease the possibility of a
neural impulse in the receiving cell in proportion to the amount of
voltage change.
b. 2 Types of Signals:
i. Excitatory PSP is a positive voltage change that increases the
likelihood that postsynaptic neuron will fire action potentials.
ii. Inhibitory PSP negative voltage changes that decreases the
likelihood that the postsynaptic neuron will fire action potentials.
c. Reuptake – process in which neurotransmitters are sponged up from the
synaptic cleft by the presynaptic membrane.
3. Integrating Signals: A Balancing Act
a. State of a Neuron is the weighted balance between excitatory and
inhibitory PSP’s.
D. Neurotransmitters and Behavior
Good Table 3.1 – Common Neurotransmitters and Their functions
1. Acetylcholine (Ache)
a. Only transmitter between motor neurons and voluntary muscles.
b. Contribute to attention, arousal, and memory.
c. Agonist – chemical that mimics the action of a neurotransmitter –
PRODUCE PSP after binding to receptor sites (i.e. Nicotine).
d. Antagonist – opposes the action of a neurotransmitter. Bind to receptor
sites but DO NOT PRODUCE PSP, but instead block action of normal
neurotransmitter.
2. Monoamines – regulate everyday behavior such as voluntary movements
(Parkinson Disease).
a. Includes 3 neurotransmitters – dopamine (DA), norepinephrine, and
serotonin.
b. Serotonin releasing neurons appear to play a role in regulation of sleep
and wakefulness. May control aggressive behavior in animals.
c. Abnormal levels of monoamines have been linked to psych disorders –
depression from lower levels.
d. Abnormalities in activity linked to schizophrenia
3. Endorphins – family of internally produced chemicals that resemble opiates
(morphine, opium) in structure and effect
II. Organization of the Nervous System
A. The Peripheral Nervous System
Those nerves that lie outside the brain and spinal cord.
1. Nerves are bundles of neuron fibbers (axons) that are routed together in the
peripheral nervous system.
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PSY100Y5 Full Course Notes
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Document Summary
Communication in the nervous system, nervous tissue: the basic hardware, 2 major categories for cells in nervous system, glia cells found throughout the nervous system that provide structural support and insulations for neurons. Help maintain the chemical environment of the neurons: neurons- the individual cells in the nervous system that receives, integrates, and transmits info. Insulating material, from glial cells, that encases some neurons. Speeds up transmission of info: multiple sclerosis due to deterioration of myelin sheath. Terminal buttons small knobs that secrete chemicals called neurotransmitters. At end of axons in clusters: synapse point at which neurons connect. Good table 3. 1 common neurotransmitters and their functions: acetylcholine (ache, only transmitter between motor neurons and voluntary muscles, contribute to attention, arousal, and memory, agonist chemical that mimics the action of a neurotransmitter . Produce psp after binding to receptor sites (i. e. nicotine): antagonist opposes the action of a neurotransmitter. Organization of the nervous system: the peripheral nervous system.
