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Chapter 3

PSY100H1 Chapter Notes - Chapter 3: Myelin, Twin Study, Zygosity


Department
Psychology
Course Code
PSY100H1
Professor
Michael Inzlicht
Chapter
3

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Chapter 3 The Biological Bases of Behaviour
Communication in the Nervous System
Nervous Tissue: The Basic Hardware
The cells in the nervous system fall into two major categories:
GLIA and NEURONS
.
Neurons
= individual cells in the nervous system that receive, integrate, and transmit information.
Majority of them communicate with other neurons but a minority receive signals from sensory organs or
carry messages to the muscles.
-
Soma (cell body)
Æ
contains the cell nucleus and much of the chemical machinery common to
most cells.
-
Dendrites
Æ
the parts of a neuron that are specialized to receive information.
-
Axon
Æ
a long, thin fibre that transmits signals away from the soma to other neurons or to
muscles or glands.
-
Myelin sheath
Æ
insulation material, derived from glial cells, that encases some axons.
-
Terminal buttons
Æ
small knobs that secrete chemicals called neurotransmitters.
-
Synapse
Æ
a junction where information is transmitted from one neuron to another.
Glia
= cells found throughout the nervous system that provide various types of support for neurons.
Smaller than neurons but outnumber them by about 10:1. Glial cells help nourish neurons, help remove
waste products, provide insulation around axons.
The Neural Impulse: Using Energy to Send Information
Behaviour depends on complex information processing in the nervous system. Cells in the
nervous system receive, integrate, and transmit information. Neurons are the basic communication
links. They normally transmit a neural impulse along an axon to a synapse with another neuron. The
neural impulse
is a brief change in a neurons electrical charge that moves along an axon. Neurons are
surrounded by fluids containing electrically charges atoms and molecules called
ions
. Positively charged
sodium and potassium ions and negatively charged chloride ions flow back and forth across the
semipermeable cell membrane. The
resting potential of a neuron
is its stable, negative charge when the
cell is inactive (about -70 millivolts).
An
action potential
is a very brief shift in a neurons electrical charge that travels along an axon.
It is an all-or-none event. The
absolute refractory period
is the minimum length of time after an action
potential during which another action potential cannot begin.
The Synapse: Where Neurons Meet
The neuron that sends a signal across the gap is called the
presynaptic neuron
and the neuron that
receives the signal is called the
postsynaptic neuron
. The arrival of an action potential at an axons
terminal buttons triggers the release of
neurotransmitters
chemicals that transmit information from
one neuron to another.
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Five keys processes involved in communication at synapses are:
1)
Synthesis
and
storage
of neurotransmitter molecules in synaptic vesicles.
2)
Release
of neurotransmitter molecules into
synaptic cleft
= a microscopic gap between the
terminal button of one neuron and the cell membrane of another neuron.
3)
Binding
of neurotransmitters at receptor sites on postsynaptic membrane.
4)
Inactivation
(by enzymes) or
removal
(drifting away) of neurotransmitters.
5)
Reuptake
of neurotransmitters sponged up by the presynaptic neuron.
Receiving Signals: Postsynaptic Potentials ~ When a neurotransmitter and a receptor molecule combine,
reactions in the cell membrane cause a
postsynaptic potential (PSP)
- a voltage change at a receptor site
on a postsynaptic cell membrane. Two types of messages can be sent from cell to cell: excitatory and
inhibitory. An
excitatory PSP
is a positive voltage shift that increases the likelihood that the postsynaptic
neuron will fire action potentials. An
inhibitory PSP
is a negative voltage shift that decreases the
likelihood that the postsynaptic neuron will fire action potentials. Whether the postsynaptic neuron fires
a neural impulse depends on the balance of excitatory/inhibitory PSPs. Our thoughts and actions
depend on patterns of activity in neural circuits and networks.
Integrating Signals: Neural Networks ~ The elimination of old synapses appears to play a larger role in
the sculpting of neural networks than the creation of new synapses. The nervous system normally forms
more synapses than needed and then gradually eliminates the less active synapses
synaptic pruning
.
Neurotransmitters and Behaviour
Acetylcholine (ACh):
-
Activates motor neurons controlling skeletal
muscles
-
Contributes to the regulation of attention,
arousal, and memory
-
Some ACh receptors stimulated by nicotine
Dopamine (DA):
-
Contributes to control of voluntary
movement, pleasurable emotions
-
Decreased levels associated with
Parkinson’s disease
-
Overactivity at DA synapses associated with
schizophrenia
-
Cocaine and amphetamines elevate activity
at DA synapses
Norepinephrine (NE):
-
Contributes to modulation of mood and
arousal
-
Cocaine and amphetamines elevate activity
at NE synapses
Serotonin:
-
Involved in regulation of sleep and
wakefulness, eating, aggression
-
Abnormal levels may contribute to
depression and obsessive-compulsive
disorder
-
Prozac and similar antidepressant drugs
affect serotonin circuits
GABA:
-
Serves as widely distributed inhibitory
transmitter
-
Valium and similar antianxiety drugs work
at GABA synapses
Glutamate:
-
Amino acid neurotransmitter with
excitatory effects
-
Contribution to learning and memory
Endorphins:
-
Resemble opiate drugs in structure and
effects
-
Contribute to pain relief and perhaps to
some pleasurable emotions
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