PSY100H1 Lecture Notes - Sympathetic Nervous System, Acetylcholine, Autonomic Nervous System

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16 Oct 2011

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Biological Bases of Behaviour
The nervous system controls everything in your body. It is the communication system throughout you.
There are two cells in the nervous system; one called glia, the other neurons.
Neurons receive, integrate and transmit information
Most do this only with other neurons.
There are those neurons that can do this with signals outside the nervous system.
Soma/Cell body is where the nucleus is and all the chemical
machinery common to most cells
Dendrites are the branched, feeler-like structures that spread
out of the Soma. These parts are specialized to receive
Axon transmits signals away from the Soma towards other
neurons, muscles, or glands.
Terminal Buttons and synapses/Axon Terminals secrete
chemicals called neurotransmitters. The synapses are located
at the same areas; this is a junction where information is
transmitted from one neuron to another.
Schwann’s Cell/Myelin Sheath is a fatty substance that many
axons are wrapped around. This material is derived from glial
cells. This speeds up the transmission of signals.
Information is received from other cells by the Dendrites. It travels through the soma, down the axon, to
the terminal buttons where it is passes through to the next cells dendrites.
Glia Cells are found throughout the nervous system and support the neurons. They outnumber them
and do things like nourishing and removing the neurons waste. They may also send and receive
chemical signals and send signals to other glia cells.
The Neural Impulse
Outside the neuron are fluids that have ions. Ions are electrically charged atoms and molecules. These
ions pass in and out the cell membrane. These ions do not cross at the same rate. There is a somewhat
higher concentration of negatively charged ions then positively charged ones inside the cell. This is
referred to as the resting potential (the potential of a neuron while it is inactive). This is when no
messages are being sent. When it is stimulated however, channels in the membrane open and allow in
positively charged ions. The charge is now less negative. This is an action potential (a brief shift in a
neurons electrical charge that travels along the axon). After the firing there is an absolute refractory
period. This is when the neuron cannot allow any more positive ions into its cell. This is only for a brief
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time. After this period there is a relative refractory period, during which time if a cell where to send a
charge down, the stimuli would need to be more intense then the first one.
The strength of a signal varies by the rate at which the neurons are fired. A weaker stimulus does not
produce a smaller action potential and vice versa.
Neural impulse transitions cell to cell in the junctions of the cell called the synapses. Between the
synapses and the membrane of the next neuron, is something called the synaptic cleft. Signals must
cross this gap in order to communicate. When an action potential reaches the terminal buttons, a
neurotransmitter is released. It travels to the membrane of the next cell and there they bind to the
postsynaptic cell membranes various receptor sites. These are tuned to respond to certain kind of
neurotransmitters. When they combine, reactions in the postsynaptic cell membrane cause a
postsynaptic potential. These are graded; they differ in size and increase/decrease the probability of a
neural impulse in the receiving cell in proportion to the amount the voltage has changed.
If the voltage has changed to a positive charge it is called an excitatory PSP; this increases the likelihood
that the postsynaptic neuron will fire action potentials. If it has changed to a negative charge, it is called
an inhibitory PSP; this decreases the chances of action potentials being fired in the postsynaptic neuron.
Since a neural impulse can only be transmitted in the synapses, and requires the neurotransmitter to be
able to connect to a certain receptor on the postsynaptic neurons cell membrane; there must be
different kinds of “neurotransmitters” so that they can be recognized as differing from one another and
fit into these certain receptors on the postsynaptic cell membrane.
There are FIVE main/different kinds of neurotransmitters that are important:
Acetylcholine (Ach): Is the only transmitter between motor neurons and voluntary muscles. These
help in our movements. Contributes to attention, arousal and memory.
Monoamines: Include three different kinds of neurotransmitters; Dopamine,
Norepinephrine,Serotonin. Regulate aspects of everyday behaviour.
Dopamine: controls voluntary movements
Serotonin: regulation of sleep and wakefulness, eating behaviour, aggression and impulse behaviour
Norepinephrine: contributes to modulation of mood and arousal.
GABA: Made of amino acids. There are two and they mostly cause inhibitory PSPs; GABA (gamma-
aminobutyric acid) and Glycine. Unlike the Ach and monomines which can produce both inhibitory and
excitatory PSP’s
Produces only excitatory PSP’s. Contributes to learning and memory. Plays a role in a process called
long-term potentiation (basic building blocks of memory formation).
The body’s own internally produced neurotransmitters that mimic the effects of morphine. In other
words they resemble opiates in structure and effects. Contributes to modulation of pain, eating
behaviour and modulation of stress.
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