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Neural and Hormonal Systems
Everything psychological is simultaneously
biological.
Phrenology, although seriously misguided, was a
tentative step in this direction. See Figure 4.1 in
your text.
But! These areas in the brain are all
interconnected, making the brain the most
complex structure in the known universe.
The brain is not a computer! This is a common
misconception.
Neural and Hormonal Systems
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Neuron: the basic building block of the nervous
system.
Each consists of a cell body and branching fibres.
The dendrites are the bushy, branching
extensions that receive messages and conduct
impulses toward the cell body. For the biology
students: dendrites are complex microtubules,
proof that neurons are specializations from
simpler cell structures.
Axon: the neuron extension that passes
messagesthrough its branches to other neurons.
Neural and Hormonal Systems
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Myelin sheath: a layer of fatty tissue which
insulates the axon and speeds up the tranmission
of neural impulses. After age 25, this sheath
deteriorates, leading in extreme cases to multiple
sclerosis.
Your brain is vastly more complex than a
computer, but slower at executing simple
responses.
Commit Figure 4.2 to memory; it is crucial to
understanding further material in this course.
Neural and Hormonal Systems
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Figure 4.3: Action potential.
Neurons generate electricity from chemical
events: electrically charged ions pump in and out
of the axon.
The best way to understand how action potential
works is to do the Wave, in class, right now!
The change in charge is what travels down the
axon, not the chemicals themselves.
Action Potential
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Neuron stimulation causes a brief change in
electrical charge. If strong enough, this produces
depolarization and an action potential.
This depolarization produces another action
potential a little farther along the axon. Gates in
this neighbouring area are now open, and sodium
ions rush in. The sodium/potassium pump in the
cell membrane transports the sodium ions back
out of the cell.
Action Potential
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As the action potential continues speedily down
the axon, the first section has now completely
recharged.
Each neuron is a miniature decision-making
device performing complex calculations as it
receives signals from hundreds, even thousands
of other neurons.
Excitatory signals push the message forward;
inhibitory signals stop it cold.
All-or-none. Neurons either fire, or they don't.
Synaptic Gap
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Commit Fig. 4.4 to memory; it is crucial for
understanding the rest of the course.
Action potentials travel down the axon until
reaching a tiny junction, the synapse.
Then, the action potential stimulates the release
of neurotransmitter molecules. They cross the
synaptic gap and bind to receptor sites on the
receiving neuron. This allows ions to enter the
recieving neuron and excite or inhibit a new
action potential.
The sender neuron reabsorbs excess
neurotransmitters. This is reuptake.
Serotonin & Dopamine
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Serotonin and dopamine are of the most interest
to psychologists, because they have the greatest
effects on high brain functions, primarily mood
and language.
Serotonin is an endogenous opiate, or an
endorphin. Morphine, heroine, (and after a
conversion at the blood-brain barrier) alcohol are
agonists to serotonin.
Dopamine also has several agonists, the best
known being lysergic acid diethylamide 25, or
LSD.
Acetylcholine
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Acetylcholine (Ach) plays a role in learning
and memory. In addition, it is the
messenger at every junction between
motor neurons and skeletal muscles.
When Ach is released, the muscle
contracts.
Curare is an antagonist of Ach, and is used
to paralyze fish, and the lips of Hollywood
starlets, the wonder of Botox.
Hormones are Thoughts Too
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Fig. 4.8 will be on the exam.
The autonomic nervous system controls our
glands and the muscles of our internal organs,
influencing such functions as glandular activity,
heartbeat, and digestion. It may be consciously
overridden.
The sympathetic nervous system arouses and
expends energy. Heartrate, blood pressure,
digestion, blood sugar, and perspiration are
controlled by it.
The parasympathetic system does the opposite.
Brains are not Computers
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The brain has some 40 billion neurons, each
connecting with 10,000 other neurons. That
creates 400 trillion synapses. And each synapse
is its own symphony orchestra of
neurotransmitters.
No modern, silicon-based microprocessor (like
the one in your smart phone) can come close to
this level of networking complexity.
The best analogy is to consider your brain as a
super-Internet.
The study of this complex connectivity is called
neural networking.
Back to Hormones!
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The endocrine system is the body's slow
communications system; a set of glands that
secrete hormones into the bloodstream.
Hormones are chemical messengers that are
manufactured by the endrocrine glands.
An example are the corticosteriods, which travel
through the bloodstream, and rebuild muscle
tissues. After a heavy workout, your hormonal
system shifts into high corticosteroid production.
For psychologists, the most important gland is the
hypothalamus, located in the middle brain.