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Ch. 2 study guide

Course Code
Robert Gerlai

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Chapter 2:
Controlling Behavior: The Role of the Nervous System
-It should be obvious from the previous chapter that the behavior of an animal is a complex
affair and one that requires a high degree of control and coordination. Of course it must
also require information about both the individuals surroundings and its internal state.
Although some hormone-mediated short-term control does take place, the proximate (short-
term) control of behavior is largely the job of the specialist cells of the nervous system.
***At a proximate level the behaviors animals perform are controlled in part by the activity
of the nervous system. This network of specialized cells provides a means of rapid
information transfer within the animal, linking sensory input to central processing and
motor responses.
***Many types of behavior can be described as reflexes, relatively simple involuntary
responses to stimuli. In some cases these stimuli (releasers) are very specific, in other cases
they are more general.
***Animals possess a range of strategies to maximize the efficiency of their information
gathering, and their behavioral performance.
***It is important to remember that nerves alone do not control behavior, the interaction
between animal and environment is vitally important
Stimulating a behavior
Fixed Action Patterns
-A Fixed Action Pattern (FAP) is an instinctive behavior. It is performed perfectly first time,
without practice and without any tuition. And always running to completion. And their
triggered by a stimulus. This trigger or stimulus is usually referred to as a releasing
mechanism or a releaser.
-Results of the herring gull experiment
1.have an innate ability to recognize appropriate stimuli
2. that the behavior is an innate reflex released by an appropriate stimulus
3. the chick doesnt need all of the other cues that describe a parent, and that it only
focuses upon the stimulus itself

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4. because non-herring-gull type stimuli did the job as well if not better then there
must be a degree of flexibility in the system
Components of the Nervous system
-main building blocks of the nervous system
-These are the cells that receive, sort and pass on the information that in approximate sense
cause the animal to behave
-Neurons are nucleate cells like any other, but they possess specialzed processes that enable
them to acquire information (the dendrites) and to transmit it often considerable distances
though the body (usually via the axon).
-Process called dendritic
-3 main classes of neuron
1. Sensory Neurons: collect information from specialized sensory receptor cells in
the nervous system
2. Motor Neurons: connect directly to muscles and stimulate them into action.
3. Interneurons: form links between these inputs and outputs
The resting potential
-the information handled by neurons takes the form of electrical signals
- these are propagated as small changes in voltage between the inside and outside of the
- to facilitate this the cell membranes of neurons are permeable to ion flow
-2 gradients
1. Chemical Gradient: difference in concentration. Results in a similar concentration
of ions on both sides of the membrane (diffusion taking place)
2. Electrical gradient: difference in charge between sodium cations and larger
anionic units (such as cellular proteins) that are too big to pass out of the cell.
-ions flow in both directions across the membrane, eventually achieving equilibrium

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(equilibrium potential)
-Ions will achieve its own equilibrium potential and summed together they will
amount to the resting potential (cells background state)
Action Potential
-If the interior of a neuron is made to have a greater positive charge than the resting
potential the membrane will depolarize
-Similarly the application of an increased negative charge within the cell will result in
membrane hyper polarization.
- Depolarizations tend to be excitatory in nature, stimulating activity in the neuron,
whereas hyperpolarizations tend to be inhibitory
-If the charge change related to a depolarization is sufficiently large, a very particular
electrical phenomenon called a spike (an action potential)will be triggered
-Action potential: when a small pulse of positive current is injected into a neuron, small
depolarizations are produced. Once threshold is achieved, an action potential is generated.
The different phases of the action potential are the resting potential, rising phase,
overshoot, falling phase, undershoot
-sometimes a single postsynaptic potential (PSP) is enough to induce a spike, but often the
combined effect of a number them is required.
-Some nerve cells exhibit a phenomenon termed summation whereby a series of small
PSPs coming from one or a number of sources have an additive effect. Their individual
charges are summed to achieve the threshold required for spike production.
-Other cells require a series of PSPs that rather than being added together each elicit a
slightly larger PSP than themselves until the action potential threshold is reached. This
phenomenon is termed Synaptic facilitation.
-The spike lasts for just one or two milliseconds, but can move along an axon at speeds in
excess of 100 m/s
-Once the depolarization of the cell membrane reaches the action potential threshold gates
in the membrane open, allowing Na+ to enter the cell, increasing the measured voltage very
rapidly. The increasing Na+ conductance is followed by an increase in K+ conductance out of
the cell as an attempt is made to return to equilibrium. The Na+ gates now begin to close
(termed Na+ inactivation) and the measured voltage begins to fall. It falls below the resting
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