Nervous Systems

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Nervous Systems
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Whats actually happening when the brain learns
new information?
1. Communication b/w neurons is basically binary
code. If the neuron fires, then something is
learned.
4. Brain power is electromagnetic energy that
carries our thoughts. Id like to keep my
thoughts to myself, thank you.
2. Im exercising my brain right now, in order to
grow new neurons increase my capacity to learn!
3. Im too old to learn anything new anymore I
hire people do that for me.
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Learning Objectives (3/5/08)

1. Use examples to illustrate the 3 overlapping
   functions of nervous systems sensory input,
   integration, and motor output.
2. Relate structure with function at various levels
   of organization in nervous systems neuron,
   synapse, reflex arc, and integrative processes.
3. Describe the increasing complexity that likely
   reflects the stages in the evolution of nervous
   systems.
4. Differentiate between inhibitory and excitatory
   post-synaptic potentials, and the generation of a
   grand synaptic potential
5. Differentiate between synaptic potentials and
   action potentials

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Structure of a Vertebrate Neuron
Fig. 45.2
What other cell types are found in nervous
tissues?
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Diversity of Nervous Systems
Simple, slow moving animals like hydra have
neurons arranged in a network of bipolar neurons
called a nerve net. What is a ganglion?
Cephalization More complex and active animals
tend to cluster ganglia together at the anterior
end to form a brain.
Fig. 48.2
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Basic Tasks of a Nervous System
Sensory Input Receptors monitor both external
and internal environments. Integration Process
the information (at synapses) and often integrate
it with stored information. Motor output If
necessary, signal effector organs to make an
appropriate response.
How is this similar to the normal function of the
endocrine system? Describe the receptor, control
center, and effector in several neural reflexes.
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Overview of the Transmembrane Electrochemical
Potential
p. 1029
How does the Na-K pump contribute to
the potential? Why is the cell membrane
described as polarized?
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Chemical Synapses
Compare with the structure and function of an
electrical synapse.
What determines whether a synapse is excitatory
or inhibitory?
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Graded Membrane Potentials
The membrane potential can be altered depending
upon which ion channels are opened by a stimulus.
These synaptic potentials are graded.
Open K channels allows K efflux from the cell
at a higher than resting rate, driving the cell
interior more negative (hyperpolarization).
Open Na channels allow Na to influx into the
cell, driving the cell interior more positive
(depolarization). Excitable cells have several
types of voltage-gated channels that respond to
changes in membrane potential.
p. 1041
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The Action Potential
p. 1032
A depolarizing potential that reaches a critical
level called the threshold potential (or firing
threshold) will trigger an action potential or
nerve impulse. Unlike the graded potentials
that get larger with increasing stimulus
strength, the action potential is an all-or-none
response. Action potential size is independent
of the stimulus and reaches a value of about 30
mV.
Name the ion channel that opens at the threshold
voltage.
What happens during repolarization?
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Unidirectional Propagation
p. 1037 1038
Refractory Period
p. 1036
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Myelinated Neuron Fibers
p. 1038

• Many vertebrate peripheral neuron fibers have an
  insulating sheath around their fibers called
  myelin which is formed by Schwann cells.
• Myelin sheathing allows these neurons to conduct
  action potentials much faster than in
  non-myelinated neurons.
• How does the structure of unmyelinated neurons in
  invertebrates allow for the rapid conduction of
  action potentials during e.g. escape responses?

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Giant Axons
Where is the nerve cord located in Chordates?
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Chemical Synapses
The calcium channels on the synaptic terminal are
________ gated. The sodium channels on the
post- synaptic membrane are ______ gated. The ion
channels involved in the propagation of the A.P.
are _______ gated.
p. 1040
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ReviewExcitatory vs. Inhibitory Synapses
Which ion channels may be opened to hyperpolarize
a cell membrane (i.e. create an inhibitory
post-synaptic protential)? What would opening
Ca channels do to the potential?
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Synaptic Summation
p. 1041-1042
Is it possible for one kind of neurotransmitter
molecule to have an excitatory effect at one
cell, and an inhibitory effect at another?
Explain, using an example.
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The Simplest Behavioral Unit of the Nervous
System Reflex Arc
What is the difference between a reflex arc and a
reflex act? Name the neurotransmitter released
by motor neurons at the muscle cells.
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Photomicrograph of the neuromuscular junction