Nervous Systems
What’s actually happening when the brain “processes” information
for learning?
1. Communication b/w
neurons is basically binary
code. If the neuron fires,
then something is learned.
2. I’m exercising my brain
right now, in order to grow
new neurons & increase my
capacity to learn!
3. I’m too old to learn
anything new anymore;
I hire people do that for
me.
4. Brain power is
electromagnetic energy that
carries our thoughts. …I’d like
to keep my thoughts to myself,
thank you.
Learning Objectives (3/4/08)
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5.
Use examples to illustrate the 3 interrelated functions of
nervous systems: sensory input, integration, and motor
output.
Relate structure with function at various levels of
organization in nervous systems: neuron, synapse, reflex
arc, and integrative processes.
Describe the increasing complexity that likely reflects
the stages in the evolution of nervous systems.
Differentiate between inhibitory and excitatory postsynaptic potentials, and the generation of a grand
synaptic potential
Differentiate between synaptic potentials and action
potentials
Structure of a Multipolar Neuron
p. 1008
What other cell types are found in nervous tissues?
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.
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.
Overview of the Transmembrane
Electrochemical Potential p. 1009
Does the
Na-K pump
contribute to the
potential?
Why is the cell
membrane
described
as “polarized”?
What would
happen to this
potential if K+
leakage channels
were blocked?
Chemical Synapses
Compare with the structure and function
of an electrical synapse.
What determines
whether a
synapse is
excitatory or
inhibitory?
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.
The Action Potential
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.
Name the ion channel that opens at
the threshold voltage.
Action potential size is independent of
the stimulus and reaches a value of
about +30 mV.
What happens during repolarization?
p. 10
Unidirectional Propagation
p. 1037 &
1038
Refractory Period
p. 1016
Myelinated Neuron Fibers
p. 1017
•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?
Giant Axons
Giant axons in the
earthworm ventral nerve
cord. A cross section of
the nerve cord is shown.
Where is the nerve cord
located in Chordates?
Squid giant axon
Stellate
ganglion
Chemical Synapses
1. The calcium channels on the synaptic terminal are ________
gated.
2. The sodium channels on the post-synaptic membrane are
________ gated.
3. The ion channels involved in the propagation of the A.P. are
_______ gated.
p. 1019
Synaptic Summation
p. 1021
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.
The Simplest Behavioral Unit of
the Nervous System: Reflex Arc
Name the
neurotransmitter
released by
motor neurons at
the muscle cells.
Photomicrograph of the
neuromuscular junction