Chapter
48
Quizzes:
Self
Activities
Chapter
Cum.
Animations
Words
Appendix
Summary
Art
Art
Unit 7: Animal Form and Function
Nervous Systems
Review
The human brain contains an estimated 100 billion nerve cells, or
. Each neuron may communicate with thousands of other
neurons.
Bundles
of neurons can be organized into
.
All animals except
sponges
have some type of
system.
Cnidarians
have neurons arranged in nerve
.
Flatworms
have a simple
nervous system (CNS), composed of a
and longitudinal nerve
, that allows for
.
arthropods
have neurons arranged in segmented clusters called
, which connect to the CNS and make up a
nervous system (PNS).
Among molluscs,
species such as clams and
chitons
have simple systems with little cephalization, while
molluscs such as
squids
possess more sophisticated systems with a large
that supports an active, predatory lifestyle.
Echinoderms
have a nerve net in each arm connected by
nerves to a central nerve
.
In
chordates
the CNS consists of a
and
spinal cord, connected to a PNS made of nerves and
.
Nervous systems process
information
in three stages:
input,
, and
output; an example is the
knee-jerk
mediated by the spinal cord.
A
neuron
is composed of a cell
, several
that receive signals from other neurons, and an
that transmits signals to other cells at
terminals.
Axons may be covered with a
sheath
formed by
cells,
Every cell maintains a voltage across its plasma membrane called a membrane
where the inside is
relative to the
outside;
the
potential is about -70 mV. A stimulus may trigger a
graded
of the membrane: if the depolarization exceeds the
of -55 mV, an all-or-none response creates an
potential of about 30 mV.
Voltage-gated ion
channels
mediate the
potential response: Na
+
channels open upon
to allow Na
+
to diffuse
the cell; as the action potential subsides, K
+
channels open and K
+
flows
of the
cell.
An action potential travels by
the depolarization event along an
axon
. Action potentials in
axons
jump between the nodes of
in a process called
conduction.
Most neurons communicate with other cells at chemical
, where a presynaptic neuron releases chemical
stored in the
synaptic
terminal.
Postsynaptic potentials can be either
postsynaptic potentials (EPSPs) or
postsynaptic potentials (IPSPs); unlike action potentials, postsynaptic potentials are
and can undergo either
or
summation.
The vertebrate nervous system exhibits a high degree of
with distinct
and
components.
The PNS is composed of a
nervous system, which regulates the
muscles, and an
nervous
system,
which regulates the internal environment, in an
manner, and comprises three divisions:
,
, and
The
cerebrum
has right and left cerebral
that each consist of cerebral
overlying white matter and
nuclei.
Each side of the cerebral cortex has four
lobes:
,
,
, and
.
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May 25, 2007
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