Transcript AP Biology Animal Form and Function Nervous ppt.

AP BIOLOGY ANIMAL
FORM AND FUNCTION
Nervous System
Nervous System

The nervous system is an organ system containing
a network of specialized cells called neurons that
coordinate the actions of an animal and transmit
signals between different parts of its body.
Central and Peripheral Nervous System
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
The Central Nervous System consists of the brain,
spinal cord and retina
The Peripheral Nervous System
consists of sensory neurons,
clusters of neurons
called ganglia, and nerves
connecting them to
each other and to the
central nervous system
Neurons
The basic structural unit of the nervous system is a nerve
cell, or neuron. It consists of the following parts:
 The cell body-main
body of the neuron
 The dendrite-short,
branched extensions
that bring impulses
to the cell
 The axon-long extensions that leave from a neuron and
carry impulses to the target cell.

Nerve Impulse

A nerve impulse begins at the tips of the dendrite
branches, passes through the dendrites to the cell
body, then through the axon and finally terminates
at branches of the axons.
Sensory neurons (Afferent Neurons)

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Sensory neurons
receive the initial
stimulus.
For example, sensory
neurons embedded in
the retina of the eye
are stimulated by light
Sensory neurons in the
hand are stimulated
by touch.
Motor Neurons (Efferent neurons)

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Motor neurons stimulate
effectors (target cells)
that produce some kind
of response.
For example, motor
neurons may stimulate
muscles, sweat glands
(to cool the body) or
cells in the stomach (to
secrete gastrin in
response to the smell of
food).
Association neurons (Interneurons)

Association neurons (interneurons) are located in the
spinal cord or brain and receive impulses from
sensory neurons or send impulses to motor neurons.
Interneurons
function to make
synaptic
connections with
other neurons.
Transmission of a nerve signal—due to
chemical changes across the membrane

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The membrane of an un-stimulated neuron is
polarized (there is a difference in charge between
the inside and outside of the cell)
Polarization is established when the inside is
negative with respect to the outside—due to an
excess of Na+ outside and an excess of K+ on the
inside.
The net negative charge on the
inside is primarily due to the
presence of large, negatively
charged proteins and nucleic acids
residing inside the cell.
Following the events in transmitting a
nerve impulse:
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1. Resting potential—the resting potential describes the unstimulated, polarized state of a neuron.
2. Action potential—in response to a stimulus, gated ion
channels in the membrane suddenly open and permit the Na+
on the outside to rush in. As this happens, the charge on the
membrane is depolarized (become more + on the inside).
Following the events in transmitting a
nerve impulse
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If the stimulus is strong enough, more Na+ gates open,
increasing the inflow of Na+ even more, causing an action
potential, or complete depolarization.
This, in turn, stimulates neighboring Na+ gates, further down
the neuron to open.
The action potential travels down the length of the neuron as
opened Na+ gates stimulate neighboring Na+ gates to open.
Following the events in transmitting a
nerve impulse

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3. Repolarization—In response to the inflow of Na+,
another kind of gated channel opens, this time allowing
the K+ on the inside to rush out of the cell.
The movement of K+ out of the cell causes
repolarization by restoring the original membrane
polarization (a condition where it is once again more
negative inside the cell)
Unlike the resting potential at the beginning, however,
this time there are more Na+ on the inside and more
K+ on the outside! Soon after the K+ gated channels
open, the Na+ gates close.
Following the events in transmitting a
nerve impulse

4. Hyperpolarization—By the time the K+ gated
channels close again, more K+ have moved out of
the cell than is actually necessary to establish the
original polarized potential. Thus, the membrane
becomes hyperpolarized.
Following the events in transmitting a
nerve impulse
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5. Refractory period. With the passage of the
action potential, the cell membrane is polarized, but
the Na+ and the K+ are on the wrong sides of the
membrane.
During this refractory period, the neuron will not
respond to a new stimulus.
To establish the original distribution of these ions,
the Na+ and K+ are returned to their resting
potential by Na+/K+ pumps in the cell membrane.
Sodium-Potassium Pumps
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A Sodium-Potassium Pump is an active transport
protein in the membrane of nerve cells. It actively
transports Na+ and K+ ions against their
concentration gradients to restore the original
polarized state of the nerve cell.
http://highered.mcgra
whill.com/sites/007249
5855/student_view0/c
hapter2/animation__h
ow_the_sodium_pota
ssium_pump_works.h
tml
Transmission of a nerve signal

http://www.biologymad.com/nervoussystem/nervei
mpulses.htm
Nerve Impulse Animations
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapte
r14/animation__the_nerve_impulse.html
http://www.biology4all.com/resources_library/sour
ce/63.swf
Synapses (aka: Synaptic Cleft)
A synapse is the gap that separates adjacent neurons.
 Transmission of an impulse across a synapse may be
electrical or chemical.
 In electrical synapses, the
action potential travels along
the membranes of gap
junctions, small tubes of
cytoplasm that connect
adjacent cells.
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Synapses (aka synaptic cleft)
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In most animals, the synapse between two neurons are
traversed by chemicals in the following steps:
1. Calcium (Ca2+) gates open. When an action
potential reaches the end of an axon, the
depolarization of the membrane causes gated channels
to open and allows Ca2+ to enter the cell
2. Synaptic vesicles release transmitters. The influx of
Ca2+ into the terminal end of the axon causes synaptic
vesicles to merge with the membrane of the next nerve
cell. This releases molecules of a chemical called
neurotransmitter into the synaptic cleft.
Synapses
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3. Neurotransmitters released by the first cell bind
to proteins on the surface of the second nerve cell.
4. The second cell’s membrane is either excited or
inhibited.
5. The neurotransmitter
is degraded and
recycled.
http://highered.mcgrawhill.com/sites/0072495855/student_vie
w0/chapter14/animation__transmission
_across_a_synapse.html
Neurotransmitters
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Common neurotransmitters:
1. Acetycholine—commonly secreted at a
neuromuscular junction, the gaps between motor
neurons and muscle cells, where it stimulates muscles
to contact.
2. Epinephrin—derived from amino acids and are
mostly secreted between neurons of the central
nervous system
3. Gamma aminobutyric acid (GABA) is usually an
inhibitory neurotransmitter
Peripheral Nervous System
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Peripheral Nervous System (All nerves going to and from the
Central Nervous System) Consists of:
Somatic Nervous System
Autonomic Nervous System
All nerves carrying sensory
Regulates bodily functions
and motor information
Automatic
Voluntary
Parasympathetic
Sympathetic
Nervous System
Nervous System
Maintains basic
Activates body to
bodily functions
deal with stress
Parasympathetic Vs. Sympathetic
Normal
everyday
life, when
not
excited,
just sitting
at home
watching
tv (unless
it’s a
really
scary
show!)
Fight or
flight
Response