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Introduction to
Vertebrate
Nervous Systems
Chapter 48
Functions of NS
 Receiving
information from environment
 Integrating information received from
environment
 Motor output in response
Neuron Structure
Neurons have different
shapes for different jobs
Vertebrate NS Structure
Central Nervous
System: brain
and spinal cord
Peripheral
Nervous
System:
peripheral
nerves
Nervous Conduction
 All
cells have a voltage potential across their
membranes
 Changes in this potential give rise to nervous
signaling
Resting Potential
Inside
the neuron
is more negative
than the outside
Ion channels allow
only some ions to
cross the
membrane
Action Potential
1.
At rest, there is more K+ inside
and more Na+ outside. Both ions’
channels are closed. Membrane
potential: -70mV
2. A stimulus causes the threshold
potential to be reached, so sodium
channels open and sodium ions
flow in and cause more Na+
channels to open. MP: -50mV
Action Potential
 3.
During depolarization, the Na+
channels are open, but the K+ channels
are closed. Cell interior becomes more
positive due to Na+ ion influx. MP:
+35mV
 4. During repolarization, Na+ channels
close and K+ channels open, causing
K+ to exit. The inside of the cell is
more negative than the outside. MP:
<+35mV
Depolarization and
Repolarization: what it
looks like
http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/action.htm
Action Potential
 5.
As the membrane potential heads
back toward resting, the K+
channels have not had a chance to
close. The membrane is
hyperpolarized and membrane
potential dips slightly below -70mV:
undershoot
 6. Eventually, ion concentrations
return to normal and resting potential
is restored. MP: -70mV
Membrane Potential
Principles of Neural
Firing
When
a nerve fires, it does not fire
“halfway” when stimulated
It will fire completely once a
stimulus is received and threshold
potential is reached: “all or
nothing” principle
No threshold, no action potential
Saltatory Conduction
Axons
are myelinated--increases
nervous signal conduction speed by
making signal jump between
Schwann cells.
Chemical Communication
 Occurs
at synapses: gaps between
neurons
 Uses neurotransmitters: substances
released from vesicles when action
potential reaches end of pre-synaptic axon
Synaptic transmission
1.
An AP depolarizes the synaptic
terminal membrane and Ca+2 ions
rush in.
2. Synaptic vesicles with
neurotransmitter fuse with
presynaptic membrane.
3. Vesicles fuse with membrane,
releasing neurotransmitter into cleft.
Synaptic transmission
4.
Neurotransmitter binds to
receptors on post-synaptic
membrane, which gets depolarized.
5. Neurotransmitter is degraded by
enzymes or taken up by another
neuron. This prevents the synaptic
response from persisting.
Synaptic transmission
Divisions of the NS
Somatic
NS
Controls the
voluntary
actions an
organism does
Example:
voluntary
muscle
movements
Autonomic
NS
Controls
involuntary
actions in an
organism
Example:
control of
heartbeat,
breathing, GI
tract
Divisions of the autonomic NS
 Sympathetic
 Activation
NS
is
correlated to
arousal and
energy
generation
 Examples: heart
beat increases,
liver converts
glycogen
glucose
 Parasympathetic
NS
 Activation
is
correlated to
calming actions
 Opposite actions
of SNS
Brain structures
Cerebrum:
conscious thought
Cerebellum: motor
coordination
Medulla oblongata:
involuntary functions
Meninges: tough
protective
membranes
Brain structures
 Corpus
callosum:
connects left and
right hemispheres
 Thalamus: relay
center for messages
 Hypothalamus:
controls 4F’s:
feeding, fleeing,
fighting, flirting
Regions of the Brain
Frontal Lobe:
personality,
control of
voluntary
muscle
movements,
thoughts
words
Regions of the Brain
Parietal Lobe:
interpretation of
textures,
understanding
symbols, verbal
articulation of
thoughts
words
Regions of the Brain
Occiptal Lobe:
organizes sight,
conscious
seeing
Regions of the Brain
Temporal Lobe:
speech,
olfaction,
interpretation of
auditory
sensations,
emotional
behavior