Download File - Mrs. LeCompte

Ch. 37: The Nervous System
Nervous tissue is unique to animals

Nerve net = simplest form; several nerves with no central organizing structure
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Cephalization = concentration of nervous tissue at the anterior end
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Ganglion = clusters of nerve tissue
o Increases in complexity  brain
PHYSIOLOGY OF NERVE CELLS
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Neuron = basic nerve cells
o Dendrites = receive signals
o Cell Body = processes signals
o Axon = sends signal to the next cell
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Myelin_ Sheath = insulating layer that coats many axons
o Keeps signals contained to a given neuron
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Schwann Cells = coated parts of axons
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Nodes of Ranvier = gaps between Schwann cells
o Increase rate of transmission of nerve impulses by being able to “jump” over
Schwann cells to next Node of Ranvier = Saltatoey Conduction
ACTION POTENTIAL (NERVE IMPULSE)
Resting Potential = when the axon is not conducting an impulse (about -70 mV)

All ion channels closed
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More Na+ on outside the axon and more K+ inside
o Maintained by the presence of the Sodium-Potassium Pump (from beginning of
year)


Requires ATP to establish
Overall, inside is more negative than the outside
Action Potential = rapid change in polarity across part of an axon as a nerve impulse occurs

Threshold Potential must be reached  all-or-none response
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Depolarization = Sodium channels open and Na+ rushes into cell
o If threshold is reached, many more Na+ channels open, and the action potential
begins
o Makes cell more and more positive (to about +40 mV)
o The reversal in polarity causes Na+ channels to close and K+ channels to open

Repolarization = as K+ enters the cell, the membrane potential swings back to slightly
below -70 mV
o Refractory Period = Change in polarity again causes K+ channels to close and for
a brief time the channels are unable to open

Ensures that the signal continues in one direction without going backward
SYNAPSE
Neurons spread signals from one end to the other and then must pass this signal on to another
cell = Synapse

Presynaptic Cell = The cell with the signal

Postsynaptic Cell = The cell that will receive the signal

Synaptic Cleft = The small gap between the two neurons
The (electrical) impulse itself cannot cross the synaptic cleft, so it must use instead
neurotransmitters = molecules that can carry the signal across a synaptic cleft

Are stored in synaptic vesicles

When nerve impulses reach the end of the presynaptic cell, gated channels for Ca+ open,
and Ca+2 enters
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The sudden rise in Ca+2 causes synaptic vesicles to merge with the presynaptic membrane
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Neurotransmitters are released into the synaptic cleft

They diffuse across the space and bind to receptors on the postsynaptic membrane

May be excitatory (cause an action potential in the postsynaptic cell) or inhibitory
(prevent an action potential in the postsynaptic cell)
Neurotransmitters to Be Familiar With:
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Acetylcholine = excites skeletal muscle but inhibits cardiac muscle
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Norepinephrine = important to dreaming, waking, and mood
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Epinephrine = important to arousal, alertness, attention, and cognition

GABA (Gamma Amino Butyric Acid) = important inhibitory neurotransmitter
o Prevents signals from continuing to be sent or from being sent in the wrong
direction
o Regulates norepinephrine, dopamine, and serotonin

Dopamine = used in emotions, learning, attention

Serotonin = used in thermoregulation, sleeping, emotions, and perception

Endorphins = produce feelings of tranquility
After neurotransmitters are produced, they must be removed quickly so the body can keep
responding to the environment

Acetylcholinesterase = enzyme that breaks down acetylcholine

In some, the presynaptic cell reabsorbs the neurotransmitter (repackaged for reuse?)
THE CENTRAL NERVOUS SYSTEM
Brain + Spinal Cord
Three Functions:
1) Receives sensory input
2) Performs integration (Processes the signal)
3) Generates motor output (response)
THE BRAIN
Different areas have different functions
Cerebrum (Forebrain) = major processing center

In charge of motor control, memory, reasoning, speech, and judgment

Cerebral Cortex = learning, memory, language, and speech
Cerebellum(Hindbrain) = maintains posture, balance, and coordinates voluntary movements
Brain Stem (Midbrain) = controls involuntary processes (digestion, heartbeat, breathing, etc.)
The Limbic System = parts of the brain that connect emotions and reasoning

Also important in learning and memory
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Amygdala = major part of brain for this system
THE PERIPHERAL NERVOUS SYSTEM
All the nerves outside of the central nervous system
Somatic System = voluntary muscle contractions
The Reflex Arc = involves only the spinal cord

Sensory Receptors generate nerve impulses that move along sensory axons  through
dorsal root ganglion  spinal cord  effector = generates a response

Allows for a quicker response than if you sent the signal all the way to the brain first
Autonomic System = involuntary muscle responses

Sympathetic Division = useful in “fight or flight” response
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Parasympathetic Division = useful when in normal (relaxed) state