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Chapter 48 ~ Nervous System
Nervous systems
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Effector cells
– muscle or gland cells
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Nerves
– bundles of neurons wrapped
in connective tissue
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Central nervous system
(CNS)
– brain and spinal cord
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Peripheral nervous system
(PNS)
– sensory and motor neurons
Simple Nerve Circuit
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Gray matter – the “hard
drive” or thought and
interpretation
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White matter – the
“cables” or carrying
signals to/from gray
matter
NEURON: Structural Unit of NS
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Cell body: nucelus and organelles
Dendrites: receive NT, relay to cell body
Axons: electrical impulses toward terminals
Myelin sheath: supporting, insulating layer
Synaptic terminals: neurotransmitter releaser
Synapse: neuron junction; space for NT release
***chemical  electrical  chemical RELAY
Neural signaling, I
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Membrane potential (voltage differences across the plasma membrane)
Intracellular/extracellular ionic concentration difference
K+ diffuses out (Na+ in); large anions cannot follow….why not?
Net negative charge of about -70mV
Science as a Process…
Neural signaling
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Excitable cells~ cells that can change membrane potentials (neurons,
muscle)
Resting potential~ the unexcited state of excitable cells
The Action Potential
The Action Potential
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1.
2.
3.
4.
5.
6.
A neuron is like a French Fry: high Na+ outside, high K+ (POTassium/potato) inside!!!
During the AP, we will turn our axon INSIDE OUT!!!
To fire an action potential, we have to be at resting potential (-70 mV), maintained by
closed Na+ and K+ channels
If enough NT molecules are picked up by dendrites, it begins with opening of Na+
channels in axon  depolarization as inside of axon becomes more positive
More and more Na+ rushes in, steadily and rapidly making inside of neuron more positive
until ~+35 mV
This alteration of charge causes 2 events: close off the open Na+ channels w/inactivation
loops AND opening of K+ channels (so K+ now rushes OUT), which together make the
inside of the neuron become more NEGATIVE again
Drops and drops until inside of axon becomes so negative (-75 to -80 mV) that the K+
channels close again. The neuron is now REFRACTORY to all signals; no more AP can
fire because the Na+ channels are in closed conformation.
But look at what we have done: we started with Na+ outside and K+ inside, and during the
AP the Na+ move IN and the K+ moved OUT, so our neuron is inside-out!!! What will we
do to fix this and restore resting potential? Enter Na+/K+ pumps  use energy from ATP
hydrolysis to pump 3 Na+ out and 2 K+ in for each ATP.
Directional signaling
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“Travel” of the action potential is self-propagating in forward direction only
Action potential speed:
– 1 - Axon diameter (larger = faster; 100 m/sec)
– 2 - Nodes of Ranvier (concentration of ion channels); salutatory conduction;
150m/sec
Synaptic communication:
signal transmission
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Presynaptic cell: transmitting cell
Postsynaptic cell: receiving cell
Synaptic cleft: separation gap
Synaptic vesicles: release
neurotransmitter
Ca+ influx: caused by action
potential; vesicles fuse with
presynaptic membrane and
release….
Neurotransmitter molecules
Synaptic Communication:
signal transmission
Neurotransmitters
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Acetylcholine (most common)
•skeletal muscle
Biogenic amines (derived from amino acids)
•norepinephrine
•dopamine
•serotonin
Amino acids
Neuropeptides (short chains of amino acids)
•endorphin
Vertebrate PNS
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Cranial nerves (brain origin)
Spinal nerves (spine origin)
Sensory division
Motor division
•somatic system
voluntary, conscious control
•autonomic system
√parasympathetic
conservation of energy
√sympathetic
increase energy consumption
The Vertebrate Brain
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Forebrain
•cerebrum~memory, learning,
emotion
•cerebral cortex~sensory
and motor nerve cell bodies
•corpus callosum~connects left
and right hemispheres
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•thalamus; hypothalamus
Midbrain
•inferior (auditory) and superior
(visual) colliculi
Hindbrain
•cerebellum~coordination of movement
•medulla oblongata/ pons~autonomic,
homeostatic functions