Lecture #21 Date

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Transcript Lecture #21 Date

Chapter 48 ~ Nervous System
Nervous systems
Effector cells
– muscle or gland cells
– bundles of neurons wrapped
in connective tissue
Central nervous system
– brain and spinal cord
Peripheral nervous system
– sensory and motor neurons
Simple Nerve Circuit
Gray matter – the “hard
drive” or thought and
White matter – the
“cables” or carrying
signals to/from gray
NEURON: Structural Unit of NS
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
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
Excitable cells~ cells that can change membrane potentials (neurons,
Resting potential~ the unexcited state of excitable cells
The Action Potential
The Action Potential
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
“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;
Synaptic communication:
signal transmission
Presynaptic cell: transmitting cell
Postsynaptic cell: receiving cell
Synaptic cleft: separation gap
Synaptic vesicles: release
Ca+ influx: caused by action
potential; vesicles fuse with
presynaptic membrane and
Neurotransmitter molecules
Synaptic Communication:
signal transmission
Acetylcholine (most common)
•skeletal muscle
Biogenic amines (derived from amino acids)
Amino acids
Neuropeptides (short chains of amino acids)
Vertebrate PNS
Cranial nerves (brain origin)
Spinal nerves (spine origin)
Sensory division
Motor division
•somatic system
voluntary, conscious control
•autonomic system
conservation of energy
increase energy consumption
The Vertebrate Brain
•cerebrum~memory, learning,
•cerebral cortex~sensory
and motor nerve cell bodies
•corpus callosum~connects left
and right hemispheres
•thalamus; hypothalamus
•inferior (auditory) and superior
(visual) colliculi
•cerebellum~coordination of movement
•medulla oblongata/ pons~autonomic,
homeostatic functions