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8.2: Structures & Processes of the Nervous System - Part II

McGraw-Hill Section 8.2
by

Ms. Klodt

on 4 April 2017

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Transcript of 8.2: Structures & Processes of the Nervous System - Part II

Nerve Impulses
Nerves use electricity to conduct impulses
At rest, inside of cell is negative, outside positive
Called resting potential, or difference across membrane
Typically -70 mV
Factors affecting charge:
Protein molecules inside cell are negative
K channels in plasma membrane are more open than Na channels
K leaves easily, Na cannot come in easily
Na-K pump
3 NA pumped out, 2 K pumped in using ATP
Overall, leads to polarization,, or lowering of the membrane potential
electrical charges change to transmit nerve impulses, called action potential
Rapid change in polarity
All or nothing principle
Steps:
Voltage-gated Na channels open
Na enters cell, making inside positive (+40 mV)
Change in membrane potential closes Na channels and opens K channels.
K moves out, making inside hyperpolarized (-90 mV)
Na-K pump and diffusion repolarize membrane (-70 mV)
Membrane rests for milliseconds, called refractory period
Action Potential
Parts of axons not covered with myelin are Nodes of Ranvier
Where depolarization occurs due to large numbers of Na channels
When NA moves in, charge flows to next node
Saltatory conduction, because it jumps node to node
Much faster than in unmyelinated neurons
Myelinated Nerve Impulses
Synapse is connection between neurons or between neuron and effector
Neuromuscular junction is synapse between motor neuron and muscle cell
Once impulse reaches synaptic terminal (end of neuron) neurotransmitters, or chemical messengers, carry impulse across synapse to next neuron
Intracellular synaptic vessicles push neurotransmitters out by exocytosis
Neurotrasmitters travel across synapse to dendrites of next neuron
Bind to receptor proteins, opening the channels and starting action potential
Neurotransmitters can be:
Excitatory: opens channels into cell, causing deplorization
Inhibitory: opens K channels out of cell, causing hyperpolarization (more neg)
Nerve Impulses Across a Synapse
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