Exercise 10, Activities 1, 6, 7 a&P I

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Introduction and Objective
The action potential is an impulse of electrical activity. Action potential occurs when a neuron sends messages electrochemically down an axon called a nerve impulse. When a neuron is not stimulated or inactive, it is at resting potential. When a neuron is at rest, the electrical charge on the inside of the neuron is negative while the electrical charge on the outside of the neuron is positive. The resting membrane potential of a neuron is about -70 mV (mV = millivolts). At rest, the outside of a neuron contains an excess of sodium ions (Na+) while the inside of a neuron contains an excess of potassium ions (K+).) At rest, potassium ions (K+) can cross through the cell membrane easily while sodium ions (Na+) have a more difficult time crossing. When a stimulus reaches a resting potential of a neuron it causes gated ion channels to open allowing the sodium ions (Na+) that was on the outside of the membrane to go into the cell. Sodium has a positive charge, which makes the neuron become more positive and depolarized. As depolarization reaches threshold of -55mV, the action potential is triggered and sodium ions (Na+) rush into the cell. If the neuron does not reach this critical threshold, then no action potential will fire. It takes longer for potassium channels to open. When they do open, potassium (K+) rushes out of the cell, reversing the depolarization. Also at this time, sodium channels (Na+) is exiting the cell and starting to close. This causes the action potential to go back toward -70 mV, which is called repolarization. When the action potential goes past -70 mV hyperpolarization occurs because the potassium channels stay open. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.

A nerve consists of a bunch of axons clustered together. An axon is a portion of a nerve cell that carries nerve impulses away from the cell body. The response of the nerve is called the compound action...
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