ex_hw_10-1[1] - Fantasia Jones Exercise Physiology...

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Fantasia Jones Exercise Physiology September 30 th , 2009 4. Describe an action potential. What is required before an action potential is activated? -An action potential is a rapid and substantial depolarization of the neurons membrane of a neuron or muscle cell that is conducted through the cell. It usually last only about 1 ms. All action potentials start off as graded potentials. When it is stimulated enough it causes depolarization of at least 15 to 20 mV, and an action potential results. The membrane voltage at which a graded potential becomes an action potential is called the depolarization threshold. Any depolarization that does not attain the threshold will not result in an action potential. 5. Explain how an action potential is transmitted from a presynaptic neuron to a postsynaptic neuron. Describe a synapse and a neuromuscular junction. - The neuron can be transmitted across a synapse in only one direction: from the axon terminals of the presynaptic neuron to the postsynaptic receptors usually on the dendrites of the postsynaptic neuron. Impulses can also go directly on the cell body. The synapse is the site of action potential transmission from one neuron to another. There are two types, both chemical and mechanical. Neuromuscular junction is the synapse or junction of the axon terminal of a motorneuron with the motor end plate, and is responsible for the initiation of the action potential. 9.Describe the role of the muscle spindle in controlling muscle contraction: -When the motor neurons are stimulated to contract the extrafusal muscle fibers, the motor neurons are also activated contracting the ends of the intrafusal fibers. This stretches the central region of the muscle spindle, giving rise to sensory impulses that travel to the spinal cord and then to the motor neurons. The muscle increases its force production and it is enhanced throughout this function of the spindles. P.119 Chapter 4
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ex_hw_10-1[1] - Fantasia Jones Exercise Physiology...

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