6.True or False: One motor unit always activates exactly one muscle fiber? 7·Exp
ID: 3509493 • Letter: 6
Question
6.True or False: One motor unit always activates exactly one muscle fiber? 7·Explain why the statement in the previous question is true or false in terms of innervation ratio? 8.In terms of orderly recruitment, describe what happens when you pick up a box that is much heavier than you anticipated? 9.A student was asked to hold some books by a stranger. While holding the books she realized that it was for a psych class experiment, so she statically held the books away from her body towards the stranger to try to give them back. What type of contraction (concentric, eccentric, or isometric) is occurring while she is holding the books? 10.Explain how fused tetanus contractions are generated in muscles. Include in the description the following terms: relaxation period and refractory period? 11. Describe and sketch the active and passive force-length relationship of muscle? Why is muscle force dependent on muscle length? (hint: discuss in terms of sarcomere components at the various locations along the force-length curve)Explanation / Answer
Answers:
Q6) One motor unit activates exactly one muscle fiber.True or False.
A: False.
Q.7) Explanation to the above statement :
A) Motor unit: It is the single motor neuron (efferent ) which can innervate a group of muscle fibers. Motor neurons could be alpha, beta or gamma. Among these alpha fibers are the main group of motor neurons supplying a group of muscle fibers.They originate from the anterior horn grey cells of the spinal cord. The beta and gamma types(mostly) are associated with muscle tone regulation, reflex activity etc. They are seen in muscle spindles.
Innervation ratio: The number of muscle fibers innervated by a motor neuron gives the innervation ratio or the total number of muscle fibers divided by the motor unit.
The ratio depends upon the type of activity done by that particular muscle. For example, the extraocular muscles controlling eyeball movements need fine motor control and hence the ratio of muscle fibers to the motor neuron would be less; a ratio of 10:1; whereas the muscle group like the gastrocnemius(leg muscle) that do not need a precision motor control the ratio would be much higher; 2000:1,which means that one motor unit supplies 2000 muscle fibers.
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