Why are action potentials sometimes described as being "all-or-none" in character?
A. The rate of propagation of an action potential down an axon is independent of stimulus strength.
B. They are associated with an absolute refractory period.
C. A supra-threshold stimulus is required to stimulate an action potential during the relative refractory period.
D. An action potential occurs whenever a suprathreshold stimulus occurs, and its amplitude does not vary with the size of a stimulus, as long as the membrane is not in the refractory period.
E. Action potentials are always the same size, even when ion gradients vary in size.
D
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Weakness in all four limbs is called ________________________________________ or ________________________________________
Fill in the blank(s) with correct word
The CNS consists of the ______ and the _____.
a. cranial nerves and spinal nerves b. brain and spinal cord c. brain and cranial nerves d. spinal nerves and spinal cord
The adaptive significance of the crossed extensor reflex when a person steps on a tack is to
A. slow the rate of removal of the foot from the tack. B. prevent the person from falling down. C. reduce the pain sensations. D. remove the foot from the tack. E. increase the rate at which withdrawal of the limb occurs.
Transamination
A. results in free fatty acids. B. requires glucose. C. can be used to synthesize essential amino acids. D. involves removing an amine group from an amino acid. E. directly produces urea.