Which statement best describes the all-or-none principle?
A) An action potential happens completely, or it doesn't happen at all.
B) All voltage-gated sodium channels will open or none will open.
C) All neurons conduct an action potential together, or none do.
D) Local, or graded, potentials will always become action potentials.
Answer: A
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Coronary vessels are open when the heart is
A. contracting. B. relaxed.
In terms of controlling micturition, the somatic nervous system innervates the ________, the 86) parasympathetic nervous system innervates the ________, and the sympathetic nervous system innervates the ________.
A) external urethral sphincter : detrusor muscle : internal urethral sphincter B) internal urethral sphincter : detrusor muscle : external urethral sphincter C) bladder : micturition reflex : external urethral sphincter D) internal urethral sphincter : external urethral sphincter : detrusor muscle E) bladder skeletal muscle : bladder smooth muscle : external urethral sphincter
The ________ is equal to the hydrostatic pressure of the blood in the capillaries minus the hydrostatic pressure of tissue interstitial fluid outside the capillaries.
A. blood pressure B. net filtration pressure C. osmotic pressure D. None of the choices are correct.
Melatonin's actions may include
a. regulation of circadian rhythms b. antioxidant activity c. induction of calcium reabsorption d. both a and b e. none of the above