20. At the peak of the action potential in normal physiological conditions, the membrane potential is usually:
(A) exactly at the equilibrium potential of .
(B) close to but more positive than the equilibrium potential of .
(C) close to but less positive than the equilibrium potential of .
(D) exactly at 0 mV.

16. Which of the following statements about blood vessel structure and function is FALSE? (A) Veins are more compliant than arteries. (B) The aorta and other large arteries serve as a pressure reservoir for the circulatory system. (C) Arterioles are small vessels whose resistance to blood flow can be varied. (D) Arterioles, capillaries, and veins all have valves that allow only one-way flow of blood.

17. In the systemic circuit, which of these best describes active hyperemia? (A) increased metabolic activity that results in vasoconstriction (B) increased metabolic activity that results in vasodilation (C) decreased blood flow to tissues that results in vasoconstriction (D) decreased blood flow to tissues that results in vasodilation

18. Normally, the hydrostatic pressure difference between capillary fluid and interstitial fluid favors movement of fluid _____ a tissue capillary. The protein osmotic pressure difference between capillary fluid and interstitial fluid normally favors movement of fluid _____ a tissue capillary. (A) into; into (B) into; out of (C) out of; out of (D) out of; into

19. Which is TRUE about the resting membrane potential? (A) It has the same value in all cells. (B) It is oriented so that the cell's interior is positive with respect to the extracellular fluid. (C) Only nerve and muscle cells have a potential difference across the membrane at rest. (D) It can be altered by changing concentration gradients of permeating ions.

21. At very low concentrations, epinephrine causes an artery to dilate. At higher concentrations epinephrine causes the same artery to constrict. How can these different effects be explained? (A) There is one type of epinephrine receptor that uses two second-messenger systems. (B) There are two types of epinephrine receptors with different affinities for epinephrine that use two different second-messenger systems. (C) There are two types of receptors for epinephrine that use the same second-messenger system. (D) At higher concentrations epinephrine can pass through the plasma membrane and directly stimulate contraction within the cell.

22. Which is TRUE regarding diffusion? (A) It depends upon the random motion of molecules. (B) It results in net movement of molecules from regions of low concentration to regions of high concentration. (C) It requires energy in the form of ATP. (D) It requires integral membrane proteins to occur.

23. Which of the following statements regarding skeletal muscle is TRUE? (A) Skeletal muscle fibers have pacemaker activity. (B) Skeletal muscle fibers are joined together by gap junctions. (C) A given skeletal muscle fiber will contract when excitatory nervous stimuli sufficiently exceed inhibitory nervous stimuli at the motor end plate. (D) A given skeletal muscle fiber will contract if excitatory synaptic inputs sufficiently exceed inhibitory synaptic inputs on the motor neuron that innervates that fiber and the motor neuron fires an action potential

24. Sensory feedback in the control of skeletal muscle activity is based on information from (A) myoneural junctions & motor end plates (B) muscle spindle apparatus & Golgi tendon organs (C) tension in the sarcomere (D) series elastic components

25. The _____ molecule hides the myosin-binding site on the actin when muscles are not contracting. (A) Calcium (B) ATP (C) Acetylcholine (D) tropomyosin

26. Muscles that are not used may degenerate or undergo a process of _____ (A) atrophy (B) hypertrophy (C) fatigue (D) tetany