WSU Biology 251 Exam 3 Updated 2026/2027
Questions with Answers
1. An End Plate Potential initiates an action potential, which propagates across the
membrane and down into the T-Tubules in the muscle cell which causes the _____ to
release _____ , - ANSWER-sarcoplasmic reticulum, Ca++
2. which then binds to _______ and causes _____ to move aside, thereby exposing the
myosin binding sites on the actin molecules. On the contact of myosin and actin, the
myosin head releases _____ and phosphate, and the myosin head strokes forward -
ANSWER-troponin; tropomyosin, ADP
3. How many motor neurons innervate a single skeletal muscle fiber? What % of muscle
fibers in a motor unit contract when the motor neuron that innervates them is activated? -
ANSWER-1; 100%
4. The functional unit (that is, the smallest component that performs all the functions of the
whole muscle) of skeletal muscle is the - ANSWER-Sarcomere
5. Which of the following statements about skeletal muscle motor units is true?
a) The number of muscle fibers in a motor unit that contract is proportional to
the strength of the action potential in the motor neuron
b) Anytime a muscle contracts all the motor units in the muscle are activated
c) Each motor unit contains all 3 muscle fiber types
d) Both a and b are true
e) None of the above are true - ANSWER-e) None of the above are true
6. Which of the following accurately describes changes in a myofibril during contraction?
a) the sarcomeres shorten
b) z-lines get closer together
c) the sarcomeres stay the same width
d) both a and b occur
e) both b and c occur - ANSWER-d) the sarcomeres shorten and the z-lines get
closer together
7. In Fig 1 part A is called _____; part C of Figure 1 is called ____ - ANSWER-Latent
period; relaxation time
8. Which can be rapidly altered (in seconds) to influence the strength of skeletal muscle
contraction? - ANSWER-motor unit recruitment and frequency of stimulation
9. Creatine phosphate is the ________ source of energy tapped by an exercising muscle.
______ is produced from creatine phosphate and _______ in the presence of the enzyme
creatine phosphatase. - ANSWER-first, ATP, ADP
, 10. Which of the following are characteristic of slow oxidative muscle fibers?
a) low myosin-ATPase activity
b) few mitochondria
c) low capacity for oxidative phosphorylation
d) few capillaries
e) none of the above are characteristic of slow oxidative fibers - ANSWER-a)
low myosin-ATPase activity
11. Mitochondrial density is high in which muscle fiber type(s)?
a) Slow oxidative
b) Fast oxidative
c) Fast glycolytic
d) Both a and b
e) Both b and c - ANSWER-d) Slow oxidative and Fast oxidative
12. In Figure 2 part A is called __________________; part C is called
___________________. - ANSWER-twitch, tetanus
13. Smooth muscle myogenic activity occurs in two different ways; by _______ and by
______. - ANSWER-slow wave potential, pacemaker activity
14. What type of muscle is (are) linked by gap junctions? - ANSWER-Single Unit Smooth
and Cardiac
15. What type of muscle contain(s) sarcomeres? - ANSWER-Skeletal and Cardiac
16. What type of muscle contract(s) using cross bridge cycling? - ANSWER-Skeletal, Multi
Unit smooth, Single Unit Smooth, Cardiac
17. During smooth muscle contraction, Ca++ enters the cell primarily from the ______ via
the process of __________. The Ca++ then activates _________, which in turn activates
______ to phosphorylate myosin. - ANSWER-ECF; diffusion; calmodulin; myosin light
chain kinase
18. Factors that modify cytosolic Ca++ levels and hence contractile strength in both single
unit and multiunit smooth muscle are - ANSWER-both branches of the autonomic
nervous system, hormones and metabolites
19. Indicate which is the proper sequence of blood flow though the circulatory system:
right atrium
left atrium
right ventricle
left ventricle
pulmonary artery
pulmonary vein
lungs
Questions with Answers
1. An End Plate Potential initiates an action potential, which propagates across the
membrane and down into the T-Tubules in the muscle cell which causes the _____ to
release _____ , - ANSWER-sarcoplasmic reticulum, Ca++
2. which then binds to _______ and causes _____ to move aside, thereby exposing the
myosin binding sites on the actin molecules. On the contact of myosin and actin, the
myosin head releases _____ and phosphate, and the myosin head strokes forward -
ANSWER-troponin; tropomyosin, ADP
3. How many motor neurons innervate a single skeletal muscle fiber? What % of muscle
fibers in a motor unit contract when the motor neuron that innervates them is activated? -
ANSWER-1; 100%
4. The functional unit (that is, the smallest component that performs all the functions of the
whole muscle) of skeletal muscle is the - ANSWER-Sarcomere
5. Which of the following statements about skeletal muscle motor units is true?
a) The number of muscle fibers in a motor unit that contract is proportional to
the strength of the action potential in the motor neuron
b) Anytime a muscle contracts all the motor units in the muscle are activated
c) Each motor unit contains all 3 muscle fiber types
d) Both a and b are true
e) None of the above are true - ANSWER-e) None of the above are true
6. Which of the following accurately describes changes in a myofibril during contraction?
a) the sarcomeres shorten
b) z-lines get closer together
c) the sarcomeres stay the same width
d) both a and b occur
e) both b and c occur - ANSWER-d) the sarcomeres shorten and the z-lines get
closer together
7. In Fig 1 part A is called _____; part C of Figure 1 is called ____ - ANSWER-Latent
period; relaxation time
8. Which can be rapidly altered (in seconds) to influence the strength of skeletal muscle
contraction? - ANSWER-motor unit recruitment and frequency of stimulation
9. Creatine phosphate is the ________ source of energy tapped by an exercising muscle.
______ is produced from creatine phosphate and _______ in the presence of the enzyme
creatine phosphatase. - ANSWER-first, ATP, ADP
, 10. Which of the following are characteristic of slow oxidative muscle fibers?
a) low myosin-ATPase activity
b) few mitochondria
c) low capacity for oxidative phosphorylation
d) few capillaries
e) none of the above are characteristic of slow oxidative fibers - ANSWER-a)
low myosin-ATPase activity
11. Mitochondrial density is high in which muscle fiber type(s)?
a) Slow oxidative
b) Fast oxidative
c) Fast glycolytic
d) Both a and b
e) Both b and c - ANSWER-d) Slow oxidative and Fast oxidative
12. In Figure 2 part A is called __________________; part C is called
___________________. - ANSWER-twitch, tetanus
13. Smooth muscle myogenic activity occurs in two different ways; by _______ and by
______. - ANSWER-slow wave potential, pacemaker activity
14. What type of muscle is (are) linked by gap junctions? - ANSWER-Single Unit Smooth
and Cardiac
15. What type of muscle contain(s) sarcomeres? - ANSWER-Skeletal and Cardiac
16. What type of muscle contract(s) using cross bridge cycling? - ANSWER-Skeletal, Multi
Unit smooth, Single Unit Smooth, Cardiac
17. During smooth muscle contraction, Ca++ enters the cell primarily from the ______ via
the process of __________. The Ca++ then activates _________, which in turn activates
______ to phosphorylate myosin. - ANSWER-ECF; diffusion; calmodulin; myosin light
chain kinase
18. Factors that modify cytosolic Ca++ levels and hence contractile strength in both single
unit and multiunit smooth muscle are - ANSWER-both branches of the autonomic
nervous system, hormones and metabolites
19. Indicate which is the proper sequence of blood flow though the circulatory system:
right atrium
left atrium
right ventricle
left ventricle
pulmonary artery
pulmonary vein
lungs
