BIOS 252 Exam 1 Questions and Answers with Rationales |
CHAMBERLAIN UNIVERSITY
Question 1. Which muscle primarily flexes the elbow and also strongly supinates the forearm?
A. Tibialis anterior
B. Triceps brachii
C. Pectoralis major
D. Biceps brachii
Correct Answer: D. Biceps brachii
Explanation: Biceps brachii flexes the elbow and is a strong supinator of the forearm, especially when the elbow is flexed.
Triceps brachii is the major elbow extensor. Pectoralis major acts mainly at the shoulder, and tibialis anterior acts at the
ankle.
Question 2. In an experiment, calcium is high and actin sites are exposed, but ATP cannot bind myosin.
Which step of cross-bridge cycling is blocked most directly?
A. Detachment of myosin from actin
B. Release of acetylcholine from the motor neuron
C. Propagation of the nerve action potential
D. Exposure of the actin binding site by tropomyosin movement
Correct Answer: A. Detachment of myosin from actin
Explanation: Calcium can expose actin binding sites, but cross-bridge detachment still requires ATP to bind myosin. If
ATP cannot bind, myosin can remain attached after the power stroke. Neuromuscular transmission and action potential
propagation are separate upstream processes.
Question 3. During maximal shortening of a skeletal muscle fiber, which sarcomere region is expected to
become smaller because it contains thin filaments not overlapping thick filaments?
A. I band
B. A band
C. M line
D. T tubule
Correct Answer: A. I band
Explanation: The I band contains regions of thin filament that do not overlap thick filament. As thin filaments slide toward
the M line, overlap increases and the I band narrows. The A band does not shorten because the length of the thick
filaments is unchanged.
Question 4. At one point on an axon, the membrane has just reached the peak of an action potential.
Sodium channels are beginning to inactivate while delayed potassium channels are opening. What change
should follow at that location?
A. The membrane will repolarize as potassium efflux becomes dominant.
B. The membrane will remain at the peak indefinitely.
C. Calcium will bind troponin and shorten the axon.
D. A second full action potential will begin immediately despite sodium-channel inactivation.
Correct Answer: A. The membrane will repolarize as potassium efflux becomes dominant.
Explanation: At the peak, sodium influx falls because sodium channels inactivate while potassium conductance rises.
Potassium efflux then drives the membrane potential back toward negative values. Sodium-channel inactivation also
contributes to the refractory period, preventing immediate re-excitation.
,Question 5. Neural stimulation of a skeletal muscle fiber stops. Which intracellular event is most
important for relaxation to proceed?
A. Collagen pulls tropomyosin off actin.
B. Myosin begins releasing acetylcholine.
C. Sodium-potassium pumps move calcium into T tubules.
D. SERCA pumps move calcium back into the sarcoplasmic reticulum.
Correct Answer: D. SERCA pumps move calcium back into the sarcoplasmic reticulum.
Explanation: Relaxation requires cytosolic calcium to fall so troponin loses bound calcium and tropomyosin reblocks
actin. SERCA pumps use ATP to transport calcium back into the sarcoplasmic reticulum. Without this calcium reuptake,
cross-bridge cycling can continue as long as ATP is available.
Question 6. A person has difficulty dorsiflexing the ankle and tends to catch the toes during the swing
phase of gait. Weakness of which muscle would contribute directly?
A. Tibialis anterior
B. Gastrocnemius
C. Gluteus maximus
D. Soleus
Correct Answer: A. Tibialis anterior
Explanation: Tibialis anterior is a major dorsiflexor of the ankle and helps clear the toes during swing. Gastrocnemius and
soleus are plantar flexors and would not produce dorsiflexion. Gluteus maximus acts at the hip rather than the ankle.
Question 7. Which region contains thick filaments but no overlapping thin filaments in a relaxed
sarcomere?
A. Terminal cisterna
B. H zone
C. I band
D. Z disc
Correct Answer: B. H zone
Explanation: The H zone is the central portion of the A band where only thick filaments are present in a relaxed
sarcomere. It narrows as contraction increases filament overlap. The I band contains thin filaments without thick-filament
overlap.
Question 8. What constitutes a motor unit in skeletal muscle?
A. One somatic motor neuron and all the muscle fibers it innervates
B. All motor neurons supplying an entire limb
C. One fascicle and its tendon
D. One muscle fiber and all the sensory neurons around it
Correct Answer: A. One somatic motor neuron and all the muscle fibers it innervates
Explanation: A motor unit includes a single alpha motor neuron and every skeletal muscle fiber supplied by its axon
branches. Activation of that neuron tends to activate all fibers in the unit. A whole muscle usually contains many motor
units of different sizes.
,Question 9. When a person rises onto the toes, the ball of the foot acts as the fulcrum, body weight is the
resistance, and the calf muscles apply effort through the Achilles tendon. Which lever class is this?
A. First-class lever
B. Third-class lever
C. No lever is present
D. Second-class lever
Correct Answer: D. Second-class lever
Explanation: A second-class lever places the resistance between the fulcrum and the effort. During standing plantar
flexion, the forefoot serves as the fulcrum, body weight lies between, and the calf-Achilles complex supplies effort. This
arrangement can provide a mechanical advantage for force.
Question 10. A muscle produces 120 N of tension while holding an object stationary. If the opposing load is
also 120 N and the joint does not move, which contraction type is present?
A. Eccentric
B. Isokinetic shortening
C. Isometric
D. Concentric
Correct Answer: C. Isometric
Explanation: Equal opposing forces with no change in joint position indicate that the active muscle develops tension
without changing overall length appreciably. That is the defining feature of an isometric contraction. A concentric or
eccentric contraction would involve shortening or lengthening while the load moves.
Question 11. A myosin head is cocked and carrying ADP and inorganic phosphate. What happens when
an exposed binding site on actin becomes available?
A. The Z disc releases acetylcholine.
B. The myosin head is immediately destroyed.
C. The sarcoplasmic reticulum closes its calcium pumps permanently.
D. The myosin head attaches to actin, forming a cross-bridge.
Correct Answer: D. The myosin head attaches to actin, forming a cross-bridge.
Explanation: An energized myosin head with ADP and phosphate can bind to an exposed site on actin to form a
cross-bridge. Subsequent phosphate release is associated with the power stroke. The binding step does not involve
acetylcholine release from the Z disc or destruction of myosin.
Question 12. Which muscle is the principal extensor of the elbow?
A. Biceps brachii
B. Deltoid
C. Brachialis
D. Triceps brachii
Correct Answer: D. Triceps brachii
Explanation: Triceps brachii is the primary muscle responsible for elbow extension. Biceps brachii and brachialis are
major elbow flexors. The deltoid primarily acts at the shoulder rather than serving as the main elbow extensor.
, Question 13. A researcher disrupts the regular alignment of sarcomeres across neighboring myofibrils.
Which visible feature of skeletal muscle would be reduced most directly?
A. Ability to bind oxygen
B. Number of nuclei
C. Presence of a sarcolemma
D. Cross-striations
Correct Answer: D. Cross-striations
Explanation: Skeletal muscle striations result from the aligned repeating pattern of dark A bands and light I bands in
sarcomeres. Disrupting that alignment would make the striped appearance less distinct. The sarcolemma, nuclei, and
oxygen-binding proteins are not what creates the banding pattern.
Question 14. Which connective tissue layer surrounds an entire skeletal muscle organ?
A. Perimysium
B. Epimysium
C. Endoneurium
D. Endomysium
Correct Answer: B. Epimysium
Explanation: The epimysium is the connective tissue sheath that encloses the whole skeletal muscle. Perimysium
surrounds fascicles, and endomysium surrounds individual muscle fibers. Keeping these levels distinct helps relate
microscopic structure to the gross muscle organ.
Question 15. All of the following are normal events at a skeletal neuromuscular junction EXCEPT which
one?
A. Acetylcholine binds ligand-gated receptors on the motor end plate.
B. Norepinephrine is the principal transmitter released by the somatic motor neuron.
C. Calcium enters the presynaptic terminal after depolarization.
D. Acetylcholinesterase helps terminate the signal.
Correct Answer: B. Norepinephrine is the principal transmitter released by the somatic motor neuron.
Explanation: The normal transmitter released by somatic motor neurons at skeletal NMJs is acetylcholine, not
norepinephrine. Presynaptic calcium entry triggers acetylcholine release, and nicotinic receptors generate the end-plate
potential. Acetylcholinesterase then helps remove the transmitter signal from the cleft.
Question 16. Which statement about a muscle's origin and insertion is generally correct?
A. The origin is usually the less movable attachment, and the insertion is usually the more movable attachment.
B. Only smooth muscle has origins and insertions.
C. Both attachments must lie on the same bone.
D. The insertion is always proximal and the origin always distal.
Correct Answer: A. The origin is usually the less movable attachment, and the insertion is usually the more
movable attachment.
Explanation: In conventional anatomical description, the origin is usually the relatively fixed attachment and the insertion
is the attachment that moves more during the named action. The exact amount of movement can vary with the activity, so
the distinction is functional rather than an absolute proximal-distal rule. Skeletal muscles commonly have named origins
and insertions on different structures.
CHAMBERLAIN UNIVERSITY
Question 1. Which muscle primarily flexes the elbow and also strongly supinates the forearm?
A. Tibialis anterior
B. Triceps brachii
C. Pectoralis major
D. Biceps brachii
Correct Answer: D. Biceps brachii
Explanation: Biceps brachii flexes the elbow and is a strong supinator of the forearm, especially when the elbow is flexed.
Triceps brachii is the major elbow extensor. Pectoralis major acts mainly at the shoulder, and tibialis anterior acts at the
ankle.
Question 2. In an experiment, calcium is high and actin sites are exposed, but ATP cannot bind myosin.
Which step of cross-bridge cycling is blocked most directly?
A. Detachment of myosin from actin
B. Release of acetylcholine from the motor neuron
C. Propagation of the nerve action potential
D. Exposure of the actin binding site by tropomyosin movement
Correct Answer: A. Detachment of myosin from actin
Explanation: Calcium can expose actin binding sites, but cross-bridge detachment still requires ATP to bind myosin. If
ATP cannot bind, myosin can remain attached after the power stroke. Neuromuscular transmission and action potential
propagation are separate upstream processes.
Question 3. During maximal shortening of a skeletal muscle fiber, which sarcomere region is expected to
become smaller because it contains thin filaments not overlapping thick filaments?
A. I band
B. A band
C. M line
D. T tubule
Correct Answer: A. I band
Explanation: The I band contains regions of thin filament that do not overlap thick filament. As thin filaments slide toward
the M line, overlap increases and the I band narrows. The A band does not shorten because the length of the thick
filaments is unchanged.
Question 4. At one point on an axon, the membrane has just reached the peak of an action potential.
Sodium channels are beginning to inactivate while delayed potassium channels are opening. What change
should follow at that location?
A. The membrane will repolarize as potassium efflux becomes dominant.
B. The membrane will remain at the peak indefinitely.
C. Calcium will bind troponin and shorten the axon.
D. A second full action potential will begin immediately despite sodium-channel inactivation.
Correct Answer: A. The membrane will repolarize as potassium efflux becomes dominant.
Explanation: At the peak, sodium influx falls because sodium channels inactivate while potassium conductance rises.
Potassium efflux then drives the membrane potential back toward negative values. Sodium-channel inactivation also
contributes to the refractory period, preventing immediate re-excitation.
,Question 5. Neural stimulation of a skeletal muscle fiber stops. Which intracellular event is most
important for relaxation to proceed?
A. Collagen pulls tropomyosin off actin.
B. Myosin begins releasing acetylcholine.
C. Sodium-potassium pumps move calcium into T tubules.
D. SERCA pumps move calcium back into the sarcoplasmic reticulum.
Correct Answer: D. SERCA pumps move calcium back into the sarcoplasmic reticulum.
Explanation: Relaxation requires cytosolic calcium to fall so troponin loses bound calcium and tropomyosin reblocks
actin. SERCA pumps use ATP to transport calcium back into the sarcoplasmic reticulum. Without this calcium reuptake,
cross-bridge cycling can continue as long as ATP is available.
Question 6. A person has difficulty dorsiflexing the ankle and tends to catch the toes during the swing
phase of gait. Weakness of which muscle would contribute directly?
A. Tibialis anterior
B. Gastrocnemius
C. Gluteus maximus
D. Soleus
Correct Answer: A. Tibialis anterior
Explanation: Tibialis anterior is a major dorsiflexor of the ankle and helps clear the toes during swing. Gastrocnemius and
soleus are plantar flexors and would not produce dorsiflexion. Gluteus maximus acts at the hip rather than the ankle.
Question 7. Which region contains thick filaments but no overlapping thin filaments in a relaxed
sarcomere?
A. Terminal cisterna
B. H zone
C. I band
D. Z disc
Correct Answer: B. H zone
Explanation: The H zone is the central portion of the A band where only thick filaments are present in a relaxed
sarcomere. It narrows as contraction increases filament overlap. The I band contains thin filaments without thick-filament
overlap.
Question 8. What constitutes a motor unit in skeletal muscle?
A. One somatic motor neuron and all the muscle fibers it innervates
B. All motor neurons supplying an entire limb
C. One fascicle and its tendon
D. One muscle fiber and all the sensory neurons around it
Correct Answer: A. One somatic motor neuron and all the muscle fibers it innervates
Explanation: A motor unit includes a single alpha motor neuron and every skeletal muscle fiber supplied by its axon
branches. Activation of that neuron tends to activate all fibers in the unit. A whole muscle usually contains many motor
units of different sizes.
,Question 9. When a person rises onto the toes, the ball of the foot acts as the fulcrum, body weight is the
resistance, and the calf muscles apply effort through the Achilles tendon. Which lever class is this?
A. First-class lever
B. Third-class lever
C. No lever is present
D. Second-class lever
Correct Answer: D. Second-class lever
Explanation: A second-class lever places the resistance between the fulcrum and the effort. During standing plantar
flexion, the forefoot serves as the fulcrum, body weight lies between, and the calf-Achilles complex supplies effort. This
arrangement can provide a mechanical advantage for force.
Question 10. A muscle produces 120 N of tension while holding an object stationary. If the opposing load is
also 120 N and the joint does not move, which contraction type is present?
A. Eccentric
B. Isokinetic shortening
C. Isometric
D. Concentric
Correct Answer: C. Isometric
Explanation: Equal opposing forces with no change in joint position indicate that the active muscle develops tension
without changing overall length appreciably. That is the defining feature of an isometric contraction. A concentric or
eccentric contraction would involve shortening or lengthening while the load moves.
Question 11. A myosin head is cocked and carrying ADP and inorganic phosphate. What happens when
an exposed binding site on actin becomes available?
A. The Z disc releases acetylcholine.
B. The myosin head is immediately destroyed.
C. The sarcoplasmic reticulum closes its calcium pumps permanently.
D. The myosin head attaches to actin, forming a cross-bridge.
Correct Answer: D. The myosin head attaches to actin, forming a cross-bridge.
Explanation: An energized myosin head with ADP and phosphate can bind to an exposed site on actin to form a
cross-bridge. Subsequent phosphate release is associated with the power stroke. The binding step does not involve
acetylcholine release from the Z disc or destruction of myosin.
Question 12. Which muscle is the principal extensor of the elbow?
A. Biceps brachii
B. Deltoid
C. Brachialis
D. Triceps brachii
Correct Answer: D. Triceps brachii
Explanation: Triceps brachii is the primary muscle responsible for elbow extension. Biceps brachii and brachialis are
major elbow flexors. The deltoid primarily acts at the shoulder rather than serving as the main elbow extensor.
, Question 13. A researcher disrupts the regular alignment of sarcomeres across neighboring myofibrils.
Which visible feature of skeletal muscle would be reduced most directly?
A. Ability to bind oxygen
B. Number of nuclei
C. Presence of a sarcolemma
D. Cross-striations
Correct Answer: D. Cross-striations
Explanation: Skeletal muscle striations result from the aligned repeating pattern of dark A bands and light I bands in
sarcomeres. Disrupting that alignment would make the striped appearance less distinct. The sarcolemma, nuclei, and
oxygen-binding proteins are not what creates the banding pattern.
Question 14. Which connective tissue layer surrounds an entire skeletal muscle organ?
A. Perimysium
B. Epimysium
C. Endoneurium
D. Endomysium
Correct Answer: B. Epimysium
Explanation: The epimysium is the connective tissue sheath that encloses the whole skeletal muscle. Perimysium
surrounds fascicles, and endomysium surrounds individual muscle fibers. Keeping these levels distinct helps relate
microscopic structure to the gross muscle organ.
Question 15. All of the following are normal events at a skeletal neuromuscular junction EXCEPT which
one?
A. Acetylcholine binds ligand-gated receptors on the motor end plate.
B. Norepinephrine is the principal transmitter released by the somatic motor neuron.
C. Calcium enters the presynaptic terminal after depolarization.
D. Acetylcholinesterase helps terminate the signal.
Correct Answer: B. Norepinephrine is the principal transmitter released by the somatic motor neuron.
Explanation: The normal transmitter released by somatic motor neurons at skeletal NMJs is acetylcholine, not
norepinephrine. Presynaptic calcium entry triggers acetylcholine release, and nicotinic receptors generate the end-plate
potential. Acetylcholinesterase then helps remove the transmitter signal from the cleft.
Question 16. Which statement about a muscle's origin and insertion is generally correct?
A. The origin is usually the less movable attachment, and the insertion is usually the more movable attachment.
B. Only smooth muscle has origins and insertions.
C. Both attachments must lie on the same bone.
D. The insertion is always proximal and the origin always distal.
Correct Answer: A. The origin is usually the less movable attachment, and the insertion is usually the more
movable attachment.
Explanation: In conventional anatomical description, the origin is usually the relatively fixed attachment and the insertion
is the attachment that moves more during the named action. The exact amount of movement can vary with the activity, so
the distinction is functional rather than an absolute proximal-distal rule. Skeletal muscles commonly have named origins
and insertions on different structures.
