PSIO 201 EXAM 3 CERTIFICATION
EXAMINATION 2026 PREMIUM QUESTIONS
AND SOLUTIONS
◉ Contraction cycle step 5:.
Answer: ATP is hydrolyzed and the energy released is used to re-
energize the myosin head back to its start position ('cocked') so a
new crossbridge can form
◉ Contraction cycle step 6:.
Answer: the contraction cycle repeats until the myosin binding sites
on actin are no longer available
◉ Rigor Complex.
Answer: the attached head group after the power stroke
◉ Rigor mortis.
Answer: the rigor of death because of the lack of ATP to detach the
crossbridge
◉ Sequence of Events in Crossbridge Cycling.
Answer: 1. Excitation
,2. Excitation Contraction coupling
3. Contraction
4. Relaxtion
◉ Excitation.
Answer: electrical signal from central nervous system
-arrives at the Neuromuscular junction
◉ Neuromuscular Junction (excitation) step 1:.
Answer: Action potential arrives at the synaptic end bulb of motor
neuron and causes opening of voltage gated Ca2+channels
◉ Neuromuscular Junction (excitation) step 2:.
Answer: Synaptic vesicles containing the neurotransmitter,
Acetylcholine (ACh) undergo exocytosis
◉ Neuromuscular Junction (excitation) step 3:.
Answer: ACh is released into the synaptic cleft and binds to ACh
receptors on the sarcolemma (motor end plate)
◉ Neuromuscular Junction (excitation) step 4:.
Answer: ACh receptors open and allow Na+ to enter the muscle fiber,
generating an action potential on the sarcolemma
, ◉ Neuromuscular Junction (excitation) step 5:.
Answer: ACh is quickly broken down to Acetate and Choline by
Acetylcholine Esterase (AChE)
◉ Excitation -Contraction Coupling.
Answer: release of Ca2+ from the SR
1. AP runs along sarcolemma, continues into T-tubules
2. Triggers release of Ca2+from SR
3. Ca2+ diffuses into sarcoplasm and myofibrils
4. Ca2+ binds to troponin on thin filament (myosin binding site on
actin gets exposed)
5. Crossbridges form --> tension is generated (starts contraction)
◉ Relaxation.
Answer: sequestration of Ca2+
1. When Action Potentials stop arriving at the NMJ, the 'trigger' to
release Ca2+ from the SR stops
2. Active Ca2+ transporters in the SR membrane pump Ca2+ back
into the SR
3. Cytoplasmic [Ca2+] decreases
4. As [Ca2+] falls, Ca2+ comes off troponin -the myosin binding sites
on actin get covered by tropomyosin
EXAMINATION 2026 PREMIUM QUESTIONS
AND SOLUTIONS
◉ Contraction cycle step 5:.
Answer: ATP is hydrolyzed and the energy released is used to re-
energize the myosin head back to its start position ('cocked') so a
new crossbridge can form
◉ Contraction cycle step 6:.
Answer: the contraction cycle repeats until the myosin binding sites
on actin are no longer available
◉ Rigor Complex.
Answer: the attached head group after the power stroke
◉ Rigor mortis.
Answer: the rigor of death because of the lack of ATP to detach the
crossbridge
◉ Sequence of Events in Crossbridge Cycling.
Answer: 1. Excitation
,2. Excitation Contraction coupling
3. Contraction
4. Relaxtion
◉ Excitation.
Answer: electrical signal from central nervous system
-arrives at the Neuromuscular junction
◉ Neuromuscular Junction (excitation) step 1:.
Answer: Action potential arrives at the synaptic end bulb of motor
neuron and causes opening of voltage gated Ca2+channels
◉ Neuromuscular Junction (excitation) step 2:.
Answer: Synaptic vesicles containing the neurotransmitter,
Acetylcholine (ACh) undergo exocytosis
◉ Neuromuscular Junction (excitation) step 3:.
Answer: ACh is released into the synaptic cleft and binds to ACh
receptors on the sarcolemma (motor end plate)
◉ Neuromuscular Junction (excitation) step 4:.
Answer: ACh receptors open and allow Na+ to enter the muscle fiber,
generating an action potential on the sarcolemma
, ◉ Neuromuscular Junction (excitation) step 5:.
Answer: ACh is quickly broken down to Acetate and Choline by
Acetylcholine Esterase (AChE)
◉ Excitation -Contraction Coupling.
Answer: release of Ca2+ from the SR
1. AP runs along sarcolemma, continues into T-tubules
2. Triggers release of Ca2+from SR
3. Ca2+ diffuses into sarcoplasm and myofibrils
4. Ca2+ binds to troponin on thin filament (myosin binding site on
actin gets exposed)
5. Crossbridges form --> tension is generated (starts contraction)
◉ Relaxation.
Answer: sequestration of Ca2+
1. When Action Potentials stop arriving at the NMJ, the 'trigger' to
release Ca2+ from the SR stops
2. Active Ca2+ transporters in the SR membrane pump Ca2+ back
into the SR
3. Cytoplasmic [Ca2+] decreases
4. As [Ca2+] falls, Ca2+ comes off troponin -the myosin binding sites
on actin get covered by tropomyosin
