Exsc 223 Exam 3 With Complete
Solutions 2026 Updated.
sliding filament model - Answer during contraction, thin and thick filaments slide past each
other so that actin and myosin overlap
*neither thick nor thin filaments actually change in length
What happens as a muscle cell shortens - Answer -I band shortens
-Distance between Z-discs shorten
-H-zone disappears
-Continuous A-bands move closer together, but their length does not change
What specific molecule binds calcium? - Answer troponin -- binds to calcium and changes
shape of troponin c
Tropomyosin - Answer covers up the myosin binding site on actin
Why is troponin important? - Answer key protein that binds to calcium and changes the
shape of troponin c
*causes us to expose the myosin binding site on the actin molecule*
Which organelles have the highest resting concentration of calcium? - Answer the SR has the
highest resting concentration of calcium
the mitochondrion provides the ATP energy a cell needs for muscle activity
What induces a skeletal muscle to contract? - Answer 1. the fiber must be activated
(stimulated by a nerve ending)
2. Action potential must be generated (electrical current) in the sarcolemma
3. action potential must be propagated along the sarcolemma
4. intracellular calcium ion levels must rise briefly, providing the trigger for contraction
What nerve cells innervate skeletal muscles? - Answer somatic motor neurons
, where/ how many neruomuscular junctions are located in a muscle fiber - Answer each
muscle fiber has 1 neuromuscular junction that is about midway in length down the muscle
fiber
What is within the axon terminal? - Answer synaptic vescicles
what are the importance of synaptic vesicles? - Answer they contain neurotransmitter --
acetylcholine
What are the components of the neuromuscular junction? - Answer -axon terminals
-synaptic cleft
-junctional folds
how is an action potential generated? - Answer a) generation of an end plate potential
b) depolarization: generation and propagation
c) repolarization: restoration of sarcolemma to its original state
How does a motor neuron stimulate a muscle fiber? - Answer a) nerve impulse reaches the
end of an axon, synaptic vesicles dock with the membrane and release ACh
b) ACh diffuses across the synaptic cleft
c) ACh attaches to receptors on the sarcolemma of the muscle fiber
d) ACh triggers an action potential
Acetylcholinesterase - Answer breaks down ACh into its building blocks: acetic acid and
choline
*helps remove ACh and thus stops muscle contraction*
Generation of an end plate potential in the formation of an action potential - Answer when
ACh attaches to the receptors on the sarcolemma, ligands open and allow Na+ and K+ to pass
*more Na+ diffuses in than K+ diffuses out*
Depolarization in the formation of an action potential - Answer the end plate potential
initiates a chain reaction of na+ channels opening to allow for the inflow of sodium
creation of a chemical gradient
Solutions 2026 Updated.
sliding filament model - Answer during contraction, thin and thick filaments slide past each
other so that actin and myosin overlap
*neither thick nor thin filaments actually change in length
What happens as a muscle cell shortens - Answer -I band shortens
-Distance between Z-discs shorten
-H-zone disappears
-Continuous A-bands move closer together, but their length does not change
What specific molecule binds calcium? - Answer troponin -- binds to calcium and changes
shape of troponin c
Tropomyosin - Answer covers up the myosin binding site on actin
Why is troponin important? - Answer key protein that binds to calcium and changes the
shape of troponin c
*causes us to expose the myosin binding site on the actin molecule*
Which organelles have the highest resting concentration of calcium? - Answer the SR has the
highest resting concentration of calcium
the mitochondrion provides the ATP energy a cell needs for muscle activity
What induces a skeletal muscle to contract? - Answer 1. the fiber must be activated
(stimulated by a nerve ending)
2. Action potential must be generated (electrical current) in the sarcolemma
3. action potential must be propagated along the sarcolemma
4. intracellular calcium ion levels must rise briefly, providing the trigger for contraction
What nerve cells innervate skeletal muscles? - Answer somatic motor neurons
, where/ how many neruomuscular junctions are located in a muscle fiber - Answer each
muscle fiber has 1 neuromuscular junction that is about midway in length down the muscle
fiber
What is within the axon terminal? - Answer synaptic vescicles
what are the importance of synaptic vesicles? - Answer they contain neurotransmitter --
acetylcholine
What are the components of the neuromuscular junction? - Answer -axon terminals
-synaptic cleft
-junctional folds
how is an action potential generated? - Answer a) generation of an end plate potential
b) depolarization: generation and propagation
c) repolarization: restoration of sarcolemma to its original state
How does a motor neuron stimulate a muscle fiber? - Answer a) nerve impulse reaches the
end of an axon, synaptic vesicles dock with the membrane and release ACh
b) ACh diffuses across the synaptic cleft
c) ACh attaches to receptors on the sarcolemma of the muscle fiber
d) ACh triggers an action potential
Acetylcholinesterase - Answer breaks down ACh into its building blocks: acetic acid and
choline
*helps remove ACh and thus stops muscle contraction*
Generation of an end plate potential in the formation of an action potential - Answer when
ACh attaches to the receptors on the sarcolemma, ligands open and allow Na+ and K+ to pass
*more Na+ diffuses in than K+ diffuses out*
Depolarization in the formation of an action potential - Answer the end plate potential
initiates a chain reaction of na+ channels opening to allow for the inflow of sodium
creation of a chemical gradient
