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PHYSIOLOGY 1
Take-Home Exam#1
KIN646
Submission Date

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PHYSIOLOGY 2
Question #1. Explain all of the biochemical events leading up to and including skeletal
muscle contraction, starting in the motor neuron.
Several steps are triggered by skeletal muscle contractions that occur almost
instantaneously. To begin the rapid process of skeletal muscle contraction, first, an action
potential must occur. A resting neuromuscular cell has a charge of -70mV and a stimulus that
suggests the required movement is needed to depolarize the cell. For this to happen, the
stimulus needs to be strong enough to cross the -55-mV threshold. Therefore, if the cell crosses
the threshold, it rapidly depolarizes as Na+ ions quickly flood the cell, causing its voltage to
leap to around +30-40 mV until closing the Na+ channels. As a consequence, causing the cell
to repolarize rapidly as K+ ions exit the cell through K+ channels until the cell hyperpolarizes
before returning to its resting state of -70 mV. In the motor neuron, these possible actions occur
consecutively before the APs hit the axon's end. When the AP enters the neuron's axon terminal,
acetylcholine is released and crosses the neuromuscular junction into a gap called the synaptic
cleft, where it attaches to the sarcolemma receptor.
The ion channels open after acetylcholine binds to the receptors, causing a similar Na+
influx, while K+ leaves the muscle cell because of the electrochemical gradient. The AP created
then moves through the t-tubules that pass through the cell of the muscle. The signal enters the
muscle fibers in the t-tubule and allows the sarcoplasmic reticulum to open its channels to
release the stored calcium. By binding to troponin, the calcium influx activates the muscle
contraction, causing the tropomyosin to shift, which exposes a binding site on the actin strand
for the myosin head.
Myosin and actin are known as the thick and thin filaments that make up the sarcomere
that line the entire muscle side by side, and they are the muscle's contractile components. The

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PHYSIOLOGY 1 Take-Home Exam#1 KIN646 Submission Date PHYSIOLOGY 2 Question #1. Explain all of the biochemical events leading up to and including skeletal muscle contraction, starting in the motor neuron. Several steps are triggered by skeletal muscle contractions that occur almost instantaneously. To begin the rapid process of skeletal muscle contraction, first, an action potential must occur. A resting neuromuscular cell has a charge of -70mV and a stimulus that suggests the required movement is needed to depolarize the cell. For this to happen, the stimulus needs to be strong enough to cross the -55-mV threshold. Therefore, if the cell crosses the threshold, it rapidly depolarizes as Na+ ions quickly flood the cell, causing its voltage to leap to around +30-40 mV until closing the Na+ channels. As a consequence, causing the cell to repolarize rapidly as K+ ions exit the cell through K+ channels until the cell hyperpolarizes before returning to its resting state of -70 mV. In the motor neuron, these possible actions occur consecutively before the APs hit the axon's end. When the AP enters the neuron's axon terminal, acetylcholine is released and crosses the neuromuscular junction into a gap called the synaptic cleft, where it attaches to the sarcolemma receptor. The ion channels open after acetylcholine binds to the receptors, causing a similar Na+ influx, while K+ leaves the muscle cell because of the electrochemical gradient. The AP created then moves through the ...
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