1. Coactivation describes a phenomenon between an antagonistic pair of muscles,
ID: 3476689 • Letter: 1
Question
1. Coactivation describes a phenomenon between an antagonistic pair of muscles, such as the biceps and triceps. Agonist muscles are sometimes called “prime movers” as they are the primary muscle responsible for generating movement through their contraction. Antagonist muscles control (or oppose) specific movement, and return the muscle to its initial position. Depending on the movement, agonist and antagonist muscles may change roles. For example, when the biceps muscle is activated forcefully, there is a minor increase of activity in the triceps. Correspondingly, when the triceps are activated, there is a minor increase of activity in the biceps.
What type of contraction does the antagonist muscle undergo?
a) concentric
b) eccentric
c) isometric
2. The removal of which ion causes the muscle to relax after contraction?
a) Ca2+
b) K+
c) Na+
3. How is an action potential passed from the motor neuron to a muscle fiber? Arrange the labels in the order in which they would occur, beginning at the presynaptic membrane. (Note: ACh = acetylcholine).
- Ach is released into the synaptic cleft and binds to receptors.
- Calcium moves into the nerve terminal of the presynaptic cell.
- Influx of Na+ initiates an action potential in the muscle fiber.
- Signal from the motor neuron arrives at the nerve terminal of the presynaptic cell.
What is the correct order?
Explanation / Answer
1. A movement which causes relaxation of muscles is known as eccentric contraction such as relaxation of biceps when triceps contract.
2. Removal of CALCIUM IONS from the active sites of ACTIN FILAMENT ceases ACTIN - MYOSIN interaction and hence contraction. So the answer is Ca+ ions.
3. Signal from the motor neuron arrives at the nerve terminal of the presynaptic cell. Calcium moves into the nerve terminal Ach is released into the synaptic cleft and binds to receptors influx of Na+ initiates an action potential in the muscle fiber.
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