MUSCLE PHYSIOLOGY

PHYSIOLOGY

MUSCLE CONTRACTION

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Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]

Which of the following occurs first in muscle contraction?

A	Calcium Ion Enters the Pre-synaptic Terminal
B	Acetylcholine Enters the Synaptic Cleft
C	Sodium Ion Enters the Sarcolemma
D	Calcium Ion Enters the Sarcoplasm (Cytoplasm).

Explanation:

Detailed explanation-1: -The correct answer is (c): calcium ions enter the synaptic bulb.

Detailed explanation-2: -Ca2+ triggers synaptic vesicle exocytosis, thereby releasing the neurotransmitters contained in the vesicles and initiating synaptic transmission.

Detailed explanation-3: -Calcium triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin.

Detailed explanation-4: -(1) Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. (2) ATP then binds to myosin. (3) ATP is then hydrolyzed. (4) A cross-bridge forms and myosin binds to a new position on actin.

Detailed explanation-5: -Calcium is stored in the sarcoplasmic reticulum at high concentrations. When neurons signal the contraction of muscle, calcium is released from the sarcoplasmic reticulum, and facilitates the contraction of muscle fibers and ATP hydrolysis, to generate muscle contraction force.

There is 1 question to complete.