Question

Given these conditions:

1. low ATP levels2. little or no transport of Ca2+ into the sarcoplasmic reticulum3. release of cross-bridges4. Na+ accumulation in the sarcoplasm5. formation of cross-bridgeschoose the conditions that occur in both physiological contracture and rigor mortis

Answer 1

The Mechanism- "Muscles contract in a repeated pattern of binding and releasing between the two thin and thick strands of the sarcomere. ATP is critical to prepare myosin for binding and to “recharge” the myosin."

Step-by-step explanation:

• Along with importance of molecules required in the muscle contraction and relaxation, the steps along with the disorders all the topics are explained below:

Importance of ATP molecules:

• Each cycle requires energy, and the action of the myosin heads in the sarcomeres repetitively pulling on the thin filaments also requires energy, which is provided by ATP.
• Ca++ ions are then pumped back into the SR, which causes the tropomyosin to reshield (or re-cover) the binding sites on the actin strands. A muscle also can stop contracting when it runs out of ATP and becomes fatigued.
• Formation Of Cross-bridge:

1. First a signal—the neurotransmitter, ACh—from the motor neuron innervating that fiber.
2. The local membrane of the fiber will depolarize as positively charged sodium ions (Na+) enter, triggering an action potential that spreads to the rest of the membrane will depolarize, including the T-tubules.
3. This triggers the release of calcium ions (Ca++) from storage in the sarcoplasmic reticulum (SR).
4. The Ca++ then initiates contraction, which is sustained by ATP (Figure 1). As long as Ca++ ions remain in the sarcoplasm to bind to troponin, which keeps the actin-binding sites “unshielded,” and as long as ATP is available to drive the cross-bridge cycling and the pulling of actin strands by myosin, the muscle fiber will continue to shorten to an anatomical limit.

• Disorders Occurring due lack of ATP molecules, Ca2+ And accumulation of Na+ molecules:

• Cramp:Low levels of electrolytes such as magnesium, potassium, or calcium.Straining or overusing a muscle. This is the most common cause.

• Strain: the muscles are not relaxed back rather are present in the stretched position, which brings pain in the body and some times the organ swells up and becomes red.

As Muscle contraction usually stops when signaling from the motor neuron ends, which repolarizes the sarcolemma and T-tubules, and closes the voltage-gated calcium channels in the SR.