Question

what is the sequence of events of skeletal muscle contraction, including stimulation by the nervous system, structure and role of myofilaments and calcium including where it is stored in the muscle and what causes its release. what role does energy play in muscle comtraction?

Answer 1

What is the sequence of events of skeletal muscle contraction, including stimulation by the nervous system, structure and role of myofilaments and calcium including where it is stored in the muscle and what causes its release. what role does energy play in muscle comtraction?

The sequence of muscle contraction begins with the signal which is the release of neurotransmitter.

• Release of Acetylcholine Ach from the motor neuron innervating that fiber.
• Membrane dopolarization begins as positively charged sodium ions (Na+) enter which leads to spreading of depolarization along the membrane, including T-tubules.
• Release of calcium ions (Ca++) from the sarcoplasmic reticulum is triggered.
• The Ca++ initiated contracction begins which is sustained by ATP.
• Availabilty of Ca++ in sarcoplasm enable binding to troponin, which keeps the actin-binding sites available for myosin to bind.
• ATP is critical for the cross-bridge cycling and the pulling of actin strands by myosin.
• Shorten of myosin fiber to an anatomical limit.the sarcolemma
• Contraction stops when signaling from the motor neuron ends causes repolarization of sarcolemma and T-tubules which in turn  closes the voltage-gated calcium channels in the SR. Contraction also stops when ATP availability is critical and becomes fatigued

The filament movement starts where thin and thick filaments overlap which is very important for muscle contraction. The thick and thin filaments should not extend completely into the central region and are anchored at their ends by the Z-discs. The central region which only contains thick filaments called M-line. Since, many sarcomeres together forms myofibril and run along its length, contraction of sarcomere brings the muscle cell contraction.

Calcium is stored in sarcoplasmic reticulum which looks like series of interconnected tubules and tiny sacs distributed throughout the cells. The change in the concnetration of sodium ion brings about large changes in calcium stores. Elevated sodium promotes the calcium release from the stores.

Availability of ATP is crucial for muscle contraction, because:

• role in the cross-bridge cycle
• provides the energy for the active-transport Ca++ pumps in the SR.

Therefore, Muscle contraction does not occur without sufficient amounts of ATP. Since, the amount of ATP stored in muscle is very low, for a sustained contraction, ATP must therefore be regenerated and replaced quickly.

ATP can be regenerated by three mechanisms are: creatine phosphate metabolism, anaerobic glycolysis, fermentation and aerobic respiration.