Energy for Muscle Contraction | NMDCAT 2021

About This Video,
How the bridges are controlled
When the muscle is at rest, the tropomyosin is disposed in such a way that it covers the sites on the
actin chain where the head of myosin becomes attached. When the muscle is required to contract,
calcium ions bind with the troponin molecule and cause them to move slightly. This has the efect
of displacing the tropomyosin and exposing the binding sites for the myosin head. Once the myosin
head has become attached to the actin ilament, ATP is hydrolysed and the bridge goes to its cycle.
This ATP is provided by the large number of mitochondria present in each muscle cell.
From the above account it is revealed that ATP is needed to break the link between the myosin and
the actin. After death, the amount of ATP in the body falls. Under these circumstances the bridges
can not be broken and so they remain irmly bound. This results in the body becoming stif, a
condition known as rigor mortis.
Controlling the Actin - Myosin Interaction By Ca++ ions
Muscle contraction is initiated by nerve impulse arriving at the neuromuscular junction. All the ibres
innervated by a single motor neuron are a “motor unit” and contract simultaneously in response
to the action potential ired by the motor neurons. The sarcolemma of muscle ibre penetrates
deep into the cell to form hollow elongated tube, the transverse tubule, T-tubule the lumen of
which is continuous with the extracellular luid. The thousands of T - tubules of each muscle cell are
collectively called T-system. It extends and encircles the myoibril at the level of Z-line or A and I -
junction. The T-tubule and the terminal portion of the adjacent envelope of sarcoplasmic reticulum
form triads at regular intervals along the length of the ibril. The nerve impulse is carried through
the T-tubule to the adjacent sarcoplasmic reticulum (SR). The calcium gates of the SR open releasing
calcium into the cytosol, thus binding calcium ion to troponin molecules of the thin ilament. The
binding sites are exposed and cross bridges with myosin can form, and contraction occurs.
All or None Response : The contraction of each muscle ibre is based on “all or none” principle
i.e. all of its ibrils participate in contraction. The degree of contraction depends upon the number
of muscle ibers that participate in contraction.
Energy For Muscle Contraction
Energy for muscle contraction comes from the ATP. Supply of ATP is. maintained by the aerobic
breakdown of glucose in muscle cell, which comes from stored glycogen in the cell. When more
energy is required due to high metabolism, it is provided by another energy storing substance
called creatine phosphate. Sometime during
oxygen deiciency or very high metabolic
activity such as (prolonged or strenuous
muscular activity), ATP requirement is met
by anaerobic breakdown of glucose into
Lactic acid. Lactic acid accumulation causes
muscle fatigue. At rest, 1/5 of the lactic acid
is broken aerobically and its energy is used
to change the remaining 4/5 lactic acid into
glucose

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