Question

Physical and chemical changes during muscle contraction

Answer 1

Physical changes during muscle contraction

 

Following physical changes are observed during a muscle contraction.


 

Shortening of muscle fibre

During muscle contraction the sarcomeres shorten to about 60-70% of the rest length. This depends on the strength of the stimulus and the number of motor units involved.

Viscosity

Viscosity during muscle contraction and density of the sarcoplasm increases.

Tonicity

The partial contraction of a relaxed muscle is called tonus. During muscle contraction, the tonicity increases as more and more motor units come into the phase of contraction.

Heat production

The energy released by ATP during muscle contraction is partially converted to heat which helps in maintaining homeothermy.

Electrical changes

The sarcolemma is with a rest potential of 90mV. During contraction an action potential of +45 to +50mV is developed.

chemical changes during muscle contraction

During muscle contraction a number of biochemical changes occurs, which were studied by Albert Szent-Gyorgyi in 1942 and later by R.E. Davies in 1963. In a resting muscle fibre, sarcolemma is electropositive outside and electronegative inside. This potential difference across a membrane is called resting potential. A membrane with such a resting potential is said to bepolarised.

Na+ ions predominate the outside of the sarcolemma and potassuim ions predominate the inside. Due to the difference in concentration on the two sides of the sarcolemma, potassium ions leave and sodium ions enter the muscle fibre.

Sarcolemma is more permeable to K+ions than to sodium ions. Hence potassium ions leave the muscle fibre faster than sodium ions enter, and this builds a positive charge outside.

When the motor nerve impulse reaches the neuro-muscular junction, then the vesicles present in the motor end plate secrete a neurotransmitter chemical calledacetylcholine(ach).

Ach binds to the receptors on the sarcolemma makes it more permeabe to Na+ than K+ so that, sodium rapidly diffuse along the concentration gradient and the electrical gradient. Now sarcolemma becomes electropositive inside and electronegative outside. This new potential difference is called action potential. Such sarcolemma is called depolarised.

Action potential stimulates the sarcoplasmic reticulum to release calcium ions which initiate the biochemical changes in muscle contraction.

Calcium and megnesium ions act as co-factors for myosine ATPase enzyme which hydrolyses ATP into ADP and inorganic phosphate releasing energy.

Answer 2

During muscle contraction, these are the physical and chemical changes occur.  

During contraction, the Actin myofilament slide over the myosin filament which reduces the length of I band and eventually the H zone disappear.  

Chemical changes like production of lactic acid, changes in ATP concentration, Inorganic phosphate and changes in the concentration of phosphocreatinine takes place.