Question

1. How does an electrical impulse from a nerve lead to muscle contraction?
2. How does skeletal muscle contract and generate force?
3. How does muscle twitch, summation, and tetanus affect the strength and duration of muscle contraction?
4. What are the different types of skeletal muscle contractions? Explain the difference?

Own Words Please.

Answer 1

1. Electrical impulse when reach the nerve ending helps in releasing calcium ions ---> calcium ions make neurotransmitter containing synaptic vesicles to move towards the end of nerve to release them ---> tis neurotransmitter attaches to receptors on the muscle ---> this makes release of sodium ions which generates an impulse which run along muscle just like along nerve ---> when it reaches sarcoplasmic reticulum , calcium ions released ---> calcium ions unmask the actin filament by attaching with troponin molecule masking the actin filament--> after unmasking of actin , myosin attaches to that site and with the help of energy released from atp , pulls the actin filament thus decreasing the muscle length hence contracting it ---> after pulling it to its limit, myosin leaves that site and attaches to a new site of actin filament and pulls it

2. as told above akeletal muscle contract when the myosin filament pulls the actin filament . The force is generated by the energy present in form of ATP inside myosin , the more number of actin-myosin filaments the more force muscle can apply thus big muscles have more filaments thus more force.

3. Muscle twitch can decrease amount of energy and neurotransmitters due to unnecessary contractions thus decreases strength of muscle contraction

summation increases strength of muscle contraction by 2 ways-

a. multiple fiber stimulation - when strength of signal increases even the large muscle fibres are involved thus strength increases

b. frequency stimulation - when frequency of stimulus increased then comes a point when a new contraction starts before preceding one is over so the second one adds to the first thus incresing the strength

when frequency increases to a high level then all these small contractions add up and appear to be one big sustained contraction which increases the strength . This level is tetanisation and stimulus above tis has no effect

4. types of skeletal muscle contraction are -

a. isometric - in which the stimulus is applied and filaments join but the length of muscle does not change

b. isotonic - in which the length of muscle change