Responds to the demands on a muscle by stimulating more moto

Responds to the demands on a muscle by stimulating more motor units within that muscle to help it contract as load increases; this is called motor unit recruitment. There are a limited number of motor units in a single muscle, so when all of the motor units are recruited, maximum stimulation has been reached. No matter how much willpower you have, if all the motor units are recruited and the force generated is not moving the load, then you are out of luck. Before you begin, familiarize yourself with the following concepts (use your textbook as a reference): Motor unit Neuromuscular Junction Skeletal muscle twitch and its parts (latent period, contraction period, relaxation period) Difference between sub threshold. threshold, and maximal stimulus. Isometric contraction and isotonic contraction State your hypothesis regarding how the isometric muscle twitch force of contraction is influenced by the changes in stimulus voltage.

Solution

before getting into answer proper lets get acquainted once with the terms....

MOTOR UNIT- group of muscle fibres which are innervated by a single motor neuron..

NEUROMUSCULAR JUNCTION- is a synapse where the motor neuron innervates the muscle fibres..and the impulse travels via chemical neurotransmitter ACETYLCHOLINE.

TWITCH- contraction of individual muscle fibres

SUBTHRESHOLD- subthreshold stimulus is that which can depolarize the membrane but not enough to excite it and bring contraction

THRESHOLD - stimulus which can depolarize a membrane to an extent which can lead to excitation and bring out contraction in muscle.

MAXIMAL STIMULUS- stimulus enough to evoke a maximal response.

ISOMETRIC CONTRACTOIN- contraction in which tension of the muscle changes without length of the fibre

ISOTONIC CONTRACTION- contraction in which length of the muscle changes without change in the tension in the fibre.

so.,

when the stimulus applied is at/crosses threshold i.e -55mv then depolarization occurs and brings in the contraction of muscle,,,.

action potential has depolarization phase in which muscle contracts

and a repolarization phase in which there is bring back of potential to the resting state for the next action potential to set in.

relaxation occurs because of SERCA PUMPS- sarcoplasmic endoplasmic reticulum calcium ATPases pumps.

threshold stimulus is needed to recruit all motor units and bring in contraction...

subthreshold stimulus cant do such;..and fails to bring in contraction..

so afterall the muscle contraction depends on

1.voltage of the stimulus

2.duration of the stimulus.( rapidly rising stimulus brings in a betterr result than slowly rising / decreasing/ static stimulus)