What is meant by threshold stimulus in muscle contraction? Name any two stimuli other than nerve threshold stimulus.

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

(Unlock A.I Detailed Solution for FREE)

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Threshold stimulus & types of stimuli

A muscle contracts only when the stimulus reaches a minimum strength called the threshold stimulus. Any stimulus below this level produces no contraction.
Besides nerve impulses, muscles can also respond to mechanical (pressure), electrical (shock), and chemical stimuli.

Sliding filament theory (how muscles contract)

Once threshold is reached, myosin (thick) filaments pull past actin (thin) filaments.
Filaments do not shorten; rather, they slide, so the sarcomere shortens.
As a result, the I band and H zonenarrow, while the A band (length of thick filaments) remains constant.

Sarcomere: the contractile unit

A sarcomere is the section of a myofibril between two Z lines—the functional unit of contraction in striated muscle.
Myofibrils show alternating I bands (light, actin-rich; isotropic) and A bands (dark, myosin-rich; anisotropic).
Each I band is bisected by a Z line (elastic protein complex). Shortening of successive sarcomeres produces overall muscle contraction.

Watch 3-min video & get full concept clarity