MICROANATOMY

Detailed explanation-1: -Muscle contraction can be graded (varied) in two ways: Frequency of the stimulation. Number of motor units stimulated.

Detailed explanation-2: -A twitch occurs when one muscle fiber contracts in response to a command (stimulus) by the nervous system. The time between the activation of a motor neuron until the muscle contraction occurs is called the lag phase (sometimes called the latent phase).

Detailed explanation-3: -As such, graded membrane response can become stimulated by multiple factors, including local humoral factors, circulating hormones, or mechanical stimulation like stretching of the cells. Action potentials in smooth muscle cells are slower than skeletal action potentials, and they can last almost fifty times as long.

Detailed explanation-4: -Stimulation of the muscle fibre, causes a wave of depolarisation to pass down the t-tubule, and the SR to release calcium ions into the sarcoplasm. Calcium is pumped back up into the SR to lower calcium ion concentration in the sarcoplasm, to relax the muscle (turn off contraction).