Shivering with cold in winter is caused by

At which site do muscle fibers receive stimulation from a motor neuron?

Identify the characteristics of red muscle fibers from the following:
$I -$ Many mitochondria
$II -$ Use large amounts of $O_2$ for $ATP$ production
$III -$ Low amount of myoglobin
$IV -$ Less sarcoplasmic reticulum
Which of the above are characteristic of red muscle fibers?

The sliding filament theory to explain muscular contraction was given by

Select the correct statement with reference to muscle structure.
$I.$ Each myosin is a polymerized protein.
$II.$ Many meromyosin constitute one thick filament (myosin).
$III.$ Each meromyosin's tail is called heavy meromyosin $(HMM)$ and head is called light meromyosin $(LMM)$.
$IV.$ The globular head is an active $ATPase$ enzyme and has binding sites for $ATP$ and active sites for actin.
Choose the option with correct statements.

What happens when a sub-threshold stimulus is applied to a muscle?