Muscles

Actin’s binding site is covered until calcium causes it to be exposed.

The muscles in choice A move the neck and head; those in choice B are in the thigh and leg, while the orbicularis oculi is a facial muscle that encircles the eye.

An agonist muscle performs the action, while the antagonist must relax (be stretched) while the action is being performed (and can reverse the action of the agonist).

An antagonist opposes a movement. All other statements are correct.

The prefix “sarco” is commonly used to describe microscopic muscle cell structures.

“Brachii” indicates location on the brachium (arm), while “biceps” refers to the two origins (attachments) of the muscle.

The myosin head cannot attach to actin until its binding site is exposed. Ca causes this to happen.

Being multinucleate (and voluntary) distinguishes skeletal muscle cells from smooth; being voluntary distinguishes skeletal muscle from cardiac muscle cells.

A sarcomere is a section of a myofibril. A muscle fibre (cell) is a bundle of myofibrils, while a fasciculus is a bundle of muscle fibres.

We are able to exercise conscious control over the other three muscles so they are skeletal muscle.