Question

The muscles that surround external body openings typically have a ________ fascicle arrangement. parallel convergent pennate circular

Answer 1

Parallel

In a parallel arrangement, the length of the fascicles runs parallel to the long axis of the muscle. Such muscles are either straplike like the sartorius muscle of the thigh, or spindle shaped with an extended belly, like the biceps brachii muscle of the arm. However, some scientists classify spindle-shaped muscles into a separate class asfusiform muscles.

Pennate

in a pennate pattern, the fascicles are short and they attach obliquely to a central tendon that runs the length of the muscle. Pennate muscles come in three forms:

Unipennate, in which the fascicles insert into only one side of the tendon, as in the extensor digitorum longus muscle of the leg. Bipennate, in which the fascicles insert into the tendon from opposite sides so the muscle “grain” resembles a feather.
The rectus femoris of the thigh is bipennate. Multipennate, which looks like many feathers side by side, with all their quills inserted into one large tendon. The deltoid muscle, which forms the roundness of the shoulder is multipennate.