10.3 , Fascicle arrangements help determine muscle shape and force

What are fascicles?

Bundles of muscle fibers that make up skeletal muscles.

What are the four most common fascicle arrangements?

Circular, convergent, parallel, and pennate.

What is a circular fascicle arrangement?

Fascicles arranged in concentric rings around an opening.

What do circular muscles do?

They surround body openings and close them when they contract.

What are sphincters?

Muscles arranged around openings that close them when they contract.

Example: Orbicularis muscles around the eyes and mouth.

What is a convergent fascicle arrangement?

Has a broad origin with fascicles that narrow toward one tendon.

What shape are convergent muscles?

Triangular or fan-shaped.

Example: Pectoralis major.

What is a parallel fascicle arrangement?

Fascicles run parallel to the muscle's long axis.

What shapes can parallel muscles have?

Strap-like or spindle-shaped (fusiform).

Examples: Sartorius (strap-like) and biceps brachii (spindle-shaped).

What are fusiform muscles?

Spindle-shaped muscles with an expanded belly.

What is a pennate fascicle arrangement?

Short fascicles attach diagonally to a central tendon.

What are the three types of pennate muscles?

Unipennate, bipennate, and multipennate.

What is a unipennate muscle?

Fascicles attach to only one side of the tendon.

Example: Extensor digitorum longus.

What is a bipennate muscle?

Fascicles attach to opposite sides of the tendon, resembling a feather.

Example: Rectus femoris.

What is a multipennate muscle?

Multiple feather-like sections attach to one large tendon.

Example: Deltoid.

Fascicle Arrangement, Range of Motion, and Power

What determines a muscle's range of motion and power?

The arrangement and number of its muscle fibers.

Which muscles shorten the most when they contract?

Parallel muscles, because their fibers are longer.

Are parallel muscles usually very powerful?

No. They shorten greatly but generally produce less force.

What determines muscle power?

The total number of muscle fibers. More fibers produce greater power

Which muscles tend to be the most powerful?

Bipennate and multipennate muscles because they contain more muscle fibers.

How much can skeletal muscle fibers shorten when contracting?

To about 70% of their resting length.

What is the relationship between muscle shortening and power?

Longer parallel fibers shorten more; densely packed pennate fibers produce more power.