Question

multiple choice question

how would you classify the muscle in the given illustration?

• circular
• fusiform
• multipennate
• bipennate

Explanation:

Identify the muscle shape in the illustration

The provided illustration shows a muscle with fibers arranged concentrically around an opening (or orifice). This arrangement forms a ring-like structure that constricts the opening when contracted. This is the characteristic shape of a sphincter or circular muscle.

Evaluate the given options

• Circular: These muscles (also called sphincters) surround external body openings, which they close by contracting. The image clearly depicts concentric rings of muscle tissue surrounding a central opening, matching this definition.
• Fusiform: These muscles are thick in the middle and tapered at each end (e.g., biceps brachii). The image does not show a spindle shape.
• Multipennate: These muscles have fascicles that insert from multiple directions into several tendons (e.g., deltoid). The image does not show this feather-like arrangement.
• Bipennate: These muscles have fascicles that insert into the tendon from opposite sides (e.g., rectus femoris). The image does not show a central tendon with fibers on both sides.

Apply student profile concepts

Using the Skeletal Muscle Shapes knowledge point, we classify muscles based on the arrangement of their fascicles. The concentric circular arrangement shown here is classified as a circular muscle.

Answer:

• Circular (Correct answer)
• Fusiform
• Multipennate
• Bipennate