Muscle fascicle
Fasciculus muscularis
Also known as: fasciculus, muscle bundle, perimysium
A bundle of tens to hundreds of muscle fibres wrapped in perimysium. It is the visible "grain" of a muscle.
Overview
Each fascicle groups muscle fibres inside a sheath of perimysium, which carries the larger arterioles, venules, lymphatics and nerve branches into the muscle. Muscle spindles sit within the perimysium between fascicles. The coarse grain of meat is made of fascicles.
The way fascicles are arranged relative to the tendon is a muscle's architecture. It is the main factor that trades force against excursion. Parallel fascicles (strap muscles such as sartorius; fusiform muscles such as biceps) favour range and speed of shortening. Pennate arrangements (uni-, bi- or multipennate) pack more fibres into the same volume, giving a greater physiological cross-sectional area and therefore more force, at the cost of excursion. Convergent (fan-shaped) muscles such as pectoralis major and temporalis can pull in several directions. Circular muscles (sphincters) close openings.
Parts & subdivisions
- PerimysiumThe connective tissue sheath around the fascicle. It is continuous with epimysium outside and endomysium inside.
- The individual multinucleated cells inside the fascicle.
Function
- Organises fibres into functional bundles
- Carries neurovascular branches into the muscle
- Determines muscle architecture and therefore force, speed and range
Test yourself
In a muscle, which connective tissue layer surrounds each fascicle?
- Endomysium
- Perimysium
- Epimysium
- Sarcolemma
Answer: Perimysium
Epimysium surrounds the whole muscle, perimysium surrounds each fascicle, and endomysium surrounds individual fibres. The sarcolemma is the fibre's plasma membrane, not connective tissue.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.