Muscle Anatomy

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Apr2010 18

What does skeletal muscle consist of? How does it contract?

Muscle anatomy can get quite complex… and that’s even without mentioning the physiology of muscle contraction! This article breaks skeletal muscle down into its smallest parts and examines the amazing processes that bring about all our movements…

Every one of the body’s 430 skeletal muscles consists of muscle tissue, connective tissue, nerves and blood vessels. A fibrous fascia called the epimysium covers each muscle and tendon. Tendons connect the muscle belly to bone and they attach to the bone periosteum – more connective tissue that covers all bones. Contraction of the muscle belly pulls on the tendon and in turn, the bone it is attached to.

Limb muscles (such as the biceps brachii in the upper arm) have two attachments to bone. The proximal or origin is the attachment closest to the trunk. The distal or insertion is the attachment furthest from the trunk. Trunk muscles (such as the rectus abdominus in the stomach) also have two attachments – superior (closer to the head) and inferior (further from the head).

A closer look at muscle anatomy shows that each muscle belly is made up of muscle cells or fibres. Muscle fibres are grouped into bundles (of up to 150 fibres) called fasciculi. Each fasiculus or bundle is surrounded by connective tissue called perimysium. Fibres within each bundle are surrounded by more connective tissue called endomysium.

Each individual fibre consists of a membrane (sarcolemma) and can be further broken down into hundreds or even thousands of myofibrils. Myofibrils are surrounded by sarcoplasm and together they make up the contractile components of a muscle.

Sources
1) Baechle TR and Earle RW. (2000) Essentials of Strength Training and Conditioning: 2nd Edition. Champaign, IL: Human Kinetics
2) McArdle WD, Katch FI and Katch VL. (2000) Essentials of Exercise Physiology: 2nd Edition Philadelphia, PA: Lippincott Williams & Wilkins
3) Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics

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