The striped tissue of the biceps, the calf and the diaphragm, made of unbranched, many-nucleated cells lying in parallel
Skeletal muscle tissue — striated, multinucleate, voluntary.
Anatomy · Cells & tissues
Skeletal muscle tissue
The voluntary, striped muscle that moves the bones
Muscle tissue · attached to the skeleton
The striped, voluntary muscle tissue that makes up the muscles attached to the skeleton by tendons and moves the body. It is built from long, cylindrical, multinucleated fibres with their nuclei at the periphery, and its cross-striations are so regular that it is called striated muscle. Each muscle is bundled by connective tissue sheaths and stimulated by somatic motor nerves. It forms roughly 40% of body weight and contracts quickly and strongly but tires.
How to spot them
- ▸Long parallel fibres with clear cross-striations, all in register, in longitudinal section
- ▸Many flattened nuclei pushed against the outer edge of each fibre
- ▸In cross-section, polygonal fibres packed in bundles with the nuclei at the rim
- ▸Fibres unbranched, running side by side without visible junction discs
- ▸Surrounded by fine connective tissue sheaths: endomysium around each fibre, perimysium around bundles, epimysium around the whole muscle
What to know
The only muscle tissue under conscious, voluntary control
Skeletal muscle tissue — supplied by somatic motor neurons at neuromuscular junctions.
Each bundle, or fascicle, is wrapped by perimysium, and the whole muscle by epimysium
Skeletal muscle tissue — the connective tissue wrappings.
Attached at its ends to bone by cords of collagen, and it makes up about two-fifths of body weight
Skeletal muscle tissue — tendons attach it to the skeleton; roughly 40% of body mass.
It wastes away (atrophies) when a limb is immobilised in plaster or its motor nerve is cut
Skeletal muscle tissue — disuse and denervation atrophy; satellite cells help repair it after injury.
Its motor units range from a few fibres per neuron in the eye to thousands in the calf
Skeletal muscle tissue — fine control needs small motor units.
Unlike heart tissue, it cannot beat by itself and contracts only when a motor nerve stimulates it
Skeletal muscle tissue — no autorhythmicity; without a nerve signal it stays relaxed.
Key ideas
- A nerve impulse releases acetylcholine at the neuromuscular junction, triggering calcium release inside the fibre; actin and myosin slide together and the muscle shortens using ATP.
- Force is graded by recruiting more motor units and by increasing their firing rate.
Quick-fire facts
- •There are roughly 600–650 named skeletal muscles in the human body
- •Muscle makes up about 40% of body mass in men and somewhat less in women
- •The sartorius is usually called the longest muscle and the gluteus maximus the largest
- •Contraction is under voluntary control, but reflexes such as the knee-jerk use the same tissue
- •Each muscle is a hierarchy: muscle, fascicle, fibre (cell), myofibril, sarcomere
- •Fibres are 50–100 micrometres across, and a whole muscle can be many centimetres long
- •Growth after exercise (hypertrophy) enlarges the existing fibres more than it adds new ones
- •Slow (type I) fibres are rich in myoglobin and resist fatigue; fast (type II) fibres are stronger but tire quickly
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