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Summary Alevel AQA biology unit 6 - skeletal muscles
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Summary notes for skeletal muscles
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3.6.3 Skeletal musclesThere are 3 types of muscle in the body:
Smooth muscles – found in the walls of blood vessels and gut
Cardiac muscle – found exclusively in the heart
Skeletal muscle – attached to bone and acts under voluntary, conscious control
Antagonistic muscle action
Muscles act in antagonistic pairs against an incompressible skeleton
Antagonistic – when two muscles pull in opposite directions
To raise the lower arm:
Bicep contracts and tricep relaxes – vice versa
Isometric contraction – when antagonistic muscles maintain posture by contracting at the joints to
keep at a certain angle so there is no motion.
Gross muscle structure
Muscles are made from bundles of muscle fibres called fascicles; these are surrounded by a layer if
connective tissue known as the perimysium. The epimysium is a think connective tissue which
surrounds the outside of the muscle fibres
Each muscles fibre contains an organised arrangement of contractile proteins in the cytoplasm
Microscopic muscle structure
Skeletal muscles are bundles of fascicles surrounded by an epimysium (fibrous elastic tissue). These
fibres are surrounded by connective tissue called perimysium. A single muscle fibre is surrounded by
a layer of endomysium (areolar connective tissue). The cytoplasm is called sarcoplasm, and this
contains mitochondria and myofibrils. Mitochondria carries out aerobic respiration to produce ATP
for muscle contraction. Myofibrils are bundles of actin and myosin filaments which slide past each
other during muscle contraction. Sarcomeres make a repeating banding pattern on the cell.
Sarcolemma is the cell membrane of the muscle cell. This membrane folds over itself to form tubules
which run close to the sarcoplasmic reticulum. Inside the SR protein pumps are present and these
transport calcium ions into the lumen of the reticulum
Fast muscle fibres
These fibres contract quickly but last for a short time: as the myosin heads bind and unbind from the
actin-binding sites five times faster. Suited for high intensity exercise. Found in the biceps and human
eyelids
Adapted to their role by:
Thicker and more myosin filaments
A higher concentration of glycogen
Large amounts of calcium ions
More enzymes for anaerobic respiration for production for ATP
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