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Movement

Topic 11
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2

Biology HL

Elbow joint
➢ Cartilage ⇒ reduces friction and absorbs compression
➢ Synovial fluid ⇒ lubricates to reduce friction and provides nutrients to the cells of
the cartilage
➢ Joint capsule ⇒ surrounds the joint, encloses the synovial cavity and unites the
connecting bones
➢ Tendons ⇒ attach muscle to bone
➢ Ligaments ⇒ connect bone to bone
➢ Biceps muscle ⇒ contracts to bring about flexion of the arm
➢ Triceps muscle ⇒ contracts to cause extension of the arm
➢ Humerus ⇒ acts as a lever that allows anchorage of the muscles of the elbow
➢ Radius ⇒ acts as a lever for the biceps muscle
➢ Ulna ⇒ acts as a lever for the triceps muscle
Muscles
➢ There are 3 kinds of muscle tissue
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Smooth

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Cardiac

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Skeletal / striated

➢ The cells of skeletal muscles are highly modified for contraction and therefore their
structure is different
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Each muscle is composed by thousands of cells called muscle fibres which
have an elongated shape

➢ Muscle tissues include surrounding connective tissues, blood vessels and nerves
➢ Structure
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Many nuclei in each cell

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The plasma membrane is called sarcolemma

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Multiple tunnel-like extensions in sarcolemma that penetrate the interior
of the cell (infoldings) called transverse tubules or T-tubules

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The cytoplasm is called sarcoplasm

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The sarcoplasm contains organelles that store glycogen as energy reserve
and myoglobin which stores oxygen and releases it when a muscle tissue is
heavily used and the supply of oxygen from haemoglobin is limited

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Many mitochondria between myofibrils

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Many myofibrils make up a muscle fibre and the contractile units called

sarcomeres are found here
2

Movement

Topic 11
...
ATP gets hydrolysed and inorganic phosphate is
released

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As myosin forms cross-bridges, ATP is released and the myosin bends due
to loss of energy
...
2
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Biology HL

The action potential moves through the T-tubules causing the release of
2+

Ca from the sarcoplasmic reticulum
2+

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Ca flood into the sarcoplasm

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Myosin heads attach to actin’s binding sites

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Myosin heads flex towards the centre of the sarcomere

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Sarcomeres shorten as the Z lines move towards each other

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ATP binds to the myosin head and myosin detaches from the actin

➢ Sarcomere light band area would be any area with actin without myosin
➢ Sarcomere dark band area would be any area with myosin or myosin with actin
Troponin and tropomyosin
➢ The binding sites on the actin aren’t always available

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