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Technical terms:

Antagonistic muscle: pair of muscles working together to move a muscle backwards and forwards.

Flexor: muscle that contracts to shorten a joint

Extensor: muscle that contracts to extend a joint

E.g: in pupil dilation and constriction the radial and circular muscles work together.(see more in the eye revision pack)

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Muscle fibres

  • Muscle fibres(cells) are multinucleate and long.
  • They contain myofibrils: Actin (thin) and Myosin (thick)
  • During contraction actin moves over myosin, H and I bands shorten whilst A band remains the same.
  • There are two types of muscle fibres: slow twitch and fast twitch.
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Slow Twitch vs Fast twitch

In different organisms and people there are different amount of slow and fast twitch fibres, E.g long distance runners have more slow twitch and sprinters have more fast twitch, this is due to their properties:

Slow Twitch: more myoglobin(redder), more respiratory enzymes, lots of mitochondria, aerobic, lots of capillaries, less sarcoplasmic reticulum, fatigue resistant.

Fast twitch: Less Myoglobin, less capillaries, anarobic, less mitochondria, lots of sarcoplasmic reticulum, fatigues quickly.

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Joint Structure

Synovial joints: are moveable joints. e.g: knee, hip and ankle
Find a picture of a synovial joint and try labelling these structures:

  • Tendons: joins muscle to bone
  • Muscle:
  • Bone:
  • Ligaments: jone bone to bone. strong and flexible
  • synovial membrane: secretes synovial fluid
  • Synovial fluid: acts as lubricant
  • Cartillage: shock absorber and also absorbs synovial fluid.(pad of cartillage provides extra protection)
  • Fibrous capsule: encloses joints
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Muscles contain myofibrils-repeated contractile units called sacromere (one Z disc to the next)

Sacromere is made up of two types of protein molecules:

 Actin (thin) and Myosin (thick) contraction is brought about when actin moves over myosin.

Actin molecules contain troponin and tropomyosin. Myosin contains myosin heads which change shape attaching to binding sites on actin to cause conttraction.

I will discuss contraction and sliding filament theory in the next card.


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Sliding Filament Theory

Sliding filament Theory

Nerve impulse arrives at a neuromuscular junction, ca2+ ions released from sarcoplasmic reticulum, Ca"+ then diffuse though sarcoplasm.

  • Ca2+ attaches to troponin causing tropomyosin to shift exposing myosin binding sites.
  • Myosin  binds with myosin binding site forming cross bridges.
  • ADP +Pi is released from myosin head.
  • Myosin head nods forward, actin moves over mysosin.(contraction)
  • ATP attaches to myosin causing it to detach, ATPase on myosin head hydrolyses ATP into ADP +Pi and myosin returns to it's original upright position.
  • this allows cycle to start again.
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3 types of muscle

1)Cardiac- Heart

2)Striated- skeletal

3) Smooth muscle

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