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Case 1 Summary - ILOs
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Case 9 SummaryGeneral ILOs:
- To demonstrate knowledge of muscle contraction, determinants of muscle
strength, blood flow to muscle and the effects of training
- To demonstrate knowledge of skeletal muscle structure; including types of fibre,
motor unit, motor end plate, transmission and excitation-contraction coupling
There are three types of muscle in the body:
Skeletal – striated and is voluntarily controlled
Cardiac – striated
Smooth – provides structure to visceral organs
Skeletal muscle originates from somites and form in waves.
When considering muscles, the prefixes ‘sarco’ and ‘myo’ are used.
Muscles are divided as follows (from large to small):
Muscle
Fascicle
Muscle fibres/Myocyte/Muscle cell
Myofibrils
Myofilament
Myofibrils are composed of myosin (thick) and actin (thin). There are areas of overlap:
Actin only – light band (I-band)
Myosin with some actin – dark bands (A-bands)
Actin is attached to a Z-disc, which crosses from myofibril to myofibril. The portion of
myofibril between two Z-dics is called a sarcomere.
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Guillaume Antem – MBChB Y2
, Titin attaches to the Z-disc and myosin, acting as a spring. In the resting state, actin is bound
to tropomyosin and troponin.
MOA – Muscle contraction
AP travels along a LMN, releasing Ach.
Na+ channels open, allowing Na+ to diffuse into the muscle membrane, depolarising
it. Co-ordinated depolarisation is enabled by the T-tubules.
Membrane depolarisation results in Ca2+ release from the sarcoplasmic reticulum.
Ca2+ binds to troponin, removing the tropomyosin from actin.
Actin and myosin bind together via the sliding filament theory (see below).
Ca2+ is then pumped back into the sarcoplasmic reticulum (using SERCA pumps),
allowing tropomyosin to block actin (separating actin and myosin).
The sliding filament theory is as follows:
Myosin moves into position (ATP ADP + Phosphate)
Myosin binds to actin
Myosin moves forward/Power stroke (ADP + phosphate released)
Myosin releases from actin (ATP molecule binds)
The above cycle repeats for each muscle contraction.
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Guillaume Antem – MBChB Y2
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