Muscle fibres

Biology Unit 5

Muscle Fibres

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Biology Unit 5
Revision Notes
Topic 7: Run for your life
2. Describe the structure of a muscle fibre and explain
the structural and physiological differences between
fast and slow twitch muscle fibres.
Muscle Structure
There are 3 main types of muscle:
Striated Muscle
Smooth Muscle
Cardiac Muscle
Skeletal Cardiac Smooth
Function Locomotion Pumping blood through Line blood vessels,
heart digestive tract
(peristalsis), uterus, etc.
Cells Striated Specialised striated Unstriated
Control of Voluntary - conscious Involuntary Involuntary
Arrangement Regular arrangement so the Cells branch and No regular arrangement
muscle contracts in one interconnect allows (different cells can
direction efficient transfer of contract in different
impulses so brings directions)
about simultaneous
Speed of Rapid Intermediate Slow
Length of time Short Intermediate Can remain contracted
Contracted for a relatively long time
Skeletal (striated) muscles are those attached to bones and are usually in antagonistic pairs. An
antagonistic pair of muscles pulls in opposite directions. E.g. Biceps and triceps.
Each skeletal muscle is a bundle of millions of muscle cells called muscle fibres. Each muscle cell can
be several cm long and contain several nuclei. Each muscle fibre contains many myofibrils. These
myofibrils contain sarcomeres which are made up of the fibrous proteins actin (thin filaments) and
myosin (thick filaments).
Text Book: p. 142-146

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Biology Unit 5
Revision Notes
Fast-twitch and Slow-twitch Muscle fibres
Slow-twitch Fast-twitch
Specialised for slower, sustained contraction and Specialised to produce rapid, intense
can cope with long periods of exercise contractions in short bursts
Many mitochondria- ATP comes from aerobic Few mitochondria- ATP comes from anaerobic
respiration (ETC) respiration (glycolysis)
Lots of myoglobin (dark red pigment) to store Little myoglobin and few capillaries. The muscle
O and lots of capillaries to supply O. This gives has a light colour
the muscle a dark colour.…read more


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