Muscle Contraction

•Describe movement and maintenance of posture in terms of antagonistic muscle action.•Gross and microscopic structure of skeletal muscle. The ultrastructure of a myofibril.•The sliding-filament theory of muscle contraction.•Muscles as effectors. The structure, location and general properties of slow and fast skeletal muscle fibres.

Antagonistic muscle actionMuscles exert a pulling force when

contracted but cannot push so an antagonistic (opposite) pair of muscles is needed e.g. biceps and triceps

Flexors- muscles that bend a limbExtensors- muscles that straighten a limbIsometric contraction- antagonistic muscles

in the leg have to both contract a little to exert the right amount of tension to remain upright

Skeletal muscleMuscle attached to the bones of the bodyAlso known as voluntary muscle because the

person has control over when these muscles are contracted and therefore when they bring about movement

Because of its appearance it is also know as striated or striped muscle

Structure of skeletal muscleMuscle fibre is surrounded by plasma

membrane called the sarcolemmaCytoplasm in muscle fibre is called

sarcoplasm and contains many mitochondriaIt is not made up of individual cells but is

more like several cells joined together, so it has many nuclei

Myofibrils cause the muscle to appear striped

The structure of a myofibril

Muscle fibres are made up of myofibrilsThey contain two different types of filaments:

Thick filaments, myosinThin filaments, actin

Sliding-filament theory

When muscles contract the myofibrils get shorter. This happens because the filaments slide over each other

Slow and fast muscle fibresSlow-twitch fibres- used during aerobic

exercise such as long distance running. They appear red because they contain a lot of myoglobin which is a pigment that stores oxygen

Fast-twitch fibres- used for intensive, short length exercise such as sprinting. Are whiter because they contain much less myoglobin. They produce their ATP from anaerobic respiration

Questions1. What are skeletal muscles also know as?2. What are the two different filaments

myofibril contain?3. Which of these is thick and which is thin?4. Draw a quick diagram of the structure of a

myofibril5. Name two differences between slow-twitch

and fast-twitch muscles6. Why do we need antagonistic pairs of

muscles?