chapter 11 - muscle contraction

Muscle contraction- 11.1

Structure of Skeletal Muscle :

Muscles are effector organs ,  that respond to nervous stimulation by contracting and so bring about movement.

Three types of muscles:

• Cardiac muscle(Heart)
• ·         Smooth muscle( vessels and guts)
• ·         Skeletal muscle- makes up bulk of body muscle in vertebrate; it is attached to bone and voluntary.

Muscles made up of many tiny muscle fibres called MYOFIBRILS.

Muscles have structure that makes them strong : The separate cells are fused together into muscle fibres . The muscle fibres share nuclei and cytoplasm called sarcoplasm, which is mostly found around circumference of the fibre. Within the sarcoplasm is a large concentration of mitochondria and endoplasmic reticulum.

MICROSCOPIC STRUCTURE OF SKELETAL MUSCLE:

Two types of protein filaments:

·         Actin- thin- consists of 2 strand twisted around one another.

·         Myosin-Thicker-consists of long rod shaped fibres with bulbous heads that project to the side.

Myofibrils appear striped because they have light and dark bands. Light bands called isotropic cause the protein filaments do not overlap while dark bands called Anisotropic  cause protein overlaps.

Centre of anisotropic band is a lighter coloured region called the H-zone. Centre of each isotropic band is line called the Z line.  The distance between adjacent z-lines is called sarcomere. When a muscle contracts, these sarcomeres shorten and pattern of light and dark bands change.

2 other important proteins:

·         Tropomyosin: forms fibrous strand around the actin filament

·         Troponin involved in muscle contraction.

Types of muscle fibre:
two types ;

Slow twitch fibres:

1.      Contract slower.

2.      Adapted to endurance work.

3.      Adapted for aerobic respiration in order to avoid a build-up of lactic acid, which would cause them to function less effectively.

These include;

Large store of myoglobin

Supply of glycogen to provide source of metabolic energy.

Rich supply of blood vessels to deliver 0,2 and glucose

Lots of mitochondria to produce ATP.

Fast twitch fibres:

1.      Contract more rapidly- powerful contraction- short time.

2.      Adapted to intense exercise

3.      Fast twitch fibres  are adapted to their role by having:

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