what is muscle

what are muscle fibres?

• Muscles made of proteins and long cells known as muscle fibres which areheld together by connective tissue.

three different types of muscle fibres

• Skeletal muscle

• Smooth muscle

• Cardiac muscle

what is skeletal muscle/striated muscle/voluntary muscle

Muscle with a striped appearance under the microscope; it moves the bones of the skeelton under voluntary control

structure of muscle fibres

• Contains an organised arrangement of contractile proteins in the cytoplasm. Can contract to do work and can be pulled back to their original length when they relax

• Is surrounded by a cell surface membrane

• Contains many nuclei (multi-nucleated) – this is why muscle fibres are not usually referred to as cells

structure of myofibrils

• Muscle fibres are made up of many myofibrils lying parallel to each other

• Each myofibrils is made up of individual units of the muscle structure sarcometes

• The structure of the sarcomeres is made of the protein thin filaments made of actin and thick filaments made of myosin

different parts of muscle fibres

• The different parts of a muscle fibre have different names to the equivalent parts of a normal cell:

  • Cell surface membrane = sarcolemma

  • Cytoplasm = sarcoplasm

  • Endoplasmic reticulum = sarcoplasmic reticulum (SR)

structure of sarcolemma

• The sarcolemma has many deep tube-like projections that fold in from its outer surface:

  • These are known as transverse system tubules or T-tubules

  • These run close to the SR and help spread electrical impulses throughout muscle fibre

structure of sarcoplasm

• The sarcoplasm contains mitochondria and myofibrils

  • The mitochondria carry out aerobic respiration to generate the ATP required for muscle contraction

  • Myofibrils are bundles of actin and myosin filaments, which slide past each other during muscle contraction

structure of SR

• The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR

  • Calcium ions are needed for the contraction of muscle

what are smooth muscle/involuntary muscle

• it is not striped and is under the control of the involuntary nervous system. It is the muscle found in the gut where it is involved in moving the food along. It is also the muscle in blood vessels. It contracts and fatigues slowly.

what is cardiac muscle

Only found in the heart. It is striated, and the fibres are joined by special cross-connections. Cardiac muscle contracts spontaneously, which means it doesn not need to be stimulated by either nerves or hormones,and it does not fatigue.