RBody Fact

Every time a muscle is used, the muscle fibres shorten along their length, therefore tension often accumulates in lines in the longer muscles (particularly those with parallel fibres such as the paravertebral muscles). In muscles with shorter fibre pennates and convergent fibres tension is often in knots rather than in lines.

• Parallel fibres — muscles with parallel fibres can vary from short, flat muscles to spindle-shaped (fusiform) muscles to long straps.

• Convergent — this is where the muscles fibres converge towards a single point for maximum concentration of the contraction. The direction of movement is determined by which sections of the muscle are activated. The muscle may be a triangular sheet (the pectoralis major muscle or the latissimus dorsi). These muscles often cross joints that have a large range of possible movements. They provide a strong but steady pull, fine-tuning the angle of movement and thus balancing movement with continuing stability in the joint.

• Pennate - this is where the fibres lie at an angle to the tendon and, therefore, also to the direction of pull. They have lots of short fibres so the muscle pull is short but strong. They may be further classified as follows:

• Uni-pennate — diagonal fibres attach to one side of the tendon only such as the soleus.

• Bi-pennate — the fibres converge onto a central tendon from both sides such as the rectus femoris.

• Multipennate — the muscle has several tendons of origin such as the deltoid.

Voluntary muscle works intimately with the nervous system and will, therefore, only contract if a stimulus is applied to it via a motor nerve. Each muscle fibre receives its own nerve impulse so that fine and varied motions are possible. Voluntary muscles also have their own small stored supply of glycogen which is used as fuel for energy. Voluntary muscle tissue differs from other types of muscle tissue in that the muscles tire easily and need regular exercise.

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