autostretching0243

The muscles are protected from injury by two kinds of nerve cells, ’muscle spindles’ and 'tendon spindles’ (Fig 3).

Muscle spindles prevent muscle cells from stretching too much when an unexpected movement occurs. They do this by making the muscle contract - puli itself tight. This happens automatically and protects the muscle from overstretching. Slow, intentional stretching of the muscles is not prevented by the muscle spindles.

Tendon spindles tell the brain, via nerve fibers, how tense the muscle is. If tension gets too high, tendon spindles send signals to stop the muscle contracting. These signals make the muscle relax.

Whcre nerve fibers from the brain reach the muscle, they split inlo many fine branches, eacli connected to one or morę muscle cells. Such a connection forms a motor unit. When the unit is acli vated, its muscle cell(s) will contract wilh rnaximum force. If the work load increases, morę motor units are activaled to help. The strength of a muscle depends directly on the number of motor units activated (Fig 4).

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