PERIPHERAL NERVES (contd) Nerve fibre type
Axons within the peripheral nerve vary structurally. This is related to function. Three distinct fibre types can be distinguished: type a 2-20 /im in diameter. Myelinated.
Function: Motor and sensory (vibration, proprioception). Conduction velocity: 10-70 metres/second. type b 3 //m diameter.
Thinly myelinated. Function: Mainly preganglionic autonomic, some pain and temperature. Conduction velocity: 7-5 metres/second. type c < 1 nm diameter Unmyelinated. Function: Sensory - pain and temperature.
Conduction velocity: <2 metres/second. The structure of the spinal peripheral nervous system has been considered but the arrangement is also important. Spinal nerves, after emerging from the intervertebral foramen pass into the brachial plexus to supply the upper limbs and the lumbosacral plexus to supply the lower limbs.
The thoracic nerves supply skeletal muscles and subserve sensation of the thorax and abdomen.
The Autonomic Nervous System is described on page 441.
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