Nerve fibres:
A nerve fibre is the axon or dendrite of a nerve cell. Bundles of nerve fibres in the PNS are called peripheral nerves (in CNS, called nerve tracts).
Two types of nerve fibres:
1) Non-myelinated fibres:
slower conducting
most post-ganglionic fibres of ANS are non-myelinated – also sensory fibres for pain
2) Myelinated fibres:
• surrounded by myelin formed by Schwann cell; faster conducting
Classification of nerve fibres:
Type A
Alpha (conducts at 70-120m/sec; largest diameter; motor nerves to skeletal muscles; least sensitive to local anaesthetics; myelinated)
Beta (conducts at 40-70m/sec; sensory nerves for cutaneous touch, pressure. vibration; myelinated)
Gamma (conducts at 10-50m/sec; motor nerves for muscle spindles; myelinated)
Delta (conducts at 6-30m/sec; sensory – pain (sharp and localised), temperature, touch; myelinated)
Type B (conducts at 3-15m/sec; pre-ganglionic autonomic nerves; myelinated)
Type C (conducts at 0.5-2m/sec; smallest diametre; sensory – pain (diffuse and deep), temperature and post-ganglionic nerve fibres; non-myelinated; most sensitive to local anaesthetics)
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