Classification of nerve fibres

Somatosensory fibres  transmitting impulses from the skin receptors and receptors of the musculoskeletal system. 

They are classified according to their types in the dorsal root into:

A Ia  and  A Ib  fibres – thick myelinated fibres (12 – 20 um), from annulospiral endings of muscle spindles (Ia) and Golgi tendon organs, conduction 80 – 120 m/sec.

A II fibres are thinner myelinated fibre (6 – 12 um), from flower spray endings of muscle spindles and from the skin mechanoreceptors, conduction 35 – 75 m/sec.

A III fibres (Aδ, 1 – 5μm) and C fibres (C IV fibres, 0.2 – 1.5 μm) are poorly myelinated or unmyelinated fibres, from the free endings (nociceptors) and skin termoreceptors and mechanoreceptors, conduction is up to 2 m/sec.

Ventral root fibres  contain efferent, motor fibres  vlákna různých tloušek, která se dělí do tří skupin:

fibres – axons of alfa-motoneurons of ventral horns. They are thick myelinated (12 – 20 μm) fibres for extrafusal muscle fibres (12 – 20 μm, conduction 72 – 120 m/sec. 

fibres- axons of gama-motoneurons. they are thinner myelinated (2 – 8 μm) fibres for intrafusal fibres of muscle spindles, conduction 12 – 48 m/sec.

B fibres– thin myelinated axons (up to 3 μm) of visceromotoneurons of the intermediolateral nucleus. They are preganglionic fibres of the sympathetic (C8-L3 segments) and parasympathetic (S2-S4 segments) system, conduction 6 – 18 m/sec. 

C fibres- very thin unmyelinated fibres (0.2 – 2 μm), postganglionic visceromotor fibres for smooth muscles glands and heart and sensory fibres for pain and warmth, conduction 0.5 – 2 m/sec.

Průřez nervem

Crossection of the peripherial nerve - overview, HE.

Myelinové pochvy

Crossection of the peripherial nerve - detail, myelin is detected by luxol blue, nuclear red stains nuclei of endoneurial fibroblasts.