Question

• Compare the type of fibers that make up the dorsal root and ventral roots
• Describe the connective tissues of nerves

Answer 1

Ans :

Dorsal root fibers :

The dorsal roots contain primary afferent fibers from the skin, subcutaneous and deep tissues, and viscera. Each dorsal root fiber is the central process of a dorsal root ganglion cell. It is estimated that there are 2–2.5 million afferent fibers in human adult dorsal roots on each side.

The dorsal (posterior) or sensory root bears a dorsal root ganglion (DRG) containing the cell bodies of the sensory neurons.

Ventral root :

The ventral roots typically have fewer fibers than do the dorsal roots, but they are of larger caliber because they contain the thick axons originating from the large lower motor neurons.

Connective tissue of nerve :

Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres.Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.