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Nerve Injuries - Principles

1. Anatomy [Also See Nervous System ]      [Back To Top] 

Of spinal nerves

  • Each segmental spinal nerve is formed by union of the dorsal/sensory root with the ventral/motor root at or before the intervertebral foramen
  • In the thoracic segments, these mixed spinal nerves maintain their autonomy, providing sensation and motor function to one intercostal segment
  • In all other areas (cervical, lumbar and sacral regions, plexuses are formed which provide a limb or special body segment without retaining the primitive myomeric pattern

Components of a mixed spinal nerve

  • Motor

The cell bodies are in the anterior horn cells and innervate skeletal muscle.

  • Sensory

Cell bodies lie within the dorsal root ganglia. The fibres arise in the pain , thermal, tactile and stretch receptors .

Proprioception, fine touch and vibration from extremities and trunk

These fibres pass cephalad in the dorsal columns and do not synapse until reaching the cervicomedullary junction.

Pathway for pressure and crude touch from extremities and trunk

These fibres enter, synapse and cross and ascend into the contralateral ventral spinothalamic tract.

Pain and temperature

These fibres synapse in the spnal cord, and cross to ascend in the lateral spinothalamic tract. There is some area of neuronal overlap explained by branches that ascend or descend via the dorsolateral column/fasciculus of Lissauer.

  • Sympathetic

The sympathetic component of all 31 spinal nerves leaves the spinal cord along only 14 motor roots (from T1 to L2). Between T1 and L2 there are white rami containing sympathetic fibres to the ganglions of the sympathetic chain. Synapses occur somewhere along the sympathetic chain and then postganglionic fibres reenter the mixed spinal nerves through grey rami.

Gross anatomy of a spinal nerve

Divides into an anterior and posterior primary ramus after leaving the intervertbral foramen.

Posterior primary ramus supplies the paraspinal musculature and the skin along the posterior aspect of the trunk neck and head

Anterior primary ramus supplies everything else, and form plexuses

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