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Question
Explain the formation of a typical spinal nerve with the help of a neat labelled diagram.
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Solution
Formation of Spinal Nerve
- All spinal nerves are of the mixed type i.e. they have some nerve fibre as sensory and some motor.
- Each spinal nerve is formed inside the neural canal of vertebral column by two roots - the posterior or dorsal sensory root and anterior or ventral root.
- Anterior root receives the sensory nerve from the dorsal root ganglion (cell bodies of sensory neurons are located in the ganglion), while the anterior/ventral root gives out the motor nerve.
- The dorsal sensory and the ventral motor nerves together form the mixed spinal nerve.
- It emerges out from both sides of the spinal cord through the intervertebral foramen.
- As soon as it emerges out of vertebral column, it shows three branches viz.
- Ramus dorsalis: From skin and to muscles of dorsal side.
- Ramus ventralis: The largest of the three supplies the organs and muscles on lateral and anterior side.
- Ramus communicans: The smallest of the three and given out from 1st thoracic upto 3rd lumbar (L3) spinal nerve. It joins the sympathetic ganglia.
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