Sacral
The spinal nerves emerging from the sacrum at the lower part of the vertebral column are commonly known as sacral nerves. These arise in form of pairs, one from left and other from right. Sacral nerves are ten in number in form of five pairs. These are denoted as S1, S2, S3, S4 and S5.
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Sacral
The nerves are basically attached to the spinal medulla (core of spinal cord), at particular points, which are known as roots. Each nerve has Anterior Root and Posterior Root. The posterior roots are usually larger and form ganglia that resides in the vertebral canal. Beyond the spinal ganglia, both anterior and posterior roots unite immediately to form sacral nerves. Each nerve receives a branch from the adjacent ganglion of the sympathetic chain (a vertical chain placed paravertebrally and is related to autonomic nervous system).
The sacral nerves then emerge from intervertebral foramina and each is divided into anterior and posterior division. Anterior Division arises from anterior sacral foramina and Posterior Division from posterior sacral foramina.
Every Sacral Nerve has got the fibres which belongs to two separate systems:
Somatic are distributed as afferent and efferent fibres. Efferents carry information to the voluntary muscles and originate from the anterior column of the spinal medulla and go outwards by the anterior root of sacral nerves. Afferent fibres receives the information through the skin and take these impulses towards the spinal medulla through posterior roots.
Splanchnic/Sympathetic fibres are also divided into afferent and efferent. Efferent fibres are preganglionic and postganglionic. The preganglionic fibres arise from the lateral column of the spinal medulla and receive fibres from the adjacent ganglion of the sympathetic chain. They end in a Ganglion formed by various nerve cells which is placed away from vertebral column or in another ganglion of the sympathetic chain. The postganglionic fibres then arise from the ganglion and are carried towards the blood vessels of the trunk and limbs. Other fibres may end in distally placed viscera. Afferent fibres emerge from the spinal ganglia and carry impulses from several viscera. From S2,S3 and S4 also arise the parasympathetic fibres, which emerge from spinal ganglia and provide postganglionic fibres to the descending colon, rectum, urinary bladder and pelvic organs. This system is knowns as Pelvic splanchnic nerves.
The branches are then formed from these divisions and form sacral plexus and lumbosacral plexus which then innervate hip, thigh, leg and foot. The branches of these plexuses are responsible for both the sensory perception and the motor supply.
NERVE ROOTS
DIVISIONS
STRUCTURE
INNERVATION
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