Pelvic splanchnic nerve : easy and brief discussion

Pelvic splanchnic nerve :

Pelvic splanchnic nerves is also known as  nervi erigentes

Pelvic splanchnic nerves are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the hindgut.

The splanchnic nerves are paired visceral nerves (nerves that contribute to the innervation of the internal organs, carrying fibers of the autonomic nervous system (visceral efferent fibers)   as well as sensory fibers from the organs (visceral afferent fibers. All carry sympathetic fibers except for the pelvic splanchnic nerves, which carry parasympathetic fibers.

      The parasympathetic nervous system is referred to as the craniosacral outflow;

       the pelvic splanchnic nerves are the sacral component.

       They are in the same region as the sacral splanchnic nerves,

        which arise from the sympathetic trunk and provide sympathetic efferent fibers.

Splanchnic nerve carrying sympathetic fibres  

·         Cardiopulmonary nerves

·         Thoracic splanchnic nerves (greater, lesser, and least)

·         Lumbar splanchnic nerves

·         Sacral splanchnic nerves

    Splanchnic nerve carrying parasympathetic fibres  

·         Pelvic splanchnic nerve

Plexuses and pelvic splanchnic nerves :

1.    Sacral plexus

2.    Inferior hypgastric plexus

3.    Superior hypogastric plexuses

4.    Inferior mesenteric plexuses

·         Formation of  Pelvic splanchnic nerves

The pelvic splanchnic nerves arise from the anterior rami of the sacral spinal nerves S2-S4 and enter the sacral plexus. They travel to their side's corresponding inferior hypogastric plexus, located bilaterally on the walls of the rectum.

Functional component of pelvic splanchnic nerve :

1.    GVA: general visceral afferent : collect sensation from pelvic viscera and hindgut

2.    GVE: general visceral efferent : innervate smooth muscle cells and gland

Distribution of

1.    GVA: general visceral afferent: location of cell body in dorsal root ganglia of 2-4 sacral spinal nerve . central process enter the cord by posterior nerve root .

Two fates of GVA fibres :    

                                            i.            some GVA fibres make local synaptic connections .  they are responsible for bladder reflexes

                                          ii.            Other GVA fibres   collect sensory information from pelvic viscera and convey these information to higher cortical center .         

SN: both sympathetic and parasympathetic pathway collect pain sensation from urinary bladder and rectum                                        

2.    GVE: general visceral efferent

Pre-ganglionic  fibres arises from pre-ganglionic neurons which are located in the 2-4 sacral segments of spinal cord

Then pre-ganglionic fibres leave the spinal cord through anterior root of spinal nerve, trunk of spinal nerve then leave the spinal nerve when they exit anterior sacral foramina  and form pelvic splanchnic nerves . The preganglionic fibres of pelvic splanchnic nerves synapse with  Intrinsic ganglia of descending and sigmoid colon, rectum and other the pelvic viscera  

 these fibres innervate smooth muscles of hindgut and urinary bladder

Three distribution of pelvic splanchnic nerve

1.      Anterolateral branch

2.      Branches join with hypogastric nerves

3.      Superolateral branch

Distribution of three branches

1.      Anterolateral branch : join with inferior hypogastric plexuses and then distributed into pelvic viscera

2.      Branches join with hypogastric nerves: after joining with the hypogastric nerve these branch ascend and join with superior hypogastric plexuses and distributed in to the inferior mesenteric artery  

3.      Superolateral branch : it passes directly into the tissue of the retroperitoneum and the mesentery of sigmoid and descending colon

Functions of pelvic splanchnic nerve :

1.    Pelvic splanchnic nerve  the innervation of smooth muscle cells of the pelvic and genital organs.

2.    It relaxes the smooth muscle cells of sphincter vesicae but contract detrusor muscle (smooth muscle cells) of urinary bladder   

3.    It influences motility in the rectum 

4.    In the distal 1/3 of the transverse colon, and through the sigmoid and rectum, and the cervix  in females,

5.     The pelvic splanchnic nerves collect the sensation of pain from the hindgut & pelvic organ but  the rest of the proximal gastrointestinal tract sensation is collected  by the vagus nerve .

6.      Vasodilator fibres to the erectile tissue of the penis and clitoris

7.      Secretomotor fibres to the hindgut