Nerves of Pelvis and Perineum Flashcards
What is the pudendal nerve?
Major somatic nerve of the sacral plexus
What are the roots of the pudendal nerve?
S2-S4 (arises from ventral rami)
What are the motor/sensory functions of the pudendal nerve?
Motor - innervates various pelvic muscles, the external urethral sphincter and the external anal sphincter.
Sensory - innervates the external genitalia of both sexes and the skin around the anus, anal canal and perineum
Describe course of pudendal nerve from pelvis to perineum
Leaves pelvis via greater sciatic foramen and crosses sacrospinous ligament. Enters perineum via lesser sciatic foramen.
Describe course of pudendal nerve after re-entering perineum
After re-entering the pelvis, it accompanies the internal pudendal artery and vein, coursing anterosuperiorly through the pudendal canal. Inside the pudendal canal, the nerve divides into branches.
What is the pudendal canal also known as?
Alcock’s canal
What is the pudendal canal formed by?
Formed by fascia of obturator internus muscle
What branches does the pudendal nerve give off?
- Inferior rectal nerve
- Perineal nerve
- Continues as dorsal nerve of penis/clitoris
What does the pudendal canal contain?
Pudendal nerve, internal pudendal artery, pudendal veins
Where does perineal branch pass?
Travels superficial to the urogenital diaphragm
Describe motor function of pudendal nerve
The pudendal nerve provides the voluntary/somatic control of faecal and urinary continence.
Perineal nerve:
- Levator ani muscles
- Bulbospongiosus (muscle overlying corpus spongiosum)
- Ischiocavernosus (muscle overlying corpus cavernosum)
- External urethral sphincter
Inferior rectal:
- External anal sphincter
What are levator ani muscles innervated by?
- Perineal nerve
- Direct innervation from anterior ramus of S4 nerve root
Describe sensory function of pudendal nerve
The pudendal nerve supplies sensation to external genitalia of both sexes and the skin around the anus, anal canal and perineum through its branches (inferior rectal, perineal, dorsal nerve of penis or clitoris)
What does inferior rectal branch innervate?
Innervates the perianal skin and lower third of the anal canal.
What does perineal nerve innervate?
Innervates the skin of the perineum, labia minora and majora or scrotum.
What does dorsal nerve of penis or clitoris innervate?
Innervates the skin of the penis or clitoris. Thus, responsible for the afferent component of penile and clitoral erection.
What is a pudendal nerve block?
A form of analgesia occasionally given before vaginal childbirth, episiotomy and other minor vaginal procedures.
Local anaesthetic is then injected into the tissues around the ischial spine (on each side)
Where is the site of pudendal nerve block?
Ischial spine
What provides sensory innervation of external genitalia?
- Ilioinguinal nerve
- Genital branch
- Perineal branch
- Posterior cutaenous nerve of thigh
Nerves project inferiorly from sympathetic chain to form what plexus?
Braid of nerves –> superior hypogastric plexus
What is the superior hypogastric plexus comprised mainly of?
Sympathetic fibres
How do sympathetic fibres enter pelvis? What then forms?
Project either side via left and right hypogastric nerve into pelvis
Forms another network of nerves within pelvis –> inferior hypogastric plexus
This network is joined by pelvic splanchnic nerves (parasympathetic)
What does the inferior hypogastric plexus consist of?
Combination of sympathetic and parasympathetic fibres
Where do sympathetic fibres of inferior hypogastric plexus come from?
Superior hypogastric plexus
Where do parasympathetic fibres of inferior hypogastric plexus come from?
Pelvic splanchnic nerves
How does sympathetic innervation reach pelvis?
Through superior hypogastric plexus (and right and left hypogastric nerves)
