Anatomy - Week 9 - Pelvic Osteology

Question 1

What is the location of the lumbar plexus?

Answer 1

Lies on the posterior abdominal wall (mostly related to the psoas major muscle)

Question 2

What is the lumbar plexus formed by?

Answer 2

Ventral rami of L1-L4
Additionally, the ventral rami of the fourth lumbar nerve pass communicating branches, the lumbosacral trunk, to the sacral plexus.

Question 3

What are the branches off the lumbar plexus?

Answer 3

Iliohypogastric
Ilionguinal nerves
Lateral cutaneous nerve of the thigh and the femoral nerve emerge from the lateral border of the psoas in that order from above

Question 4

Where does the iliohypogastric nerve supply?

Answer 4

It supplies sensory branches to the skin of the abdominal wall just above the inguinal ligament.
It gives off motor branches to the ant abd wall muscles except rectus femoris.

Question 5

Where does the inguinal nerve L1 supply?

Answer 5

It passes through the inguinal canal to supply the skin of the groin and scrotum or labium majus through its sensory branches. It gives off motor branches to ant abd. Wall muscles except rectus femoris.

Question 6

Where does the lateral cutaneous nerve of the thigh enter and what does it supply?

Answer 6

Crosses the iliac fossa in front of the iliacus muscle and enters the thigh behind the inguinal ligament. In supplies the skin over the lateral surface of the thigh.

Question 7

Where does the femoral nerve enter and what does it supply?

Answer 7

(L2, 3 and 4)
Runs between the psoas and the iliacus muscles and enters the thigh behind the inguinal ligament. It supplies the iliacus muscle. It gives motor and sensory innervation to muscles and skin at the front of the thigh

Question 8

Where does the obturator nerve (L2, 3, 4) emerge and what does it supply?

Answer 8

It passes in front of the sacroiliac joint. It leaves the pelvis by passing through obturator foramen into the thigh. It supplies motor branches to adductor group of muscles in the thigh and sensory branches to skin on the medial surface of the thigh.

Question 9

What is the 4th lumbar root of the lumbosacral trunk?

Answer 9

Takes part in the formation of the sacral plexus. It descends anterior to the ala of the sacrum and joins 1st sacral nerve.

Question 10

Where does the Genitofemoral nerve (L1 - 2) enter and what does it supply?

Answer 10

It runs in front of the psoas major and divides into the genital branch, which enters the spermatic cord in male and passes through inguinal canal in female and supplies cremaster muscle (motor), and a femoral branch, which supplies a small area of the skin of the thigh (sensory)

Question 11

What are then two important ligaments in linking each pelvic bone to the sacrum and the coccyx?

Answer 11

The sacrospinous ligament

The sacrotuberous ligament

Question 12

What is the sacrospinous ligament?

Answer 12

It is a thin triangular ligament with its apex attached to the ischial spine and its broad base to the lateral margins of the sacrum and coccyx.

Question 13

What is the sacrotuberous ligament?

Answer 13

It is situated on the posterior aspect of the os coxae. It runs from the sacrum to the ischial tuberosity.

Question 14

What do the sacrospinous ligament and the sacrotuberous ligament convert the two notches on the pelvic bones?

Answer 14

The convert them into the greater and lesser sciatic foramina on the lateral pelvic walls.

Question 15

What is the sacrum bone?

Answer 15

It is formed by fusion of the five sacral vertebrae. The lateral surfaces of the bone has a large facet for articulation with ilium forming the sacroiliac joint. Posterior to this facet is the sacral tuberosity for the attachments of ligaments of the sacroiliac joint. The anterior edge of the vertebral body of S1 projects forward as the sacral promontory.

Question 16

Both the anterior and posterior surfaces of the sacrum contain anterior and posterior sacral foramina. Why?

Answer 16

For the passage of the anterior of posterior rami of the sacral nerves respectively.

Question 17

How many fused Bones does the pelvis consist of?

Answer 17

4

Question 18

What are the main gender differences of the pelvis in men and women?

Answer 18

• the pelvic inlet in a woman is circular, compared to the male heart shaped pelvic inlet. The more circular shape is partly caused by the less distinct promontory and broader alae in women.
• the subpubic angle (angle formed by the two arms of the pubic arch) is larger in women (80-85) than it is in men (50- 65 degrees)
• the ischial spines do not project as far medially into the pelvic cavity in women as they do in men
• the sacrum in males is more curved, in females it is flatter
• the pelvic outlet in a female is larger than in a male

Question 19

What is the development of the vertebral column like?

Answer 19

During fetal development, the spine assumes the shape of the letter ‘C’
The cervical secondary curvature of the neck is the first to develop. Within the first few months of life as the infant develops sufficient strength to hold his head up, the cervical curve begins to develop.
The development the lumbar secondary curvature when he starts to stand, walk and run. Bodies of the 5 lumbar vertebrae project into the midline of the posterior abdominal wall.

Question 20

What is the pelvic diaphragm/ floor formed by?

Answer 20

Levator ani and coccygeus muscles

Question 21

What is the levator ani anterior fibres?

Answer 21

The levator prostate or sphincter vaginae form a sling around the prostate or vagina and are inserted into a mass of fibrous tissue, Called perineal body, infront of the anal canal. Levator prostatae support prostate sphincter vaginae constrict the vagina.

Question 22

What is the levator ani intermediate fibres?

Answer 22

The puborectalis forms a sling around the junction of the rectum and anal canal
The pubococcygeus passes posteriorly to be inserted into the anococcygeal body, between the tip of the coccyx and the anal canal

Question 23

What are the posterior fibres of the levator ani?

Answer 23

Is inserted into the anococcygeal body and the coccyx

Question 24

What is the action of the levator ani muscle?

Answer 24

The levator ani of the two sides form an efficient muscular sling that supports the pelvic viscera in position. They resist a rise in intra- pelvic pressure during the straining as occurs in coughing
They also have an important sphincter action on the anorectal junction, and in female they serve also as a sphincter of the vagina.

Question 25

What is the nerve supply of the levator ani ?

Answer 25

Branches of the sacral plexus (S3-S5) and the pudendal nerve

Question 26

What is is the pelvic formed of?

Answer 26

The pelvic floor is formed by the pelvic diaphragm which is composed of levator ani (puborectalis, pubococcygeus, iliococcygeus) and coccygeus (ischiococcygeus)

Question 27

What is the diaphragm?

Answer 27

The diaphragm forms the superior border of the posterior abdominal wall separating the abdominal cavity from the thoracic cavity

Question 28

What is the origin of the diaphragm?

Answer 28

1- it is anchored to the lumbar vertebrae by musculotendinous crura
The right crus is attached to the vertebral bodies of L1 and L2 and the associated vertebral disc.
The crura are connected across the midline by the median accurate ligament which passes anterior to the aorta.
Lateral to the crura there is a second tendinous arch formed by the fascia which covers the upper part of the psoas major muscle, the medial arcurate ligament. A third tendinous arch the lateral arcurate ligament is formed by a thickening of the fascia that covers the quadratus lumborum muscle
2- the medial and lateral arcurate ligament serve as points of origin to the diaphragm
3- sternocostal origin from the lower six ribs and posterior aspect of xiphoid process

Question 29

What is the insertion of the diaphragm?

Answer 29

The diaphragm has a central tendon into which muscle fibres attach.
The height of the domes varies during breathing, but during normal expiration the left dome is the fifth intercostal space and the right dome at rib V

Question 30

What is the arterial supply of the diaphragm?

Answer 30

Superiorly (thoracic side) - receives its blood supply from the musculophrenic and pericardiophrenic arteries (branches of the internal thoracic artery) and the superior phrenic artery (from the thoracic aorta)
Inferiorly (the abdominal side) - is supplied by the inferior phrenic arteries (form the abdominal aorta)

Venous drainage is from corresponding accompanying veins

Question 31

What is the the diaphragms nervous supply?

Answer 31

Nerve innervation phrenic nerves which arise from spinal nerves C3-C5

Question 32

What is the action of the diaphragm?

Answer 32

The diaphragm is the primary respiratory muscle of the body. On contraction, it increases the vertical diameter of the chest cavity by pulling its central tendon downwards. In this way, the lungs get extra space to expand and air rushes into them.