W3: Abdominal walls

Question 1

How many layers of the anterior abdominal wall are there? List them

Answer 1

Question 2

Describe neurovascular plane of abdominal wall

Answer 2

All of the neurovascular structures supplying the abdominal muscles run in the plane between the internal oblique and transversus abdominis muscles, except for the iliohypogastric and ilioinguinal nerves.

Question 3

Borders of anterior wall

Answer 3

Costal margin

ASIS

Pubic tubercle

Question 4

What is anterior wall made up of?

Answer 4

The anterior abdominal wall is formed from skin, superficial fascia, muscles and parietal peritoneum.

Question 5

What can superficial fascia of ant wall be divided into?

Answer 5

fatty (superficial Camper) and membranous (deeper Scarpa) types, is found deep to the skin and subcutaneous tissue of the anterior abdominal wall.

Superficial vessels lie between these two layers

Question 6

What are the flat muscles of the ant wall?

Answer 6

3 stacked
External oblique
internal oblique
Transversus abdominis

Question 7

What happens to flat muscles at anteromedial aspect of ant. wall?

Answer 7

each flat muscle forms an aponeurosis (a broad, flat tendon), which covers the vertical rectus abdominis muscle. The aponeuroses of all the flat muscles become entwined in the midline, forming the linea alba (a fibrous structure that extends from the xiphoid process of the sternum to the pubic symphysis).

Question 8

External oblique

Answer 8

The external oblique is the largest and most superficial flat muscle in the abdominal wall. Its fibres run inferomedially.

Attachments: Originates from ribs 5-12, and inserts into the iliac crest and pubic tubercle, also linea alba - fibres run inferomedially
Functions: Contralateral rotation of the torso.
Innervation: Thoracoabdominal nerves (T7-T11) and subcostal nerve (T12).

Question 9

Internal oblique

Answer 9

Passes from the anterior part of the iliac crest and thoracolumbar fascia to the linea alba, pectineal line of the pubis via the conjoint tendon (shared with transversus abdominis) and inferior borders

of ribs 10-12.

Fibres run in a superomedial direction.

Functions: Bilateral contraction compresses the abdomen, while unilateral contraction ipsilaterally rotates the torso.

Innervation: Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus.

Question 10

Transversus abdominis

Answer 10

The transversus abdominis is the deepest of the flat muscles, with transversely running fibres. Deep to this muscle is a well-formed layer of fascia, known as the transversalis fascia.

Attachments: Originates from the inguinal ligament, costal cartilages 7-12, the iliac crest and thoracolumbar fascia. Inserts into the conjoint tendon, xiphoid process, linea alba and the pubic crest.

Functions: Compression of abdominal contents.

Innervation: Thoracoabdominal nerves (T7-T11), subcostal nerve (T12) and branches of the lumbar plexus

Question 11

Discuss conjoint tendon

Answer 11

Attaches transversus abdominis and internal olique to the pubic symphysis

Question 12

Rectus abdominis

Answer 12

The rectus abdominis is long, paired muscle, found either side of the midline in the abdominal wall. It is split into two by the linea alba. The lateral borders of the muscles create a surface marking known as the linea semilunaris.

At several places, the muscle is intersected by fibrous strips, known as tendinous intersections. The tendinous intersections and the linea alba give rise to the ‘six pack’ seen in individuals with a well-developed rectus abdominis.

Attachments: Originates from the crest of the pubis, before inserting into the xiphoid process of the sternum and the costal cartilage of ribs 5-7.

Functions: As well as assisting the flat muscles in compressing the abdominal viscera, the rectus abdominis also stabilises the pelvis during walking, and depresses the ribs.

Innervation: Thoracoabdominal nerves (T7-T11).

Question 13

Arcuate line

Answer 13

At 1/3 of the distance between the umbilicus and the pubic symphysis.

The rectus sheath becomes deficient after this point

Question 14

Blood supply of anterior wall

Answer 14

The anterior abdominal wall is supplied by the superior and inferior epigastric arteries, which arise from the internal thoracic and external iliac arteries respectively. The superior and inferior epigastric arteries form an anastomosis within the rectus sheath at the umbilicus.

Internal thoracic - subclavian - down inside of ribs

Question 15

Innervation of anterior abdominal wall

Answer 15

The skin overlying the anterior abdominal wall is innervated by the segmental intercostal nerves (T6-T12). These nerves lie between the internal oblique and transversus abdominis muscles (the neurovascular plane) and when reaching the mid-axillary line, produce perforating branches to innervate the lateral abdominal wall. Within the muscle sheath of rectus abdominis, the nerves produce perforating branches to innervate the an- teromedial wall.

Question 16

Borders of posterior wall

Question 17

What are the 5 muscles that contribute to the posterior wall? What is their innervation?

Answer 17

Psoas major (L1-L3 anterior rami)

Psoas minor (L1 anterior ramus)

Iliacus (femoral nerve)

Quadratus lumborum (T12-L4 anterior rami)

Diaphragm (phrenic nerve)

Question 18

What vascular structures are in the posterior abdominal wall? What levels are they?

Answer 18

 Aorta (T12-L4)
 Inferior vena cava (T8 -L5)  Cisterna chyli (L1-L2)

(right and posterior to Aorta).

Question 19

Quadratus lumborum

Answer 19

Attachments: It originates from the iliac crest and iliolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L1 – L4 and the inferior border of the 12th rib.

Actions: Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is not wasted.

Innervation: Anterior rami of T12- L4 nerves.

Question 20

Psoas major

Answer 20

Attachments: Originates from the transverse processes and vertebral bodies of T12 – L5. It then moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur.

Actions: Flexion of the thigh at the hip and lateral flexion of the vertebral column.

Innervation: Anterior rami of L1 – L3 nerves.

Question 21

Psoas minor

Answer 21

Attachments: Originates from the vertebral bodies of T12 and L1 and attaches to a ridge on the superior ramus of the pubic bone, known as the pectineal line.

Actions: Flexion of the vertebral column.

Innervation: Anterior rami of the L1 spinal nerve.

Question 22

Iliacus

Answer 22

Attachments: Originates from surface of the iliac fossa and anterior inferior iliac spine. Its fibres combine with the tendon of the psoas major, inserting into the lesser trochanter of the femur.

Actions: Flexion and lateral rotation of the thigh at the hip joint.

Innervation: Femoral nerve (L2 – L4).

Question 23

Discuss paravertebral gutters

Answer 23

The para-vertebral gutters are deep, vertical recesses passing either side of the vertebral column. Quadratus lumborum passes within the para-vertebral gutters, just lateral to psoas.

Question 24

Which muscle is the lumbar plexus found in?

Answer 24

Psoas major

Question 25

What are lumbar and sacral plexus formed by?

Answer 25

Anterior rami of lumbar and sacral spinal nerves

Question 26

Branches of lumbar plexus

Answer 26

Femoral nerve – supplies iliacus and the muscles of the anterior compartment of the thigh. Also provides cutaneous innervation to the thigh and leg.

Obturator nerve – passes through the obturator foramen to supply the adductor muscles of the thigh.

Subcostal, iliohypogastric and ilioinguinal nerves – equivalent of the intercostal nerves, passing around the abdominal wall within the neurovascular plane. The ilioinguinal nerve supplies the anterior part of the scrotum or labia.

Genitofemoral nerve – emerges on the anterior surface of psoas major. Supplies a small area of skin over the femoral triangle and the cremaster muscle.

Question 27

Branches of sacral plexus

Answer 27

superior and inferior gluteal nerves, sciatic nerve, nerve to quadratus lumborum and the posterior cutaneous nerve of the thigh.

Question 28

Discuss lumbar and sacral parts of the sympathetic chain

Answer 28

The lumbar and sacral parts of the sympathetic chain, which supply the distal GI tract, pelvic viscera, posterior abdominopelvic wall and the lower limbs, are found in the para-vertebral region of the posterior abdominal wall.

Question 29

hiccoughing Reflex

Answer 29

Hiccoughs are spontaneous, myotonic, repetitive contractions of the diaphragm and intercostal musculature, which may be triggered by a range of stimuli including a large oral intake, carbonated drinks, alcohol, excitement and over-breathing.

The afferent component of the reflex arc begins with sensory fibres travelling with the Vagus nerve, phrenic nerve or sympathetic nerve fibres. Ultimately, these sensory fibres converge at the upper spinal cord, medulla, reticular formation and hypothalamus.

The efferent pathway is carried by the phrenic nerve to the diaphragm, typically causing unilateral, but occasion- ally bilateral contraction. This reflex is completed by closure of the glottis, triggered by the recurrent laryngeal branch of the Vagus nerve.

Question 30

Abdominal skin Reflex

Answer 30

This is a superficial reflex obtained by firmly stroking the skin of the abdomen around the umbilicus. The reflex arc, carried by the anterior primary rami of T7-T12, normally results in a contraction of abdominal muscles, leading to the umbilicus moving toward the site of the stimulus.