Dermatomes of the Abdominal Wall

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Questions and Answers

Which spinal nerve is responsible for supplying the area of skin just above the inguinal ligament and the symphysis pubis?

L1 (correct)

T10

What is the primary source of blood supply to the skin near the midline of the abdominal wall?

Branches of the superior and inferior epigastric arteries (correct)

Branches of the intercostal arteries

Branches of the lumbar arteries

Branches of the femoral artery

Which of the following veins is responsible for draining the lower abdominal wall?

Axillary vein

Great saphenous vein

Lateral thoracic vein

Femoral vein (correct)

What is the name of the deep membranous layer of the superficial fascia?

Scarpa's fascia Signup and view all the answers

Which spinal nerve is responsible for supplying the area of skin over the xiphoid process?

T7 Signup and view all the answers

What is the name of the fatty layer of the superficial fascia?

Camper's fascia Signup and view all the answers

Which of the following arteries supplies the skin in the inguinal region?

All of the above Signup and view all the answers

Where does the venous drainage from the upper abdominal wall mainly pass?

Axillary vein Signup and view all the answers

What is the main function of the dartos muscle in the scrotum?

To regulate the temperature of the testes Signup and view all the answers

Which of the following muscles is NOT part of the Anterior Abdominal Wall?

Pectoralis major Signup and view all the answers

What is the insertion point of the External oblique muscle?

Xiphoid process, linea alba, iliac crest, pubic crest, and tubercle Signup and view all the answers

What forms the anterior wall of the rectus sheath above the costal margin?

Aponeurosis of the external oblique Signup and view all the answers

What is the function of the deep fascia in the perineum?

To enter the wall of the scrotum (or labia majora) Signup and view all the answers

What is the innervation of the External oblique muscle?

Lower six thoracic nerves, iliohypogastric and ilioinguinal nerves (L1) Signup and view all the answers

What forms the posterior wall of the rectus sheath above the costal margin?

Thoracic wall Signup and view all the answers

At which level do the aponeuroses of all three muscles form the anterior wall of the rectus sheath?

Between the arcuate line and the pubis Signup and view all the answers

What is the primary function of the Rectus abdominis muscle?

To support and compress abdominal contents Signup and view all the answers

What is the function of the aponeurosis?

To connect muscles to bones Signup and view all the answers

What is the name of the fascia that forms a tubular sheath for the penis (or clitoris)?

Deep fascia Signup and view all the answers

What is the linea alba?

A fibrous band that separates the two rectus sheath from each other Signup and view all the answers

How many muscles are part of the Anterior Abdominal Wall?

5 Signup and view all the answers

What is the level at which the aponeurosis of the internal oblique splits to enclose the rectus muscle?

Between the costal margin and the arcuate line Signup and view all the answers

What is the posterior wall of the rectus sheath composed of between the level of the arcuate line and the pubis?

Transversalis fascia Signup and view all the answers

What is a characteristic of aponeuroses?

They are similar to tendons Signup and view all the answers

Which muscle has a posterior border that is free?

External oblique Signup and view all the answers

What is the function of the conjoint tendon?

To protect a weak area in the abdominal wall Signup and view all the answers

What is the origin of the Rectus abdominis muscle?

Symphysis pubis and pubic crest Signup and view all the answers

What is the innervation of the Transversus abdominis muscle?

As previous Signup and view all the answers

What is the function of the Internal oblique muscle?

As previous Signup and view all the answers

What is the attachment site of the conjoint tendon medially?

Linea alba Signup and view all the answers

What is the name of the curved ridge formed by the rectus abdominis muscle when it contracts?

Linea semilunaris Signup and view all the answers

What is the level of the second transverse tendinous intersection of the rectus abdominis muscle?

Level of the umbilicus Signup and view all the answers

What type of fascia lines the transversus abdominis muscle?

Transversalis fascia Signup and view all the answers

What type of membrane lines the walls of the abdomen?

Serous membrane Signup and view all the answers

Which artery anastomoses with the inferior epigastric artery?

Superior epigastric artery Signup and view all the answers

What drains into the femoral vein via the superficial epigastric and great saphenous veins?

Superficial veins network Signup and view all the answers

What type of fat is found between the fascia transversalis and the parietal peritoneum?

Extra-peritoneal fat Signup and view all the answers

Which artery arises from the external iliac artery?

Deep circumflex iliac artery Signup and view all the answers

What forms an important portal-systemic venous anastomosis?

Paraumbilical veins Signup and view all the answers

Which artery supplies the lateral part of the abdominal wall?

Deep circumflex iliac artery Signup and view all the answers

Study Notes

Dermatomes of the Anterolateral Abdominal Wall

A dermatome is an area of skin supplied mainly by afferent nerve fibers from the dorsal root of a spinal nerve.
The anterolateral abdominal wall is divided into dermatomes:
- T7: Over the xiphoid process
- T10: Umbilicus
- L1: Lies just above the inguinal ligament and the symphysis pubis

Skin Blood Supply and Venous Drainage

The skin near the midline is supplied by branches of the superior and inferior epigastric arteries.
The skin of the flanks is supplied by branches of the intercostal, lumbar, and deep circumflex iliac arteries.
The skin in the inguinal region is supplied by the superficial epigastric, superficial circumflex iliac, and superficial external pudendal arteries, which are branches of the femoral artery.
Venous drainage from the upper abdominal wall passes mainly into the axillary vein via the lateral thoracic vein.
The lower abdominal wall drains into the femoral vein via the superficial epigastric and great saphenous veins.

Superficial Fascia

Divided into two layers:
- Superficial fatty layer (Camper's fascia)
- Deep membranous layer (Scarpa's fascia)
The superficial fatty layer is continuous with the superficial fat over the body, and may be extremely thick (8 cm or more) in obese individuals.
The deep membranous layer is thin and fades out laterally and superiorly, where it becomes continuous with the superficial fascia of the back and thorax, respectively.

Deep Fascia

A thin layer of connective tissue covering the muscles.
Lies immediately deep to the membranous layer of superficial fascia.

Muscles of the Anterior Abdominal Wall

Three broad thin sheets of muscle:
- External oblique
- Internal oblique
- Transversus abdominis
Additionally, there are two muscles:
- Rectus abdominis (on either side of the midline anteriorly)
- Pyramidalis (may be present in the lower part of the rectus sheath)

External Oblique Muscle

Origin: lower eight ribs
Insertion: xiphoid process, linea alba, iliac crest, pubic crest, and tubercle
Action: support and compress abdominal contents, assist in flexion and rotation of the trunk, assist in forced expiration, micturition, defecation, and vomiting
Innervation: lower six thoracic nerves, iliohypogastric and ilioinguinal nerves (L1)

Internal Oblique Muscle

Origin: iliac crest and lateral 2/3 of inguinal ligament
Insertion: lower three ribs, xiphoid process, linea alba, and symphysis pubis
Action: same as external oblique
Innervation: same as external oblique

Transversus Abdominis Muscle

Origin: lower six costal cartilages, iliac crest, and lateral 2/3 of inguinal ligament
Insertion: xiphoid process, linea alba, and symphysis pubis
Action: compress abdominal contents
Innervation: same as external oblique

Conjoint Tendon

Formed by the lowest tendinous fibers (aponeurosis) of the internal oblique and transversus abdominis muscles
Attaches medially to the linea alba, with a lateral free border
Has an essential role in protecting a weak area in the abdominal wall, where a weakening of the conjoint tendon may lead to a direct inguinal hernia

Rectus Abdominis Muscle

Origin: symphysis pubis and pubic crest
Insertion: 5th, 6th, and 7th costal cartilages, and xiphoid process
Action: compress, flex vertebral column, and act as an accessory muscle of expiration
Innervation: lower six thoracic nerves

Rectus Sheath

The composition of the walls of the rectus sheath changes at different levels
The anterior wall is formed by the aponeurosis of the external oblique above the costal margin
The posterior wall is formed by the thoracic wall above the costal margin
Between the costal margin and the arcuate line, the aponeurosis of the internal oblique splits to enclose the rectus muscle
Below the arcuate line, the aponeuroses of all three muscles (external oblique, internal oblique, and transversus abdominis) form the anterior wall, and the posterior wall is absent

Linea Alba

A fibrous band that separates the two rectus sheaths from each other
Extends from the xiphoid process to the symphysis pubis
Formed by the fusion of the aponeuroses of the lateral muscles of the two sides

Transversalis Fascia

A thin layer of fascia that lines the transversus abdominis muscle
Named according to the structure it overlies (e.g., diaphragmatic fascia, psoas fascia, iliac fascia)

Extra-peritoneal Fat

A thin layer of connective tissue that contains a variable amount of fat
Lies between the fascia transversalis and the parietal peritoneum

Parietal Peritoneum

A thin serous membrane
Lines the walls of the abdomen
Continuous below with the parietal peritoneum lining the pelvis

Anterolateral Abdominal Wall Arteries

Superior epigastric artery (from internal thoracic artery)
Inferior epigastric artery (from external iliac artery, from common iliac artery)
Deep circumflex iliac artery (from external iliac artery)
Lower two posterior intercostal arteries (from descending thoracic aorta)
Four lumbar arteries (from abdominal aorta)

Anterolateral Abdominal Wall Veins

Superficial veins network radiates out from the umbilicus
Above the umbilicus: drains into the axillary vein via the lateral thoracic vein
Below the umbilicus: drains into the femoral vein via the superficial epigastric and great saphenous veins
Paraumbilical veins form an important portal-systemic venous anastomosis

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Description

Understand the dermatomes of the anterolateral abdominal wall, including the areas supplied by spinal nerves T7, T10, and L1. Learn about the cutaneous nerve supply to the anterior abdominal wall.