NRE Step 1: Anatomy Made Simple – Pass with Precision

Upper Limb Anatomy

The upper limb has three parts:

• Shoulder joint
• Arm (brachium): This part connects the shoulder to the elbow.
• Forearm (antebrachium): This part connects the elbow to the wrist. It contains 8 carpal bones.
• Hand (manus): The hand has 5 metacarpal bones and 14 phalanges (finger bones).

Nerve Injuries of the Upper Limb

• Waiter’s tip position (Erb’s Palsy): This happens when the upper trunk of the brachial plexus is injured. The arm is extended, turned inward, adducted (pulled towards the body), and pronated (palm facing down).
• Klumpke’s Palsy (claw hand): This occurs from an injury to the lower part of the brachial plexus, specifically affecting the lower part of the hand.
• Winging of the Scapula: This is caused by an injury to the long thoracic nerve, which supplies the serratus anterior muscle.
• Axillary Nerve Palsy: Injury to the axillary nerve, often occurring at the neck of the humerus, can lead to weakness or paralysis of the deltoid muscle, making it hard to lift the arm.
• Wrist Drop: This is caused by damage to the radial nerve, which can happen if the shaft of the humerus is injured.
• Ape Hand: This results from a median nerve injury, often at the supracondylar region of the humerus.
• Claw Hand: This is caused by an ulnar nerve injury, typically at the medial epicondyle.

Brachial Plexus The brachial plexus is a network of nerves that come from the spinal cord (C5, C6, C7, C8, T1) and supply the upper limb. It has roots, trunks, divisions, cords, and branches.

• The long thoracic nerve (C5​+C6​+C7​) supplies the serratus anterior muscle.
• The musculocutaneous nerve comes from the lateral cord.
• The axillary and radial nerves come from the posterior cord.
• The ulnar nerve comes from the medial cord.
• The median nerve has both a lateral and medial root.

Rotator Cuff Muscles These muscles help stabilize and move the shoulder joint. They are often remembered by the acronym SITS:

• Supraspinatus (most common injury site)
• Infraspinatus
• Teres minor
• Subscapularis

The most common direction for a shoulder to dislocate is anterior (forward), which can also injure the axillary nerve.

Arm Muscles and Nerves

• Flexor muscles (like Biceps Brachii and Brachialis) in the arm are supplied by the musculocutaneous nerve.
• Extensor muscles in the arm are supplied by the radial nerve.

Cubital Fossa (Elbow Pit) This is a triangular area in front of the elbow joint. It contains:

• Biceps tendon
• Brachial artery
• Median nerve
• Radial nerve
• Veins: median cubital, basilic, and cephalic veins.

Arm Abduction (Lifting the Arm Away from the Body)

• 0-15 degrees: Supraspinatus muscle, supplied by the suprascapular nerve.
• 15-90 degrees: Deltoid muscle, supplied by the axillary nerve.
• Greater than 90 degrees: Trapezius muscle, supplied by the accessory nerve.

Wrist Bones (Carpals) There are 8 carpal bones in the wrist, arranged in two rows:

• Proximal row: Scaphoid, Lunate, Triquetral, Pisiform.
  • The scaphoid is the most commonly fractured carpal bone and can be felt in the anatomical snuffbox.
• Distal row: Trapezium, Trapezoid, Capitate, Hamate.
  • The lunate is the most commonly dislocated carpal bone and can lead to median nerve injury.
  • A fracture of the hamate can injure the ulnar nerve.

Hand Muscles

• Thenar muscles: Located at the base of the thumb (e.g., Opponens muscle).
• Hypothenar muscles: Located at the base of the little finger.
• Dorsal interossei: These muscles abduct (spread) the fingers.
• Palmar interossei: These muscles adduct (bring together) the fingers.
• Lumbricals:
  • Lateral lumbricals supply fingers 1 and 2.
  • Medial lumbricals supply fingers 3 and 4.

Superficial Veins of the Arm

• Basilic vein: Runs along the inside (medial) of the arm and is superficial.
• Cephalic vein: Runs along the outside (lateral) of the arm and then drains into the axillary vein.

Lower Limb Anatomy

Thigh Muscles and Nerves

• Anterior compartment: Muscles like the Quadriceps femoris (Rectus femoris and three Vasti muscles) are supplied by the Femoral nerve.
• Medial compartment: Adductor muscles (Adductor Longus, Adductor Brevis, Adductor Magnus) are supplied by the Obturator nerve.
• Posterior compartment (Hamstrings): Muscles like the Biceps femoris (short head), Semimembranosus, and Semitendinosus are supplied by the Sciatic nerve.
  • The Sciatic nerve is formed by spinal nerves L4-S3 and divides into the Common fibular nerve and Tibial nerve.

Nerves of the Leg and Foot

• Anterior leg: Supplied by the Deep peroneal nerve. Injury here can cause “foot drop” (loss of dorsiflexion, which is pulling the foot upwards).
• Lateral leg: Supplied by the Superficial peroneal nerve.
• Posterior leg: Supplied by the Tibial nerve. Injury can lead to permanent dorsiflexion.
• The Common fibular nerve divides into the Deep and Superficial peroneal nerves at the neck of the fibula.

Femoral Triangle This is a triangular area in the upper thigh. Its borders are:

• Lateral: Sartorius muscle
• Medial: Adductor longus muscle
• Superior: Inguinal ligament It contains structures arranged from lateral to medial (NAVEL): Nerves, Artery, Vein, Empty space, Lymph Nodes. The Femoral sheath contains the femoral artery, femoral vein, and lymph nodes, but not the femoral nerve.

Veins of the Lower Limb

• Great saphenous vein: Runs medially and drains into the femoral vein. It is often used for grafting procedures.
• Short saphenous vein: Drains into the popliteal vein.

Abdominal Aorta and its Branches The abdominal aorta is a continuation of the thoracic aorta. It passes through the diaphragm at the level of T12 and divides into common iliac arteries at the level of L4. It gives off visceral branches that supply the organs:

Foregut Blood Supply The foregut includes the esophagus, stomach, first two-thirds of the duodenum, liver, gallbladder, spleen, and pancreas. It is supplied by the Celiac trunk, which branches at the level of T12. Branches of the Celiac trunk:

• Left gastric artery: The shortest branch; commonly bleeds in gastric ulcers. It supplies the lower end of the esophagus and part of the stomach.
• Hepatic artery: Divides into the proper hepatic artery and gastroduodenal artery.
  • The Right hepatic artery supplies the gallbladder.
  • The Gastroduodenal artery supplies the stomach, duodenum, and head of the pancreas. Bleeding from this artery can cause a duodenal ulcer.
• Splenic artery: The longest branch. It gives off pancreatic arteries, left gastroepiploic artery, and short gastric arteries, supplying the spleen, greater curvature of the stomach, and upper half of the pancreas.

Midgut Blood Supply The midgut includes the last third of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and the proximal two-thirds of the transverse colon. It is supplied by the Superior Mesenteric Artery (SMA) at the level of L1. Branches of the SMA:

• Inferior pancreaticoduodenal artery (supplies the head of the pancreas and part of the duodenum)
• Jejunal arteries (supply the jejunum)
• Ileocolic artery (supplies the ileum, cecum, and appendix)
• Right colic artery (supplies the ascending colon and hepatic flexure)
• Middle colic artery (supplies the hepatic flexure and proximal two-thirds of the transverse colon).
• Occlusion of the SMA can lead to abdominal angina.

Hindgut Blood Supply The hindgut includes the distal one-third of the transverse colon, splenic flexure, descending colon, sigmoid colon, and the upper part of the rectum. It is supplied by the Inferior Mesenteric Artery (IMA) at the level of L3. Branches of the IMA:

• Left colic artery (supplies the distal one-third of the transverse colon, descending colon, and splenic flexure)
• Sigmoidal arteries (supply the sigmoid colon)
• Superior rectal artery (supplies the upper part of the rectum) The splenic flexure is a “watershed area,” meaning it’s at the end of the blood supply from both the SMA and IMA, making it vulnerable to ischemia.

Paired Branches of the Abdominal Aorta

• Renal arteries: Branch at L2 and enter the hilum of the kidneys. The right renal artery is slightly longer than the left.
• Suprarenal arteries: Supply the adrenal glands.
• Gonadal arteries:
  • Males: Testicular arteries
  • Females: Ovarian arteries
  • The left testicular vein drains into the left renal vein. Compression of the left renal vein can cause a varicocele (enlargement of veins in the scrotum).

Portal Vein The portal vein is formed behind the neck of the pancreas by the union of the Superior Mesenteric Vein (SMV) and Splenic Vein (SV). The Inferior Mesenteric Vein (IMV) usually drains into the splenic vein or SMV. The portal vein has no valves.

Porto-Systemic Anastomosis These are connections between the portal venous system and the systemic venous system. If there is a blockage in the portal vein, blood can bypass it through these connections. Important sites for porto-systemic anastomosis include:

• Lower end of the esophagus: Left gastric vein (portal side) connects with the Azygos vein (caval side). Ruptured esophageal varices can occur here.
• Upper part of the rectum: Superior rectal vein (portal side) connects with the internal iliac vein/middle rectal vein (caval side). This can lead to internal hemorrhoids.
• Umbilicus: Paraumbilical veins (portal side) connect with the anterior abdominal wall veins (caval side). This can result in “Caput Medusae” (swollen veins around the navel).