Clinical Anatomy: Thorax Nerves

• Clinical anatomy emphasizes the practical application of anatomical knowledge in the diagnosis and treatment of diseases.
• It involves understanding anatomical structures and their relationships, variations, and clinical significance.

Thorax

• The phrenic nerve (C3-C5) innervates the diaphragm, providing motor and sensory innervation.
• Injury to the phrenic nerve can paralyze the corresponding half of the diaphragm, leading to breathing difficulties.
• The vagus nerve (CN X) has parasympathetic functions in the thorax, including innervating the heart, lungs, and esophagus.
• Vagus nerve damage can affect heart rate, digestion, and breathing.
• The recurrent laryngeal nerve, a branch of the vagus nerve, innervates the intrinsic muscles of the larynx (except the cricothyroid).
• Damage to the recurrent laryngeal nerve can cause vocal cord paralysis, leading to hoarseness.
• The thoracic duct drains lymph from the entire body except for the right upper quadrant and empties into the left subclavian vein.
• Blockage or injury to the thoracic duct can result in chylothorax (lymph in the pleural space).
• The intercostal nerves (T1-T11) run along the inferior border of the ribs within the costal groove, along with the intercostal artery and vein.
• Intercostal nerve damage can cause pain, muscle weakness, or altered sensation in the chest wall.
• The nipple is typically located at the level of the fourth intercostal space (T4 dermatome).
• The heart's apex is located in the left fifth intercostal space at the midclavicular line.
• The aortic arch gives rise to the brachiocephalic trunk, left common carotid artery, and left subclavian artery.
• Variations in the branching pattern of the aortic arch are common.
• The azygos vein drains blood from the posterior thoracic and abdominal walls into the superior vena cava.
• It can serve as a collateral pathway in cases of vena cava obstruction.
• The esophagus passes through the diaphragm at the esophageal hiatus (T10 vertebral level).
• Hiatal hernias can occur when part of the stomach protrudes through this opening.

Abdomen

• The abdominal aorta bifurcates into the right and left common iliac arteries at the level of the fourth lumbar vertebra (L4).
• The inferior vena cava is formed by the union of the right and left common iliac veins at the level of L5.
• The celiac trunk supplies blood to the stomach, spleen, liver, and pancreas.
• Compression of the celiac trunk can cause abdominal angina.
• The superior mesenteric artery (SMA) supplies blood to the small intestine, ascending colon, and transverse colon.
• SMA occlusion can lead to intestinal ischemia or infarction.
• The inferior mesenteric artery (IMA) supplies blood to the descending colon, sigmoid colon, and rectum.
• IMA occlusion can lead to ischemia of the distal colon.
• The portal vein is formed by the union of the splenic vein and the superior mesenteric vein.
• Portal hypertension can result from liver cirrhosis, leading to ascites, esophageal varices, and hemorrhoids.
• The liver has dual blood supply: the hepatic artery (25%) and the portal vein (75%).
• The hepatic portal system drains blood from the digestive tract and spleen to the liver, where it is filtered and processed.
• The gallbladder stores and concentrates bile produced by the liver.
• Cholecystitis (inflammation of the gallbladder) is often caused by gallstones blocking the cystic duct.
• The pancreas has both endocrine (insulin and glucagon) and exocrine (digestive enzymes) functions.
• Pancreatitis (inflammation of the pancreas) can be caused by gallstones, alcohol abuse, or other factors.
• The spleen filters blood and removes old or damaged blood cells.
• Splenomegaly (enlargement of the spleen) can occur in various conditions, such as infections, hematologic disorders, and portal hypertension.
• The kidneys filter blood and produce urine.
• Renal artery stenosis can cause secondary hypertension.
• The ureters transport urine from the kidneys to the bladder.
• Kidney stones can cause severe pain as they pass through the ureters.
• The adrenal glands produce hormones such as cortisol, aldosterone, and adrenaline.
• Adrenal tumors can cause hormonal imbalances.
• The inguinal canal is a passageway through the anterior abdominal wall.
• Inguinal hernias can occur when abdominal contents protrude through the inguinal canal.
• The layers of the abdominal wall include skin, superficial fascia, external oblique muscle, internal oblique muscle, transversus abdominis muscle, transversalis fascia, and parietal peritoneum.

Pelvis and Perineum

• The obturator nerve (L2-L4) innervates the adductor muscles of the thigh.
• Obturator nerve damage can cause weakness in adduction of the thigh.
• The sciatic nerve (L4-S3) is the largest nerve in the body and innervates the posterior thigh muscles and all muscles below the knee.
• Sciatic nerve compression (e.g., by a herniated disc) can cause sciatica, characterized by pain radiating down the leg.
• The pudendal nerve (S2-S4) innervates the perineum, including the external genitalia and anal sphincter.
• Pudendal nerve block can provide anesthesia for vaginal delivery or anorectal surgery.
• The pelvic diaphragm (levator ani and coccygeus muscles) supports the pelvic organs.
• Weakness of the pelvic diaphragm can contribute to pelvic organ prolapse.
• The uterus is supported by several ligaments, including the broad ligament, round ligament, and uterosacral ligaments.
• Uterine prolapse can occur if these ligaments are weakened.
• The ovaries produce eggs and hormones (estrogen and progesterone).
• Ovarian cysts and tumors are common gynecologic conditions.
• The prostate gland surrounds the urethra and contributes to seminal fluid.
• Benign prostatic hyperplasia (BPH) can cause urinary obstruction.
• The bladder stores urine.
• The detrusor muscle contracts to expel urine during urination.
• The rectum stores feces.
• The anal canal terminates at the anus, which is controlled by the internal and external anal sphincters.
• Hemorrhoids are caused by swollen veins in the anal canal.
• The perineum is the region between the thighs, extending from the pubic symphysis to the coccyx.
• Episiotomy is an incision made in the perineum during childbirth to enlarge the vaginal opening.

Upper Limb

• The brachial plexus (C5-T1) provides innervation to the upper limb.
• Brachial plexus injuries can cause weakness, paralysis, or sensory loss in the upper limb.
• Erb's palsy (waiter's tip deformity) results from injury to the upper trunk of the brachial plexus (C5-C6).
• Klumpke's palsy (claw hand) results from injury to the lower trunk of the brachial plexus (C8-T1).
• The axillary nerve (C5-C6) innervates the deltoid and teres minor muscles.
• Axillary nerve damage (e.g., from shoulder dislocation) can cause weakness in shoulder abduction.
• The musculocutaneous nerve (C5-C7) innervates the biceps brachii, brachialis, and coracobrachialis muscles.
• Musculocutaneous nerve damage can cause weakness in elbow flexion and supination.
• The radial nerve (C5-T1) innervates the triceps brachii, brachioradialis, and wrist extensor muscles.
• Radial nerve damage (e.g., from a midshaft humerus fracture) can cause wrist drop.
• The median nerve (C6-T1) innervates the forearm flexors (except flexor carpi ulnaris) and thenar muscles.
• Median nerve compression in the carpal tunnel can cause carpal tunnel syndrome.
• The ulnar nerve (C8-T1) innervates the flexor carpi ulnaris and intrinsic hand muscles.
• Ulnar nerve damage (e.g., at the elbow) can cause claw hand and difficulty with finger adduction and abduction.
• The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) stabilize the shoulder joint.
• Rotator cuff tears are common causes of shoulder pain.
• The biceps brachii muscle flexes the elbow and supinates the forearm.
• Biceps tendon rupture can cause a Popeye deformity.
• The carpal bones are arranged in two rows: scaphoid, lunate, triquetrum, pisiform (proximal) and trapezium, trapezoid, capitate, hamate (distal).
• Fracture of the scaphoid bone is the most common carpal fracture.

Lower Limb

• The lumbar plexus (L1-L4) and sacral plexus (L4-S4) provide innervation to the lower limb.
• The femoral nerve (L2-L4) innervates the quadriceps femoris and sartorius muscles.
• Femoral nerve damage can cause weakness in knee extension.
• The obturator nerve (L2-L4) innervates the adductor muscles of the thigh.
• Obturator nerve damage can cause weakness in thigh adduction.
• The sciatic nerve (L4-S3) innervates the posterior thigh muscles and all muscles below the knee.
• Sciatic nerve compression (e.g., by a herniated disc) can cause sciatica, characterized by pain radiating down the leg.
• The tibial nerve (L4-S3) is a branch of the sciatic nerve that innervates the posterior leg muscles and plantar foot muscles.
• Tibial nerve damage can cause difficulty with plantarflexion and inversion of the foot.
• The common fibular (peroneal) nerve (L4-S2) is another branch of the sciatic nerve that innervates the anterior and lateral leg muscles.
• Common fibular nerve damage can cause foot drop.
• The gluteal muscles (gluteus maximus, gluteus medius, and gluteus minimus) abduct and rotate the hip.
• Injury to the superior gluteal nerve can cause a Trendelenburg gait.
• The quadriceps femoris muscle extends the knee.
• The hamstring muscles (biceps femoris, semitendinosus, and semimembranosus) flex the knee.
• The anterior compartment of the leg contains the dorsiflexor muscles of the foot.
• The lateral compartment of the leg contains the fibularis (peroneus) muscles, which evert the foot.
• The posterior compartment of the leg contains the plantarflexor muscles of the foot.
• The arches of the foot distribute weight and provide shock absorption.
• Plantar fasciitis is a common cause of heel pain.