spinal nerves

Networks of intertwining nerves stemming from all ventral rami (except T2-T12) are referred to as plexuses.
- These plexuses innervate muscles in the limbs and skin.
The ventral rami that do not form plexuses (T2-T12) create intercostal nerves that innervate the intercostal muscles, abdominal wall, and anterolateral thorax.

The cervical plexus consists of ventral rami from spinal nerves C1 through C5.
- It branches into nerves that innervate the posterior neck and head.
A notable nerve from the cervical plexus is the phrenic nerve, which connects to the diaphragm at the base of the thoracic cavity.
- Formed from spinal nerves C3, C4, and C5.
- A mnemonic to recall its innervation is: “C3, C4, C5 help keep the diaphragm alive.”

Lesser occipital nerve: innervates areas of the skin on the head.
Great auricular nerve: supplies sensory innervation to the skin over the parotid gland, external ear, and neck.
Transverse cervical nerve: innervates the skin of the anterior neck.
Supraclavicular nerve: provides sensory information from the skin over the clavicle and shoulder.
Phrenic nerve: vital for innervating the diaphragm.

The brachial plexus arises from spinal nerves C5-T1 and innervates the pectoral girdles and upper limbs.

Axillary Nerve
- Supplies three muscles: deltoid, teres minor, and the long head of the triceps brachii.
- Carries sensory information from the shoulder joint.
Radial Nerve
- Supplies the triceps brachii muscle and twelve muscles in the forearm that control wrist and finger extension.
- Carries sensory information from associated joints and overlying skin.
- Follows the posterior surface of the humerus, wraps around to the anterior near the elbow, and travels along the radial bone in the forearm.
Median Nerve
- Supplies flexor muscles of the forearm and skin of the first three and a half fingers.
- Travels medially on the anterior surface of the elbow.
Ulnar Nerve
- Supplies part of the flexor muscles of the forearm, wrist, hands, and skin of half the ring finger and pinky finger.
- Travels posteriorly behind the medial side of the elbow and along the ulnar side of the forearm.
Musculocutaneous Nerve
- Responsible for flexor muscles of the arm, including biceps brachii and brachialis.
- Travels along the radial side of the forearm.

Spinal Segments	Nerve and Distribution
C5-T1	Musculocutaneous: Flexor muscles on the arm (biceps brachii, brachialis, coracobrachialis); sensory from skin over lateral surface through lateral antebrachial cutaneous nerve.
C5-T1	Radial: Extensor muscles on the arm and forearm (triceps brachii, anconeus, extensor carpi radialis, extensor carpi ulnaris, brachioradialis); sensory from skin over the posterolateral surface through posterior brachial cutaneous nerve, posterior antebrachial cutaneous nerve, and superficial branch.
C6-T1	Median: Flexor muscles on the forearm (flexor carpi radialis and palmaris longus); pronator quadratus and teres; digital flexors via anterior interosseous nerve; sensory from skin over anterolateral surface of the hand.
C8-T1	Ulnar: Flexor carpi ulnaris, flexor digitorum profundus, adductor pollicis, small digital muscles by deep branch; sensory from skin over medial surface of the hand via superficial branch.

Plexus	Origin (from ventral rami)	Important nerves	Body areas served	Result of damage
Cervical	C1-C5	Phrenic, Axillary	Diaphragm; skin/muscles of shoulder and neck	Respiratory paralysis (and death if not treated promptly)
			Deltoid muscle and skin of shoulder; muscles/skin of superior thorax	Paralysis and atrophy of deltoid muscle
Brachial	C5-C8 and T1	Radial, Median, Musculocutaneous, Ulnar	Triceps/Extensor muscles of forearm; skin of posterior upper limb	Wrist drop (inability to extend hand at wrist)
			Flexor muscles and skin of forearm; some muscles of hand	Decreased ability to flex forearm at elbow
			Flexor muscles of arm; skin of lateral forearm	Claw hand (inability to spread fingers apart)

The lumbar plexus nerves arise from the ventral rami of T12-L4 and branch into nerves that supply the pelvis and lower extremities.

Femoral Nerve: Major nerve supplying hip flexors and knee extensors, as well as sensory detection from the skin of the anterior thigh.
Lateral Femoral Cutaneous Nerve: Receives sensory information from the skin of the anterior, lateral, and posterior surfaces of the thigh.
Obturator Nerve: Supplies adductor muscles of the medial thigh.

Arises from the ventral rami of L4-S4.
Sciatic Nerve: The largest nerve in the human body, supplies inferior trunk and posterior surface of the thigh, innervating hip extensors and knee flexors.
- Common Fibular (Peroneal) Nerve: Travels laterally, innervating the lateral aspect of the lower leg and foot.
- Tibial Nerve: Travels along the posterior surface of the tibia to innervate the posterior lower leg and posterior foot.
- Superior and Inferior Gluteal Nerves: Innervate the gluteal muscles of the hip.

Plexus: Origin (from ventral rami) | Important Nerves | Body Areas Served | Results of Damage
Lumbar: L1-L4 | Femoral: flexors and extensors of hip/knee, sensory from anteromedial leg | Inability to extend leg and flex hip; loss of cutaneous sensation
Lumbar: L1-L4 | Obturator: adductor and small hip muscles | Inability to adduct thigh
Sacral: L4-S4 | Sciatic: lower trunk and posterior thigh; splits to common fibular and tibial nerves | Inability to extend hip and flex knee; sciatica
Sacral: L4-S4 | Common Fibular: lateral aspect of leg and foot | Foot drop (inability to dorsiflex foot)
Sacral: L4-S4 | Tibial: posterior leg and foot | Inability to plantar flex and invert foot; shuffling gait
Sacral: L4-S4 | Superior and Inferior Gluteal Nerves: gluteus muscles | Inability to extend hip (maximus) or abduct and medially rotate thigh (medius)

The discussion covers the anatomy of spinal nerves, including various plexuses, major nerves within those plexuses, their functions, and the implications of injuries to these nerves. Understanding the distribution of these nerves is essential for diagnosing and managing injuries and neurological conditions in the body.