Spinal Nerves & Plexuses
Cervical, lumbar and sacral spinal nerves into plexuses and the pattern of poterior rami in the back.
The cervical plexus is formed from the anterior rami of cervical spinal nerves 1 through 4 (C1-C4). Branches of the plexus supply the stermocleidomastoid (C2) and trapezius (C3 and C4) muscles (recall plate 6-25) as well as several superficial and deep (prevertebral) muscles of the neck. The phrenic nerve (A1; from C3, C4 and C5) innervates the thoracic diaphragm, which is responsible for about 75 percent of the respiratory effort. Fibers from C1 through C3 form the ansa cervicalis (recall plate 6-26), which sends fibers to the infrahyoid muscle group and geniohyoid. Cutaneous nerves supply the skin at the side of the head, the neck, and the shoulder.
The brachial plexus (B) is formed from the anterior rami of cervical spinal nerves 5 through 8 and the first thoracic nerve (C5-T1). this plexus is found in the lower neck and axilla of the upper limb. In addition to its major terminal branches, the plexus gives off several nerves to neighboring muslces and cutaneous areas in the superficial back and the lateral and anterior chest.
The major nerves are directed to the shoulder, arm, forearm and hand. The musculocutaneous nerve (B1 C5-C7) supplies the muscles of the anterior oarm and the skin of the lateral forearm. The median nerve (B2; C6-T1) supplies muscles of the anterior compartment of the forearm, muscles of the thumb, and the skin of the anterior forearm and two-thirds of the hand. The ulnar nerve (C8-T1) supplies the muslces in the lateral forearm and hand and the skin of the fourth and fifth digits. The radial nerve (B4; C5-C8) supplies a muscle of the posterior arm and muscles (largely extensors) of the posterior compartment of the forearm. It sends cutaneous fibers to the lower lateral arm, the fposterior forearm, and the posterior web of skin between the thumb and index finger. The axillary nerve (B5; C5-C6) runs round the posteior aspect of the humerus at the surgical neck to supply the deltoid muscle of the shoulder, in part, and the skin of the shoulder and upper arm.
The intercostal nerves (C; T1-T12) run between the ribs and supply the intercostal muscles and the overlying skin (recall plate 7-3; the first rib and first intercostal nerve are not shown here). The lumbar plexus (D; L1-L4) forms in the posterior abdominal wall and supplies the muslces there. It contributes cutaneous fibers to the anterior and lateral abdominal wall below the level of the navel, including the inguinal region (not shown). It also sends fibers to the skin of the lateral thigh. Its two major branches are the femoral (D1) and the obturator nerves (D2). The femoral nerve supplies the anterior muscles of the thigh and sends cutaneous nerves to the anterior and medial thigh, the knee, and the medial leg. The smaller obturator nerve supplies the adductor muscles of the medial thigh and the overlying skin.
Major contributions from L4 and L5 anterior rami merge as the lumbosacral trunk, which joins in the formation of the sciatic nerve. This is the largest nerve of the body and is formed from the sacral plexus (E; L4, L5, S1-S3), on the posterior wall of the pelvis. The sacral plexus sends fibers to the muscles of the pelvis, the buttock,posterior thigh, and entire leg and foot. It also sends cutaneous fibers to the skin of the posterior thigh, leg and foot. The pudendal nerve (E2) from the sacral plexus supplies the external genitrals, anal sphincter, and skin around the anus. The coccygeal plexus (F) consists of small loops of fibers from S4, S5 and Co1 spinal nerves; they supply the skin around the coccyx.
The cervical posterior rami pass into the deep neck to supply suboccipital and other local muscles The greater occiptial nerve supplies the cutaneous area at the back of the head. Other cervical cutaneous nerves, including those of thoracic posterior rami T1 hrough T6 come up to the skinalong a vertical line about 3 cemtimeters lateral to the cervical and throacic spines (except for C7 and C8 which hve no cutaneous branches. The lower thoracic and lumbar posterior rami project their cutaneous branches more laterally than thos avobe. The muscular branches of these rami supply the deep muscles of the back, called the erectror spinae group. The posterior rami fo L4 and L5 send only muscular branches. The sacral and coccygeal posterior rami supply the skin of the medial aspect of the buttock and over the cocccys. In addiotn, the upper three sacral fibers supply deep muscles.)
The cervical plexus is formed from the anterior rami of cervical spinal nerves 1 through 4 (C1-C4). Branches of the plexus supply the stermocleidomastoid (C2) and trapezius (C3 and C4) muscles (recall plate 6-25) as well as several superficial and deep (prevertebral) muscles of the neck. The phrenic nerve (A1; from C3, C4 and C5) innervates the thoracic diaphragm, which is responsible for about 75 percent of the respiratory effort. Fibers from C1 through C3 form the ansa cervicalis (recall plate 6-26), which sends fibers to the infrahyoid muscle group and geniohyoid. Cutaneous nerves supply the skin at the side of the head, the neck, and the shoulder.
The brachial plexus (B) is formed from the anterior rami of cervical spinal nerves 5 through 8 and the first thoracic nerve (C5-T1). this plexus is found in the lower neck and axilla of the upper limb. In addition to its major terminal branches, the plexus gives off several nerves to neighboring muslces and cutaneous areas in the superficial back and the lateral and anterior chest.
The major nerves are directed to the shoulder, arm, forearm and hand. The musculocutaneous nerve (B1 C5-C7) supplies the muscles of the anterior oarm and the skin of the lateral forearm. The median nerve (B2; C6-T1) supplies muscles of the anterior compartment of the forearm, muscles of the thumb, and the skin of the anterior forearm and two-thirds of the hand. The ulnar nerve (C8-T1) supplies the muslces in the lateral forearm and hand and the skin of the fourth and fifth digits. The radial nerve (B4; C5-C8) supplies a muscle of the posterior arm and muscles (largely extensors) of the posterior compartment of the forearm. It sends cutaneous fibers to the lower lateral arm, the fposterior forearm, and the posterior web of skin between the thumb and index finger. The axillary nerve (B5; C5-C6) runs round the posteior aspect of the humerus at the surgical neck to supply the deltoid muscle of the shoulder, in part, and the skin of the shoulder and upper arm.
The intercostal nerves (C; T1-T12) run between the ribs and supply the intercostal muscles and the overlying skin (recall plate 7-3; the first rib and first intercostal nerve are not shown here). The lumbar plexus (D; L1-L4) forms in the posterior abdominal wall and supplies the muslces there. It contributes cutaneous fibers to the anterior and lateral abdominal wall below the level of the navel, including the inguinal region (not shown). It also sends fibers to the skin of the lateral thigh. Its two major branches are the femoral (D1) and the obturator nerves (D2). The femoral nerve supplies the anterior muscles of the thigh and sends cutaneous nerves to the anterior and medial thigh, the knee, and the medial leg. The smaller obturator nerve supplies the adductor muscles of the medial thigh and the overlying skin.
Major contributions from L4 and L5 anterior rami merge as the lumbosacral trunk, which joins in the formation of the sciatic nerve. This is the largest nerve of the body and is formed from the sacral plexus (E; L4, L5, S1-S3), on the posterior wall of the pelvis. The sacral plexus sends fibers to the muscles of the pelvis, the buttock,posterior thigh, and entire leg and foot. It also sends cutaneous fibers to the skin of the posterior thigh, leg and foot. The pudendal nerve (E2) from the sacral plexus supplies the external genitrals, anal sphincter, and skin around the anus. The coccygeal plexus (F) consists of small loops of fibers from S4, S5 and Co1 spinal nerves; they supply the skin around the coccyx.
The cervical posterior rami pass into the deep neck to supply suboccipital and other local muscles The greater occiptial nerve supplies the cutaneous area at the back of the head. Other cervical cutaneous nerves, including those of thoracic posterior rami T1 hrough T6 come up to the skinalong a vertical line about 3 cemtimeters lateral to the cervical and throacic spines (except for C7 and C8 which hve no cutaneous branches. The lower thoracic and lumbar posterior rami project their cutaneous branches more laterally than thos avobe. The muscular branches of these rami supply the deep muscles of the back, called the erectror spinae group. The posterior rami fo L4 and L5 send only muscular branches. The sacral and coccygeal posterior rami supply the skin of the medial aspect of the buttock and over the cocccys. In addiotn, the upper three sacral fibers supply deep muscles.)