The Peripheral Nerves of the Neck, Shoulders and Arms Many spinal nerves form interlacing nerve networks – the cervical, brachial, lumbar and sacral nerve plexuses. The cervical plexus in the neck involves the upper 4 cervical nerves and forms the phrenic nerve which supplies both sensory and motor innervation to the diaphragm which is important for breathing. The brachial plexus in the neck and armpit (axilla) involves C4-T2 and innervates the upper limb (arm and shoulder). These give rise to the axillary nerve, musculocutaneous nerve, median nerve, ulnar nerve and radial nerve (and a few others). The axillary nerve comes out behind the head of humerus to innervate the shoulder joint and the deltoid and teres minor muscles. The musculocutaneous nerve comes down the anterior arm innervates flexion of the forearm and sensory for the laterally forearm. The median nerve comes all the way down the central anterior arm to innervate the forearm flexor muscles and activate pronation of the forearm, flexion of the wrist and fingers and opposition of the thumb. It receives sensory from the forearm skin The ulnar nerve comes down the medial and the lateral palm. side of the arm, goes behind medial condyle of the elbow, down the medial forearm and innervates muscles of the forearm and fingers for wrist and medial finger flexion, adduction and abduction. It receives sensory from the medial side of the hand. The radial nerve is the largest of the nerves off the brachial plexus. It comes down the posterior arm, then wraps around the anterior aide of the lateral epicondyle of the elbow, then splits into a superficial branch and deep branch. It innervates all the extensor muscles of the upper limb and receives sensory from the skin of the posterior arm. ©Sheri Amsel www.exploringnature.org The Peripheral Nerves of the Neck, Shoulders and Arms brachial plexus axillary nerve musculocutaneous nerve median nerve radial nerve ulnar nerve ©Sheri Amsel www.exploringnature.org The Cervical Plexus The cervical plexus is deep in the neck and is fed by the ventral rami of C1-C4. It supplies both sensory (afferent) and motor (efferent) fibers to the phrenic nerve which controls the diaphragm - the main muscle that allows breathing movements. The cervical plexus also brings in sensory impulses from the skin of the neck, ears and shoulders. There is some motor for the muscles of the anterior neck as well. C1 accessory nerve (cranial XI) hypoglossal nerve (cranial XII) C2 lesser occipital nerve greater auricular nerve ansa cervicalis C3 transverse cervical C4 supraclavicular C5 nerves phrenic nerve ©Sheri Amsel www.exploringnature.org The Cervical Plexus C1 accessory nerve (cranial XI) hypoglossal nerve (cranial XII) C2 lesser occipital nerve greater auricular nerve ansa cervicalis C3 transverse cervical C4 supraclavicular C5 nerves phrenic nerve ©Sheri Amsel www.exploringnature.org The Brachial Plexus The brachial plexus is the source of almost all the nerves that innervate the upper limb (arm and shoulder. It lies in the neck and armpit (axilla) and involves nerve fibers from C4 -T2. These give rise to the axillary nerve, musculocutaneous nerve, median nerve, ulnar nerve and radial nerve (and a few others). Below is an illustration of the complex structure of the brachial plexus and it’s source off the cervical and thoracic nerves. From C4 dorsal scapular nerve C5 C6 suprascapular nerve C7 Upper Trunk lateral pectoral nerve C8 Middle Trunk musculocutaneous T1 nerve Lateral Cord Lower Trunk Posterior Cord axillary Medial Cord long thoracic nerve nerve medial pectoral nerve medial nerve upper suprascapular nerve thoracodorsal nerve radial nerve medial cutaneus nerves of arm lower suprascapular nerve ulnar nerve and forearm ©Sheri Amsel www.exploringnature.org The Brachial Plexus From C4 dorsal scapular nerve C5 C6 suprascapular nerve C7 Upper Trunk lateral pectoral nerve C8 Middle Trunk musculocutaneous T1 nerve Lateral Cord Lower Trunk Posterior Cord axillary Medial Cord long thoracic nerve nerve medial pectoral nerve medial nerve upper suprascapular nerve thoracodorsal nerve radial nerve medial cutaneus nerves of arm lower suprascapular nerve ulnar nerve and forearm ©Sheri Amsel www.exploringnature.org The Lumbosacral Plexus (The Peripheral Nerves of the Pelvis, Buttock and Lower Limbs) The lumbosacral plexus is the overlapping of the lumbar and sacral plexuses and innervates the lower limb and parts of the abdomen, pelvis and buttock. The lumbar plexus comes off L1-L4. It innervates the anterior and medial thigh and parts of the abdominal wall and iliopsoas muscle. It’s largest branch, the femoral nerve, splits into many branches to innervate the anterior thigh muscles for thigh flexion and knee extension. It receives sensory input from the anterior thigh and medial leg between the knee and foot. The obturator nerve innervates the medial thigh adductor muscles. The sacral plexus comes off L4-S4. It’s largest branch is the sciatic nerve, which is made up of the tibial nerve and the common peroneal nerve. The sciatic nerve enters the back of the thigh just medial to the hip joint and gives off branches to innervate the hamstring muscles, which are thigh extensors and knee flexors. Right above the knee it splits into the tibial and common peroneal nerves. The tibial nerve goes behind the knee (called the popliteal fossa) and innervates the posterior calf muscles. It receives sensory from the skin behind the calf and the sole of the foot. It gives off the sural nerve which receives sensory from the posterior-lateral calf and the plantar nerves which innervates the foot. When the common peroneal nerve splits off the sciatic nerve, it wraps around the head of the fibula and splits into the superficial and deep branches which innervate the anterior-lateral calf muscles, which are extensors and dorsiflexors of the foot. It receives sensory from the knee joint, lateral calf and top (dorsum) of the foot. The sacral plexus also gives off the superior and inferior gluteal nerves which innervate the gluteal muscles of the buttock and a lateral muscle of the thigh (tensor fascia lata). It also gives of the pudendal nerve, which innervates structures in the pelvis. Lumbar Plexus Sacral Plexus ©Sheri Amsel • www.exploringnature.org The Peripheral Nerves of the Pelvis, Buttock and LEGS anterior view posterior view inguinal ligament posterior femoral cutaneous lateral femoral nerve cutaneous nerve femoral obturator nerve nerve sciatic nerve saphenous common common nerve peroneal peroneal nerve nerve tibial nerve superficial peroneal nerve deep peroneal nerve sural nerve sural nerve ©Sheri Amsel • www.exploringnature.org The Lumbar Plexus The lumbar plexus comes off L1-L4. It innervates the anterior and medial thigh and parts of the abdominal wall and iliopsoas muscle. It’s largest branch, the femoral nerve, splits into many branches to innervate the anterior thigh muscles for thigh flexion and knee extension. It receives sensory input from the anterior thigh and medial leg between the knee and foot. The obturator nerve innervates the medial thigh adductor muscles. L1 L2 iliohypogastric nerve ilioinguinal nerve L3 genitofemoral nerve L4 lateral femoral nerve L5 femoral nerve lumbosacral trunk obturator nerve ©Sheri Amsel www.exploringnature.org The Lumbar Plexus L1 L2 iliohypogastric nerve ilioinguinal nerve L3 genitofemoral nerve L4 lateral femoral nerve L5 femoral nerve lumbosacral trunk obturator nerve ©Sheri Amsel www.exploringnature.org The Sacral Plexus The sacral plexus comes off L4-S4. It’s largest branch is the sciatic nerve, which is made up of the tibial nerve and the common peroneal nerve. The sciatic nerve enters the back of the thigh just medial to the hip joint and gives off branches to innervate the hamstring muscles, which are thigh extensors and knee flexors. Right above the knee it splits into the tibial and common peroneal nerves. The tibial nerve goes behind the knee (called the popliteal fossa) and innervates the posterior calf muscles. It receives sensory from the skin behind the calf and the sole of the foot. It gives off the sural nerve which receives sensory from the posterior-lateral calf and the plantar nerves which innervates the foot. When the common peroneal nerve splits off the sciatic nerve, it wraps around the head of the fibula and splits into the superficial and deep branches which innervate the anterior-lateral calf muscles, which are extensors and dorsiflexors of the foot. It receives sensory from the knee joint, lateral calf and top (dorsum) of the foot. The sacral plexus also gives off the superior and inferior gluteal nerves L4 which innervate the gluteal muscles of the buttock and a lateral muscle of the thigh (tensor fascia lata). It also gives of the pudendal nerve, which innervates structures in the pelvis. lumbosacral trunk L5 superior gluteal nerve S1 inferior gluteal nerve The Sacral S2 Plexus common peroneal nerve S3 tibial nerve S4 sciatic nerve posterior temporal pudendal nerve cutaneous nerve The Sacral Plexus L4 lumbosacral trunk L5 superior gluteal nerve inferior gluteal nerve S1 S2 common peroneal nerve S3 tibial nerve S4 sciatic nerve posterior temporal cutaneous nerve pudendal nerve ©Sheri Amsel www.exploringnature.org.