1) The musculocutaneous nerve arises from the lateral cord of the brachial plexus and pierces the coracobrachialis muscle.
2) The median nerve has two roots. The lateral root of the median nerve arises from the lateral cord of the brachial plexus. The medial root of the median nerve arises from the medial cord of the brachial plexus.
3) The ulnar nerve arises from the medial cord of the brachial plexus
Nerves Of The Hand
The hand is innervated by 3 nerves: the median, ulnar, and radial.
- Median nerve
The median nerve is responsible for innervating the muscles involved in the fine precision and pinch function of the hand. It originates from the lateral and medial cords of the brachial plexus (C5-T1). In the forearm, the motor branches supply the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis muscles. The anterior interosseus branch innervates the flexor pollicis longus, flexor digitorum profundus (index and long finger), and pronator quadratus muscles.
Proximal to the wrist, the palmar cutaneous branch provides sensation at the thenar eminence. As the median nerve passes through the carpal tunnel, the recurrent motor branch innervates the thenar muscles (abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis). It also innervates the index and long finger lumbrical muscles. Sensory digital branches provide sensation to the thumb, index, long, and radial side of the ring finger.
- Ulnar nerve
The ulnar nerve is responsible for innervating the muscles involved in the power grasping function of the hand. It originates at the medial cord of the brachial plexus (C8-T1). Motor branches innervate the flexor carpi ulnaris and flexor digitorum profundus muscles to the ring and small fingers. Proximal to the wrist, the palmar cutaneous branch provides sensation at the hypothenar eminence. The dorsal branch, which branches from the main trunk at the distal forearm, provides sensation to the ulnar portion of the dorsum of the hand and small finger, and part of the ring finger.
At the hand, the superficial branch forms the digital nerves, which provide sensation at the small finger and ulnar aspect of the ring finger. The deep motor branch passes through the Guyon canal in company with the ulnar artery. It innervates the hypothenar muscles (abductor digiti minimi, opponens digiti minimi, flexor digiti minimi, and palmaris brevis), all interossei, the 2 ulnar lumbricals, the adductor pollicis, and the deep head of the flexor pollicis brevis.
- Radial nerve
The radial nerve is responsible for innervating the wrist extensors, which control the position of the hand and stabilize the fixed unit. It originates from the posterior cord of the brachial plexus (C6-8). At the elbow, motor branches innervate the brachioradialis and extensor carpi radialis longus muscles.
At the proximal forearm, the radial nerve divides into the superficial and deep branches. The deep posterior interosseous branch innervates all the muscles in the extensor compartment: supinator, extensor carpi radialis brevis, extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, extensor indicis proprius, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus.
The superficial branch provides sensation at the radial aspect of the dorsum of the hand, the dorsum of the thumb, and the dorsum of the index finger, long finger, and radial half of the ring finger proximal to the distal interphalangeal joints.
Peripheral Nervous System
The peripheral nervous system is divided into two major parts: the somatic nervous system and the autonomic nervous system.
- Somatic Nervous System
The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system AND motor nerve fibers that project to skeletal muscle.
The cell body is located in either the brain or spinal cord and projects directly to a skeletal muscle.
- Autonomic Nervous System
The autonomic nervous system is divided into three parts: the sympathetic nervous system, the parasympathetic nervous system and the enteric nervous system. The autonomic nervous system controls smooth muscle of the viscera (internal organs) and glands.
This picture shows the general organization of the autonomic nervous system. The preganglionic neuron is located in either the brain or the spinal cord. This preganglionic neuron projects to an autonomic ganglion. The postganglionic neuron then projects to the target organ. Notice that the somatic nervous system has only one neuron between the central nervous system and the target organ while the autonomic nervous system uses two neurons.
The enteric nervous system is a third division of the autonomic nervous system that you do not hear much about. The enteric nervous system is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, gall bladder).
diencephalon /di·en·ceph·a·lon/ (di″en-sef´ah-lon)
1. the posterior part of the forebrain, consisting of the hypothalamus, thalamus, metathalamus, and epithalamus; the subthalamus is often recognized as a distinct division.
2. the posterior of the two brain vesicles formed by specialization in embryonic development.
Showing: Brachial Plexus
4 major nerve plexuses are found, which - together with their peripheral nerves -
are described below:
1. Cervical plexus
- arises from the ventral rami of C1 - C5
- supplies muscles of the shoulder and neck
- major motor branch is the phrenic nerve
- arises from C3 - C5
- innervates the diaphragm
“The primary danger of a ‘broken neck’ is that the phrenic nerve may have been severed, leading to paralysis, cessation of breathing and death …”
2. Brachial plexus
- arises from ventral rami of C5 - C8, and T1
- subdivides into 5 major peripheral nerves which are:
1. Axillary nerve
- serves the muscles and skin of the shoulder, e.g. deltoid muscle
- damage causes paralysis and atrophy of deltoid
2. Radial nerve
- large peripheral nerve which innervates all extensor muscles of the arm, forearm and hand; and all the skin along the way;
- e.g. triceps brachialis
- damage causes wrist drop and inability to extend hand at wrist;
3. Median nerve
- runs down anterior of the arm
- supplies most of the flexor muscles in the forearm and several muscles in the lateral part of the hand;
- damage causes inability to pick up small objects due to decrease ability to flex and abduct thumb and index finger;
4. Musculocutaneous nerve
- innervates the arm muscles that flex the forearm and of the skin of the lateral surface of the forarm;
- damage leads to decreased ability to flex the forearm;
5. Ulnar nerve
- runs down along the postero-medial surface of the arm;
- supplies the flexor carpi ulnaris muscle and all intrinsic muscles of the hand not served by the median nerve;
- damage causes typical “clawhand” with inability to spread fingers apart;
3. Lumbar plexus
- arises from the central rami of L1 - L4;
- innervates the lower abdominal region and the anteromedial thigh;
- the largest nerve of this plexus is the femoral nerve;
- innervates the anterior thigh muscles, lower abdomen, buttocks, and the skin of the anteromedial leg and thigh;
- damage causes inability to extend leg and to flex the hip;
- another important nerve associated with this plexus is the obturator nerve;
- innervates the adductor muscles of the medial thigh and small hip muscles; also serves the skin of the medial thigh and hip joint;
- damage leads to inability to adduct the thigh;
4. Sacral plexus
- arises from L4 - S4
- peripheral nerves of this plexus innervate the buttock, the posterior thigh and virtually all of the leg and foot;
- the major nerve of this plexus is the sciatic nerve;
- it is the largest nerve of the human body!
- travels through the greater sciatic notch of the hip bone down to the posterior thigh;
- innervates the lower trunk and the posterior surface of thigh and leg;
- damage leads to inability to extend hip and to flex the knee —> “sciatica”
- divides in the popliteal region into the:
1. Common fibular nerve
- innervates the lateral aspect of the leg and foot;
- damage leads to inability to dorsiflex the foot —> “footdrop”
2. Tibial nerve
- innervates the posterior aspect of the leg and foot;
- damage leads to inability to plantar flex and invert the foot —> “shuffling gait”;
- another important nerve of this plexus is the superior and inferior gluteal nerve;
- innervates the gluteal muscles of the hip;