#lumbar 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"

                        and

                        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;