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Innervation of Limbs

Organisation of the Body

QuestionAnswer
Nervous System Central nervous system - brain, spinal cord, optic nerve and retina Peripheral nervous system - cranial and spinal nerves, autonomic nervous system and senses
Spinal Cord Info is carried to the spinal cord in the dorsal nerve root Info is carried from the spinal cord in the ventral nerve root These fuse that the spinal nerve trunk, which splits to form the dorsal and ventral rami
Spinal Segments The spinal cord is divided into 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal) Each segment gives off a spinal nerve bilaterally Rootlet fuse to form dorsal/ventral roots which form the spinal nerve proper
Brachial Plexus Innervates the upper limb C5 to T1 spinal segments Formed from the ventral rami of the spinal nerves
Lumbar Plexus T12 to L5 spinal segments
Lumbo Sacral Plexus L4 to S3 spinal segments Innervates the lower limb Formed from the ventral rami of the spinal nerves
Dermatome Through the rami, the spinal nerve from each segment innervates the cutaneous components Dermatome map distribution is useful for neurologists as a guide to identifying the location of peripheral sensory defects Upper - C5-T1 Lower - T12-S3
Myotome Through the rami, the spinal nerve from each segment innervates the motor components
Myotome of the upper limb Abduction of the arm - C5 Flexion of the forearm - C6 Extension of the forearm - C7 Flexion of the fingers - C8 Abduction/adduction of the index, middle and ring fingers - T1
Myotome of the lower limb Flexion of the hip - L1 and L2 Extension of the knee - L3 and L4 Knee flexion - L5 to S2 Plantarflexion - S1 and S2 Adduction of the digits - S2 and S3
Myotome reflex/deep tendon reflex test Achilles - S1-S1 - 1,2 buckle my shoes Patella - L3-L4 - 3,4 kick the floor Biceps - C5-C6 - 5,6 pick up sticks Triceps - C7-C8 - 7,8 lay them straight
Stretch reflex Stimulus detected by neuromuscular spindles (stretch receptors) Afferent impulse to spinal cord Efferent impulse to quadriceps which contract The agonist hamstrings are also signalled to relax
Major nerves of the upper limb Arm - Mucocutaneous (anterior) Radial (posterior) Forearm - Median and Ulnar nerves (anterior) Radial (posterior) Hand - Ulnar and median nerves (anterior) Radial (posterior)
Major nerves of the lower limb Thigh - Femoral (anterior) Obturator (medial) Tibial (posterior) Leg - Deep peroneal (anterior) Superficial peroneal (lateral) Tibial (posterior) Foot - Medial and lateral plantar nerve (plantar surface)
Divisions of the Brachial plexus Roots - C5-T1 anterior rami Trunks - Superior, middle and inferior Divisions - Anterior and posterior Cords - Lateral, posterior and medial Terminal nerves
Nerves of the upper limb Musculocutaneous - C5,6,7 Axillary - C5,6 Radial - C5,6,7,8,T1 Median - C6,7,8,T1 Ulnar - C7,8,T1
Deltoid Supplied by the axillary nerve Fracture of the humerus surgical neck can lead to damage
Serratus Anterior Supplied by the long thoracic nerve Damage leads to winging of the scapula as the SA is paralysed do cannot pronate the scapular
Musculocutaneous nerve From the lateral cord Supplies the anterior compartment of the arm Tested by checking elbow flexion
Median nerve Supplied the anterior compartment of the arm Median nerve passes through the arm
Anterior interosseus nerve Deep branch of the median nerve Supplies muscles that allow flexion of the fingers
Palmar Cutaneous branch Extension of the anterior interosseous nerve Runs under the carpal tunnel to the thumb
What does the median nerve supply in the hand Palm - thenar muscles (except adductor pollicis) and 1st and 2nd lumbricals Cutaneous - 3 1/2 area of palm and digits
Anterior interosseous syndrome To check for damage to the median nerve, have the patient make an O with their fingers If it appears flat there is paralysis of the flexor digitorum Profundis and flexor pollicis longus
Compression of the median nerve Common to get compression of the median nerve in the carpal tunnel Inflammation of the tendons puts pressure on the nerve
Ulnar nerve Forearm - Medial half to flexor carpi Profundus (ring and little finger) FDP and Flexor carpi ulnaris Palm - All intrinsic muscles of hand including adductor pollicis. Except thenar muscles and 1st/2nd lumbricals Sensory - 1 1/2 palm and digits
Location of ulnar nerve Passes behind the medial epicondyle Superficial to carpal tunnel - Guyon's Canal
Damage to the ulnar nerve Leads to 'claw hand' - damage gives hyper extension of the digits (Lumbar claw hand) Compression of the ulnar nerve is common in the hand
Radial nerve Supplies posterior compartment of arm and forearm Deep branch - posterior interosseous nerve Superficial cutaneous branch Supplies dorsal aspect of hand except the tips
Wrist drop Compression of the radial nerve leads to weakness in wrist extension Common injury - can be trapped in supinator and can be damaged on fracture of the elbow
Lumbar Plexus Ventral rami of lumbar plexus Two main nerves - femoral and obturator nerves
Femoral nerve Supplies anterior compartment of the thigh Cutaneous tissue it is known as the Saphenous nerve
Obturator nerve Supplies the medial compartment of the thigh
Sciatic nerve Just below the piriformis Splits into the common fibular nerve and the tibial nerve
Sciatica Piriformis syndrome - leads to muscle spasm and hypertrophy - due to nerve running through or just above the piriformis Lesion or injury to sciatic nerve - stab wounds Site of safety (lateral) Site of danger (medial)
Gluteal nerves Superior gluteal nerve - L4,L5,S1 - Gluteus medius and minimus Inferior gluteal nerve - L5,S1,S2 - Gluteus maximus Paralysis of these leads to tilting to the opposite side whilst walking Injections in the glutes have to be placed to miss these nerves
Tibial component of sciatic nerve Supplies the posterior compartment of the thigh All hamstring muscles At midthigh splits into tibial and common peroneal (at popliteal fossa) Splits to form plantar nerves which supply the plantar face of the foot
Common peroneal/fibular nerve Superficial peroneal nerve supplies the lateral compartment of the leg Deep peroneal nerve supplies the anterior compartment of the leg
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