Nerve Supply to Fore Limb (Unit 2) - GADVASU LUDHIANA PDF

Unit 2 Innervations of the fore limb and diseases caused due to damage and paralysis of nerves to fore limb Thoracic limb is innervated by the brachial plexus. Brachial Plexus: Definition: Brachial plexus is the network of nerves that supplies...

Unit 2 Innervations of the fore limb and diseases caused due to damage and paralysis of nerves to fore limb Thoracic limb is innervated by the brachial plexus. Brachial Plexus: Definition: Brachial plexus is the network of nerves that supplies most structures of the thoracic limb with both sensory and motor innervations. – Sensory includes cutaneous information as well as sensory information from muscle spindle fibres, periosteum and joint capsule. Formation of Brachial Plexus: Roots: The brachial plexus of the horse, ox, and dog consists of the ventral rami of cervical nerves 6,7 and 8 (C6, C7 and C8) and thoracic spinal nerves 1 &2 (T1&T2). These nerves are referred as roots of brachial plexus. – Ventral branches of the contributing spinal nerves cross the Scalenus muscle, extending into traversing the axilla (triangular space between the medial shoulder region and the lateral body wall). – As the ventral branches of the contributing spinal nerves traverse the axillary space, they intercommunicate extensively to form the brachial plexus. Derivatives of brachial plexus: – Fibers from multiple nerves coalesce to form the named nerves of the plexus and pass into the thoracic limb along constant routes. [email protected] Page 1 Unit 2 – The spinal cord enlargement associated with the brachial plexus lies primarily in the caudal cervical vertebrae and is consequently described as the cervical intumescence. Formation of Brachial Plexus Branches of Brachial Plexus: There are 12 named branches of brachial plexus 1. External thoracic nerve 2. Thoracodorsal nerve 3. Long Thoracic nerve 4. Nerve to Pectorals 5. Suprascapular nerve 6. Nerve to Subscapular 7. Nerve to Teres Major 8. Axillary Nerve 9. Ulnar Nerve 10. Musculocutaneous nerve 11. Median Nerve 12. Radial nerve [email protected] Page 2 Unit 2 1. Long thoracic nerve Thoracodorsal nerve Formed by C7 and C8 Innervates the Serratus Ventralis m. 1. External (lateral) thoracic nerve: Formed by C8, T1 and T2 Innervates the cutaneous trunci muscle (motor) Sensory to skin ventral thoracic and abdominal wall. pectoral muscles 2. Thoracodorsal nerve: Formed by the C8 and T1 spinal nerves Motor supply to Latissimus dorsi muscle 3. Pectoral n. Formed by C7, C8 and T1 spinal nerves Innervates the pectoral m 4. Suprascapular n. Formed by C6 and C7. Innervates the Suprascapular and subscapular m. 5. Subscapular n. Formed by C6 and C7. Innervates the Suprascapular and subscapular m. 6. Nerve to Teres Major Innervates the Teres Major muscle 7. Axillary nerve: Formed by C7, C8 spinal nerves It dives between teres major and subscapularis muscle to reach to lateral surface of shoulder Innervates the Deltoideus, teres major and teres minor Sensory cutaneous innervation to arm and forearm region. [email protected] Page 3 Unit 2 8. Musculocutaneuos branch Innervates the Biceps brachii, coracobrachialis and brachialis. Gives off Median cutaneous antebrachial nerve (Supply craniomedial aspect of forearm). 9. Ulnar Nerve: Runs from medial side of forearm with median and musculocutaneous nerve. At elbow it separates from rest of the nerves to reach at caudal aspect of forearm Motor to some caudomedial forearm muscles (flexors) and muscles of manus. Sensory to caudal forearm and palmer manus. In dog it is cutaneous innervation to 5th digit. Just above the carpus it divides into Superficial  continue as anterior lateral abaxial digital nerve. deep branches  descends along carpus, gives few fibres to the suspensory ligament, joins with a branch of median nerve and continue as posterior lateral abaxial digital nerve. [email protected] Page 4 Unit 2 10. Median Nerve: Runs with ulnar nerve and musculocutaneous nerve and forms a loop through which axillary artery passes. It continues on the medial side of the forearm to divide into medial and lateral palmer nerves just proximal to carpus. Motor supply to some caudomedial forearm muscles (flexors) and muscles of manus along with ulnar nerve. Sensory to palmer surface of manus. It runs down medial aspect of arm, crosses elbow and reaches beneath the pronator teres muscle  passes below flexor carpi radialis [email protected] Page 5 Unit 2 Descends through the carpal canal  reaches lower third of Meta carpus and divides into lateral and medial branches  each of them divides into axial and abaxial digital nerves. Abaxial nerve joins with branch of ulnar nerve and continues downward as posterior lateral abaxial digital nerve. Both the axial of medial and lateral branches of median unite to form single trunk  continue downwards as posterior common axial digital nerve. 11. Radial nerve: Supplies extensor of the elbow, carpus and digits. Extending from the brachial plexus into the triceps brachii muscle, it then passes around the caudal aspect of the humerus to reach the lateral side of the arm. Branches into superficial and deep branches to the forearm. The superficial branch of radial nerve supplies the skin of the cranio lateral forearm in all domestic animals. It is sensory to the dorsal surface of the manus in all except the horse. Deep branch passes between brachialis and extensor carpi radialis and innervates all extensor muscles and ulnaris lateralis of the forearm. Superficial trunk joins with branch of median nerve above carpus  reaches middle of metacarpus and finally divides to form anterior common axial digital nerve and anterior medial abaxial digital nerve. [email protected] Page 6 Unit 2 Cutaneous and autonomous zones of fore limb [email protected] Page 7 Unit 2 Clinical conditions associated with problems in nerve supply to fore limb: A. Sweeny or shoulder Slip: A condition seen in horses due to the injury of the suprascapular n. Results in rapid atrophy of supraspinatus and infraspinatus muscles which produces a prominent scapular spine. Before atrophy, the shoulder is unstable and slips laterally, appearing to be dislocated. B. Ulnar or median nerve damage: has little clinical manifestation due to the overlap of their motor innervations C. Radial nerve paralysis: The most common and clinically significant nerve problem of the thoracic limb. It occurs due to trauma, and clinical manifestation varies with the location of the injury. a. High radial nerve paralysis: i. Proximal to where the nerve innervates the triceps brachii muscle. ii. This results in an inability to extend the elbow and, thus, an inability to bear weight on the limb. b. Low radial nerve paralysis: i. Distal to the triceps innervation, thus weight can be born on the limb. ii. Extensors of carpus and digits are affected iii. Manifested clinically in “Knuckling over” dragging the dorsum of the foot on the ground D. Brachial Plexus avulsions: results in damage of the many nerves of the limb, resulting in a flaccid limb that is dragged. 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