2- Thoracic Nerves (Small Animal).docx

- **Brachial Plexus** - The brachial plexus is composed of the ventral branches of spinal nerves from C6-T2. - The innervation to the forelimb is mixed with "sensory afferent" and "motor efferent". - The brachial plexus is located in the axillary region. - *...

- **Brachial Plexus** - The brachial plexus is composed of the ventral branches of spinal nerves from C6-T2. - The innervation to the forelimb is mixed with "sensory afferent" and "motor efferent". - The brachial plexus is located in the axillary region. - **Proximal Nerves of the Forelimb** - **Cranial pectoral nerve** - The cranial pectoral nerve runs with the external thoracic artery. - The cranial pectoral nerve targets the superficial pectoral muscle. - **Caudal pectoral nerve** - The caudal pectoral nerve targets the deep pectoral muscle. - **Lateral thoracic nerve** - The lateral thoracic nerve runs with the lateral thoracic artery, near the axillary lymph node. - The lateral thoracic nerve targets the motor neuron to the cutaneous trunci muscle, where it is involved in the panniculus reflex. - **Thoracodorsal nerve** - The thoracodorsal nerve runs with the thoracodorsal artery. - The thoracodorsal nerve targets the latissimus dorsi muscle. - **Nerves of the Forelimb** - **Suprascapular nerve** - The suprascapular nerve travels laterally between the subscapularis muscle and the supraspinatus muscle. - The suprascapular nerve targets the infraspinatus muscle and supraspinatus muscle. - The suprascapular nerve is protected by the acromion of the scapula. - **Subscapular nerve** - The subscapular nerve will sometimes have multiple visible branches. - The subscapular nerve targets the subscapularis muscle. - **Musculocutaneous nerve** - The musculocutaneous nerve provides somatic motor innervation to the coracobrachialis muscle, biceps brachii muscle, and brachialis muscle. - The motor function provided by the musculocutaneous nerve is elbow flexion. - The musculocutaneous nerve also provides sensory to the medial aspect of the antebrachium via the **medial cutaneous antebrachial nerve**. - **Axillary nerve** - The axillary nerve enters the space between the subscapularis muscle and the teres major muscle. - The axillary nerve provides somatic motor innervation to the teres major muscle, teres minor muscle, deltoideus muscle, and part of the subscapularis muscle. - The axillary nerve provides sensory to the caudal scapular region and craniolateral brachium. - **Radial nerve** - The radial nerve enters the triceps brachii muscle between the long head and medial head. It also spirals caudally around the humerus and emerges laterally between the triceps brachii muscle and the brachialis muscle. - The radial nerve is the largest nerve in the forelimb, and it travels parallel to the deep brachial artery. - The radial nerve provides somatic motor innervation to the triceps brachii muscle, tensor fascia antebrachii muscle, and anconeus muscle. - The radial nerve is **necessary for weight bearing**!!! - The **deep branch** of the radial nerve has the main function of providing somatic motor innervation to the extensors of the carpus and digits. - The **superficial branch** of the radial nerve, known as the "**lateral cutaneous antebrachial nerve**", travels with the cephalic vein on the cranial aspect of the antebrachium. - The superficial branch of the radial nerve provides sensory innervation to the dorsal manus. - The cephalic vein gives off a medially directed branch, known as the "Medial cubital vein", near the cranial (flexor surface) of the elbow to the anastomose with the brachial vein. - **Median nerve** - Both the median nerve and the ulnar nerve start as a common trunk, and they both innervate flexors of the carpus and manus/digits (motor). - Specifically, both the median nerve and the ulnar nerve share the job of providing sensory innervation to the palmar aspect of the manus. - The median nerve is in contact with the caudal surface of the brachial artery. - The median nerve is immediately cranial to the medial epicondyle of the humerus. - The median nerve targets and provides sensory innervation to the pronator teres muscle, pronator quadratus muscle, flexor carpi radialis muscle, superficial digital flexor (SDF) muscle, and deep digital flexor muscle (DDF). - The median nerve continues distally with the median artery through the carpal canal. - **Ulnar nerve** - The ulnar nerve is in contact with the collateral ulnar artery and runs towards the caudal aspect of the elbow. - The ulnar nerve is lateral to the medial epicondyle of the humerus. - The ulnar nerve provides somatic motor innervation to the flexor carpi ulnaris muscle, and DDF muscle. - The ulnar nerve also provides sensory innervation to the palmar aspect of the antebrachium where it passes through the carpal canal to the palmar aspect of the manus. - The ulnar nerve is the reason why the caudomedial aspect of the antebrachium is referred to as the "funny bone". - **Autonomous Zones** - An **autonomous zone** refers to an area of sensation that is provided by only one nerve without the overlap from adjacent nerves. - An example of an autonomous zone is the sensory innervation to the 5^th^ digit is considered to be an autonomous zone for the ulnar nerve. - Most areas of the skin are innervated by multiple nerves. - Nerves supplying autonomous zones in the forelimb include the: ulnar nerve, radial nerve, and musculocutaneous nerve. - **Radial Nerve Damage** - **Proximal injury** - Proximal injury of the radial nerve will result in the loss of the ability to extend the elbow, carpus, or digits, which will cause the patient to also lose the ability to support their weight on that forelimb. - Proximal injury to the radial nerve refers to damage that occurs at the brachial plexus prior to innervation to the triceps muscle. - **Distal injury** - Distal injury of the radial nerve refers to damage occurring after innervation to the triceps muscle. - Distal injury to the radial nerve will result in loss of cutaneous sensation (superficial branch) on the cranial aspect of the antebrachium and the dorsal aspect of the paw. - **Median and Ulnar Nerve Damage** - Damage to the median and ulnar nerves could result in: - Reduction or complete loss of the ability to flex the carpus and digits - Sinking (hyperextension) of the carpus and fetlock - Loss of sensation to the palmar aspect of the paw - Loss of cutaneous sensation to the lateral aspect of the 5^th^ digit would be specifically linked to ulnar nerve damage. - **Axillary Nerve Damage** - Axillary nerve damage would result in: - The motor innervation being loss to the flexors of the shoulder (which include the deltoideus, teres major, teres minor, and part of the subscapularis muscle), causing the appearance of a "dropped shoulder". - The loss of sensation to the lateral aspect of the brachium and caudal scapular region. - **Musculocutaneous Nerve Damage** - Musculoskeletal nerve damage would result in decreased or lack of ability to flex the elbow, due to the impacts on the coracobrachialis, biceps brachii, and brachialis muscles. - Musculoskeletal nerve damage can also result in loss of sensory on the medial aspect of the forearm.