Nerve, blood and lymph supply to the forelimb
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What spinal nerves form the brachial plexus?
Which extrinsic muscles of the forelimb are supplied by the brachial plexus?
- Latissimus dorsi
- Serratus ventralis
List the nerves that supply the forelimb
Subscapularis nerve, suprascapularis nerve, musculocutaneous nerve, axillary nerve, median and ulnar nerves, radial nerve
What is the function of the subscapular nerve? And what muscle does it innervate?
Function = medial shoulder support. Innervates the subscapularis muscle.
What is the function of the suprascapular nerve? And what muscles does it innervate?
Function = lateral shoulder support. It innervates the supraspinatous muscle and infraspinatous muscle.
What is the function of the musculocutaneous nerve? And what muscles does it innervate?
Function = elbow flexion. It innervates the brachialis muscle and biceps brachii muscle
What area of the leg does the musculocutaneous nerve provide peripheral sensation to?
The cranial and medial aspect of the elbow and medial aspect of the antebrachium
What does damage to the musculocutaneous nerve result in?
Loss of elbow flexion and cutaneous sensation
What is the function of the axillary nerve? And what muscles does it innervate?
Function = shoulder flexion. It innervates deltoideus muscle and teres major muscle.
What area of the forelimb does the axillary nerve provide peripheral sensation to?
Lateral aspect of the shoulder and brachium
What does damage to the axillary nerve result in?
No loss of shoulder flexion, as it is still possible due to the action of latissimus dorsi and long head of triceps.
What is the function of the median and ulnar nerves? And what muscles does it innervate?
Function = carpal and digital extensors. They innervate flexor carpi ulnaris muscle, flexor carpi radialis muscle, superficial digital flexor muscle and deep digital flexor muscle
What area of the forelimb does the median and ulnar nerves provide peripheral sensation to?
Caudal and palmar aspect of the limb and dorsal aspect of the 5th digit
What does damage to the median and ulnar nerves result in?
Loss of distal limb flexion
What is the function of the radial nerve? And what muscles does it innervate?
Function = carpal and digital extension. It innervates the triceps brachii muscle, common digital extensor muscle, extensor carpi ulnaris muscle, and extensor carpi radialis muscle.
What area of the forelimb does the radial nerve provide peripheral sensation to?
The cranial and dorsal aspect of the limb (except the dorsal aspect of the 5th digit)
Describe the route of the radial nerve
The radial nerve starts in the axilla, passes caudal to the shoulder, through the triceps muscle, wraps around the humerus and then branches: one branch runs over the lateral epicondyle to supply the distal limb extensors and another branches over the cranial/dorsal aspect of the limb, running alongside the cephalic vein, to supply cutaneous sensation.
What is the most common cause of radial nerve damage?
What would happen to the function of the forelimb if there was proximal nerve damage?
All the extensor muscles would be affected so the animal would not be able to extend the elbow, carpus or digits. This means the animal cannot weight bear on that limb.
What would happen to the function of the forelimb if there was distal nerve damage?
The animal would not be able to extend its carpus or digits. However, the triceps supply would still be intact so the animal would be able to extend its elbow. Most animals learn to swing their leg to compensate.
What would happen to the function of the forelimb if there was complete disruption of the brachial plexus?
The animal would no longer be able to retract/adduct, extend/flex or weight bear on the limb. However, it would still be able to protract/adduct the limb (as the brachiocephalicus and trapezius nerve supply would still be intact). There would also be no cutaneous sensation on the limb or lateral thorax to the level of the 3rd intercostal space.
Describe how the equine nerve supply of the forelimb differs to that of the dog
Proximal to the carpus there are several differences to that of the dog: the median and ulnar nerves combine to supply the distal limb and the musculocutaneous nerve merges with the radial nerve to supply the medial aspect of the metacarpal area.
What are equine nerve blocks used for?
Routinely used in equine practice to help localise lameness
What are the branches of the median and ulnar nerves distal to the carpus in horses?
Palmar metacarpal nerves and palmar nerves (which become palmar digital nerves)
Where are the palmar metacarpal nerves located?
On the medial and lateral aspect of the limb, between metacarpal 3 and the splint bones.
Where are the palmar nerves located? What bones do they pass over?
On the medial and lateral aspect of the limb, between the suspensory ligament and SDFT. They pass over the abaxial aspect of the proximal sesamoids.
What structures do the a) palmar metacarpal nerves b) palmar digital nerves supply?
- a) Dorsal aspect of digit
- b) Hoof contents
What are the three different types of nerve blocks used?
- Palmar digital nerve block
- Abaxial sesamoid nerve block
- Palmar metacarpal nerve block
Describe the blood supply to the forelimb
The forelimb is supplied by one major vessel, whose name changes with the region of the forelimb. Subclavian artery - axillary artery - brachial artery, etc
What superficial vein is found in the forelimb?
What nerve runs alongside the cephalic vein?
What arteries can you use to take a pulse in the forelimb of a horse?
- Brachial artery - on the medial aspect of the elbow
- Medial and lateral digital arteries - abaxial aspect of proximal sesamoids
What lymph nodes are located in the forelimb? Which is palpable?
Prescapular (palpable) and axillary (not palpable)
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