Thoracic Limb Innervation Flashcards
What does innervation of the thoracic limb include?
Motor innervation
Sensory innervation
Autonomic innervation
Motor innervation
To skeletal muscles, through the ventral branches of the spinal nerves (motor nerves)
Sensory innervation
To the skin, through the ventral branches of spinal nerves (cutaneous branches)
Autonomic innervation (ANS)
To the smooth muscles and glands through the sympathetic portion of the autonomic nerves that join the spinal nerves
Brachial Plexus
C6-T2
Network of the ventral branches of the cervical spinal nerves (C6-8) and the 1st and 2nd thoracic spinal nerves (T1, T2)
The brachial plexus gives origin to the nerves that innervate what structures?
- Thoracic limb
- Parts of the shoulder muscles
- Lateral wall of the thorax/ abdomen
- Diaphragm (phrenic nerve)
Suprascapular nerve
Origin: C6 and C7
Courses in between the supraspinatus and the subscapularis
S: supraspinatis and infraspinatus muscles
What does the suprascapular nerve pass?
Around the neck of the scapula
Across the scapular notch (vulnerable to trauma)
Clinical significance of the Suprascapular nerve
Shoulder slip- injury leads to muscle atrophy
Musculocutaneous Nerve
Arises from C6, C7, C8 (caudal to the suprascapular)
What nerve won’t give you any problems?
The subscapular nerve
What does the muscular branch of the musculocutaneous nerve innervate?
Biceps brachii, coracobrachialis and Brachialis (flex elbow)
What does cutaneous branch mean?
Branch to the skin and sensory
Cutaneous branch of the musculocutaneous nerve
Medial cutaneous antebrachial nerve
Runs between flexor carpi radialis and pronator teres
What is the function of the medial cutaneous antebrachial nerve?
Innervate the medial aspect of the antebrachium
Axillary Nerve
Origin: C7 and C8
Motor innervation of the axillary nerve
Innervates teres major, teres minor, deltoideus and the subscapular muscles
Sensory branches of the axillary nerve
- Cranial lateral cutaneous brachial: Innervate the lateral surface of brachium, cd. scapular
- Cranial cutaneous antebrachial: cr. antebrachium
What does the axillary nerve share the cutaneous area with?
Radial nerve branches
Radial Nerve
Origin: C6-T2
Largest nerve of the brachial plexus and causes most problems
Innervates the elbow extensors, carpus & digits
What are the two branches of the radial nerve?
Deep branch
Superficial branch
What is the superficial branch of the radial nerve?
Lateral cutaneous antebrachial nerve that divides into the medial and lateral branches
Innervates the skin over the cr. and lat. surface of the forearm
Proximal Radial paralysis
Common in cases of brachial plexus avulsion
Signs: knuckling, extreme gait, deficit and lack of ability to support weight on the thoracic limb
Proximal injury paralysis (mid arm)
Non weight bearing lameness
Hyperflexion
Loss of sensation on the cranio-lateral aspect of the limb distal to the elbow
Dragged toes
Distal injury parlysis
Paralysis of carpal and digital extensors
Flicking of paw to compensate
Hyperextention
What muscle is innervated by the deep branch of the radial nerve?
Extensor carpi radialis
What does paralysis of the common digital extensor cause?
Knuckling over during attempts to walk with radial nerve paralysis
What is the main difference in proximal and distal radial nerve injuries?
The animal will show preserved weight support in those with distal injuries
What happens in patients with paresthesia from radial nerve injuries?
Experience burning, itching and tingling
Chew on the paw (dorsal aspect)
Ulnar nerve
Origin: C8-T2
United with median at origin, the diverges towards the olecranon
What is the motor innervation of the ulnar nerve?
Innervation to carpal and digital flexors
What is the sensory innervation of the ulnar nerve?
Cd. cutaneous antebrachial n.
Dorsal branch
Palmar branch (suprfical/ deep)
Median Nerve
Origin: C8-T1
Motor innervation of the median nerve
Innervation flexors of the carpals/ digits
Pronator teres/ quadratus
Flexor carpi radialis
Superficial and deep digital flexors
Sensory innervation to the median nerve
Innervation to cd. antebrachium and palmer paw
Traditional brachial plexus block
Insert spinal needle into axillary region:
Med. to and at the level of the shoulder joint
Directed to the costochondral junction
Parallel to the vertebral column
Paravertebral brachial plexus block
C6, C7, C8 and T1 spinal nerves are blocked close to the intervertebral foramina (not axillary)
Provide analgesia to the entire forelimb with lower volumes of local anesthetic
Where do you insert analgesia for a traditional brachial plexus block?
Distal to the elbow
Steps for paravertebral brachial plexus block
- Move scapula caudally to expose the large transverse process of the 6th cervical vertebra and first rib
- Block ventral branches of C6 and C7
- Ventrla branches of C8 and T1 blocked on lateral dorsal surface of 1st rib close to vertebra
What is a brachial plexus block?
Injection (shot) of numbing medicine that helps keep your pain level lower during and after surgery.
Autonomous zones
Areas of the skin innervated solely by specific nerve (no overlap)
Cutaneous zones
An entire area of the skin innervated by more than 1 peripheral nerve (overlap occurs)
How would procedures for the elbow and antebrachium be blocked?
The radial, median, ulnar and musculocutaneous nerves may be blocked proximal to the humeral
epicondyles
T/F: The nerves can often be palpated, which makes this technique straightforward to perform
True
Where is the radial nerve palpable?
Just proximal to the lateral epicondyle
