Thoracic Nerves Flashcards
What makes up the Brachial Plexus?
Ventral branches of C6,C7, C8, T1, and T2
occasionally ventral branch of C5
Nerves that Originate from The Brachial Plexus
- Thoracodorsal
- Lateral Thoracic
- Long Thoracic
- Cranial Pectoral
- Caudal Pectoral
- Suprascapular
- Subscapular
- Axillary
- Musculocutaneous
- Radial
- Median
- Ulnar
Nerves of Brachial Plexus with cutaneous branches
- Axillary
- Musculocutaneous
- Radial
- Median
- Ulnar
cutaneous area (CA)
total area of skin innervated by a given cutaneous nerve
overlap zone (OZ)
- located at periphery of CA
- area where adjacent CA overlap
autonomous zone (AZ)
- located centrally within a CA
- innervated by ONLY one cutaneous nerve
How is cutaneous sensation tested for clinically? Describe the method.
Two-step pinch technique
Instrument: mosquito hemostats
Step 1 - Small skin fold at test site is lifted and gently grasped with the hemostats
If the animal responds, no need to continue to step 2 - animal has sensation there
Step 2 - Skin pinch. Starts gentle at first and gradually increases until response occurs of until dog is obviously responding to maximal stimulus
Any reflex or response to pinching indicates the cutaneous nerve being tested is functional!
Nerves of Brachial Plexus that innervate the extrinsic muscles of the thoracic limb
Cranial pectoral N.(C6-C8) Caudal Pectoral N.(C8-T2) Long thoracic N. (C7) Thoracodorsal N.(C8) Lateral thoracic N. (C8-T1)
Cranial Pectoral N. (C6-C8)
- arises from cranial part of plexus
- innervates superficial pectoral muscles
- no cutaneous branches
Caudal Pectoral N. (C8 - T2)
- passes caudoventrally to deep pectoral muscle
- innervates deep pectoral muscle
- no cutaneous branches
Long Thoracic N. (C7)
- passes caudally (horizontally) on lateral surface of thoracic part of serratus ventralis m.
- innverates serratus ventralis m.
- no cutaneous branches
Thoracodorsal N. (C8)
- runs caudodorsally, in close relation to thoracodorsal vessels, on medial surface of latissiumus dorsi muscle
- innervates latissimus dorsi muscle
- no cutaneous branches
Lateral Thoracic N. (C8)
- accompanies lateral thoracic artery and vein, passing medial to the axillary ln.
- lies between adjacent borders of latissimus dorsi and deep pectoral m.
- innervates cutaneus trunci m. and preputial muscle
- no cutaneous branches
What is the panniculus reflex?
- localizing spinal cord lesion from C8-T3 spinal cord segment
- sensory stimulus is a mild compression of skin
- motor response is brief contraction of cutaneus trunci muscle, which causes the skin of the trunk to twitch
- cutaneous nerves stimulated are from the dorsal branches of the lumbar and thoracic spinal nerves
- GSE neurons exit the ventral gray columns of spinal cord segments C8 and T1 to innervate the cutaneus trunci muscle, via lateral thoracic nerve
Nerves of Brachial Plexus that innervate Intrinsic Muscles of Thoracic Limb
Suprascapular N. (C6,C7) Subscapular N. (C6,C7) Musculocutaneous N. (C6-C8) Axillary N. (C6,C7) Radial N. (C7-T2) Median N. (C8-T2) Ulnar N.
Suprascapular N. (C6,C7)
- passes between supraspinatus and subscapularis muscles on medial side
- runs over scapular notch and continues across neck of scapula
- innervates supraspinatus muscle and infraspinatus muscle
- Injury: usually caused by trauma
What does damage to the suprascapular N. do?
- usually caused by trauma
- paralysis of suprascapular n. usually results in atrophy of supraspinatus and infraspinatus muscles
- Standing animal -> shoulder will be abducted and this is more pronouced during locomotion (“shoulder slip”)
Subscapular N. (C6,C7)
- arises closely caudal to suprascapular n.
- innervates subscapularis muscle
- no cutaneous branches
Musculocutaneous N. (C6-C8)
- arises caudal to suprascapular n., runs parallel to median nerve
- located caudally to biceps brachii m. and cranially to brachial artery and vein
- proximal muscular branch = biceps brachii muscle
- communicating branch = joins median nerve - distal part of brachium
- distal muscular branch = brachialis muscle
- medial cutaneous antebrachial N. -> skin -medial aspect of antebrachium
- innervates:
- flexor muscles of cubital joint - biceps brachii m. and brachialis m.
- skin over the medial aspect of antebrachium
- test site= 2cm distal to medial epicondyle of humerus
What would injury to the musculocutaneous n. do?
While uncommon, it would paralyze the main flexor muscles of the cubital joint
What is the action of the teres major, teres minor, and deltoideus on the humeral joint?
Flex the humeral joint
Axillary N. (C7, C8)
- passes from medial side to lateral side proximal to teres major m.
- innervates:
- flexor muscles of the humeral joint = teres major m., teres minor m., and deltoideus m.
- skin over lateral aspect of brachium
- skin over cranial aspect of antebrachium
- test site is 2cm caudal to humeral joint
Radial N. (C7-T2)
- Most important nerve on thoracic limb!
- largest nerve of brachial plexus and has widest distribution
- runs distally, caudal, and parallel to the brachial artery
- passes from medial side to lateral side distal to teres major m.
- gives off tricipital branches to extensor muscles of cubital joint
- between brachialis m. and lateral head of triceps brachii m., proximal to the elbow divides into a superficial and deep branch
Superficial branch of Radial N.
- lateral branch = runs distal on lateral side of cephalic vein
- lateral cutaneous antebrachial nerve = innervates teh skin on craniolateral aspect of antebrachium
- dorsal common digital nerves (II,III,IV) = on metacarpus
- medial branch -runs distally on medial side of cephalic vein
- dorsal common digital nerve (I) = on metacarpus
Deep branch of Radial N.
- travels deep to extensor carpi radialis m. and finally lies under the supinator muscle
- innervates extensor muscles of carpus and digit
What does the radial n. innervate?
Where is the test site?
Innervates:
- extensor muscles of the elbow = triceps brachii m., tensor fascia antebrachii m., anconeus m.
- extensor muscles of the carpus and Ulnaris Lateralis m. = extensor carpi radialis m.
- extensor muscles of the digit = common digital extensor m, lateral digital extensor m.
- Supinator, Brachioradialis, and abductor digit I longus m.
- Skin = over craniolateral aspect of antebrachium and carpus; over dorsal aspect of forepaw
Test site= proximal end of the 2nd and 3rd metacarpal bones
Injuries to the Radial N.
- Avulsion of the brachial plexus = most common cause hit by car (trauma)
- The more proximal the damage, more severe the syndrome and more grave the prognosis
Proximal to the tricipital branches
- paralysis of extensor muscles of elbow, carpus, and digit
- flaccid paralysis of effected thoracic limb
- non-weight bearing lameness
- foot is dragged with its dorsal surface on the ground
Distal to the tricipital branches
- paralysis of the extensor muscles of the carpus and digit
- normal stance of the should and elbow are maintained
- affected animal knuckels over - rests the dorsal surface of the toe on the ground
Median N. (C8-T2)
Innervates: flexor carpi radialis m. superficial digital flexor m. deep digital flexor m. - radial and humeral head pronator teres pronator quadratus
Skin - over palmar aspect of the metacarpus and digits
Test site = no autonomous zone
Ulnar N.
Innervates:
flexor carpi ulnaris m.
deep digital flexor m. - ulnar and humeral head
interosseous muscles 0 palmar branch
Skin
- caudal aspect of antebrachium = caudal cutaneous antebrachial nerve
- palmar surface of the carpus, metacarpus, and digits = palmar branch
- lateral surface of the fifth digit = dorsal branch
Test site
- 4 cm distal to olecranon = caudal cutaneous antebrachial nerve
- lateral surface of the fifth digit = dorsal branch
- palmar branch = no autonomus zone
Ulnar N. and Median N.
Innervates
- flexor muscles of the carpus
- flexor muscles of the digit
- interosseous muscls
