Neuro signs and neuro exam

Question 1

Explain “bunny-hopping”

Answer 1

simultaneous bilateral flexor responses at the onset of protraction and when both limbs respond when the withdrawal reflex is stimulated in one limb (instead of normal gait where the initial flexor muscle activation at the onset of protraction in one limb is accompanied by extension in the opposite limb and inhibition of the flexors of that opposite limb). Could be due to an alteration of the functional connections in the commissural interneurons (disorder of the central pattern generator network of the pelvic limbs).

Question 2

Name 3 abnormalities detected on the hands-on neuro exam of patients with prosencephalic disease

Answer 2

1) reduced menace response
2) slow postural reactions
3) reduced nasal septal nociception

(all contralateral in a unilateral disease)

Question 3

Name 3 abnormalities detected on the hands-off neuro exam of patients with prosencephalic disease

Answer 3

behavioural changes
seizures
pleurototonus (adversive syndrome)

Question 4

Explain the pathway and how to perform the patellar tendon reflex

Answer 4

The patellar reflex is a tendon reflex that is composed of only two neurons.
It is a monosynaptic reflex arc. The sensory neuron terminates directly on the GSE neuron in the ventral gray horn without involving a synapse on a second neuron (interneuron) in the gray horn. The peripheral sensory neuron of the flexor, or withdrawal reflex, has its telodendron on an interneuron in the dorsal gray horn, which, in turn, terminates on a GSE neuron in the ventral gray horn.

The patellar tendon reflex is the only reliable tendon reflex. Both the sensory and motor components are in the femoral nerve. The femoral nerve is formed from the spinal nerves of the L4, L5, and L6 spinal cord segments. The L5 segment makes the largest contribution to this nerve.178 The L6 segment may not contribute to this nerve in some dogs. The patient should ideally be held in lateral recumbency and must be relaxed. This reflex cannot be tested in a struggling patient. With the limb relaxed and flexed at the stifle, lightly strike the patellar tendon with a blunt instrument.

Question 5

Explain the pathway and performance of the withdrawal reflex

Answer 5

The withdrawal reflex (also called the flexor reflex) in the pelvic limb is a test primarily for the sciatic nerve and its spinal cord segments L6, L7, and S1. Within the sciatic nerve, the neurons that are associated with the fibular nerve tend to be components of the L6 and L7 spinal cord segments, and those associated with the tibial nerve are components of the L7 and S1 segments. The S2 components primarily innervate muscles in the pelvis that do not participate in this test or in the animal’s posture or gait. The sensory component of the reflex depends on the area of skin that is stimulated. In a routine examination, the skin at the base of the claw of the fifth digit is compressed by using a pair of forceps. Finger pressure may be used but is not always sufficient, in our experience. In addition, hemostats apply a more consistent pressure between different patients. This area of skin is innervated by cutaneous branches of the fibular nerve dorsally and by the tibial nerve on the plantar surface. The motor response is a flexion of all the joints in the limb to withdraw the limb from the stimulus.

Question 6

Explan which musscles and nerves are involved in the flexion of the hip

Answer 6

Except for the hip, flexion of the pelvic limb is a function of the GSE components of the sciatic nerve. The major flexor muscle of the hip is the iliopsoas, which is innervated by all the lumbar spinal nerve ventral branches, with a contribution caudally from the femoral nerve. The latter also innervates the rectus femoris, which is the one component of the quadriceps muscle that also flexes the hip. Because of this anatomy, a patient with complete sciatic nerve dysfunction will have no reflex (or nociception) if the fifth digit is stimulated using a noxious stimulus, but if the first digit is compressed, the hip will flex to pull the limb away from the stimulus, but the rest of the joints will not flex. The first digit usually receives its cutaneous innervation from the saphenous nerve branch of the femoral nerve. It is important to look for this disparity. The same strong hip flexion in the absence of any flexion in the other joints will occur with severe but not complete sciatic nerve dysfunction when the fifth digit is compressed. As a rule, there is more clinical evidence of loss of motor function with some preservation of sensory function in a partially compressed nerve

Question 7

Which nerve innervates the first and which the fifth digit of the pelvic limb?

Answer 7

The first digit usually receives its cutaneous innervation from the saphenous nerve branch of the femoral nerve.

The skin of the fifth digit is innervated by cutaneous branches of the fibular nerve dorsally and by the tibial nerve on the plantar surface.

Question 8

Name the reflexes of the pelvic limbs, the nerves involved in them, spinal cord segments and level in the vertebral canal where the SCS reside:

Answer 8

Question 9

Name the reflexes of the thoracic limbs, the nerves involved in them, spinal cord segments and level in the vertebral canal where the SCS reside:

Answer 9

Question 10

Name the nerves and muscles innervated by these nerves:

Answer 10

Question 11

Which nerve is tested with the perineal reflex?

Answer 11

Pudendal nerve (S1-3)

The perineal reflex is a test of the branches from the sacral plexus that is located in the pelvic canal. These branches supply the external sphincter muscle of the anus; the striated muscles of the penis, vulva, and vestibule; the urethralis muscle; and the skin of the anus, perineum, and caudal thigh. It is not necessary to learn the names of the specific nerve branches or their individual areas of innervation. Mild compression of the skin of the perineum or anus with forceps elicits an immediate contraction of the external anal sphincter and flexion of the tail. The latter response requires that the caudal spinal cord segments and nerves be intact.

Question 12

Which muscles are involved in the flexor reflex of the thoracic limbs?

Answer 12

For shoulder flexion, it is primarily the axillary, radial, and thoracodorsal nerves; for elbow flexion, it is primarily the musculocutaneous nerve; for carpal and digital flexion, it is primarily the median and ulnar nerves.

Question 13

Which nerves innervate the autonomous skin zones of the thoracic limb paws (afferents for the withdrawal reflex)?

Answer 13

1st toe - radial nerve
5th toe - ulnar nerve
dorsal aspect of toes - radial
ventral aspect of paw - median + ulnar

Question 14

Which SCS are tested with the m. cut. trunci reflex?

Answer 14

C8-T1

Question 15

Pathway of the m.cut.trunci reflex?

Answer 15

cutaneous nerves -> dorsal branches of the lumbar and thoracic spinal nerves -> dorsal rootlets –> dorsal grey column –> synapse on the long interneurons -> fasciculus proprous bilaterally to C8-T1 -> synapse on GSE neurons -> ventral grey matter -> ventral rootlets -> ventral branches -> lateral thoracic nerve -> m. cut. trunci bilateral

Question 16

How do you explain an assymmetric m.cut.trunci reaction?

Answer 16

This is particularly helpful in cases such as brachial plexus injuries, asymmetric spinal cord lesions in the thoracolumbar spinal cord, or unilateral fibrocartilaginous embolic myelopathy of the cervical intumescence. In dogs with asymmetric spinal cord lesions, the cutaneous trunci reflex is absent caudal to the lesion on the ipsilateral side of the body. The cutaneous trunci muscle reaction (skin twitch) on the side contralateral to the lesion remains intact, providing evidence of the bilateral projection of this pathway.

Question 17

Name the nerves and muscles innervated by these nerves if the cervical intumescence

Answer 17

Question 18

Explain “skipping gait”

Answer 18

the skipping-­type gait in the pelvic limbs, which is related to the brisk overflexion of the hips. This has sometimes been confused with a cerebellar hypermetria. It represents the loss of tone in the antagonistic caudal thigh hip extensor muscles that are innervated by the sciatic nerve.

Question 18

Describe the gait in LMN paresis

Answer 18

The lack of ability to support weight characterizes LMN paresis. If the patient is ambulatory, the gait will include short strides and will appear as a lameness. The gait in LMN disease is identical to that of an animal that has discomfort when the diseased limb attempts to support weight. The inability to support weight looks the same as when an animal expresses pain whenever weight is supported. Animals with LMN disease walk as you would with a stone in your shoe. The stride is shortened. Consequently, it is important to rule out any orthopedic disorder in the evaluation of an animal with LMN disease by doing a complete orthopedic examination.

Question 19

For the thoracic limb, which nerve is important for waight bearing, which for advancing the limb by extending the shoulder, which to flex the elbow and which to flex the carpus?

Answer 19

The inability to support weight is caused by the loss of function of the radial nerve (C7, C8, T1).

Extending the shoulder (suprascapular nerve, C6, C7; nerve to brachiocephalicus muscle, C6)

To lift the limb off the floor by flexing the elbow (musculocutaneous nerve, C6, C7).

Flexion of the carpus: median nerve (C8, T1)

Question 20

Explain Horner syndrome with brachial plexus avulsion

Answer 20

Avulsion of the ventral roots of T1 or of the T1 spinal nerve causes a miosis because of the interruption of the GVE preganglionic neuronal axons located there that provide sympathetic innervation to the eye. An elevated third eyelid and ptosis require interruption of the ventral roots of the T2 and T3 spinal cord segments.

Question 21

In which domestic animal does the radial nerve have no autonomous zone for the branches that provide cutaneous innervation

Answer 21

Horse

Question 22

Dysfunction of which nerve causes lateral deviation of the lip and nose in the horse?

Answer 22

CN VII, buccal branches

Question 23

Which muscles are medial and which lateral rotators of the shoulder joint?

Answer 23

• medial rotators (subscapularis and teres major muscles)
• lateral rotators (infraspinatus and teres minor muscles).

Question 24

Neuroanatomic diagnosis?

Answer 24

Lateral rotation of the shoulder, Medial displacement of the elbow.
–> infraspinatus contracture

A 2-­year-­old doberman pinscher that was struck by a vehicle and 1 month later was presented for a persistent abnormality in the use of the left thoracic limb. This dog sits with the characteristic posture of a dog with excessive lateral rotation of the shoulder, which results in medial displacement of the elbow. This is an example of the infraspinatus contracture that follows an injury to the muscle and the healing by fibrosis.

Could also arise from a lesion in the spinal cord contained within the foramen of the C5 vertebra. This was likely the C6 spinal cord segment; the suprascapular nerve arises from the C6 and C7 spinal cord segments.

Question 25

What could cause a significant carpal overextension (palmigrade posture)

Answer 25

loss of the integrity of the palmar carpal ligaments.

If all the nerves and muscles are removed from a thoracic limb specimen, the carpus cannot be manually forced into a palmigrade position as long as the palmar carpal ligaments are intact. These ligaments become stretched when the thoracic limb must bear more weight than usual, as when a young dog has a fracture in one thoracic limb and bears all its weight on the normal limb for a period of weeks. That normal limb slowly assumes a more palmigrade posture. Older dogs that are overweight often assume this carpal posture. Chronic neuromyopathies cause dogs that have lost the normal muscle strength necessary to support weight to assume a palmigrade posture. This clinical sign reflects the secondary loss of integrity of the palmar carpal ligaments and is not a sign of a specific neuromuscular disorder. A plantigrade posture in a pelvic limb has a very different pathogenesis;

Question 26

Which nerves are involved in the sensory innervation of the penis?

Answer 26

Skin of the penis:
dorsal penis nerve (branch of pudendal n., S1-3)

Skin of the prepuce:
genitofemoral n. (ventral branches of L3-4)

The distinction between sensation of the skin of the penis and the skin of the prepuce may be helpful in making a correct anatomic diagnosis in male dogs with diseases affecting the lumbar spinal cord.

Question 27

Which nerve deficit could cause a hyperflexion of the tarsus?

Answer 27

Tibial nerve (part of sciatic nerve).

Neuronal cell bodies are in
L7-S1 SCS.

Question 28

Which nerve is involved if there is an overflexion of the tarsus?

Answer 28

Tibial nerve (inability to flex it)

Question 29

Which nerve is involved if a dog is standing on the dorsum of his pelvic limb paw?

Answer 29

Fibular nerve

Question 30

Which nerve and muscle are involved in hip flexion?

Answer 30

Lumbar spinal nerves (ventral branches) -> psoas major muscle

Question 31

What causes the limb defomities contractures/arthrogryposis?

Answer 31

These joint abnormalities are the result of denervation atrophy in a young dog whose bones are growing in length.
These limb deformities (contractures, arthrogryposis) result from the disparity in the normal growth of bones in the limbs and the abnormal shortening of the associated muscles.

Denervation atrophy does not cause this in the adult dog.

Question 32

Which nerves provide cutaneous sensory innervation of the proximal medial thigh (1) and which to the craniolateral thigh (2)?

Answer 32

1) genitofemoral (L3, L4)

2) lateral cutaneous femoral (L3, L4)

Question 33

Which nerves are commonly damaged with pelvic fracture?

Answer 33

The sciatic nerve is commonly injured in pelvic trauma because it is formed by the L6 and L7 spinal nerve ventral branches that pass across the ventral surface of the sacroiliac joint, where they are at risk for injury by luxations.
These two branches are joined by the ventral branch of S1 to form the sciatic nerve, which then courses across the dorsal surface of the body of the ilium where fractures are common.

The obturator nerve courses on the medial surface of the ilium and is at risk for injury by these iliac fractures, but the slight sliding-­out of the limb laterally during weight bearing when the dog is walking on a slippery surface is probably not recognized.

The femoral nerve is rarely affected by these pelvic fractures because it is never directly associated with bones of the pelvis in its course from the psoas major muscle, where it is formed primarily by the ventral branches of the L4 and L5 spinal nerves and enters the quadriceps femoris.

Question 34

Which nerve is affected?

The limb is protracted by hip flexion and the ability to support weight, but the paw is often placed on its dorsal surface. The stifle flexors and the tarsal flexors and extensors are hypotonic.

Answer 34

Sciatic (predominantly fibular nerve) L6-S1

Question 35

Dysfunction of which nerve causes this stance in cows?

Answer 35

Tibial nerve (S1,2)

The overflexed tarsus is the result of loss of the innervation to the tarsal extensors (gastrocnemius and superficial digital flexor muscles). The basis for the dorsal buckling of the metatarsophalangeal joints is not clearly understood but presumably represents the loss of the function of the digital flexors.

Question 36

How would the posture of a cow with fibular nerve dysfunction look like?

Answer 36

A ruminant with fibular nerve paralysis stands on the dorsal aspect of the digits because of loss of the function of the digital extensor muscles, but the posture of the metatarsophalangeal joints is normal.

Question 37

How can you differentiate a loss of sensation to the face (CN V) from loss of motor function (CN VII) clinically?

Answer 37

No palpebral reflex exists, but note the spontaneous blinking of the eyelids, which indicates normal facial nerve function. Stimulating the skin of the external ear canal tests multiple cranial and cervical spinal nerves and is not reliable for cranial nerve V. The ear movement supports normal facial nerve function.