UMN and Spinal Cord Learning Objectives

Question 1

describe the meaning of GP and GSA

Answer 1

GP: general proprioception; the sensory system that detects the state of the position and the movement in muscles and joints

GSA: general somatic afferent: sensory for touch, temperature, and nociception

Question 2

what do sensory nerves carry?

Answer 2

both GSA (general somatic afferent) and GP (general proprioceptive) information

Question 3

what are the 2 components of proprioception? describe

Answer 3

unconscious transmission to the cerebellum: via sensory nerve input, the cerebellum knows where the limb/body is before you move it so that the cerebellum can modify that movement by influencing the UMN in the brain that will then generate gait

conscious: GP info goes to the cerebral cortex for conscious recognition of body movement (I moved my arm and I know I moved my arm)

Question 4

define and describe GP ataxia

Answer 4

looks the same as UMN paresis! not knowing where your limbs are in space, crossing legs, scuffing

Question 5

broadly define the course and components involved in postural reaction testing

Answer 5

1. proprioceptors convey sensory information proximally along peripheral nerves
2. this information ascends in the spinal cord to the cerebellum (unconscious) and the cerebrum (conscious)
3. UMN from brain descend spinal cord to LMN to flip paw back over

need both normal proprioception and a functioning LMN unit for normal postural reactions!!

Question 6

how do postural reactions in part assess the GP system?

Answer 6

need to be able to perceive that paw has been flipped over in order to know that you need to flip it back

Question 7

is postural reaction testing specific for the assessment of the GP system or its components?

Answer 7

nope, also need a function LMN unit to be able to move limb or flip it back over!

Question 8

what is needed for normal postural reactions?

Answer 8

normal function of UMN, LMN, and GP (tests everything!!)

Question 9

what are the 4 major collections of UMN that project into the spinal cord? which are more important for gait generation? is the motor cortex of the cerebrum and corticospinal tracts necessary for gait development?

Answer 9

according to barber all we need to know about this right now is that the UMN cell bodies are located in the cerebrum an the brainstem and only the ones in the brainstem are important for gait generation!

Question 10

how does UMN affect LMN?

Answer 10

UMN both facilitate AND inhibit the LM responsible for flexor muscles and the extensor muscles/tone

Question 11

broadly describe the course of UMN from their origin (brain) through the spinal cord

Answer 11

UMN are found in various locations throughout the cerebrum and brainstem and descend from the brain mainly in lateral and ventral funiculus of the spinal cord

Question 12

what does loss of UMN info result in?

Answer 12

UMN quality paresis

Question 13

define UMN paresis/paralysis

Answer 13

inability to generate a gait;
1. paresis
2. spasticity
3. hyperreflexia
4. NO muscle atrophy

Question 14

contrast LMN versus UMN gait quality

Answer 14

LMN is short and choppy, UMN is long and lopey/overreaching

Question 15

in naturally occurring disease, can ascending GP and descending UMN be affected separately?

Answer 15

no they are bth affected and the resulting gait involves both GP ataxia and UMN paresis

Question 16

describe reflexes, tone, and muscle size with a UMN lesion cranial to the intumescense

Answer 16

reflexes: normal to increased
tone: normal to increased
muscle size: normal/no atrophy

Question 17

contrast UMN lesions with LMN lesions in assessment of reflexes, tone, and muscle size

Answer 17

LMN: decreased to absent reflexes, decreased/flaccid tone, decreased muscle size/atrophy

UMN: normal to increased reflexes, normal to increased tone, normal muscle size

Question 18

list the 5 functional divisions of the spinal cord

Answer 18

1. C1-C5: UMN only
2. C6-T2: UMN plus LMN to thoracic limbs
3. T3-L3: UMN to pelvic limbs only
4. L4-S1: UMN plus LMN to pelvic limbs
5. S1-S3/5 +/- caudal segments

Question 19

is there any difference observed in the clinical signs of a lesion affecting one segment within a function division of the spinal cord versus a lesion that diffusely affects all segments within the same functional division?

Answer 19

nope; except for lumbar intumescence femoral versus sciatic signs (cranial or caudal in the intumescence)

Question 20

are you able to assess any area of the spinal cord cranial to a lesion resulting in LMN signs?

Answer 20

nope, LMN signs mask UMN signs (win the game and show up clinically)

Question 21

how can you tell if a lesion is central (spinal cord) or peripheral (in a plexus)?

Answer 21

for the thoracic limb:
if the pelvic limbs are normal, the lesion is peripheral; if the pelvic limbs are affected, then the lesion is central

for the pelvic limb: if the tail is normal, the lesion is peripheral, but if the tail is affected, the lesion is central

Question 22

for a C1-C5 myelopathy:
describe postural reactions, reflexes, tone, muscle size; explain why pelvic limbs may be more severely affected compared to thoracic limbs, can horner syndrome occur?

Answer 22

1. affect UMN to all 4 limbs, but LMN not affected
2. will see UMN weakness/paralysis so normal to increased reflexes (withdrawal reflex), normal to increased tone, no atrophy
3. pelvic limbs may be more severely affected than thoracic limbs because the tracts for pelvic limbs are located more superficially than the tracts for thoracic limbs
4. horner syndrome can occur

Question 23

describe horner syndrome and why it might be observed in both C1-C5 and C6-T2 myelopathy

Answer 23

1. horner syndrome results from disruption of sympathetic innervation to the eye; can see miosis (small pupil), ptosis (smaller palpebral fissure), enopthalmos (eye sunken further back into orbit, resulting in 3rd eyelid elevation)
2. this can be seen in C1-C5 or C6-T2 myeolpathies because the UMN for sympathetic innervation of the eye originate in the hypothalamus, then descend the brainstem and cervical spinal cord to exit at T1-T3, where the LMN for sympathetic innervation to the eye will the run cranially via the vagosympathetic trunk, located in the brachial plexus before synapsing with the cervical ganglion through the middle ear to the eye, so if you put a myelopathy anywhere cranial in the spinal cord to T1-T3, this innervation could be affected

Question 24

why can hypoventilation be observed in a C1-C5 myelopathy?

Answer 24

1. the tracts involved in respiration project caudally from the cervical spinal cord to influence the diaphragm and intercostal muscles
2. LMN for phrenic nerve located in C5-C7, so lesions in this area MAY result in diaphragm paralysis if the lesion is transverse; if lesion not transverse, abdominal musculature and breathing may keep the patient alive

Question 25

for a C6-T2 myelopathy:
list spinal reflexes used to assess, describe postural reactions, reflexes, tone, and muscle size observed, what additional reflex may be affected, and can horner syndrome be observed?

Answer 25

1. LMN and UMN affected in thoracic limbs, but LMN signs visible in thoracic limbs; used withdrawal reflex (will be decreased to absent), hypotonia, decreased muscle size
2. UMN and proprioceptive ataxia in pelvic limbs (normal withdrawals, myotactic reflexes will be normal to increased), normal to increased tone and normal muscle mass
3. cutaneous trunci reflex may also be affected
4. horner syndrome can be observed

Question 26

for a T3-L3 myelopathy: list spinal reflexes used to assess, describe postural reactions, reflexes, tone, and muscle size observed

Answer 26

1. normal thoracic limbs
2. UMN weakness with proprioceptive ataxia in pelvic limbs, so abnormal postural reactions, normal to increased reflexes, normal to increased tone and muscle mass (myotactic reflexes)

Question 27

T3-L3 myelopathy: List 3 ways to help define a focal lesion between T3-L3 spinal cord segments

Answer 27

1. paraparetic/pareplegic
2. abnormal postural reactions in pelvic limbs
3. normal reflexes and tone in pelvic limbs

Question 28

T3-L3 myelopathy: (painful area) Describe how to identify a focally painful area.

Answer 28

conscious response needed!!

just because a dog has a withdrawal reflex does NOT mean it can consciously feel pain

use cutaneous trunci reflex to determine where animal is painful = approximate location of lesion +/- 1 or 2 vertebrae

Question 29

T3-L3 myelopathy: (nociception) Describe how a transverse/complete lesion results in a loss of nociception caudal to the lesion (3)

Answer 29

1. the pathways for nociception are multisynaptic pathways with axons that frequently cross midline at multiple levels of the spinal cord, meaning that nociception is transmitted bilaterally up the spinal cord
2. this means that a loss of nociception is the result of a SEVERE lesion BILATERALLY
3. this also means that there CANNOT be loss on nociception to ONE limb from a spinal cord lesion cranial to the intumescence as the system is BILATERAL (BOTH limbs will have to be affected if nociception is lost)

Question 30

T3-L3 myelopathy: Recognize the importance of loss of nociception has on prognosis for return of walking

Answer 30

the C fibers involved in nociception are located very deep within spinal cord white matter and are relatively protected; due to this protection, nociception is the last function to be lost in compressive spinal cord disorders, so if nociception is lost, return to walking has a poor prognosis

Question 31

T3-L3 myelopathy: Describe how an abnormal cutaneous trunci reflex helps localize a lesion within with the T3 – L3 spinal cord segments

Answer 31

the point at which the reflex can be observed is 1-2 vertebrae cranial to where the lesion is located in the spinal cord segment

Question 32

T3-L3 myelopathy: Describe the predictable/orderly loss of function with increasing severity of a compressive lesion in the spinal cord/the relationship between deficits and severity of spinal cord injury

Answer 32

1. feeling pain in the region only = most mild
2. ambulatory paraparesis and GP ataxia = mild
3. non-ambulatory paraparesis = moderate
4. paraplegia (loss of all voluntary control) = moderate
5. pareplegia and loss of sensation = worst/severe

Question 33

T3-L3 myelopathy: Describe clinical findings in spinal shock (7)

Answer 33

1. peracute/acute onset
2. normal thoracic limbs
3. T3-L3 lesion but with decreased tone and decreased withdrawal in pelvic limbs is common presentation!!
4. immediately after a severe injury, everything caudal to the lesion inexplicably becomes LMN (even though lesion is actually affected UMN)
5. perineal reflex returns to normal within minutes, and patellar (femoral) reflex returns to normal within hours (usually before you can examine the patient)
6. HOWEVER, the withdrawal (sciatic) reflex can take days to weeks to normalize, which is why you will see fake LMN signs (might even be only in one limb)
7. BUT look for other signs of T3-L3 to confirm is actually UMN damage, like cutaneous trunci cut-off and pain int eh T3-L3 region!!

Question 34

T3-L3 myelopathy: describe Schiff-Sherrington syndrome

Answer 34

1. when some patients with severe T3-L3 myelopathies can have pronounced hypertonia in the thoracic limbs
2. this is due to ascending UMN tracts that have their cell bodies in lumbar segments (called border cells) that project cranially and inhibit extensor tone in the thoracic limbs

Question 35

L4-S1 myelopathy: List the spinal reflexes that assess the L4-S1 segments; Describe the postural reactions and the reflex findings/tone/muscle size
associated with a lesion affecting the L4-S1 spinal cord/sp nerve/named nerve(s)

Answer 35

1. normal thoracic limbs
2. LMN in pelvic limbs
3. L4-L6 only: femoral nerve, decreased to absent patellar reflex, decreased weight bearing and stifle extension
4. L6-S1 only: sciatic, and its branches of common fibular and tibial; decreased withdrawal
5. tibial damage: plantigrade, decreased extension of hock
6. fibular nerve damage: increased flexion of hock

Question 36

L4-S1 myelopathy: Describe the posture/reflexes with a lesion affecting the L4-L6 spinal cord segments

Answer 36

this is the location of the femoral nerve within the intumescence, so a lesion here will result in inability to extend the stifle, reduced to absent ability to bear weight on the limb, and a decreased to absent patellar reflex

Question 37

L4-S1 myelopathy: Describe the posture/reflexes with a lesion affecting the L6-S1 spinal cord segments

Answer 37

this is the location of the sciatic nerve within the intumescence, so a lesion here will affect the ability to extend the hip, flex the stifle, and affect the movement of the tarsus and digits; additionally, the withdrawal reflex will be decreased to absent

Question 38

L4-S1 myelopathy: Recognize that if the patient is plegic, that the entire intumescence has to be affected

Answer 38

if the patient cannot move the limb at all, then both the femoral and sciatic nerves are affected, so the entire intumescence is affected

Question 39

L4-S1 myelopathy: Recognize that unlike C6-T2 localization, with L4-S1 lesions are
challenging to know if lesion involves spinal cord vs. spinal nerves/lumbosacral
plexus/named nerves of pelvic limb

Answer 39

since there is not much to examine caudal to the lumbosacral plexus to determine LMN versus UMN as with thoracic limbs; you also have to consider that the lesion may not be in L4-L6 spinal cord segments where the LMN cell bodies are located, but that it would also be in the spinal nerve roots, the spinal nerves, or the named nerves of the pelvic limb

Question 40

L4-S1 myelopathy: Recognize the importance of whether tail is affected

Answer 40

if affected = lesion
within the vertebral column vs. tail is normal = extravertebral lesion

Question 41

S1-caudal segments: List the spinal reflexes that assess the S1-S3 segments.
* S1-caudal segments: Describe the reflex findings/tone/muscle size associated with a lesion affecting the S1-S3 spinal cord/sp nerve/named nerve(s)

Answer 41

perineal reflex, anal tone, bladder function; will see sensory changes associated with these tests in the dorsum/perineum (lack of shudder with contact if lesion), in tail tone (decreased if lesion), and rectal palpation (anal tone decreased if lesion)

Question 42

S1-caudal segments: Recognize that gait/postural reactions are unaffected

Answer 42

gait is normal but the animal may or may not be incontinent

Question 43

S1-caudal segments: With a lesion affecting the S1-S3 spinal cord/sp nerve/named nerve(s), describe the effect on micturition and fecal continence

Answer 43

pudendal nerve (S1-S3): if affected perineal reflex will be decreased to absent and the animal may be incontinent in the bowels

pelvic nerve: if affected animal may be incontinent in bladder

Question 44

Where does the spinal cord end? Epidural? CSF collecton?

Answer 44

1. spinal cord ends at cona medullaris
2. give an epidural in the space between the periosteum that covers the vertebrae and the dura in the vertebral canal
3. collect CSF from the subarachnoid space in the cerebromedullary cistern and the lumbosacral region (the two areas where the subarachnoid space expands in the CNS)