LMN learning objectives

Question 1

list the 4 components of the lower motor neuron unit

Answer 1

1. LMN neuron cell body
2. axon
3. NMJ
4. muscle

Question 2

describe what intumescences are

Answer 2

spinal cord swellings of the ventral horn where all cell bodies come together before leaving as named nerves of either the thoracic or pelvic limb

Question 3

list the spinal cord segments and vertebral location that comprise the cervical and lumbar intumescences

Answer 3

cervical: segment C6-T2 between vertebrae C5-T1; brachial plexus
lumbar: segment L4-S1 between L3-L6; lumbosacral plexus

Question 4

define/describe the cauda equina

Answer 4

after the conus medullaris (where the spinal cord ends) and the nerves flare out to directly innervate muscles

Question 5

list the major names nerves of the thoracic and pelvic limbs and pelvis

Answer 5

thoracic: suprascapular, musculocutaneous, radial, median, ulanr

pelvic: femoral, obturator, sciatic, common fibular, tibial

Question 6

list the spinal cord segments/spinal nerves that contribute to the named nerves of the thoracic limbs

Answer 6

suprascapular: C5-C7

musculocutaneous: C6-C8

radial: C7-T2

median: C8-T2

ulnar: C8-T2

Question 7

list the spinal cord segments/spinal nerves that contribute to the named nerves of the pelvic limbs

Answer 7

femoral: L4-L6

obturator: L4-L6

sciatic: L6-S1; gives rise to common fibular and tibial

Question 8

list the spinal cord segments/spinal nerves that contribute to the named nerves of the pelvis

Answer 8

pudendal: S1-S3

Question 9

list the major muscles innervated by the the named nerves of thoracic limb

Answer 9

suprascapular: supraspinatus and infraspinatus

subscapular: subscapularis (not major nerve?)

musculocutaneous: BICEPS BRACHII, brachialis, corachobrachialis

axillary: deltoideus, teres major, teres minor (not major nerve?)

radial: triceps brachii, extensor carpi radialis, ulnaris lateralis, common digital extensor, lateral digital extensor

median: flexor carpi radialis, superficial and deep digital flexors

ulnar: flexor carpi ulnaris and deep digital flexor

Question 10

list the major muscles innervated by the named nerves of the pelvic limb and pelvis

Answer 10

femoral: iliposoas, quadriceps, sartorius

obturator: pectineus, adductor, gracilis, external obturator (PAGE)

cranial gluteal: middle and deep gluteal, tensor fascia latae (not major named nerve?)

caudal gluteal: superficial gluteal and middle gluteal (not major names nerve?)

sciatic: biceps femoris, semimembranosus, semitendinosus

common fibular: peroneus longus, lateral digital extensor, long digital extensor, cranial tibial

tibial: gastrocnemius, popliteal, superficial and deep digital flexors

Question 11

describe the function of the important named nerves in the thoracic limb

Answer 11

suprascapular: extend and flex the shoulder

subscapular: extend/stabilize shoulder

axillary: flex shoulder and rotate arm medially

musculocutaneous: flex elbow, extend shoulder

radial: extend elbow, digits, carpus

median: flex carpus and digits

ulnar: flex carpus and digits

Question 12

describe the function of the important named nerves in the pelvic limb and pelvis

Answer 12

femoral: flex hip and extend stifle

obturator: adduct limb, extend hip and hock

sciatic: extend hip, extend/flex stifle, extend hock

fibular: flex tarsus/hock, extends digits

tibial: extend tarsus/hock, flex stifle, flex digits

Question 13

name the vertebrae that mark the caudal end of the spinal cord in the dog, cat, horse, pig, and cow

Answer 13

dog: L6-L7

cat: L7-S3

ruminants: L6-S1

swine: S1-S2

horses: S2

Question 14

explain the general process of neuromuscular transmission (3)

Answer 14

1. impulse reaches presynaptic terminal, causing an influx of calcium
2. calcium binds to presynaptic vesicles that contain ACh, causing exocytosis of ACh into NMJ
3. binds to postsynaptic membrane (nicotinic receptors on muscle) and depolarizes the muscle, causing actin and myosin interaction and muscle contraction

Question 15

name the neurotransmitter for neuromuscular transmission and the postsynaptic receptor

Answer 15

acetylcholine, nicotinic receptor on muscle membrane

Question 16

explain the components of a monosynaptic reflex arc and a polysynaptic reflex arc

Answer 16

monosynaptic: only one synapse; sensory in, synapse with LMN, efferent out (example is patellar reflex); sensory and motor neurons linked in series

polysynaptic: sensory and motor neurons plus interneurons in between the sensory and motor (interneurons are found in gray matter of spinal cord and either directly terminate on motor neurons or on other interneurons) (ex. withdrawal, perineal, crossed extensor, and cutaneous trunci reflexes)

Question 17

define paresis, paralysis, and the prefixes: mono, para, and tetra

Answer 17

paresis: weakness/inability to support weight against gravity/decreased voluntary movement

paralysis/plegia: lack of voluntary movement

mono: single limb
para: pelvic limbs
tetra: all 4 limbs

Question 18

define LMN quality paresis

Answer 18

an inability to support weight

Question 19

describe the effect on the reflex when a lesion is affecting the LMN

Answer 19

decreased to absent (hyporeflexia-areflexia)

Question 20

describe the effect on muscle tone when a lesion is affecting the LMN

Answer 20

decreased muscle tone/flaccid paresis or paralysis

Question 21

describe the effect of muscle size when a lesion is affecting LMN

Answer 21

muscle atrophy (decreased size)

Question 22

describe gait characteristics associated with LMN paresis (3)

Answer 22

1. short-strided, choppy
2. crouched stance: overflexion of joints and posture with limbs under the body
3. exercise intolerance

Question 23

name the reliable reflexes that can be assessed in the thoracic limb, pelvic limb, and pelvis/tail

Answer 23

thoracic limb: withdrawal reflex

pelvic limb: withdraw and patellar reflex

pelvis/tail: perineal reflex, anal sphincter tone, tail tone

Question 24

name the nerves and spinal cord segments involved with patellar reflex and how to perform

Answer 24

femoral nerve: L4-L6

to perform, strike patellar ligament

Question 25

name the nerves and spinal cord segments involved with withdrawal reflex in thoracic limb and pelvic limb and how to perform

Answer 25

thoracic: all named nerves: C6-T2

pelvic: sciatic nerve, fibular branch (tarsal flexion):

to perform, pinch a toe

Question 26

name the nerves and spinal cord segments involved with perineal reflex and how to perform

Answer 26

perineal nerve: S1-S3

to perform, stroke or pinch perineum, L and R separate

Question 27

name the nerves and spinal cord segments involved with the cutaneous trunci reflex and how to perform

Answer 27

lateral thoracic nerve: C8-T1

to perform: start at the pelvic and pinch the skin on either side of the spinous processes, if see sin move at this most caudal location = lateral thoracic nerve is good; if no reaction, move up vertebrae by vertebrae until observe a reaction to localize lesion

Question 28

describe posture/placement of limbs associated with LMN paresis

Answer 28

crouched stance: overflexion of joints and posture with limbs under the body

Question 29

describe the clinical findings associated with deficits in radial, ulnar, suprascapular, and musculocutaneous nerves in thoracic limb

Answer 29

see functions of these nerves

Question 30

describe the clinical findings associated with deficits in femoral, sciatic-tibial, sciatic-fibular, pudendal, and caudal nerves in the pelvic limb

Answer 30

see functions of these nerves

Question 31

name the important sensory nerves of the thoracic limb pertaining to withdrawal reflex and cutaneous sensation

Answer 31

sensory: varies with area stimulated; but have cutaneous autonomous zones for radial, median, and ulnar

motor: all named nerves! musculocutaneous, axillary, median, ulnar, radial contribute to withdrawal

Question 32

name the important sensory nerves of the pelvic limb pertaining to withdrawal reflex and patellar reflex and cutaneous sensation

Answer 32

patellar: sensory and motor of femoral nerve

withdrawal: sensory and motor of sciatic nerve (L6-S2)

Question 33

recognize the importance in determining sensory nerve function

Answer 33

if a bone is fractured, no point fixing it if the nerve doesn’t work; also can determine if nerve damage present even if orthopedic issues are preventing other reflexes

Question 34

describe what cutaneous area, overlap zone, and autonomous zone mean

Answer 34

cutaneous area: where a nerve innervates the skin

overlap zone: an area innervated by multiple nerves

autonomous zone: an area innervated by one single nerve

Question 35

list the location on the foot for thoracic limb to test cutaneous sensation/autonomous zones

Answer 35

dorsal: radial

palmar and digits II-IV: median and ulnar so avoid?

digit 5: ulnar

elbow: musculocutaneous

Question 36

list the location on the foot for pelvic limbs to test cutaneous sensation/autonomous zones

Answer 36

dorsal: fibular

palmar and digits II-V: tibial

digits 1: saphenous branch of femoral nerve (less reliable)

Question 37

recognize the difference between assessing reflex activity versus nocicpetion

Answer 37

reflexescan happen when UMN are damaged whether the animal can feel the limb or not; so you are looking for a conscious reaction to determine that they can still feel

Question 38

describe how nociception is assessed

Answer 38

pinch skin over a cutaneous/autonomous zone and look for a reaction

Question 39

describe how presence or absence of nociception is determined

Answer 39

if you squeel you feel! or even less dramatic, if pupils dilate, facial expression changes, they turn head to acknowledge sensation (any reaction other than withdrawal essentially)