LMN learning objectives Flashcards
list the 4 components of the lower motor neuron unit
- LMN neuron cell body
- axon
- NMJ
- muscle
describe what intumescences are
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
list the spinal cord segments and vertebral location that comprise the cervical and lumbar intumescences
cervical: segment C6-T2 between vertebrae C5-T1; brachial plexus
lumbar: segment L4-S1 between L3-L6; lumbosacral plexus
define/describe the cauda equina
after the conus medullaris (where the spinal cord ends) and the nerves flare out to directly innervate muscles
list the major names nerves of the thoracic and pelvic limbs and pelvis
thoracic: suprascapular, musculocutaneous, radial, median, ulanr
pelvic: femoral, obturator, sciatic, common fibular, tibial
list the spinal cord segments/spinal nerves that contribute to the named nerves of the thoracic limbs
suprascapular: C5-C7
musculocutaneous: C6-C8
radial: C7-T2
median: C8-T2
ulnar: C8-T2
list the spinal cord segments/spinal nerves that contribute to the named nerves of the pelvic limbs
femoral: L4-L6
obturator: L4-L6
sciatic: L6-S1; gives rise to common fibular and tibial
list the spinal cord segments/spinal nerves that contribute to the named nerves of the pelvis
pudendal: S1-S3
list the major muscles innervated by the the named nerves of thoracic limb
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
list the major muscles innervated by the named nerves of the pelvic limb and pelvis
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
describe the function of the important named nerves in the thoracic limb
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
describe the function of the important named nerves in the pelvic limb and pelvis
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
name the vertebrae that mark the caudal end of the spinal cord in the dog, cat, horse, pig, and cow
dog: L6-L7
cat: L7-S3
ruminants: L6-S1
swine: S1-S2
horses: S2
explain the general process of neuromuscular transmission (3)
- impulse reaches presynaptic terminal, causing an influx of calcium
- calcium binds to presynaptic vesicles that contain ACh, causing exocytosis of ACh into NMJ
- binds to postsynaptic membrane (nicotinic receptors on muscle) and depolarizes the muscle, causing actin and myosin interaction and muscle contraction
name the neurotransmitter for neuromuscular transmission and the postsynaptic receptor
acetylcholine, nicotinic receptor on muscle membrane
explain the components of a monosynaptic reflex arc and a polysynaptic reflex arc
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)
define paresis, paralysis, and the prefixes: mono, para, and tetra
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
define LMN quality paresis
an inability to support weight
describe the effect on the reflex when a lesion is affecting the LMN
decreased to absent (hyporeflexia-areflexia)
describe the effect on muscle tone when a lesion is affecting the LMN
decreased muscle tone/flaccid paresis or paralysis
describe the effect of muscle size when a lesion is affecting LMN
muscle atrophy (decreased size)
describe gait characteristics associated with LMN paresis (3)
- short-strided, choppy
- crouched stance: overflexion of joints and posture with limbs under the body
- exercise intolerance
name the reliable reflexes that can be assessed in the thoracic limb, pelvic limb, and pelvis/tail
thoracic limb: withdrawal reflex
pelvic limb: withdraw and patellar reflex
pelvis/tail: perineal reflex, anal sphincter tone, tail tone
name the nerves and spinal cord segments involved with patellar reflex and how to perform
femoral nerve: L4-L6
to perform, strike patellar ligament
name the nerves and spinal cord segments involved with withdrawal reflex in thoracic limb and pelvic limb and how to perform
thoracic: all named nerves: C6-T2
pelvic: sciatic nerve, fibular branch (tarsal flexion):
to perform, pinch a toe
name the nerves and spinal cord segments involved with perineal reflex and how to perform
perineal nerve: S1-S3
to perform, stroke or pinch perineum, L and R separate
name the nerves and spinal cord segments involved with the cutaneous trunci reflex and how to perform
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
describe posture/placement of limbs associated with LMN paresis
crouched stance: overflexion of joints and posture with limbs under the body
describe the clinical findings associated with deficits in radial, ulnar, suprascapular, and musculocutaneous nerves in thoracic limb
see functions of these nerves
describe the clinical findings associated with deficits in femoral, sciatic-tibial, sciatic-fibular, pudendal, and caudal nerves in the pelvic limb
see functions of these nerves
name the important sensory nerves of the thoracic limb pertaining to withdrawal reflex and cutaneous sensation
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
name the important sensory nerves of the pelvic limb pertaining to withdrawal reflex and patellar reflex and cutaneous sensation
patellar: sensory and motor of femoral nerve
withdrawal: sensory and motor of sciatic nerve (L6-S2)
recognize the importance in determining sensory nerve function
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
describe what cutaneous area, overlap zone, and autonomous zone mean
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
list the location on the foot for thoracic limb to test cutaneous sensation/autonomous zones
dorsal: radial
palmar and digits II-IV: median and ulnar so avoid?
digit 5: ulnar
elbow: musculocutaneous
list the location on the foot for pelvic limbs to test cutaneous sensation/autonomous zones
dorsal: fibular
palmar and digits II-V: tibial
digits 1: saphenous branch of femoral nerve (less reliable)
recognize the difference between assessing reflex activity versus nocicpetion
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
describe how nociception is assessed
pinch skin over a cutaneous/autonomous zone and look for a reaction
describe how presence or absence of nociception is determined
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)
