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Neuroscience > Lower Motor Neurons (LMN) > Flashcards

Lower Motor Neurons (LMN) Flashcards

1
Q

What is lower motor neuron

A

Anterior/ventral horn cells (efferent neuron) of PNS

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2
Q

What does lower motor neuron do

A

Connects the CNS with innervated striated muscles
- the entire CNS function is expressed through LMN
CNS EXERTS ITS CONTROL OVER PNS THROUGH LMN

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3
Q

What are the two components of lower motor neuron

A

General somatic efferent (GSE)

General visceral efferent (GVE)

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4
Q

Function of lower motor neuron GSE component

A

Final motor innervation to the muscles

Contraction of these muscles maintains posture, supports weight and provides gait

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5
Q

What is included in GSE (general somatic efferent)

A

Neuron that innervates striated voluntary skeletal muscles so –> all neurons of spinal nerves and all cranial nerves except CN1, 2, and 8

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6
Q

Why is the shape and size of the ventral grey column important

A

It correlates with the number of neurons present

It is determined by the volume of muscles innervated

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7
Q

What do the GSE neurons in the medial portion of the ventral grey horn innervate

A

Axial muscles

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8
Q

What do the GSE neurons of lateral portion of the grey column innervate

A

Appendicular muscles

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9
Q

Specifically, what do the GSE neurons of the ventral lateral grey column innervate

A

Proximal limb muscles

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10
Q

Specifically, what do the GSE neurons of the dorsal lateral grey column innervate

A

Distal limb muscles

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11
Q

Where are axons in the white matter

A

Between lateral and ventral funiculi

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12
Q

What is the spinal cord portion of the axon myelinated by

A

oligodendrocytes

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13
Q

What is the peripheral portion of the axon myelinated by

A

Schwann cells

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14
Q

A motor unit is

A

Muscle cells innervated by one neuron

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15
Q

What does the strength of muscle contraction depend on

A

Motor unit activation in muscle

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16
Q

How does the axon progress from spinal nerve to peripheral nerve

A
  • leave through ventral root, spinal nerve to motor end-plate of neuromuscular ending of the limb muscles as peripheral nerve
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17
Q

What is the synaptic cleft

A

Space formed by axolemma in sarcoplasmic trough (presynaptic membrane) and folds of the postsynaptic membrane (sarcolemma membrane)

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18
Q

What is contained in the synaptic vesicles at the presynaptic ending

A

Acetylcholine

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19
Q

What occurs upon arrival of an action potential

A

Opening of Ca channels and in flow

  • formation of substructure which directs ACH vesicle to move down and fuse with membrane
  • release ACH to activate receptor and depolarize membrane
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20
Q

What is excess ACH broken down by

A

Acetylcholinesterase

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21
Q

What is LMNL

A

Lower motor neuron lesion

22
Q

Where can damage occur on LMN and do the signs differ

A

cell body, along axon and at innervated muscle

- regardless of where it occurs, signs are the same

23
Q

What are the signs of an LMNL

A

Muscle paresis or paralysis
Hyporeflexia or areflexia (LMN is motor component)
Hypotonia or atonia (muscle tone depends on stimulation from LMN)
Neurogenic atrophy

24
Q

What is flaccid paresis

A

Weakness and loss of muscle strength, difficulty supporting weight and deficiency in generation of gait (short strides, lameness)

25
Q

What is paralysis

A

Severe paresis with complete absence of any movement

26
Q

What is hypoflexia

A

Weakness of spinal reflexes

27
Q

What is areflexia

A

Loss of spinal reflexes

28
Q

What occurs if the sacrocaudal LMN is damaged

A

Anal, perineal and tail reflexes are affected

29
Q

What is hypotonia

A

Weakness in muscle tone

30
Q

Atonia is

A

Loss of muscle tone

31
Q

Neurogenic atrophy

A

Loss of muscle function and atrophy because of complete loss of innervation

32
Q

What happens if multiple limbs are affected by LMNL

A

Animals tend to collapse with difficulty standing up from recumbent position

33
Q

What happens if both pelvic limbs are affected

A

Animal tends to flex both hips to advance limbs –> bunny-hopping

34
Q

Is ataxia a sign of LMNL

A

No, it is a sensory system abnormality

35
Q

What is the significance of LMNL of the oculomotor nucleus or nerve

A
  • Dysfunction of dorsal, ventral and medial rectus and ventral oblique muscles
  • Lateral strabismus/deviation will occur do to lateral rectus pulling with now resistance
  • Paralysis of lavatory muscle of eye lid –> drooping eyelid
36
Q

What is the significance of a lesion of parasympathetic nucleus of oculomotor nerve

A

Paralysis of constrictor muscle of pupil
Leads to constantly dilate pupil (Mydiasis)
Animal shows no pupillary light reflex

37
Q

What are the clinical signs of an LMNL of trochlear nucleus

A

Paralysis of dorsal oblique leads to ventral rotary deviation of lateral part of the eye distorting line of vision dorsomedially

38
Q

What is the clinical significance of LMNL in trigeminal nerve (motor)

A

Bilateral: difficult chewing and dropped jaw
Unilateral: mandibular deviation to unaffected side

39
Q

What is the clinical significance of LMNL in trigeminal nerve (sensory)

A

Loss of sensation to head

40
Q

Where is oculomotor nucleus located

A

midbrain

41
Q

Where is the trochlear nucleus located

A

Decussate in rostral medullary velum, emerges caudal to caudal colliculus

42
Q

Where is the trigeminal nucleus located

A

In Tegmentum

43
Q

Where is the abducen nucleus located

A

In pontine medullary boundary, fiber emerges ventrally behind pons

44
Q

What is the clinical significance to LMNL in abducens nucleus

A

Medial deviation (strabismus) and protrusion of eye due to lack of innervation to lateral rectus and retractor bulbus

45
Q

Where is facial nucleus located

A

Rostral medulla

46
Q

What is the clinical significance of LMNL in facial nucleus (motor)

A

paralysis of mouth and inability to close eyelid

  • lack of innervation of orbicularis oculi
47
Q

What is the clinical significance of LMNL in facial nucleus (sensory)

A

Malfunction of lacrimal gland resulting in dry cornea

due to sensory innervation of lacrimal and salivary glands

48
Q

Where is the hypoglossal nucleus located and what does it innervate

A

Caudal medulla

Intrinsic muscle of tongue

49
Q

What does LMNL in hypoglossal nucleus result in

A

Paralysis of tongue shown by difficulty in swallowing

50
Q

What is nucleus ambiguus

A

“Small nucleus”

Supplies fibers to vagus and glossopharyngeal nerves so innervates larynx and pharynx

51
Q

What is the clinical significance of LMNL in nucleus ambiguus

A

Pharyngeal paralysis and laryngeal paralysis

Neuroscience (10 decks)

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