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Lower Motor Neurons (LMN) Flashcards

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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

Study These Flashcards
A

Lower motor neuron lesion

22
Q

Where can damage occur on LMN and do the signs differ

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
A

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

25
What is paralysis
Severe paresis with complete absence of any movement
26
What is hypoflexia
Weakness of spinal reflexes
27
What is areflexia
Loss of spinal reflexes
28
What occurs if the sacrocaudal LMN is damaged
Anal, perineal and tail reflexes are affected
29
What is hypotonia
Weakness in muscle tone
30
Atonia is
Loss of muscle tone
31
Neurogenic atrophy
Loss of muscle function and atrophy because of complete loss of innervation
32
What happens if multiple limbs are affected by LMNL
Animals tend to collapse with difficulty standing up from recumbent position
33
What happens if both pelvic limbs are affected
Animal tends to flex both hips to advance limbs --> bunny-hopping
34
Is ataxia a sign of LMNL
No, it is a sensory system abnormality
35
What is the significance of LMNL of the oculomotor nucleus or nerve
- 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
What is the significance of a lesion of parasympathetic nucleus of oculomotor nerve
Paralysis of constrictor muscle of pupil Leads to constantly dilate pupil (Mydiasis) Animal shows no pupillary light reflex
37
What are the clinical signs of an LMNL of trochlear nucleus
Paralysis of dorsal oblique leads to ventral rotary deviation of lateral part of the eye distorting line of vision dorsomedially
38
What is the clinical significance of LMNL in trigeminal nerve (motor)
Bilateral: difficult chewing and dropped jaw Unilateral: mandibular deviation to unaffected side
39
What is the clinical significance of LMNL in trigeminal nerve (sensory)
Loss of sensation to head
40
Where is oculomotor nucleus located
midbrain
41
Where is the trochlear nucleus located
Decussate in rostral medullary velum, emerges caudal to caudal colliculus
42
Where is the trigeminal nucleus located
In Tegmentum
43
Where is the abducen nucleus located
In pontine medullary boundary, fiber emerges ventrally behind pons
44
What is the clinical significance to LMNL in abducens nucleus
Medial deviation (strabismus) and protrusion of eye due to lack of innervation to lateral rectus and retractor bulbus
45
Where is facial nucleus located
Rostral medulla
46
What is the clinical significance of LMNL in facial nucleus (motor)
paralysis of mouth and inability to close eyelid - lack of innervation of orbicularis oculi
47
What is the clinical significance of LMNL in facial nucleus (sensory)
Malfunction of lacrimal gland resulting in dry cornea | due to sensory innervation of lacrimal and salivary glands
48
Where is the hypoglossal nucleus located and what does it innervate
Caudal medulla | Intrinsic muscle of tongue
49
What does LMNL in hypoglossal nucleus result in
Paralysis of tongue shown by difficulty in swallowing
50
What is nucleus ambiguus
"Small nucleus" | Supplies fibers to vagus and glossopharyngeal nerves so innervates larynx and pharynx
51
What is the clinical significance of LMNL in nucleus ambiguus
Pharyngeal paralysis and laryngeal paralysis

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