L4: Flaccid dysarthria - LMN Disorders Part A

Question 1

lower motor neuron refers to

Answer 1

the nerves that connect from the spinal cord (brainstem) - the lower motor neurons relay the movement instructions provided by the UMNs to the muscles

also called the final common pathway (FCP)

Question 2

LMN includes…

Answer 2

neuron cell body

peripheral nerve

nerve-muscle synapse

muscle fibres

Question 3

motor neuron disorders (ex. motor neuron disease) effect what part of the LMN

Answer 3

neuron cell body

Question 4

peripheral nerve disorders (ex. gullian-barre) effect what part of the LMN

Answer 4

peripheral nerve

Question 5

neuromuscular junctin disorders (ex. myasthenia gravis) effect what part of the LMN

Answer 5

nerve-muscle synapse

Question 6

neurogenic disorders effect what parts of the LMNs

Answer 6

neuron cell body
peripheral nerve
nerve-muscle synpase

Question 7

myopathic disorders of LMN effect what part of LMN… ex of a disorder?

Answer 7

muscle fibres

aka muscle disorders (ex. muscular dystrophy)

Question 8

what are the 4 causes of motor neuron disorders (nerve cell body)?

Answer 8

viral infections
tumours
strokes
motor neuron diseases

Question 9

viral infections (ex. poliomyelitis) effects only ____ neurons, acute infection can produce _____

Answer 9

motor

permanent paralysis

Question 10

tumors can cause motor neuron disorders (nerve cell body) by

Answer 10

invading the motor nuclei

Question 11

strokes can cause motor neuron disorders (nerve cell body) by

Answer 11

impairing blood supply to motor nuclei

Question 12

motor neuron diseases are

Answer 12

progressive degeneration of motor neurons by unknown cause

neurotropic virus or autoimmune disorder w antibodies directed against the motor neuron or its parts

specifically target cell bodies of motor neurons

Question 13

progressive (spinal) muscular atrophy is an example of a _____ disorder, and involves…

Answer 13

motor neuron disease (nerve cell body)

spinal lower motor neruons - mostly affecting the spinal sys (legs, trunk, arms)

Question 14

progressive bulbar palsy is an example of a _____, and involves…

Answer 14

motor neuron disease (nerve cell body)

cranial lower motor neurons, bulbar = oral facial speech sys

Question 15

amyotrophic lateral sclerosis (ALS) is an example of a ____ and involves….

Answer 15

motor neuron disease (nerve cell body)

both upper and lower motor neurons - spinal and/or bulbar (or combo of both)

Question 16

what are the 5 clinical symptoms/pathophys of motor neuron disorders (nerve cell body)

Answer 16

weakness
fasiculations
muscle wasting
reduced/lost reflexes
reduced muscle tone

Question 17

describe the weakness associated w motor neuron disorders (nerve cell body)

Answer 17

due to loss of neurons and muscle fibres

distal weakness more common than proximal (ex. longer axon to your toes more weak, more susceptible to damage)

Question 18

describe the fasiculations associated w motor neuron disorders (nerve cell body)

Answer 18

visible muscle twitches that can be seen under the skin

result from spontaneous involuntary contractions of muscle fibres that are innervated by the same motor neuron

appear to relate to spontaneous activity in an axon

Question 19

describe the muscle wasting associated w motor neuron disorders (nerve cell body)

Answer 19

denervated muscle fibres eventually degenerate

weakness reduces muscle use and causes further atrophy

Question 20

describe the reduced or lost reflexes associated w motor neuron disorders (nerve cell body)

Answer 20

distributed degen of neurons disrupts the normal synchronized volleys of motor units that are necessary for reflex muscle contractions

Question 21

describe the reduced muscle tone associated w motor neuron disorders (nerve cell body)

Answer 21

weakness causes a reduction in muscle tone

Question 22

what are the 3 pieces of EMG evidence for motor neuron disorders (nerve cell body)

Answer 22

fibrillations

reduced number of active motor units during voluntary movement

inc in amplitude of muscle unit potentials

Question 23

describe fibrillations as EMG evidence for motor neuron disorders (nerve cell body)

Answer 23

spontaneous activation of muscle fibres at rest

differs from fasciculations (small vs large EMG impulse, diff causes, firing of motor unit vs single muscle fibres)

Question 24

“reduced number of active motor units during voluntary movement” as EMG evidence for motor neuron disorders (nerve cell body) is due to…

Answer 24

degeneration of neurons

Question 25

describe "inc in amp of muscle unit potentials" as EMG evidence for motor neuron disorders (nerve cell body)

Answer 25

remaining motor units try to incorporate muscle fibres from degen nerves more fibres per motor unit results in large potentials

Question 26

describe muscle histology of motor neuron disorders (nerve cell body)

Answer 26

muscle atrophy is characterized by "group atrophy" when a motor unit dies a large group of muscle fibres die - aka group atrophy rather than diffuse atrophy

Question 27

peripheral nerve disorders effect what primarily? ... small or large # of disorders?

Answer 27

axons and myeline of peripheral nerves a very large number of diseases and disorders associated w peripheral nerve damage

Question 28

what are the 8 possible causes of peripheral nerve disorders (axon)?

Answer 28

trauma (ex. nerve cut) genetic diseases (ex. hereditary motor sensory neuropathies) metabolic disorders (ex. diabetes) toxins (ex. lead) drugs (ex. nitrous oxide) nutrition (ex. alcoholism) carcinomas (ex. lymphoma) immunologic disorders (ex. HIV, guillan bare)

Question 29

what is Guillian-Barre Syndrome (GBS)?

Answer 29

peripheral nerve disorder (axon) paralysis or weakness of resp and cranial nerves 2-4 weeks following an ordinary resp or upper resp infection (70%) triggers some sort of autoimmune response that attacks the peripheral nerves 30% require ventilation - most return to normal or near normal, but some left disabled 6.9% of pts w covid who had neurological symps

Question 30

what are the 6 symptoms of peripheral nerve disorders (axon)?

Answer 30

weakness absence of fasciculation (rarely observed - more common to see it now but more mild than motor neuron disorders) muscle wasting reduced or lost reflexes reduce muscle tone sensory loss

Question 31

describe the sensory loss associated w peripheral nerve disorders (axon)

Answer 31

peripheral nerves contain both motor and sensory axons so damage to nerve usually effects both can have large fibre or small fibre neuropathies loss of position sense, vibration, or touch loss of pain and temp distal loss more than proximal

Question 32

in demyelinating peripheral nerve diseases the nerve conduction velocity is...

Answer 32

reduced due to loss of myelin

Question 33

neuromuscular junction disorders are disorder of the...

Answer 33

motor units pre- or post-synaptic processes

Question 34

what are the two causes of neuromuscular junction disorders?

Answer 34

autoimmune disorders toxins

Question 35

Eaton-Lambert disease is a _____ disorder

Answer 35

presynaptic neuromuscular junction disorder ~60 years old, Inc strength w use, Generally associated a lung cancer, and devs an autoimmune condition, can be seen 3 years bf detection of lung cancers

Question 36

myasthenia gravis is a ___ disorder

Answer 36

postsynaptic neuromuscular junction disorder Peak 30-40 years old, F>M slightly, Dec strength w use

Question 37

botulinum causes what type of neuromuscular junction disorder

Answer 37

presynaptic

Question 38

bungerotoxin (snake venom) causes what type of neuromuscular junction disorder

Answer 38

post synpatic

Question 39

describe myasthenia gravis - what is responsible for clinical symptoms?

Answer 39

a neuromuscular junction disorder - an autoimmune disorder which involves the abnormal production of antibodies that destroy acetlycholine receptors on the postsynaptic muscle end plates the reduced Ach receptors are responsible for clinical symptoms

Question 40

what do the reduced Acetylcholine receptors cause in MG?

Answer 40

makes it more difficult for the Ach to produce a muscle contraction - w repeated attempts at contraction the # of available receptors becomes progressively reduced

Question 41

onset of MG

Answer 41

onset usually after age 50 especially in men but women can have onset earlier (20-40yrs); M/F about 1:1; near normal life span, 3-4% mortality.

Question 42

how does the weakness fluctuate w MG/

Answer 42

The severity of weakness fluctuates during the day, usually being least severe in the morning and worse as the day progresses, especially after prolonged use of affected muscles. Improves with rest.

Question 43

describe extraocular muscle weakness in MG

Answer 43

Around 85% of patients will have this on the initial presentation (diplopia, ptosis). These symptoms can progress and cause generalized MG involving the bulbar, axial, and limb muscles in 50% of patients in two years

Question 44

describe bulbar muscle weakness in MG

Answer 44

This can be the initial presentation in 15% of patients and causes symptoms like difficulty chewing or frequent choking, dysphagia, hoarseness, and dysarthria

Question 45

what are the 6 pieces of clinical evidence for MG (neuromuscular junction disorder)?

Answer 45

weakness (cranial and limb muscles) progressive weakness during continuous or repeated activity no fasciculations no loss of tendon reflexes no wasting of muscles weakness reversed by drugs that inhibit Acetylcholinesterase (the enzyme that degrades Ach)

Question 46

what is the lab evidence for MG? (3)

Answer 46

EMG shows reduced action potentials over repeated stimulation or activation blood test for Ach receptor antibody (80%) test w acetyllcholinesterase inhibitor

Question 47

what are the 2 treatment options for MG?

Answer 47

acetylcholinesterase inhibitors immunological: thymus removal, immunosuppresive drugs, plasmaphoresis

Question 48

muscle (myopathic disorders) are

Answer 48

diseases of muscle tissue

Question 49

4 types of muscular dystrophy (inherited myopathy)

Answer 49

duchenne type facioscapulohumeral type limb-girdle type myotonic type

Question 50

duchenne muscular dystrophy

Answer 50

only males early onset bf 5 years progresses rapidly, death bf 40 often starts in legs

Question 51

facioscapulohumeral muscular dystrophy

Answer 51

both sexes adolescent onset slower onset, close to normal lifespan effects face and shoulder initially

Question 52

limb-girdle muscular dystrophy

Answer 52

both sexes adolescent onset slow progression diverse symptoms, may include several subtypes

Question 53

myotonic muscular dystrophy

Answer 53

both sexes infancy or adolescence slow progression often involves the cranial muscles as well as limbs myotonia

Question 54

3 symps for muscular dystrophy

Answer 54

weakness due to degen muscle fibres muscle wasting myotonia

Question 55

myotonia

Answer 55

impaired relaxation of muscle after contraction abnormality in muscle membrane transport of chloride or sodium causes persistent depolarization

Question 56

lab evidence for muscular dystrophy (2)

Answer 56

no spontaneous EMG at rest reduced amplitude of EMG potentials bc of fewer muscle fibres per motor unit