L4: Flaccid dysarthria - LMN Disorders Part A Flashcards
lower motor neuron refers to
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)
LMN includes…
neuron cell body
peripheral nerve
nerve-muscle synapse
muscle fibres
motor neuron disorders (ex. motor neuron disease) effect what part of the LMN
neuron cell body
peripheral nerve disorders (ex. gullian-barre) effect what part of the LMN
peripheral nerve
neuromuscular junctin disorders (ex. myasthenia gravis) effect what part of the LMN
nerve-muscle synapse
neurogenic disorders effect what parts of the LMNs
neuron cell body
peripheral nerve
nerve-muscle synpase
myopathic disorders of LMN effect what part of LMN… ex of a disorder?
muscle fibres
aka muscle disorders (ex. muscular dystrophy)
what are the 4 causes of motor neuron disorders (nerve cell body)?
viral infections
tumours
strokes
motor neuron diseases
viral infections (ex. poliomyelitis) effects only ____ neurons, acute infection can produce _____
motor
permanent paralysis
tumors can cause motor neuron disorders (nerve cell body) by
invading the motor nuclei
strokes can cause motor neuron disorders (nerve cell body) by
impairing blood supply to motor nuclei
motor neuron diseases are
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
progressive (spinal) muscular atrophy is an example of a _____ disorder, and involves…
motor neuron disease (nerve cell body)
spinal lower motor neruons - mostly affecting the spinal sys (legs, trunk, arms)
progressive bulbar palsy is an example of a _____, and involves…
motor neuron disease (nerve cell body)
cranial lower motor neurons, bulbar = oral facial speech sys
amyotrophic lateral sclerosis (ALS) is an example of a ____ and involves….
motor neuron disease (nerve cell body)
both upper and lower motor neurons - spinal and/or bulbar (or combo of both)
what are the 5 clinical symptoms/pathophys of motor neuron disorders (nerve cell body)
weakness
fasiculations
muscle wasting
reduced/lost reflexes
reduced muscle tone
describe the weakness associated w motor neuron disorders (nerve cell body)
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)
describe the fasiculations associated w motor neuron disorders (nerve cell body)
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
describe the muscle wasting associated w motor neuron disorders (nerve cell body)
denervated muscle fibres eventually degenerate
weakness reduces muscle use and causes further atrophy
describe the reduced or lost reflexes associated w motor neuron disorders (nerve cell body)
distributed degen of neurons disrupts the normal synchronized volleys of motor units that are necessary for reflex muscle contractions
describe the reduced muscle tone associated w motor neuron disorders (nerve cell body)
weakness causes a reduction in muscle tone
what are the 3 pieces of EMG evidence for motor neuron disorders (nerve cell body)
fibrillations
reduced number of active motor units during voluntary movement
inc in amplitude of muscle unit potentials
describe fibrillations as EMG evidence for motor neuron disorders (nerve cell body)
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)
“reduced number of active motor units during voluntary movement” as EMG evidence for motor neuron disorders (nerve cell body) is due to…
degeneration of neurons
describe “inc in amp of muscle unit potentials” as EMG evidence for motor neuron disorders (nerve cell body)
remaining motor units try to incorporate muscle fibres from degen nerves
more fibres per motor unit results in large potentials
describe muscle histology of motor neuron disorders (nerve cell body)
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
peripheral nerve disorders effect what primarily? … small or large # of disorders?
axons and myeline of peripheral nerves
a very large number of diseases and disorders associated w peripheral nerve damage
what are the 8 possible causes of peripheral nerve disorders (axon)?
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)
what is Guillian-Barre Syndrome (GBS)?
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
what are the 6 symptoms of peripheral nerve disorders (axon)?
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
describe the sensory loss associated w peripheral nerve disorders (axon)
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
in demyelinating peripheral nerve diseases the nerve conduction velocity is…
reduced due to loss of myelin
neuromuscular junction disorders are disorder of the…
motor units pre- or post-synaptic processes
what are the two causes of neuromuscular junction disorders?
autoimmune disorders
toxins
Eaton-Lambert disease is a _____ disorder
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
myasthenia gravis is a ___ disorder
postsynaptic neuromuscular junction disorder
Peak 30-40 years old, F>M slightly, Dec strength w use
botulinum causes what type of neuromuscular junction disorder
presynaptic
bungerotoxin (snake venom) causes what type of neuromuscular junction disorder
post synpatic
describe myasthenia gravis - what is responsible for clinical symptoms?
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
what do the reduced Acetylcholine receptors cause in MG?
makes it more difficult for the Ach to produce a muscle contraction - w repeated attempts at contraction the # of available receptors becomes progressively reduced
onset of MG
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.
how does the weakness fluctuate w MG/
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.
describe extraocular muscle weakness in MG
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
describe bulbar muscle weakness in MG
This can be the initial presentation in 15% of patients and causes symptoms like difficulty chewing or frequent choking, dysphagia, hoarseness, and dysarthria
what are the 6 pieces of clinical evidence for MG (neuromuscular junction disorder)?
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)
what is the lab evidence for MG? (3)
EMG shows reduced action potentials over repeated stimulation or activation
blood test for Ach receptor antibody (80%)
test w acetyllcholinesterase inhibitor
what are the 2 treatment options for MG?
acetylcholinesterase inhibitors
immunological: thymus removal, immunosuppresive drugs, plasmaphoresis
muscle (myopathic disorders) are
diseases of muscle tissue
4 types of muscular dystrophy (inherited myopathy)
duchenne type
facioscapulohumeral type
limb-girdle type
myotonic type
duchenne muscular dystrophy
only males
early onset bf 5 years
progresses rapidly, death bf 40
often starts in legs
facioscapulohumeral muscular dystrophy
both sexes
adolescent onset
slower onset, close to normal lifespan
effects face and shoulder initially
limb-girdle muscular dystrophy
both sexes
adolescent onset
slow progression
diverse symptoms, may include several subtypes
myotonic muscular dystrophy
both sexes
infancy or adolescence
slow progression
often involves the cranial muscles as well as limbs
myotonia
3 symps for muscular dystrophy
weakness due to degen muscle fibres
muscle wasting
myotonia
myotonia
impaired relaxation of muscle after contraction
abnormality in muscle membrane transport of chloride or sodium causes persistent depolarization
lab evidence for muscular dystrophy (2)
no spontaneous EMG at rest
reduced amplitude of EMG potentials bc of fewer muscle fibres per motor unit
