Lecture 21/22: Skeletal Muscle Disorders Flashcards
Which of the following conditions is an autoimmune condition associated with anti-Ach receptor antibodies?
Myasthenia gravis
A patient comes into clinic with complains of weakness in eye, face, neck, and limb muscles. They have noticed eyelids are droopy and difficulty holding their head up. What condition do they most likely have?
Myasthenia gravis
A patient with Myasthenia gravis is most likely to have:
A. T cell hyperplasia
B. Thymic B cell hyperplasia
B. Thymic B cell hyperplasia
True or False: Repetitive EP stimulation (exercise) can worsen Myasthenia gravis
True - worsens muscle weakness
What are three ways to treat Myasthenia gravis?
- Acetylcholinesterase Inhibitor
- Immunosuppression
- Plasmapheresis
_____ is an auto-immune disorder that can be transferred by serum and is characterized by the presence of antibodies that inhibit function of pre-synaptic VG Ca channels
Lambert-Eaton Syndrome
Which drug can be used to treat Lambert-Eaton syndrome? How does it work?
3,4 DAP
- Prolongs AP
- Decreased amount of K reflux
- More Ca entry
True or False: Unlike myasthenia gravis, weakness may temporarily improve with exercise (exertion) in Lambert-Eaton Syndrome
True
Autonomic nervous system dysfunction may occur in Lambert-Eaton Syndrome. What is the most common symptom?
Dry mouth
Which of the following condition is usually associated with small cell lung carcinoma?
A. Lambert-Eaton Syndrome
B. Myasthenia Gravis
A. Lambert-Eaton Syndrome
True or False: Acetylcholinesterase inhibitors can be used to treat Myasthenia Gravis and Lambert-Eaton Syndrome
False - does not help in case of Lambert Eaton
Why is the prognosis for Lambert-Eaton Syndrome worse than myasthenia gravis?
Small cell lung cancer association
___ ____ ____: Rare autosomal recessive mutations that disrupt function of NMJ proteins
Congenital Myasthenic Syndromes
What is the most common CMS mutation?
LOF mutations in gene encoding episolon-subunit of Ach receptor
True or False: CMS is characterized by weakness and fatigue, results from problems at NMJ
True
Tetrodotoxin and Saxitoxin act on the NM to inhibit
A. K channel/Neuronal Na channel
B. Neuronal Ca/Na channel
C. Neuronal Na/Muscle Na Channel
C. Neuronal Na/Muscle Na Channel
True or False: Lambert Eaton Syndrome inhibits neuronal calcium channels
True
True or False: Ach and Nicotine positively act on Ach receptor, while Myasthenia gravis has an inhibitor effect
True
Tetanus and Botulinum toxin inhibit Ach release while _____ increases release
Black widow spider venom
True or False: Dendrotoxin inhibits K+ channel
True
Which of the following prevents INACTIVATION of Ach?
A. Black Widow Spider Venom
B. Botulinum toxin
C. Lambert-Eaton Syndrome
D. OP’s
D. OP’s
Which two conditions involves BLOCKING of Ach-R sites?
Curare and Myasthenia Gravis
True or False: Botulinum, LE Syndrome, and black widow spider venom alters release of Ach
True
True or False: Botulinum blocks Ach release while black widow spider venom causes explosive release of Ach
True
Which condition is characterized by self-produced antibodies to Cal channels, which diminish calcium influx, thereby reducing Ach release?
Lambert Eaton
In myasthenia gravis, self produced antibodise inactivate N1 receptors while in Lambert-Eaton syndrome, autoantibodies inactivate VG Ca channels in synaptic terminals . Which of the following phenomena will be found in both diseases?
Reduced PS potential
Which of the following fibers have low oxidative capacity and high fatigue, but is good for short periods of high intensity?
A. Slow Oxidative Fibers
B. Fast Ox-Glycolytic Fibers
C. Fast Glycolytic Fibers
C. Fast Glycolytic Fibers (IIb)
True or False: Slow oxidative fibers (Type 1) have a high oxidative capacity (many mitochondria!) and therefore can maintain low-intensity contractions for long periods, without fatigue
True
True or False: A single motor unit consists of one motor neuron and the muscle fibers it innervates, while TWO motor units have intermingled fibers
True
Motor units size = ____ / ____
of myocytes / motor neuron
note: the more myocytes there are, the stronger the muscle force and the less control
Motor units with the lowest thresholds are the first to be activated. Given this, which is activated first?
A. Slow Twitch (Type I) Fibers
B. Fast Twitch (Type II) Fibers
A. Slow Twitch (Type I) Fibers
- low threshold
True or False: Neurogenic muscle fiber atrophy is due to destruction of a motor neuron, leads to denervation
atrophy
True
True or False: Prolonged disuse (i.e. immobilization) causes focal or generalized atrophy
True
Which fiber exhibits more atrophy: Type II or Type I?
A. Type II
B. Type I
A. Type II
What do Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy have in common, as far as how they are inherited genetically?
X-linked
- Also, they’re both due to mutations in Dystrophin
What is the function of the DGC (dystrophin-glycoprotein complex)?
Structural stability to muscle cell membrane during contraction/relaxation
Important for cardiac and skeletal muscle function
a2 laminin’s
mutations causes:
A. Duchenne/Becker Muscular
Dystrophy
B. Congenital Muscular Dystrophy
C. Limb Girdle Muscle Atrophy
B. Congenital Muscular Dystrophy
Which drug class causes atrophy due to increased proteolysis for gluconeogenesis?
A. NSAID’s
B. Glucocorticoids
C. Anti-virals
B. Glucocorticoids
- atrophy primarily in Type II fibers and proximal muscles
Dystrophin mutation causes:
A. Duchenne/Becker Muscular
Dystrophy
B. Congenital Muscular Dystrophy
C. Limb Girdle Muscle Atrophy
A. Duchenne/Becker Muscular
Dystrophy
Mutation in sarcoglycans causes:
A. Duchenne/Becker Muscular
Dystrophy
B. Congenital Muscular Dystrophy
C. Limb Girdle Muscle Atrophy
C. Limb Girdle Muscle Atrophy
True or False: In DMD (Duchenne Muscular Dystrophy) dystrophin is ABSENT - however, in Becker’s there is partial function of dystrophin, making it a milder form of DMD
True
____ is an X-linked recessive condition that is characterized by progressive, severe muscle weakness. It ultimately causes death in late teens due to respiratory or cardiac muscle failure.
Duchenne Muscular Dystrophy
True or False: DMD results in loss of muscle fibers, increased fibrosis and adipose tissue
True
Muscular Dystrophy treatment?
1) Corticosteroids
2) ACE Inhibitors or B-blockers if there are cardiac effects
“Anticipation” –the idea that there are increasing repeats of a particular genetic abnormality with each passing generation–is found in DM1/DM2, also known as ____
Myotonic Dystrophy or Dystrophia Myotonica
True or False: Myotonic Dystrophy or Dystrophia Myotonia are characterized by sustained involuntary contractions and trinucleotide CTG expansions on chrom 19
True
Mutation in Na channel can lead it to FAIL to INACTIVATE. Which of the following conditions may arise?
A. Ion Channel Myopathy
B. Hyperkalemic Periodic Paralysis
B. Hyperkalemic Periodic Paralysis
Which condition results due to mutations in Ryanodine receptor, a Ca release channel protein, and is trigged by halogenated anesthetics?
A. Malignant Hyperthermia
B. Hyperkalemic Periodic Paralysis
A. Malignant Hyperthermia
True or False: Ca is stored and released via SR cisterna
True
True or False: In skeletal muscle, the DHPR and RyR are physically associated; therefore: polarization induced DHPR activation results in opening of RyR
True
In malignant hyperthermia, there is reduced affinity for Mg to calcium binding site. Therefore: Mg does not block activation
True
True or False: Malignant Hyperthermia PROMOTES Ca release - channel becomes more active and does not inactivate
True
True or False: There’s reduced threshold for luminal calcium activation of RyR1 in malignant hyperthermia
True
True or False: Myofilament contraction and activation of Ca2/ATPase leads to excess heat, therefore: malginant hyperthermia
True
