Lec 15 Muscle Flashcards
What surrounds entire muscle?
epymysium
What surrounds myofiber?
endomysium
What is type 1 muscle?
red; slow twitch
sustained action
lots of mitochondria and myoglobin
oxidative phosphorylation
What is type 2 muscle?
white; fast twitch
less mitochondria/myoglobin
anaerobic glycolysis
What is a motor unit?
anterior horn motor neuron axon terminating in motor end plate muscle fibers that the nerve innervates
How is AP propagated for muscle contraction?
via T-tubules –> AP produces Ca efflux from SR causing muscle contraction
What do you see histologically with acute dennervation?
angular myofibers
What is myofiber type grouping?
due to partial chronic dennervation from collateral
What happens to muscle in stroke?
you are taking out the upper motor neruon but anterior horn cell still intact –> selective atrophy of type 2 fibers due to disabuse
When do you get type 2 myofiber atrophy?
when muscle isnt used [not same as dennervation]
What does proximal muscle disorder suggest?
intrinsic muscle process problem
What does distal muscle disorder suggest?
usually neurogenic
What do you see in Duchennes muscular dystrophy?
steadily progressive; onset first 5 years
X recessive
gowers sign = difficulty rising from floor
often have cardiomyopathy
lordotic posture
hypertrophy of calf muscles
What is pathogenesis of duchenne’s?
no dystrophin gene –> replace myofiber with connect tissue
What is beckers?
less severe form of duchenne
onset mid childhood; uncommon to have cardiac involvement; do have calf hypertrophy + weakness
What is pathogenesis of Becker?
normal amount of abnormal sized dystrophin protein OR markedly reduced levels of normal dystrophin
What is myotonic dystrophy?
CTG repeat expansion in DMPK gene –> abnormal expression myotonin protein kinase –> myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, arrhythmia
What is pathogenesis of myotonic dystrophy?
CTG repeat expansion in DMPK gene –> abnormal expression myotonin protein kinase
What do you see in congenital myopathy
- floppy infant = muscle weakness
- symmetric proximal weakness
- typ 1 myofiber predominance
What is polymyositis?
inflammation of muscle body itself
What are criteria for polymyositis/ dermatomyositis?
progressive symmetrical proximal weakness
high sarcoplasmic enzymes in serum [CK, LDH, ANA, anti-Jo-1, anti-SRP]
skin rash, periorbital edema
What is myasthenia gravis?
post synaptic antibodies to ACh receptor
decrease strength w/ repetitive stimulation
assocaited w/ thymoma or thymic hyperplasia
What is eaton-lambert?
presynaptic antibodies to Ca receptor
increase strength w/ repetitive stimulation
small cell lung carcinoma
