Skeletal Muscle: NMJ Flashcards
What is muscle tissue derived from?
Embryonic mesodermal germ cells
What are the collective tissue components of muscles?
Epimysium - Surrounds entire muscle
Perimysium - Surrounds bundles of muscle fibers
Endomysium - Surrounds individual muscle fibers
Basement Membrane - Below endomysium
What are satellite cells?
- Play a role in muscle growth/repair
- Increase # nuclei in mature fibers
- strength training
What is the motor end plate?
Pocket formed around motor neuron by sarcolemma
Describe the events which occur which lead to an action potential at the NMJ.
- Neuron AP
- Ca Entry
- Ach release
- Na entry via Nicotinic receptors
- EPP local Na current brings Vm to threshold
- Muscle fiber AP Na entry cia Voltage ganged channels
- AP propagation
- Ach degradation
What are the two types of Nicotinic receptors?
Nicotinic Muscle - NMJ
Nicotinic NEuronal - Autonomic Ganglia
What is a quanta?
Release of individual synaptic vesicle
Describe pathology of myasthenia gravis.
- Autoimmune disorder wher Abs block Ach receptors at NMJ
- Decreases # receptors by 80%
- 10% have Ab against other plasma proteins NOT Cholinesterase
What is Lambert-Eaton Syndrome?
- Ab saga isn’t Ca channels of NEuron of NMJ and there’re no transmitter release
- Commonly leads to small cell lung Carcinoma
How is Lambert-Easton diagnosed?
- Uses EMG
- Repetitive stimulation of nerve muscle leads to progressive increase in contraction as Ca builds up in nerve terminal, while MG has a decrease in contraction strength
What are Ach-esterase agonists?
Carbachol and suxamethonium
What are Ach-esterase antagonists?
- Tubocurarine
- a-bungarotoxin
- a-conotoxin
- pancuronium
What is Strychnos Toxifera?
Plant poison contains alkaloid tubocurarine which blocks Nicotinic receptors
What is physostigmine?
- Reversible cholinesterase inhbiitor
- Obtained from calabar bean
- treats glaucoma and delayed gastric emptying
What are symptoms f Ach overdose?
Abdominal cramps, Diarrhea, salivation, pinpoint pupils, and respiratory difficulty
What are common effects and mechanisms of insecticides and chemical warfare agents? Treatment?
Acetylcholinesterase inhibitors
- Muscle twitches, Convulsions, pinpoint pupils, respiratory arrest
- Treat wth atropine
Describe the action of pyridostigmine. Compared to other similar drugs?
- Inhibits muscarinic action of acetylcholine on structures innervated by postganglionic cholinergic nerves but not Nicotinic receptors
- Longer half life than others
- Fewer cholinergic side effects
- Does not crocs BBB
What is the actions of tetrodotoxin?
Na Channel Inhibitor
What is the action of Botulinum and tetanus?
Inhibit synaptic release
What is the effect of curare
Inhibits receptors
What is the effect of lead poisoning?
Calcium mediated toxicity
What are three common sources of endogenous neurotoxins?
NO. Glutamate, and dopamine
How does the action nod different Botulinum Toxins differ?
A/E - Cleave SNAP-25
B,D,F,G - Cleaves synaptobrevin
C1 - SNAP-25/syntaxin
