Excitation of Skeletal Muscle: Neuromuscular Transmission & Excitation-Contraction Coupling Flashcards Preview

cell phys final > Excitation of Skeletal Muscle: Neuromuscular Transmission & Excitation-Contraction Coupling > Flashcards

Flashcards in Excitation of Skeletal Muscle: Neuromuscular Transmission & Excitation-Contraction Coupling Deck (24):
1

•Highly branched nerve fiber outside of muscle fiber plasma membrane

Motor End Plate

2

Synthesized in cytoplasm of neuron using ATP
Found in synaptic vesicles

Acetylcholine

3

vesicles/end plate

300,000

4

located in synaptic cleft

in synaptic space degrades ACH to acetyl-CoA & choline

Acetylcholinesterase

5

Nerve impulse reaches neuromuscular junction

Ca2+ channels open & flux into presynaptic terminal

Ca2+ attract ACH vesicles to membrane next to dense bars

125 vesicles fuse with terminal membrane

Acetylcholine (ACH) Secretion

6

•Chemical-gated ion channels
•Small diameter & negatively charged amino acids (acidic) at mouth = keep out negative ions
•Na+, K+ & Ca2+ have the ability to diffuse through
•In reality, Na+ almost exclusively flows through
•Stimulates contraction of muscle
Hall.

ACH receptors

7

Na+ influx creates positive potential charge =

end plate potential

ACH receptors

8

Localized

Can be weakened & not reach threshold levels with some meds & toxins (botox)
•End result = paralysis

neuromuscular junction is 3x as much end plate potential

fatigue Due to utilization of most ACH vesicles

End Plate Potential

9

Nerve gases & Alzheimer’s meds
•Decreased breakdown of ACH

Binds ACH receptors, so ACH can’t

Acetylcholinesterase inhibitors

Drugs that Affect the Neuromuscular Junction

10

Increase GI secretions & urination, pupil constriction Anticholinergic: reduce GI secretions & motility, inc. heart rate, dec. lung secretions, urine retentions, pupil dilation

muscarinic receptor

11

Increased heart rate, blood pressure & GI activity
Blockers: hypotension, dec. GI secretions & motility, dec. urination

nicotinic receptor on autonomic ganglia

12

Depolarization & muscle contraction

Blockers: muscle relaxation

nicotinic receptor on autonomic ganglia

13

Nausea, vomiting, diarrhea, blurred vision, tremors, hypotension, bronchoconstriction

Cholinergic

14

Dry mouth, urinary retention, constipation, flushing, fever, depression, tachycardia

Anticholinergic

15

Nausea, vomiting, diarrhea, headache, confusion

Anticholinesterases

16

Altered taste, nausea, heartburn

Nn agonist

17

Dry mouth, constipation, hypotension, impotency

Nn blocker

18

Paralysis of respiratory muscles

Nm blocker

19

Antibodies attack ACH receptors at neuromuscular junction

Inability to transmit enough signals from nerves to muscles

Myasthenia Gravis

20

Does not penetrate into fiber

Action potential transmitted along transverse tubules (T tubules

T tubules penetrate into muscle fiber

Stimulate release of Ca2+ & contraction

Muscle Action Potential

21

One end open to extracellular fluid
•Electrical current that spreads over muscle fiber

Transverse (T) Tubule

Excitation-Contraction Coupling

22

action potential reaches T tubule next to sarcoplasmic reticulum

Calcium release stimulates contraction

Ca2+ release from sarcoplasmic reticulum

23

in sarcoplasmic reticulum pump Ca2+ back in

Calcium pump

24

Ca2+ concentration increases 500x

(10x more than level for maximum contraction)

This pulse of Ca2+ lasts ~1/20 second

Calcium ‘Pulse’