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

Question 1

•Highly branched nerve fiber outside of muscle fiber plasma membrane

Answer 1

Motor End Plate

Question 2

Synthesized in cytoplasm of neuron using ATP

Found in synaptic vesicles

Answer 2

Acetylcholine

Question 3

vesicles/end plate

Answer 3

300,000

Question 4

located in synaptic cleft

in synaptic space degrades ACH to acetyl-CoA & choline

Answer 4

Acetylcholinesterase

Question 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

Answer 5

Acetylcholine (ACH) Secretion

Question 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.

Answer 6

ACH receptors

Question 7

Na+ influx creates positive potential charge =

Answer 7

end plate potential

ACH receptors

Question 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

Answer 8

End Plate Potential

Question 9

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

Binds ACH receptors, so ACH can’t

Answer 9

Acetylcholinesterase inhibitors

Drugs that Affect the Neuromuscular Junction

Question 10

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

Answer 10

muscarinic receptor

Question 11

Increased heart rate, blood pressure & GI activity

Blockers: hypotension, dec. GI secretions & motility, dec. urination

Answer 11

nicotinic receptor on autonomic ganglia

Question 12

Depolarization & muscle contraction

Blockers: muscle relaxation

Answer 12

nicotinic receptor on autonomic ganglia

Question 13

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

Answer 13

Cholinergic

Question 14

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

Answer 14

Anticholinergic

Question 15

Nausea, vomiting, diarrhea, headache, confusion

Answer 15

Anticholinesterases

Question 16

Altered taste, nausea, heartburn

Answer 16

Nn agonist

Question 17

Dry mouth, constipation, hypotension, impotency

Answer 17

Nn blocker

Question 18

Paralysis of respiratory muscles

Answer 18

Nm blocker

Question 19

Antibodies attack ACH receptors at neuromuscular junction

Inability to transmit enough signals from nerves to muscles

Answer 19

Myasthenia Gravis

Question 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

Answer 20

Muscle Action Potential

Question 21

One end open to extracellular fluid

•Electrical current that spreads over muscle fiber

Answer 21

Transverse (T) Tubule

Excitation-Contraction Coupling

Question 22

action potential reaches T tubule next to sarcoplasmic reticulum

Calcium release stimulates contraction

Answer 22

Ca2+ release from sarcoplasmic reticulum

Question 23

in sarcoplasmic reticulum pump Ca2+ back in

Answer 23

Calcium pump

Question 24

Ca2+ concentration increases 500x

(10x more than level for maximum contraction)

This pulse of Ca2+ lasts ~1/20 second

Answer 24

Calcium ‘Pulse’