4a. Skeletal Muscle and Neuromuscular Junction (NMJ)

Question 1

motor unit

Answer 1

motor neuron and all the fibers that it innervates

direct innervation (no ganglia)

Question 2

motor end plates

Answer 2

located at skeletal muscle membrane
synapse with motor nerve terminal

Question 3

motor neuron site of action potential

Answer 3

axon hillock

Question 4

tetrodotoxin

Answer 4

blocks Na+ channel

Question 5

botulinum toxiun

Answer 5

cleaves SNARE proteins
decrease NT release

Question 6

physostigmine/neostigmine

Answer 6

blocks AChE
increases ACh at NMJ

Question 7

curare
(d-tubocurarine)

Answer 7

competitive antagonist for ACh to bind to the AChR
less ACh able to bind
=muscle relaxant

Question 8

end plate potential

Answer 8

graded potential (20mV)
generated by stimulation causing a change in membrane potential

almost always triggers AP

Question 9

dihydropyridine receptor (DHPR)

Answer 9

functions as a voltage sensor in skeletal muscle
triggers intracellular Ca++ release from SR

Question 10

T- tubules inside charge

Answer 10

+

Question 11

T-tubules outside charge

Answer 11

-

Question 12

t tubules function

Answer 12

conduct AP into interior muscle fibers

Question 13

DHPRs activated by AP

Answer 13

results in physical contact w/RyR to release Ca++

Question 14

Calcium-Induced Calcium Release
(CICR)

Answer 14

Ca++ release by the action of Ca++ alone without simultaneous action of other activating processes

Question 15

Primary mechanism of Ca++ release

Answer 15

• direct protein-protein interaction between the DHPR and RyR

Question 16

Ryanodine Receptor

Answer 16

responsible for Ca++ release from SR

Question 17

when DHPR connects w/RyR

Answer 17

Ca++ is released

Question 18

Excitation-Contraction Coupling

Answer 18

DHPR connecting w/RyR to facilitate Ca++ release
increase intracellular Ca++

Question 19

myosin head

Answer 19

attaches to actin
power stroke (hydrolysis products released)
binds to new ATP
detaches from actin

Question 20

myosin chains

Answer 20

heavy chain
light chain (regulatory)

Question 21

Actin filaments

Answer 21

provide cells w/mechanical support and driving forces for movment

Question 22

Troponin C (TnC)

Answer 22

Ca++ binding subunit

(during excitation)

Question 23

Troponin

Answer 23

works w/tropomyosin to unblock active sites between myosin and actin
allows cross-bridge cycling
contraction of myofibrils for systole

Question 24

Tropomyosin

Answer 24

binds w/troponin to help position it on the actin molecule

prevents myosin from forming cross-bridges while in a resting state

Question 25

actin

Answer 25

protein that interacts with myosin filaments to generate tension

Question 26

Hydrolysis of ATP/Power Stroke

Answer 26

1. ATP binds to myosin head (Attached) - dissociation of actin-myosin complex for myosin to bind to ATP (RELEASED) 2. ATP is hydrolyzed - myosin heads return to resting conformation 3. cross-bridge forms - myosin head binds to new action position 4. Phosphate release - power stroke: filaments slide past each other 5. ADP released

Question 27

During muscle contraction, what happens to the H zones and I/A bands

Answer 27

H zones shrink/narrow I band shrink/narrow A band does not change

Question 28

sarcomere optimal overlap

Answer 28

produces optimal force

Question 29

too much overlap

Answer 29

lower force

Question 30

not enough overlap

Answer 30

lower force

Question 31

AChE breaks down ACh into

Answer 31

Choline + Acetic Acid

Question 32

choline acetyltransferase (ChAT)

Answer 32

converts choline and acetyl CoA into ACh

Question 33

3 ways to terminate contraction-reuptake of Calcium

Answer 33

1. NCX (Na/Ca exchanger) 2. SERCA 3. Calsequestrin

Question 34

Na+/Ca++ exchanger

Answer 34

secondary active transporter requires ATP pumps one ion down gradient and the other up gradient

Question 35

Sarcoendoplasmic Reticulum Calcium ATPase (SERCA)

Answer 35

pump transports Ca++ from cytosol back into SR against concentration gradient after muscle contraction primary active transport requires ATP

Question 36

Calsequestrin

Answer 36

major Ca++ binding protein in SR main Ca++ storage regulator of Ca++ release channels in skeletal/cardiac muscle

Question 37

fiber summation

Answer 37

recruit additional motor units

Question 38

frequency summation

Answer 38

of individual fibers

Question 39

unfused tetanus

Answer 39

muscle fibers do not completely relax before next stimulus b/c they are being stimulated at at fast rate Ca++ not at highest level (can trigger more Ca++ release from SR) partial relaxation between twitches (partial summation)

Question 40

fused tetanus

Answer 40

complete tetanus no relaxation period between muscle contractions Ca++ reached highest level (cannot trigger more Ca++ release from SR) (full summation)

Question 41

muscle relaxants

Answer 41

depolarizing non depolarizing

Question 42

depolarizing agent

Answer 42

succinylcholine (partial agonist)

Question 43

succinylcholine mechanism

Answer 43

activates NAChR maintains depolarization (keep open) causes paralysis - muscle fatigue - ion conc gradient? stops breathing

Question 44

non-depolarizing agent

Answer 44

d-tubocurarine (antagonist)

Question 45

d-tubocurarine mechanism

Answer 45

blocks binding of receptor ACh cannot bind No conformational change of receptor No EPP No AP

Question 46

Rhabdomyolysis

Answer 46

damaged muscle tissue releases its proteins and electrolytes into the blood

Question 47

Rhabdo symptoms

Answer 47

reddish/brown urine muscle pain/weakness/fatigue

Question 48

Rhabdo blood serum

Answer 48

high creatine kinase high potassium high myoglobin low Ca++

Question 49

Rhabdo kidney damage

Answer 49

myoglobin is filtered out by the kidneys which causes damage to the kidneys

Question 50

Myasthenia Gravis

Answer 50

autoimmune diease antibodies bind to nAChR weakening skeletal muscles