Deck 22: Neuromuscular Junction and Ec Coupling

Question 1

If we excite a motor neuron to fire an action potential in the presence of EGTA to complex all of the Ca₂+

A) Acetylcholine release will be re du ce d a nd the EP P w ill be red uc ed , bu t the m us cle will contract
B) Neurotransmission will be unaffected but contraction will be blocked because it requires Ca₂+
C) Neurotransmission will be blocked and so there will be no contraction
D) Neurotransmission block can be overcome by repetitive stimulation
E) The neuron cannot fire an action potential in the absence of Ca₂+

Answer 1

C

Question 2

A nerv e ha s a re sting m em bran e po tential of -70 m V. E Cl = -80 m V; E K = -95 mV and E Na = +65 mV. Increasing gCl should produce

A) An inward current and an EPSP
B) An outward current and an EPSP
C) An inward current and an IPSP
D) An outward current and an IPSP
E) It is impossible to tell from the information given

Answer 2

D

Question 3

Relaxation of skeletal muscle is caused by

A) Reuptake of activator Ca₂+ by the SR Ca-ATPase pump
B) Efflux of Ca₂+ into the extracellular space
C) Uptake of activator Ca₂+ into the m itoc ho nd ria
D) Closing of the ryanodine-sensit ive Ca₂+channel
E) Binding of Ca₂+ to c als eq ue str in

Answer 3

A

Question 4

The action potential on the axon at a neuromuscular junction

A) Opens ryanodine-sensitive channels on the SR m embrane
B) Increases cytoplasmic [Ca₂+] in the terminal by opening voltage-gated Ca₂+ cha nn els
C) O pe ns the DH PR on the T -tu bu le
D) Is conveyed electrotonically to the muscle mem brane
E) Both A and C are correct

Question 5

All of the following are true about EPSPs EXCEPT

A) They are depolarizations
B) They decay with distance from the site of stimulation
C) The decay with time
D) They can vary in magnitude
E) They ar e ac tion po ten tials

Question 6

The end-plate potential

A) Is g ra de d (v ar ies co ntin uo us ly)
B) Is a hyperpolarization
C) Passively spreads to the adjacent muscle mem brane
D) Is an action potential
E) Both A and C are correct

Question 7

Opening of acetylcholine receptors by acetylcholine directly produces

A) An end-plate potential on the muscle
B) An ac tion po ten tial o n th e m us cle
C) An inward current and muscle membrane depolarization
D) The hyperpolarization afterpotential
E) Both A and C are correct

Question 8

The acetylcholine receptor at the neuromuscular junction is located in the

A) Muscle membrane
B) Basement m embrane
C) Pre-synaptic mem brane
D) Synaptic vesicles
E) Syn ap tic m itoc ho nd ria

Question 9

The fina l intr ac ellu lar ac tiva tor of s ke leta l m us cle co ntr ac tion is

A) Phosphorylation of the myosin light chains
B) The m uscle membrane action potential
C) Ca₂+ influx through voltage-dependent Ca₂+ ch an ne ls
D) Ca₂+ released through the ryanodine receptors from the SR
E) Inos itol trispho sph ate

Question 10

The acetylcholinesterase at the neuromuscular junction is located in the

A) Muscle mem brane
B) Basement membrane
C) Pre-synaptic mem brane
D) Synaptic vesicles
E) Syn ap tic m itoc ho nd ria

Question 11

The m os t co m m on ca us e o f m yas the nia gra vis is

A) Excess acetylcholinesterase
B) Failure of vesicle fusion on the presynaptic neuronal mem brane
C) Increased diffusion distance to the muscle mem brane
D) Autoimmune destruction of the acetylcholine receptor
E) Poisoning by curare

Question 12

The acetylcholine in the neuromuscular junction is stored in the

A) Muscle mem brane
B) Basement m embrane
C) Pre-synaptic mem brane
D) Synaptic vesicles
E) Syn ap tic m itoc ho nd ria

Question 13

Control of interaction of thin filament with thick filament in skeletal muscle is amplified because

A) Binding of Ca to calmodulin activates CAMK phosphorylation of the myosin light chains
B) Binding of Ca to TnC causes mo vement of tropomyosin that cov ers m ultip le m yos in binding sites on the thin filament
C) Gr eate r relea se o f Ca from the s arc opla sm ic reticu lum activa tes m ore m yofilam ents
D) Ca inhibits the protein phosphatases that dephosphorylate the myosin light chains
E) Repet it ive stimulat ion keeps the [Ca₂+] up longer

Question 14

Sp atial su m m ation re fers to

A) Sum ma tion of sim ultaneo us syn aptic inpu ts
B) Su m m atio n o f re pe titive stim uli
C) The beginning of tetany
D) Su m m atio n o f re pe titive EP SP on ly
E) Arrangement of dendrites in space

Question 15

In the neuromuscular junction, the junctional folds are folds of the

A) Muscle membrane
B) Basement m embrane
C) Pre-synaptic mem brane
D) Synaptic vesicles
E) Syn ap tic m itoc ho nd ria

Question 16

The voltage-sensor on the muscle membrane is the

A) AchR
B) DHPR
C) R yR
D) IP3R
E) VDCC

Question 17

A neurotransmitter released onto a motor neuron opens a Ca₂+ channel. This typically causes

A) An IPSP
B) An EPSP
C) A MEPP
D) An action potential
E) An EPP

Question 18

A neurotransmitter released onto a motor neuron opens a Cl- channel. This typically causes

A) An IPSP
B) An EPSP
C) A MEPP
D) An action potential
E) An EPP

Question 19

In a motor neuron, the action potential typically originates at the

A) Axon hillock or initial segment
B) Node of Ranvier
C) De ndrite
D) S oma
E) Nerve terminal

Question 20

All of the following are true about IPSPs EXCEPT

A) IPSPs are hyperpolarizations
B) IPSPs are conducted electrotonically through the cytoplasm
C) Simultaneous IPSPs are summ ed by spatial summation
D) Repetitive IPSPs are summ ed by temporal summ ation
E) IPSPs are all or none.

Question 21

The protein that confers Ca₂+ se ns itivity o nto the m yof ilam en ts is

A) DHPR
B) SERCA1
C) C als eq ue str in
D) TnC
E) Pa rva lbu m in

Question 22

The Ca₂+ release channel on the SR m embrane is the

A) AchR
B) DHPR
C) RyR
D) IP3R
E) VDCC

Question 23

Force lags behind the Ca₂+ transient because

A) Myofilament activation is slow
B) It takes time for the active m yofilamen ts to stretch the series elastic elem ents
C) Ca₂+ binding to TnC is slow
D) Ca₂+ diffusion to TnC is slow
E) Ca₂+ release by RyR is slow

Question 24

There is no force developed in the absence of Ca₂+ because

A) The m yos in b ind ing site o n ac tin is c ov ered up by tro po m yos in
B) T he m yos in b ind ing site on ac tin is co ve re d u p b y tro po m od ulin
C) The ac to-m yosin c ros s brid ges are in th e rigo r state
D) The RyR is closed
E) T he m yos in h ea ds rem ain bo un d to ac tin a nd ca n't c ycle

Question 25

W ave summ ation and tetany of muscle contraction is caused by

A) Spat ial integration of the Ca₂+ trans ients
B) Co m pres sion of the serie s elas tic elem ents
C) Electrotonic spread of the end plate potential
D) Su m m atio n o f m inia tur e e nd pla te p ote ntia ls
E) Release of Ca₂+ from the SR before the Ca₂+ transient has returned to baseline