The Neuromuscular Junction and The Nicotinic Acetylcholine Receptor

Question 1

What is the diameter of an alpha motor fibre?

Answer 1

10 micrometers

Question 2

What is the speed of conduction down an alpha motor fibres?

Answer 2

50-100 m/s

Question 3

Regarding Acetylcholine (true of false):

Acetylcholine is synthesised in α-motor neurons

Answer 3

True.

Question 4

Regarding Acetylcholine (true of false):

Acetylcholine contains a tertiary amine group

Answer 4

False. Acetylcholine contains a quaternary ammonium ion.

Question 5

Regarding Acetylcholine (true of false):

Choline is an essential amino acid

Answer 5

False. Choline is an essential nutrient but not an amino acid.

Question 6

Regarding Acetylcholine (true of false):

Acetylcholine requires oxidative phosphorylation of pyruvate for its precursor acetyl-CoA

Answer 6

False. Acetyl-CoA is formed from oxidative decarboxylation of pyruvate.

Question 7

Regarding Acetylcholine (true of false):

Acetylcholine contains a single ester linkage

Answer 7

True

Question 8

During neuromuscular transmission (true or false):

Motor nerves conduct at 5-10 m/s

Answer 8

False. Motor neurones conduct faster than this at 50-100 m/sec.

Question 8

During neuromuscular transmission (true or false):

Nodes of Ranvier contain ligand-gated ionic channels

Answer 8

False. There are voltage-gated ion channels at the nodes of Ranvier.

Question 9

During neuromuscular transmission (true or false):

Schwann cells provide insulation of the nerve fibre

Answer 9

True

Question 10

During neuromuscular transmission (true or false):

Saltatory conduction involves the opening of sodium channels

Answer 10

True

Question 11

During neuromuscular transmission (true or false):

NAChRs are present in the clefts of the post-synaptic membrane

Answer 11

False. The nicotinic receptors are on the shoulder and crests of the post-synaptic membrane.

Question 12

Regarding presynaptic motor nerve terminals at the NMJ (true or false):

Ligand-gated calcium channels regulate vesicle exocytosis

Answer 12

False. Voltage-gated calcium channels mediate vesicle release.

Question 13

Regarding presynaptic motor nerve terminals at the NMJ (true or false):

ACh provides presynaptic feedback-inhibition

Answer 13

False. ACh mediates increased release of ACh presynaptically.

Question 13

Regarding presynaptic motor nerve terminals at the NMJ (true or false):

L-type calcium channels are found presynaptically at the NMJ

Answer 13

False. N-type calcium channels are present presynaptically at the NMJ.

Question 14

Regarding presynaptic motor nerve terminals at the NMJ (true or false):

NAChRs are found presynaptically

Answer 14

True

Question 15

Regarding presynaptic motor nerve terminals at the NMJ (true or false):

In Lambert-Eaton syndrome, there are antibodies against presynaptic calcium channels

Answer 15

True

Question 16

At the post-synaptic membrane of the NMJ (true or false):

AChE is found in the clefts of the folded membrane

Answer 16

True

Question 17

At the post-synaptic membrane of the NMJ (true or false):

Individual AChE molecules are free in the synaptic cleft

Answer 17

False. AChE tends to form clusters and is loosely anchored to the membrane.

Question 18

At the post-synaptic membrane of the NMJ (true or false):

NAChR have four different types of subunit

Answer 18

True. NAChR has five subunits, but two α subunits.

Question 19

At the post-synaptic membrane of the NMJ (true or false):

ACh binds to the β subunit of the nicotinic receptor

Answer 19

False. ACh binds to the α subunits.

Question 20

At the post-synaptic membrane of the NMJ (true or false):

Only sodium ions pass through the opened ion channel

Answer 20

False. Potassium ions can also pass through, but move outward.

Question 21

Regarding the motor endplate (true or false):

The resting potential of skeletal muscle is -70 mV

Answer 21

False. The resting potential of skeletal muscle is between -90 mV and -85 mV. -70mV is the threshold for voltage-gated sodium channels to open.

Question 22

Regarding the motor endplate (true or false):

MEPPs reflect spontaneous release of ACh

Answer 22

True

Question 23

Regarding the motor endplate (true or false): Current flow through a single ion channel is around 50 pA

Answer 23

False. Current flow through a single ion channel is around 5 pA

Question 24

Regarding the motor endplate (true or false): The Nernst potential for sodium is -50 mV

Answer 24

False. The Nernst potential for sodium is around +50 mV.

Question 25

Regarding the motor endplate (true or false): The muscle depolarises when the EPP reaches +15 mV

Answer 25

False. Muscle depolarises when the EPP reaches the threshold for voltage-gated sodium channels to open, around -70 mV.

Question 26

Pre-synaptically at the NMJ (true or false): Calcium entry is essential for vesicle exocytosis

Answer 26

True

Question 27

Pre-synaptically at the NMJ (true or false): SNARE proteins provide the mechanism for membrane fusion

Answer 27

True

Question 28

Pre-synaptically at the NMJ (true or false): Nicotinic receptors have the same subunit composition as at the autonomic ganglia

Answer 28

False. Nicotinic receptors and autonomic ganglia have different types of α and β subunits.

Question 29

Pre-synaptically at the NMJ (true or false): The calcium channel is of the same type as found in myocardial muscle

Answer 29

False. T-type and L-type calcium channels are found in cardiac muscle and N-type pre-synaptically.

Question 30

Pre-synaptically at the NMJ (true or false): All vesicles are anchored to the presynaptic membrane

Answer 30

False. Some vesicles are attached awaiting release, but some are free in the cytoplasm.

Question 31

The muscle membrane has (true or false): Ligand-gated sodium channels that depolarise when the EPP is reached

Answer 31

False. Voltage-gated sodium channels are responsible for depolarisation when the endplate potential is reached.

Question 32

The muscle membrane has (true or false): T-tubules that fold into the cell

Answer 32

True

Question 33

The muscle membrane has (true or false): L-type voltage-gated calcium channels in the T-tubules

Answer 33

True

Question 34

The muscle membrane has (true or false): Ryanodine RyR2 receptors

Answer 34

False. Ryanodine RyR1 receptors are in the membrane of the sarcoplasmic reticulum; RyR2 are found in myocardial cells.

Question 35

The muscle membrane has (true or false): Voltage-gated calcium channels with pore-forming domains in the α1 subunit

Answer 35

True

Question 36

At the NMJ (true or false): ACh acts exclusively through nicotinic receptors

Answer 36

True

Question 37

At the NMJ (true or false): Neostigmine is a competitive inhibitor at nicotinic receptors

Answer 37

False. Neostigmine inhibits AChE.

Question 38

At the NMJ (true or false): Nicotine causes receptor up-regulation

Answer 38

False. Nicotine causes down-regulation of receptors.

Question 39

At the NMJ (true or false): Plasma cholinesterase is present in the synaptic cleft

Answer 39

False. Plasma cholinesterase is not present at all.

Question 40

At the NMJ (true or false): Organophosphates increase ACh levels in the synaptic cleft

Answer 40

True. Organophosphates increase ACh levels in the synaptic cleft and lead to flaccid paralysis.