EX1; Neuromuscular Junction

Question 1

The amount of contractile activity in a skeletal muscle is regulated by what

Answer 1

the nervous system; the site is the neuromuscular junction

Question 2

Most skeletal muscles have now many NMJs

Answer 2

they have one NMJ on the surface membrane (sarcolemma)

Question 3

The NMJ comprises what percentage of the sarcolemma area

Answer 3

less than 0.1%

Question 4

True or False

The NMJ is a “synapse” a point of contact/communication between two excitable cells

Answer 4

True

Question 5

What are the first two steps involving an AP in a motor neuron to an AP in the sarcolemma

Answer 5

AP travels along motor neuron axon and invades the motor neuron presynaptic terminal

Question 6

What ion influx is in presynaptic terminal after the AP reaches

Answer 6

Calcium

Question 7

These fuse to the membrane of the presynaptic terminal and release what

Answer 7

vesicles release acetylcholine

Question 8

ACh diffuses across what (from the presynaptic terminal) to bind with receptors in the postsynaptic membrane (motor endplate)

Answer 8

neuromuscular cleft

Question 9

Upon the binding of ACh to its receptors, this triggers the opening of what

Answer 9

Na and K channels which are chemically regulated (as opposed to voltage regulated) at the motor endplate, there is then a Na influx and a small K influx

Question 10

Upon the Na and K influx, there is generation of what

Answer 10

endplate potential

Question 11

The generation of the endplate potential causes the opening of what

Answer 11

voltage-regulated Na channels in the sarcolemma immediately surrounding the motor endplate (AP initiation in the sarcolemma)

Question 12

True or False

Endplate potentials are graded, not an all-or-none response

Answer 12

True

Question 13

Endplate potentials do not do this, but can undergo this

Answer 13

do not propagate

can undergo summation

Question 14

These are small EPPs that occur spontaneously and result from the release of ACh from one or a few vesicles in the pre-synaptic terminal and subsequent binding to its receptor

Answer 14

miniature endplate potentials

Question 15

Which one, EEP or MEPP occurs at rest

Answer 15

MEPPs at rest

EPPs occur following an AP in a motor neuron

Question 16

Which one, EEP or MEPP is not sponatneous

Answer 16

EPPs

MEPPs are spontaneous

Question 17

Which one, EEP or MEPP is confined to the end-plate region

Answer 17

Both!!

Question 18

Which one, EEP or MEPP has an amplitude of 1-2mV

Answer 18

MEPPs

EPPs have an amplitude of ~10mV

Question 19

Both EEPs and MEPPs can undergo summation, but which one usually leads to an AP in adjacent region of membrane

Answer 19

EPPs

Question 20

This is located on the motor endplate membrane and in the basal lamina and is involved with the breakdown of ACh

Answer 20

acetylcholinesterases

Question 21

What are the two products of ACh breakdown

Answer 21

choline and acetic acid

Question 22

Where do the acetate and choline end up after breakdown of ACh

Answer 22

acetate; circulation

choline; taken up by presynaptic terminal where in it reacts with Acetyl-CoA and then back around to ACh

Question 23

This is a plant derative that binds to AChR so ACh cannot bind; ACh will still be released, but APs will not occur

Answer 23

curare

Question 24

This blocks ACh release so skeletal muscle activation will not occur

Answer 24

botulinum toxin

Question 25

This blocks action of AChE so ACh will not be hydrolyzed; cannot activate skeletal muscle in its presence because Na channels remain in a refractory state

Answer 25

organophosphates (some, not all)