Neuromuscular Junction - Smith

Question 1

How does the nervous system communicate with muscle?

Answer 1

via nueromuscular junctions

Question 2

Are NM junctions and synapses similar in structure/function?

Answer 2

Yes

Question 3

What ion diffuses across the muscle cell membrane to generate an action potential?

Answer 3

Na

Question 4

Are motor end plates directly on muscle fibers?

Answer 4

yes

Question 5

What does Sherington’s Law describe about the relationship of flexor/extensor muscles in a reflex arc?

Answer 5

when one set of muscles is activated, the opposing set is inhibited

Question 6

Describe the process of events that occur when a reflex is triggered?

Answer 6

1. Hammer hits knee, stretching tendon and sensory fibers in the tendon
   2 A. Sensory neurons synapses/excites motor neuron in the spinal cord
   2 B. Sensory neuron synapes with spinal interneuron, which activates an inhibitory neuron to flexor muscles
2. Motor neurons cause extensor contraction
   3B. flexor muscles relax due to inhibition

Question 7

Describe the shape of the action potential from a sensory neuron

Answer 7

Sharp, tall, positive depolarizing peak

Question 8

Describe the shape of the action potential from an internueron?

Answer 8

sharpt, tall, positive depolarizing peak

Question 9

Describe the shape of the action potential from an EPSP (extensor muscle in reflex)?

Answer 9

Long, broad, positive depolarizing peak

Question 10

Describe the shape of the action potential from an IPSP (flexor muscle in reflex)?

Answer 10

long, broad NEGATIVE, HYPERPOLARIZING peak

Question 11

what do Renshaw cells do?

Answer 11

they are inhibitory interneurons

Question 12

Where are Renshaw cells found?

Answer 12

gray matter of spinal cord

Question 13

What cells does Clostridium tetani act on?

Answer 13

Renshaw cells

Question 14

What is the cause of death from strychnine?

Answer 14

Muscular convulsions leading to asphyxia via sheer exhaustion

Question 15

How do Renshaw cells alter AP’s to cause inhibition?

Answer 15

Renshaw cells are interneurons, so when one neuron fires an AP, the Renshaw cell will fiber numerous AP’s in succession, releasing a TON of glycine and inhibiting the other motor neurons.

Question 16

Where are the cell bodies of motor neurons located?

Answer 16

Brainstem or spinal cord

Question 17

What are the parts of a motor unit?

Answer 17

1. Motor neuron

2. All the muscle fibers it innervates

Question 18

T/F? The motor neurons axons are myelinated and large in diameter.

Answer 18

TRUE

Question 19

T/F? Once an alpha motor neuron is activated to produce an action potential, all of the fibers innervated by this neuron are activated and contract simultaneously.

Answer 19

TRUE

Question 20

T/F? Each motor unit is made up of one type of muscle fibers: i.e., slow twitch, fast-twitch fatigable or fast-twitch fatigue resistant.

Answer 20

TRUE

Question 21

What is the EPSP equivalent for the motor end plate?

Answer 21

End Plate Potential (EPP)

Question 22

When does a motor end plate generate an AP?

Answer 22

When it reaches threshold.

Question 23

Do the EPP and AP work by the same mechanisms?

Answer 23

NO

Question 24

does the motor end plate, once stimulated, always fire an action potential?

Answer 24

YES

Question 25

Is there a summative mechanism in motor end plates to generate an action potential?

Answer 25

No, it's either all or none

Question 26

Is EPP always supra-threshold?

Answer 26

YES

Question 27

What is the effect of curare on EPP with respect to its threshold?

Answer 27

It takes the EPP from suprathreshold (firing an AP) to sub threshold (no AP and therefore no muscle contraction)

Question 28

Where does curare act at the nueromuscular junction?

Answer 28

ACh receptors in the muscle membrane

Question 29

What ions flow and in which directions do they flow at the neuromuscular junction?

Answer 29

Na into muscle | K out of muscle

Question 30

A subthreshold EPP is identical to a (blank)

Answer 30

spontaneous MEPP (miniature end plate potential)

Question 31

The single quanta which causes the MEPP is equivalent to the release of one (blank)

Answer 31

ACh vesicle

Question 32

The release of numerous ACh vesicles from the neuron causes (blank) at the muscle

Answer 32

EPP

Question 33

What is the "safety factor" of the neuromuscular junction?

Answer 33

the AP created by the neuron is always sufficient to create a EPP and muscle contraction

Question 34

What kind of receptor does ACh bind to on the muscle cell?

Answer 34

Nicotinic

Question 35

What does ACh esterase break down ACh into?

Answer 35

Acetate and choline

Question 36

What is the fate of the acetate from ACh

Answer 36

broken down in the blood

Question 37

what is the fate of the choline from ACh?

Answer 37

it is recycled into the neuron

Question 38

Are MEPPs calcium dependent?

Answer 38

NO

Question 39

Is the EPP calcium dependent

Answer 39

yes!

Question 40

What is the effect of AChE blocking drugs (prostigmine)?

Answer 40

They increase the amplitude and duration of the EPPs

Question 41

Do AChE blockers (prostigmine) alter MEPP frequency? What does this indicate about the way MEPP's work?

Answer 41

NO. it means each MEPP is due to a QUANTAL PACKET (vesicular release) of ACh.

Question 42

Describe the five steps of transmission across the NMJ?

Answer 42

1. An action potential arrives at the end of a motor neurone, at the neuromuscular junction. 2. Depolarization causes Ca2+ entry into nerve terminal and vesicle mobilization. 3. This causes the release of the neurotransmitter acetylcholine. 4. Acetycholine diffuses across synaptic cleft and binds to nicotinic receptor on sarcolemma. 5. Activation of nicotinic receptors generates EPP.

Question 43

The AP is carried into the muscle by invaginations in the cell membrane called (blank)

Answer 43

T-tubules

Question 44

The action potential causes depolarization of T-tubule membrane that opens (blank) receptor on the sarcoplasmic reticulum.

Answer 44

ryanodine

Question 45

Activation of ryanodine receptors leads to the store release of (blank) ions into the myofibrils.

Answer 45

calcium

Question 46

Ca2+ causes (blank) to be displaced uncovering myosin binding sites on actin.

Answer 46

tropomyosin

Question 47

(blank) cross bridges can now attach and the cross bridge cycle can take place.

Answer 47

myosin

Question 48

(blank) ion based action potential depolarizes T-tubule membranes

Answer 48

Na

Question 49

Ca channels, aka (blank) receptors, are stimulated by the Na depolarization to change ryanodine receptor confirmation

Answer 49

dihydropyridine

Question 50

ryanodine receptors release calcium from what structure?

Answer 50

sarcoplasmic reticulum or ER

Question 51

Ryanodine receptors are concentrated in what tissue type?

Answer 51

Skeletal muscle

Question 52

T-tubules transmit signals from the sarcolemma to the (blank)

Answer 52

sarcoplasmic reticulum

Question 53

organophosphates act by blocking what enzyme?

Answer 53

ACh esterase

Question 54

What is the acronym to remember organophosphate poisoning?

Answer 54

SLUDGE: salivation, lacrimation, defecation, urination, GI upset, emesis

Question 55

Bungarotoxin from cobra venom causes paralysis how?

Answer 55

by IRREVERSIBLY binding to ACh receptors in muscle, causing paralysis and death

Question 56

What other ion actively competes with Ca at the NMJ?

Answer 56

Mg

Question 57

How does black widow toxin lead to paralysis?

Answer 57

By causing a massive release and subsequent depletion of ACh

Question 58

Botulinum toxin and tetanus prevent the release of (blank)

Answer 58

quanta

Question 59

In Lambert-Eaton syndrome, antibodies bind to the (blank) on the presynaptic terminal?

Answer 59

calcium channels

Question 60

Are the amplitudes of EPPs changed in Lambert Eaton syndrome?

Answer 60

Yes, they are reduced

Question 61

Are the amplitudes of MEPPs changed in Lambert Eaton syndrome? What does this tell us about the role of MEPPs with regard to presynaptic calcium?

Answer 61

NO, they are normal! MEPP are NOT DEPENDENT on calcium!

Question 62

Myasthenia gravis effects what part of the NMJ?

Answer 62

the muscle nicotinic receptors

Question 63

After repetitive nerve stimulation, Myasthenia gravis patients show increased (blank)

Answer 63

fatigue and decreased signal amplitude

Question 64

Are the MEPPs the same between normal people and people with myasthenia gravis?

Answer 64

No, pt's with MG have smaller MEPPs.

Question 65

Vesicle synaptic proteins bind the vesicle the pre or post synaptic membrane?

Answer 65

PREsynaptic!

Question 66

Botulinum toxin acts on what proteins?

Answer 66

Cleaves vesicle synaptic proteins

Question 67

What is the effect of botulinum toxin on nerve signaling?

Answer 67

It reduces the release of ACh

Question 68

(blank) has also been associated with clean wounds, surgical procedures, insect bites, dental infections, and intravenous drug use.

Answer 68

Tetanus

Question 69

Tetanus prevents release of (blank) from Renshaw cells

Answer 69

glycine! and GABA

Question 70

The type of paralysis caused by tetanus is flaccid or spastic?

Answer 70

Spastic

Question 71

the type of paralysis caused by botulinum is flaccid or spastic?

Answer 71

Flaccid

Question 72

What are the three proteins botulinum cleaves?

Answer 72

1. Synaptobrevin 2. syntaxin 3. SNAP-25

Question 73

What protein does tetanus cleave?

Answer 73

synaptobrevin