Hsf: Neuromuscular Junction

Front 1

What is a synapse?

Back 1

-A specialized connection between a presynaptic cells that delivers information, and a postsynaptic cell that receives it

Front 2

2 Types of Synapses

Back 2

-Electrical
-Chemical

Front 3

Electric Synapse (def)

Back 3

-Electrical current flows directly from the presynaptic cell to the postsynaptic one through large proteins called gap junctions, which form large pores connecting the two cells
-Common in invertebrates but less so in mammals

Front 4

Chemical synapses (def)

Back 4

-A presynaptic cell releases a chemical neurotransmitter that diffuses across the synaptic cleft to interact with receptors on the postsynaptic membrane

Front 5

Often, when a ________ binds to its receptor, an ____ channel is opened inducing a change in the membrane voltage of the postsynaptic cell.

Back 5

-Neurotransmitter
-Ion

Front 6

How does a cascade effect occur by a neurotransmitter?

Back 6

-The neurotransmitter released from the presynaptic cell binds to a receptor and initiates a cascade of biochemical events that alter the electrical properties of the post-synaptic cell
-Tends to act more slowly than when the transmitter directly interacts with a channel

Front 7

Neuromuscular Junction (def)

Back 7

-specialized synapse between the alpha-motoneuron and skeletal muscle fiber that it innervates

Front 8

Alpha-motoneuron (def)

Back 8

-the neuron in the spinal cord that has direct control over skeletal muscle

Front 9

2 New Ion channels that are key to the function of neuromuscular transmission

Back 9

-Voltage-Gated Ca2+ channel
-"chemically-gated", "nicotinic" acetylcholine receptor channel (AChR)

Front 10

Ca2+ channel vs Na+ Channel

Back 10

-Similar: structure and function
-Difference: Selectivity, Sensitivity to variety of drugs and chemicals

Front 11

How is an AChR channel opened?

Back 11

-By binding of a chemical

Front 12

What type of channel is AChR?

Back 12

-chemically-gated (or "ligand-gated") ion channel

Front 13

What is the AChR channel permeant to?

Back 13

-Na+ and K+ ions to a similar degree

Front 14

What is the overall purpose of the neuromuscular junction?

Back 14

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 15

Steps of Neuromuscular Transmission (8)

Back 15

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 16

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 16

-equally
-(-5mV)

Front 17

End Plate Potential (def)

Back 17

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 18

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 18

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 19

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 19

-motoneuron
-muscle fiber

Front 20

What is each muscle fiber innervated by?

Back 20

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 21

How is an AChR channel opened?

Back 21

-By binding of a chemical

Front 22

What type of channel is AChR?

Back 22

-chemically-gated (or "ligand-gated") ion channel

Front 23

What is the AChR channel permeant to?

Back 23

-Na+ and K+ ions to a similar degree

Front 24

How is an AChR channel opened?

Back 24

-By binding of a chemical

Front 25

How is an AChR channel opened?

Back 25

-By binding of a chemical

Front 26

What type of channel is AChR?

Back 26

-chemically-gated (or "ligand-gated") ion channel

Front 27

What type of channel is AChR?

Back 27

-chemically-gated (or "ligand-gated") ion channel

Front 28

What is the overall purpose of the neuromuscular junction?

Back 28

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 29

Steps of Neuromuscular Transmission (8)

Back 29

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 30

What is the AChR channel permeant to?

Back 30

-Na+ and K+ ions to a similar degree

Front 31

What is the AChR channel permeant to?

Back 31

-Na+ and K+ ions to a similar degree

Front 32

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 32

-equally
-(-5mV)

Front 33

What is the overall purpose of the neuromuscular junction?

Back 33

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 34

What is the overall purpose of the neuromuscular junction?

Back 34

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 35

End Plate Potential (def)

Back 35

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 36

Steps of Neuromuscular Transmission (8)

Back 36

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 37

Steps of Neuromuscular Transmission (8)

Back 37

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 38

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 38

-equally
-(-5mV)

Front 39

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 39

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 40

How is an AChR channel opened?

Back 40

-By binding of a chemical

Front 41

How is an AChR channel opened?

Back 41

-By binding of a chemical

Front 42

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 42

-equally
-(-5mV)

Front 43

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 43

-motoneuron
-muscle fiber

Front 44

End Plate Potential (def)

Back 44

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 45

What type of channel is AChR?

Back 45

-chemically-gated (or "ligand-gated") ion channel

Front 46

What is each muscle fiber innervated by?

Back 46

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 47

End Plate Potential (def)

Back 47

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 48

How is an AChR channel opened?

Back 48

-By binding of a chemical

Front 49

What type of channel is AChR?

Back 49

-chemically-gated (or "ligand-gated") ion channel

Front 50

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 50

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 51

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 51

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 52

What is the AChR channel permeant to?

Back 52

-Na+ and K+ ions to a similar degree

Front 53

What type of channel is AChR?

Back 53

-chemically-gated (or "ligand-gated") ion channel

Front 54

How is an AChR channel opened?

Back 54

-By binding of a chemical

Front 55

What is the AChR channel permeant to?

Back 55

-Na+ and K+ ions to a similar degree

Front 56

What is the AChR channel permeant to?

Back 56

-Na+ and K+ ions to a similar degree

Front 57

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 57

-motoneuron
-muscle fiber

Front 58

What is the overall purpose of the neuromuscular junction?

Back 58

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 59

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 59

-motoneuron
-muscle fiber

Front 60

What is the overall purpose of the neuromuscular junction?

Back 60

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 61

What type of channel is AChR?

Back 61

-chemically-gated (or "ligand-gated") ion channel

Front 62

What is the overall purpose of the neuromuscular junction?

Back 62

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 63

Steps of Neuromuscular Transmission (8)

Back 63

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 64

What is each muscle fiber innervated by?

Back 64

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 65

What is each muscle fiber innervated by?

Back 65

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 66

Steps of Neuromuscular Transmission (8)

Back 66

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 67

Steps of Neuromuscular Transmission (8)

Back 67

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 68

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 68

-equally
-(-5mV)

Front 69

What is the AChR channel permeant to?

Back 69

-Na+ and K+ ions to a similar degree

Front 70

What is the overall purpose of the neuromuscular junction?

Back 70

-To produce an action potential in the muscle fiber for every action potential in the presynaptic motoneuron
-The muscle action potential trigers muscle contraction

Front 71

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 71

-equally
-(-5mV)

Front 72

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 72

-equally
-(-5mV)

Front 73

End Plate Potential (def)

Back 73

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 74

End Plate Potential (def)

Back 74

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 75

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 75

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 76

End Plate Potential (def)

Back 76

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 77

Steps of Neuromuscular Transmission (8)

Back 77

1. Nerve action potential in presynaptic cleft
2. Depolarization opens Ca2+ channels; Ca2+ enters terminal causes vesicle fusion; ACh is released
3. ACh diffuses across synaptic cleft
4. ACh binds to receptor opens pire to Na+ and K+
5. ACh unbinds from receptor and diffuses away
6. Hydrolysis of ACh by AChEsterase
7. Choline taken up
8. Choline acetylated and packaged into vesicle

Front 78

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 78

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 79

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 79

-motoneuron
-muscle fiber

Front 80

The Na+ and K+ ions are almost _____ permeable through the ACh pore and the zero-current potential is near ____ mV.

Back 80

-equally
-(-5mV)

Front 81

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 81

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 82

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 82

-motoneuron
-muscle fiber

Front 83

End Plate Potential (def)

Back 83

-the release of ACh from the presynaptic nerve terminal opens the ACh receptor and produces a very large depolarization that approaches the zero-current potential from this pore

Front 84

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 84

-motoneuron
-muscle fiber

Front 85

What is each muscle fiber innervated by?

Back 85

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 86

Under normal conditions the End Plate Potential is always ______ than the threshold for initiation of an action potential in the skeletal muscle.

Back 86

-Larger
=1-1Synapse (every presynaptic action potential results in an action potential in the post synaptic cell (the muscle))

Front 87

What is each muscle fiber innervated by?

Back 87

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 88

What is each muscle fiber innervated by?

Back 88

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 89

The presynaptic cell of the NMJ is a ________ and the postsynaptic cell is a ______ _____.

Back 89

-motoneuron
-muscle fiber

Front 90

What is each muscle fiber innervated by?

Back 90

-A single motoneuron through one end-plate complex containing NMJ end-plates

Front 91

What is a motor unit?

Back 91

-Motor neuron and the innervated muscle fibers

Front 92

Muscles used in fine motor functions have ____ innervation ratios permitting _____ control of the muscle contraction.

Back 92

-Lower
-Precise

Front 93

Large muscles that provide forceful but ________ contractions have ____ innervation ratios.

Back 93

-Unprecise
-Higher

Front 94

Neuromuscular Blocking Drugs (def)

Back 94

-Suppress neuromuscular transmission by comptetively inhibiting the binding of ACh with the postsynaptic receptor

Front 95

How can the effect of neuromuscular blocking drugs be reversed?

Back 95

-By using drugs that inhibit ACh esterase (anti-cholinesterase) elevating ACh cleft concentrations to competitively inhibit the binding of the blocking drug from the ACh receptor

Front 96

Myasthenia Gravis (def)

Back 96

-A neuromuscular disease in which the body makes antibodies to the ACh receptor

Front 97

Treatment for myasthenia gravis; how is this done?

Back 97

-Anti-cholinesterase drugs to elevate ACh cleft concentration such that those receptors not blocked by antibody are more likely to bind ACh

Front 98

Many insecticides and nerve gas act on _______ synapses like the neuromuscular junction.

Back 98

-Cholinergic

Front 99

What do insecticides and nerve gasses do to the neuromuscular junction?

Back 99

-Disrupt neurotransmission by covalently binding to cholinesterases causing ACh to pathologically linger in the synaptic cleft

Front 100

Insecticides and Nerve Gasses: Low doses? Higher doses?

Back 100

-Low dose: spontaneous, asynchrounous excitation and fibrillation occurs
-High dose: chronic depolariztion of the muscel of the muscle end plate membrane in activates Na+ channels and abolishes action potential activity