Lecture 7 9/1/23

Question 1

What are the two types of synapses?

Answer 1

-electrical synapse
-chemical synapse

Question 2

What are the characteristics of electrical synapses?

Answer 2

-in smooth and cardiac muscle
-gap junctions allow free movement of ions

Question 3

What are the characteristics of chemical synapses?

Answer 3

-majority in CNS and at NMJ
-release neurotransmitters

Question 4

What are the characteristics of innervation?

Answer 4

-one nerve can innervate multiple muscle fibers
-each muscle cell only has one neuron

Question 5

How does muscle contraction work in terms of action potentials?

Answer 5

-each muscle contraction is an all-or-nothing action potential
-the number of motor neurons firing determines the strength of the muscle contraction

Question 6

What are the synaptic vesicles?

Answer 6

packets of acetylcholine neurotransmitters

Question 7

What are the junctional folds of the post-synaptic membrane?

Answer 7

areas of increased surface area allowing for more receptors

Question 8

What is the synaptic cleft?

Answer 8

the space where acetylcholine is released between the presynaptic terminal and the muscle cell

Question 9

What type of ACh receptors are in skeletal muscle?

Answer 9

nicotinic receptors

Question 10

What is the role of Ca2+ ions in neuro-muscular junctions?

Answer 10

-voltage changes associated with APs opens voltage-gated Ca2+ channels
-Ca2+ influxes into pre-synaptic terminal
-Ca2+ triggers vesicles to release ACh

Question 11

What is the safety factor associated with NMJ?

Answer 11

-more than enough ACh and more than enough receptors
-ensures that muscle contraction occurs with every AP

Question 12

Why is it important that there is a process to stop muscle contraction?

Answer 12

we only want one muscle contraction to occur per AP

Question 13

How is muscle contraction stopped?

Answer 13

-acetylcholinesterase exists within synapse and breaks down ACh
-breakdown of ACh stops the muscle contraction
-choline is recycled for use in future APs and contractions

Question 14

What is myasthenia gravis?

Answer 14

-condition in which there are not enough available ACh receptors
-leads to exercise fatigue

Question 15

What are the two types of myasthenia gravis?

Answer 15

-immune-mediated: immune system attacks ACh receptors
-congenital: animal is not born with enough receptors

Question 16

Why is the lack of NMJ safety factor important in myasthenia gravis?

Answer 16

-safety factor typically ensures that, as amount of ACh decreases, there are still enough receptors for the remaining ACh to find
-with fewer receptors, remaining ACh struggles to find receptors and carry out AP/contraction

Question 17

Why is myasthenia gravis a dangerous condition in dogs?

Answer 17

-muscles controlling the esophagus and breathing functions are skeletal muscle in dogs
-can lead to difficulty breathing
-also results in animal not being able to properly swallow
-end result can be regurgitation, aspiration, and pneumonia

Question 18

How can immune-mediated myasthenia gravis be treated?

Answer 18

suppression of the immune system to prevent it from attacking receptors

Question 19

How can congenital myasthenia gravis be treated?

Answer 19

inhibition of acetylcholinesterase to prevent ACh breakdown

Question 20

Why does inhibition of acetylcholinesterase treat myasthenia gravis?

Answer 20

it allows for acetylcholine to exist within the synaptic cleft for an extended time, increasing the likelihood it reaches the ACh receptors

Question 21

What are the potential downfalls of acetylcholinesterase inhibition?

Answer 21

-can lead to increased weakness due to not having enough time to reset between APs
-can overstimulate parasympathetic nervous system

Question 22

How can neurotransmitters function on a cell?

Answer 22

-excitatory/cause APs
-inhibitory/prevent APs

Question 23

How do different neurotransmitters function with different ion channels?

Answer 23

-excitatory neurotransmitters will open channels that allow for influx of + ions or efflux of - ions
-inhibitory neurotransmitters will open channels that allow for influx of - ions or efflux of + ions

Question 24

What is glycine?

Answer 24

an inhibitory transmitter, especially in the spinal cord/reflexes

Question 25

What is the effect of tetanus?

Answer 25

-toxins bind irreversibly to glycine receptors
-animal has no muscle relaxation
-must wait for animal to regenerate new glycine receptors following infection