Exam 2 - Lecture 25 (Neuromuscular Junction)

Question 1

What do somatic motor neurons innervate?

Answer 1

skeletal muscle

Question 2

Why are multipolar neurons named so?

Answer 2

They have many dendrites that shoot out of the cell body

Question 3

What is a motor unit?

Answer 3

Functional unit of somatic motor system, made of a single motor neuron and all the muscle it innervates

Question 4

The _____ the # of motor units involved, the more forceful the contraction is.

Answer 4

greater

Question 5

What is present at the terminal end of a motor axon?

Answer 5

Motor end plate with many nerve endings

Question 6

What are the components of a neuromuscular junction?

Answer 6

Motor end plate + junctional fold of sarcolemma

Question 7

What NTM is present in NMJs?

Answer 7

ACh

Question 8

What is the postsyn. receptor in NMJs?

Answer 8

AChR

Question 9

What is found at the periphery of the nerve ending at the NMJ?

Answer 9

Schwann cell

Question 10

What are the 5 steps of neuromuscular transmission?

Answer 10

1. AP opens VG Ca2+ channels
2. Synaptic vesicles release ACh by exocytosis
3. ACh binds to AChR; opens ligand-gated channels for Na+
4. Na+ influx and membrane depolarization occur
5. VG Na+ and K+ channels open when membrane voltage > threshold voltage of muscle cell
6. APs of sarcolemma

Question 11

What is the postsyn. site in a NMJ?

Answer 11

Sarcolemma

Question 12

What are 2 deficits of the NMJ?

Answer 12

1. Tic paralysis

2. Myasthenia gravis

Question 13

What type of NMJ deficit is tick paralysis?

Answer 13

presynaptic deficit

Question 14

What type of NMK deficit is Myasthenia gravis?

Answer 14

Postsyn. deficit

Question 15

What happens in tick paralysis?

Answer 15

NTX secreted by feeding female wood tick interferes with release of ACh

Question 16

What are the symptoms of tick paralysis?

Answer 16

Generalized muscle weakness

Question 17

When do clinical signs of tick paralysis show?

Answer 17

7-9 days after attachment of ticks

Question 18

When does recovery from tick paralysis occur?

Answer 18

1-3 days after removal of ticks

Question 19

What is the pain sensation of the body during tick paralysis and why?

Answer 19

Normal because disease acts on motor neuron, not sensory (pain is still present).

Question 20

What happens in myasthenia gravis?

Answer 20

Autoimmune disease where Ab’s block, alter, or destroy AChR, decreasing the number of available receptors

Question 21

What are the consequences of myasthenia gravis?

Answer 21

Progressive loss of muscle strength, exercise-induced motor weakness that improves following rest

Question 22

What drug is used to treat myasthenia gravis and how does it work?

Answer 22

Anti-ACh-esterase; prevents ACh esterase from degrading AChR so that more of them are available for attachment of ACh.