Unit:B-1A Neuromuscular Junction

Where is the cell body of a efferent neuron located?

ventral horn of spinal cord

Where is the cell body of the afferent neuron located?

dorsal root ganglion

A motor unit consists of what 2 things?

-A single spinal motor neuron

-all the fibers it innervates

(Ratios range from 1:6 to 1:2000)

What happens to a muscle as threshold is reached from an AP?

All muscle fibers innervated by the motor unit will contract simultaneously

What is an EPP?

End-plate potential

-EPSP for NMJ

What is an important characteristic of EPPs?

They always reach threshold to produce an AP

What are the two types of post-synaptic potentials?

-EPPs

-MEPPs

What is an MEPP?

Slight depolarization

-random events that are sub-threshold and occur between APs where no muscle contraction occurs

What is denervation hypersensitivity?

Can a nerve that experiences this return to normal?

-When a muscle becomes denervated the nAch Receptors will migrate to the surface all over the muscle and become hyper sensitive.

-yes it can return to normal once innervation occurs

What is fibrillation concerning a muscle and when does it usually occur?

-spontaneous twitching of a muscle

-occurs approximately 2 weeks after losing motor innervation

What are the 2 competitive inhibitor toxins we learned in class?

-curare

-alpha bungarotoxin

(Both are nAch R antagonists)

Is botulism a pre synaptic or post synaptic disorder and why?

-Pre synaptic

-it will block Ca2+ channels so the APs won't propagate

Answer the following questions on the honey clinical.

1. What percent of honey in the US contains clostridium botulinum?

2. What individuals can eating this one's affect?

3. Is this bacteria pre or post synaptic inhibiting

4. What are the 4 symptoms of this bacteria seen in affected individuals?

1. 10%

2. Children under 1 years old

3. Presynaptic. Blocks calcium entry in terminal zone

4. Weak cry, constipation, breathing problems, excessive drool

what will be the changes to the EPP and MEPP of a electrophysiologic test from a pre-synaptic disorder?

EPP: Decrease of amplitude

MEPP: remain the same

--(the MEPPs can still randomly release and the channel can still receive)

what will be the changes to the EPP and MEPP of a electrophysiologic test from a post-synaptic disorder?

EPP: Decrease of amplitude

MEPP: Decrease of amplitude

--(the MEPPs can still randomly release however the channel cannot receive them)

what type of disorder is Myasthenia Gravis?

post-synaptic, auto immune

how does Myasthenia Gravis work?

antibodies will block, alter, or destroy the receptors for ACh at the NMJ

What are Myasthenia Gravis's two major characteristics?

widening of the synaptic cleft, decreased MEPP amplitude

what drug is often given to people with Myasthenia Gravis?

Physostigmine (anticholinesterase)

what kind of associated tumor occurs with Myasthenia Gravis?

Thymoma(15%)

what age groups and gender ratio does Myasthenia Gravis affect?

-all age groups

-male:female(1:2)

(10-40/100,000)

how does Lambert-Eaton Myasthenic Syndrome(LEMS) work?

antibodies will block, alter, or destroy the Ca2+ channels at the nerve endings, leading to loss of channels.

what type of disorder is Lambert-Eaton Myasthenic Syndrome(LEMS)?

pre-synaptic, autoimmune

What are Lambert-Eaton Myasthenic Syndrome(LEMS)s two major characteristics?

condition often gets better with increased movement(post-tetanic potentiation), Normal MEPP amplitude

What is post-tetanic potentiation?

refers to the leaking of Ca2+ channels after a high train of action potentials

what kind of associated tumor occurs with Lambert-Eaton Myasthenic Syndrome(LEMS)?

Oat-cell carcinoma of lung (70%)

what kind of autonomic issues would someone present with Lambert-Eaton Myasthenic Syndrome(LEMS)?

dry mouth

what age groups and gender ratio does Lambert-Eaton Myasthenic Syndrome(LEMS) affect?

-older individuals (>55)

-male:female(10:1)

(1/100,000)

Does Lambert-Eaton Myasthenic Syndrome(LEMS) respond to anticholinesterases?

minimally