Part Five: The Neuro-Muscular Junction or Synapse Flashcards Preview

A&P I Muscular System Review > Part Five: The Neuro-Muscular Junction or Synapse > Flashcards

Flashcards in Part Five: The Neuro-Muscular Junction or Synapse Deck (13)
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The entire structure “A” represents the knobby end of a nerve cell. 
What TWO names is this structure known as?


A= presynaptic terminal or synaptic knob (part of nerve cell)


The entire structure "I" represents the surface of a muscle cell.
What is it called?

I= postsynaptic terminal (part of the sarcolemma, or covering of 
the muscle cell)



What is "G" called?

G= synaptic cleft or gap (small space between nerve & muscle)


What is substance “C,” the neurotransmitter released by the nerve 
cell's presynaptic vesicles ("D")?


C= acetylcholine (ACh)


What must happen first in the nerve cell to allow “C” to be released?
(Hint: See “B.”)


Calcium enters the synaptic knob of the nerve through the calcium 
channels (B), which is what triggers the release of the ACh.


Substance “C” binds to a specific receptor (“E"), causing it to open. 
What substance, shown at “F,” enters the muscle cell through this 

The ACh receptor is a sodium (Na+) channel that allows sodium to 
enter the muscle.



Once substance “F” enters the muscle cell, what has been started
 in the muscle cell?

Once sodium has entered the muscle, an action potential 
(electrical current) has now been started that flows into the muscle and causes it to contract.


What happens if substance “C” remains in the synaptic cleft for too 


If ACh remains in the synapse for too long, action potentials 
will continue to be made, causing a constant contraction in the 
muscle (spastic paralysis).



What enzyme, shown at "H," prevents substance “C” from remaining in 
 the synapse for too long?


The enzyme Cholinesterase (AChE) breaks apart ACh as soon as it 
is used and sends the pieces of ACh back to the presynaptic 
terminal where they are reused to make more ACh. 


What two types of poisons prevent enzyme "H" from working? What 
is the result in the muscle?


Insecticides and military nerve gases kill by preventing AChE 
(the enzyme) from breaking apart ACh quickly enough. The result 
is that ACh stays in the synapse, causing spastic paralysis of 
the muscle. The muscle is “stuck” in a contraction and cannot 


What specific part of the synapse (choose from A-I) is affected by
the poison curare and in the disease Myasthenia Gravis? 

Both the poison curare and the disease Myasthenia Gravis affect 
E, the acetylcholine receptor.



With curare poisoning and with Myasthenia Gravis, what type of 
paralysis results?


Flaccid paralysis results. The muscle cannot contract. 


Explain exactly what happens in the synapse with Myasthenia Gravis 
and with curare poisoning.

In Myasthenia Gravis, white blood cells slowly destroy the ACh 
receptors over time. Curare binds to ACh receptors and causes 
them to close. The result in both situations is that, with the 
ACh receptors impaired, no sodium can enter the muscle cells and 
thus no electrical currents (action potentials) can be started in 
the muscle. The muscle is then unable to contract.