L6: Neuromuscular junction Flashcards Preview

Physiology I - EXAM 1 > L6: Neuromuscular junction > Flashcards

Flashcards in L6: Neuromuscular junction Deck (20):

Does a single axon terminal have an abundance of mitochondria?



what are synaptic vesicles?

have acetylcholine and release the neuro transmitter via exocytosis


what are dense bars?

anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments


what is the synaptic gutter (tough)?

this is a groove or furrow in the surface of a sarcolemma in which the axon terminal makes contact with the sarcolemma


what is a subneural cleft?

smaller clefts or trough in the bottom of the synaptic trough


what is a synaptic cleft?

20-30nm wide/ a very narrow but real gap between the axolemma of the axon terminal and the sarcolemma of the innervated muscle fiber


Describe the structure of acetylcholine.

2 alpha proteins
1 beta protein
1 gamma protein
1 delta protein


Identify the subunits to which acetylcholine attaches.

alpha subunit


Where are vesicles for neurotransmitters formed in the neuron? How are they transported?

Formed in the golgi apparatus and carried by axonal transport to the axon terminus where they are filled with Ach


Compare concentrations of calcium ion outside the axon and inside the axoplasm.

Calcium is much greater in the intercellular = < 10^-6 M
Smaller amounts in extracellular = 1-2mM


How does calcium enter the axon during the transmission of action potential?

When action potentional arrive at terminus of axon
Voltaged gated calcium channels open
calcium enters the axon terminus


What is the number of acetylcholine molecules that attach to each ligand-gated channel?

two Ach molecules


Define: "end-plate potential"

Initiates an AP on the sarcolemma
Not all-or-none
More Eps will result in more Na Channels to open
Na causes membrane to become less negative (more positive)
If enough Na, then can cause a reaction
Can result in either a negative or positive end point (AP or not)
EP may lead to AP but not and AP itself


what is the mechanism by which acetylcholine is removed from the synaptic cleft?

Degradation into choline & acetate by acetylcholinesterase
Reuptake of choline by axon end terminal
Diffusion of Ach away from site


What is meant by excitation-contraction (electro-mechanical) coupling?

When a Neuron talks to a muscle- membrane phenomenon called Action Potential
Involves ions moving across the membrane (electrical force)
Activates sliding mechanism (mechanical force)


What drugs mimic acetylcholine but are not broken down by acetylcholinervse?

Methacholin, carbachol, and nicotine
They cause spasms


What drugs inactive acetylcholine but are not broken down by acetylcholinervse?

Neostigmine, physostigmine, and diisopropyl fluorophosphates
Cause muscle spasms


Describe effect of curare on skeletal muscle contraction.

Prevents passage of impulse from nerve ending into muscle.


Describe the underlying cause of myasthenia gravis and its effects.

Autoimmune disease
Antibodies attack acetylcholine receptors
End plate potentials are too weak to initiate opening of the voltage-gated sodium channels


Explain how neostigmine can help to alleviate the effects of myasthenia gravis.

Neostigmine can be used to inactivate acetylcholinesterase.