CTCS Quiz 3 Flashcards
How does rate compare to diameter of axon?
Larger axon = faster rate
How does diameter of an axon affect charge?
Larger the charge, the less resistance.
To double the velocity, how must the diameter change?
4x
What does myelin do?
It reduces number of sites needed for depolarization. So it leads to larger spacing from node to node.
How is the threshold different during relative refractory period?
The threshold is higher.
When can an action potential not be fired?
During absolute refractory period.
What makes acetylcholine, and what happens to it after it is degraded?
Acteyl CoA + Cholin > choline acetyltransferase > Acetylocholine
Acetylocholine > acetylicholinesterase > Acetic Acid and Choline
What is the membrane resting potential of a muscle cell?
-90mV
What causes the EPP?
ACh is released on cholinergic receptors in the muscle.
What type of receptors does ACh bind to?
Nicotinic Cholinergic
Where does the EPP happen? Close to or far away from the motor neuron?
Close to it.
How many proteins make up the ACh receptor? Each subunit has how many transmembrane sections?
- 4.
What accounts for the ACh receptor’s selectivity? What makes this region?
Three rings of negative charge, arising from asp, glu and gln. Gln is neutral.
What happens to the ACh receptor after it catches an ACh?
It flickers. Probably about 3 times in 1 or 2 ms.
What is the resting membrane potential of a cell?
-70mV
What causes the membrane potential difference?
It is caused by the fact that the membrane is highly permeable to K+ than it is to Na+. It is not base on the stoichiometry of the Na/K pump.
Explain the role of Ca++ in an EPP.
The AP gets to the end of the neuron, it opens Ca++ gates, Ca++ goes into the neuron and causes ACh to be exocytosed out of the cell.
What are the 7 steps of an EPP?
- an APP propagates down a motor neuron to the end plate.
- voltage gated Ca++ channels open and Ca++ goes into the neuron.
- Ca++ causes vesicles to exocytose ACh.
- ACh binds to receptors (2 ACh per recptor) which contain ligand gated channels.
- the channels open.
- Na+ ions enter muslce, and K+ leaves the muscle. the Na+ influx is greater causing the membrane potential to depolarize.
- once membrane potential reaches a threshold, the AP propagates along the muscle.
What breaks down ACh in the synapse?
Acetylcholinesterase (AChE) which breaks it down into acetic acid and choline. Choline goes back into the neuron terminal and is made back into ACh.
What are 5 differences between the CNS and NMJ synapses?
- CNS PSPs are much smaller and almost always require summation.
- NMJ receives a signal from only one synapse. CNS uses many.
- NMJ always uses ACh. CNS can use many neurotransmitters.
- Different PS cation channels have different selectivities.
- CNS synapse is often variable, helping to produce the plasticity. The NMJ is almost always a 1:1 ration of AP and muscle contraction.
What is a fundamental concept to make the neuromuscular junction work?
Amplification. 2 ACh molecules start a cascade that invites 50,000 net + charges into the cell in 1-2 ms.
What is a competitive block for ACh? What effect does it have?
It binds to the ACh receptor but does nothing. The effect is that it lowers the EPP amplitude.
How does one desensitize the ACh receptor?
Some agonists bind to the ACh receptor, alter the conformation and prevent them from opening. These substances cannot be hydrolized by normal means.
What is a partial ACh block?
An agonist that binds, but does not fully allow or prevent the EPP from happening.
