Neurons Flashcards
What is Playtoxin?
A toxin found in marine animals, which binds and locks the Na/k toxin in a way that causes it to allow passive diffusion of ions. Kills the gradient. Extremely toxic
What do Digoxin and Ouabain do?
Bind and inhibit Na/k ATPase in the heart and increase contracibility
What creates the membrane potential across neurons?
Leaky K + channels, also sometimes known as background channels, because they are always open
What maintains the membrane potential of a cell?
The na/k ATPase pump
What are isoflurane and halothane
They are general anesthetic gases that activate leaky potassium channels, making neurons less excitable
What is the name of the potassium leak channels that set the resting potential in Cardiac Myocytes?
Inward Rectifier Potassium Channels
Example of ligand gated voltage channel?
Neurotransmitter binding at synapse
Example of Phosphorylation mediated ion channel?
Leaky potassium channels
Example of voltage gated ion channel?
Voltage gated Na+ channel
VG K+ channel
VG Ca 2+ channel
What are the 3 factors that cause K+ channels to open slightly slower than Na+ channels?
- Na+ channels activate more quickly
- Na+ channels activate a positive feedback loop, while K+ channels activate a negative feedback loop
- The K+ channel’s V1/2 occurs at a more depolarized potential than Na+ channel.
What is the speed of activation and deactivation in vNa+?
Fast activation and Fast deactivation
What is the speed of activation and deactivation in vK+?
Activates slowly, and stays open for longer
What are the three states of a vNa+ channel?
Closed, Inactive, Open
What’s the difference between the closed and inactive state of vNa+?
The inactive state is not competent to open even due to depolarization. The closed state can be induced to open due to depolarization.
What is the absolute refractory period?
The absolute refractory period is period where regardless of the stimulus, an action potential cannot be fired. This is due to the vNa+ being in the inactivate form.
What is the relative refractory period?
This is a period where an action potential can be fired, however, the stimulus must be larger than normal, because at this point the membrane potential is more negative than the resting potential (hyperpolarization) due to the vK+ channels being opened for a long time.
What is orthodromic?
Means that the action potential moves from the axon hillock to the terminal synapse. In normal neurons.
What is antidromic?
An experimental condition where the action potential moves from the terminal synapse to the axon hillock.
What is Accomodation?
it occurs when there is a prolonged depolarization. It makes it so that the threshold for depolarization is higher. This is due to inactivated vNa+ channels
What are Lidocaine and Procaine, and what is their mechanism of action?
They are local anesthetics which function by blocking vNa+ channels
What are Phenytoin and Carbamazepine, and what is their mechanism of action?
They are antiepilepletical/anticonvulsatory drugs which inhibit vNa+ channels
What is Dofetilide, and what is its mechanism of action?
It is an antiarythmic agent, which functions by blocking delayed rectifer vK+ channels
What are Tetrodotoxin and Saxitoxin, and what is their mechanism of action?
They are natural toxins which are paralytic. They inhibit sodium channels. Saxitoxin is found in certain shellfish, and sometimes administered in proper dosages by sushi chefs to give a tingle
What is propofol?
It is a general anesthetic which functions by blocking vNa+ channels as well as GABA
What are the two ways to get channelopathies?
Genetic or acquired
What are periodic paralysis?
Periodic paralysis is a group of rare genetic diseases that lead to weakness or paralysis. The underlying mechanism of these diseases are malfunctions in the ion channels in skeletal muscle cell membranes that allow electrically charged ions to leak in or out of the muscle cell, causing the cell to depolarize and become unable to move, because action potentials can’t be generated. Could lead to myotonia, which is uncontrolled contraction of muscle
What is Myotonia?
It is the inability to relax your muscle. Myotonia often diminishes with the repeated contractions. It doesn’t affect strength.
What is the characteristic EMG abnormality of myotonia?
The EMG has a characteristic abnormality known as the myotonic run, which consists of repetitive discharges that persist for several seconds after a voluntary contraction
What does myotonia sound like on a speaker?
like a chainsaw revving up.
What is the defected channel in hyperkelemic periodic paralysis and paramyotonia congenita? What type of inheritance is it?
Defect in the Nav 1.4 channel. Dominant inheritance.
Where is vNa1.4 expressed?
In skeletal muscle
which synapse is bidirectional? Which is one-directional?
Electrical synapse is bidirectional, chemical synapse is one directional
Which occurs faster: electrical or chemical synapse?
Electrical. it has no delay
An electrical synapse is connected by gap junctions. What is a gap junction made up of?
It is made up of two hemmicahnnels that connect
What is a hemmichannel made up of?
A hemmichannel is made up of 6 connexins
What are two disease associated with defective gap junctions?
- Charcot Marie Tooth Syndrome
2. Metestatic Cancer. Gap junctions function in holding the cells together.
How would you describe electrical synapse transmission?
It is graded, so even when the threshold isn’t reached, the signal is transmitted to the post synaptic cell.
What organ has a large distribution of gap junctions, that are integral to its function?
The heart. Gap junctions are necessary to transmit signals causing the cells to contract in tandem.
Do muscles contain excitatory or inhibitory neurotransmitters or both?
Just excitatory
Is Acetylcholine excitatory, inhibitory, or both?
It is both. It is seen as excitatory in the nicotinic receptor, which is in muscles. And it is excitatory/inhibitory in muscorinic receptors.
What is GABA derived from?
Glutamate
What are the principle inhibitory neurotransmitters in the nervous sytem?
GABA and Glycine
What is the principle excitatory neurotransmitter in the nervous system?
Glutamate
What are the 3 Glutamate receptors that trigger cation channels?
AMPA
NMDA
Kainate