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Foundations Part II > Synapse and Action Potentials > Flashcards

Flashcards in Synapse and Action Potentials Deck (18)

What are the different kinds of synapses

There are 3 kinds of synapses:

1. Axosomatic synapses: Axons making synapses with the cell body

2. Axodendritic synapses: with dendrites, sometimes these are formed with dendiritic spines which are protruding dendrites

3. Axo-axonic synapses: with the axon


What are the 2 kinds of synapses

Electrical and chemical, the latter one being the most common


Proteins associated with vesicles fusion

What class of proteins are they

Synaptotagmin and synaptobrevin - SNARE proteins class

Synataxin and SNAP are at the plasma membrane at the pre synaptic cleft


How does the neurotransmitter vesicles fuse

As the action potential reaches the pre synaptic cleft, there is an influx of Ca ions inside the axon. This causes the Ca to bind with proteins called Synaptotagmin and Synaptobrevin. This causes a conformational change in these proteins which leads to the fusion of these vesicles and the release of neurotransmitter


What does toxins do

Tetanus and other toxins cleave these snare proteins


What is the mechanism in electrical synapses

Operate through gap junctions


Structure of a gap junction

6 connexins combine to form a pore, 2 of these pore form a gap junction


Why doesn't cells use electrical synapse

The signal fades with distance


What is Mysthenia Gravis

Autoantibodies to the receptors for acetyl choline, muscle function goes down


Lambert Eaton Syndrome

Reduction in neurotransmitter since antibodies are created towards voltage gated calcium channels


What are the two types of neuron signals

Excitatory and inhibitory, there are actually inhibitory neurons in the body


What are the excitory and inhibitory neurotransmitters

GABA and Glycine are inhibitory

Acetyle choline, Dopamine and Glutmate are both


How does the same neurotransmitter can cause inhibitory and excitory signals

By binding to different receptors


How does psychoactive drugs perform

By mimicing the neurotransmitters strucutre and administering them externally


There is a well know fact that there are K channels that are open. Then why doesnt the K ions flow out of the cell through facilitated diffusion with the help of these channels

Due to the Na-K pum, there are 3 Na pushed out for every 2 K taken in by the cell. That makes the cell negatively charged from the inside whereas the outer membrane is positively charged.

This causes an electrochemical gradient to set up which is in fine equilibrium with the chemical gradient. Thats why K channels do not flow out (there are more K inside but the outside is positively charged)


How does the action potential travel along in one direction in the axon

When an action potential reaches a part of the axon it causes the opening of the Na channels. When these channels open, Na rushes in to the axon segment, the elctrochemical gradient is less downstream than up stream so these Na ions move downstream due to diffusion due to chemical and electrical gradient. This downstream movement of the Na causes further downstream Na channels to open up, so the signal keeps travelling downstream

The signal doesn't travel backwards as there are K channels that open up, causing loss of K and puts that part of the axon segment in refractory period.


Why doesn't the action potential travel backwards mathematically

The excitatory potential does travel backward, as it can since the lumen is continuous and excess Na can travel either way. This is Excitatory Post Synaptic Potential (EPSP). Causes the an excitation to about -55V

However there is an Inhibitory Post Synaptic Potential (IPSP) which is due to the opening of K channels. This causes the cell to hyperpolarize, dropping the potential to -70V.

When you combine these two IPSP and EPSP you dont cross the membrane threshold potential


What is MS disease

It is a disease of the CNS, mainly affects young adults. It is an autoimmune disease.

Nerve cells are demyelinated by the T cells. Symptoms include impair function of the nervous system