Synapse and Action Potentials

Question 1

What are the different kinds of synapses

Answer 1

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

Question 2

What are the 2 kinds of synapses

Answer 2

Electrical and chemical, the latter one being the most common

Question 3

Proteins associated with vesicles fusion

What class of proteins are they

Answer 3

Synaptotagmin and synaptobrevin - SNARE proteins class

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

Question 4

How does the neurotransmitter vesicles fuse

Answer 4

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

Question 5

What does toxins do

Answer 5

Tetanus and other toxins cleave these snare proteins

Question 6

What is the mechanism in electrical synapses

Answer 6

Operate through gap junctions

Question 7

Structure of a gap junction

Answer 7

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

Question 8

Why doesn’t cells use electrical synapse

Answer 8

The signal fades with distance

Question 9

What is Mysthenia Gravis

Answer 9

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

Question 10

Lambert Eaton Syndrome

Answer 10

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

Question 11

What are the two types of neuron signals

Answer 11

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

Question 12

What are the excitory and inhibitory neurotransmitters

Answer 12

GABA and Glycine are inhibitory

Acetyle choline, Dopamine and Glutmate are both

Question 13

How does the same neurotransmitter can cause inhibitory and excitory signals

Answer 13

By binding to different receptors

Question 14

How does psychoactive drugs perform

Answer 14

By mimicing the neurotransmitters strucutre and administering them externally

Question 15

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

Answer 15

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)

Question 16

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

Answer 16

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.

Question 17

Why doesn’t the action potential travel backwards mathematically

Answer 17

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

Question 18

What is MS disease

Answer 18

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