Neurons Shy Too

We all have been in a situation when we want to speak to a special person, but we shy because we feel like we don’t have enough potential to speak. In similar way, neurons too shy to speak to its special neuron because neurons feels that they don’t have enough potential. Like humans, neurons sometimes overcome their shyness and speak to special neuron but sometimes they never gather enough potential to speak.

Neuroscientist has scientific term for neurons showing this type of behavior known as Synaptic Integration.

Before we talk about the synaptic integration, we need to understand the basic functions of neuron.

(Those who have basic knowledge about the neuron and how action potential works can skip this part and can jump to the synaptic integration.)

• The inside of the neuronal membrane at rest is negatively charged in relation to the outside.
• When the neuronal membrane is at rest, the voltmeter reads a steady potential difference of about -65 mV.
• The entry of Na depolarizes the membrane.
• Axon hillock(junction between soma and axon) contain large amount of Na gated channel. An action potential begins at the axon hillock as a result of depolarization(positive change in membrane potential).
• The critical level of depolarization that must be reached in order to trigger an action potential is called threshold.
• Action potentials are caused by depolarization of the membrane beyond threshold.
• When the membrane potential is changed from -65 to -40mv, the sodium gated channels pop open.
• Action potential propagates down the axon when adjacent segment of membrane depolarized due to the influx of positive charge spreads inside the axon. In this way, the action potential works its way down the axon until it reaches the axon terminal, thereby initiating synaptic transmission.

Synaptic Integration

So, what synaptic integration do? The Initiation of action potential depend on the synaptic integration because it collects synaptic signals from different synapses present on the same neuron and it can either be inhibitory or excitatory signal.

Synaptic integration combines:-

EPSP(excitatory signal) and IPSP (inhibitory signal).

1.EPSP(Excitatory Postsynatic Potential): It causes the small amount of depolarization (remember we need many EPSPs to initiate the action potential).

EPSP summation: EPSPs add together to produce a significant postsynaptic depolarization in order to initiate action potential.

• Spatial summation is the adding together of EPSPs generated simultaneously at many different synapses on a dendrite.
• Temporal summation is the adding together of EPSPs generated at the same synapse if they occur in rapid succession.

2.IPSP(Inhibitory Postsynaptic Potential):It causes hyperpolarization(more negative change in membrane potential).

IPSP acts as an electrical shunt, preventing the current from flowing through the soma to the axon hillock. This type of inhibition is called shunting inhibition. The actual physical basis of shunting inhibition is the inward movement of negatively charged chloride ions.

In this project I explained how synaptic integration works and initiate action potential

Supplies

Thick and thin cardboard

A4 Craft papers(any 3 colors you like)

Glue

Scissor

Threads

Beads

Cutter

Step 1: Basic Structure of Neuron

1. Draw a neuron on the thick cardboard acc. to your cardboard size.
2. Take a glue and overline the neuron with a glue except the myelin sheath, put the craft paper and remove immediately so you trace down drawing on the craft paper then cut and paste it.

Step 2: Axon

1. Create a box acc. to the myelin sheath size.
2. Cover it with craft paper.
3. Stick it on the thick cardboard.
4. Make the small strips in order to cover a myelin sheath as shown in the picture.
5. Now, make a voltage gated Na channel and pass the two threads separately as shown in the picture.
6. Cut the strips for the axon terminal, cover it and give the shape according to its structure.

Step 3: Soma

1. Take a thin cardboard and cut the strips acc. to the shape of soma.
2. I cut many strips and width is around 1.2 cm. You can see the 1st picture.
3. Cover it with craft paper.
4. Give the number to each particular strip and soma portion, so you don't get confused where to stick them.
5. Make a necessary hole on the strips acc. to the position of synapse on soma.
6. At axon hillock create a voltage gated channel and pass the three threads separately at three points as shown in the picture.

Step 4: How It Works

1. Temporal Summation of EPSPs

1. Put the brown beads from single excitatory synapse.
2. Each bead represents one EPSP. When you add many beads, at one point the connection break which show threshold point
3. This starts the action potential from the axon hillock and continue down the axon end by opening of the voltage gated Na channels which transfers Na ions(dark green beads) inside the neuron

2. Spatial Summation of EPSPs

1. This show many synapses also contribute in initiating action potential.
2. Process is same except you add brown beads from two points

3. IPSPs and Shunting inhibition

1. Put the white bead from inhibitory synapse.
2. Add the brown beads from excitatory synapse you will see point do not break because of shunting(for showing this, struck the thread between the joints of soma so the point do not break).
3. This happens for very short duration of a time and after that it starts working normally until it receives any new IPSP.