Neuronal Communication -EPSP & IPSP

Neurons communicate using both electrical and chemical signals. Sensory stimuli are converted to electrical signals.

1. Topic- EPSP and IPSP Online Classes Course Biomedical Instrumentation Presented by Mr. Gaurav Pandey

2. Two Neurons

3. Polaried State Depolarization Repolarization Hyperpolarization Cell membrane in polarised state which means the inside of the cell is negatively charged due to high concentration of proteins and inorganic anions (phosphate, sulphates), and the outside is positively charged due to high concentration of sodium ions. When a cell is stimulated the permeability of its membrane increases so sodium ions will get inside and inside becomes positive the amplitude will slowly increases until it reaches a threshold point. The voltage gated sodium channels will open and the sodium inside will increase rapidly this will lead to reversal polarity. When the cell is no longer stimulated and the amplitude reaches a certain point the voltage gated sodium channels will close and the membrane will be permeable to potassium ions to get outside the cell (potassium efflux) which will lead to more positive ions outside again and more negative ions inside. This ia   repolarization . Hyperpolarization  is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization. It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.

4. Neurons communicate with each other by their dendrites and Axon terminal. Incoming signals are received at dendrites terminals. Outgoing Signals travels along axon to the axon nerve terminal. To achieve fast communication over its long axon, the neuron sends Electrical Signals from the cell body to the nerve terminal, along the axon, known as nerve impulses or action potentials . Nerve Impulses

5. Action potential is brief reversal of electrical polarity across the cell membrane . 6. Cells are polarized, meaning there is no electrical voltage across the cell membrane . 7. In resting phase of neuron, the typical voltage known as the resting membrane potential is about -70 mV, the negative value means cell is more negative on the inside. 8. At this resting state, there are concentration gradients of sodium and potassium across the cell membrane. 9. More sodium outside the cell and the more potassium inside the cell and maintained by sodium potassium pump.

6. 1. Action Potential reaches the nerve terminal and depoalrizes it. The Depolarization open the Ca 2+ channels, enabling the Ca 2+ to enter the nerve terminal. Increase in intracellular Ca 2+ concentration is signal whereby release of neurotransmitter by vesicles by exocytosis . This produces high concentration of neuro transmitter in synaptic cleft. The released neurotransmitter briefly binds the the receptors of the postsynaptic neuron. Important Steps – Neuronal Communication

7. 6. After the activation of receptors, transmitter must be inactivated quickly. 7. Inactivation occurs partly by diffusion of the transmitter partly by enzymatic degradation and partly by transporter protein . 8. There are two types of Receptors Ionotropic - Fast and Precise. Metabotropic - Slow and long lasting. 9. The change in membrane potential arises as a change in synaptic influence is called as synaptic potential.

8. Synaptic potential and the type of Synapses: EPSP & IPSP 1. An excitatory postsynaptic potentials (EPSP) is a temporary depolarization of postsynaptic membrane caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand -sensitive channels . An EPSP is received when an excitatory presynaptic cell, connected to the dendrite, fires an action potential . The EPSP increases the neurons membrane potential. When the membrane potential reaches threshold the cell will produce an action potential and send the information down the axon to communicate with postsynaptic cells. EPSP

9. An inhibitory postsynaptic potentials (IPSP) is a temporary hyperpolarization of postsynaptic membrane caused by the flow of negatively charged ions into the postsynaptic cell. An IPSP is received when an inhibitory presynaptic cell, connected to the dendrite, fires an action potential. The IPSP signal is propagated down the dendrite and is summed with other inputs at the axon hilllock . 3. The IPSP decreases the neurons membrane potential and makes more unlikely for an action potential to occur. A postsynaptic cell typically has less inhibitory connections but the connections are closer to the soma . IPSP