6 Steps of Neural Communication
Neurons communicate with each other at structures called synapses. The green pre-synaptic neuron in the figure above is making a connection with the blue postsynaptic neuron. When an action potential arrives at the synapse, pores open up in the presynaptic cell membrane and the neurotransmitter vesicles release their contents.
The chemical signal travels across the synapse, where it binds to receptor proteins on the postsynaptic neuron. This alters its function, either excitatory or inhibitory.
1. Electrical Communication
Neurons are the basic information processing structures in the brain. They are specialized cells that can receive INPUT from other neurons (at synapses), process the input, and send OUTPUT to other neurons (via chemical or electrical transmission at synapses).
A neuron has dendrites and a single long fiber called an axon that extends from its cell body. The axon is insulated by a sheath of cells called myelin.
The electrical signal called an action potential runs from the dendrites to the axon terminals via a mechanism called conduction. Its arrival at the axon terminals allows neurotransmitter molecules to bind to receptor cells and initiate the release of other ions that increase or decrease the likelihood that a neuron will fire an impulse.
2. Chemical Communication
The nervous system is the body’s way of receiving, transmitting, integrating and responding to stimuli. These stimuli are received from the outside world, internal organs or by sensory receptors in your skin, eyes and ear.
Neurons communicate with each other using chemical signals, or neurotransmitters, that are passed through special connections called synapses. There are two main types of synapse: the chemical synapse and the electrical synapse.
Each neuron has a cell body (or soma), which acts as its metabolic “control center” and protein-manufacturing plant. Signals from other neurons come into the cell body through dendrites and outgoing signals flow along axons. A synapse is where these two paths meet.
Neurons are like adding machines that constantly sum up all the excitatory and inhibitory synaptic input in time (temporal summation) and space (spatial summation). If the sum is above a certain threshold for firing, an action potential will be initiated.
When an action potential reaches the presynaptic terminal, it opens voltage-gated calcium channels and causes synaptic vesicles to fuse with the inner surface of the presynaptic membrane and release their neurotransmitter contents through a process called exocytosis.
The released transmitter diffuses across the gap between the presynaptic terminal and the postsynaptic dendrite or cell body and binds to receptors. This binding changes the permeability of ion channels in the postsynaptic cell.
Inhibition is the ability to suppress or countermand a prepotent response. Psychologists typically study inhibition using a set of carefully designed tasks such as the color Stroop or Go/No-Go task that measure a subject’s ability to inhibit their responses to stimuli.
Inhibition takes place at a cellular level, where the neurotransmitter released by the green presynaptic neuron binding to receptors in the blue postsynaptic cell decreases the probability that the cell will fire an action potential. This is because EPSPs and IPSPs can cancel each other out at the axon hillock and it takes several EPSPs to reach threshold. Psychoanalytic theory suggests that inhibition is a unconscious mechanism by which the superego controls instinctual or id impulses that could threaten the ego in a conscious manner.
A protein found on the surface of a neuron called a receptor detects stimuli like changes in temperature or mechanoreceptors that register mechanical change. Receptors bind to a specific ligand (which cannot pass through the plasma membrane) and then perform signal transduction by changing the permeability of ion channels.
Neurons add up the sum of excitatory and inhibitory inputs in time and over the area they receive them from dendrites and then fire an action potential if the sum exceeds a threshold value. Neuroscientists refer to this as temporal or spatial summation.
The action potential reaches the axon terminal and depolarizes the membrane of the target cell – the blue postsynaptic neuron in this figure. This triggers the release of a chemical messenger called a neurotransmitter.
6. Action Potential
Neurons use an electrical signal called the action potential to communicate with other neurons. The action potential is a temporary change in membrane potential caused by sodium (Na+) rushing into the cell and potassium rushing out. This change in membrane potential triggers a nerve impulse to travel down the length of the axon. The action potential only propagates forward, not backward, because patches of axon that have already experienced an action potential become refractory and cannot be stimulated again.
An action potential causes the neuron to release a chemical called a neurotransmitter into a gap between two cells, known as a synapse. The neurotransmitter binds to receptors on the postsynaptic cell and opens various types of channels in the membrane. The action potential then passes through the synapse and can excite or inhibit that cell.