How do excitatory and inhibitory signals affect neural transmission?

Excitatory signals increase the likelihood of a neuron firing, while inhibitory signals decrease this likelihood.

Neurons communicate with each other through a process known as synaptic transmission. This involves the release of chemicals, known as neurotransmitters, from the axon terminal of a neuron (the presynaptic neuron) into the synaptic cleft. These neurotransmitters then bind to receptors on the next neuron (the postsynaptic neuron), triggering a response.

Excitatory signals are typically associated with neurotransmitters like glutamate. When these neurotransmitters bind to the postsynaptic receptors, they cause the opening of ion channels that allow positive ions to flow into the neuron. This influx of positive ions increases the voltage inside the neuron, a process known as depolarisation. If the voltage reaches a certain threshold, it triggers an action potential, which is the electrical signal that travels down the neuron and leads to the release of neurotransmitters at the next synapse. Therefore, excitatory signals increase the likelihood of the neuron firing an action potential.

On the other hand, inhibitory signals are often associated with neurotransmitters like GABA (gamma-aminobutyric acid). When these neurotransmitters bind to the postsynaptic receptors, they cause the opening of ion channels that allow negative ions to flow into the neuron or positive ions to flow out. This change in ion flow decreases the voltage inside the neuron, a process known as hyperpolarisation. Hyperpolarisation moves the voltage further away from the threshold needed to trigger an action potential, thus making it less likely that the neuron will fire.

The balance between excitatory and inhibitory signals is crucial for the proper functioning of the nervous system. Too much excitation can lead to conditions like epilepsy, where neurons fire too frequently and out of sync with each other, causing seizures. Conversely, too much inhibition can lead to conditions like depression, where certain areas of the brain are less active than they should be. Understanding how these signals work can therefore help in the development of treatments for these and other neurological conditions.