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Neurotransmitters: Excitatory vs Inhibitory

Neurotransmitters can be classified as either excitatory or inhibitory in their action because they have one of these two effects on the neighbouring neuron.

Inhibitory neurotransmitters

Inhibitory neurotransmitters

  • The neurotransmitter serotonin causes inhibition in the receiving neuron. This results in the neuron becoming more negatively charged and less likely to fire.
  • Inhibitory neurotransmitters are like the nervous system’s “off switches” and are generally responsible for calming the mind and body inducing sleep and filtering out unnecessary excitatory signals. An inhibitory neurotransmitter binding with a postsynaptic receptor results in an inhibitory postsynaptic potential (IPSP), so is less likely to fire.
Excitory neurotransmitters

Excitory neurotransmitters

  • Neurotransmitters like noradrenaline are excitatory; they are the nervous system’s “on switches”. These cause excitation of the post synaptic neuron by increasing its positive charge and making it more likely to fire.
  • It causes an electrical charge in the membrane of that cell resulting in excitatory post synaptic potential (EPSP) making it more likely to fire.
Likelihood of a cell firing

Likelihood of a cell firing

  • A nerve cell can receive both EPSPs and IPSPs at the same time.
  • The likelihood of the cell firing is determined by adding up the excitatory and the inhibitory synaptic input.
  • The net sum of this calculation (summation) determines whether or not the cell fires.
Dopamine

Dopamine

  • Dopamine can be both an excitatory or inhibitory neurotransmitter depending on the receptor it binds to. Dopamine is associated with rewards as the brain releases it in response to pleasure.
  • It is also responsible for movement co-ordination and is implicated in Parkinson’s Disease.
  • The dopamine hypothesis suggests that an excess of the neurotransmitter dopamine in certain regions of the brain is associated with the positive symptoms of schizophrenia.
Serotonin

Serotonin

  • Serotonin is an inhibitory neurotransmitter.
  • It regulates mood, appetite and sleep.
  • SSRI (Selective Serotonin Reuptake Inhibitors) relieve the symptoms of depression by increasing levels of serotonin in the brain.
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