Neurotransmitters are chemical messengers released into the synaptic cleft by neurons
- They maintain signals in the nervous system by binding to receptors on post-synaptic neurons and triggering electrical impulses
- They also activate responses by effector organs (such as contraction in muscles or hormone release from endocrine glands)
Neurotransmitters may be either excitatory or inhibitory in their effect (some may be both depending on the receptor they bind to)
- Excitatory neurotransmitters trigger depolarisation, increasing the likelihood of a response
- Inhibitory neurotransmitters trigger hyperpolarisation, decreasing the likelihood of a response
Major Classes of Neurotransmitter
Examples of Neurotransmitters
Adrenaline
- Adrenaline is primarily a hormone released by the adrenal gland, but some neurons may secrete it as a neurotransmitter
- It increases heart rate and blood flow, leading to a physical boost and heightened awareness
- It is produced during stressful or exciting situations
Noradrenaline
- In contrast to adrenaline, noradrenaline is predominantly a neurotransmitter that is occasionally released as a hormone
- It contracts blood vessels and increases blood flow, improving attention and the speed at which responsive actions occur
Dopamine
- It is primarily responsible for feelings of pleasure, but is also involved in movement and motivation
- People tend to repeat behaviours that lead to dopamine release, leading to addictions
- Abnormal dopamine secretion is common in specific movement disorders, like Parkinson’s disease
Serotonin
- Contributes to feelings of well-being and happiness
- Is affected by exercise and light exposure, and plays a role in the sleep cycle and digestive system regulation
GABA
- Inhibits neuron firing in the CNS – high levels improve focus whereas low levels cause anxiety
- Also contributes to motor control and vision
Acetylcholine
- Involved in thought, learning and memory within the brain
- Activates muscle contraction in the body and is also associated with attention and awakening
Glutamate
- Most common brain neurotransmitter
- Regulates development and creation of new nerve pathways and hence is involved in learning and memory
Endorphins
- Release is associated with feelings of euphoria and a reduction in pain (body’s natural 'pain killers’)
- Released during exercise, excitement and sex