Types and Functions of Neurotransmitters

Neurotransmitters are chemical messengers in the body. Their job is to transmit signals from nerve cells to target cells.

Communication between two neurons happens in the synaptic cleft (the small gap between the synapses of neurons). Here, electrical signals that have travelled along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron.

A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory.

Classification of Neurotransmitters

Neurotransmitters can be classified by their function:

• Excitatory neurotransmitters: These types of neurotransmitters have excitatory effects on the neuron, meaning they increase the likelihood that the neuron will fire an action potential. So basically, encourage a target cell to take action. Some of the major excitatory neurotransmitters include epinephrine and norepinephrine.
• Inhibitory neurotransmitters: These types of neurotransmitters have inhibitory effects on the neuron; they decrease the likelihood that the neuron will fire an action potential. So, basically they decrease the chances of the target cell taking action. Some[ of the major inhibitory neurotransmitters include serotonin and gamma-aminobutyric acid (GABA).

Modulatory neurotransmitters: These neurotransmitters, often referred to as neuromodulators, are capable of affecting a larger number of neurons at the same time. These neuromodulators also influence the effects of other chemical messengers.

 

Types and Functions of Neurotransmitters

There are a number of different ways to classify and categorize neurotransmitters. the most common way to divide them up by their molecular structure into amino acids, peptides, monoamines and others. Neurotransmitters can also be categorized into one of six types:

Amino Acids

Gamma-aminobutyric acid (GABA):

Functional classification: inhibitory chemical messenger

Location: brain regions: hippocampus, thalamus, basal ganglia, hypothalamus, and brain stem.

 

Functions

• Its main functions are to regulate anxiety, vision, and motor control.

Symptoms of lack/ excess

• Lack causes poor impulse control
• Lack causes brain seizures
• Lack causes bipolar disorder and mania.
• If there is too much GABA, however, this could result in hypersomnia (oversleeping) and a lack of energy.

 

Glutamate:

Functional classification: Glutamate is an excitatory neurotransmitter

Location: found in the central nervous system in the neurons and the glia

Functions

supports cognitive functions such as memory formation and learning.

Symptoms of lack/ excess

• If there is an excess amount of glutamate, this could result in excitotoxicity – meaning that neurons are killed due to overactivations of glutamate receptors this could lead to conditions such as Alzheimer’s disease, stroke, and epilepsy.
• If there are not enough glutamate, this could result in psychosis, insomnia, concentration problems, mental exhaustion, or even death.

 

Peptides

Oxytocin:

Functional classification: Excitatory and Inhibitory neurotransmitters

Location: This powerful hormone acts as a neurotransmitter in the brain. It is produced by the hypothalamus

Functions

plays a role in social recognition, bonding, and sexual reproduction.

Synthetic oxytocin such as Pitocin is often used as an aid in labor and delivery. Both oxytocin and Pitocin cause the uterus to contract during labor.

 

Endorphins:

Functional classification: inhibitory

Location: Endorphins are primarily made within the hypothalamus and pituitary glands

Functions

works in lowering the transmission of pain signals to the brain and promotes feelings of euphoria.

Symptoms of lack/ excess

• There are not many known symptoms of having too many endorphins, but it could lead to an addiction to exercise.
• If there were a deficit in endorphins, this could result in feelings of depression, headaches, anxiety, mood swings, and a condition called fibromyalgia (chronic pain).

Monoamines

Epinephrine:

Functional classification: excitatory

Location: adrenal glands

Functions

Also known as adrenaline, epinephrine is considered both a hormone and a neurotransmitter

Generally, epinephrine is a stress hormone that is released by the adrenal system. This is an excitatory class of neurotransmitter as it stimulates the central nervous system.

 

Symptoms of lack/ excess

•  If there is too much adrenaline in the blood stream, this could lead to high blood pressure, anxiety, insomnia, and increased risk of a stroke.
• If there is too little adrenaline, however, this can lead to diminished excitement and not being able to react appropriately in stressful situations, diminishing the stress response.

Norepinephrine: also known as noradrenaline

Functional classification: excitatory

Location:

Also produced in the adrenal glands

also produced within the brainstem and hypothalamus

Functions

it stimulates the brain and body

This chemical helps in activating the body and brain to take action during time of stress or when in dangerous situations.

It is especially prevalent during the fight-or-flight response, aiding in alertness. Noradrenaline is at its peak during times of stress, but lowest during sleep cycles

Symptoms of lack/ excess

• If levels of noradrenaline are too high, this can lead to high blood pressure, excessive sweating, and anxiety.
• Low levels of this chemical could mean that energy levels are lower, concentration is lacking, and could also contribute to depressed feelings.

 

Histamine:

Functional classification: excitatory

Location: brain and spinal cord

Functions

It plays a role in allergic reactions and is produced as part of the immune system’s response to pathogens.

Dopamine:

Commonly known as the feel-good neurotransmitter

Functional classification: excitatory and inhibitory neurotransmitter, as well as a neuromodulator

Location:

Functions

dopamine is involved in reward, motivation, and additions.

 

Symptoms of lack/ excess

A deficiency in dopamine could result in feelings of depression dopamine can also play a role in the coordination of body movements and a shortage can be seen in those with Parkinson’s disease – resulting in tremors and motor impairments.

Serotonin:

Functions

A hormone and neurotransmitter, serotonin plays an important role in regulating and modulating mood, sleep, anxiety, sexuality, and appetite.

 

Symptoms of lack/ excess

 Selective serotonin reuptake inhibitors (SSRIs) are a type of antidepressant medication commonly prescribed to treat depression, anxiety, panic disorder, and panic attacks. SSRIs work to balance serotonin levels by blocking the reuptake of serotonin in the brain, which can help improve mood and reduce feelings of anxiety.

 

Purines

Adenosine

Functional classification: neuromodulator

Location: brain, Adenosine is commonly found in the presynaptic regions of the hippocampus

Functions

involved in suppressing arousing and improving sleep.

acts as a central nervous system depressant.

Symptoms of lack/ excess

• Consistently high levels of this neurotransmitter can cause hypersensitivity to touch and heat.
• If there is too little adenosine, this can cause anxiety and trouble sleeping. Caffeine is what is known as an adenosine blocker which causes the adenosine receptors to be blocked. This is why caffeine can cause issues with sleeping and is not recommended to drink too late in the day.

 

• Adenosine triphosphate (ATP): Considered to be the energy currency of life, ATP acts as a neurotransmitter in the central and peripheral nervous systems. It plays a role in autonomic control, sensory transduction, and communication with glial cells. Research suggests it may also have a part in some neurological problems including pain, trauma, and neurodegenerative disorders.

 

Gasotransmitters

• Nitric oxide: This compound plays a role in affecting smooth muscles, relaxing them to allow blood vessels to dilate and increase blood flow to certain areas of the body.
• Carbon monoxide: This colorless, odorless gas can have toxic and potentially fatal effects when people are exposed to high levels of the substance. However, it is also produced naturally by the body where it acts as a neurotransmitter that helps modulate the body’s inflammatory response.

Acetylcholine

• Acetylcholine: Acetylcholine is the only known neurotransmitter of its kind, found in both the central nervous system and the parasympathetic nervous system. The main function of this type is focused on muscle movements, memory, and learning, associated with motor neurons.

Too much acetylcholine is linked with increased salivation, muscle weakening, blurred vision, and paralysis.

Too little acetylcholine is linked to learning and memory impairments, as well as being shown to have links to dementia and Alzheimer’s, according to research (Haam & Yakel, 2017; Tabet, 2006).