Psychology: Neurotransmitters, Neuromodulators & Neural Mechanisms

Neurons

The building blocks of the brain and the rest of the nervous system. Neurons specialise in the reception and transmission of information throughout the nervous system.

Types of Neurons

sensory, interneurons, motor

Sensory Neuron

Neurons that carry incoming information from the sensory organs, muscles and internal organs to the brain and spinal cord.

Interneurons

Makes the connection between neurons that rarely connect themselves. They relay messages from the sensory to motor neuron.

Motor Neuron

Initiates contraction in muscles causing movement as well as initiating contractions in glands causing hormones.

Neurotransmitter

A chemical substance produced by a neuron that carries a message to other neurons or cells in the muscles, organs or other tissue.

Synapse

It is the site where communication typically occurs between presynaptic and postsynaptic neurons.

Synaptic Gap

Also known as the 'synaptic cleft', it is the small space between the axon terminal of a presynaptic neuron. It is the space that allows neurotransmitters to be transferred from the presynaptic neuron to the post synaptic neuron.

Axon

Transmits messages (electrical/neural impulse) from the soma to the axon terminals.

Axon Terminal

Also known as terminal buttons, they are responsible for storing and secreting neurotransmitters.

Soma

Part of the neuron that contains the nucleus and structures that maintain functioning.

Dendrite

Receives messages (absorbs neurotransmitters) from other neurons and carries it towards the soma.

Myelin

A fatty substance that helps insulate neurons and speeds the transmission of nerve impulses.

Presynaptic Neuron

Sending neuron

Postsynaptic Neuron

Receiving neuron

Reuptake

Refers to the reabsorption of neurotransmitter that have not been bound to receptors in the postsynaptic neuron. The neurotransmitter is reabsorbed into the terminal buttons.

Excitatory Effect

A neurotransmitter effect that allows postsynaptic neurons to fire more easily.

Inhibitory Effect

A neurotransmitter effect that blocks and prevents postsynaptic neurons from firing.

Glutamate (Glu)

The main excitatory neurotransmitter in the CNS. It enhances information transmission by making the postsynaptic neurons more likely to fire.

Functions of Glutamate

It is involved in most aspects of normal brain function such as: learning, memory, perception, thinking and movement.

Effects of Glutamate

- too little glutamate results in poor communication between neurons
- too much can result in over-excitation of receiving neurons, leading to neuronal damage/death

Gamma-Amino Butyric Acid (GABA)

The primary inhibitory neurotransmitter in the CNS. It works throughout the brain to make postsynaptic neurons less likely to fire.

Functions of GABA

Fine-tunes neurotransmission in the brain and maintains neurotransmission at an optimal level.

Effects of GABA

- low GABA levels in the brain has been linked to anxiety symptoms
- without the inhibitory effect of GABA, activation of postsynaptic neurons might get out of control, causing seizures

Neuromodulators

Also known as 'modulatory neurotransmitters', they influence the effects of other neurotransmitters. For example, it can change the reactivity of receptors to another type of neurotransmitter to enhance their excitatory or inhibitory responses.

Dopamine

A neuromodulator that has multiple functions depending on where in the brain it acts. Primarily an excitatory neurotransmitter, it can also have an inhibitory effect depending on the type of receptors that are present.

Functions of Dopamine

It has important roles in voluntary movements, the experience of pleasure, motivation, appetite, reward-based learning and memory.

Effects of Dopamine

- low levels are associated with fatigue, depression, parkinsons disease
- high levels are associated with hallucinations and delusions

Dopamine Reward System

Occurs when two dopamine pathways (mesolimbic and mesocortical) overlap and are strongly associated with rewarding behaviour through the experience of pleasure. Healthy behaviours that may be perceived as rewarding can include: eating when hungry and drinking water when thirsty. Harmful behaviours that involve a loss of impulse control and have caused addiction can include: gambling.

Serotonin

An inhibitory neuromodulator that has a wide range of functions depending on where in the brain it acts. Unlike dopamine, serotonin only has inhibitory effects and so doesn't stimulate brain activity.

Functions of Serotonin

It can affect mood regulation, emotional processing, sleep onset and appetite and pain perception

Effects of Serotonin

- low levels are associated with mood disorders, OCD, anxiety disorders
- excessive amount of serotonin may cause serotonin syndrome, which can be life threatening in some people

Neuroplasticity

The ability of the brain and other parts of the nervous system to change in response to experience.

Synaptic Plasticity

The ability of a synapse to change in response to experience. It enables a flexible, efficient and effectively functioning nervous system and its the biological basis of learning and memory formation.

Sprouting

The creation of new extensions on a neuron to allow it to make new connections with other neurons. This occurs through the growth of nerve endings on axons or dendrites.

Rerouting

Occurs when new connections are made between neurons to create alternate neural pathways. These alternate 'routes' may be entirely new neural pathways or connections to other pathways in the brain.

Pruning

The elimination of weak, ineffective or unused synapses, therefore severing the connections to other neurons. Experience determines which synapses will be retained and those that are not frequently used will decay or disappear.

Long-Term Potentiation

Refers to the long-lasting enhancement of synaptic transmission (excitability) due to repeated strong stimulation. LTP strengthens synaptic connections in a way that enables postsynaptic neurons to be more easily activated.

Long-Term Depression

Refers to the long-lasting decrease in the strength of synaptic transmission (excitability) due to a lack of stimulation of pre- and postsynaptic neurons or prolonged low level stimulation.