Chemical Messengers

Action potential

A rapid change in electrical potential that occurs when a neuron is stimulated, allowing for the transmission of signals.

Voltage-gated calcium ion channels

open in response to action potential arrival. Calcium ions enter cell and stimulate neurotransmitter vesicles to move towards membrane

Exocytosis

The process by which synaptic vesicles release neurotransmitters into the synaptic cleft.

Post-synaptic receptors

neurotransmitters bind, leading to a response

monoamine neurotransmitters

dopamine, noradrenaline, adrenaline, serotonin and histamine

non-peptide neurotransmitters

acetylcholine, ATP and nitric oxide

neurotransmitter classification

• synthesised in neuron, stored in nerve terminal

• calcium-ion dependent release

• specific inactivation mechanisms

• exogenously applied substance can mimic endogenous response

• antagonist inhibits neurotransmitter and exogenously applied substance

dopamine synthesis

• from tyrosine (primarily dietary)

• tyrosine → L-DOPA via tyrosine hydroxylase

• L-DOPA → dopamine via Dopa decarboxylase

What happens to dopamine after it binds its receptors?

transported back into presynaptic cell and either recycled or broken down in the mitochondria by monoamine oxidase

nigrostriatal projection (motor control)

projection of dopamine from substantia nigra to the striatum

mesolimbic pathway (reward, motivation and mood)

Dopaminergic axons in ventral tegmental area ascend in brainstem and forebrain to supply limbic structures and the nucleus accumbens

mesocortical pathway

axons ascend and innervate frontal and cingulate cortices.

dopamine in the hypothalamus - effect on prolactin release

Hypothalamic arcuate nucleus projects to median eminence. Dopamine directly released → hypophyseal portal circulation. Dopamine → anterior pituitary lobe. Inhibits prolactin release

Glutamate

amino acid neurotransmitter involved in memory, epilepsy and relay of sensory information

GABA

Gamma-aminobutyric acid. Amino acid neurotransmitter in anxiety and epilepsy.

What is dopamine involved in regulating?

motor control, reward, mood and motivation

What does adrenaline regulate?

mood, sleep, arousal and blood pressure

Noradrenaline release and distribution

released from brain stem and distributed throughout the cortex, limbic system, cerebellum and brain stem

Serotonin (5-HT) release and distribution

Released from brain stem and distributed to the cortex, limbic system, thalamus, hypothalamus and cerebellum

What is serotonin involved in regulating?

sleep, wakefulness, temperature regulation and mood

Acetylcholine release

released from basal forebrain and interneurons in basal ganglia

What is acetylcholine involved in regulating?

arousal, learning and motor control

Glycine

inhibitory neurotransmitter mainly found in spinal cord interneurons. Modulates NMDA receptors, may be involved in epilepsy

Neuropeptides

Small proteins which act as neurotransmitters with various functions eg substance P's in pain

Slow neurotransmission eg binding serotonin to type 1 and 2 receptors

Indirect transmission of signals via G proteins and cytoplasmic second messengers, taking seconds to minutes.

serotonin binding 5-HT1R

cAMP decrease

serotonin binding 5-HT2R

increased IP3/DAG

Fast neurotransmission

Direct transmission of signals via receptor-operated ion channels