Neurotransmitters

Communicating between neurones

Synapses The synapse is the small gap between two neurones. When the nerve impulse reaches the knobs at the end of an axon, a chemical called a neurotransmitter is released into the space between the neurones. The neurotransmitter that is secreted from the presynaptic neurone affects the activity of the postsynaptic neurone.

Neurotransmitters A neurotransmitter is a chemical messenger that transmits signals from a neurone to a target across a synapse. Target cell may be a neurone or a muscle or gland. Neurotransmitters are packaged into synaptic vesicles in the presynaptic neurone.

How a synapse works

How a synapse works

How a synapse works After binding to the receptors, neurotransmitters are released. The neurotransmitters can travel back through the synapse and be reabsorbed by the pre- synaptic neurone, or be broken down by enzymes located in the synapse.

Neurotransmitters About 50 different neurotransmitters have been found. They control which nerves fire. Some drugs can stop or block the release of chemicals and slows brain function.

Neurotransmitters Acetylcholine: Lack of acetylcholine: An excitatory neurotransmitter that is responsible for the contraction of muscles, including the muscles of the gastro- intestinal system.  It is also found in sensory neurons and in the autonomic nervous system. Lack of acetylcholine: Associated with Alzheimers disease. Results in memory loss, confusion, loss of reasoning ability and illogical behavior.

Neurotransmitters Dopamine: Lack of dopamine: Involved in controlling movement and posture. Plays a role in emotional behaviour. Associated with positive reinforcement and dependency. Lack of dopamine: A lack of dopamine in certain regions of the brain result in muscle rigidity, similar to Parkinson’s disease. Also associated with Schizophrenia.

Neurotransmitters Serotonin: Involved in regulating body temperature, sleep, mood, appetite and pain. Lack of serotonin: Causes depression, impulsive behavior, and aggression. Excess can cause anxiety. Noradrenalin: Involved in our state of alertness, emotions, and sleeping. Causes blood vessels to contract and heart rate to increase. Lack of noradrenalin: Plays a role in mood disorders such as manic depression.

Psychoactive Drugs Psychoactive drugs alter communication between neurons. Some substances are able to mimic the effects of neurotransmitters. While others may alter neurone function in the brain by inhibiting the neurotransmitter, or by altering the way they are stored, released and removed. Psychoactive drugs can inhibit the reuptake of a neurotransmitter after it is released from the presynaptic neurone. Reuptake is a normal mechanism by which the transmitter is removed from the synapse. By inhibiting reuptake, the normal effects of the neurotransmitter are exaggerated.

Psychoactive Drugs Psychoactive drugs can be divided into four main groups: Depressants – alcohol Stimulants – nicotine, cocaine, amphetamines, ecstasy Opioids – heroin Hallucinogens – LSD, marijuana Caffeine

Psychoactive Drugs Cocaine – Inhibits the uptake of neurotransmitters such as dopamine, thereby prolonging its effects. Amphetamines – Increases release of dopamine and inhibits it reuptake. Ecstasy – Increased serotonin release and blockade of reuptake. Marijuana – Increases dopamine activity. Long-term exposure may produce long-lasting cognitive impairment. Risk of mental disorder such as Schizophrenia is also increased. The Chemistry of Addiction