B6 – BRAIN AND MIND

SYNAPSES

GCSE SCIENCE AND ADDITIONAL SCIENCE

Sig’s School Work Help

WHAT IS A SYNAPSE?A tiny gap between neurones that transmits nerve impulses

from one neurone to the next

STAGES: DIAGRAM:

1) An electrical impulse travels along an axon.

2) This triggers the nerve-ending of a neuron to release chemical messengers called neurotransmitters.

3) These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron.

4) The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse.

NEUROTRANSMITTERS

What Are They?• Neurotransmitters are the brain chemicals that communicate information

throughout our brain and body

• They relay signals between nerve cells, called “neurons.” The brain uses neurotransmitters to tell your heart to beat, your lungs to breathe, and your stomach to digest.

TYPES OF NEUROTRANSMITTERS• Acetylcholine

• Motor control, learning, memory, sleep, dreams

• Serotonin

• Emotion, impulses, dreams

• Norepinephrine

• Alertness, vigilance, fear reaction

• Epinephrine

• Energy boost

• Dopamine

• Rewards, motivations, motor control

• Frequently associated with addictions

• Melatonin

• Sleep cycle regulation

• Endorphins

• Rewards, pain reduction

• Glutamate

• Regulates learning and memory

HOW DO DRUGS AFFECT SYNAPSES?

• Some drugs stop the impulse from passing across the synapse. Drugs such as curare (the South American plant toxin used in arrow poison) do this. They cause complete paralysis, and even stop the person from breathing

• Other drugs stimulate the synapse so that once an impulse crosses the gap the impulse is repeated over and over again. Drugs such as strychnine do this. They cause all the muscles in the body to go into a continuous spasm of constriction. This also stops the person from breathing.

HOW DO DRUGS AFFECT SYNAPSES?

Serotonin

• A transmitter substance found at the synapses in the brain

• An increase in serotonin levels in the synapses makes us feel happier.

• Serotonin is normally absorbed by receptor molecules on the other side of the synapse. This prevents the levels of serotonin from increasing.

Ecstasy

• An illegal drug that affects the working of the chemical transmitter substance in nerve synapses in a similar way to antidepressants

• Ecstasy (also called MDMA) is a drug that blocks the serotonin receptor sites in the synapses in the brain. This prevents the serotonin from being absorbed by the receptor molecules. As a result, the level of serotonin in the synapse increases. This produces a feeling of wellbeing.

HOW DO DRUGS AFFECT SYNAPSES?Dopamine• In the normal communication

process, dopamine is released by a neuron into the synapse, where it can bind to dopamine receptors on neighboring neurons.

• Normally, dopamine is then recycled back into the transmitting neuron by a specialized protein called the dopamine transporter.

Cocaine• If cocaine is present, it attaches to

the dopamine transporter and blocks the normal recycling process, resulting in a buildup of dopamine in the synapse, which contributes to the pleasurable effects of cocaine.

SCIENTISTS WHO RECEIVED A NOBEL PEACE PRIZE FOR THEIR WORK ON NERVES

Arvid Carlsson, Paul Greengard and Eric Kandel

• Nobel Prize Winners in Physiology or Medicine for 2000

• For their discoveries concerning "signal transduction in the nervous system”

Arvid Carlsson:

• His research has led to the realization that Parkinson's disease is caused by a lack of dopamine in certain parts of the brain and that an efficient remedy (L-dopa) for this disease could be developed.

Paul Greengard:

• Rewarded for discovery of how dopamine and a number of other transmitters exert their action in the nervous system. The transmitter first acts on a receptor on the cell surface. This will trigger a cascade of reactions that will affect certain "keyproteins" that in turn regulate a variety of functions in the nerve cell

Eric Kandel:

• Rewarded for discoveries of how the efficiency of synapses can be modified, and which molecular mechanisms that take part. With the nervous system of a sea slug as experimental model he has demonstrated how changes of synaptic function are central for learning and memory.