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SITI NUR BAIZURY BT HASSAN

10-3-96

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DEFINITION OF NEUROTRANSMITTER

Neurotransmitters are endogenous chemicals

that transmit signals from a neuron to a target

cell across a synapse

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DIFFERENCE OF NEUROTRANSMITTER

AND NEUROHORMONENEUROTRANSMITTER NEUROHORMONE

Endogenous chemicals that transmit

signals from a neuron to a target cell

across a synapse

Any hormone produced and released by

neuroendocrine cells into the blood.

packaged into synaptic vesicles clustered

beneath the membrane in the axon

terminal, on the presynaptic side of a

synapse.

secreted into the circulation for systemic

effect and also have a role of

neurotransmitter or other roles as

autocrine (self) or paracrine (local)

messenger.

Examples: acetylcholine, GABA or

dopamine.

Examples: TRH (Thyrotropin releasing

hormone), dopamine or epinephrine.

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MECHANISM OF ACTION

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IONOTROPIC AND METABOTROPIC

RECEPTORIONOTROPIC METABOTROPIC

transmembrane molecules that can open

or close a channel that would allow

smaller particles to travel in and out of the

cell

do not have a channel that opens or

closes but are linked to another small

chemical called a G-protein.

Not opened (or closed) all the time. They

are generally closed until another

neurotransmitter binds to the receptor.

Ligand binds, receptor activates G-

Protein. Once activated, the G-protein

itself goes on and activates another

molecule secondary messenger.

Act very quickly.

As soon as a ligand binds to them, theychange shape and allow ions to flow in.

Take a longer times depending on the

number of steps (secondarymessengers), required to produce a

response

Ligand doesnt stay in place very long and

channel closes back very quickly.

Wider range of responses.

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CLASSIFICATION OF

NEUROTRANSMITTER

Neurotransmitter effects may be excitatory

(depolarizing) and/or inhibitory(hyperpolarizing)

Determined by the receptor type of thepostsynaptic neuron

GABA and glycine are usually inhibitory

Glutamate is usually excitatory Acetylcholine-Excitatory at neuromuscularjunctions in skeletal muscle

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GASEOUS NEUROTRANSMITTER

Nitric oxide

Unlike other neurotransmitters that transmit informationfrom presynaptic to postsynaptic neuron,the small,uncharged, fat-soluble NO molecule can diffuse widely and

readily enters cells

NO-cGMP cascade is involved in learning and memorythrough the maintenance of long-term potentiation (LTP).

NO neurotransmitter in various parts of the GIT-causesrelaxation of the gastrointestinal smooth muscle -In thestomach it increases the capacity of the fundus to storefood and fluids.

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Carbon Monoxide

Carbon monoxide used to cement memories inthe hippocampus of the brain and thatestablished memories

Carbon monoxide might protect against excessneuronal activity, dampening nerves that arefiring too much

In large concentrations

Carbon monoxide poison

binds so tightly to the heme chemical group

prevents oxygen from binding red blood cells unable to carry oxygen to body

tissues.

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References

http://www.nytimes.com/1993/01/26/science

/carbon-monoxide-gas-is-used-by-brain-cells-

as-a-neurotransmitter.html

http://web.williams.edu/imput/synapse/page

s/III.html

http://en.wikipedia.org/wiki/Neurohormone

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