Download - my assignment on neurotransmitter

7/29/2019 my assignment on neurotransmitter

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SITI NUR BAIZURY BT HASSAN

10-3-96

Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a

target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clusteredbeneath the membrane in the axon terminal, on the presynaptic side of a synapse. They are

released into and diffuse across the synaptic cleft, where they bind to specific receptors in the

membrane on the postsynaptic side of the synapse.They can be divided according to their

chemical structure which are amino acid, monoamines and peptides.

Differences between neurotransmitter and neurohormones

NEUROTRANSMITTER 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 sideof 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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neurohormones

neurotransmitter


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Mechanism of action

1. The action potential in the presynaptic cell is transmitted to the postsynaptic cell via achemical signal, which, in turn, triggers an action potential in the postsynaptic cell.

2. When the action potential of the presynaptic cell reaches the terminal bulb, it triggersthe opening of voltage-gated calcium channels in the plasma membrane.

3.

Calcium ions flow into the presynaptic cell.4. The elevated intracellular concentration of calcium triggers the fusion of synaptic

vesicles with the plasma membrane of the terminal bulb. The synaptic vesicles reside

in the terminal bulb, filled with neurotransmitters.

5. When they fuse with the plasma membrane, the neurotransmitters are released into thesynaptic cleft.

6. Extracellular neurotransmitters bind to specific receptors in the plasma membrane ofthe postsynaptic cell.

7. Upon the binding of neurotransmitter to its receptor, an action potential is triggered inthe postsynaptic cell

.Release of neurotransmitters usually follows arrival of an action potential at the synapse, but

may also follow graded electrical potentials. Low level "baseline" release also occurs without

electrical stimulation.Some neurotransmitters are commonly described as "excitatory" or

"inhibitory". The only direct effect of a neurotransmitter is to activate one or more types of

receptors. The effect on the postsynaptic cell depends, therefore, entirely on the properties of

those receptors


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Few examples of important neurotransmitter actions:

Glutamate:

fast excitatory synapses in the brain and spinal cord. It is also used at most synapses

that are "modifiable", i.e. capable of increasing or decreasing in strength. Excess glutamate

can overstimulate the brain and causes seizures. Modifiable synapses are thought to be the

main memory-storage elements in the brain. Excessive glutamate release can lead to

excitotoxicity causing cell death.

GABA:

fast inhibitory synapses in virtually every part of the brain. Many

sedative/tranquilizing drugs act by enhancing the effects of GABA. Correspondingly glycine

is the inhibitory transmitter in the spinal cord.

Acetylcholine:

transmitter at the neuromuscular junction connecting motor nerves to muscles. The

paralytic arrow-poison curare acts by blocking transmission at these synapses. Acetylcholine

also operates in many regions of the brain, but using different types of receptors, including

nicotinic and muscarinic receptors.


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Dopamine:

more than one functions in the brain; this includes regulation of motor behavior,

pleasures related to motivation and also emotional arousal. It plays a critical role in the

reward system; people with Parkinson's disease have been linked to low levels of dopamineand people with schizophrenia have been linked to high levels of dopamine.

Serotonin

is a monoamine neurotransmitter. Most is produced by and found in the intestine

(approximately 90%), and the remainder in central nervous system neurons. It functions to

regulate appetite, sleep, memory and learning, temperature, mood, behaviour, muscle

contraction, and function of the cardiovascular system and endocrine system. It is speculated

to have a role in depression, as some depressed patients are seen to have lower concentrations

of metabolites of serotonin in their cerebrospinal fluid and brain tissue.


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Substance P

undecapeptide responsible for transmission of pain from certain sensory neurons to the

central nervous system. It also aids in controlling relaxation of the vasculature and lowering

blood pressure through the release of nitric oxide.

There are two types of Neurotransmitter receptors: ligand-gated receptors or ionotropic

receptors and G protein-coupled receptors or metabotropic receptors


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Functional Classification of Neurotransmitters

Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory

(hyperpolarizing)

Determined by the receptor type of the postsynaptic neuron

GABA and glycine are usually inhibitory

Glutamate is usually excitatory

Acetylcholine-Excitatory at neuromuscular junctions in skeletal muscle

Gaseous neurotransmitter

Nitric oxide

Nitric oxide (NO) plays important roles in the brain in general and in neuroendocrine

functions in particular.

IONOTROPIC 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, they

change shape and allow ions to flow in.

Take a longer times depending on the number of

steps (secondary messengers), 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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Nitric oxide serves as a neurotransmitter between nerve cells, part of its general role in redox

signaling. Unlike most other neurotransmitters that only transmit information from a

presynaptic to a postsynaptic neuron, the small, uncharged, and fat-soluble nitric oxide

molecule can diffuse widely and readily enters cells. Thus, it can act on several nearby

neurons, even on those not connected by a synapse. At the same time, the short half-life ofNO means that such action will be restricted to a limited area, without the necessity for

enzymatic breakdown or cellular reuptake. NO is also highly reactive with other free radicals,

lipids, and proteins.

NO-cGMP cascade is involved in learning and memory through the maintenance of long-

term potentiation (LTP).

Nitric oxide is an important non-adrenergic, non-cholinergic (NANC) neurotransmitter in

various parts of the gastrointestinal tract. It causes relaxation of the gastrointestinal smooth

muscle. In the stomach it increases the capacity of the fundus to store food and fluids.

Carbon Monoxide

Carbon monoxide used to cement memories in the hippocampus of the brain and that

established memories might be erased when carbon monoxide is absent.

Carbon monoxide might protect against excess neuronal activity, dampening nerves that are

firing too much. In this way, it could counter some of the adverse effects of nitric oxide, Dr.

Snyder said. For example, nitric oxide seems to cause damage in strokes, when nerve cells

are stimulated to fire repeatedly. Carbon monoxide, he said, could counter that effect.

In large concentrations, carbon monoxide is a poison. It binds so tightly to the heme chemical

group at the heart of hemoglobin molecules that it prevents oxygen from binding. In the

presence of carbon monoxide, red blood cells are unable to carry oxygen to body tissues. But

it was this very ability of carbon monoxide to bind to heme that gave the researchers a clue to

the gas's normal role in transmitting nerve signals.

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/pages/III.html

http://en.wikipedia.org/wiki/Neurohormone
http://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.htmlhttp://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.htmlhttp://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.htmlhttp://web.williams.edu/imput/synapse/pages/III.htmlhttp://web.williams.edu/imput/synapse/pages/III.htmlhttp://en.wikipedia.org/wiki/Neurohormonehttp://en.wikipedia.org/wiki/Neurohormonehttp://en.wikipedia.org/wiki/Neurohormonehttp://web.williams.edu/imput/synapse/pages/III.htmlhttp://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.htmlhttp://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.html

Download - my assignment on neurotransmitter

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