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Neurotransmitters

Neurotransmitters 

About neurotransmitters

 

      Neurotransmitters are chemicals in the body that transmit signals from a nerve cell (neuron) to a target cell across a synapse

 

-       A neurotransmitter is released from a nerve cell  by the arrival of an electrical impulse – the impulse is transferred across the synapse to a target cell when the neurotransmitter binds to a receptor in the membrane on the postsynaptic side of the synapse.

 

-       The receiving target cell can be:

 

         An adjacent nerve cell

         A muscle fiber -  to stimulate movement

         A body organ cell

         Other tissue cell

 

 

      Release of neurotransmitters:

 

-       Usually follows arrival of an action potential at the synapse – whereby the voltage across the cell membrane (membrane potential) of a cell (in this case a presynaptic neuron) rapidly rises and falls.

 

Myelin sheath - consists of Schwann cells that encircle axon like a jelly roll, act as insulators and are separated by gaps of unsheathed axon called Nodes of Ranvier. Instead of a continuous traveling down the axon, the action potential  jumps from node to node (called saltatory conduction), thereby speeding up propagation of impulse.

 

         Follows a graded electrical potential.

 

         Occurs without electrical stimulation as a low level “baseline” release.

 

      Neurotransmitter synthesis – made via just a few biosynthetic steps, from simple precursors, such as amino acids readily available from diet.

 

      Have excitory or inhibitory effect (or both), depending only on the type of receptors they activate – an excitory effect increases the probability that the target cell will fire an action potential.

 

      Types of Neurotransmitters (packaged in neurotransmitter vesicles - membrane enclosed sacks that store and release neurotransmitters into synapse at presynaptic neuron terminal so that they can be detected by receptors on the postsynaptic neuron)

 

 

         Amino acids - E.g. GLUTAMATE (excitatory at >90% of the brain’s synapses), ASPARTATE, GABA (inhibitory at >90% of synapses that do not use GLUTAMATE), glycine

         Monoamines – DOPAMINE, NOREPINEPHRINE

         Peptides – E.g. ß-endorphin (engages with opioid receptors in CNS)

 

Also considered neurotransmitters (shown to be released by presynaptic terminals to produce an action, but are not packaged in vesicles)

 

         Single ions – E.g. zinc

         Gas molecules  E.g. carbon monoxide, NITRIC OXIDE

 

 

      Re-uptake of neurotransmitters - for nerve cells to communicate, neurotransmitters are secreted by one neuron and picked up by receptor proteins on the surface of another neuron. Once the message has been delivered, a neurotransmitter is either destroyed or reabsorbed into the cell that made it and its activity  is over. This process is known as re-uptake.

 

      Most psychoactive drugs exert their effects by altering the actions of some neurotransmitter systems – E.g. Addictive drugs, such as cocaine and amphetamines,  primarily affect the dopamine system. Addictive opiate drugs primarily indirectly regulate dopamine levels.

 

-       Cocaine – blocks reuptake of DOPAMINE back into the presynaptic neuron leaving DOPAMINE in the the synapse for a longer time to bind to receptors on postsynaptic neuron. This elicits a pleasurable emotion, until prolonged exposure causes down-regulation of receptors.

 

-       Prozac  - is a selective SEROTONIN reuptake inhibitor (SSRI), which blocks reuptake of SEROTONIN by the presynaptic cell and potentiates longer effect of SEROTONIN;

 

 

-       Alpha-methyl-p-tyrosine (AMPT) – prevents conversion of tyrosine to the DOPAMINE precursor (L-Dopa);

 

       

Neurotransmitter Related Links

Neurotransmitter

Related Links

ABOUT

About Neurotransmitters

-  Nervous System 101

SPECIFIC

Neurotransmitter Chart

-  NITRIC OXIDE

-  MELATONIN

-  Some Neurotransmitters of Special Mention