The Human Brain : From Neurone to Nervous System

CNS NEUROTRANSMITTERS


  1. A Synapse is a close functional contact between the membranes of an axon terminal and another nerve cell, and a site of cellular communication.

  2. The simpler synapse has been described previously. More complex synaptic mechanisms occur within the brain and involve neurotransmission using Glutamate, GABA, monoamines and peptides.

  3. These depend on the presence of receptors that have greater strength, or act for longer duration.

  4. They also affect not only on membrane potentials, but the trafficking of membrane proteins, and the synthesis of proteins and other materials, so much so that the shape of synaptic contacts can change.

  5. Key Words: NMDA receptors, GABA-B receptors, ionotropic and metabotropic mechanisms, Co-transmission.



Cotransmission

Some synapses contain and can release more than one neurotransmitter, and a well-studied example is the autonomic, sympathetic synapse in the vas deferens.

This synapse uses ATP, noradrenaline and NPY as transmitters.

ATP produces a rapid depolarisation by opening an ion channel that allows calcium entry and a rapid contraction of the smooth muscle.

Noradrenaline (NA) interacts with alpha adrenoceptors which utilise a second messenger that also results i an increase in intracellular calcium concentration, and results i a slower contraction

NPY is also released at this synapse and interacts with the ATP and NA release and binding with the receptors.

Co-transmission can also occur in parasympathetic, enteric and sensory pathways, and the table shows some of the transmitters involved

Also shown is a list of sites in the CNS where ATP is invovled in co-transmission.

In the CNS one example is the nociceptive nerve endings in the dorsal horn that release glutamate and Substance P.

The latter can sensitize post-synaptic neurones, but not initiate EPSPs themselves; Substance P is an example of a neuromodulator - a transmitter that can alter the sensitivity of a neurone to other transmitters.


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