Chemical Messengers

The presynaptic nerve ending is separated by a small gap from the post synaptic component, electric current responsible for propagation of action potential along axons cannot bridge the synaptic gap, thus transmission along this gap is accomplished by neurotransmitters

Dendritic spine

They are stored in tiny spherical bags called synaptic vesicles in the endings of axons

The arrival of an action potential leads to the opening of ion-channels that let in calcium (Ca2+). This activates enzymes that act on a range of presynaptic proteins, snare, tagmin and brevin, these synaptic proteins race around tagging and trapping others, causing releasable synaptic vesicles to fuse with the membrane, burst open and release chemical messenger out of nerve endings

Synaptic vesicles reform when their me,braces are swallowed back up into the nerve ending where they become refilled with neurotransmitter

It diffuses across the synaptic cleft and once it gets to the other side, it interacts with receptors in the membrane of the next neuron

They have transporters that suck up the transmitter in the cleft which clears the neurotransmitters out of the way before the next action potential comes, these glial cells then process the transmitter and send it back to be stored in the storage vesicles of nerve endings for future use

• Nerve cells pump the transmitter molecules back directly into their nerve endings • transmitter is broken down by other chemicals in the synaptic cleft

The neurotransmitter binds with the receptors to cause the opening of ion channel

They are receptors that respond to binding by opening an ion channel

Ion channel allow positive ions (Na+ or Ca2+) to enter, this inflow of positive current leads to excitation which causes excitatory post-synaptic potential (epsp). If the sum of these epsps reaches the threshold for firing an impulse, a new action potential is set up and signals are passed down the axon of the receiving neuron

Glutamate

Activation of receptors leads to the opening of ion channels that allow the flow of negatively charged ions, causing inhibitory post-synaptic potential (ipsp). This opposes membrane depolarisation and therefore initiation of an action potential at the cell body of receiving neuron

GABA and glycine

1ms

Different neurons have to time their delivery of glutamate on to others within a short window of opportunity if the epsps in the receiving neurons are going to add up to trigger a response and the inhibition also has to operate within the same interval to be effective in shutting things down

They adjust or modulate the vast array of chemical processes going on inside neurons

Action of metabotropic receptors

They are found in complex particles linking the outside of the cell to enzymes inside the cell that affect cell metabolism

Bridging molecules called G-proteins and other membrane-bound molecules are collectively triggered. It kickstarts intracellular second messengers into action, engaging a sequence of biochemical events

Changes in ion channels, receptors, transporters and expression of genes, these changes are slower onset and more long-lasting than those triggered by excitatory and inhibitory transmitters and their effects extend well beyond the synapse

Acetylcholine, dopamine, noradrenaline

1600

It is released in response to various forms of unfamiliarity and stress to organise response of individuals to these challenges