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Neurophysiology; Chemical Synapses Part 2 (Chemical Synaptic Transmission…
Neurophysiology; Chemical Synapses
Part 2
Synapses
Nervous system formed of individual neurons but
collectively forms a continuous transmission system
Synapses- connections between individual cells
Region of contact where the Presynaptic Neuron comes into close or near contact with another Presynaptic Neuron
Electrical Synapse:
-Very narrow intercellular space
-Essentially gap junctions in the
membrane between too cells
Eg retina of the eye
Chemical Synapse:
Presynaptic axon breaks up into series of branches
Terminate usually on dendrites or on the soma in synaptic knobs or Boutons
Three elements are present:
Presynaptic Terminal:
Contains synaptic vesicles, mitochondria
and dense projections
Dense projections allow tethering and
docking of vesicles at the pre-synapse
Synaptic Cleft:
20 to 30 nm wide
Separated the axon terminal from
the dendrites of the next cell
Post Synaptic Process:
With thickened membrane
on a dendritic spine
Chemical Synaptic Transmission
Nerve impulse reaches the axon terminals the depolarization opens Voltage Gated Ca2+ channels in the membrane
Since Ca2+ concentrations are 1000 times greated in the interstitial fluid, Ca2+ ions flow into the bouton
Increase in Ca2+ conc. causes the synaptic vesicles to fuse with the pre-synaptic membrane and release chemicals into the synaptic cleft- 'Excitation-secretion coupling'
Chemical substance diffuses across the cleft to the Postsynaptic Gated Ion channel receptors
These receptors convert chemical signals into electrical signals at chemical synapses
Ion Channels now open briefly and allow, depending on the receptor, Na+ ions to enter causing a local membrane depolarization
This may open Voltage Gated Na+ channels in the membrane allowing more Na+ ions to enter