What are the two broad classes of synapses?
chemical and electrical
What feature clearly allows you to identify the pre-synaptic cell in an electron micrograph?
vesicles in the pre-synaptic cleft
By which mechanism is neurotransmitters released from an axon terminal?
exocytosis
What happens to the membrane potential of a postsynaptic cell when an excitatory neurotransmitter binds to its receptors on the postsynaptic cell?
excitatory post-synaptic potentials are elicited by stimuli of increasing strenght. once the critical firing level is achieved the action potential is initiated
What happens to the membrane potential of a postsynaptic cell when an inhibitory neurotransmitter binds to its receptors on the postsynaptic cell?
the membrane potential is driven away from the critical firing level. the increasing stimulus strengths, and as the stimulus strength increases, so does the amplitude of the IPSP
What type of image does the confocal laser scanning microscope allow you to produce?
three-dimensional structures can be re-constucted from the obtained images
Which class of synapse is predominant in mammals?
chemical synapses
how do nerve cells communicate with each other?
at specialised junctions known as synapses
what forms the synapses?
the axon terminals of one neuron and dendrites or cell bodies of another neuron.
what is a chemical synapse?
where the action potential triggers the opening of calcium-sensitive channels
what does the binding of the neurotransmitter to receptors on the post-synaptic cell (after being released from pre-synaptic cell) cause?
changes in membrane potential
what is characteristic of the chemical synapse?
there is a delay of 0.5 milliseconds between the arrival of the impulse at the pre-synaptic terminal and the detection of a post-synaptic potential change
what is an electrical synapse?
where current flows directly from the presynaptic to the post-synaptic neuron via gap junctions
is there a delay in electrical synapses?
no
are electrical synapses common in mammals?
no - but there are examples in the retina of the eye and during development of the nervous system
how can a tissue be optically sectioned?
using immunocytochemistry combined with confocal microscopy
what does immunocytochemistry allow?
locate terminals containing particular transmitters precisely
what should be used to confirm the presence of an active synapse?
Transmission Electron Microscopy (TEM) or electrical recording from the cells
which technique is the only one that allows us to view synapses?
electron microscope - resolution of light microscope is not sufficient
events at the synapse
- action potential depolarises the axon terminal
- the depolarisation opens voltage-gated Ca2+ channels and Ca2+ enters the cell
- Calcium entry triggers exocytosis of synaptic vesicle contents
- neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell
what two subsequent stages can be added to the events at the synapse?
- excess transmitter is removed by enzyme action, reuptake or diffusion
- vesicle membrane is recycled