Synapses and synaptic transmission Flashcards
What do gap junctions do?
-Mediate the electrical coupling of cardiomyocytes and dictate the speed and direction of conduction
Describe end plates in neuromuscular junction
-Nerve bundle -> myelinated motor neurone -> end plates
-Acetylcholine causes end plate potential
-If end plate potential is strong enough, action potential is triggered
Types of synapses
-Axodendritic
-Axosomatic
-Axoaxonic
Steps in neuronal communication
Dendrites -> cell body -> axon -> transmission
Electron microscopy of synapse
PSD - Post synaptic density
-Anchors the post synaptic receptors across the cleft
Synaptic transmission
-Action potential arrives
-Voltage gated Calcium channels open
-Calcium activates snare complex which triggers exocytosis of synaptic vesicle content and release of NT
-Botox blocks snare complex so NT is not released and muscles don’t contract
3 ways of reducing synaptic transmission
1) Astrocyte uptake transporter takes NT into astrocyte or presynaptic terminal
2)Enzyme on post synaptic terminal (e.g. acetylcholinesterase) breaks down NT
3)Simple diffusion of NT away from the synapse
What are graded potentials?
-Vary according to size of stimulus
-Wave of depolarisation throughout cytoplasm
-Potential will diminish quickly
How is action potential propagated?
-Driven by acetylcholine at end plate
-As signal propagates sodium and potassium channels take over
How is action potential triggered?
-Impulse reaches Axon Hillock - dense with voltage gated sodium channels
-If response is sub-threshold, no AP generated
-Sub-threshold stimuli filtered out of nervous system
Excitatory and inhibitory synapses examples
What is effect of inhibiting end plate potentials?
-Spontaneous quantal release of NT
What are EPSPs (excitatory postsynaptic potential) and IPSPs (inhibitory postsynaptic potential)?
-EPSPs and IPSPs are sub threshold events which determine whether a cell will reach threshold to fire an action potential
-EPSPs add to generate depolarisation (more likely to fire AP)
-IPSPs add to generate hyperpolarisation (less likely to fire AP)
-EPSPs and IPSPs act to cancel each other out
Spatial summation
-Sum of responses to reach Axon Hillock strong enough to cause action potential
Temporal summation
-If multiple nerves fire in a short window, signals will sum to trigger action potential
Knee jerk reaction
Knee jerk in terms of synaptic transmission
-AP from sensory afferent
-Ap splits into extensor motor neurone and interneurone
-EPSP at extensor motor neurone causes quadricep to contract
-EPSP at interneurone cause release of NT on flexor motor neurone
-This causes IPSP on flexor neurone and hamstring relaxes
