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Neurophysiology
| Term | Definition |
|---|---|
| Short receptor features | Electrotonically compact as lambda > length of neuron -> no axons (immediately synapse w/ 2nd order cell) -> graded potentials |
| Short receptor examples | Taste receptors -> sometimes fire AP spikes, auditory receptors -> graded potentials, optic receptors -> graded potentials |
| Graded potentials | Short neurons -> graded changes in synaptic nt release, graded generator potential in 2nd order cell (modulate spike firing rate) |
| Long receptor features | Afferent axons sent to CNS -> AP spike firing |
| Long receptor features | Cutaneous mechanoreceptor/touch receptor, cranial nerves, olfactory receptor -> directly to olfactory bulb |
| How is stimulus magnitude usually encoded? | Stimulus magnitude encoded as frequency of AP |
| What do sensory receptors normally do? | Adapt to constant stimulus -> diminution of firing frequency over time -> rapid/slow -> increases subsequent excitation threshold |
| Adaptation in vitro | Slow rising depolarisation -> in/activation of Na+/K+ channels -> raise threshold |
| Adaptation in vivo | Slow rising depolarisation excites nerve fibres at near constant intensity |
| Direct nerve transduction | Mechanoreceptors (hearing) -> stretch-sensitive channels mechanically open -> small cation influx -> depolarisation, salt receptors in tongue -> Na+ stimulating influx |
| Indirect nerve transduction | Stimulate 2ndary messenger cascade -> retinal photoreceptors, taste/smell chemoreceptors |
| NMJ neural integration | Single endplate for one/many muscle fibres (divergence) -> sufficient EPP to reach threshold -> AP always produced |
| Alpha-motor neuron in spinal cord neural integration | Muscle fibre receives 1000s of spindle group IA fibres (convergence) -> each generates small EPSP -> simultaneous excitation -> monosynaptic spinal stretch reflex |
| Spinal motor neuron channels | Excitatory AMPA Glu channel -> Na+ influx > K+ efflux -> EPSPl, inhibitory interneurons release Gly -> Cl- influx -> IPSP |
| Simultaneous EPSP/IPSP | Non-linear summation of synaptic conductance |
| Synaptic locations | Axosomatic, axodendritic, axoaxonic (presynaptic) |
| Axosomatic synapse | Type II -> inhibitory -> flat vesicle release |
| Axodendritic spine synapse | Type I -> excitatory -> round vesicles |
| Axodendritic shaft synapse | Type I (mostly) -> excitatory -> round vesicles |
| Where is AP initiated? | Axon hillock -> lowest threshold -> irrespective of stimulation site, AP always recorded first at soma -> spreads back to dendrites |
| Length constant and equation | Lambda = sqrt (rm/ri) |
| Unmyelinated nerve length constant equation | Lambda = sqrt (rm x d / ri x 4) unmyelinated nerve lambda varies w/ sqrt of diameter -> potentials smaller/slower conducted decrementally towards cell body |
| Short cell time constant | 2 stimuli almost simultaneous to stimulate axon hillock |
| Short cell length constant | 2 stimuli close together to stimulate axon hillock |
| Excitatory synapse + excitatory synapse | Addition of depolarising currents |
| Excitatory synapse + inhibitory synapse | Subtraction of currents -> draw axon hillock further from firing threshold |
| Excitatory synapse + inhibitory synapse close to soma | Division of currents (shunting inhibition) -> constant fraction of depolarising current leaves cell -> less excitatory current available |
| Axo-axonic presynaptic inhibition | Inhibitory Cl-/K+ channel opening -> reduce presynaptic AP magnitude -> slight primary afferent depolarisation (partially inactivates postsynaptic Na+ channels) and reduces VGCaC opening (reduce nt release) |
Created by:
vykleung
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