Skip to main content Accessibility help
×
  1. Home
  2. Browse subjects
  3. Life Sciences
  4. Neurosciences
  5. Content listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

5335 results in Neurosciences

Page 38 of 267

  • 7 - Neuromuscular Transmission

  • Christopher L.-H. Huang, University of Cambridge
  • Book:
    Keynes & Aidley's Nerve and Muscle
    Published online:
    07 November 2020
    Print publication:
    19 November 2020, pp 88-105

  • Summary

    Numerous terminal branches of motor nerves each end on individual component muscle fibres making up their motor unit. Each ramification terminates in a neuromuscular junction comprising pre- and postsynaptic membranes separated by the synaptic cleft. The neurotransmitter acetylcholine is released in response to depolarisation from presynaptic vesicles as discrete quanta. Each such event elicits a postsynaptic miniature endplate potential. This probabilistic release process follows a Poisson distribution whose probability increases with presynaptic depolarisation. The released acetylcholine diffuses across the synaptic gap to access postsynaptic ACh receptors, proteins each comprising five transmembrane subunits surrounding a central pore. Two of these (α) subunits each include an ACh binding site. ACh binding to both sites causes pore opening, permitting Na+ and K+ permeation, generating endplate currents demonstrable under voltage clamp. The resulting endplate potentials trigger a propagated action potential in the innervated muscle fibre when the resulting depolarisation attains the Na+ channel threshold.

  • 4 - Membrane Permeability Changes During Excitation

  • Christopher L.-H. Huang, University of Cambridge
  • Book:
    Keynes & Aidley's Nerve and Muscle
    Published online:
    07 November 2020
    Print publication:
    19 November 2020, pp 41-54

  • Summary

    The association between membrane excitation and alterations in membrane electrical impedance, its dependence on extracellular Na+ and the accompanying transmembrane Na+ fluxes measurable by isotope tracer methods, gave rise to the Na+ hypothesis for the action potential. Here, suprathreshold depolarising stimulation increases the voltage-dependent Na+ membrane conductance. The latter in turn initiates a regenerative cycle of membrane depolarisation and further channel opening, culminating in the action potential upstroke phase. Subsequent action-potential recovery to the resting potential then follows a voltage-dependent Na+ channel inactivation and more gradual K+ channel opening. This hypothesis was tested by voltage-clamp experiments determining the ionic currents required to drive depolarising membrane-potential steps in cephalopod giant axons from the resting to varying test levels. These revealed Na+ and K+ conductances whose voltage-dependences and kinetic properties could be incorporated into a successful mathematical reconstruction of the timecourse and properties of experimentally observed propagating action potentials.

Page 38 of 267