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Related Experiment Videos

Excitability changes in crayfish motor neurone terminals.

R S Zucker

    The Journal of Physiology
    |August 1, 1974
    PubMed
    Summary

    Investigating crayfish motor nerve terminals revealed a supernormal excitability period after activation. This excitability, influenced by ions and temperature, is not linked to transmitter release facilitation.

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    Area of Science:

    • Neuroscience
    • Cellular physiology

    Background:

    • Post-activation excitability changes in nerve terminals are crucial for understanding neuronal function.
    • Afterpotentials in nerve terminals may play a role in transmitter release facilitation.

    Purpose of the Study:

    • To investigate the nature of post-activation afterpotentials in crayfish motor nerve terminals.
    • To determine if these afterpotentials are related to the facilitation of transmitter release.

    Main Methods:

    • Electrophysiological recordings of crayfish motor nerve terminals.
    • Manipulation of ionic concentrations (potassium, sodium, calcium) and temperature.
    • Application of specific ions (manganese, cobalt) and pharmacological agents (strophanthidin, proteolytic enzymes, hyperosmotic solutions).

    Main Results:

    • A period of supernormal excitability (decreased threshold) follows nerve impulse activation, peaking at ~15 msec and decaying with a time constant of ~25 msec at 13°C.
    • High-frequency tetanus enhances supernormal excitability; low temperatures reduce and delay this peak, prolonging decay (Q10 ≈ 2.5).
    • External potassium concentration, depolarization/hyperpolarization, and cobalt ions significantly affect supernormal excitability, while sodium and manganese have less impact. Calcium's effect is variable, and strophanthidin is ineffective.

    Conclusions:

    • A depolarizing afterpotential, likely due to transient external potassium accumulation, follows action potentials in nerve terminals.
    • The observed supernormal excitability is distinct from and not related to the facilitation of transmitter release.

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