All or none

(neuroscience) The principle that transmission of a nerve impulse is either at full strength or not at all.

A law stating that certain structures, such as a neurone or a muscle fibre, either respond completely (all) or not at all (none) to a stimulus. There is no partial nerve impulse in a neurone, or partial contraction of a muscle fibre. Compare graded potential.

The principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will either give a complete response or no response at all.

The noun has one meaning:

Meaning #1: (neurophysiology) a nerve impulse resulting from a weak stimulus is just as strong as a nerve impulse resulting from a strong stimulus

All or none (AON) is a term used most notably in financial transactions in investment banking or securities transactions.

In securities transactions, AON is an attribute attached to a buy or sell order to indicate that the transaction has to be executed in its entirety, i.e. the specified number of shares have to be filled and no partial execution is acceptable. AON does not automatically cancel an order if it cannot be filled as designated, but could be executed without the AON requirement.

In investment banking, an all-or-none clause in an underwriting contract or investment prospectus gives a securities issuer the right to cancel an issue in its entirety if the underwriting is not fully subscribed.

In biology, sometimes the phrase all-or-none is also used to describe the behavior of the action potentials of neurons, where, if a neuron fires at all, it will be propagated all the way from the beginning to the end of the axonal process.

See also

• Underwriting

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