An attempt is made at interpreting the results of recent mechanical, optical, and thermal measurements of the nerve membrane during excitation on a structural and physicochemical basis. This interpretation is based on the results of electrophysiological and electron microscopic studies which suggest that the excitable membrane consists of two structurally distinct strata, namely, an inner layer and an outer layer. The outer layer is presumed to correspond to the axolemma, whereas the inner layer consists of the superficial portion of the ectoplasm. These two layers are exposed to different physicochemical environments. In the resting state of the axon, the outer layer is rich in calcium ion, and the inner layer filled with potassium ion. It is proposed that the protein molecules in the outer membrane layer are capable of undergoing a transition from a compact, Ca-rich state to a swollen, monovalent-cation rich state by virtue of a cooperative ion-exchange process. At present, no inconsistency is encountered between the experimental facts and the proposed mechanism of nerve excitation. © 1982.
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