The median eminence : an electron microscopic study with special reference to gonadotropin release in the rat

Adaptation of an organism to changes in the external and internal environment is in vertebrates brought about by two more or less separate integrative systems: the nervous system and the endocrine system. The nervous system is primarily equipped for rapid and short lived responses, the endocrine system for slower but longer lasting ones. The cells of nervous system and endocrine system have many features in common but they differ, apart from rapidity and duration of the effects exerted, in the way they achieve "privacy" (Wurtman, 1970) in their intercellular conununication. In the nervous system "privacy" is attained primarily by anatomical means whereas chemical messengers, operating over a long distance, are particularly used in the endocrine system. In the nervous system, neurons are the cells adapted for reception, integration and rapid transmission of information. Transmission occurs along dendrites and axons, which are elongated parts of the neurons themselves, and from one cell to another at morphologically identifiable sites of contact, the synapses. Transmission is mediated by a limited number of substances, neurotransmitters, which are released extremely close to receptors of the affected cells.