In the dog, pressosensitive endings of the sinus nerve extend along the border between the adventitia and media of the carotid sinus wall. The axon endings, containing a great number of mitochondria, can be divided into small (600-2,000 nm) and large (6,000-8,000 nm) end swellings. In the terminal region the pressosensitive fibers are surrounded by ramified and highly structured Schwann "terminal cells". The topographic location in relation to elastic and collagenous tissue indicates a functional connection between receptors and efferent nerve endings in the immediate surroundings has been discussed in this report. Several axon endings contain variable amounts of glycogen which is regarded as an indication for the inactive metabolic state of the ending. Axonal swellings demonstrate considerable modification in structure, such as loss of structural integrity in mitochondria, the formation of lamellar fields, vesicular irregularities and disintegration of axoplasm, all of which are considered as the morphological expression of "wearing out", degeneration and possibly regeneration.

In the rabbit, baroreceptive intercalated and terminal receptor segments of the sinus nerve extend in the border region of adventitia and media of the carotid sinus wall. These receptors measuring 600–6,500 nm harbour a great number of mitochondria. They are either round, ovoid or elongated. Round receptors are present over the whole area of the carotid sinus. Large receptors appear to be missing in the upper region, where only very elongated receptors are present, which are arranged in circular array in relation to the vascular axis. The baroreceptors are enveloped by special organelle-rich terminal cells of Schwann cell origin. The receptors have a special orientation in regard to the muscle-elastic system and to collagen. Receptors contain osmiophilic and laminated bodies, signs of degeneration and vesicles of different sizes. Many tubuli as well as glycogen granules are apparent. Some of these axoplasmatic changes appear to be related to metabolic processes (turnover) occurring in young and old animals.

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