title: Innervation patterns in rat saccular macula. A structural basis for complex sensory processing.
abstract: Serial sections through the anterior part of rat saccular macula were reconstructed as montages. Findings are that type II hair cells are integrated into the neural circuitry of type I cells, chiefly by synapses with neighboring calyces and their collaterals; and that complex interactions between afferent- and efferent-type nerve elements take place. Three basic types of nerve/calyx pattern are present: U-type nerves lose their myelin before they enter the macula and have complex calyces with several collaterals; M-type nerves are myelinated up to the calyx, which lacks collaterals; and M/U-type nerves have short, unmyelinated segments proximal to their calyces, which have few collaterals. Both afferent- and efferent-type collaterals spring from calyces, chiefly from those of U-type nerves. Type II cells are presynaptic both to electron-lucent and to vesiculated terminals; some synapses are reciprocal. Electron-lucent boutons sometimes are presynaptic to calyces and to type II hair cells; and morphologically afferent-to-afferent kinds of synapses occur in the neuroepithelium. The anatomical findings indicate that complex information processing must occur in mammalian gravity receptors.
mesh_terms: D000818:Animals; D006112:Gravitation; D006198:Hair Cells, Auditory / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D009412:Nerve Fibers / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000648:ultrastructure; D009476:Neurons, Efferent / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D012444:Saccule and Utricle / Q000294:innervation* / Q000648:ultrastructure; D012677:Sensation / Q000502:physiology*; D013047:Specific Pathogen-Free Organisms; D013569:Synapses / Q000648:ultrastructure