Cochlear nuclei

When a sound pressure wave impinges on the ear, it is amplified by the external auditory meatus and causes the tympanic membrane to vibrate in a characteristic manner. This vibration is transformed by the auditory ossicles of the middle ear into movements of the stapedial footplate. These movements create pressure waves in the fluids of the inner ear which displace the basilar membrane of the cochlear duct and cause the hair cells located on the top of the basilar membrane to generate electrical potentials. This potential elicits impulses in the auditory nerve. After the auditory nerve, the nerve impulses are transmitted through the cochlear nuclei, the trapezoid body, the... 

GrA granule cell layer of the accessory olfactory bulb 2-3, 82 GrC granular layer of the cochlear nuclei 62-65 GrDG granular layer of the dentate gyrus 35, 47, 87,106 GrO granular cell layer of the olfactory bulb 1-4, 80... 

Fig. 147. Photographs and diagrams of AChE-stained sections from rabbit flocculus. The compartments Cj and 1-4 of the flocculus white matter are indicated in the diagrams with different symbols, a-d. Rostralmost section, c-f. Caudalmost section. Arrows indicate the AChE-postive borders between the compartments, bp = brachium pontis Cj = compartment CO = cochlear nuclei f (1-4, p) = folium 1-4 and folium p of the flocculus L = lateral cerebellar nucleus m = folium m of the flocculus pf = floccular peduncle PFLDA = dorsal and ventral paraflocculus. Tan et al. (1995a).

Cochlear Nuclei Superior Olivary Complex Nuclei of... 

Human hearing arises from airborne waves alternating 50 to 20,000 times a second about the mean atmospheric pressure. These pressure variations induce vibrations of the tympanic membrane, movement of the middle-ear ossicles connected to it, and subsequent displacements of the fluids and tissues of the cochlea in the inner ear. Biomechanical processes in the cochlea analyze sounds to frequency-mapped vibrations along the basilar membrane, and approximately 3,500 inner hair cells modulate transmitter release and spike generation in 30,000 spiral ganghon cells whose proximal processes make up the auditory nerve. This neural activity enters the central auditory system and reflects sound patterns as temporal and spatial spike patterns. The nerve branches and synapses extensively in the cochlear nuclei, the first of the central auditory nuclei. Subsequent brainstem nuclei pass auditory information to the medial geniculate and auditory cortex (AC) of the thalamocortical system. 

The auditory nerve of the human contains about 30,000 afferent fibers. Most (93%) are heavily myelinated and arise from Type I SGCs whose distal processes synapse on IHCs. The rest are from smaller, more lightly myehnated Type II SGCs. Each IHC has, on average, a number of Type I SCCs that synapse with it, 8 in the human and 18 in the cat. In contrast, each Type II SGC contacts OHCs at a rate of about 10 to 60 cells per fiber. The tonotopicaUy organized nerve (low-frequency fibers in the center and high-frequency fibers in the outer layers) exits the modiolus and enters the internal auditory meatus of the temporal bone on its path to the cochlear nuclei. 

The central auditory system consists of the cochlear nuclei groups of brainstem nuclei including the superior olivary complex (SOC), nuclei of the lateral lemniscus (LL), and inferior colliculus (1C) and the auditory thalamocortical system consisting of the medial geniculate in the thalamus and multiple areas of the cerebral cortex. Figure 5.4 schematically indicates the nuclear levels and pathways. Efferent pathways are not shown. Page constraints prevent us from providing uniform detail for all levels of the auditory system. 

FIGURE 5.5 PSTH categories obtained for neural spike activity in the nerve and cochlear nuclei in response to brief tone bursts (stimulus envelope shown in lower left). Discharges in the nerve have the PL pattern while the others are associated with regions of the VCN and DCN and with specific morphological types. 

Young E.D. (1984). Response characteristics of neurons of the cochlear nuclei. In Hearing Science Recent Advances. C.I. Berlin (Ed.), San Diego, Cahfomia CoUege-HiU Press. 

Results in newborn kittens showed a selective nuclear staining by bilimbin in thalamic nuclei, subthalamic nuclei, inferior colliculi, cuneate nuclei, and cochlear nuclei. The intensity of staining correlated with the time of exposure. Histologically, changes were seen in some neurons, and consisted of vacuoladon and pyknotic nuclei. 

Volume 239 —The Mammalian Cochlear Nuclei Organization and Function... 

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