Geniculate ganglion

Figure 22.3 Possible links in the induction of circadian rhythm between daylight, the suprachiasmatic nucleus and melatonin release from the pineal gland. Some fibres in the optic nerve, projecting from the eye to the lateral geniculate nucleus (LGN) in the thalamus, innervate the suprachiasmatic nucleus (SCN) in the anterior hypothalamus, via the retinohypothalamic tract (RHT). Others project to the SCN from the LGN in the geniculohypothalamic tract (GHT). The release of melatonin into the circulation from the pineal gland (PG) is maximal at night and appears to be controlled partly by noradrenaline released from sympathetic nerves originating in the superior cervical ganglion (SCG). Melatonin receptors are found in the SCN, the removal of which dampens melatonin secretion...

Neurotrophin 4/5 is not as well characterized as other members of the neurotrophin family. Much of what is known is derived from analysis of NT4/5 and TrkB knockout mice. Elucidating the actions of NT4/5 is complicated by virtue of the fact that both NT4/5 and BDNF exert their effects via the TrkB receptor. It appears that NT4/5 functions largely overlap with those of other neurotrophin family members, particularly BDNF. NT4/5 knockout mice are essentially normal, in contrast to BDNF knockout mice, which do not live long. NT4/5 is likely to have unique actions on a subpopulation of neurons in the nodose and geniculate ganglia, which are not supported by BDNF. Like BDNF, NT4/5 acts on sensory neurons and retinal ganglion cells, supporting their survival. 

Figure 6. Spontaneous and evoked spike activity recorded from taste neurons of the geniculate ganglion of the cat. The classification of the three different sensory neurons is indicated by Groups I, II, and III.

Figure 8. Chemical formulas for some of the most active stimuli for the cat geniculate ganglion neural groups...

Table I Summary of Neurophysiological Investigations on Mammalian Geniculate Ganglion Taste Systems.

Studies on human taste sensations confirm and extend our understanding of the types of chemical signals measured by these oral chemoreceptor systems. There are, for instance, several distinct sensations elicited by chemical stimulation of fungiform papillae innervated by the geniculate ganglion, indicating that a neural functional complexity similar to that described above for... 

The sensation of pleasant is postulated on the basis of cat neurophysiology and human psychophysics. The pleasant sensation is assumed to arise from the stimulation of a. small fiber geniculate ganglion system. The stimuli eliciting the pleasant sensation are lactones and other carbon-oxygen compounds (23). 

Figure 1. Diagram of the three cranial nerves and associated sensory ganglia that innervate taste buds. As illustrated, electrical recordings were taken from single neurons in the ganglia. Geniculate ganglion in facial nerve petrosal in glossopharyngeal nodose in vagus.

Salt Responsive Units. One of the neural groups with the simplest stimulus chemistry is the GG salt system found only in the geniculate ganglion of the rat and goat. These units are only responsive to sodium or lithium salts. When a series of Cl salts with different cations are examined, only those with Na and Li elicit large responses (Fig. 3). Na and Li are effective with other anions as well, although responses are largest with I and F (6). 

Geniculate Ganglion (Facial Nerve) GG. Petrosal Ganglion (Glossopharyngeal Nerve) PG... 

The ganglion cell layer (GCL) contains the cell bodies of retinal ganglion cells, with their axons running across the retinal surface (nerve fiber layer) toward the optic nerve head, and on through the optic nerve to the lateral geniculate nucleus in the mid-brain. The inner retinal blood supply (outside the foveal avascular zone), the nerve fiber layer, and a thin membrane (the inner limiting membrane) form the most superficial retinal structures. 

Information is passed to the brain in parallel circuits that are further divided at each synaptic relay. In the OPL, information from cones is divided into two pathways. One depolarizes in response to increases in photon capture (the ON channel, composed of bipolar cells, ganglion cells, and many cells of the lateral geniculate and visual cortex). The other depolarizes in response to decreases in... 

Yucel YH, Zhang Q, Weinreb RN, Kaufman PL, Gupta N. 2003. Effects of retinal ganglion cell loss on magno-, parvo-, koniocellular pathways in the lateral geniculate nucleus and visual cortex in glaucoma. Prog Retin Eye Res 22 465-481. 

Clinical evidence, lesion, and stimulation studies all point toward the participation of vitally important neural sites in the control of saccades, including the cerebellum, superior colliculus (SC), thalamus, cortex, and other nuclei in the brain stem, and that saccades are driven by two parallel neural networks [Enderle, 1994, 2002]. From each eye, the axons of retinal ganglion cells exit and join other neurons to form the optic nerve. The optic nerves from each eye then join at the optic chiasm, where fibers from the nasal half of each retina cross to the opposite side. Axons in the optic tract synapse in the lateral geniculate nucleus (a thalamic relay), and continue to the visual cortex. This portion of the saccade neural network is concerned with the recognition of visual stimuli. Axons in the optic tract also synapse in the SC. This second portion of the saccade neural network is concerned with the location of visual targets and is primarily responsible for goal-directed saccades. 

---