Bipolar Neuron

The Na" channel has a receptor site for cyclic GMP when cyclic GMP is bound, the channel is closed. This leads to a decrease in the intracellular Na ion concentration, resulting in hyperpolarisation of the cell membrane. This decreases the release of the neurotransmitter glutamate into the synapse that connects the photoreceptor cell to the bipolar neurones. In this specific case, a decrease in the neurotransmitter concentration in the synapse is a signal that results in depolarisation of the bipolar cell. The action potential in the bipolar cells communicate with ganglion cells, the axons of which form the optic nerve. Thus action potentials are generated in the axons which are... 

The taste cells are situated in the lingual epithelium with the apical membrane exposed to the mucosal surface of the oral cavity and the basal surface in contact with the nerve [interstitial fluid] [FIGURE 10]. Within the basolateral surface are the nerves which respond to the chemestiietic stimulants, i.e. direct nerve stimulation. The microvilli at the apical membrane contain receptor proteins which respond to sweeteners, some bitters and possibly coolants. The olfactory cells are bipolar neurons with dendritic ends containing cilia exposed to the surface and axons linked to the brain, where they synapse in the olfactory bulb. The transfer of information from this initial stimulus-receptor interaction to the brain processing centers involves chentical transduction steps in the membrane and within the receptor cells. The potential chemical interactions at the cell membrane and within the cell are schematically outlined in FIGURE 10. 

Anatomically, the chemosensory cells of these animals share a unifying set of characteristics they are bipolar neurons with ciliated dendrites closely apposed to the environment and axons that project into the central nervous system from a peripherally located cell body. This is a cellular bodyplan that is characteristic of chemosensory cells from a broad range of metazoan phyla, so much that has been learned by the study of crustacean chemosensory neurophysiology has been of heuristic value to the understanding of chemoreception in other organisms. 

Figure 20.1 Olfactory sensory cells of both insects and vertebrates are primary sensory cells, i.e. they are bipolar neurons extending a sensory dendritic process towards the odorous environment and projecting an unbranched axon directly to specialized target regions in the central nervous system.

Coggins, M. R., Grabner, C. P., Aimers, W., and Zenisek, D. (2007). Stimulated exocytosis of endosomes in goldfish retinal bipolar neurons.. Physiol. 584, 853—865. 

One of the lesser functions of the nose in man is that of olfaction. The olfactory region of the nose, a small patch of tissue containing the smell receptors, is located towards the roof of the nasal cavity and is lined with non-ciliated neuro-epithelium. Approximately 20% of the air flowing through the nasal cavity is directed upwards to the olfactory region. Here, bipolar neurones react to inspired air and initiate impulses in the olfactory nerves. 

Bipolar neurons have tw o processes extending from the cell body (Figure 14.2). Most sensory (or afferent) neurons are this type, carrying messages from the body s sense receptors (eyes, ears, etc.) to the CNS. Sensory neurons account for 0.9% of all the neurons. Examples of sensory neurons are retinal cells, olfactory epithelium cells, and the cochlear and vestibular ganglia. 

Berrebi AS, Oberdick J, Sangameswaran L, Christakos S, Morgan JI, Mugnaini E (1991) Cerebellar Purkinje cell markers are expressed in retinal bipolar neurons. J. Comp. Neurol, 308, 630-649. 

Oberdick J, Smeyne J, Mann JR, Zackson S, Morgan JI (1990) A promoter that derives transgene expression in cerebellar Purkinje and retinal bipolar neurons. Science. 248, 223-226. 

The peripheral organ for the olfactory system is the olfactory sensory epithelium, located in the dorsal-posterior portion of the nasal cavity. This epithelium, composed of several different types of cells, contains bipolar neurons (also known as olfactory receptor cells) whose axons extend to the brain and terminate in the main olfactory bulb. The VN organ is also situated in the periphery, and similarly contains several different types of cells, the most numerous being bipolar neurons whose axons terminate in the accessory olfactory bulb. The VN organ opens into the roof of the mouth via a very narrow channel, the VN duct. In snakes the tongue delivers odorants to the opening of the VN duct and, by a mechanism at present not understood, these odorants reach the dendritic tips of the bipolar neurons (Halpern and Kubie, 1980). 

Olfactory and vomeronasal bipolar neurons may differ in their responsiveness to stimulating substances and these differences in response characteristics could provide important clues to their differential functions. In garter snakes a spectrum of chemical stimuli (standard odorants, amino acids and prey products, including purified proteins from earthworms, a favored prey of garter snakes) applied to the vomeronasal epithelium modify unit responses in the AOB (Inouchi et al., 1993 Wang et al., 1993 Taniguchi et al., 1998,2000). 

Bipolar neuron Neuron with output signal between — 1 and +1. 

Intemeurons, as the name implies, are bipolar neurons that connect two other neurons. They are located in all areas of the spinal cord, not just the anterior horn. Intemeurons are small, highly excitable, and often spontaneously active. They can fire as rapidly as 1,500 times per second. 

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