Special Sense Cells

OLFACTION GUSTATION Studies on olfaction and gustation both support the labeled-line theory as the method for specificity of encoding. That is, one cell expresses only one type of receptor, and thus a specific odour or Taste receptor cells release a variety of neurotransmitters, including ATP, serotonin, GABA, acetylcholine, and norepinephrine onto afferent taste neurons. Olfactory sensory- neurons (OSNS) each extend one dendrite to the nasal · Taste receptor cells are located within taste buds, taste pore can be perceived. taste which are embedded in tongue cavity epithelium, where cilia from these OSNS receive odorants. In humans, there are papillae. They express both ion channels and GPCRS on their surface membranes. Each type of receptor is reactive to a different class of sapid substances - what we perceive as taste. olfactory sensory neurons approximately 400 different types of G-protein coupled receptors (GPCRS) that are sensitive to specific odours, and are located on the cilia of OSNS. olfactory bulb papilla afferent taste neuron SPECIFICITY: Sour: direct influx of H* contained in foods through H* ion channels cause depolarization. Each OSN expresses only one type of GPCR, and in turn will only react to one specific odour. The OSNS that express the same receptors converge and SPECIFICITY: OSNS release AMPA, • kainate, and NMDA Umami: perceived taste of umami is similar to sweet, but the Sweet: presence of sweet tastants activates the GPCR complex composed of gustducin protein and TIR2, T1R3 receptors. synapse onto the same as neurotransmitters glomerulus in the olfactory bulb. This odour receptor complex is composed of TIR1 and T1R3. onto glomeruli in the olfactory bulb, which is a part of the limbic system in the brain. facilitates discrimination. taste buds Moreover, the many combinations of GPCR activation can also code for different smells, allowing us distinguish many more odours than the 400 receptor types available. Bitter: detected by the T2R family of GPCRS. Salty: Na* presence greater than 10mM opens Ca² gated ion channels, causing depolarization. to SPECIAL SENSE CELLS Energy Conversion and Categorization ·Photoreceptors convert light into electrical impulses that are sent to the brain, through phototransduction. The Hair cells located on the• Our perception of the world is mediated through special sense cells.Although primary sensory cells may look different and require different mechanisms of action, parallels between these cells give us insight into how they work in energy conversion - from the outside world into electrical energy to be sent to the brain. These ciliated cells are the gatekeepers of our perception, and provide us with what we know of the world. basilar membrane have stereocilia that are in contact with the tectorial membrane. presence of photons closes cyclic nucleotide gated channels on the surface of photoreceptor cells, causing hyperpolarization. This increases activity of downstream bipolar cells, propagating the light response. Sound waves converted into vibrations in the inner ear displace the basilar membrane and deflect the stereocilia. This opens mechanically gated ion channels, leading to hair cell depolarization, and downstream auditory nerve stimulation. SPECIFICITY: Whereas rods are responsible for scotopic vision, cones provide us with photopic vision. Trichomacy, coupled with colour SPECIFICITY: Differing frequencies of sound affect different locations of vibration on the cochlea retina opponency, allow us different to distinguish of light. basilar membrane, as well as different wavelengths sized stereocilia. This is called place coding in the ear. Another theory that allows for specificity of frequency detection is temporal coding: it is the pattern of firing of auditory nerve fibres that codes for what we perceive as pitch. As a result of sterocilia deflection, the hair cells release bursts of glutamate, which stimulates afferent Downstream processing of information obtained from the three cone types (each sensitive to different wavelengths) and the signalling of information between photoreceptors and ganglion cells, codes for what we eventually perceive as colour. Phototransduction results• in glutamate release onto postsynaptic bipolar cells, causing depolarization of these cells, and subsequent downstream signalling. rod cone nerve fibres that form the Both hair cells and photoreceptors are activated by conformational changes in ion channels on the cilia membrane. As well, they commonly use glutamate the signaling neurotransmitter. auditory nerve. AUDITION human visible spectrum (nm) VISION 20 human hearing range (Hz) 20,000 380 740 as © Jennifer Gu 2020 oracton inner hair cells taste receptor