Neurophysiology: Special Senses (Fall 2024) PDF

Andre Azevedo, DVM, MSc Assistant Professor of Veterinary Physiology [email protected]  At the end of the lecture, students should be able to: Describe the function of the taste and smell Describe olfactory cells and their location Describe the basic stimulation...

Andre Azevedo, DVM, MSc Assistant Professor of Veterinary Physiology [email protected]  At the end of the lecture, students should be able to: Describe the function of the taste and smell Describe olfactory cells and their location Describe the basic stimulation of olfactory cells Describe taste buds and their location Describe the basic stimulation of taste cells Understand the relationship between taste/smell and the limbic system Describe the location and structure of the auditory sensory receptors Describe how sound waves are transduced to action potentials Summarize the events involved in hearing  smell The olfactory system is essential for: Localization of food/prey Reflex-stimulated secretion of digestive enzymes Detection of danger  The olfactory system consists of the following: info OLFACTORY BULB receive olfactory OLFACTORY TRACT send info LATERAL OLFACTORY GYRUS PIRIFORM LOBE receive info  The olfactory cells are part of the specialized epithelium found on the ethmo-turbinate bones of the nasal cavity Olfactory mucosa of dogs have 220 million olfactory receptors Humans = 5 million The olfactory cells give rise to the olfactory nerve fibers that terminate in the olfactory bulb  The olfactory cells are the receptor cells for smell sensation They are bipolar neurons derived originally from the central nervous system They are located in the olfactory epithelium interspersed among supporting cells Have cilia projecting into the mucus that coats the inner surface of the nasal É cavity notvisible hairs nose The cilia reacts to odors in the air and stimulate the olfactory cells Spaced among the olfactory cells are many olfactory glands Secrete mucus onto the surface of the nasal cavity Supporting only neurons that can regenerate over time cells receives  Bindtolevels a coupled receptors open catinatchannels openchloridechannel depot cAMP ion The OLFACTORY CILIA responds to olfactory chemical stimuli ODORANT MOLECULES THAT EPSP TRAVELS FROM THE CILIA ENTER THE NASAL CAVITY TO THE TRIGGER ZONE OF THE DIFUSES INTO THE MUCUS OLFACTORY CELL TO GENERATE AN ACTION POTENTIAL BIND TO GPCR IN THE MEMBRANE OF EACH CILIUM MEMBRANE DEPOLARIZES AND THE ALFA SUBUNIT ACTIVATES GENERATE AN EXCITATORY POST ADENYLYL CYCLASE, WHICH SYNAPTIC POTENTIAL (EPSP) IN PRODUCES cAMP THE CILIA cAMP ACTIVATES A GATED Na/Ca ION CHANNEL AND INFLUX OF Ca ACTIVATES ALLOW INFLUX OF CATIONS CLORIDE CHANNELS TO OPEN (MOSTLY CALCIUM) AND Cl LEAVES THE CELL specificcells  The olfactory nerve fibers terminate and synapse in the olfactory bulb to form the olfactory tract (CN I) Specific cells are present in the olfactory bulb TUFTED CELLS into MITRAL CELLS Dendrites from these cells synapse with E terminal ends of olfactory cells forming the glomeruli of the olfactory bulb  education miffy s The olfactory tract reaches: 1. the ipsilateral piriform lobe (olfactory area) 2. non-olfactory portions of the brain (part of the limbic system) Amygdala, entorhinal cortex, hippocampal formation, septal nuclei These areas also send olfactory signals to the hippocampus and frontal cortex OLFACTORY SIGNALS DO NOT DIRECTLY PROJECT TO THE THALAMUS Eistitiesor The limbic system is responsible for forming olfactory memories Olfaction can evoke emotional and autonomic responses  FYI OOT – Olfactory-occipital tract (orange) OCST – Olfactory-corticospinal tract (turquoise) OPT – Olfactory-piriform tract (green) OLT – Olfactory-limbic tract (blue) OET – Olfactory-entorhinal tract (pink)  THE CONNECTION BETWEEN TASTE, SMELL, AND MEMORY Both senses are strongly tied to primitive emotional and behavioral functions of the nervous system There are many connections between the olfactory and gustatory systems and the regions responsible for emotion and memory  Taste is mainly a function of TASTE BUDS which contains a taste receptor cell In dogs, they are located in various types of PAPILLAE Protrusions on the dorsal and lateral surface of the tongue 1. FUNGIFORM PAPILLAE Throughout the dorsal surface of the rostral two-thirds of the tongue Especially on the lateral margins and the tip 2. VALLATE PAPILLAE Occupy the caudal portion of the dorsal tongue FOL VAL FOL 3. FOLIATE PAPILLAE Dorsolateral part of the caudal part of the tongue FUNGI  Dogs have about 1700 taste buds, while humans have 9000 CATS ONLY 470! Dogs seem to have a sense of taste for sweet, salt, sour, and bitter not in one area all over  y Taste buds are composed of groups of columnar taste receptor cells microvini Bundled together like a bunch of bananas Taste receptors are arranged such that their tips form a small taste pore Through this pore extends microvilli Each taste cell has receptors for only one type of flavor I tastecellreceptor 1typeofflavor  Chemical molecules that trigger the sense of taste are dissolved by the saliva They enter the taste bud through a pore Bind to the receptors located in the membrane of the microvilli The binding of molecules with receptors depolarizes the membrane of the taste cells The mechanism depends on the taste molecule that binds to their specific receptors FEE  The taste cells are into innervated by bipolar to send g neurons that contribute to brain axons to 2 cranial nerves: Thalamus Emittae FACIAL (CN VII) GLOSSOPHARYNGEAL (CN IX) Afferent fibers send the message to the ipsilateral cerebral cortex (insular area) sensoryareafortaste Also projects to the amygdala of the limbic system! Brainstem  FYI Can minimize sometimes  FYI thanEg getsftp.tc delivered drugfuses  The auditory system is designed to detect and analyze sounds in the environment Much of animal communication relies on this system Hearing requires at least 1 ear, but localization of sound requires 2 ears Auditory system must detect the difference in time arrival or intensity of sounds in 2 ears Animal’s sense of hearing is enhanced by their ability to move their ears around Scan the environment for different sounds Localize the sounds  Hearing involves the external ear, middle ear, and inner ear The sensory receptor is located in the inner ear Outer ear Middle ear Inner ear  The external ear directs the sound waves into the ear canal Is composed by: The fleshy part – Pinna 8 The ear canal (L shaped) Is separated from the middle ear o by the tympanic membrane or eardrum o  The middle ear is an air-filled cavity in the temporal bone Connected to the nasopharynx by the auditory tube EUSTACHIAN TUBE Drains the middle ear cavity Contain the OSSICLES 3 tiny bones Mostly Air father Eustachian tube  cut a bulb The OSSICLES are 3 tiny bones connected to each other MALLEUS connected to the eardrum INCUS Between malleus and stapes STAPES connected to the oval/round window membrane separation between the middle and the inner ear Transmit vibrations via tympanic  we The OSSICLES transfer vibration of the eardrum to the oval window Avoids significant loss of vibration as the sound wave is transferred from the air-filled outer ear to the fluid-filled inner ear Where the sensory receptor is located Decrease the amplitude of sound waves protecting the sensitive sensory cells  The inner ear (LABYRINTH) contains the sensory organs for both the auditory system and vestibular system Vestibular system detects acceleration and static tilt of the head ftp.f ayEtifnedw  The auditory portion of the inner ear complex is called COCHLEA Spiral shaped Comes from the Greek word for snail Filled with fluid (perilymph) eqti.ie Contains COCHLEAR DUCT Filled with fluid (endolymph) ORGAN OF CORTI interfild Hair cell receptors  fluid detect vibration The sensory hair cells are mechanoreceptors Have 50-100 stereocilia in their apical surface more Eisen Connected by tip links at their tips a Tip links seem to be attached to K channels Open when bending of the stereocilia pulls the tip links apart Sterocilia do not regenerate and can cause hearing loss Excessively loud sounds can destroy them by moving them excessively  of K plots surrounded by endolymph The TECTORIAL MEMBRANE overlies the sensory cells An anchored gel-coated ridge The BASILAR MEMBRANE is the floor of the Organ of Corti More elastic Both are very important for sound transmission  9 pratfa s vibYEtgmpn TL waves w particular frequency can cross to get shortcut sounds differenciate diff through organofcortiis beingpassed  Sound waves are transmitted to the inner ear and cause vibration to the Organ of Corti The base of the hair cells sits on the basilar membrane, and the cilia are embedded in the tectorial membrane Vibration of the Organ of Corti causes bending of cilia on the hair cells by a shearing force as the cilia push against the tectorial membrane  more kt insid cel theathporatite Bending of the cilia produces a change in the K + conductance of the hair cell membrane Bending in one direction causes DEPOLARIZATION lotsof Triggers potassium influx from endolymph (High concentration) K+ Leads to Ca channel opening and release of neurotransmitter i Glutamate Function as an excitatory neurotransmitter Cause action potentials in the cochlear afferent nerve fibers Bending in the other direction causes HYPERPOLARIZATION Stops potassium influx Glutamate is not released Action potential is not formed  stueoiia mistificia amque.ae amount sweet closalness poet  This oscillatory pattern is called COCHLEAR MICROPHONIC POTENTIAL Intermittent release of glutamate – intermittent firing of afferent nerves Mirrors the waveform of the acoustic stimulus µ it Iii  Apex Different auditory hair cells are activated by different frequencies Base Hair cells located at the base of the basilar membrane respond best to high frequencies 0 Hair cells located at the apex respond best to low frequencies base apex  The basilar membrane act as a sound frequency analyzer The spatial mapping of frequencies is also present in the brain: TONOTOPIC MAP Map that tells where sounds of different frequencies are processed in the brain  Information is transmitted from the hair cells along the cochlear nerve Relays auditory impulses to the cochlear nuclei in the medulla oblongata Axons ascend the brainstem (making several synapses) and reach the thalamus The information is processed in the auditory cerebral cortex synapse Cindrosses  3ilat bothauditory toterfe https://www.youtube.com/watch?v=PeTriGTENoc FYI generort white FYI bad hearing  FYI can be deaf  FYI Congenital sensorineural deafness Dogs carrying the piebald or merle genes and breeds of cats carrying the white gene (pure white) The vascular bed, stria vascularis, is responsible for secretion of endocochlear fluid and maintenance of its high K+ concentration Absence of strial melanocytes, whose presence or postnatal development is suppressed by the piebald or merle genes, leads to degeneration of the stria vascularis The hair cell loss is secondary to degeneration of the cochlear blood supply Hair cell loss starts 1-3 weeks old, and is irreversible, leading to deafness  FYI Congenital sensorineural deafness More info: https://www.lsu.edu/deafness/VetClinNA.htm https://www.lsu.edu/deafness/deaf.htm https://www.merckvetmanual.com/ear-disorders/deafness/deafness-in-animals https://www.researchgate.net/publication/24421886_Brainstem_auditory_evoked_resp onse_BAER_testing_in_animals https://www.vin.com/apputil/content/defaultadv1.aspx?pId=11165&meta=generic&id=3 848661 https://www.cliniciansbrief.com/article/white-cat-genetic-deaf