Lecture 5 - Special Senses III JK-3 PDF

Special senses III HLTH1030 – Anatomy & Physiology of Body Systems Dr Jade Kenna School of Health Sciences Fremantle | University of Notre Dame Australia [email protected]  The ear – hearing and balance The three parts...

Special senses III HLTH1030 – Anatomy & Physiology of Body Systems Dr Jade Kenna School of Health Sciences Fremantle | University of Notre Dame Australia [email protected]  The ear – hearing and balance The three parts of the ear are the inner, outer, and middle ear The outer and middle ear are involved with hearing The inner ear functions in both hearing and equilibrium Receptors for hearing and balance: – Respond to separate stimuli – Are activated independently  Anatomy of the ear External ear – Pinna – Ear canal (EAM) – Tympanic membrane Middle ear – 3 ossicles – Oval and round windows – Eustachian tube Internal ear – Cochlea – Semi-circular canals  The inner ear Bony labyrinth – Tortuous channels worming their way through the temporal bone, filled with perilymph – Contains the vestibule, the cochlea, and the semicircular canals Membranous labyrinth – Series of membranous sacs within the bony labyrinth – Physiology of hearing – Summary The outer ear and external auditory canal act passively to capture the acoustic energy Sound waves strike the tympanic membrane causing it to vibrate Formation of a fluid wave within the cochlea Vibrations of the stapes footplate cause the perilymph to form a wave. This wave travels the length of the cochlea = Displacement of the basilar membrane Stereocilia are bent due to a shearing force causing change in resting membrane potential of the hair cell  Sound Transduction by Hair Cells Perilymph causes displacement of basilar and vestibular membranes (collectively known as cochlear membranes) Oscillations of cochlear membranes cause hair cell stereocilia to bend Stereocilia are different lengths Bend either towards or away from tallest stereocilium Signals from hair cells transmitted to brain via cochlear nerve  Sound Transduction by Hair Cells Bending of stereocilia causes increased opening or closing of mechanically-gated K+ channels Ca2+ Channel in hair cells ® Bending towards tallest stereocilium ® allows K+ to enter cell ® depolarisation ® Ca2+ enters cell increases release of neurotransmitter increases action potentials Principles of Animal Physiology, Moyes & Schulte, 1 st Edition, Benjamin Cummings Auditory pathway to the brain Organ of Corti (which contains all of the hair cells) sends signals via cranial nerve VIII Spiral ganglion transmit to the brainstem Synapses on the 2 cochlear nuclei Main pathway involves axons from the ventral cochlear nucleus to the inferior colliculus Travels to and synapses at the MGN Finish at the auditory cortex in the temporal lobe  Deafness -Hearing research Cochlear implant has been widely used but requires surgery to implant an electrical device Varying effects – positive and negative New research using stem cells to generate immature hair cells Immature hair cells produced from stem cells can respond to mechanical stimuli Oshima, 2010, Cell  Motion and Position Detectors in Invertebrates and Vertebrates Many invertebrates have simple form of gravity receptor, called statocyst In lobsters, statocyst is chamber lined with hairs at base of 2 antennae Each statocyst contains statolith comprising grains of sand held together by mucus Mechanoreceptors in vertebrates are contained in set of interconnected chambers in inner ear (vestibular labyrinth) Animal Physiology, Sherwood et al., 1st Edition, Thompson  Mammalian Vestibular Apparatus Comprises: - 3 semicircular canals - 1 utricle (otolith organ) - 1 saccule (otolith organ) Semicircular canals contain endolymph At base of each semicircular canal is ampulla (jug) Within each ampulla is cupula (cap)  Structure of Ampullae Each ampulla has ridge (crista) that extends into lumen of ampulla Mechanoreceptor hair cells extend out of crista into gelatinous cupula Cupula bridges width of ampulla Forms mobile barrier through which endolymph cannot circulate Mechanoreceptor hair cells transmit information to vestibulocochlear nerve (CN VIII) Neuroscience, Purves et al., 3rd Edition  Transduction of Rotation Principles of Animal Physiology, Moyes & Schulte, 1 st Edition, Benjamin Cummings Movement of stereocilia towards or away from kinocilium causes K+ channels to open or close Causes depolarisation or hyperpolarisation of hair cells, increasing or decreasing Ca2+ concentration within cells End result is increase or decrease in number of action potentials  Anatomy of Utricle and Saccule Utricle and saccule detect linear acceleration in same way that semicircular canals detect rotational acceleration Receptor cells are hair cells with stereocilia that extend into gelatinous layer containing small calcium carbonate crystals (otoliths) Glutamate is the key neurotransmitter  Chemoreception: Smell (Olfaction) Chemoreceptor response that depends on mechanisms similar to those involved in taste In olfaction, chemicals must dissolve in mucus in nasal passages before they can bind to specific chemoreceptors and be “registered” as smell by brain  Species Differences in Olfactory Ability Domestic animals have much better olfactory ability than humans This superior ability is reflected in – Greater surface area of nasal cavity lining – The size of the olfactory region of the brain Neuroscience, Purves et al, 4th Edition  Olfactory anatomy Smell is difficult to research At least 1000 ‘smell genes’ active only in the nose Extremely sensitive Air and odours Olfactory epithelia span 1cm2 ↑↑↑ on each side of the nose Nasal cavity also contains pain receptors Cilia located on dendrites Pifferi, 2010, Neurobiology of Olfaction, Chapter 8  Olfaction physiology Detection of odours at 1 in 10 million molecules – Stronger the odour = increased odour molecules Odorant molecules must cross the mucosal layer Odorant binding proteins mostly work via G coupled activation – Triggers depolarisation – leads to AP Smell depends on the pattern of activation of olfactory receptor neurons Mitral cells form the olfactory tract, eventually terminate in the olfactory cortex and limbic system How chemical signal is transduced to electrical signal  Taste - Gustation Receptors on cell membrane selectively bind to various chemicals in food Binding of chemical to receptor causes opening or closing of ion channels in cell membrane Causes change in electrical potential of receptor cell membrane Increase in intracellular Ca2+ causes release of transmitter, which signals afferent nerve  Neural Coding for Taste In humans, localisation of receptors means that some regions are more sensitive to certain tastes Several receptors communicate with single afferent system, making perception of taste quite complex  Taste bud distribution Most taste buds respond to 2-4 taste qualities Bitter buds most sensitive (protective) Sugar & salt most pleasurable (CHO/ minerals) Taste receptors are fast adaptors (partial 3-5 sec/ complete 1-5 min) Principles of anatomy and physiology, Tortora, 11 th Edn, Wiley  Signal Transduction in Taste: Sweet, Bitter and Umami Chemicals from each group bind to specific taste cell receptors linked to protein messengers in cell membrane Protein messengers linked to several different signal transduction pathways Cause release of Ca2+ from intracellular stores and/or allow Ca2+ to enter cell In all 3 tastes, final step is increase in intracellular Ca 2+, causing release of neurotransmitter  Gustatory pathway Facial nerve (anterior 2/3 of tongue) & Glossopharyngeal nerve (posterior 1/3 of tongue) Solitary nucleus of medulla (initiate PsNS reflexes to trigger saliva & gastric secretion) Thalamus to gustatory cortex of parietal lobes and limbic system  Lecture objectives Identify the main structures of the ear (middle + inner) Explain how sound transduction occurs Know the auditory pathway (from the spiral ganglion to the auditory cortex) What structures are involved in maintaining balance? What are the structures involved in olfaction? Explain the olfactory pathway Explain how taste is perceived and what pathway is involved in gustation Recommended reading: Tortora G et al. (2022) Principles of Anatomy and physiology, 3 rd ed., Chapter 17