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Beyond the Brain: Special senses revision for Yr 1 MBChB By Gregory KC AnyaegbunamILOs
 T aste, Smell and Hearing - Brief anatomy of nose, tongue and ear - Properties of sound, taste and smell - Transmission of impulses from sense organs to the brain - Overcoming impedance mismatch - Taste and smell in enjoyment of food Wednesday, 7 December,Sample Footer Text 2 • Gross anatomy of the ear Wednesday, 7 December, 2022 Sample Footer Text 3Middle Ear Wednesday, 7 December, 2022 Sample Footer Text 4Inner Ear Wednesday, 7 December, Sample Footer Text 5 • Sound is the vibration of any object propagated as waves via a Sound and material medium (air or water) till it gets to human ear and subsequent interpretation by the brain. Hearing Wednesday, 7 December, 2Sample Footer Text 6Properties of sound • Pitch as a measure of frequency. Humans hear 20Hz to 20,000Hz • Loudness/intensity as a measure of amplitude in decibels. • The most quiet sound (by pitch and amplitude) humans can hear is regarded as the threshold sound. Wednesday, 7 December, 2022 Sample Footer Text 7Physiology of hearing • Humans have two ears to help them locate direction of sounds. • Sound waves pass through air in the outer and middle ear chamber to fluid medium in the inner ear before triggering neurotransmission to the brain. • Sound waves moving from air to fluid medium will have to overcome impedance mismatch. • The outer and middle ear chamber functions to amplify the sound wave to overcome impedance mismatch. • Pinna and ear canal amplifies sound waves by 20decibels • Tympanic membrane has big surface area to amplify vibrations transmitted to the 3 ossicles of the middle ear. • Malleus (hammer), incus (anvil), stapes (stirrup) smallest bones in human body. • Eustachian tube serves to balance the air pressure in the middle ear with outside world. th Wednesday, 7 December, 2022 Sample Footer Text 8 Inner ear physiology Made of oval and round windows, semi- circular canal, cochlea and vestibulo- cochlea nerve Malleus hits on the incus that hits stapes that hits on oval window sending sonic wave through the fluid (perilymph) in the scala vestibuli and scala tympani till the round window dissipates the wave. The cochlea duct contains the endolymph The Sonic waves causes vibration to the organ of conti in the cochlea which converts sound waves into neurochemical impulses for onward journey to the brain Tuesday, February 2, 20XX Sample Footer Text 9 Organ of Conti Contains tectorial and basilar membrane, outer (OHC) and inner hair cells(IHC) (stereocilia), cochlear duct and cochlear nerve fibres. Waves from perilymph in scala tympani, vibrates the basilar membrane where the hair cells sit, leading to movement of hair cells in coordinated fashion. Wednesday, 7 December, Sample Footer Text 10Signal transduction OHC acts as amplifier by increasing the vibration rate in the basilar membrane IHC has cochlear nerves underneath them and transmits sensory stimuli via glutamate neurotransmitter to cochlear nerve Wednesday, 7 December, 2022 Sample Footer Text 11 OHC and IHC Wednesday, 7 December, 2022 Sample Footer Text 12 Physiology of taste and smell connected in humans very muchMechanism of taste and smell Humans have 5 main taste buds present in papilla of the tongue. They sense 5 major substances. Salty (NaCl), sweet (glucose), sour (acid), umami (glutamate) and bitter (alkaline) There are olfactory receptors that detect odorant substances. The main mechanism of action is that these substances/molecules act as ligands that bind unto specific taste and neurochemical signal to the brainiggers Cranial Nerve 1 (olfaction) projects into the limbic system (amygdala, hippocampus) Cranial nerve V, VII and IX (taste) to gustatory cortex, solitary nucleus of medulla and thalamusT aste and smell in enjoyment of food • The sense of taste is limited to 5 tastes. • The sense of smell has huge variety of sensations • The closeness between the nose and mouth allows for the nose to pick up sensations in the form of smell that compensates what the tongue senses. • This allows a synergy and complementarity of sensations coming from the nose and mouth to the brain to lead to proper appreciation of food taste Wednesday, 7 December, 20Sample Footer Text 16Thanks for coming Wednesday, 7 DecemberSample Footer Text 17Question 1 • What is the neurotransmitter produced by stereocilia cells in the Organ of conti? a. Acetylcholine b. Dopamine c. Norepinephrine d. Glutamate e. ATP Wednesday, 7 December, 202Sample Footer Text 18 Question 2 What cranial nerve supply the posterior 1/3 of the tongue? a. CN X (Vagus) b. CN IX (Glossopharyngeal) c. CN V (Trigeminal) d. CN XII (Hypoglossal) e. CN XI (Accessory) Tuesday, February 2, 20XX Sample Footer Text 19 Question 3 The olfactory bulb projects into what part of the brain? a. Thalamus b. Hypothalamus c. Limbic system d. Cerebral cortex e. Medulla Tuesday, February 2, 20XX Sample Footer Text 20Thank Y ou Gregory KC Anyaegbunam On behalf of Glasgow Neuro BEYOND THE BRAIN SERIES Wednesday, 7 DecembSample Footer Text 21