Special Senses. Olfaction via CNI. Biol 219 Lect 19 Fall Olfaction, Gustation, Hearing, Equilibrium. Figure 10.13b The Olfactory System

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1 Special Senses Olfaction, Gustation, Hearing, Equilibrium Olfaction via CNI Link between smell, memory, and emotion Olfactory sensory neurons Olfactory epithelium in nasal cavity Odorants bind to odorant receptors, G protein linked membrane receptors Figure 10.13a The Olfactory System Figure 10.13b The Olfactory System Olfactory Pathways The olfactory epithelium lies high within the nasal cavity, and its olfactory neurons project to the olfactory bulb. Sensory input at the receptors is carried through the olfactory cortex to the cerebral cortex and the limbic system. Ce re bra l c orte x The olfactory neurons synapse with secondary sensory neurons in the olfactory bulb. Olfactory bulb Limbic Olfac tory bulb Olfac tory tra c t Olfac tory c ortex system Bone Secondary sensor y neur ons Cranial Nerve I Olfactory sensory neur ons Olfactory epithelium Olfac tory neurons in olfactory epithelium FIGURE QUESTION Multiple pr im ar y neur ons in the epithelium synapse on one secondary neuron in the olfactory bulb. This patter n is an exam ple of what principle? 1

2 Olfactory neurons in the olfactory epithelium live only about two m onths. They ar e r eplaced by new neur ons whose axons must find their way to the olfactory bulb. Gustation Olfactory neuron axons (cranial nerve I) car r y infor m ation to olfactory bulb. Lam ina pr opr ia Basal cell layer includes stem cells that replace olfactory neurons. Olfactor y sensory neuron Capillary Olfactory (Bowman s) gland Developing olfactory neuron Closely linked to olfaction Tas te is a combination of five bas ic s ens ations : sweet, sour, salty, bitter, umami. Additional taste sensations may be linked to TRP pathways, same as thermoreceptors and nocireceptors: minty, hot spicy Supporting cell Olfactory cilia (dendr ites) contain odorant receptors. Mucous layer : Odorant molecules must dissolve in this layer. Gustation - via CN VII, IX, X Tas te receptor cells are non-neural epithelium. Each taste cell is sensitive to only one taste. Taste transduction Gustducin Humans and animals may develop specific hunger, such as salt appetite. Figure 10.14a Taste Taste Buds. Each taste bud is composed of taste cells joined near the apical surface with tight junctions. Taste buds are located on the dorsal surface of the tongue. Taste pore Taste ligands create Ca 2+ signals that release serotonin or ATP. Sweet Um a m i Bitte r Sour ATP Presynaptic cell (III) Tight junction Type I support cells may sense salt whe n Na + enters through channels. Salt? (Based on Tomchik et al., J Neurosci 27(40): , 2007.) Receptor cells (type II) Serotonin Light micrograph of a taste bud Primary sensory neurons 2

3 The Ear: Hearing CN VIII Perception of energy carried by sound waves Frequency is translated into pitch Loudness is an interpretation of intensity, a function of wave amplitude The Ear The pinna directs sound wa v e s into the ear. EXTERNAL EAR MI DDL E EAR INNER EAR Ma l l e u s Stapes The oval window and the round window separate the fluid-filled inner ear from the air-filledmiddle ear. Semicircular canals Vestibular apparatus Ov a l window Cochlea Ne rv e s Ear canal Tympanic membrane window To pharynx Eustachian tube Figure 10.16a Sound waves Sound waves are distinguished by their frequency, measured in hertz (Hz), and amplitude, measured in decibels (db). Figure 10.16b Sound waves (1) 1 Wavelength Sound waves alternate peaks of compressed air and valleys where the air is less compressed. Wavelength Intensity (db) Amplitude (db) 0 Time (sec) 0.25 (2) Tuning for k Intensity (db) Time (sec) Amplitude (db) FIGURE QUESTIONS 1. What ar e the fr equencies of the sound waves in graphs (1) and (2) in Hz (waves/second)? 2. Which set waves would be interpreted as having lower pitch? 3

4 Sl i d e 2 Sound Transduction So u n d Sound waves to mechanical vibrations when striking the tympanic membrane (ear drum) Three middle bones vibrate and transfer to membrane in oval window Vibrations generate fluid waves in the cochlea Hair cells bend in the cochlea and ion channels open Action potential travel to the brain Sl i d e 3 Sl i d e 4 So u n d wave e n e rgy i s tran sfe rre d to Th e stap e s i s wave e n e rgy i s attach e d to th e transmission sfe rre d to me mb e o f th e o val through the ear So u n d. Vi b rati o n s o f th e oval win d o w cre ate fl u i d within the cochlea. 4

5 Sl i d e 5 Sl i d e 6 Th e stap e s i s Th e fl u i d p u sh o n wave e n e rgy i s attach e d to th e e fle xib le s transmission sfe rre d to me mb e o f th e o val through of the cochlear duct. Hair the ear So u n d. Vi b rati o n s o f th e oval win d o w cre ate fl u i d within the cochlea. ce l l s b e n d an d i on ch an n e l s o p e n, cre ati n g an electrical signal that alters neurotransmitter release. Th e stap e s i s Th e fl u i d p u sh o n Ne urotransmitte r wave e n e rgy i s attach e d to th e e fle xib le s re le ase o n to se n so ry transmission sfe rre d to me mb e o f th e o val through of the cochlear duct. Hair neurons the creates action ear So u n d. Vi b rati o n s o f th e oval win d o w cre ate fl u i d within the cochlea. ce l l s b e n d an d i on ch an n e l s o p e n, cre ati n g an electrical signal that alters neurotransmitter release. potentials that travel th ro u gh th e co ch le ar nerve to the brain. Sl i d e 7 Th e stap e s i s Th e fl u i d p u sh o n Ne urotransmitte r wave e n e rgy i s attach e d to th e e fle xib le s re le ase o n to se n so ry transmission sfe rre d to me mb e o f th e o val through of the cochlear duct. Hair neurons the creates action ear So u n d. Vi b rati o n s o f th e oval win d o w cre ate fl u i d within the cochlea. ce l l s b e n d an d i on ch an n e l s o p e n, cre ati n g an electrical signal that alters neurotransmitter release. potentials that travel th ro u gh th e co ch le ar nerve to the brain. Energy from the waves tran sfe rs acro ss th e cochle ar duct into the tympanic duct and is dissipated back into th e mid d le e ar at th e round window. 5

6 Figure Signal transducti on in hair cells At rest: About 10% of t he i on channel s ar e open, and a t oni c si gnal is sent by the sensory neuron. Ti p l i nk St ereoci l i um Som e channel s open. Hai r cel l Exci t ati on: When the hai r cel l s bend i n one di rect i on, t he cel l depol ari zes, w hi ch increases action potential frequency in the associated sensory neuron. More channels open. Cat i on ent r y depol ari zes cel l. Inhibition: If the hair cells bend in the opposi t e di r ect i on, i on channel s cl ose, the cel l hyperpol ari zes, and sensory neur on si gnal i ng decr eases. Channel s cl osed. Less cat i on ent r y hyperpol ari zes cel l. Pr i m ary sensor y neur on Act i on pot ent i al s Act i on pot ent i al s i ncr ease. No act i on pot ent i al s mv Action potentials in pri mary sensory neuron Ti m e 0 mv 30 Rel ease Rel ease Membrane of hai r cel l potenti al Exci t at i on opens Inhibition closes ion channels. ion channels. Auditory Pathways Cochlea transforms sound waves into electrical signals Primary auditory neurons to brain in medulla oblongata Secondary sensory neurons project to nuclei Synapse in nuclei in midbrain and thalamus before projecting into auditory cortex The localization of a sound source requires simultaneous input from both ears. Hearing Loss Conductive No transmission through either external or middle ear Central Damage to neural pathway between ear and cerebral cortex or damage to cortex itself Sensorineural Damage to structures of inner ear 6

7 The Vestibular Apparatus via CN VIII The Vestibular Apparatus Series of interconnected fluid-filled chambers Otolith organs Saccule and utricle Linear acceleration and head position Semicircular canals Rotational acceleration Filled with endolymph Equilibrium projects primarily to the cerebellum The semicircular canals sense three-dimensional rotation. 7

8 The otolith organs (utricle and saccule) sense linear movement and position of the head. Figure Equilibrium pathways Ce re bra l cortex Thalamus Re ticular Vestibular apparatus Vestibular branch of vestibulocochlear nerve (VIII) Ce re bellum formation Vestibular nuclei of medulla Somatic motor neurons controlling eye movements 8