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The Special Senses 3) Hearing and Equilibrium 13th edition Chapter 17 Pages 635 - 671 12th edition Chapter 17 Pages 598 - 633 The Special Senses 3) Auditory Anatomy of the ear Anatomy of the ear Anatomy of the ear Anatomy of the ear Anatomy of the ear Anatomy of the ear Hearing Pathway Anatomy of the ear Anatomy of the ear Anatomy of the ear Anatomy of the ear Orientation of Vestibular Receptors A. Lateral View The horizontal semicircular canal & utricle: Lie in a plane that is tilted anterodorsally relative to the naso-occipital plane. B. Axial View Anterior & posterior semicircular canals, and Saccule: Arranged vertically in the head at 900 angles to the horizontal canal. The anterior & posterior canals: Also lie at 900 angles to each other. The anterior canal on one side is co-planar with The posterior canal on the opposite side. Text Fig. 22-3 © 2005 Elsevier Ménière Disease Disease results from a disruption of normal endolymph volume Symptoms include: Severe vertigo Positional nystagmus (nystagmus when head in a particular position) Nausea Affected individuals can also experience-unpredictable attacks of auditory & vestibular symptoms: Vomiting Tinnitus (ringing in ears) Inability to make head movements Inability to stand passively Low frequency hearing loss Treatment: administration of a diuretic (hydrochlorothiazide) & a salt restricted diet Persistent condition: shunt implantation into swollen endolymphatic sac, or delivery of a vestibulotoxic agents (gentamicin) into perilymph. Ampulla of Semicircular canal Hair Cell Activation Rotational head movements Angular accelerations Displace endolymph in membranous ducts Push cupula to one side or other Displace stereocilia/kinocilium of hair cells in same direction Macula and otolith organ Macula and otolith organ = Movement of endolymph toward ampulla Movement of endolymph Movement of endolymph away from ampulla Responses of the utricular maculae to head tilts Striola Similar in principle to semicircular canals. Hair cells & innervating afferents will be excited or inhibited, depending on their position relative to the striola. Weight of otoconia depolarized depolarized The weight of the otoconia causes stereocilia to be deflected. Hair cells on “upslope” side of the striola increase their firing rate, and those on the “downslope” side decrease their firing rate. Text Fig. 22-11 © 2005 Elsevier Equilibrium PATHWAY Vestibulospinal Network: Influences muscle tone & produces reflexive postural adjustments of the head and body vestibular nucleus Projects to all levels of the spinal cord Terminate on alpha & gamma motor neurons Excite extensor muscle motor neurons Stabilize body’s center of gravity & preserves upright posture
