Biosciences: Audiology Lecture 4 Adam Beckman Head of Audiology Services, Plymouth Hospitals NHS Trust

Introduction Physics of sound ✔ The ear – anatomy and physiology Hearing –How it works ✔ Introduction – function ✔ –Pathology ✔ –How we measure it ✔ The vestibular system - today

The vestibular system Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI: /wjm/ ISSN Own work. Licensed under CC BY 3.0 via Wikimedia Commons -

The vestibular system "Sobo " by Dr. Johannes Sobotta - Sobotta's Atlas and Text-book of Human Anatomy Licensed under Public Domain via Wikimedia Commons -

The vestibular system Sobo " by Dr. Johannes Sobotta - Sobotta's Atlas and Text-book of Human Anatomy Licensed under Public Domain via Wikimedia Commons -

Semi-circular canals 3 canals –Orthogonal (at right angles) to each other –Horizontal or lateral semi-circular canal –Superior or anterior semi-circular canal –Posterior semi-circular canal

Semi-circular canals Filled with endolymph End open up into bulge –Osseous ampulla –Inside this is the crista ampullaris

Semi-circular canals "Vestibular system's semicircular canal- a cross-section" by United States government - Licensed under Public Domain via Wikimedia Commons -

Semi-circular canals Rotational movement –Displaces hair cells Semi-circular canals in action Push-pull system –Left and right –Excitatory on one side = inhibitory on the other side

Semi-circular canals Horizontal or lateral semi-circular canal –12-15mm long –Arched horizontally – laterally and backwards –Head rotating sideways E.g. “No”, crossing road Superior or anterior semi-circular canal –15-20mm long –Arched upwards –Head rotating front-back E.g. nodding “yes”

Semi-circular canals Posterior semi-circular canal –18-22mm long –Arched upwards at the back –Rotation Head tilting onto shoulder

Semi-circular canals Movement stops –Endolymph continues to move Lag Endolymph moving Continuous movement –Habituates No longer aware turning

Otolith organs

Utricle and saccule Sensitive to –Linear acceleration –Gravity

Otolith organs "Bigotolith" by Original uploader was Password at en.wikipedia - Transferred from en.wikipedia; Transfer was stated to be made by User:Padawane.. Licensed under Public Domain via Wikimedia Commons -

Otolith organs Endolymph Hair cells Otoliths –Calcium carbonate crystals in gelatinous material Change of direction of force –Otoliths move, shearing motion on hair cells Otolith video

Otolith organs Utricle –Larger otolith organ –Linear acceleration Start in a car –Crystals have more mass –Take longer to start moving – drag the stereocilia Stop in a car –Crystals have intertia –Continue to move – drag the stereocilia in the opposite direction

Otolith organs Saccule –Smaller otolith organ –Vertical acceleration Gravity Going up or down in a lift

Otolith organs Information utilised from –Left and right organs –Proprioception Neck –Eyes –example; Tilt head backwards –Is head tilting or body tilting? –We know head is tilting from combined information from neck and otolith organs

Vestibulo-ocular reflex When we walk, why doesn’t this happen? Film trailer.....

Vestibulo-ocular reflex Steadicam Tracking shot with steadicam......

Vestibulo-ocular reflex (VOR) Image stabilised on retina When head moves, eyes move in opposite direction –Head move right, eyes move left and vice versa Head moving all the time –So essential

VOR – rotation to the left Movement of endolymph in semi-circular canal –Signal to: VIII nerve Nucleus vestibularis Contralateral VI nerve –Nucleus abducens Lateral rectus AND also medial longitudinal fasciculus of contraleteral eye Medial rectus muscle of each eye Eyes move to the right

Vestibulo-ocular reflex Problems with VOR will make everyday activities challenging –Reading –Driving –Walking down stairs –………..

Summary Summary video Vestibular system –Semi-circular canals –Otolith organs –Vestibulo-ocular reflex (VOR)