Biosciences: Audiology Lecture 4 Adam Beckman Head of Audiology Services, Plymouth Hospitals NHS...
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Transcript of Biosciences: Audiology Lecture 4 Adam Beckman Head of Audiology Services, Plymouth Hospitals NHS...
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:10.15347/wjm/2014.010. ISSN 20018762. - Own work. Licensed under CC BY 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/
The vestibular system
"Sobo 1911 773" by Dr. Johannes Sobotta - Sobotta's Atlas and Text-book of Human Anatomy 1911. Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/”
The vestibular system
Sobo 1911 773" by Dr. Johannes Sobotta - Sobotta's Atlas and Text-book of Human Anatomy 1911. Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/
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 - http://www.cami.jccbi.gov/aam-400/phys_intro.htm.. Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/
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
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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 (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– ………..