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

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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

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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

Otolith organs • Utricle and saccule

• Sensitive to– Linear acceleration– Gravity

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• 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)