MOB TCD Ear Professor Emeritus Moira OBrien FRCPI
MOB TCD Ear Professor Emeritus Moira O’Brien FRCPI, FFSEM (UK), FTCD Trinity College Dublin
MOB TCD External Ear • • Auricle One third cartilaginous Two thirds bony Medial tympanic membrane
MOB TCD Haematoma of Ear
MOB TCD External Ear • • • Roof shorter than floor Lined with columnar epithelium Ceruminous glands Otis externa (swimmer’s ear) Pain on pulling lobule
MOB TCD Tympanic Membrane • • • Three layers Outer squamous Middle fibrous Deficient superiorly Flaccid in upper portion Handle of malleolus embedded in fibrous layer • Inner mucous membrane • Concave laterally • Umbo
MOB TCD Tympanic Membrane • • • Set at angle 55°horizontal Nerve supply Great auricular Post inferior quadrant facial Tympanic branch of glossopharyngeal • Facial nerve • Blood supply • Superior more vascular
MOB TCD Middle Ear • Biconcave • Roof: tegmen tympani • Floor: bone separates it from carotid canal • Tympanic branch of glossopharyngeal nerve
MOB TCD Middle Ear • • Lateral wall Tympanic membrane Epitympanic recess Medial wall Lateral semicircular canal Canal facial nerve Promontory Tympanic plexus
MOB TCD Middle Ear Anterior Wall • Canal tensor tympani muscle • Opening Eustachian tube • Anterior opening for chorda tympani nerve • Bone separates it from carotid canal • Caroticotympanic nerves
MOB TCD Middle Ear Posterior Wall • Opening mastoid antrum • Pyramid • Opening for stapedius muscle • Canal for facial nerve • Posterior opening of chorda tympani
MOB TCD Contents Middle Ear • • Air Ossicles Tensor tympani muscle Stapedius muscle Chorda tympani Facial nerve Caroticotympanic nerves
MOB TCD Middle Ear • Malleous • Head, neck, handle, anterior process, posterior process • Incus, body long and short process
MOB TCD Stapes • • • Stapes Neck Anterior and posterior Foot piece fits into Oval window Stapedius muscles inserted back of neck of stapes • Facial nerve
MOB TCD Middle Ear Chorda Tympani
MOB TCD Joints • Synovial joints • Capsule consists mainly of elastic tissue • Transmits sound waves from air to scala vestibuli • Otosclerosis
MOB TCD Eustachian Tube • Two thirds cartilaginous • One third bony • Medial forms tubal elevation in lateral wall nasopharynx • Opens into anterior wall of middle ear • Levator and tensor palati muscles open Eustachian tube • Equalise pressure on tympanic membrane
MOB TCD Auditory Pathway • • • Cochlear nerve Cochlear nuclei Central auditory pathway Cortex temporal lobe
MOB TCD Cochlea • 2 ¾ turns • Modiolus central pillar • Axis of internal acoustic meatus • Spiral lamina • Basilar membrane • Vestibular membrane
MOB TCD Cochlea • • Oval window Scala vestibuli Scala tympani Secondary tympanic membrane • Contain perilymph • Scala media or duct of cochlea endolymph
MOB TCD Scala Media • • • Basilar membrane Spiral organ Hair cells of organ of corti Tectorial membrane Single row of inner hair cells • Each one has 20 large afferent • Outer hair cells
MOB TCD Sound Waves • • • Auricle External ear Tympanic membrane Malleous, incus, stapes Oval window Pressure waves in scala vestibuli, scala media, scala tympani • Round window
MOB TCD Cochlea • Travelling wave theory • Low tones peak at apex • High tones at base
MOB TCD Auditory Nerve • Receptors are hair cells of organs of corti • Bipolar cells • Cell bodies are in the spiral ganglion on the • Spiral lamina • Auditory nerve attached to lower border of pons • Cerebellar-pontine angle
MOB TCD Auditory Pathway • First order neurones end on ventral and dorsal cochlear nuclei • On inferior cerebellar peduncle • 2 nd order neurones • Trapezoid body • Lateral leminiscus • Inferior colliculus • Superior olivary nucleus
MOB TCD Auditory Pathway • • • Inferior colliculus Via inferior brachium Medial geniculate body 3 rd order neurones Auditory radiations to auditory cortex in temporal lobe
MOB TCD Lateral Leminiscus • • Fibres arise from Ventral cochlear nucleus Dorsal cochlear nucleus Form lateral leminscus Superior olivary nucleus Mainly contra lateral Fibres end in inferior colliculi nuclei back of midbrain
MOB TCD Superior Olivary Nucleus • Receives inputs from both ears • Intensity and timing • Ipsilateral are excitatory and earlier and more intense • Contralateral inhibitory via nucleus in trapezoid • Projects to inferior colliculi
MOB TCD Inferior Colliculi • Spatial information • Superior olivary nucleus • Intensity from ventral cochlear nucleus • Pitch from dorsal cochlear nucleus • Projects to medial geniculate body • Inhibitory to opposite collicular nucleus
MOB TCD Medial Geniculate Body • Medial geniculate body • Specific thalamic nucleus for hearing • Laminated and tone topic • Fibres project as auditory radiations to primary auditory cortex • Superior temporal gyrus and adjoining part of insula
MOB TCD Auditory Radiations
MOB TCD Primary Auditory Cortex • Temporal lobe • Heschl gyrus • Posterior portion high tones • Anterior low tones • Bilateral represented
MOB TCD Primary Auditory Cortex
MOB TCD Auditory Reflexes • Auditory to motor nucleus of 5 th and 7 th • Contraction of tensor Tympani and stapedius • Dampen vibrations • Auditory to reticular nuclei arousal • Connect to facial
MOB TCD Deafness • • • Conduction External Middle Inner ear Nerve deafness
MOB TCD Position of Body in Space • Visual system • The conscious proprioceptive system • Vestibular system
MOB TCD Vestibular Apparatus • • Bony labyrinth Bony cochlea Vestibule Bony semicircular canals Contain perilymph Communicates with CSF Subarachnoid space
MOB TCD Vestibular Apparatus • Membranous labyrinth • Superior and posterior common opening at non ampullary end • Lateral semicircular canals • Five openings into utricle • Endolymphatic duct • Saccule • Ductus reuiens • Duct of cochlea • Contain endolymph
MOB TCD Vestibular Receptors
MOB TCD Receptors • Sensory static receptors in macula of the utricle and saccule • Cristae of the ampullae are the end organs of the dynamic movement semicircular canals • Maculae respond to linear acceleration of head in horizontal or vertical plane during walking
MOB TCD Receptors • Hair cells are found in the macula discharge all the time • Cilia on the hair cells embedded in gelatinous substance containing calcium carbonate crystals
MOB TCD Vestibular Pathway • Cell bodies are in the vestibular ganglion in the internal acoustic meatus • Relay in vestibular nucleus
MOB TCD Vestibular Pathway • Vestibular nucleus to contra lateral • Ventral posterior nucleus of thalamus • Behind face area of somato-sensory cortex
MOB TCD Vestibular Pathway • Lateral vestibulospinal tract arises from lateral or Deiter’s nucleus • Descends in anterior column of same side • Synapse on anti-gravity motor neurones • Active during walking • Antigravity in utricle • Free fall saccule
MOB TCD Vestibular Pathway • Medial vestibulo-spinal • Descend bilaterally • Medial longitudinal Fasciculus (MLF) to cervical cord • Head righting reflex • Eye righting reflex • Arise from lateral vestibular nucleus • Extra ocular nuclei
MOB TCD Vestibular Pathway • Afferents from the cristae end in medial and superior vestibular nuclei • Two way connection with • Flocculo nodular lobe to all vestibular nuclei
MOB TCD Vestibular Pathway
MOB TCD Vestibular Pathway
MOB TCD Vestibulo-Ocular Reflexes • Rightward head turn activates in the right lateral semicircular canal • Resulting in contraction of left lateral rectus and right medial rectus
MOB TCD Vestibulo-Ocular Reflexes • Under cerebellar guidance • Right medial vestibular nucleus • Responds to rightward head turn • Impulse to opposite para median region • Medial rectus
MOB TCD Nystagmus • Horizontal vestibulo-ocular reflex • Fast and slow phase • Called after fast phase • Nystagmus accompanied by vertigo
MOB TCD Cortical Eye Fields
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