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Extrinsic ◦ ◦ ◦ ◦ Connect pinna to skull & scalp Supplied by facial nerve Very little voluntary control in humans But auditory stimuli may evoke responses => some clinical value (electromyography) Intrinsic ◦ Connect different parts of pinna ◦ Supplied by facial nerve ◦ Very occasionally humans can activate 1 EAM has complex sensory innervation derived from cranial nerves V (trigiminal), VII (facial), IX (glossopharyngeal) and X (vagus) Mechanical stimulation (e.g. in wax removal, taking impressions) can cause: ◦ Coughing, altered cardiac function, fainting 2 Lecture 3 Anatomy and physiology of the ear 3 Eardrum Concave, disk like structure Viewed with the structures of the outer ear It is a boundary between the OE and ME The tymapanic membrane is composed of three layers 1. Outer layer made of skin (cutaneous) that is stretched to the osseous meatus 2. The middle layer made of tough fibrous connective tissue which contributes to the membranes ability to vibrate with impinging sound waves 3. Inner layer lined with mucous membrane Anatomy and physiology of the ear 4 Anatomy and physiology of the ear 5 The total area of the TM is about 63.3 mm2 It is extremely thin averaging about 0.07 mm Efficient vibrating surface Rich in blood supply The malleus (largest bone of the ME) is embedded in the fibrous portion of the TM (_______ layer) The handle of the malleus runs 11 o'clock in the left ear The tip of the malleus ends in the approximate centre of the TM and angles downward and backward. Anatomy and physiology of the ear 6 Umbo is the point of greatest retraction, at the centre of the TM The TM is observed by directing light from a device called an otoscope that contains a magnifying lens The TM is semi-transparanet thus the light allows some of the ME structures to become visible, the light rays directed against the TM are reflected and refracted producing a light reflex The light reflex is a cone shaped, gives indication of the ear tested (same direction of the tested ear) The tympanic annulus is a ring of tissues that hold the TM in position at the end of EAC Anatomy and physiology of the ear 7 Pars tensa – most of surface ◦ Taut ◦ Made up of four layers of tissue Most lateral – thin layer of skin (continuous with EAM) Then two dense fibrous layers – radial & circular fibres (in that order) Most medial – mucous layer (continuous with mucous membrane of middle ear) 8 Pars flaccida – superior region ◦ Thin, lax ◦ Only two layers of tissue (lacks fibrous layers) Manubrium of malleus is usually visible under otoscopy ◦ Tip is at umbo ◦ Runs to eleven-o-clock position in left ear ◦ (‘Cone of light under otoscopy – ___________________________ region) 9 Anatomy and physiology of the ear 10 It is the first mobile link in the chain of auditory events, and it reproduces the same spectrum of sounds that enter the EAC Movement of the TM causes identical vibration of the malleus Anatomy and physiology of the ear 11 - - 28th day of conception the human embryo bulges begin to appear on either side of the tissue that will develop into the head and neck, pharyngeal arches 6 arches separated by grooves or clefts Significant information is only available about the first three Mandibular arch Hyoid arch Glossopharengeal arch Anatomy and physiology of the ear 12 These arches are known to have three layers 1. Ectoderm- outer layer 2. Endoderm- inner layer 3. Mesoderm- inner core Each arch contains Artery Mesoderm Muscle Cartilage Nerve -ectoderm Anatomy and physiology of the ear 13 The auricle develops from the first two pharyngeal arches The tragus forms from the first arch Helix and antitragus from the second arch 2nd foetal month, the development of the auricle The EAC forms from the first pharyngeal groove and is very shallow until after birth By the fourth gestational week a primitive meatus is formed, by the 8th week solid core Anatomy and physiology of the ear 14 28th gestational week the solid core canalizes (form tube), although the entire osseous meatus is not complete until the time of puberty Pneumatisation or the formation of air cavities in the temporal bone surrounding the EAC begins at 35th foetal week, accelerated at the time of birth By the third foetal month the TM annulus is formed The formation of the TM begins by the start of the second embryonic month Anatomy and physiology of the ear 15 Anatomy and physiology of the ear 16 Congenital – Microtia (small ear size) - Prominent auricle that stand away from the head - Anotia (absent auricle) Acquired -accidents - Cancer - Burns - Trauma Anatomy and physiology of the ear 17 - - - - Congenital Atresia (the absence of the EAC) Stenosis (narrowing of the ear canal) Acquired Burns Trauma Collapsed ear canal (narrowing or closure of the canal caused by pressure of compressing the pinna against the side of the head Foreign bodies in the EAC Ear wax in the EAC External otitis Anatomy and physiology of the ear 18 Perforation in the TM Grommet in the TM Scarred TM Anatomy and physiology of the ear 19