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Line 278: − ==The External Ear== − − [[image: Canine Auricular Cartilages.jpg|thumb|250px|right|The auricular cartilages of the left canine ear. Image by Rachael Wallace]] − − This includes the '''pinna''' and the '''ear canal''' (''external auditory meatus'') down to the level of the '''tympanic membrane'''. − − The pinna comprises the '''auricular [[Cartilage - Anatomy & Physiology#Structure and Function of Cartilage|cartilage]]''', which is flared distally into a flattened cone shape, covered by skin on both sides - more tightly on the medial or concave side than the convex side. The [[Hair - Anatomy & Physiology|hair]] covering on the convex side is usually similar to the rest of the body but the hair covering on the concave or medial aspect is variable. There are also irregularities on the concave surface with ridges and prominences, the '''medial and lateral crus of the helix''' on the medial aspect of the opening of the external ear canal, opposite the rectangular '''tragus''' on the lateral aspect. − − [[image: Rabbit ears.jpg|thumb|250px|left|Two rabbits: one with wild-type erect pinnae, the other with pendulous pinnae for comparison]] − − The functional shape of the pinna in wild-type mammals is erect, and the muscular connections at the base of the pinna allowing positional adjustments to efficiently collect sound. Many domesticated species, however, have non-erect, pendulous pinnae, as a result of selective breeding. This and other conformational changes may contribute to aural disease, particularly in the dog, but also other species including the lop-eared rabbit. − − Proximally, the auricular cartilage is rolled into a funnel shape, known as the '''concha'''. The '''scutiform''' cartilage lies rostromedially in the lower ear canal and provides support. The '''annular''' cartilage lies between the proximal horizontal ear canal and the bony '''acoustic process''' of the [[Skull and Facial Muscles - Anatomy & Physiology#Temporal Bone (os temporale)|typmanic bulla]], connected by ligaments. The vertical ear canal lies in a rostroventral orientation before bending medially to become the horizontal canal. − − ===Innervation and Vascularisation of the Ear=== − − The vascular supply to the outer ear is provided by the '''great auricular arteries''' (ex internal carotid artery). Venous drainage is via satellite veins to the '''internal maxillary veins'''. Innervation is provided by the '''auriculopalpebral branches of cranial nerve VII''' to the auricular muscles and sensory supply by cervical nerve II and cranial nerve V. − − In the tissues medial to the ear canal lie the auricular and superficial temporal arteries. Laterally is the '''parotid salivary gland''' and also a branch of the [[Cranial Nerves - Anatomy & Physiology|facial nerve]], external maxillary vein and branches of the external carotid artery. The facial nerve exits the skull through the stylomastoid foramen behind the osseous bulla; it passes below the rostroventral aspect of the horizontal ear canal. The '''auriculo-temporal''' branch of the mandibular portion of the [[Cranial Nerves - Anatomy & Physiology|trigeminal nerve]] (CN V) and branches of the facial nerve pass rostral to the vertical ear canal. − − The cartilage and bony process of the external ear and the tympanic membrane are covered by skin. The skin of the normal ear has a thin stratified keratinising epidermis and a thin dermis containing adnexal structures – [[Hair - Anatomy & Physiology|hair follicles]], [[Skin - Anatomy & Physiology#Glands|sebaceous and apocrine glands]]. The density of hair follicles on the concave pinna is variable, as is the density and distribution of hair follicles in the ear canal itself. Some species are devoid of hair in the lower (proximal) ear canal (eg horse); hair follicle density in the dog is variable – usually simple but in some breeds compound hair follicles. − − ===Glands of the Ear Canal=== − The apocrine glands in the ear canal are modified and known as ceruminous glands. The material secreted into the ear canal, '''cerumen''' (or wax), is compromised of exfoliated epithelial cells (squames) and glandular secretions. Sebaceous glands predominate distally and are largely responsible for the lipid component of cerumen. The density of ceruminous glands increases proximally, towards the tympanic membrane. The secretions of the ceruminous glands contain mucopolysaccharides and phospholipids. Immunoglobulins [[IgA]], [[IgG]] and [[IgM]] have been identified in canine cerumen, predominantly [[IgG]]. − − The epithelial cells in the [[Skin - Anatomy & Physiology#Epidermis|stratum granulosum]] of the tympanic membrane migrate centripetally, and this migration comprises the natural cleaning mechanism keeping the tympanum free of debris. The upward/distal migration of epithelial cells clears desquamated cells, secretions, debris and microbes. The more aqueous secretions of the ceruminous glands, present proximally, allow easier upward migration, whereas the higher lipid content of the distal secretions offers better barrier protection. − − ===Microclimate of the Ear Canal=== − The microclimate of the external ear canal remains surprisingly stable in spite of marked changes in the ambient temperature and humidity of the surrounding environment. The temperature in the healthy ear canal is between 38.2 and 38.4 C, and 0.6 C below rectal temperature. The mean relative humidity in the ear canal is 80.4%, with mean pH of 6.1-6.2. − − '''Otitis externa''' is associated with an increase in temperature, relative humidity and a rise in pH within the external ear canal. The nature of the secretions alters, with a decrease in the lipid content of cerumen. −
→The External Ear
==Content Requiring integration from 'The Ear' page==
==Content Requiring integration from 'The Ear' page==
==The Tympanic Membrane==
==The Tympanic Membrane==
This epithelial structure separates the external from the middle ear. Below the stratified keratinising outer epithelium is a connective tissue lamina propria, with a cuboidal mucosal epithelium on the inner surface. The tympanic membrane is divided into the '''pars flaccid''' dorsorostrally, which lies next to the '''manubrium of the malleus''', and the '''pars tensa''' ventrally. The C-shaped manubrium inserts into the '''lamina propria''', extending towards the middle of the pars tensa. Foreign bodies and other damage (severe otitis externa, ascending pathology from middle ear) can result in rupture of the tympanic membrane in the pars tensa region. Defects of the tympanic membrane heal by epithelial migration bridging over the defect, then development of a granulation bed below.
This epithelial structure separates the external from the middle ear. Below the stratified keratinising outer epithelium is a connective tissue lamina propria, with a cuboidal mucosal epithelium on the inner surface. The tympanic membrane is divided into the '''pars flaccid''' dorsorostrally, which lies next to the '''manubrium of the malleus''', and the '''pars tensa''' ventrally. The C-shaped manubrium inserts into the '''lamina propria''', extending towards the middle of the pars tensa. Foreign bodies and other damage (severe otitis externa, ascending pathology from middle ear) can result in rupture of the tympanic membrane in the pars tensa region. Defects of the tympanic membrane heal by epithelial migration bridging over the defect, then development of a granulation bed below.