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Line 58: − + + − 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. Line 71:
Line 68: − + − 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. Line 125:
Line 123: −
→Structure
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.
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===
===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.
===Glands of the Ear Canal===
===Glands of the Ear Canal===
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.
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===
===Structures surrounding the Ear===
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.
===Middle Ear===
===Middle Ear===
- ''Cochlea'': forms a spiral around a central hollow core of bone, called the modiolus,which contains the cochlear nerve. The spiral lamina projects into the spiral canal, partially bisecting the lumen into two parts, which are called the scala tympani and the scala vestibuli. The scala media (the cochlear duct) is inbetween these two parts.
- ''Cochlea'': forms a spiral around a central hollow core of bone, called the modiolus,which contains the cochlear nerve. The spiral lamina projects into the spiral canal, partially bisecting the lumen into two parts, which are called the scala tympani and the scala vestibuli. The scala media (the cochlear duct) is inbetween these two parts.
==Function - Hearing==
==Function - Hearing==