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Line 73: + + − 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.
→Structure
[[Image:Outer Ear.jpg|thumb|right|150px|Outer Ear - Copyright David Bainbridge]]
[[Image:Outer Ear.jpg|thumb|right|150px|Outer Ear - Copyright David Bainbridge]]
The pinna (or auricle) is defined as the outer projecting part of the ear, that is the part of the ear that can be seen. It consists of the auricular cartilage, surrounded by skin, which allows for flexibility and elasticity. The auricular cartilage connects to scutiform cartilage, which itself connects to annular cartilage, which allows for articulation. These cartilages fit into the bony passage of the ear canal - also called the external auditory meatus, which leads to the tympanic membrane. This is the deepest boundary of the outer ear.
The pinna (or auricle) is defined as the outer projecting part of the ear, that is the part of the ear that can be seen. It consists of the auricular cartilage, surrounded by skin, which allows for flexibility and elasticity. The auricular cartilage connects to scutiform cartilage, which itself connects to annular cartilage, which allows for articulation. These cartilages fit into the bony passage of the ear canal - also called the external auditory meatus, which leads to the tympanic membrane. This is the deepest boundary of the outer ear.
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.
Foreign bodies can become lodged in the external auditory meatus, but glands are present that produce wax which can trap these.
Foreign bodies can become lodged in the external auditory meatus, but glands are present that produce wax which can trap these.
Muscles around the base of the ear that are attached to the skull allow movement of the pinna, so the ear can be directed to the source of sound:
Muscles around the base of the ear that are attached to the skull allow movement of the pinna, so the ear can be directed to the source of sound:
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[[image: Canine Auricular Cartilages.jpg|thumb|250px|right|The auricular cartilages of the left canine ear. Image by Rachael Wallace]]
[[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'''.
This includes the '''pinna''' and the '''ear canal''' (''external auditory meatus'') down to the level of the '''tympanic membrane'''.
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.
===Microclimate of the Ear Canal===
===Microclimate of the Ear Canal===
'''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.
'''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.
===Structures surrounding the Ear===
===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.
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.