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Equine Special Senses - Horse Anatomy (view source)
Revision as of 12:39, 22 November 2012
, 12:39, 22 November 2012→Outer Ear
===Outer Ear===
===Outer Ear===
[[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.
[[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 (or auricle) 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. This is the outer projecting part of the ear that can be seen. 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. The functional shape of the pinna in horses is erect, and the muscular connections at the base of the pinna allowing positional adjustments to efficiently collect sound. 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. 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.
====Innervation and Vascularisation of the Outer 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 [[Equine Cranial Nerves - Horse Anatomy#Facial Nerve (VII)|cranial nerve VII]] to the auricular muscles and sensory supply by [[Equine Cranial Nerves - Horse Anatomy#Opthalmic Nerve (II)|cranial nerve II]] and [[Equine Cranial Nerves - Horse Anatomy#Trigeminal Nerve (V)|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 [[Equine Cranial Nerves - Horse Anatomy#Facial Nerve (VII)|facial nerve (VII)]], external maxillary vein and branches of the external carotid artery. The [[Equine Cranial Nerves - Horse Anatomy#Facial Nerve (VII)|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 [[Equine Cranial Nerves - Horse Anatomy#Trigeminal Nerve (V)|trigeminal nerve]] (CN V) and branches of the [[Equine Cranial Nerves - Horse Anatomy#Facial Nerve (VII)|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 – [[Integument of the Horse - Horse Anatomy#Hair|hair follicles]], [[Integument of the Horse - Horse Anatomy#Skin Glands|sebaceous and apocrine glands]]. The density of [[Integument of the Horse - Horse Anatomy#Hair|hair follicles]] on the concave pinna is variable, as is the density and distribution of [[Integument of the Horse - Horse Anatomy#Hair|hair follicles]] in the ear canal itself. Horses are devoid of [[Integument of the Horse - Horse Anatomy#Hair|hair]] in the lower (proximal) ear canal.
====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. The epithelial cells in the [[Integument of the Horse - Horse Anatomy#Skin|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.
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: