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Ear - Anatomy & Physiology (view source)
Revision as of 10:25, 11 November 2019
, 10:25, 11 November 2019→Innervation
==Introduction==
==Introduction==
The ear is a paired sensory organ, that is involved in both hearing and balance. For this reason, the ear is known as the vestibulocochlear organ.
The ear is a paired sensory organ, that is involved in both hearing and balance. For this reason, the ear is known as the vestibulocochlear organ.
==Structure==
==Structure==
[[Image:Sections of the Ear.jpg|thumb|right|150px|The Mammalian Ear - Copyright David Bainbridge]]
[[Image:Sections of the Ear.jpg|thumb|right|250px|The Mammalian Ear - Copyright David Bainbridge]]
Anatomically, the ear can be looked at in three parts:
Anatomically, the ear can be looked at in three parts:
3. '''Inner ear''' - contains the membranous and bony labyrinths, and the cochlea
3. '''Inner ear''' - contains the membranous and bony labyrinths, and the cochlea
===Outer Ear===
===Outer Ear===
[[Image:Outer Ear.jpg|thumb|right|150px|Outer Ear - Copyright David Bainbridge]]
[[Image:Outer Ear.jpg|thumb|right|250px|Outer Ear - Copyright David Bainbridge]]
The pinna consists of the '''auricular [[Cartilage - Anatomy & Physiology#Structure and Function of Cartilage|cartilage]]''', and skin which allows for flexibility and elasticity. The auricular cartilage 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.
The pinna consists of the '''auricular [[Cartilage - Anatomy & Physiology#Structure and Function of Cartilage|cartilage]]''', and skin which allows for flexibility and elasticity. The auricular cartilage 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.
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)|tympanic bulla]], connected by ligaments. The vertical ear canal lies in a rostroventral orientation before bending medially to become the horizontal 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.
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.
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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]]
===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.
===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.
===Middle Ear===
===Middle Ear===
[[Image:Middle Ear.jpg|thumb|right|150px|Middle Ear - Copyright David Bainbridge]]
[[Image:Middle Ear.jpg|thumb|right|250px|Middle Ear - Copyright David Bainbridge]]
*The middle ear consists of the tympanic cavity, the auditory ossicles and the eustachian tube. The boundary between the middle and inner ear is the oval window.
*The middle ear consists of the tympanic cavity, the auditory ossicles and the eustachian tube. The boundary between the middle and inner ear is the oval window.
*The auditory ossicles are attached to the wall of the tympanic cavity by many ligaments and mucosal folds.
*The auditory ossicles are attached to the wall of the tympanic cavity by many ligaments and mucosal folds.
[[image: Canine Ear Canal.jpg|thumb|250px|right|The Canine Middle Ear]]
[[image: Canine Ear Canal.jpg|thumb|250px|right|The Canine Middle Ear]]
The auditory ossicles are supported by ligaments and muscles, which alter their position and influences the tension of the tympanic membrane. The ratio of the malleus:incus in dogs and cats is 2-3 times that of man, and may explain the increased acuity of hearing. Opposite the lateral tympanic membrane on the medial aspect of the cavity is a bony promontory. Associated structures close to or in channels in the wall of the tympanic cavity (bulla) are the '''facial nerve''', '''vagus nerve''' and branches of the '''carotid and lingual arteries'''. Post-ganglionic fibres of the '''cervical sympathetic trunk''' run in the region of the dorsomedial wall of the tympanic cavity.
The auditory ossicles are supported by ligaments and muscles, which alter their position and influences the tension of the tympanic membrane. The ratio of the malleus:incus in dogs and cats is 2-3 times that of man, and may explain the increased acuity of hearing. Opposite the lateral tympanic membrane on the medial aspect of the cavity is a bony promontory. Associated structures close to or in channels in the wall of the tympanic cavity (bulla) are the '''facial nerve''', '''vagus nerve''' and branches of the '''carotid and lingual arteries'''. Post-ganglionic fibres of the '''cervical sympathetic trunk''' run in the region of the dorsomedial wall of the tympanic cavity.
The middle ear is lined by cuboidal to columnar mucosal epithelium with scattered '''goblet cells'''. The auditory tube is lined by pseudostratified, ciliated columnar epithelium with scattered goblet cells. The goblet cells are more prominent at the tympanic cavity end, contributing to the surfactant nature of the secretions- containing '''lecithin''', lipids and '''mucopolysaccharides''' - that decreases surface tension and keeps the tube patent. The density of '''cilia''' increases as the tube runs dorsolaterally to open into the nasopharynx behind the soft palate, facilitating movement and drainage of mucus and other material.
The middle ear is lined by cuboidal to columnar mucosal epithelium with scattered '''goblet cells'''. The auditory tube is lined by pseudostratified, ciliated columnar epithelium with scattered goblet cells. The goblet cells are more prominent at the tympanic cavity end, contributing to the surfactant nature of the secretions- containing '''lecithin''', lipids and '''mucopolysaccharides''' - that decreases surface tension and keeps the tube patent. The density of '''cilia''' increases as the tube runs dorsolaterally to open into the nasopharynx behind the soft palate, facilitating movement and drainage of mucus and other material.
===Inner Ear===
===Inner Ear===
[[Image:Inner, Membranous Labyrinth.jpg|thumb|right|150px|Inner, Membranous Labyrinth - Copyright David Bainbridge]]
[[Image:Inner, Membranous Labyrinth.jpg|thumb|right|250px|Inner, Membranous Labyrinth - Copyright David Bainbridge]]
[[Image:Outer, Bony Labyrinth.jpg|thumb|right|250px|Outer, Bony Labyrinth - Copyright David Bainbridge]]
[[Image:Outer, Bony Labyrinth.jpg|thumb|right|150px|Outer, Bony Labyrinth - Copyright David Bainbridge]]
[[Image:Section through a Cochlear Turn.jpg|thumb|right|250px|Section through a Cochlear Turn - Copyright David Bainbridge]]
[[Image:Section through a Cochlear Turn.jpg|thumb|right|150px|Section through a Cochlear Turn - Copyright David Bainbridge]]
*The inner ear is located within the petrous temporal bone.
*The inner ear is located within the petrous temporal bone.
*The inner ear contains the membranous labyrinth, which is surrounded by the bony labyrinth.
*The inner ear contains the membranous labyrinth, which is surrounded by the bony labyrinth.
- ''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==
The main function of the ear is to recieve auditory and vestibular input.
The main function of the ear is to recieve auditory and vestibular input.
The external ear receives sounds, which cause vibrations of the tympanic membrane. These vibrations move along the ossicles of the middle ear, to be transmitted to the inner ear. The stapes is connected to the oval window, so when the stapes transmits vibrations, this causes movement of perilymph that is in the inner ear. The movement of the perilymph is transmitted via the scala vestibuli and the scala tympani, to the round window, where it induces movement of the secondary tympanic membrane. This results in the movement of the endolymph of the cochlear duct, causing pressure on the tectorial membrane, which then induces pressure on the sensory hairs, stimulating the receptor cells within the cochlear duct to send impulses to the spiral ganglion. The axons of the spiral ganglion form part of the vestibulocochlear nerve.
The external ear receives sounds, which cause vibrations of the tympanic membrane. These vibrations move along the ossicles of the middle ear, to be transmitted to the inner ear. The stapes is connected to the oval window, so when the stapes transmits vibrations, this causes movement of perilymph that is in the inner ear. The movement of the perilymph is transmitted via the scala vestibuli and the scala tympani, to the round window, where it induces movement of the secondary tympanic membrane. This results in the movement of the endolymph of the cochlear duct, causing pressure on the tectorial membrane, which then induces pressure on the sensory hairs, stimulating the receptor cells within the cochlear duct to send impulses to the spiral ganglion. The axons of the spiral ganglion form part of the vestibulocochlear nerve.
===The Outer and Middle Ear===
===The Outer and Middle Ear===
*Amplification due to the bony lever is only 1.5 times, as the stapedius muscle prevents the stapes from vibrating too much.
*Amplification due to the bony lever is only 1.5 times, as the stapedius muscle prevents the stapes from vibrating too much.
*The tympanic membrane is 20 times larger than the oval window.
*The tympanic membrane is 20 times larger than the oval window.
===The Cochlea===
===The Cochlea===
*Displacement of the basilar membrane during sound transmission is 200 times that of the tympanic membrane.
*Displacement of the basilar membrane during sound transmission is 200 times that of the tympanic membrane.
*This is due to the relative inertia of the tympanic membrane, so it remains relatively still as the basilar and hair cells move relative to it.
*This is due to the relative inertia of the tympanic membrane, so it remains relatively still as the basilar and hair cells move relative to it.
===The Hair Cell Receptor===
===The Hair Cell Receptor===
This shows that if the cilia is pushed in one direction, it will be excited, but if pushed in the other direction it will be inhibited.
This shows that if the cilia is pushed in one direction, it will be excited, but if pushed in the other direction it will be inhibited.
===Hair Cell Resting Potentials===
===Hair Cell Resting Potentials===
*Cilia are in endolymph, but hair cell body is in perilymph.
*Cilia are in endolymph, but hair cell body is in perilymph.
*There is a high concentration of potassium ions (K+) in endolymph, which is maintained by ion pumps in the stria vascularis.
*There is a high concentration of potassium ions (K+) in endolymph, which is maintained by ion pumps in the stria vascularis.
===Cochlear Microphonics===
===Cochlear Microphonics===
*Non-nervous: no latency, refractoriness, and persists after death.
*Non-nervous: no latency, refractoriness, and persists after death.
*Generated by hair cells.
*Generated by hair cells.
===Tone===
===Tone===
3. '''Phase Locking''': allows extremely fine discrimination of pitch within the musical range. The action potential occurs at a particular point in the sound wave. The brain can determine frequency information from this.
3. '''Phase Locking''': allows extremely fine discrimination of pitch within the musical range. The action potential occurs at a particular point in the sound wave. The brain can determine frequency information from this.
===Direction Discrimination===
===Direction Discrimination===
3. Head 'shadowing' of sound
3. Head 'shadowing' of sound
===Deafness===
===Deafness===
*'''Nerve Deafness''': hearing loss due to a lesion to the auditory nerve within the central neural pathway. May be congenital or genetic, for example in white cats with blue eyes or in dalmatians, a problem created due to highly selective in-breeding. Histological examinations carried out on the organ of Corti from affected dogs shows the absence of sensory cells. Nerve deafness may also be due to age.
*'''Nerve Deafness''': hearing loss due to a lesion to the auditory nerve within the central neural pathway. May be congenital or genetic, for example in white cats with blue eyes or in dalmatians, a problem created due to highly selective in-breeding. Histological examinations carried out on the organ of Corti from affected dogs shows the absence of sensory cells. Nerve deafness may also be due to age.
===Central Auditory Pathways===
[[Image:Central Auditory Pathway.jpg|thumb|right|250px|Central Auditory Pathway - Copyright David Bainbridge]]
[[Image:Central Auditory Pathway.jpg|thumb|right|150px|Central Auditory Pathway - Copyright David Bainbridge]]
*The signal that has been created from the sound waves that were picked up by the ear, is carried to the brain by the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]), which synapses in the cochlear nucleus.
*The signal that has been created from the sound waves that were picked up by the ear, is carried to the brain by the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]), which synapses in the cochlear nucleus.
*From here, the auditory information is then split.
*From here, the auditory information is then split.
*Both of the above pathways are bilateral. This means that if there is a lesion at any point along the pathway, it usually has no effect on hearing. Deafness is only usually caused if there is damage to either the auditory nerve, the cochlea, or the middle ear.
*Both of the above pathways are bilateral. This means that if there is a lesion at any point along the pathway, it usually has no effect on hearing. Deafness is only usually caused if there is damage to either the auditory nerve, the cochlea, or the middle ear.
*From the inferior colliculus, the information from both pathways is sent to the medial geniculate nucleus of the thalamus, which then leads on to the primary auditory cortex of the cerebral cortex.
*From the inferior colliculus, the information from both pathways is sent to the medial geniculate nucleus of the thalamus, which then leads on to the primary auditory cortex of the cerebral cortex.
==Function - Balance==
==Function - Balance==
[[Image:Vestibular Receptors and Balance.jpg|thumb|right|150px|Vestibular Receptors and Balance - Copyright David Bainbridge]]
[[Image:Vestibular Receptors and Balance.jpg|thumb|right|250px|Vestibular Receptors and Balance - Copyright David Bainbridge]]
*The vestibular sense is rather more unconscious than that of hearing.
*The vestibular sense is rather more unconscious than that of hearing.
*Otoliths are denser than endolymph - they are calcareous and crystalline. They are contained within the maculae, and detect gravity and linear acceleration. Linear acceleration is the detection of motion along a line, for example when you lean to one side.
*Otoliths are denser than endolymph - they are calcareous and crystalline. They are contained within the maculae, and detect gravity and linear acceleration. Linear acceleration is the detection of motion along a line, for example when you lean to one side.
*Movement of the sensory hair cells triggers impulses, which are carried by the vestibular portion of the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]).
*Movement of the sensory hair cells triggers impulses, which are carried by the vestibular portion of the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]).
===Unilateral Vestibular Signs===
===Unilateral Vestibular Signs===
[[Image:Unilateral Vestibular Signs.jpg|thumb|right|150px|Unilateral Vestibular Signs - Copyright David Bainbridge]]
[[Image:Unilateral Vestibular Signs.jpg|thumb|right|250px|Unilateral Vestibular Signs - Copyright David Bainbridge]]
*The vestibular system is a common site for pathology. Brain infection, tumours and inflammation are often shown up by vestibular signs. These signs may include:
*The vestibular system is a common site for pathology. Brain infection, tumours and inflammation are often shown up by vestibular signs. These signs may include:
5. ''Nystagmus with slow phase to lesion'' - nystagmus is rapid, involuntary, oscillatory motion of the eyeball in any direction, and can be caused by a lack of coordination
5. ''Nystagmus with slow phase to lesion'' - nystagmus is rapid, involuntary, oscillatory motion of the eyeball in any direction, and can be caused by a lack of coordination
===Central Vestibular Pathways===
[[Image:Central Vestibular Pathways.jpg|thumb|right|250px|Central Vestibular Pathways - Copyright David Bainbridge]]
[[Image:Central Vestibular Pathways.jpg|thumb|right|150px|Central Vestibular Pathways - Copyright David Bainbridge]]
*The sensory hair cells produce signals, which are carried by the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]) first of all through the bipolar vestibular ganglion cells.
*The sensory hair cells produce signals, which are carried by the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]) first of all through the bipolar vestibular ganglion cells.
*Most nerve fibres that have come from the hair cells terminate in the vestibular nuclei, which are located in the fourth ventricle of the cerebral cortex.
*Most nerve fibres that have come from the hair cells terminate in the vestibular nuclei, which are located in the fourth ventricle of the cerebral cortex.
*After entering the vestibular nuclei, some of the processes of the nerve fibres divide into ascending and descending branches. Some processes pass directly into the cerebellum.
*After entering the vestibular nuclei, some of the processes of the nerve fibres divide into ascending and descending branches. Some processes pass directly into the cerebellum.
==Vasculature==
==Vasculature==
*The tympanic membrane is highly vascularised.
*The tympanic membrane is highly vascularised.
==Innervation==
==Innervation==
Sensory innervation to the outer ear:
Sensory innervation to the outer ear:
*Ce2 (second cervical spinal nerve) to medial pinna
*Ce2 (second cervical spinal nerve) to medial pinna
*Auriculopalpebral branch of trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V]]) to most of the lateral pinna
*Auriculopalpebral branch of facial nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) to most of the lateral pinna
*Facial ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) and vagus nerves ([[Cranial Nerves - Anatomy & Physiology|CN X]]) via small auricular branches to pinna
*Facial ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) and vagus nerves ([[Cranial Nerves - Anatomy & Physiology|CN X]]) via small auricular branches to pinna
*The tensor tympani muscle is innervated by the pterygoid nerve, which is a branch of the mandibular nerve, itself being the third branch of the trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V]]).
*The tensor tympani muscle is innervated by the pterygoid nerve, which is a branch of the mandibular nerve, itself being the third branch of the trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V]]).
*The stapedius muscle is innervated by the facial nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]]).
*The stapedius muscle is innervated by the facial nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]]).
==Histology==
==Histology==
[[Image:Section through Cochlea - Histology.jpg|thumb|right|150px|Section through Cochlea - Copyright David Bainbridge]]
[[Image:Section through Cochlea - Histology.jpg|thumb|right|250px|Section through Cochlea - Copyright David Bainbridge]]
*'''Tympanic Membrane''': the outer surface is lined with an epithelium that is continuous with that of the external acoustic meatus. The inner surface is lined by the mucosa that lines the tympanic cavity. This inner mucosal layer is made up of simple squamous epithelium.
*'''Tympanic Membrane''': the outer surface is lined with an epithelium that is continuous with that of the external acoustic meatus. The inner surface is lined by the mucosa that lines the tympanic cavity. This inner mucosal layer is made up of simple squamous epithelium.
*'''Tympanic Cavity''': lined by a single-layer of epithelium, and the underlying soft tissue has a rich vascular and nervous supply. The single-layered epithelium also covers the ossicles and the tympanic membrane.
*'''Tympanic Cavity''': lined by a single-layer of epithelium, and the underlying soft tissue has a rich vascular and nervous supply. The single-layered epithelium also covers the ossicles and the tympanic membrane.
==Species Differences==
==Species Differences==
[[Image: Rabbit ears.jpg|thumb|250px|right|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
* 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.
*'''The Cochlea''': the spiral has 3 turns in carnivores, 2.5 turns in horses, 4 turns in the pig, and 3.5 turns in ruminants.
*'''The Cochlea''': the spiral has 3 turns in carnivores, 2.5 turns in horses, 4 turns in the pig, and 3.5 turns in ruminants.
*'''Fish''': to detect high frequency sound, some fish use the swim bladder as an acoustic detecror. It is connected to the '''lagena''' (the stumpy piscine cochlea) by three ''Weberian'' bones. These are derived from vertebrae.
*'''Fish''': to detect high frequency sound, some fish use the swim bladder as an acoustic detecror. It is connected to the '''lagena''' (the stumpy piscine cochlea) by three ''Weberian'' bones. These are derived from vertebrae.
* The [[Guttural Pouches - Anatomy & Physiology|guttural pouch]] is an anatomical structure that is only found in the horse and other perissodactyla.[[Image:Equine Guttural Pouch.jpg|thumb|right|150px|Equine Guttural Pouch - Copyright David Bainbridge]]
* The [[Guttural Pouches - Anatomy & Physiology|guttural pouch]] is an anatomical structure that is only found in the horse and other perissodactyla.
==Recommended Reading==
-Miller's Anatomy of the Dog, 4th edition, Evans and de Lahunta, Chapter 20, pages 731-745
-Veterinary Anatomy of Domestic Mammals, 3rd edition, König and Liebich, Chapter 17, pages 593-608
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{{Learning
{{Learning
|flashcards = [[Facial_Muscles_-_Musculoskeletal_-_Flashcards|Facial Muscles Flashcards]]<br>[[Ear flashcards - Anatomy & Physiology|Ear Flashcards]]<br>[[Feather flashcards - Anatomy & Physiology|Feather Flashcards]]
|flashcards = [[Ear flashcards - Anatomy & Physiology|Ear Flashcards]]
|OVAM = [http://www.onlineveterinaryanatomy.net/content/special-senses-imaging-quiz Special Senses Imaging Quiz - University of Glasgow]<br>
[http://www.onlineveterinaryanatomy.net/content/interactive-avian-anatomy-ear-0 Interactive Avian Anatomy of the Ear - University of Murcia]<br>
|Vetstream = [https://www.vetstream.com/canis/Content/Disease/dis02287.asp Otitis interna]
}}
}}
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{{OpenPages}}
[[Category:Special Senses - Anatomy & Physiology]]
[[Category:Special Senses - Anatomy & Physiology]]