12.2.0 SENSORY ORGANS: EAR: INTRODUCTION
The human ear can be divided into an external, middle and internal part.
12.2.2 - images: External ear (auris externa) consists of:
The auricle only has an irregular thin plate of elastic fibrocartilage covered by thin skin that is continuous with that of the acoustic meatus into the auditory canal.
Sebaceous glands and associated thin hairs are present as well as sweat glands on the posterior surface of the external ear. In the thick subcutaneous tissue of the auditory canal additionally so-called cerumen glands (modified apocrine glands) produce the cerumen (wax).
See: 12.2.2 POJA-L2597 et al.
The auditory canal is slightly S-curved. The outer two-thirds of the canal is surrounded by an outer elastic cartilage (ca. 16 mm long), while the inner third (ca 8 mm long) is embedded in the temporal bone of the skull.
12.2.3 - images: Middle ear (auris media)
The tympanic membrane (= eardrum) separates the external auditory canal from the cavity of the middle ear (the bony tympanic cavity). The tympanic membrane is semitransparent and consists of the outer thin skin, middle fibrous layer with radiating fibres and an inner flat epithelium continuous with the lining of the middle ear.
Within the narrow tympanic cavity (filled with air) ear ossicles are present such as the malleus (attached with its manubrium to the eardrum) connected to the incus and stapes. The base of the stapes (footplate) is fixed to the oval window (fenestra vestibuli) and below it the round window (fenestra cochleae) is located. It is closed by a membrane (secondary tympanic membrane) of elastic connective tissue.
See: 12.2.4 POJA-L2629 et al.
The ca 36 mm long auditory tube (or pharyngotympanic tube, eustachian tube) connects the middle ear with the nasopharynx. It allows passage of air to equalizes the air pressure between these two spaces as well as for the air spaces of the bony mastoid process. Middle ear infection (otitis media) is a very common infectious condition in children after respiratory tract infections. Complications such as perforated eardrum, otitis interna (labyrinthitis), affected facial nerve with facial palsy e.a. might occur.
See: 12.2.3 POJA-L4338 et al; 12.2.3 POJA-L2601 et al; 12.2.3 POJA-L3381 et al.
Muscles of the middle ear comprises the tensor tympani (inserts on the manubrium of the eardrum, originates from the eustachian tube and innervated by the trigeminal nerve (V) through the trigeminal ganglion) and the stapedius muscle (runs from the neck of the stapes to the posterior wall of the middle ear), innervated by the tympanic branch of N VII).
The tensor tympani dampens noise, when it contracts it pulls the malleus medially, tensing the eardrum and dampens vibration in the ear ossicles, thereby reducing the perceived amplitude of sounds. The stapedius dampens the vibrations of the stapes and protects the inner ear from high noise level.
12.2.4 - images: Inner ear (auris interna)
The inner ear consists of fluid-filled sacs (membraneous labyrinth) within cavities in the temporal bone of the skull (bony or osseous labyrinth).
The osseous labyrinth (1) is composed of three cavities: cochlea, vestibule and semicircular canals.
All periosteum-lined cavities are filled with perilymph (resembling cerebrospinal fluid). The bony cochlea is formed as a spiral channel (in man 2.5 turns, in guinea pig 5 turns) just like a snail shell (ca. 5 x 9 mm). The modiolus is the central axis from which the osseous spiral lamina projects, dividing the cochlear canal in an upper scala vestibule and a lower scala tympani.
Within the bony labyrinth, the membranous labyrinth (2) is localised and filled with endolymph fluid.
See: 12.2.4.1 POJA-L2962; 12.2.4 POJA-L2629 et al.
Sound waves via the acoustic meatus are converted to vibrations by the eardrum and transmitted by the ossicles to the perilymphe in the vestibule. The fluid shift displaces the basilar membrane and hairs cells in the organ of Corti are stimulated by deflection of their stereocilia. See: 12.2.4.1 POJA-La0115 et al.
The base of the cochlea picks up high frequency sounds while lower frequencies are detected throughout the cochlear duct till the apex.
The vestibular membranous labyrinth serves as a receptor organ for detection of gravity, static position and balance c.q. orientation and comprises the saccule, utricle, three semicircular ducts as well as the endolymphatic duct and sac. These cavities and small channels form a closed system that is also connected to the membranous cochlear duct. Free circulation of endolymph is warranted.
See: 12.2.4.2 POJA-L2637 et al; 12.2.4.2 POJA-La0125 et al; 12.2.4.2 POJA-L2639 et al.
12.2.4.1 - images: Cochlea
Within this shell lies the membranous cochlear duct as a spiral tube running along the outer wall of the bony cochlea. The duct terminates as a blind end at the cupula of the cochlea while the basal turn of the duct connects with the sacculus of the vestibular labyrinth via the ductus reuniens. The membranous cochlear duct is triangular in section with the Reissner’s membrane (vestibular membrane) as the roof, a thickened endosteum as outer wall and the basilar membrane and outer part of the osseous spiral lamina as floor.
The spiral organ of Corti is the sensory area along the entire length of the cochlear duct and is set on the basilar membrane.
See: 12.2.4.1 POJA-La0106+L3587; 12.2.4.1 POJA-L4337 et al; 12.2.4.1 POJA-La0110 et al.
12.2.4.2 - images: Vestibular labyrinth
The vestibular membranous labyrinth serves as a receptor organ for detection of gravity, static position and balance c.q. orientation and comprises the saccule, utricle, three semicircular ducts as well as the endolymphatic duct and sac. These cavities and small channels form a closed system that is also connected to the membranous cochlear duct. The semicircular ducts open in the utricle that is in contact with the saccule via the ductus utriculosaccularis which joins the ductus endolymphaticus. The saccule contacts the cochlear duct by the ductus reuniens.
See: 12.2.4.2 POJA-L2637 et al; 12.2.4.2 POJA-La0125 et al; 12.2.4.2 POJA-L2639 et al.
12.2.5 - images: Pathology.
Tubal obstruction: See: 12.2.3 POJA-La0100+L3385+3384+La0102
Degeneration hair cell: See: 12.2.5 POJA-L3386+3388
12.2.2 - images: External ear (auris externa) consists of:
- The auricle (pinna),
- The lobule (lobus auriculae) with fat tissue
- The external auditory canal (acoustic meatus).
The auricle only has an irregular thin plate of elastic fibrocartilage covered by thin skin that is continuous with that of the acoustic meatus into the auditory canal.
Sebaceous glands and associated thin hairs are present as well as sweat glands on the posterior surface of the external ear. In the thick subcutaneous tissue of the auditory canal additionally so-called cerumen glands (modified apocrine glands) produce the cerumen (wax).
See: 12.2.2 POJA-L2597 et al.
The auditory canal is slightly S-curved. The outer two-thirds of the canal is surrounded by an outer elastic cartilage (ca. 16 mm long), while the inner third (ca 8 mm long) is embedded in the temporal bone of the skull.
12.2.3 - images: Middle ear (auris media)
The tympanic membrane (= eardrum) separates the external auditory canal from the cavity of the middle ear (the bony tympanic cavity). The tympanic membrane is semitransparent and consists of the outer thin skin, middle fibrous layer with radiating fibres and an inner flat epithelium continuous with the lining of the middle ear.
Within the narrow tympanic cavity (filled with air) ear ossicles are present such as the malleus (attached with its manubrium to the eardrum) connected to the incus and stapes. The base of the stapes (footplate) is fixed to the oval window (fenestra vestibuli) and below it the round window (fenestra cochleae) is located. It is closed by a membrane (secondary tympanic membrane) of elastic connective tissue.
See: 12.2.4 POJA-L2629 et al.
The ca 36 mm long auditory tube (or pharyngotympanic tube, eustachian tube) connects the middle ear with the nasopharynx. It allows passage of air to equalizes the air pressure between these two spaces as well as for the air spaces of the bony mastoid process. Middle ear infection (otitis media) is a very common infectious condition in children after respiratory tract infections. Complications such as perforated eardrum, otitis interna (labyrinthitis), affected facial nerve with facial palsy e.a. might occur.
See: 12.2.3 POJA-L4338 et al; 12.2.3 POJA-L2601 et al; 12.2.3 POJA-L3381 et al.
Muscles of the middle ear comprises the tensor tympani (inserts on the manubrium of the eardrum, originates from the eustachian tube and innervated by the trigeminal nerve (V) through the trigeminal ganglion) and the stapedius muscle (runs from the neck of the stapes to the posterior wall of the middle ear), innervated by the tympanic branch of N VII).
The tensor tympani dampens noise, when it contracts it pulls the malleus medially, tensing the eardrum and dampens vibration in the ear ossicles, thereby reducing the perceived amplitude of sounds. The stapedius dampens the vibrations of the stapes and protects the inner ear from high noise level.
12.2.4 - images: Inner ear (auris interna)
The inner ear consists of fluid-filled sacs (membraneous labyrinth) within cavities in the temporal bone of the skull (bony or osseous labyrinth).
The osseous labyrinth (1) is composed of three cavities: cochlea, vestibule and semicircular canals.
All periosteum-lined cavities are filled with perilymph (resembling cerebrospinal fluid). The bony cochlea is formed as a spiral channel (in man 2.5 turns, in guinea pig 5 turns) just like a snail shell (ca. 5 x 9 mm). The modiolus is the central axis from which the osseous spiral lamina projects, dividing the cochlear canal in an upper scala vestibule and a lower scala tympani.
Within the bony labyrinth, the membranous labyrinth (2) is localised and filled with endolymph fluid.
See: 12.2.4.1 POJA-L2962; 12.2.4 POJA-L2629 et al.
Sound waves via the acoustic meatus are converted to vibrations by the eardrum and transmitted by the ossicles to the perilymphe in the vestibule. The fluid shift displaces the basilar membrane and hairs cells in the organ of Corti are stimulated by deflection of their stereocilia. See: 12.2.4.1 POJA-La0115 et al.
The base of the cochlea picks up high frequency sounds while lower frequencies are detected throughout the cochlear duct till the apex.
The vestibular membranous labyrinth serves as a receptor organ for detection of gravity, static position and balance c.q. orientation and comprises the saccule, utricle, three semicircular ducts as well as the endolymphatic duct and sac. These cavities and small channels form a closed system that is also connected to the membranous cochlear duct. Free circulation of endolymph is warranted.
See: 12.2.4.2 POJA-L2637 et al; 12.2.4.2 POJA-La0125 et al; 12.2.4.2 POJA-L2639 et al.
12.2.4.1 - images: Cochlea
Within this shell lies the membranous cochlear duct as a spiral tube running along the outer wall of the bony cochlea. The duct terminates as a blind end at the cupula of the cochlea while the basal turn of the duct connects with the sacculus of the vestibular labyrinth via the ductus reuniens. The membranous cochlear duct is triangular in section with the Reissner’s membrane (vestibular membrane) as the roof, a thickened endosteum as outer wall and the basilar membrane and outer part of the osseous spiral lamina as floor.
The spiral organ of Corti is the sensory area along the entire length of the cochlear duct and is set on the basilar membrane.
See: 12.2.4.1 POJA-La0106+L3587; 12.2.4.1 POJA-L4337 et al; 12.2.4.1 POJA-La0110 et al.
12.2.4.2 - images: Vestibular labyrinth
The vestibular membranous labyrinth serves as a receptor organ for detection of gravity, static position and balance c.q. orientation and comprises the saccule, utricle, three semicircular ducts as well as the endolymphatic duct and sac. These cavities and small channels form a closed system that is also connected to the membranous cochlear duct. The semicircular ducts open in the utricle that is in contact with the saccule via the ductus utriculosaccularis which joins the ductus endolymphaticus. The saccule contacts the cochlear duct by the ductus reuniens.
See: 12.2.4.2 POJA-L2637 et al; 12.2.4.2 POJA-La0125 et al; 12.2.4.2 POJA-L2639 et al.
12.2.5 - images: Pathology.
Tubal obstruction: See: 12.2.3 POJA-La0100+L3385+3384+La0102
Degeneration hair cell: See: 12.2.5 POJA-L3386+3388
COPYRIGHTS
All rights reserves worldwide for the POJA collection are hold by L.G. Poels and P.H.K. Jap and Radboud University Medical Center (Radboud UMC Nijmegen). No one may modify, copy, distribute, transmit, display, or publish any materials contained in the POJA collection without prior written permission of the authors Poels and Jap or the UMC St Radboud. Any commercial use of the POJA collection is forbidden. POJA images are partly deposited in the Health Education Assets Library (HEAL database) as well as in the MedEdPortal/AAMC database).
All rights reserves worldwide for the POJA collection are hold by L.G. Poels and P.H.K. Jap and Radboud University Medical Center (Radboud UMC Nijmegen). No one may modify, copy, distribute, transmit, display, or publish any materials contained in the POJA collection without prior written permission of the authors Poels and Jap or the UMC St Radboud. Any commercial use of the POJA collection is forbidden. POJA images are partly deposited in the Health Education Assets Library (HEAL database) as well as in the MedEdPortal/AAMC database).