(21) Oido Y Ojo

El oido es una unidad anatómica relacionada con la audición y el equilibrio.

Oído

Se desarrolla a partir de tres partes: Oído externo (órgano que recoge los sonidos)

Prof. Héctor A. Hurtazo

Oído medio y (conduce los sonidos del al oído interno) Oído interno (convierte las ondas sonoras en estímulos nerviosos y registra las cambios de equilibrio).

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OIDO INTERNO

Aproximadamente a los 22 días se observa un engrosamiento del ectodermo superficial a cada lado del rombencéfalo. Las placas óticas se invaginan rapidamente y forman las vesículas óticas o auditivas (otocistos). A

B Chapter 16: Ear

Figure 16.1 A. Scanning electron micrograph of a mouse embryo equivalent to approximately 28 days of human development. The otic placodes, as shown in B, are invaginating to form the otic pits (arrows). Arrowhead, second arch; H, heart; star, mandibular prominence. B. Region of the rhombencephalon showing the otic placodes in a 22-day embryo.

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Placoda ótica

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Fosa ótica Vesícula ótica

fashion until at the end of the eighth week it has completed 2.5 turns (Fig. 16.3, D and E ). Its connection with the remaining portion of the saccule is then confined to a narrow pathway, the ductus reuniens (Fig. 16.3E ; see also Fig. 16.8). Mesenchyme surrounding the cochlear duct soon differentiates into cartilage (Fig. 16.4A). In the 10th week, this cartilaginous shell undergoes vacuolization, and two perilymphatic spaces, the scala vestibuli and scala tympani, are formed (Fig. 16.4, B and C ). The cochlear duct is then separated from the scala vestibuli by the vestibular membrane and from the scala tympani by the basilar membrane (Fig. 16.4C ). The lateral wall of the cochlear duct remains attached to the surrounding cartilage by the spiral ligament, whereas its median angle is connected to and partly supported by a long cartilaginous process, the modiolus, the future axis of the bony cochlea (Fig. 16.4B ). Initially, epithelial cells of the cochlear duct are alike (Fig. 16.4A). With further development, however, they form two ridges: the inner ridge, the future spiral limbus, and the outer ridge (Fig. 16.4B ). The outer ridge forms one row of inner and three or four rows of outer hair cells, the sensory cells of the auditory system (Fig. 16.5). They are covered by the tectorial membrane, a fibrillar gelatinous substance attached to the spiral limbus that rests with its tip on the hair cells (Fig. 16.5). The sensory cells and tectorial membrane together constitute the organ of Corti. Impulses received by this organ are transmitted

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Figure 16.2 A to C. Transverse sections through the region of the rhombencephalon showing formation of the otic vesicles. A. 24 days. B. 27 days. C. 4.5 weeks. Note the statoacoustic ganglia. D and E. Scanning electron micrographs of mouse embryos equivalent to stages depicted in A and B showing development of the otic vesicles (OV ).

C

to the spiral ganglion and then to the nervous system by the auditory fibers of cranial nerve VIII (Figs. 16.4 and 16.5). UTRICLE AND SEMICIRCULAR CANALS OV

During the sixth week of development, semicircular canals appear as flattened

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En el curso del desarrollo cada vesícula se divide en:

C

a) Un componente ventral que da origen al sáculo y al conducto coclear y b) Un componente dorsal que forma el utrículo, los conductos semicirculares y el conducto endolinfático. Estas estructuras epiteliales constituyen en conjunto el laberinto membranoso.

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Sáculo, caracol y órgano de Corti F En la sexta semana el sáculo forma una evaginación tubular en su polo inferior (el conducto coclear), que se introduce en el mesénquima circundante a modo de espiral. En la octava semana a completado dos vueltas y media. Su conexión con la porción restante del sáculo se limita a un pasaje estrecho (conducto reuniens o de Hensen)

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Figure 16.3 A and B. Development of the otocyst showing a dorsal utricular portion with the endolymphatic duct que and rodea a ventral saccular portion. to diferencia E. Cochlear duct at El mesénquima al conducto coclearCse 6, 7, and 8 tempranamente weeks, respectively. Note formation of the ductus reuniens and the utricuen cartílago. losaccular duct. F and G. Scanning electron micrographs of mouse embryos showing similar stages of theeste otocyst as depicted in A and B. Arrowheads, enEnofladevelopment décima semana, cartílago experimenta dolymphatic duct; S, saccule; small arrow, opening of semicircular canal; U , utricle. G vacuolización y se forman dos espacios perilinfáticos, la also shows initial stages of cochlear duct formation (large arrow).

rampa vestibular y la rampa timpánica.

acusticae, develop in the walls of the utricle and saccule. Impulses generated in sensory cells of the cristae and maculae as a result of a change in position of the body are carried to the brain by vestibular fibers of cranial nerve VIII. During formation of the otic vesicle, a small group of cells breaks away from its wall and forms the statoacoustic ganglion (Fig. 16.2C ). Other cells of this ganglion are derived from the neural crest. The ganglion subsequently

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Scala vestibuli

Basement membrane Cochlear duct Spiral ligament Outer ridge Vestibular membrane

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Inner ridge

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Cochlear duct (scala media)

Modiolus

El conducto coclear queda separado de la rampa vestibular por la membrana vestibular y de la rampa timpánica por la membrana basilar.

Scala vestibuli Spiral ligament Auditory nerve fibers

Basilar membrane

La pared lateral del conducto coclear se mantiene unida al cartílago adyacente por el ligamento espiral.

Spiral ganglion Scala tympani

C Figure 16.4 Development of the scala tympani and scala vestibuli. A. The cochlear duct is surrounded by a cartilaginous shell. B. During the 10th week large vacuoles appear in the cartilaginous shell. C. The cochlear duct (scala media) is separated from the scala tympani and the scala vestibuli by the basilar and vestibular membranes, respectively. Note the auditory nerve fibers and the spiral (cochlear) ganglion.

splits into cochlear and vestibular portions, which supply sensory cells of the organ of Corti and those of the saccule, utricle, and semicircular canals, respectively.

Middle Ear TYMPANIC CAVITY AND AUDITORY TUBE The tympanic cavity, which originates in the endoderm, is derived from the

El ángulo interno esta unido a una larga prolongación cartilaginosa y parcialmente sostenido por esta la columela, futuro eje del caracol óseo.

Las células epiteliales del conducto coclear son al comienzo todas iguales. Al continuar el desarrollo forman dos crestas: la interna, futuro limbo de la lámina espiral y la cresta externa. La cresta externa produce una hilera interna y tres o cuatro hileras externas de células ciliadas, que son las células sensitivas del sistema auditivo.

Están cubiertas por la membrana tectoria, substancia gelatinosa fibrilar que está unida al limbo de la lámina espiral y cuyo extremo se apoya sobre sobre las células ciliadas. Las células sensitivas y la membrana tectoria constituyen el órgano de Corti. Los impulsos que recibe este órgano son transmitidos al ganglio espiral y luego al sistema nervioso por las fibras del octavo par craneal o nervio auditivo.

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Utrículo y conductos semicirculares Part Two: Special Embryology

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En la sexta semana aparecen los conductos semicirculares como evaginaciones aplanadas de la parte utricukar de la vesícula ótica. Las porciones centrales de estas evagginaciones se adosan entre sí, desaparecen y se forman los tres conductos semicirculares. Figure 16.5 Development of the organ of Corti. A. 10 weeks. B. Approximately 5 months. C. Full-term infant. Note the appearance of the spiral tunnels in the organ of Corti.

Walls of central portion of outpocketing are apposed

Superior semicircular canal

Crus commune nonampullare

Figure 16.5 Development of the organ of Corti. A. 10 weeks. B. Approximately 5 months. C. Full-term infant. Note the appearance of the spiral tunnels in the organ of Corti.

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Figure 16.6 Development of the semicircular canals. A. 5 weeks. C. 6 weeks. E. 8 weeks. B, D, and F. Apposition, fusion, and disappearance, respectively, of the central portions of the walls of the semicircular outpocketings. Note the ampullae in the semicircular canals. Crus

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Figure 16.6 Development of the semicircular canals. A. 5 weeks. C. 6 weeks. E. 8 weeks. B, D, and F. Apposition, fusion, and disappearance, respectively, of the central portions of the walls of the semicircular outpocketings. Note the ampullae in the semicircular canals.

La cavidad timpánica deriva de la primera bolsa faríngea, que crece rápidamente en dirección lateral y se pone en contacto con la primera hendidura faríngea. Su porción distal forma la cavidad timpánica primitiva, la proximal permanece estrecha y forma la trompa de Eustaquio (que comunica con la nasofaringe).

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Auditory ossicles embedded in loose mesenchyme

Endolymphatic duct

Huesecillos

Wall of inner ear

Utricular portion of otic vesicle Saccular portion Mesenchymal condensation

Auditory tube

1st pharyngeal cleft

El martillo y el yunque derivan del primer arco faríngeo. Inervado por el trigémino.

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A Tubotympanic recess

External auditory meatus

Meatal Primitive tympanic plug cavity

El estribo deriva del segundo. Inervado por el nervio facial.

Figure 16.7 A. Transverse section of a 7-week embryo in the region of the rhombencephalon, showing the tubotympanic recess, the first pharyngeal cleft, and mesenchymal condensation, foreshadowing development of the ossicles. B. Middle ear showing the cartilaginous precursors of the auditory ossicles. Thin yellow line in mesenchyme indicates future expansion of the primitive tympanic cavity. Note the meatal plug extending from the primitive auditory meatus to the tympanic cavity.

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Incus Meckel’s cartilage

Stapes

Ligaments Malleus

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Incus Petrous bone Perilymphatic space

OÍDO EXTERNO

Wall of Figure 16.8 Ear showing the external auditory meatus, the middle ear with its ossicles, Styloid process inner ear and the inner ear.

Oval window Malleus Stapes AURICLE Eardrum Intermediate Hyoid from bone six mesenchymal The auricle develops proliferations at the dorsalTympanic ends of mesoderm layer the first and second pharyngeal arches, surrounding the first pharyngealcavity cleft Stylohyoid ligament

(Fig. hillocks), three on each side A 16.10, A and E ). These swellings (auricular B of the external meatus, later fuse and form the definitive auricle (Fig.Endodermal 16.10, Ectodermal epithelium epithelium

El conducto auditivo externo se desarrolla a partir de la porción dorsal de la primera hendidura faríngea. Al trecer mes, las células epiteliales del fondo del conducto proliferan y dan origen a una placa epitelial maciza (el tapón meatal).

Figure 16.9 A. Derivatives of the first three pharyngeal arches. Note the malleus and incus at the dorsal tip of the first arch and the stapes at that of the second arch. B. Middle ear showing the handle of the malleus in contact with the eardrum. The stapes will establish contact with the membrane in the oval window. The wall of the tympanic cavity is lined with endodermal epithelium.

B–D and G ). As fusion of the auricular hillocks is complicated, developmental abnormalities of the auricle are common. Initially, the external ears are in the lower neck region (Fig. 16.10F ), but with development of the mandible, they ascend to the side of the head at the level of the eyes. CLINICAL CORRELATES

Deafness and External Ear Abnormalities Congenital deafness, usually associated with deaf-mutism, may be caused 410 Part Two: Special Embryology by abnormal development of the membranous and bony labyrinths or by malformations the auditory ossicles and eardrum. In the most extreme Roof of of rhombencephalon ossicles embedded cases theEndolymphatic tympanic cavity and external meatus areAuditory absent. in loose mesenchyme Most forms duct of congenital deafness are caused by genetic factors, but enviWall of ronmental internal Utricularfactors portion may also interfere with normal development of the inner ear of otic vesicle and middle ear. Rubella virus, affecting the embryo in the seventh or eighth week, may cause severe damage to the organ of Corti. It has also been sugSaccular portion gested that poliomyelitis, erythroblastosis fetalis, diabetes, hypothyroidism, Mesenchymal condensation and toxoplasmosis can cause congenital deafness. Auditory tube abExternal ear defects are common; they include minor and severe 1st pharyngeal cleft (Fig. 16.11). They are significant from the standpoint of the psynormalities B cause and for the fact they are chological andAemotional trauma they may Meatalas clues to examTubotympanic External auditory often associated withrecess other malformations. Thus, they serve Primitive tympanic plug ine infants carefully for other abnormalities.meatus All of the frequently cavity occurring chromosomal and of most of the lessincommon ones have ear Figure 16.7 A.syndromes Transverse section a 7-week embryo the region of the rhombencephalon, showing recess, the first pharyngeal cleft, and mesenchyanomalies as one the of tubotympanic their characteristics. mal condensation, foreshadowing development of the ossicles. B. Middle ear showing the cartilaginous precursors of the auditory ossicles. Thin yellow line in mesenchyme indicates future expansion of the primitive tympanic cavity. Note the meatal plug extending from the primitive auditory meatus to the tympanic cavity.

Oreja El pabellón de la oreja se desarrolla a partir de seis proliferaciones mesenquimatosas situadas en los extremos dorsales del primer y segundo arcos faríngeos, alrededor de la primera hendidura. Estas prominencias auriculares, tres de cada lado del conducto auditivo externo, se fusionan y se convierten en la oreja definitiva.

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Figure 16.11 A. Microtia with preauricular pit (arrow). B. Preauricular pits (arrows). C and D. Preauricular appendages (skin Note the low position of the the tag in auricular D. A. Lateral view of the head oftags). an embryo showing six

Figure 16.10 hillocks surrounding the dorsal end of the first pharyngeal cleft. B to D. Fusion and progressive Preauricular appendages and pits (Fig. 16.11) are skin tags and shaldevelopment of the hillocks into the adult auricle. E. The six auricular hillocks from low depressions, respectively, anterior to the ear. Pits may indicate abnormal the first and second pharyngeal arches. H, whereas heart; appendages NP, nasalmay placode. F. The hillocks development of the auricular hillocks, be due to becoming moreaccessory defined. NoteLike the position ears with hillocks. other external of earthe defects, both are respect associated to withthe mouth and other malformations. eyes (e). G. External ear nearly complete. Growth of the mandible and neck region places the ears in their permanent position. Summary The ear consists of three parts that have different origins, but that function as one unit. The internal ear originates from the otic vesicle, which in the fourth week of development detaches from surface ectoderm. This vesicle divides into a ventral component, which gives rise to the saccule and cochlear duct, and a dorsal component, which gives rise to the utricle, semicircular canals, and endolymphatic duct (Figs. 16.3, 16.6, and 16.8). The epithelial structures thus formed are known collectively as the membranous labyrinth. Except for the cochlear duct, which forms the organ of Corti, all structures derived from the membranous labyrinth are involved with equilibrium. The middle ear, consisting of the tympanic cavity and auditory tube, is lined with epithelium of endodermal origin and is derived from the first

G Figure 16.10 A. Lateral view of the head of an embryo showing the six auricular hillocks surrounding the dorsal end of the first pharyngeal cleft. B to D. Fusion and progressive development of the hillocks into the adult auricle. E. The six auricular hillocks from the first and second pharyngeal arches. H, heart; NP, nasal placode. F. The hillocks becoming more defined. Note the position of the ears with respect to the mouth and eyes (e). G. External ear nearly complete. Growth of the mandible and neck region places the ears in their permanent position.