UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2009)

Acknowledgements

Practical: Embryology of the Face and Ear

3. Late Embryo

	(More? Face Development cartoon)
	The animation on the left shows the early fusion of the primary palate in the human embryo between stage 17 and 18, going from an epithelial seam to the mesenchymal bridge.

 

Face - 5 prominences

otic vesicle development (inner ear)
pharyngeal arch (middle, external ear)

Tongue Development Contributions from all arches
which changes with time
begins as swelling rostral to foramen cecum
median tongue bud

Skull
cranial vault
chondrochranium

 

Stage 22

Optic and Nasal region of head A5: Root of nose with interorbital ligament behind. Developing calvaria. Olfactory bulbs. A6: Nose. Interorbital ligament. Nasal septum and nasal capsule. Eyes and eyelids. Thalamus/hypothalamus. Part of circle of Willis. A7: Eyes. Nasal septum. Middle conchae. Sphenoid cartilage.

B1: Optic nerve.

B2: Neurohyophysis and adenohypophysis. Remnant of Rathke's pouch (residual lumen) in adenohypophysis. Trigeminal ganglion. Internal carotid arteries. Vomeronasal organs, lateral to nasal septum. Nasal plug (transient). Nasal conchae.

B3: Trigeminal nerve and ganglion, with maxillary division emerging. Pterygopalatine ganglion. Nasalconchae. Adenohypophysis.

B4: Tongue. Otic capsule. Cochlea. Between B3 and B4, the junction of nasopharynx and oropharynx.

B5: Tongue with palatal process either side. Pharyngotympanic tubes (Eustachian tube -derived from pharyngeal pouch 1). External ear pinna.

Stage 22 Embryo - Selected Images

Transverse section of the stage 22 Head

Selected regions shown in blue boxes and details below. Orientation - ventral top of image, dorsal bottom of image. (More? Original Section Image)

The dark "pear-shaped" central structure at the top is the developing tongue. The two pale regions either side are the palatal shelves, note that they have not yet fused in the midline (failure of this process is cleft palate). Behind that a pale cartilagenous region (that later ossifies) encloses the structuctures of the inner ear, beside which middle ear bones are forming. On the righthand side of the head the external ear is visible. The lower half of the image shows the developing brainstem with a large ventricular space occupied in part by an extensive choroid plexus (manufacturer of cerebrospinal fluid).

Now look at the detailed images and descriptions below.

Head - Hearing

These selected images show the development of the inner and middle ear at this late embryonic stage.

Regions of stage 22 embryo head (mouth at top) in selected images of inner ear below

B5 Inner and Middle ear components.

Inner - Cross-sections of turns in the cochlear. Position of the spiral ganglia (auditory) laying adjacent to the duct. Large cavity of the utricle with the small saccule attached. Within the utricle the developing cristae ampullaris. Adjacent to the utricle a cross-section through a semi-circular canal.

Middle - the maleus, a middle ear ossicle. The developing tensor tympani muscle. The auditory tube (tubo tympanic recess) extending from the oral cavity towards the middle ear.

B6Cochlear Region

The differentiating wall of the organ of corti. The division of the VIII cranial nerve into a vestibular and auditory (spiral ganglia) component. The VIII cranial nerve exiting through the space known as the internal auditory meatus. The cartilage surrounding all these structures that will later ossify to form bone.

Next

Link to next page in this Practical - Fetal The next page will look at the fetal events in face and ear development.

 

Glossary

Use the alphabetical list below to find definitions of terms that are new to you or use the Google search window to search UNSW Embryology site.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Terms

adenohypophysis - (anterior pituitary, pars distalis) The anterior part of the pituitary, which develops in the early embryo from a transient region on the roof of the pharynx called Rathke's pouch. (More? Endocrine Development - Pituitary)

ampulla - Term used to describe an anatomical dilation of a tube or canal lumen. Anatomical description of the opening end of the uterine tube lying above the ovary and the enlarged initial segmeny of the semicircular canals of the inner ear vestibular system. (More? Inner Ear | Genital System - Female Uterus)

auricular hillocks - External ear (auricle) embryonic origin, a series of 6 external "bumps" three on each of pharyngeal arch 1 and 2. (More? External Ear | Hearing Notes)

canalis reuniens – (ductus reuniens, canaliculus reuniens, canalis reuniens, Hensen's canal, Hensen's duct, uniting canal, canalis reuniens of Hensen) Short narrow canal connecting the cochlea duct to the saccule. (Victor Hensen, 1835-1924)

chondrified – The developmental differentiation of cartilage from mesenchye, an embryonic connective tissue.

Claudius cells - (cells of Claudius) columnar cells with microvilli overlying the basilar membrane and extend from Hensen's cells to the spiral prominence. Barrier cells that lie external to the organ of corti in endolymph.

Cochlear sac – embryonic structure, which will form the coiled cochlear duct and contribute to the saccule.

cochlear aqueduct - a bony channel containing the fibrous periotic duct. It connects the basal turn of the cochlea perilymphatic space with the subarachnoid space of the posterior cranial cavity.

cristae ampullaris – located in the ampulla of the membranous semicircular canals a region with both supporting and hair cells. The hair cell cilia are embedded in the gelatinous cupula.

ectomesenchyme - The term used to describe ectoderm derived neural crest which contributes in the head region skeletogenic mesenchyme (cartilage, bone, and connective tissue) which in the body region are typically derived from mesoderm. (More? Neural Crest Notes)

endolymphatic sac - (Greek, endo = inside) An inner ear structure of the membranous labyringth that has anatomically both an intraosseous and extraosseous component. The sac is connected to membranous labyringth by the endolymphatic duct and has functions regulating endolymph that are both secretory and absorptive. Also the site of endolymphatic sac tumours (papillary cystadenoma of the vestibular aqueduct) either occurring sporadically or associated with the autosomal-dominant von Hippel-Lindau (VHL) disease, due to a germ line mutation. (More? Hearing - Inner Ear)

epiglottis - (Greek, epi = above, upon; glotta = "tongue") Anatomical structure which covers the trachea during swallowing, preventing substances from entering the trachea and then lung. The cartilaginous part of the larynx above the glottis, which in infancy directs food into the esophagus and not the trachea. Embryologically it develops in the foregut from the hypobranchial eminence, behind the undeveloped tongue, from which it separates at about 7 weeks. Postnatal anatomical development in humans involves a maturational descent in infancy (4 and 6 months of age). Contains lymphoid tissue (larynx-associated lymphoid tissue, LALT and Bronchus-associated lymphoid tissue, BALT). (More? Respiratory Notes | Gastrointestinal Tract Notes)

eustacian tube - (auditory tube) A narrow canal connecting the middle ear space to the back of the oral cavity. The direct physical connection has two main functions to allow pressure equalization in, and fluid drainage from, the middle ear. In development, the canal is initially both horizontal and very narrow leading to poor drainage and easy blockage (More? Hearing Notes | Abnormal Hearing Notes)

first trimester - Clinical term used to describe and divide human pregnancy period (9 months) into three equal parts of approximately three calendar months. The first trimester corresponds approximately to embryonic development (week 1 to 8) of organogenesis and early fetal. The second and third trimester correspond to the fetal period of growth in size (second trimester) and weight (third trimester), as well as continued differentiation of existing organs and tissues. (More? Embryo Stages | Human Fetal Period | Development Week by Week)

internal auditory meatus - (internal acoustic meatus, IAM) An anatomical canal in which CN VII and CN VIII ganglia reside and pass through to the brainstem. This bony canal lies between the posterior surface of the petrous pyramid and the bony labyrinth within the dense petrous bone. Also associated clinically with the site where acoustic neuromas may occur. (More? Inner Ear - Internal Auditory Meatus | Hearing Development - Inner Ear | Sensory Development - Hearing)

labyrinth - inner ear system of fluid-filled passages which provides the sense of balance (semicircular canals, vestibule). Named by analogy with the Greek mythology maze that imprisoned the Minotaur.

lingual - (Latin, lingua = tongue) Term used to describe structures and features related to the tongue: lingual papilla, lingual plate, lingual plexus, lingual thyroid nodule. (More? Tongue Notes | Head Notes)

meatal plate - An ectodermal plug that temporarily blocks the external auditory meatus of the ear. (More? Senses Notes)

meatus - (Latin, meatus = a channel or way) An anatomical description of an opening or passageway (external auditory meatus, female urethral meatus). (More? Senses - Hearing)

Meckel's cartilage - A temporary cartilage located in the first pharyngeal arch (mandibular component) that forms the template for formation of the mandible and middle ear bones. Named after Johann Friedrich Meckel, the Younger a German anatomist (1781 - 1833). (More? Head Notes | Who Named it? Johann Friedrich Meckel | PalaeosThe Gill Arches: Meckel's Cartilage )

otolithic membrane – a membrane within the utricle and saccule containing embedded hair cell cilia and small crystalline bodies of calcium carbonate (otoliths). Functions to detect head motion.

pharynx - (throat) Forms the initial segment of the gastrointestinal and upper respiratory tract divided anatomically into three regions: nasopharynx, oropharynx, and laryngopharynx (hypopharynx). Anatomically extends from the base of the skull to the level of the sixth cervical vertebra. (More? Respiratory Notes)

primary palate - The fusion of the maxillary processes of the first pharyngeal arches with the medial nasal prominences to form the upper jaw. In human embryos this occurs between stage 17 and 18, going from an epithelial seam to the mesenchymal bridge. This is a separate and earlier event than secondary palate, palatal shelf fusion, which occurs during the early fetal period.

retina - The stratified sensory structure of the eye, formed from the neural ectoderm that extends from the forebrain (diencephalon) to form initially the folded optic cup. Vertebrates have ten identifiable layers formed from nerve fibers, neurons, membranes, photoreceptors and pigmented cells. Light must pass through nearly all these layers to the photoreceptors. (1. Inner limiting membrane - Müller cell footplates; 2. Nerve fiber layer; 3. Ganglion cell layer - layer of retinal ganglion cells their axons form the nerve fiber layer and eventually the optic nerve; 4. Inner plexiform layer - another layer of neuronal processes; 5. Inner nuclear layer; 6. Outer plexiform layer; 7. Outer nuclear layer; 8. External limiting membrane - layer separating inner segment portions of photoreceptors from their cell nuclei; 9. Photoreceptor layer - rods and cones that convert light into signals; 10. Retinal pigment epithelium). (More? Vision Notes)

scala tympani – one of the three Cochlea cavities, it is filled with perilymph.

Scarpa's ganglion – (vestibular ganglion) primary afferent vestibular neuron ganglion of the vestibular nerve. Located within the internal auditory meatus.

secondary palate - The palatal shelves develops bilaterally during embryonic week 7, grow, elevate and fuses by week 9. This forms the hard palate separating the nasal and oral cavities. The secondary palate shelves fuse togenter and with the earlier primary palate (stage 17 and 18) and nasal septum.

semicircular canals – series of fluid-filled loops of the inner ear required for balance and sensing acceleration.

sensorineural – term used to describe one of the two major classes of hearing loss involving the central pathway from the cochlear (other form is conductive loss).

space of Nuel – within the cochlea, an organ of Corti space between the outer pillar cells and the phalangeal and hair cells. Named after Jean-Pierre Nuel (1847-1920) a Belgian ophthalmologist.

spiral ganglion neurons - (SGN) innervate the inner (Type I) and outer (Type II) hair cells of the cochlea.

stapes – (stirrup) a middle ear auditory ossicle (bone).

stereocilia –finger-like projections from the apical surface of sensory hair cells forming the hair bundle in the cochlea. Formed by tightly cross-linked parallel actin filaments in a paracrystalline array with cell surface specializations (tip links, horizontal top connectors, and tectorial membrane attachment crowns).

stria vascularis – forms the outer wall of the cochlear duct of the mammalian cochlea is composed primarily of three types of cells. Marginal cells line the lumen of the cochlear duct and are of epithelial origin. Basal cells also form a continuous layer and they may be mesodermal or derived from the neural crest. Intermediate cells are melanocyte-like cells, presumably derived from the neural crest, and are scattered between the marginal and basal cell layers. The stria forms endolymph and also contains a rich supply of blood vessels. (2612372)

synostotically – anatomically normally separate skeletal bones fused together.

tectorial membrane - extracellular matrix that cover the sensory epithelial hair cells of the organ of corti within the cochlea.

tonotopy – term describing the mapping along the tectorial membrane within the cochlea of the different sound frequencies.

vestibular ganglion - (Scarpa's ganglion) primary afferent vestibular neuron ganglion of the vestibular nerve. Located within the internal auditory meatus.

vestibular membrane - (Reissner’s) extends from the spiral lamina to the outer wall and divides the cochlea into an upper scala vestibuli, a lower scala tympani.

Vestibulocochlear Nerve - Cranial Nerve VIII

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