Stage 22 Embryo
B3:
Rhombic lip (developing cerebellum). IVth
ventricle. Trigeminal ganglion.
Adenohypophysis. Sphenoid cartilage.
B4:
Cochlear duct and temporal cartilage.
Semicircular duct (ampulla on L).
precartilage of auricle (pinna). malleus
(medial, L). Incus (lateral, L).
B5:
Extemal auditory meatus. Auricle. Incus
(dorsal). Malleus (ventral). Tubotympanic
recess (auditory rube). Tensor tympani m.
(L). Utricle. Semicircular ducts. Intemal
auditory meatus (R), containing vestibular
and spiral ganglia. Endolymphatic sac (L).
Note proximity of sac to choroid plexus of
4th ventricle.
B6:
External auditory meatus. Primordium of
tympanic membrane (L). Manubrium of
malleus(L). Basal turn of cochlea duct
(L). Endolymphatic sac (R). Common crus
(R). Junction of utricle and saccule (R).
Meckel's cartilage. Stapes (R). Auditory
tube.
Development Timing
Week 3 - otic placode, otic vesicle
Week 5 - cochlear part of otic vesicle elongates (humans 2.5 turns)
Week 9 - Mesenchyme surrounding membranous labrynth (otic capsule) chondrifies
Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic space)
around membranous labrynth and fills with perilymph
Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone.
Continues to ossify to form mastoid process of temporal bone.
3rd Trimester - Vibration acoustically of maternal abdominal wall induces startle respone in fetus.
(These are Human embryonic timings, not clinical which is based on last menstral period +2 weeks)
3 Sources:
Inner ear - epidermal otic placode at level of hindbrain.
Middle ear - cavity: 1st pharyngeal pouch, ossicles: mesenchyme 1st and 2nd pharyngeal arches.
Outer ear - external auditory meatus: 1st pharyngeal cleft, auricle: 6 hillocks 1st and 2nd pharyngeal arches.
Glossary of Terms
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Comments
These notes introduce the development of hearing and balance. Due to its complex development, hearing is the most prone of
all our senses to abnormal development and to be impacted upon by materal effects.
there is a second page covering Hearing Abnormalities.
If you have not studied hearing development before, there is a set of Science Lecture (2004) slides on Hearing Development,
an overview of developmental timing and a text overview.
This first page introduces a broad overview of this sense, links on this page will take you to more specific information.
Please email Dr Mark Hill if you wish to make a comment about this current project.
