NS 7: The eye and ear special sense organs Flashcards
embryological origin of external ear?
1st pharyngeal cleft= ectoderm, forms EAM
proliferation in 1st and 2nd pharyngeal arches= auricle
embryological origin of middle ear?
1st pharyngeal pouch= endoderm, forms tympanic cavity and eustachian tube
1st and 2nd pharygeal arch cartilages- meckel’s = malleus and incus, reichert’s= stapes.
embryological origin of inner ear?
otic placodes= ectodermal thickening which invaginate to form auditory vesicles, detaching from surface ectoderm which then closes over the top.
how are fibres in optic nerve that are involved in pupillary reflexes routed?
by way of superior colliculi to the Edinger Westphal nucleus= parasympathetic part of oculomotor nerve nucleus- nerve responsible for motor limb of pupillary response to light with innervation of sphincter pupillae muscle.
which fibres cross over in the optic chiasm?
fibres from the nasal 1/2 of the optic disc= origin of optic nerve within the retina. Optic disc= no photoreceptors= blind spot.
which fibres are carried by the right optic tract?
fibres from right 1/2 of each retina (nasal retina of left eye, temporal retina of right eye) = left hemifield
which fibres are carried by the left optic tract?
fibres from left 1/2 of each retina (temporal retina of left eye and nasal retina of right eye)= right hemifield
where do 90% of retinal axons terminate?
the lateral geniculate nucleus in the thalamus
provides orderly representation of contralateral 1/2 of visual field
where is the left 1/2 of the visual field represented?
in the right primary visual cortex
how do ears move from their original position in the neck?
growth of mandible
2 different parts of the auditory (otic) vesicle formed from invagination of otic placodes and subsequent covering by surface ectoderm, and their location?
saccule= ventrally, cochlear duct is formed from this as an outpocketing which pentrates the surrounding mesenchyme is a spiral fashion and allows development of the cochlea. utricle= dorsally, gives rise to the semi-lunar (circular) canals.
what does expansion of the 1st pharyngeal pouch distally create?
tympanic cavity
pouch expands in a lateral direction to contact floor of 1st pharyngeal cleft- gives rise to EAM.
structure of the EAM?
lined by skin throughout, but skin lining outer 1/3 has hairs, sebaceous glands, and ceruminous glands- brown wax, bactericidal.
outer 1/3= elastic cartilage
inner 2/3= tympanic plate of temporal bone
structure of tympanic membrane?
outer 1/3= skin- stratified squamous K epithelium
middle= fibrous layer, CT, forms membrane skeleton
inner= respiratory epithelium= low columnar.
describe how the auricle of the ear develops
mesenchymal proliferation in 1st and 2nd pharyngeal arches surrounding EAM- 3 on each side= auricular hillocks. These fuse to form the auricle.
what happens if the choroid fissure fails to close?
coloboma= cleft in the iris
how is the choroid fissure formed and what is its function?
invagination of inferior surface of optic cup. Allows hyaloid artery to reach inner eye chamber.
describe the formation of the retina
derived from optic vesicle= outpocketing of the diencephalon. Vesicle invaginates forming a double walled optic cup, outer layer= pigmented layer of retina, inner=neural layer, the 2 initally separated by an intra-retinal space but lumen disappears with apposition of the layers.
what does the optic vesicle give rise to?
the retina, lens and ciliary body
how is the lens formed?
derived from lens placode= thickening of surface ectoderm. Optic vesicle developing as outpocketing of diencephalon makes contact with the surface ectoderm helping to induce changes necessary for lens formation.
Lens placode invaginates forming lens vesicle which comes to lie inside mouth of optic cup when loses contact with surface ectoderm, and forms the lens.
when the choroid fissure closes, what happens to the hyaloid artery which ran in it?
degenerates distally
proximal portion becomes central artery of the retina
what is the ciliary body derived from and what does it do?
from optic vesicle, connects choroid with lens.
how is the optic cup, formed from the invagination of the optic vesicle, connected to the brain?
by the optic stalk= outgrowth of diencephalon
what is the groove on the ventral surface of the optic stalk?
choroid fissure- contains hyaloid vessels
what does the optic nerve form from?
the optic stalk following closure of choroid fissure and increasing numbers of nerve fibres and nerve fibres of retina returning to brain lie among cells of inner wall of stalk, and as inner wall then grows, inside and outside walls of stalk fuse.
Contains central artery of retina
what are extraocular muscle of eye derived from?
preotic myotomes
how are eyes moved from side of head to front of face?
growth of facial prominences
what does the optic radiation carry visual information to and from?
from the lateral genicualte nucleus to the primary visual cortex in the occipital lobe of the brain.
what is the primary visual cortex (V1) known as histologically?
Broadman’s Area 17