Transcript Eye & Ear - WordPress.com

EYE
The eye is the organ of vision and consists of the eyeball and
the optic nerve.
The orbit contains the eyeball and its appendages.
The orbital region is the area of the face overlying the orbit
and eyeball and includes the upper and lower eyelids and
lacrimal apparatus.
The orbits are bilateral bony cavities in the facial skeleton
that resemble hollow quadrangular pyramids.
The eyelids and lacrimal fluid, secreted by the lacrimal
glands, protect the cornea and eyeballs from injury and
irritation (e.g., by dust and small particles).
The inner layer of the
eyeball is the retina.
The iris, which literally lies
on the anterior surface of
the lens, is a thin contractile
diaphragm with a central
aperture, the pupil, for
transmitting light.
The oculomotor nerve innervates the inferior oblique.
The oculomotor nerve innervates the superior and inferior rectus muscles.
The oculomotor nerve [III] innervates the medial rectus, and the abducent nerve [VI] innervates
the lateral rectus.
The trochlear nerve [IV] innervates the superior oblique.
The levator palpebrae superioris is innvervated by the occulomotor nerve [III] .
Vision is generated by photoreceptors in the retina, a layer of cells
at the back of the eye.
The information leaves the eye by way of the optic nerve, and
there is a partial crossing of axons at the optic chiasm.
After the chiasm, the axons are called the optic tract.
The optic tract wraps around the midbrain to get to the lateral
geniculate nucleus (LGN), where all the axons must synapse.
From there, the LGN axons fan out through the deep white matter
of the brain as the optic radiations, which will ultimately travel
to primary visual cortex, at the back of the brain.
EAR
The ear is the organ of hearing and balance. It has three
parts:
1st part external ear
2nd part is middle ear
3rd part is the internal ear
The tympanic
membrane
separates the
external acoustic
meatus from the
middle ear.
Auditory ossicles
The bones of the middle ear consist of the malleus, incus,
and stapes. They form an osseous chain across the middle
ear from the tympanic membrane to the oval window of the
internal ear.
Muscles associated with the auditory ossicles modulate
movement during the transmission of vibrations.
The inner ear is the innermost part of the ear.
It consists of the bony labyrinth, a hollow cavity in the
temporal bone of the skull with a system of passages
comprising 2 main functional parts:
Cochlea: dedicating to hearing; converting sound pressure
impulses from the outer ear into electrical impulses which
are passed on to the brain via the auditory nerve.
Vestibular system: dedicated to balance.
Information proceeds from the Organ of
Corti to spiral ganglion cells and the VIIIth
nerve afferents in the ear, to the cochlear
nuclei, many crossing in the trapezoid
body to the superior olive in the brain
stem. Then all ascending fibers stop in the
inferior colliculus in the midbrain and the
medial geniculate body in the thalamus,
before reaching the cortex in the superior
temporal gyrus.
All auditory afferents synapse in the cochlear nuclei and in the thalamus.
Beyond that simplification, second order fibers from the cochlear nuclei
proceed rostrally in several different pathways.
Thalamic afferents reach the superior temporal gyrus through the sublenticular portion of the internal capsule.
A fast acting system- Lateral lemniscus
Fibers from dorsal cochlear nucleus
decussate and ascend in the lateral
lemniscus to the inferior colliculus.