EYE & EAR

Kaan YüceM.D., Ph.D. 12. May.2014 Monday

EYEThe 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] .

VISUAL PATHWAYSVision 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.

VISUAL PATHWAYSThe 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.

EARThe ear is the organ of hearing and balance. It has three parts: 1st part external ear 2nd part is middle ear3rd 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.

AUDITORY PATHWAYSInformation 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.

AUDITORY PATHWAYSAll 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 sub-lenticular 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.