Question

Describe the structures and their function involved in vision. Be sure to start with the anatomy of the eyeball and retina. Be sure to describe the cell layers present in the retina. Then describe the nervous pathways involved in the sensation and perception of vision. What is the cranial nerve involved in vision? Then be sure to include the location and description of the lateral geniculate nucleus, primary visual cortex, and visual association cortex. Within what structure is the lateral geniculate nucleus located? Where the superior colliculus located and what is is its function in vision? How does visual perception affect visual sensation? That is, do we only see what we want to see? This is referred to as “top-down processing” of visual perception.

Answer 1

ANATOMY OF EYE :

Eye is made up of Outer covering of Sclera (Post 2/3 rd - white opaque), and anterior 1/3rd cornea - transparet.

Eye has anterior segment - in front of lens & posterior segment - behind the lens.

The anterior segment is further divided into anterior chameber - from back of cornea to Iris & posterior chamber - Iris to lense.

Light travels from ::

outside --> cornea -->anterior chamber --> posterior chamber --> lens --> vitreous --> retina --> stimulus genreated & sent via optic nerve.

LAYERS OF RETINA :

1. Inner limiting membrane
2. Nerve fiber layer
3. Ganglion cell layer
4. Inner plexiform layer
5. Inner nuclear laryer
6. outer plexiform layer
7. outer nuclear laryer
8. external limiting membrane
9. layer of rods & cones
10. retinal pigment epithelium

visual pathway :

Cornea --> Lense --> light falls on retina ---> Photoreceptors (rods & cones) ---> Optic nerve --> Optic Chiasma --> optic tract --> Lateral Genicualte body --> Geniculo calcarine tract --> primary visual cortex.

Lateral Geniculate Body - Located in thalamus

Primary visual cortex - located in occipital lobe, Broadmann area 17.

Visual association area - occipital loeb broadmann area 18

superior colliculus - It is located in the lateral part of superior half of the midbrain. Its upper layer receives visual signals from the retina of the eye.

Top down phenomenon - Best example of visual perception affecting the visual sensation is while reading a text we often read correclty over typographical error. This is due to visual perception of the word from the preceeding word.