TOPIC 2- 25. The visual pathway. The pupil-reflex. Accommodation.

The pathway extends from the eye, and all the way back to the occipital lobe

Visual pathway - generally?

- Photoreceptors
- Bipolar cells
- Ganglionic cells

What are the three first neurons of the visual pathway?

Axons of the ganglionic cells in the retina

What forms the fibers of the optic nerve?

Below the base of the diencephalon

Where is the optic chiasm located?

Divides into a medial and a lateral root
- these fibers will go to different locations

What happens with the optic tracts?

Lateral geniculate body

Where does 90% of the fibers from the optic tract go?

- Retina
- Optic nerve
- Optic chiasm
- Optic tract
- Lateral geniculate body
- Optic radiation
- Primary visual cortex

Geniculate part of the visual pathway?

Area around the calcarine sulcus

Where can we find the primary visual cortex?

Br. 17

Which brodmann area is the primary visual cortex?

Concerned with the conscious part of the visual perception

What is the geniculate part of the visual pathway concerned with?

- From lateral geniculate body
- Winds around the inferior and posterior horns of the lateral ventricle
- One division goes above and one goes below the calcarine sulcus

Where does the optic radiation go?

- Superior colliculus
- Suprachiasmatic nucleus
- Pretectal area
- Edinger-Westphal nucleus (accessory nucleus of CNIII)

Where does 10% of the fibers from the optic tract go?

- Retina
- Optic nerve
- Optic chiasm
- Optic tract

-> Suprachiasmatic nucleus
-> Superior colliculus
-> Pretectal area
-> Edinger-Westphal nucleus

Nongeniculate part of the visual pathway?

Its signals are not consciously perceived
- plays an important role in the regulation of various vision-related processes

What is the function of the nongeniculate part of the visual pathway?

- Temporal field
- Nasal field

What can the visual field be divided into?

Involved in the circadian rhythms

What is the retinohypothalamic tract involved in?

Retinotectal tract

Pathway between the retina and superior colliculus (tectal area)?

Involved in orienting the eye toward a stimulus, that initially appears in its peripheral field of vision

What is the retinotectal tract involved in?

Retinopretectal tract

Pathway between the retina and the pretectal area?

Involved in the pupillary reflex

What is the function of the retinopretectal tract?

Retinohypothalamic tract

Pathway between retina and suprachiasmatic nucleus?

- Temporal half
- Nasal half

What can the retina be divided into?

Does not cross in the optic chiasm

What happens with the fibers from the temporal half of the retina?

Crosses in the optic chiasm

What happens with the fibers from the nasal half of the retina?

Cross in the optic chiasm

What happens with the information from the temporal visual fied?

Does not cross in the optic chiasm

What happens with the information from the nasal visual field?

A reflex that controls the diameter of the pupil - in response to the intensity of the light

What is the pupillary light reflex?

Pupil constriction
- contraction of sphincter pupillae

Large amount of light?

Pupil dialation

Light fades?

- Optic tract sends collaterals to the pretectal nuclei

- The pretectal nuclei sends signals to the Edinger-westphal nucleus

- The accessory nucleus of the Edinger-westphal nucleus (VM) fibers (through the oculomotor nerve)

- The preganglionic fibers synapse in the cilliary ganglion, and the postganglionic fibers innervate the sphincter pupillae

How does the visual pathway affect the innervation of sphincter pupillae muscle?

Edinger-Westphal nucleus

What is another name of the accessory nucleus of the oculomotor nerve?

Direct pupillary light reflex

The pupillary reflex on the stimulated eye?

Consensual pupillary light reflex

The pupillary reflex on the unstimulated eye?

Synapses in the superior cervical ganglion, and innervate dilator pupillae muscle

What does sympathetic fibers have to do with the pupillary light reflex?

Accomodation is a process by which the eye increases its optical power to maintain a clear focus

What is accomodation?

- Medial rectus
- Ciliary muscle
- Sphincter pupillae muscle

Which muscles are stimulated in accomodation?

The lens becomes more convex

What happens when the ciliary muscles contract?

VM fibers, through oculomotor nerve

What stimulates the contraction of the ciliary muscles?

- Sends fiber to perlia's accomodation nucleus

- Perlia's accomodation nucleus stimulates edinger-wesphal nucleus which synapses in the ciliary ganglion and innervate ciliary muscle and sphincter pupillae muscle

- Also stimulates the motor nucleus of oculomotor nerve which innervates medial rectus muscle

How does the visual cortex stimulate the muscles for accomodation?