3. Visual System

Retina converts light to neural signals, retinal nerve fibers, optic disc, optic nerve, optic chiasm, optic tract, lateral geniculate body/nucleus, Primary visual cortex (optic radiations), visual cortex

Describe the visual pathway conveying signals from the retina to the thalamus and cortex.

primary visual cortex, secondary visual cortex, other areas that use visual info to adjust movements or visually identify objects, midbrain

Describe the 4 aspects of visual processing

Crosses midline in optic chiasm. Projects to contralateral visual cortex

Explain the nasal half of the retina and the visual fields and the causes and presentations of visual field deficits

Continues ipsilaterally thru optic chiasm. Projects to ipsilateral visual cortex

Explain the temporal half of the retina and the visual fields and the causes and presentations of visual field deficits

sign of nervous system abnormality.

Describe pathologic nystagmus.

normal response elected in an intact nervous system

Describe physiologic nystagmus.

switch vision from one object to another. Voluntarily or elicited by a variety of stimuli

define saccades

used to follow a moving object. image is maintained on the fovea

define smooth pursuit

aims eyes toward the midline. objects fall on core

define convergence.

visual information to stabilize images during slow movements of the head or when visual objects are moving relative to the head. purpose keeps image stable on retina, allows eyes to follow large objects in teh visual field.

Describe the optokinetic nystagmus and their purposes.

action of vestibular information on eye movements during fast movements of the head. purpose to stabilize visual images during head movement. move the eyes in the opposite direction of the head movement to maintain stability of the objects.

Describe the vestibulo-ocular reflex (VOR) and their purposes.

loss of information in both temporal visual fields. damage to fibers in the center of the optic chiasm

Describe the deficits and locations of lesions causing bitemporal hemianopia

loss of visual information from the same visual field. complete lesion anywhere posterior to the optic chiasm

Describe the deficits and locations of lesions causing homonymous hemianopia

no awareness of any visual information dur to a lesion in the brain

Describe the deficits and locations of lesions causing cortical blindness.

bitemporal hemianopsia

What is 2

homonymous hemianopsia

What is 3

Contracts when looking at near objects, increasing the curvature of the lens, lens of eye adjusts to focus light on the retina. Afferent limb optic n. Efferent limb oculomotor n.

Describe the stimulus, afferent limb and efferent limb, and response for the accommodation reflex

pupil constricts in eye stimulated by light, pupil of contralateral eye constricts. Afferent limb Optic n. Efferent limb oculomotor n.

Describe the stimulus, afferent limb and efferent limb, and response for the pupillary reflex

3( moves eye up, down and medially raises the upper eyelid), 4 (moves eye down, especially when adducted), 6 (abducts the eye). Medial longitudinal fasciculus (MFL) looking right

List the 3 CN's and MLF and their contributions to normal eye movements.

internuclear ophthalmoplegia. eye ipsilateral to the lesion cannot adduct past midline when contralateral eye moves laterally

Identify the deficits associated with lesions affecting the MLF

Ipsilateral blindness and loss of the direct pupillary light reflex

Identify the deficits associated with lesions affecting CN 2

sever ptosis (drooping of eyelid_, ipsilateral eye is aimed outward and down, diplopia (double vision), deficits in moving ipsilateral eye medially, downward, and upward, loss of direct (ipsilateral) pupillary light reflex, loss of constriction of pupil in response to focusing on a near object

Identify the deficits associated with lesions affecting CN 3

prevents activation of superior oblique muscle

Identify the deficits associated with lesions affecting CN 4

eye deviates inward. Unable to voluntarily abduct the eye will have double vision.

Identify the deficits associated with lesions affecting : CN 6.

eye movement disorders

Lesions affecting the CNs innervate extraocular muscles and result in what?

eye movements will not be coordinated with each other or with movements of the head

Lesions affecting the MLF result in what?