Neuro Guiding Questions 9 03.08 Sensory - Optic

What does the ventral stream do?

"what" pathway - object recognition, (shape, color)

What does the dorsal stream do?

"where" pathway; spatial organization, movement

2. Explain the three layers of the eye, describing component of each layer.

1.) The outer, or fibrous layer, 2.) the middle, or vascular layer, and 3.) the inner, or retinal layer

What is the minimum distance you need to read?

25 centimeters

How many cortical fields are there? What are they?

4: frontal, temporal, parietal, occipital

4. Explain the process of accommodation. Which muscles help in accommodation? What do you think: is the process of accommodation is under voluntary or reflexive control (check the answer in book under the middle layer, you already read that as one of the guiding question above).

Accommodation is the process by which the ciliary muscles contract in a sphincteric fashion, which causes the suspensory ligaments to relax their tension on the lens. The lens then relaxes, becoming more curved. This is a parasympathetic reflex.

As the image is ___________by the lens system, the superior (top) half of each eye's visual field is projected onto the __________ half of each eye's retina. Also, as the lens produces a _________ image, the __________ half of each visual field is projected onto the __________ half of each eye's retina. Therefore, the_____ (left) hemifield of the left eye is projected onto the _________ half of the left eye's retina and the ________ hemifield of right eye is projected onto _______ half of the right eye's retina. Consequently, the left hemifields of both eyes are projected onto the corresponding (right) halves of the two retinas. (This is a very important concept)

As the image is inverted by the lens system, the superior (top) half of each eye's visual field is projected onto the inferior (bottom) half of each eye's retina. Also, as the lens produces a reversed image, the temporal half of each visual field is projected onto the nasal half of each eye's retina. Therefore, the temporal (left) hemifield of the left eye is projected onto the nasal (right) half of the left eye's retina and the nasal (left) hemifield of right eye is projected onto temporal (right) half of the right eye's retina. Consequently, the left hemifields of both eyes are projected onto the corresponding (right) halves of the two retinas.

How does binocular vision helps with depth perception?

Binocular fusion permits the perception a single clear image and also provides extra cues for depth perception. That is, the binocular disparity between the two images is used by the nervous system to allow the perception of a three-dimensional world where the approximate distance of an object can be determined.

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): efferent pathway (preganglionic)

CN III vs spinal nerve t1

2. When viewing an object, which is located at a distance < 30 feet, what would happen if the eye's lens system are not adjusted?

Consequently, the image focal point would be beyond the retina if the eye's lens system were not adjusted.

3. In the middle layer, what is the function of the ciliary muscles?

Contraction of the ciliary muscles results in decreased tension on the suspensory ligaments, and, in turn, on the lens, which allows it to focus on near objects. They are innervated by the parasympathetic nervous system.

What is the distance at which the eye can emit or reflect light and focus on the retina in a normal relaxed state?

Distant objects (greater than 30 feet or 9 meters away from the eye) emit or reflect light that can be focused on the retina in a normal relaxed eye (Figure 14.8).

What are the parallel pathways of the visual system?

Dorsal stream, ventral stream

Explain the pathway of the pupillary dilator reflex

Fear/arousal -> pupillodilator cell bodies in hypothalamus - > pupillodilator tract -> lateral horn of c8 and t1 - > preganglionic sympathetic c8/t1 spinal nerve - > superior cevical ganglion - > post ganglionic fibers - > long ciliary nerve - > target dilator muscle (of the iris).

2. What is refraction? Explain the process of refraction used to form the image on the focal point on the retina. Understand how the lens of the eye refracts the light rays after entering the eye and form the image on the focal point on the retina.

If the light strikes the lens surface at an angle, the light rays will be bent in a line perpendicular to the lens surface (Figure 14.5, right). A biconvex lens, which is functionally similar to the eye's lens system, is flat only at its center. The surface of the area surrounding the center is curved and not perpendicular to parallel light rays (Figure 14.6). Consequently, the curved surfaces of a biconvex lens will bend parallel light rays to focus an image of the object emitting the light a short distance behind the lens at its focal point. Focal point is a point on the retina, where the lights meet and form the image after getting refracted from the lens).

4. What is amblyopia

In fact, strabismus at birth, if uncorrected, may result in a form of central blindness, amblyopia, where the image from the deviant eye is no longer represented at cortical levels of the nervous system. The uncorrected, long-term amblyope is functionally blind in one eye and has poor depth perception.

What are the two main parts of the retina?

It consists of two parts, the retinal pigment epithelium, which separates the middle, choroid coat of the eyeball from the other innermost component and the neural retina.

What are smooth pursuit movements?

Movements that keep an image of a moving target fixed on the retinae

What are conjugate movements?

Occur when eyes move in the same direction, that is, to the right, left, up, or down.

What is the pathway of the accommodation reflex?

Perception of near object;

What does the horizontal gaze center control? Where is it located?

Pons. The center on each side is responsible for conjugate movements on that side.

How is homomynous hemianopsia "sided"?

Side of temporal field loss.

What is the pathway for the accommodation reflex?

Stimulus - > Receptor (the vergence gaze center of the brain) - > occipital cortex - > corticotectal tract - > tectum - > EW nuclues - > oculumotor nerve - > ciliary ganglion - > short ciliary nerve - > ciliary muscles, constrictor muscle, convergence muscle (medial rectus, innervated directly by medial rectus without ganglion)

What are the characteristics of M cells?

The M ganglion cell is much larger than P ganglion cells synapses with many bipolar cells is color insensitive has a large concentric receptive field is more sensitive to small center-surround brightness differences responds with a transient, rapidly adapting response to a maintained stimulus. responds maximally, with high discharge rates, to stimuli moving across its receptive field.

5. What is the refractory index of the aqueous humor relative to the cornea? Don't worry about the secretion and flow of aqueous humor.

The aqueous humor has about the same refractive index as the cornea

1. What is accommodation?

The change in the refractive properties of the eye is called the accommodation or "near point" process. Changes occur to create "near" vision.

5. How is the monocular field determined (test procedure)? What is the name of the test?

The clinical examination of the visual fields most commonly used is the confrontation field test. It defines the outer limits of our subjective visual space.

2. What is visual field? Generally speaking what disorders damage visual field?

The inability to detect objects in specific areas of space (i.e., visual field defects) is often related to neural damage.

Explain the order of the different neurons starting from outer to inner in the neural retina.

The innermost layers are located nearest the vitreous chamber, whereas the outermost layers are located adjacent to the retinal pigment epithelium and choroid. From outer to inner: Retinal Pigment epithelium, photoreceptor receptors photoreceptor cell bodies synapse b/w photoreceptor and horizontal and bipolar cells horizontal, bipolar, and amacrine cell bodies. bipolar, retinal, amacrine, and retinal ganglion synapse retinal ganglion cell bodies ganglion axons to optic disc

Fovea and macula are parts of the optic nerve layer. Which neurons form the optic disc? How is this related to the blind spot?

The optic disc is formed by the retinal ganglion cell axons that are exiting the retina. It is located nasal to the fovea (Figure 14.19). This region of the retina is devoid of receptor cells and composed predominantly by the optic nerve layer. Consequently, it is the structural basis for the 'blind spot" in the visual field.

What is binocular vision? How is tested clinically?

The process of producing a single image from the two disparate monocular images is called binocular fusion. Clinically, binocular fusion is tested by holding up one or two fingers in front of the patient and asking the patient (who should be wearing corrective lenses if they are normally worn) how many fingers they see. If the patient reports seeing four fingers when only two are presented, the patient is unable to produce binocular fusion.

What are the two main types of eye movements?

Vergence and conjugate.

What is vergence?

When eyes shift between near and distant objects.

1. The transparent media of the eye functions as ___________ lens.

a biconvex

3. What is the blind spot? Where is it located?

a small area in which objects cannot be viewed which is located within the temporal hemifield.

1. What are the two structures, which compose the eye?

a wall made up of three coats and internal refractive media that bend the light rays as they pass toward the photoreceptors

For each eye, the visual field is . . .

about 150 degrees (the visual area that can be picked up by one eye)

The ciliary muscle is responsible for which eye reflex?

accomodation

Hyperopia is . . .

aka hypermetropia; farsightedness. caused by the refractive power of the lens being too weak or the eyeball too short

The monocular visual fields of the left and right eyes overlap to form the _________________________________________. Objects within the ________________ are visible to __________________.

binocular vision field. overlap, both eyes

If you shine a light in the left eye, which pupil constricts?

both do!

Damage to the loop of meyer will affection vision on the (ipsilateral/contralateral) side

both sides! E.g., in the case of the right, temporal loss on the left and nasal loss on the right.

In fright or flight stimulation of the pupillary dilation reflex, the ________________ are the stimulus.

brainstem gaze centers, hypothalamus

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): stimulus

bright light; dim light, flight/right

Dorsal fibers from the optic radiation . . .

bring information from the inferior quadrants.

Ventral fibers of the optic radiation . . .

bring information from the superior quadrants.

Pupillary dilation is a (sympathetic/parasympathetic) response. Where are the cell bodies for this?

c8 and t1

Myopia is . . .

caused by the refractive power of the lens being too strong or the eyeball too long (nearsightedness)

The middle layer of the eye is also known as the

choroid or uvea

How does the lens alter its shaped

ciliary muscles

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): ganglion

ciliary; superior cervical

What is vitreous humor?

clear, gelatinous substance that fills the posterior four-fifths of the eyeball.

What is horner's syndrome?

combination of three symptoms; miosis, ptosis, and anhidrosis

How is myopia corrected?

concave lens

Are optokinetic reflexes conjugate or vergence? What are they?

conjugate reflex, occur during continuous movement of the person or target.

Are vestibulo-ocular movements conjugate or vergence? What are they?

conjugate. keep targets fixed on the retinae during brief movements of the head. (see vestibular system).

If the optic nerve is damaged one side, what would happen to the light reflex?

consensual reflex can still happen and cause both eyes to contract.

What is the direct light reflex?

constriction of the ipsilateral pupil in the light reflex

What is the consensual light reflex?

constriction of the opposite pupil in the light reflex

Which structures of the eye cause the dilation and constriction of the pupil in the pupillary reflex

constrictor and dilator muscles of the iris

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): muscle

constrictor muscle of the iris; dilator muscle of the iris

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): function

constrictor muscle; dilator muscle

Lateral visual fields are carried in the . . .

contralateral

What does the suprachiasmatic nucleus of the hypothalamus do?

control of diurnal rhythms and hormonal changes

What does the superior colliculus do?

control of eye movements, orienting movements of the head and eye

What does the pretectum do?

control of the pupillary light reflex

How is hyperopia corrected?

convex lens

What are the refractive apparatuses of the eye?

cornea, aqueous humor, lens, vitreous body. The cornea is the main refractive structure of the eye.

What causes horner's syndrome

damage to the pupillo-dilator tract

What is the action of the inferior rectus

depression

What is visual acuity? Generally speaking what disorders damage visual acuity?

detect and identify small objects. can be affected by disorders in the transparent media of the eye and/or visual nervous system.

What is the main clinical application of the pupillary light reflex?

differentiate lesions in front of and sital to the optic tract

What is midriasis?

dilation of the pupil

4. Vision in the peripheral visual field is more sensitive to ______.

dim light.

M layers are (dorsal stream/ventral cells?)

dorsal

What is the action of the superior rectus?

elevation

What is the action of the inferior oblique

extorsion

What kind of emotions cause pupillary dilation

fear, rage, pain, sexual arousal

P cells are responsible for detecting

fine features, spatial resolution, and color

. The cornea has a _____ refractive power.

fixed.

The resting state of the lens is

flattened

Visual field is subdivided into two ________ known as __________. A horizontal line drawn from 0-180 degrees divides the ______ into __________. A vertical line drawn from 90 to 270 degrees divides the ______ into __________, which are often termed as __________________________________________.

halves known as hemifields. superior and inferior; left and right (nasal and temporal)

3. Vision in the visual field center operates best under ______.

high illumination.

Damage to the entire optic radiation will result in

homonymous hemianopisa

Damage to the striate areawill result in

homonymous hemianopsia, BUT with macular preserveration

What are the three brainstem gaze centers?

horizontal center, vertical center, and vergence center.

Presbyopia is . . .

hyperopia caused by loss of ability to accommodate the lens; caused by old age.

Where are the pupillodilator neuron cell bodies located?

hypothalamus

Where is the lateral geniculate nucleus?

in the thalamus

The farthest distance at which you can see is . . .

infinite

Where is the fovea located?

inside of the macula

What is the action of the superior oblique

intorsion

3. The image formed is______________ and _________ reversed.

inverted and left-right reversed

What is the action of the medial rectus

inward movement

Medial visual fields are carried in the . . . . pathways

ipsilateral

binocular fusion

is the process by which your brain creates the 3d image

What are the four nuclei within the brain that the optic tracts go to?

lateral geniculate of the thalamus superior colliculus of the midbrain the pretectum of the midbrain the suprachiasmatic nucleus of the hypothalamus

What is the refractive index of the lens relative to the cornea? Can this be altered?

lens is not as refractive as the cornea, but also can be altered

What is anhidrosis

loss of sweating

Syringomyelia most likely effects what parts of the spinal cord?

lower cervical and upper thoracic. especially upper thoracic

The M cells are also known as

magnocellular

What does the vertical gaze center control? Where is it?

midbrain. Upward and downward movements. acts bilaterally.

constriction of the pupils is also known as

miosis

What is extorsion

move top of the eye away from the nose and elevation

What is intorsion

move top of the eye toward the nose and depression

M cells are responsible for detecting

movement and contrast

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): damage to the pathway results in

mydriasis; miosis

What is the other name for the accommodation reflex

near reflex

Somatic motor functions of the oculomotor nerve are performed by

oculomotor nerve without ganglion

3. What is Stabismus?

one eye deviates from the normal position and/or is paralyzed)

Before the optic chiasm, the fibers are the

optic nerve

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): afferent pathway

optic nerve; optic nerve and pupillodilator tract

After the optic chiasm, the fibers are the

optic tract

What is the action of the lateral rectus

outward movement

Lesion of a horizontal gaze center results in

paralysis of gaze toward the ipsilateral side.

The accommodation reflex is sympathetic/parasympathetic?

parasympathetic

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): control

parasympathetic vs sympathetic

The dorsal portion of the optic radiations go to the

parietal lobe.

The P cells are also known as the

parvocellular

What is the stimulus for the accommodation reflex?

perception of an object that is less than 30 feet away

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): receptor

photoreceptor; photoreceptor (dim light) or gaze centers (ff)

Any lesion that has homonymous hemianopsia must be located

posterior to the optic chiasm, including both the optic tract and the optic radiations.

What area of the brain is responsible for reflex control of pupil to light?

pretectum

What are the three phenomena that occur together as a part of the accommodation reflex?

pupillary constriction, convergence, thickening of the lens

2. The visual field can further be subdivided into four ________________, namely _______________________________________________________________________.

quadrants, superior and inferior nasal quadrants; superior and inferior temporal quadrants

Visual acuity depends upon the ___________________________.

refractory (focusing) power of the eye's lens system and the cytoarchitecture of the retina.

The axons of the _______form the optic nerve

retinal ganglion cells

Human eye has a tri_________ system, where colors are visible by a mixture of ______, ______, and ____ colors.

richromatic visual system, whereby visible colors can be created by a mixture of red, green and blue lights.

The frontal eye field controls

saccades, and planning of visual movements.

What are the two main types of conjugate movements?

saccadic and smooth pursuit

The external layer is formed by the

sclera and cornea.

What does the retinal pigment epithelium do?

separates the middle, choroid coat of the eyeball from the other innermost component and the neural retina. The dark pigments within the retinal pigment epithelium and choroid coat function to absorb light passing through the receptor layer, thus reducing light scatter and image distortion within the eye.

Astigmatism is . . .

shape of the natural lens of the eye doesn't represent the surface of a sphere.

The post ganglionic fibers of the oculumotor nerve responsible for the constriction of the pupil in the light reflex are known as?

short ciliary nerve

ANS functions of the oculomotor nerve are performed by

short ciliary nerve (post ganglionic fiber); long ganglionic nerve (post ganglionic fiber)

compare and contrast: pupillary constriction (light reflex) versus pupillary dilation (dark reflex): post ganglionic fiber

short ciliary nerve; long ciliary nerve

2. How is visual acuity measured? What is the name of this test (** look the name online, Hint it starts with S).

snellen chart

Describe the pathway of the direct light reflex?

stimulus -> photoreceptor - > optic nerve - > pretectum - >BRANCHES - > 1 set of fibers to oculomoto nucleus in midbain - > oculomotor nerve - > preganglionic parasympathetic - > ciliary ganglion - > post ganglionic oculumotor nerve - > constrictor muscle in the iris

What are the "steps" in a somatomotor reflex?

stimulus, receptor, afferent N, synapse w/ motor nucleus, synapse w efferent n, muscle

What are the "steps" in a sympathetic reflex?

stimulus, receptor, afferent N, synapse w/ sympathetic cell body (lateral horn of t1-l2), preganglionic fiber, ganglion, postganglionic fiber, muscle or target organ

What are the "steps" in a parasympathetic reflex?

stimulus, receptor, afferent N, synapse with parasympathetic cell body (cranial nerve in brainstem or lateral horn of s1-s5 (actually s2 to s4)), preganglionic fiber, ganglion, post ganglionic fiber, muscle or target organ.

What are the six primary muscles of the eye

superior, inferior, medial, lateral rectus, and superior inferior oblique

What clinical conditions can cause horner's syndrome

syringomelia

The superior colliculus is the origination of what descending tract?

tectospinal

The ventral portion of the optic radiations go to the

temporal lobe

1. What is color vision? How is it tested clinically?

the ability to detect differences in the wavelengths of light is called color vision. Clinically it may be tested with an Ishihara chart: a chart with spots of different colors that are spatially organized to form numbers that differ for ``normal" and color-blind eyes

1. What is monocular visual field?

the area of space visible to one eye

Where is the control of the eye muscles located in the brain?

the brainstem gaze centers

What are the three parts of the middle layer of the eye?

the choroid proper, the ciliary body, and the iris.

The middle layer of the eye is formed by

the iris, the ciliary body (muscles), and the choroid layer. The lens is also located here

What is the retinal field . . .

the most interior portion of the eye - the rays of light that can be picked up by the retina

What kinds of cells are in the neural retina

the neural retina contains five types of neurons (Figure 14.17): the visual receptor cells (the rods and cones), the horizontal cells, the bipolar cells, the amacrine cells, and the retinal ganglion cells.

The fibers that come out of the lateral geniculate nucleus are known as

the optic radiations. (a.k.a geniculostriate).

How does the consenual portion of the light reflex?

the pretectum innervates the homologous (edinger-westphal) nucleus on the opposite eye. (in order words, the "cross-over" happens at the pretectum

Binocular fixation is

the process by which both eyes fix on a single object and is necessary for depth perception

How is visual acuity measured?

under high illumination, smallest size of a small, dark object on a light background

P layers are (dorsal stream/ventral stream) cells?

ventral

The loop of meyer is in the (dorsal/ventral) portion of the optic radiation

ventral

What is the receptor for the "near" reflex?

vergence center of the brainstem

What does the vergence center control?

vergence, accomodation reflex

What does the lateral geniculate nucleus do?

visual perception

What are saccadic movements? are they reflexive or voluntary?

voluntary when vision is being moved rapidly from one target to another. Reflexive, as in nystagmus and REM sleep

When does the lens become more CONVEX?

what it needs to focus on more NEAR objects

How is astigmatism corrected?

with a cylindrical lens that replaces the shape of the natural lens of the eye

If the optic radiation is damaged on one side, you would not see the light reflex in the . . . eye

you would see it in both eyes! it's behind the thalamus!

What are the characteristics of P cells?

ype P retinal ganglion cells are color-sensitive object detectors. The P ganglion cell(s) outnumber the M-ganglion cells, by approximately 100 to 1 in the primate retina makes synaptic contact with one to a few cone bipolars that are innervated by cone receptors in the macula fovea is color sensitive has a small concentric receptive field produces a sustained, slowly adapting response that lasts as long as a stimulus is centered on its receptive field. produces weak responses to stimuli that move across its receptive field.

The lens is attached to the ciliary muscle via the

zonule fibers