Lab 8: Vision, Eyeball Movement And Balance Systems II

Question 1

Impulses to the Extraocular Motor Nuclei

Answer 1

In addition to impulses from the vestibular system……

• from brainstem saccade centers (PPRF) in the caudal pons for horizontal gaze
• vertical gaze centers in the rostral midbrain

Question 2

Frontal Eye Field (FEF)

Answer 2

The motor cortex for VOLUNTARY horizontal and vertical movements of the eyeball. The path for horizontal eye movements involves transmission through the PPRF and MLF to reach the extraocular motor nuclei

Question 3

Posterior (parietal, temporal, occipital) Eye Fields

Answer 3

Paths through the cerebellum and vestibular nuclei to the Extraocular motor nuclei for visual tracking of an object in space and the slow component of the optokinetic reflex; unknown paths for convergence of eyeballs during near vision

Question 4

Impulse for reflex responses to bright light (pupillary constriction)

Answer 4

Travel from the retina through the optic nerve and optic tract. Bypass LGN via the brachium of the superior colliculus to reach the pretectal area bilaterally. Impulses travel from the pretectal nuclei bilaterally to the Edinger-Westphal nuclei of the oculomotor complex. This nucleus sends axons to the ciliary ganglion, which sends fibers to the sphincter pupillae muscles

Question 5

Accommodation (pupil constriction and lens bulge)

Answer 5

pathway is similar to that for pupillary Light Reflex, except that it involves integration in the superior colliculus rather than the pretectal area, and the target is the ciliary muscle, which when contracted, causes the lens to bulge

It’s a response to spatial info from parietal cortex and includes: pupillary constriction, ciliary muscle contraction and convergence of eyeballs (contraction of both medial rectus muscles)

Question 6

Petrous Parts of the left and right Temporal bones

Answer 6

Contain inner ear and middle ear

Question 7

Internal Acoustic Meatus

Answer 7

Location of passage of the vestibulocochlear (VIII) and facial (VII) nerves from the petrous part of the temporal bone into the posterior cranial fossa
-location of the vestibular (Scarpa’s) Ganglion

Question 8

Semicircular Canals

Answer 8

Spaces in the petrous temporal bone

• observe horizontal, anterior and posterior semicircular canals
• relations of semicircular canals to the facial nerve, cochlea and mastoid air cells
• the orientation of the horizontal canal, which is parallel to the ground when the head is tilted 30 degrees downward, so that the eyes look at the ground in front of the feet

Question 9

Vestibular Nerve Fibers

Answer 9

• enter the CNS at the lateral edge of the brainstem tegmentum
• contain central processes of 1st order vestibular neurons

Question 10

Vestibular Nuclei

Answer 10

Termination of most vestibular nerve fibers

Question 11

MLF (medial longitudinal fasciculus)

Answer 11

-contain axons from vestibular nuclei en route to extraocular motor nuclei

Question 12

Inferior Cerebellar Peduncle

Answer 12

-contains fibers from the vestibular nuclei and vestibular nerve en route to the cerebellum; contain fibers from cerebellum to vestibular nuclei

Question 13

Frontal Eye Field (location)

Answer 13

in the central part of the middle frontal gyrus, area 8 is the motor cortex for horizontal voluntary eyeball movement

Question 14

Posterior Eye Fields (parietal, temporal, occipital) Location

Answer 14

Areas in parietal, Temporal and occipital association cortices involved in:

• convergence of eyeballs during near vision
• tracking (pursuit) of an object in space
• the slow component of the optokinetic reflex

Question 15

Abducens Nuclei

Answer 15

• contains lower motor neurons to the ipsilateral lateral rectus muscle
• inteneurons that send axons to the contralateral MLF

Question 16

Abducens Nerve Fibers

Answer 16

Intra-axial

Question 17

Paramedian Pontine Reticular Formation or PPRF

Answer 17

General location: dorsomedial reticular formation, lateral to the MLF

This saccade center is involved in voluntary horizontal gaze. It sends axions to abducens neurons and abducens interneurons

Question 18

MLF

Answer 18

Fibers from the vestibular nuclei and the PPRF (via the abducens interneurons) that transmit signals to extraocular motor nuclei

Question 19

Vestibular Nuclei

Answer 19

Send fibers into the MLF for vestibulo-ocular reflexes

Question 20

Trochlear Nucleus

Answer 20

Motor nucleus to the superior oblique muscle and target of the MLF

Question 21

Oculomotor Nucleus

Answer 21

Motor nucleus to extraocular muscles and target of the MLF, vertical gaze center, and convergence paths

Question 22

Superior Colliculus

Answer 22

Involved in the generation of saccadic eye movements and eye-head coordination

Question 23

General Area of the Entrance of the Vestibular Nerve into the brainstem

Answer 23

Lateral edge of the tegmentum (caudal pons?)

Question 24

Brachium of superior colliculus

Answer 24

• a continuation of optic tract fibers that bypass the LGN

- terminate in the nuclei of the pretectal area and the superior colliculus

Question 25

Pretectal Area

Answer 25

Lateral to the posterior commissure in the rostral midbrain

• a synaptic center for the pupillary light reflex
• receives input from the retina
• sends axons bilaterally to the Edinger-Westphal nucleus for the pupillary light response

Question 26

Posterior Commissure

Answer 26

Dorsal to the rostral cerebral aqueduct

-a decussation of fibers between the pretectal nuclei, contributing to the bilateral (consensual) light response

Question 27

Superior colliculus

Answer 27

Reflex center for visual system

• receives impulses from the retina and the visual cortex
• sends axons to the Edinger-Westphal nucleus for lens accommodation

Question 28

Edinger-Westphal Nucleus

Answer 28

In oculomotor complex

• a preganglionic parasympathetic (GVE) nucleus
• receives fibers from the pretectal area and superior colliculi
• sends axons via CN III to the ciliary ganglion for supply of the constrictor papillae and the ciliary muscle (lens accommodation)

Question 29

Oculomotor Nucleus

Answer 29

The GSE group of nuclei that supply extraocular muscles

Question 30

Oculomotor nerve fibers

Answer 30

Contain axons from:

• GVE Edinger-Westphal nucleus to terminate at the ciliary ganglion for supply of intraocular muscles
• oculomotor nucleus to supply the GSE extraocular muscles

Question 31

Sympathetic Supply to the Dilator Pupillae

Answer 31

Review the path from the hypothalamus, through the brainstem reticular formation and thoracic spinal cord, sympathetic chain and ganglia, internal carotid plexus, to the dilator pupillae muscle

Question 32

Pupillary Dilation Response

Answer 32

Involves descending fibers from the hypothalamus that reach the upper thoracic spinal cord and sympathetic neurons that reach the orbit by way of the sympathetic chain, superior cervical Ganglion, and the internal Carotid Plexus. This pathway can be affected by pathology in the brainstem, upper spinal cord, neck and internal Carotid Arterial system

Question 33

Reticular Formation of the Brainstem

Answer 33

Contains descending fibers from the hypothalamus en route to the spinal cord

Question 34

Cervical Spinal Cord

Answer 34

Also contains descending fibers en route to the intermediolateral cell column of the upper thoracic spinal cord

Question 35

Internal Carotid Artery

Answer 35

Is covered by the internal carotid Plexus that sends fibers onto the ophthalmic artery to reach the dilator pupillae muscle

Question 36

Near-Vision Visceral Reflex Test

Answer 36

Have patient look at near object; look for pupillary constriction of both eyes

Question 37

Counter-Rolling Test for VOR

Principle

Answer 37

if you have an old-fashioned doll, hold it in front of you. If you turn the dolls head down, the eyes will turn up to remain looking at you in the eye. If you turn the dolls head up, the eyes will rotate down to remain looking at you in the eye. Counterweights behind the eyes cause this counter-rolling action, which essentially keeps the eyes on visual target when the head moves

Question 38

Counter-Rolling Test

Technique

Answer 38

Hold the patient’s head so the eyes are in primary position. Then, briskly rotate it to the right and left and up and down, and stop it in each rotated position. For example, rotate the head to the right and stop in that position. During the initial rotation to the right, the eyes counter-roll opposite the direction of the head turning (to the left relative to the head), but actually they simply maintain their original position, the eyes quickly turn and align straight ahead of the new head position. Failure of the eyes to counter-roll and remain looking in the direction of the head rotation (think of dolls who have their pupils painted on) indicates failure of the VOR

Question 39

Counter-Roll Test

Sum up

Answer 39

In an unconscious patient, “looking straight ahead” is common and is maintained during head rotation by counter-rolling if the vestibulo-ocular pathways are intact.

Called “doll’s eyes” response

Question 40

Caloric Irrigation

Principle

Answer 40

Oculovestibular responses are reflex eye movement in response to irrigation of the external ear canals with cold or warm water

Question 41

Caloric Irrigation

Example

Answer 41

Ice water: the head is raised to 30 degrees relative to the horizontal plane, and the external ear canals are inspected for cerulean or a perforated tympanic membrane. 50 to 100 ml of ice water is instilled into the canal and the resulting eye movements are noted. Ice water produces a downward convection current in the horizontal semicircular canal and decrease as the tonic firing rate of the vestibular end organ on that side. Consequently, the contralateral vestibular output drives the eyes toward the irrigated side. In an awake patient who is trying to maintain fixation, the slow phase is followed by a fast phase of nystagmus away from the stimulated ear

Question 42

Caloric Irrigation

Warm water example

Answer 42

Induces the opposite response of the cold water

-COWS (cold opposite, warm same), which refers to the direction of nystagmus in an awake patient. In an unconscious patient, there’s a loss of the fast-phase Nystagmus, and only the tonic deviation of the eyes are seen

Question 43

Caloric Irrigation Abnormalities

Answer 43

A lack of oculovestibular responses suggests pontine-midbrain dysfunction. Movement of the ipsilateral eye toward the irrigated ear, but no movement of the contralateral eye, suggests an abnormality of the contralateral MLF