Eye movement Flashcards
Otoconia:
calcium carbonate and protein
What maintains the Ionic composition of the Endolymph
Darkcells
What happens when the MET cells open
Due to the high ION concentration K+ ions flow into the hair cells and depolarize them
bending of stereocilia toward the kinocilium does what?
depolarizes the hair cell
bending of stereocilia away the kinocilium does what?
bending away hyperpolarizes the hair cell
what divides the hair cells direction
Striola
The ampulla dont have
Striola
Depolarization is when ?
Steriocillia lean towards kinocillia
Hyperpolorization is when?
Steriocillia lean away from Kinocillia
Left rotation of head results in polorization of which ampulla?
Left
Right rotation of the head results in polorization of which ampulla?
Right
How are signials sent to the brain from the ear?
Bipolar neurons in the Scarpa Ganglion
Acoustic Nuroma
Something that impinges on the nerves in the internal acustic meatus
The vestibular nuclei are situated where?
laterally in the medulla and pons- beneath the floor of the fourth ventricle, they occupy a substantial portion of its superior-inferior extent.
How many Vestibular Nuclei are there?
There are 4 nuclei: superior, lateral, medial, and inferior.
semicircular canals primarily project to the
superior and medial vestibular nuclei
the utricle and saccule primarily project to the
lateral and medial vestibular nuclei
Vesibulocervical reflex (VCR)
Semicircular canals to medial vestibular nucleus to cervical cord to initiate reflexive movements of the neck in response to head rotation
Vestibulospinal reflex (VSR)
- Otolith organs
- lateral vestibular nucleus
- lower levels of spinal cord
- initiate reflexive postural adjustment to stabilize balance in response to gravitational force and linear movements of body
Otolith organs
saccule, utricle
Vestibulocerebellar pathways
The cerebellum and vestibular nuclei are reciprocally connected. Detection and adjustments of “motor error”.
The phenomenon of perceiving illusory self-motion from vision alone:
vection.
vestibulo-ocular reflex
keeps the line of sight fixed in the world by counter rotating the eyes during movements of the head
optokinetic response
stabilizes the line of sight with respect to the moving visual surround, but does so after a longer latency.
Which CN innervates the Contralateral side of the eye
Trochlear CN IV
Head turning activates the Kinocilium in the same/opposite turning direction.
Same direction
Dolls eyes test Normal: Abnormal: Indications:
Turn head in comotose pt with eyes open Eyes stay pointed in the original direction Eyes track with the head. Potential problem with vestibular system
nystagmus
slow opposite eye movement to head rotation fast recenter of eyes to center
COWS
Cold water - Opposite Warm water - Same (Fast response)
Non-conjugete movement of the eyes test
Damage at the MLF level
Mydriasis
pupil dilation
Relaxation of sphincter pupillae
Contraction of dilator pupillae
Miosis
pupil Constriction
Contraction of sphincter pupillae
Relaxation of dilator pupillae
Anisocoria:
asymmetric pupil sizes
unilateral oculomotor nerve damage
Innervation of the Pupil
Parasympathetic - Cilicary Ganglion Sympathetic - Superior Cervical Ganglion (sits behind the Jugular Vein)
Path of pupil innervation for Parasympathetic
Edinger-Westphal Nucleus - Preganglionic
Ciliary Ganglion (synapse)
Sphinctor Pupillae
Damage to optic nerve
Damaged eye will have a consentual response
Damaged eye will not have a direct response and will not ilicit a consentual response.
No direct or consensual response of opposite eye if light is shined in eye. Consensual response if light is shined in unaffected eye
Damage to oculomotor nerve
damaged pupli will not constrict with light in either eye
Will ilicit a consentual response with light in the damaged eye.
No direct response to light in affected eye. No consensual response for light in unaffected eye.
Near Reflex Triad
1- The Medial Rectus M moves eyes toward midline
2- The pupils dialate to assist in keeping focus
3- The lenses are thickened to keep object in focus
oculomotor nerve damage
- -Mydriasis (dilated pupil) -damage to input from ciliary ganglion
- -Ptosis (drooping eyelid) -lack of innervation to levator palpebrae
- -Eye is deviated down and lateral - lack of innervation to medial rectus, superior rectus, inferior rectus, inferior oblique
- -Near response impaired -lack of innervation to ciliary muscle for accommodation, lack of input to sphincter pupillae for pupil constriction, lack of input to medial rectus for convergence
Signs of trochlear nerve damage
hypertropia and extorsion of the affected eye.
This causes the patient to tilt their head and tuck their chin to keep the eyes aligned.
Contralateral inervation - right side affected = left side nerve.
Damage to the abducens nerve
inability to abduct the affected eye, affecting the primary position of the eye and the ability to gaze laterally. Leftward gaze ok Primary position of right eye shifted nasally Inability to abduct affected eye
abducens nucleus damage
Damage to the abducens nucleus on one side will cause a lateral gaze palsy of both eyes because of the interconnections between the abducens nucleus and the oculomotor nucleus.
Saccades
changing the line of sight to place the retinal image of visual targets onto the fovea. They are characterized by rapid changes in eye position
Smooth pursuit
continuously changes the line of sight to minimize blurring of the target’s retinal image. These movements are characterized by smooth and continuous changes in eye position (ramp in eye position trace) involving lower eye velocities (smooth step in eye velocity trace).
mesencephalic reticular formation or MRF
midbrain center related to vertical movements
the paramedian pontine reticular formation or PPRF
pontine center related to horizontal movements
left frontal eye field and the left superior colliculus respond to signals in the
Right Hemifield
The right frontal eye field and the left superior colliculus respond to signals in the
Left Hemifield
paramedian pontine reticular formation activates the ?
ipsilateral abducens nucleus - oculomotor nucleus on the opposite side to mediate a conjugate contraction of the lateral rectus and medial rectus.
Frontal eye field damage can cause gaze preference toward ? Why
the side of the lesion, - due to an imbalance of activity in the left and right PPRF.
Strabismus
(misalignment of eyes, 2% of children), can result in amblyopia (brain ignores input from one eye
Nystagmus,
initiation of smooth pursuit or saccades
Cortex/basal ganglia
Problems with voluntary eye movements. Initiating saccades and/or suppressing unwanted saccades (Huntington’s and Parkinson’s disease) Difficulties with smooth pursuit movements (Schizophrenia)
Path of Sympathetic Pupile innervation
Ciliospinal Center
Superior Cervial Ganglion
Travel Through the Cilicary Ganglion
Dialator Pupillae
