Lesson 8: Vision (& Smell) Flashcards
What is the pathway of olfactory information?
Cells in the olfactory epithelium
Olfactory bulb’s mitral cells
Olfactory tract - may cross in the medial olfactory stria
Temporal lobes - primary olfactory cortex
What is the pathway of reflex activity, compared to conscious information, for vision? Why is this important?
Conscious info: retina to optic chiasm to optic tract to LGB
Reflex: from optic tract to superior colliculus.
If damage occurs after the optic tract, reflexes may still be present
What vision is present in a lesion to the optic nerve?
Monocular blindness
What is present in optic chiasm damage?
Bitemporal hemianopia
One half of the optic chiasm is injured before decussation - what happens
Nasal hemianopia
Injury to the optic tract or the lateral geniculate body - how does vision seem?
Contralateral homonymous hemianopia
Injury to upper/lower optic raditiation
contralateral homonymous superior/inferior (opposite) quadrantanopia
What is macular sparing? Why does it occur?
A lesion in the PCA may occur, but the macula is spared due to irrigation from the MCA
What is hypermetropia?
Far-sighted: focal point is behind the retina
Convex lens: puts focal point at the retina
What is myopia?
Near-sighted: Focal point is in front of the retina
Concave lens: adds focal length
What is astigmatism?
Refractive error due to irregular shape of cornea or lens
Combined cylindrical and spherical lens
What are the 3 main types of color vision, and which cone is missing with each?
Protanomaly: no red
Deuteranomaly: no green
Tritanomaly: no blue
What are the three ocular nerves?
Oculomotor, trochlear and abducens
What are the three aspects of accomodation of distance in vision?
Ocular convergence
Pupillary constriction
Lens thickening
What two structures are responsible for coordination of eye muscles?
The medial longitudinal fasciculus and the pontine paramedian reticular formation
What disease targets MLF?
MS - it commonly dymyelinates
What is the MLF connected to?
The vestibular nuclei
What movement is the superior rectus responsible for?
Eyeball upward
What movements is the medial rectus responsible for?
Eyeball inward
Inferior rectus movements?
Eyeball down
Inferior oblique movements?
Up and out
Superior oblique movements?
Eye down and in
Levator palpebrae superior muscle eye movements? What two aspects does it have?
Lifts upper eyelid
Voluntary muscles - via the oculomotor nerve
Smooth muscles - via the sympathic nerves
What does sympathetic nerve loss result in, regarding the levator palpebrae superior muscle?
Horner’s syndrome - constricted pupil, ipsilaterally dry red face
What does damage to the voluntary muscle result in, regarding the levator palpebrae superior muscle?
oculomotor nerve palsy
Why is pupil constriction so vulnerable to compression?
It is the parasympathetic portion of the oculomotor nerve, and thus is on the outside and in between the PCA and the superior cerebellar artery
What is the pathway to pupil constriction, from light to muscles?
Light to the optic nerve, to the prectal nucleus bilaterally
To the Edinger-Westphal nucleus bilaterally
To the oculomotor nerve
To the ciliary ganglion, to the constrictor pupillae muscle
What 3 nerve pathways are involved in pupil constriction?
Optic nerve for info in, oculomotor nerves (both) for info out
What is the difference between and indirect and a direct response in pupil constriction?
Direct response: eye being tested constricts
Indirect: other eye constricts
What’s the difference between the accommodation reflex and pupil constriction?
Accommodation: conscious
Pupil: automatic
What is the pathway of the accommodation reflex (3 parts)?
Signal to the occipital cortex to the frontal eye fields, to the LGB, to the Edinger-Westphal nucleus, to the ciliary ganglion: for constrictor pupillae muscle (pupil constriction) and to the ciliary muscle (lens focusing)
Fibers to the oculomotor nucleus - innervate the medial rectus muscles (eye convergence)
Where is the nuclei for the oculomotor nerve? What is its pathway to the ventral brainstem?
in the upper tegmentum
Through the red nucleus and the basis pedunculi to the ventral brainstem
What muscles does the oculomotor nerve innervate?
The superior, medial and inferior rectus
The inferior oblique
The levator palpebrae superior
What are the two nuclei of the oculomotor nerve?
The somatic motor nucleus - extrinsic ocular muscles
The Edinger-Westphal nucleus: visceral motor nucleus
What are the symptoms of trauma to the oculomotor nerve? (3)
Dilated pupils, eyes directed outward, diplopia
Where does the trochlear nerve exit?
The posterior surface of the brainstem
Where is the nucleus of the trochlear nerve?
In the periaqueductal gray matter in the midbrain
What muscle does the trochlear nerve innervate?
The superior oblique
What does trauma with the trochlear nerve ressemble (1)?
Diplopia when looking down
Where is the nucleus of the abducens, and what does it pass through?
In the upper tegmentum of the pons
Through the pontine tegmentum and the corticospinal tract
To the pontomedullary junction
What muscle does the abducens nerve innervate?
The lateral rectus
What does a lesion in the abducens nerve ressemble?
The eye directed in
How is the pupillary light reflex tested? What type of patient can be tested?
They must be conscious
Optic nerve damage: no response in either eye
Oculomotor nerve damage: no response in one eye - side of damage
