Visual, auditory, vestibular Flashcards
What is the correct anatomical pathway for visual information from the eye to the brain?
- Retina –> optic nerve –> optic chiasm –> optic tract –> lateral geniculate nucleus –> optic radiation –> primary visual cortex
Which cranial nerves serve as the afferent and efferent limbs of the pupillary light reflex?
Efferent: CN 3 (oculomotor)
Afferent: CN 2 (optic)
Why do both pupils constrict when light is shone in only one eye?
Bilateral connect between pretectal area and Edinger-Westphal nuclei
What happens to the pupillary reflex with lesions at different sites?
Oculomotor nerve lesion: The affected eye will not constrict, but the opposite eye will.
Ciliary ganglion lesion: Prevents constriction in the affected eye only.
Pupil ?
- where light enter eye
- Control amount of light enter
- Appear dark
Iris?
Colored part
Cornea
glassy, transparent external surface of eye.
- involve eye’s refraction
Conjunctiva
Membrane that fold back and attach to sclera
Extraocular muscles
3 pairs that move eye in ORBIT
Optic nerve
Bundle of axon from retina
What are the three layers of tissue in the human eye?
- Sclera and cornea
- Choroid - vascular layer w/ ciliary muscle
- Retina - innermost layer w/ visual neurons
What is the function of the retina?
- Light-sensitive tissue of eye that receive and process visual info before sending it to the brain.
- Contain photoreceptors (rod and cone) for phototransduction
Phototransduction ?
- process of detect light and convert into electrical signal
What is the function of the lens ?
forms sharp images of near objects by changing shape (accommodation)
What makes the fovea unique in the retina?
has the highest visual acuity, the smallest visual field, and contains only cone receptors.
Optic disc
blind spot
Vitreous humor
jelly-like fluid
what is role and parts of extraocular muscle>
- control movement of eyes
- 4 rectus muscles: lat/med, and sup/inf
- 2 oblique muscles: sup/inf - rotate upward or downward
5 types of neuron in retina
- Photoreceptors
- Bipolar
- Ganglion
- Amacrine
- Horizontal
What are the roles of photoreceptor (rods and cones) in the retina?
- Only light sensitive cell in retina
- Graded membrane potential
- rod - black/white
- Cone “co” - colored
What is unique about ganglion cells in the retina?
- Only source of output to optic nerve
- Only retina cells that fire action potential
- Process different types of visual information (form,color,contrast, etc)
What is the function of the pigment epithelium in the retina?
- contain melanin to reduce “backscattering” of light + prevent blurring
- Photoreceptor sit on it
How is the retina organized,?
inside out arrangement
What is the role of the inner neuronal layer in the retina?
contains a three-neuron chain that is essential for phototransduction (convert light into neural signal)
What are the types and roles of interneurons in the retina
- Horizontal - connect photoreceptors and bipolar
- Amacrine - connect bipolar and ganglion cells
What happens when photoreceptors release neurotransmitters?
The generation of action potential in ganglion cells
What are cone receptors responsible for?
- Colored vision
- low light sensitivity, small receptive field, day vision
What are rod receptors responsible for?
- Black/white
- High light sensitivity, large receptive field, night vision
What is the path of the 2nd order neuron cell body from the lateral geniculate body
- Lateral geniculate body –> optic radiation –> primary visual cortex
What parts of the calcarine fissure process upper and lower visual fields?
- Cuneus (upper) - lower visual field
- Lingula (lower) - upper visual field
What does it mean that the primary visual cortex is retinotopically organized?
- Each part of retina correspond to a specific area in the visual cortex
How does the primary visual cortex reflect the layout of the visual field?
1 region processes foveal (central) vision
3 peripheral regions represent ipsilateral and contralateral peripheral visual hemifield
what is the tract of optic radiation ?
Geniculocalcarine tract
What is the dorsal stream in visual processing?
- process in parieto-occipital cortex
- Called “action stream”
- Used to direct movement
: What is the ventral stream in visual processing?
- process in occipital-temporal
- called “perception stream”
- Recognizes objects, faces, & color
key features of the reflex pathway in the visual system
- Involve pretectal and superior colliculus
- Control size of pupil and curvature of len.
- Eye movement control
- Postural and limb movement control
What is peripheral visual processing?
- nasal –> see temporal
- temporal –> see nasal
What is central visual processing?
Contralateral visual image
What happens to the visual image when projected onto the retina?
Inverted (up/down flipped)
And reversed (left/right flipped)
How is the entire visual field processed by the retina?
Monocular zone → ipsilateral nasal hemi-retina
Binocular zone → both nasal and temporal hemi-retinas
What are the two functional categories of eye movement motor control?
Stabilize gaze
Direct gaze to visual targets (saccade and smooth pursuit)
What are conjugate eye movements?
Both eyes move in the same direction
What are the two types of vergence movements and their functions?
Convergence: eyes move toward midline to focus on near objects that move from far,
Divergence: eyes move away from midline to focus on far objects
Saccade ?
Ballistic, rapid eye movement
- Align fovea w/ particular part of the scene
- max 700 deg/sec
Smooth pursuit
- Slow tracker movement
- Keep moving object on fovea
- max 100 deg/sec
Vestibulo-Ocular Reflex (VOR)
- Elicited by moving head
- Eye moves same distant/speed but opposite direct as head
- Keep image same place in retina
Optokinetic
- Elicited by moving visual stimuli
- Adjust eyes during slow movement (<1 Hz)
- allow eye follow large object in visual field
What structure in the reticular formation controls horizontal gaze?
Paramedian pontine reticular formation (PPRF)
What is the function of the rostral interstitial nucleus in the midbrain reticular formation?
Controls vertical gaze
Which cranial nerves and nuclei are involved in the vestibulo-ocular and optokinetic reflexes??
CNs III (oculomotor), IV (trochlear), and VI (abducens)
Vestibular nuclei
What is the function of the frontal eye field in eye movement?
Initiates contralateral saccades and smooth pursuit; connected to contralateral PPRF
The parieto-occipital-temporal cortex is responsible for what type of eye movement?
Ipsilateral smooth pursuit
What connections does the parieto-occipital-temporal cortex have in coordinating eye movement?
- Connected with the vestibular nucleus, cerebellum, and PPRF
- Ipsi smooth pursuit
What are the effects of a lesion in the superior colliculus (optic tectum)?
Increases latency (= delay in initiating eye movements) and reduces accuracy, frequency, and velocity of saccades
What is the role of the basal ganglia in eye movement control?
proper initiation of eye movements
Involves the oculomotor loop and prefrontal loop
What is the role of the cerebellum in eye movement control?
Ensures correct execution of eye movements
Involves vestibulocerebellum and spinocerebellum (vermis)
Lesion to R optic N
Loss of vision in R eye
Lesion to optic chiasm
Bitemporal (heteronomous)
hemianopsia
Lesion to R optic tract
L homonymous hemianopsia.
Lesion to R Meyer’s loop
L superior homonymous
quadrantanopsia
Lesion to R V1
L homonymous hemianopsia with macular sparing.
Which parts does external ear include?
- Pinna: the visible portion of the ear, which collect sounds
- Auditory canal: entrance to internal ear, transmit sound waves to vibrate the tympanic
Which parts does middle ear include?
- Tympanic membrane: ear drum (separate outer and inner ear)
- Ossicles: bone connect to tympanic membrane and oval window to transfer movement
- Oval window: membrane covering a hole in the skull
- ## Muscles: tensor tympani (V3), stapedius (VII)
Which part does internal ear include?
- Cochlea (auditory)
- Semicircular canal, utricle, saccule (Vestibular)
What are the three ossicles in the middle ear?
- malleus (hammer)
- Incus (anvil)
- stapes (stirrup)
What is the role of the footplate of the stapes, and why are the ossicles important?
The footplate of the stapes moves the oval window, transmitting vibrations to the cochlea
Ossicles amplify sound force
What structure in the middle ear is moved by sound waves and transmits movement to the ossicles?
Tympanic membrane
What are the three parallel fluid-filled chambers of the cochlea?
Scala vestibuli
Scala media
Scala tympani
What causes the basilar membrane to vibrate?
Sound
What is the function of the Organ of Corti
- contains auditory receptor cells and sits on the basilar membrane
What happens when hair cells in the Organ of Corti bend?
They initiate mechanoelectrical transduction
This activates the cochlear nerve, part of CN VIII
Mechanoelectrical Transduction process step by step ?
- Sound wave hit tympanic membrane –> ossicle to move causing membrane at opening to cochlea to move –> fluid in cochlea to move –> vibration of basilar membrane and its hair cell –> cause hair cell to bend which cause depolarization –> activate cochlea nerve ending
List the brainstem auditory centers involved in the auditory pathway.
- Cochlea
- Superior olive (pons)
- Nucleus of lateral lemniscus and reticular formation
- Inferior colliculi
What cranial nerve carries information from the cochlea to brainstem auditory centers?
CN VIII - the Auditory (Vestibulocochlear) nerve
Where does auditory information go after the brainstem centers and before reaching the primary auditory cortex?
- Medial geniculate body of thalamus
Which structure in the pons is responsible for detecting “interaural time differences” during sound localization?
Medial Superior Olive (MSO)
What structure in the pons processes “interaural intensity differences” for sound localization?
Lateral Superior Olive (LSO)
Which structures are responsible for processing bilateral ear aural cues for sound localization?
Superior olivary complex (MSO and LSO) and nuclei of the lateral lemniscus
What auditory functions are carried out by the inferior colliculus?
processes sound frequencies and integrates cues for localizing sound in space.
What structures make up the vestibular apparatus?
three semicircular canals (anterior, posterior, horizontal), each with a swelling called an ampulla.
What is the role of the crista within the ampulla of each semicircular canal?
- serve as the sensory organ in the ampulla, containing support cells and hair cells that detect head movement.
When are the hair cells in the semicircular canals active?
only during acceleration or deceleration of rotational head movements.
What happens to the hair cells in the semicircular canals when the head moves at a steady rate?
The endolymph catches up with the head movement and the hair cells return to baseline firing.
What structures are found within the macula of the otolithic organs?
supporting cells and hair cells embedded in a gelatinous mass topped with calcium carbonate crystals (otoconia).
What type of movement do the otolithic organs respond to?
linear acceleration/deceleration and head position relative to gravity.
Where are the four vestibular nuclei located?
Bilaterally at the junction of the pons and medulla – the pontomedullary junction.
What are the names of the four vestibular nuclei?
Lateral (Deiter’s)
Medial
Inferior (spinal)
Superior
What systems provide input to the vestibular nuclei?
The cerebellum, visual system, somatosensory system, and contralateral vestibular nuclei.
six central vestibular pathways.
5 start w/ vestibulo….
1 is medial longitudinal fasciculus
What input does the vestibulocerebellum receive and what does it impact?
It receives vestibular input and impacts postural muscle control and eye movements.
structures that connect with the vestibulocerebellum.
vestibular apparatus, vestibular nuclei, inferior olive, and spinal cord
Why is the vestibulocerebellum essential in patients with vestibular disorders?
It is essential for adaptations in the postural and balance systems.
What is the function of the vestibulo-cervical reflex (VCR)?
postural adjustments of the head
What tract is involved in the vestibulo-cervical reflex (VCR)?
The medial vestibulospinal tract to the medial vestibular nucleus.
What is the role of the vestibulo-spinal reflex (VSR)?
postural and tone adjustments of the body.
What are the main tracts involved in the VSR?
- Medial and lateral vestibulospinal tract and reticulospinal tract
which pathways go to CN XI nucleus to affect cervical muscles’ postural
control
Vestibulocolic
What reflex is mediated by the medial longitudinal fasciculus, and what does it do?
- Mediates vestibulo-ocular reflex (VOR)
- adjust eye movement based on change in head position
What is the pathway of vestibulothalamocortical/cerebello-thalamocortical pathways?
Lateral and superior vestibular nuclei –> thalamus –> S1 facial area and posterior parietal cortex
Lesions of R posterior parietal cortex cause ?
altered perceptions of personal and extrapersonal space
First order neurons in the vestibular system are located where?
vestibular ganglion, located in inner ear.
What is the role of the ipsilateral lateral vestibulospinal tract (VST)?
It primarily controls extensor muscles
What does the bilateral medial vestibulospinal tract (VST) primarily affect?
influences neck muscles and head movement.
Visual and vestibular cortices are reciprocally activated/inhibited, True of False?
True
