Lecture 14 - Special Sensory Systems Flashcards
Describe how an image is formed on the retina.
Inverted and reversed
Describe the visual representation on the retina.
Temporal visual field is projected on to the nasal retinal area.
Nasal visual field is projected on to the temporal retinal area.
Define what it means by visual field.
It is the total amount of space that can be viewed by the retina when the eye is fixated straight ahead
T/F: When testing for visual field deficits you always test both eyes at the same time.
False (one eye at a time)
What are the 3 components of the retina.
- Photoreceptors
- Fovea
- Optic Disc
What are the 2 types of photoreceptors found on the retina?
- Cons
2. Rods
What is the significance of the fovea?
The place where the receptors are in the highest density and are very sensitive - also means that if the image falls on fovea it will be the sharpest.
What is the significance of the optic disc?
A part of the retina where there are no receptors - it’s a natural blind spot on retina.
Trace the path of light coming into the eye starting at the photoreceptors and ending at the optic nerve.
Light -> photoreceptors -> bipolar neurons -> ganglion cells -> optic nerve cells
What type of cells form the optic nerve?
ganglion cells
At what structure do the two optic nerves unite? Where on the midbrain is this?
optic chiasm
anterior midbrain
T/F: All the fibers of the optic nerve cross.
False
The fibers from the ______ half of each retina cross midline and enter optic tract of ____ side.
median (nasal);
opposite
The fibers from the _______ half of each retina pass posteriorly in optic tract of ____ side.
lateral (temporal);
same
The optic ____ wraps around the midbrain.
Tract
Where do fibers of the optic tract terminate.
lateral geniculate nucleus of the thalamus
How does visual info get from the thalamus to the primary visual cortex in the occipital lobe?
Axons project posteriorly from the thalamus in the form of optic radiations to the primary visual cortex.
Which 2 arteries supply the optic radiation.
deep branches of middle cerebral artery and posterior cerebral artery
How many times does the visual information cross?
1 - at the optic chiasm
The primary visual cortex is located on the border of which fissure?
superior and inferior borders of the calcarine fissure
How does visual info processing occur at the primary visual cortex?
First part of the processing occurs posteriorly in the cortex and the info moves anteriorly for additional processing
Interpretation of visual signals occurs where?
Visual association cortex
Differentiate between the WHERE and the WHAT pathway.
Where pathway: finds where the object is within the visual field
What pathway: analyzes what the visual image actually is
Name the two additional pathways taken by visual information.
Some pathways bypass the lateral geniculate nucleus and project onto:
- Superior colliculus
- Pretectal nucleus
What is the role of the superior colliculus in relation to vision?
Uses the tectospinal tract to coordinate head and eye movements
What does the pretectal nucleus do in terms of vision? Outline the pathway it uses.
Responsible for the pupilary light reflex.
Pretectal neucleus in midbrain -> parasympathetic neurons in occulomotor N nucleus -> parasympathetic fibers in occulomotor N -> for pupil constriction
T/F: The left visual field is processed by the left hemisphere.
False (right hemisphere)
How would vision be affected if the left optic nerve is severed?
total loss of vision from left eye
How would vision be affected if there was partial damage to the left optic nerve?
information from nasal visual field of left eye (temporal part of left retina) is lost
What kind of damage would lead to loss of the temporal portions of the visual field? What is this called?
Severing of crossing fibers of the nasal part of the retina (at the optic chiasm)
Bitemporal hemianopia
A lesion in left optic tract OR pathway from lateral geniculate nucleus to cortex OR optic radiation would result in what kind of vision loss? What is this called?
loss of vision of the right side from both eyes
Contralateral homonymous hemianopia
List the 5 types of eye movements.
- Saccadic eye movements
- Smooth pursuit eye movements
- Nystagmus
- Vergence eye movements
- Reflex eye movements
Describe saccadic eye movements.
- rapid, ballistic movements of both eyes in the same direction
- made spontaneously in response to a suddenly appearing (or jumping) object
- produced while we scan a visual scene or read
T/F: Saccadic eye movements are always voluntary.
False (can be involuntary too)
Describe smooth pursuit eye movements.
slower eye movements to track or follow a moving object
•occur automatically in presence of moving target
Describe nystagmus eye movements.
Involuntary eye movement characterized by alternating smooth pursuit in one direction and saccadic movement in the other direction.
You would test ________ eye movements all the time, especially in people with cerebellar deficits.
nystagmus
Describe vergence eye movements.
To maintain foveation/fixation by both eyes as targets move toward or away from viewer
Describe reflex eye movements.
- Stabilize the eyes relative to the external world
* Compensate for head movements
The ____ -_____ reflex allows for reflex eye movements.
vestibulo-ocular
What are the two ocular muscles allowing for horizontal control of the eye?
medial and lateral rectus muscles
How does the medial longitudinal fasciculus allow for horizontal eye movement?
It coordinates the actions of the two cranial nerves that are responsible for the medial and lateral rectus muscles. It also forms a connection between the cranial nerve nuclei of eye muscles and superior vestibular nuclei.
What is the function of the paramedian pontine reticular formation?
It provides input from the cortex and other pathways to the abducens nucleus. Especially important for lateral horizontal gaze.
What is the term for a lesion at the medial longitudinal fasciculus?
Internuclear Ophthalmoplegia (INO)
** Brain Break**
What did the policeman say to his belly button?
“You’re under a vest!”
An INO interrupts input to the ____ rectus. The eye that is ______ to the lesion will not ____ fully when trying to look to the side.
medial
ipsilateral
adduct
T/F: There are descending pathways from cerebral cortex travel to brainstem neuclei to control eye movements
True
What are the 3 cortical areas controlling eye movements?
frontal eye fields
parieto-occipito-temporal cortex
primary visual cortex and visual association cortex
The external auditory ear canal is called ______.
The ear drum is called ______.
meatus
tympanic membrane
The 3 bones in the ear are called ______, ______, and _____ and are located in the ________ ear.
malleus, incus, stapes
middle
What moves the fluid in the chamber of the cochlea?
The stapes vibrating against the oval window of the cochlea.
T/F: The cochlea is located in the middle ear.
False (inner ear - labyrinth)
List the 2 regions (and their functions) of the labyrinth.
- vestibular apparatus - equilibrium
2. cochlea - hearing
The receptors for sound are hair cells, which are a form of ______receptor. The hair cells are in the ______ membrane in the _____ compartment of the cochlear duct.
mechano
basilar
middle
What causes depolarization of the hair cells? Which nerve transmits this information?
bending of hair cells;
cochlear division of Vestibulocochlear cranial nerve
T/F: Hair cells are deferentially sensitive to different frequencies.
True
High frequency sounds are detected by hair cells near the ____ ____ while low frequency sounds are detected by hair cells farther down the length of the ____ duct.
oval window;
cochlear
Trace the path that the auditory information takes starting with the depolarization of hair cells and ending at the primary auditory cortex.
depolarization of hair cells -> CN 8 (Vestibulocochlear nerve - cochlear division) -> cochlear nuclei in rostral medulla -> ascend bilaterally through lateral leminiscus -> inferior colliculi ->inferior brachium ->medial geniculate nuclei of thalamus -> primary auditory cortex.
T/F: Auditory info ascends unilaterally from brainstem.
False (bilaterally)
List the 3 main functions of the vestibular system.
- regulation of posture and muscle tone
- coordination of eye and head movements
- conscious perception of spatial orientation
The vestibular system is part of the _____ ear.
inner
What are the names of the two static labyrinth/otolith organs?
utricle and saccule
What are the roles of the utricle and saccule?
- detect linear acceleration
2. head orientation in relation of gravity
The specialized epithelial lining located within both saccule and utricle is called the _______.
macula
What are the 3 components of the macula?
- calcified crystals – Otoconia
- gelatinous layer
- hair cells
How do the hair cells in the macula get activated?
Changes in head position pull on the otoconia which in turn activates the hair cells.
Once depolarization of the hair cells occur in the static labyrinth, it sends the info via CN 8 to the _____ nuclei. about _______ acceleration.
Vestibular;
linear
What is Scarpa’s ganglia?
A collection of the cell bodies of the primary sensory neurons; located in the vestibular ganglia.
Static labyrinth conveys info about _____ acceleration while kinetic labyrinth conveys info about ______ acceleration.
linear;
angular
The kinetic labyrinth is composed of the semicircular canals which are ____ labyrinths in the _____ bone containing _______ fluid.
bony;
temporal;
perilymph
The ________ labyrinth is in the bony labyrinth and contain ____ fluid.
membranous;
endolymph
Define and ampulla.
The swelling on one end of each semicircular canal.
What structure, which contains hair cells is found in the ampulla?
cupula
What process lets you know that you’re moving your head?
Endolymph moves with head movement and as it flows it bends and excites the hair cells. (HINT: think seaweed)
Describe how the information pathway between the static and kinetic labyrinths are similar.
For both kinetic and static:
- primary sensory neurons are excited (cell bodies in Scarpa’s ganglia)
- info travels from the semicircular canals -> CN 8 -> vestibular nuclei
List and describe the two tracts found in the vestibular nuclei.
Lateral vestibulospinal tract: •descends through length of spinal cord •facilitates activity of extensor muscles to maintain balance Medial vestibulospinal tract: •descends to cervical spinal cord •for controlling neck and head position
The ascending pathways from vestibular nuclei travel to what 3 areas of the brain?
- thalamus
- primary vestibular cortex
- posterior insula
Why are connections (via some neurons in Scarpa’s ganglia) with the cerebellum important?
They regulate balance and eye movement
Benign paroxysmal positional vertigo, the most common cause of vertigo, is caused by ______ in the semicircular canals, almost always in _____ canal
loose debris (mainly otoconia); posterior
What are some symptoms and causes of benign paroxysmal positional vertigo.
Symptoms: room spinning (NOT head spinning)
Causes: sudden deceleration of the head (whiplash, sports collision, fall)
