Section 3b Notes Flashcards
1
Q
Give the function of the vestibular system for sensorimotor contribution
A
- Vestibular apparatuses on both sides of the head work together to signal head movement or orientation which allows for a greater signal to noise ratio and increases sensitivity to motion
- it detects head acceleration to help determine head position/motion and body orientation
2
Q
Give the function of otoliths in general
- then give the function of 2 different types that exist in the ear
A
- otoliths: sense linear head acceleration and changes in head orientation relative to gravity
- saccule: detects acceleration in the vertical plane
- utricle detects acceleration in horizontal plane; head tilt
3
Q
Give the function of semicircular canals
A
- sense angular head acceleration from turning and tilting of the head and/or rotary body movements
4
Q
Define: roll, yaw, and pitch
A
- roll: rotation around the x axis
- yaw: rotation around the z axis
- pitch: rotation around the y axis
5
Q
Define: stereocilia
A
hair cells
6
Q
Describe how otoliths convert linear head motion into electrical signals
A
- individual stereocillia are connected by “tip links” so the appendages may open/close multiple spring-gated ion channels together
- positive mechanical deformation (hair cells bend toward the kinocilum) opens the K+ channels in the stereocilia
- negative mechanical deformation closes channels
- there is a small amount of discharge of K+ ions when the hairs are in the middle position. this comes from otoliths and semicircular canals and is because the tip links slightly open the ion channels.
7
Q
Define: kinocilium
A
tallest hair cell appendage
8
Q
Depolarization and hyperpolarization of the ear mean what?
A
depolarization: hair cells bend toward the kinocilium and open channels. increase impulse frequency leading to excitation
hyperpolarization: hair cells bend away from the kinocilium and close channels. decrease impulse frequency and results in inhibition
9
Q
Describe how the semicircular canals convert head motion into electrical signals
A
- canals are filled with endolymph (viscous fluid that is rich in K+)
- when the head rotates, the endolymph will wash over the cupula (gelatinous structure in the canal) and displace it
- the cupula has hair cells embedded in it which also are displaced. sensory fibres connected to the hair bundles sense this change and fire
10
Q
Describe what happens when the head rotates to the left
A
- relative to the head, endolymph pushes cilia toward kinocilia on the left side which increases firing of afferent fibres on that side
- endolymph pushes cilia away from kinocilia on the right side which decreases firing of afferent fibres on that side
- when thinking for an external frame of reference, endolymph stays still and the head, cupula, and hair cells are what’s moving
11
Q
Describe how otoliths convert linear head acceleration information into electrical signals
A
- linear head motion or change in head orientation relative to gravity (e.g. head pitch downward) causes the otolithic membrane to move
- otolithic membrane lags behind head motion
- hair cells will deflect as the membrane slides forward or back following the movement of the head
12
Q
List the functions of the vestibular system
A
- postural stabilization (maintenance of balance; Vestibular afferents project to vestibular nuclei in brainstem, which
gives rise to descending tracts that activate muscles) (keeps head upright) - gaze stabilization via the vestibular-ocular reflex (When head moves, the eyes rotate in orbit to maintain gaze fixation on target
of interest) - perception of self motion (head motion can tell your CNS about your motion)
- role in spatial navigation (orientation)
13
Q
Define; Galvanic vestibular stimulation (GVS)
A
- Weak direct current is applied through electrodes placed over the mastoid bones behind the ears. It is similar to tDCS
- GVS activates the vestibular afferents of the otoliths and semicircular canals causing illusory perception of head (and body) tilt and compensatory tilt in the opposite direction
- GVS causes the illusory perception of sway toward the cathode and there is resulting compensatory sway toward the anode.
- example: subject stands upright; anode on right side and cathode on left, vestibular afferent firing increases with cathodal stimulation and decreases with anodal stimulation, you will sway to the right side as a compensatory action
- when you stand with your feet apart, this reduces sway greatly
14
Q
When a physician looks into your eye with a ophthalmoscope, what do they see?
A
the fundus
15
Q
Fill in the blank: Eye is designed to focus the _______ on the retina with minimal __________
A
- visual image
- optical distortion
16
Q
Fill in the blank: light rays must converge at the _____ for light to be in focus. When it hits this part of the eye, the visual image is _____
A
- retina
- inverted
17
Q
Where is light refracted in the eye?
A
- 2/3 of refraction occurs when light passes through cornea
- 1/3 occurs at lens
18
Q
What is the term for when the lens changes shape to alter the distance at which objects will be in focus?
A
accommodation
19
Q
How does the eye lens change shape?
A
contraction and relaxation of the ciliary muscles
20
Q
Photoreceptors
- function
- location
A
- function: rods and cones that transduce light into electrical signals
- location: retina
21
Q
fovea
- function
- location
- contains?
A
- allows vision of fine details
- part of the retina
- contains only cones
22
Q
Retina ganglion cells
- function
- location
A
- form the optic nerve and propagate the signal to visual areas of the brain
- retina
23
Q
pigment epithelium - function - contains - location -
A
- prevents light from being reflected off the back of the eye which would degrade the visual image
- melanin (black pigment)
- back of the eye, behind the retina
24
Q
Define:
- visual field
- central vision
- peripheral vision
A
visual field
- the region of space the eye sees; shifts with eye movements
central vision
- deals with identifying details; makes up the central ~5deg of visual field; predominantly contains cones
peripheral vision
- deals with where things are; provides information regarding environmental context and moving limbs; contains mostly rods and sparse cones
25
Fill in the blank: the retinal ganglion cells that originate in the _______ cross at the ________
- nasal hemiretina
| - optic chiasm
26
Where do ganglion cells synapse at?
lateral geniculate nucleus (LGN)
27
Fill in the blank: the left visual field is processed in the ____ hemisphere and the right visual field is processed in the ____ hemisphere
- right
| - left
28
Describe the visual field deficit from a lesion at: optic nerve
- total loss of vision in one eye (eye on same side)
29
Describe the visual field deficit from a lesion at: optic chiasm
bitemporal hemianopsia: loss of vision in the temporal half of each visual hemifield
30
Describe the visual field deficit from a lesion at: optic tract
contralateral hemianopsia: loss of vision in the opposite half of the visual hemifield (example if lesion is on the right side of the head, left vertical side of visual field for both eyes will be missing)
31
Describe the visual field deficit from a lesion between the optic tract and visual cortex
contralateral superior quadrantanopia
32
Describe the visual field deficit from a lesion before the superior visual cortex
contralateral inferior quadrantanopia
33
Describe the visual field deficit from a lesion before the inferior visual cortex
contralateral superior quadrantanopia
34
Define: binocular disparity
difference in image location of an object seen by the left and right eyes, resulting from the eyes' horizontal separation
35
Define: parallax
a displacement or difference in the apparent position of an object viewed along two different lines of sight (reason for binocular disparity)
36
What facilitates depth perception?
difference in image location of an object as viewed by the left and right eyes
37
Fill in the blank: Binocular retinal disparity can be used to process __________-
object motion
- If object moves (e.g., from A to B) and the eyes remained fixed,
the image actives the retina continuously more laterally
38
What is happening when an object in the visual field appears doubled?
the image is falling on mismatched places on the retina
39
What is the other name for the primary visual cortex (aka V1). Give the context behind this other name
- visual striate cortex (also Brodmann area 17)
- striate = striped
- this area has a prominent layer 4 that gives rise t a striped appearance in V1 cross sections
40
Describe the structure of the primary visual cortex
- 2mm thick with 6 layers
| - neurons carrying visual input from LGN enter layer 4
41
Retinotopic representation
Light (images) from specific areas of visual field hit a specific part of retina; each specific part of retina is mapped onto the visual cortex. So, like the somatotopically organized somatosensory cortex (Section 3a.4.8), adjacent points in sensory space are represented at adjacent points in the brain.
42
Describe the receptive field of the retinal ganglion and lateral geniculate nucleus
each neuron responds to only a tiny spot of light (think of this as a tiny region of the visual field)
43
Describe the receptive field of simple cells in the primary visual cortex (V1)
- elongated receptive fields
- senses lines and edges of a particular orientation
- respond to bars of lights and borders between light and dark (thus they can detect an edge of an object)
44
Describe the receptive field of complex cells in the primary visual cortex (V1)
- larger receptive fields
- Sense lines/edges of a particular orientation anywhere within the receptive field
- Many also are sensitive to moving lines/edges
- Respond to moving bars of light
45
Describe how the receptive fields change as you move from LGN to visual cortex (from layer 4c to simple to complex cells)
- receptive fields get bigger as you move from LGN to visual cortex (layer 4c to simple to complex cells)
- At each step in the hierarchy, when receptive fields get more complex, a receptive field
is the sum of multiple, smaller receptive fields from “upstream” neurons (those that synapse onto the “downstream” neuron).
46
Define: extrastriate visual cortex
all cortical visual areas outside of the primary visual cortex
47
Describe the middle temporal (MT) region (also known as V5)
- Neurons have large receptive fields
- Neurons have preference for a certain direction of motion
- Neuronal activity is sensitive to (i.e., discharge is based on) speed of motion
- Projects to MST region
48
Describe the medial superior temporal (MST) region
- Divided into two sub-regions that process object-motion or self-motion
- Neurons have large receptive fields (larger than MT)
49
Define: optic flow
the continuous change over time of the spatial pattern of light (variations in intensity and wavelength composition) reaching a point as it moves through its surroundings
50
Define: whole field motion
```
Motion of an image sweeping across the eye when an eye rotates in its socket with the
head stationary (from the image moving relative to the retina)
```
51
Define: image flow
optic flow caused by eye moving through the environment as a person moves and the eye turning in its socket which is comprised of translational flow and rotational flow
52
Define: translational flow
• Motion due to movement of eye through environment
53
Define: rotational flow
• Motion due to the eye turning within the environment
54
Define: radial outflow
The lines appear to originate from the centre. This is what
| your eyes see as you walk forward with gaze straight ahead
55
Two factors are important for generating optic flow
1. speed and direction of the eye's movement through the surrounding
2. distances from the eye to the points in the surrounds that hit the retina. images of closer objects flow across the eye faster when the eye moves through space
56
What are some things optic flow provides information on (5)?
- stability and balance
- velocity and direction of movement
- movement of objects in the environment
- time to contact object
57
What are 3 ways to calculate TTC
- optic flow (calculate ratio of the object's image size to the rate of its radial expansion on the retina; a variable called tau)
- bioncular retinal disparity
- oculomotor vergence feedback (feedback from muscle spindles in the eyes as the eyes rotate inward or outward to track an object)
58
Describe the vision for perception system
- the ventral stream is the primary visual cortex to the temporal lobe pathway
- Responsible for fine analysis of the visual scene (form, colour) and object recognition
– Uses object-centered frame of reference
• E.g., The laptop is X distance to the coffee mug
- aka the "what stream ("what is that?")
59
Describe the vision for action system
- dorsal stream is the primary visual cortex to the posterior parietal cortex and beyond
– Guiding movement and spatial characteristics of the environment
– Uses various egocentric frames of reference (e.g., retinotopic, head-centered, limb-
centered, gaze-centered); i.e., body-based frame of reference
• E.g., The laptop is X distance to your hand
– A.k.a., the ‘how’ or ‘where’ stream (i.e., “where is it” and “how do I interact with it”)
60
When given a task discrimination task and an object manipulation task to someone with damage to the dorsal stream vs damage to the ventral stream, what will be the difference?
dorsal stream damage: improper grip of object but ability to discriminate object shape
ventral stream damage: inability to discriminate between shapes but proper grasping of object
61
Describe some examples where vision plays an essential role in guiding locomotion
- implementing avoidance strategies
- accommodating different terrain
- navigation and determining direction of walking
- planning and controlling precise foot placement
