Sensory Systems Flashcards
1
Q
Sensory information
A
Neural activity originating from stimulation of receptor cells in specific parts of the body
2
Q
Vision
A
- Electromagnetic energy emitted in the form of waves
- Input to the retina is light (=stimuli)
- Vision is very limited
- The eye has been perfected by evolution to transform light into action potential.
- Human visual field: 400-750nm
3
Q
Anatomy of the eye
A
- Pupil: opening where light enters the eye – contains light-absorbing pigments
- Iris: gives colour to eyes
- Sclera: white of the eye
- Cornea: glassy transparent external surface of the eye - plays an important role in aiding light to reach us in a very specific way
- Optic nerve: bundle of axons from the retina
4
Q
Structure of the eye
A
5
Q
Image formation
A
- The eye collects the light rays emitted by or reflected off objects in the environment and focuses them onto the retina to form images.
- Refraction by the cornea: As the light enters our eyes after being reflected off other objects, it is refracted by the cornea first which refracts it onto the lens which also refracts it and focuses it onto the retina.
- Accommodation by the lens: The lens is involved in the forming crisp images of objects located closer than ~ 9 m. The muscles will contract or relax in a process called accommodation.
- At a near point, the muscles will need to contract more, which is why older people often need glasses. Their muscles is not as strong anymore
6
Q
Focus
A
Refractive powers of the cornea and the lens
7
Q
Accommodation
A
Changing the shape of the lens
8
Q
Pupillary light reflex
A
- Pupil adjust for different ambient light levels.
- This reflex involves connections between the retina and neurons in the brain stem that control the muscles that constrict the pupils
- Pupils are reflexive i.e. if one eye contracts, so should the other. Otherwise it’s indicator of a lesion.
9
Q
Visual field
A
- Amount of space viewed by the retina when the eye is fixated straight ahead
- Roughly 150 degrees wide
- Image is inverted
- Left visual field is imaged on the right side of the retina
- Right visual field is imaged on the left side of the retina
- Upper visual field is imaged on the bottom of the retina
- Lower visual field is imaged on the upper retina
10
Q
Visual acuity
A
- Ability to distinguish two nearby points - if points are too close by, they stop looking like multiple points, and merge
11
Q
Visual angle
A
Distances across the retina described in degrees
12
Q
Retinal disparity
A
A binocular cue for perceiving depth. By comparing images from the retinas in the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.
13
Q
Blind spot
A
- Toward the nose is the “optic disk”, the place where all nerve fibers leave the eye, forming the optic nerve – no photoreceptors, consequently creating the “blind spot” in the visual field.
- “filling in” – fills in a background pattern, or it fills in an object passing through the blind spot. The visual system uses information from cells around the blind spot for “completion,”
14
Q
Fovea
A
- High acuity area at center of retina
- Thinning of the ganglion cell layer reduces distortion due to cells between the pupil and the retina
15
Q
Retina
A
- Cellular structure includes:
- Retinal ganglion cells
- Amacrine cells
- Bipolar cells
- Horizontal cells
- Photoreceptor: rods and cones
- Transduction: transforming light information into chemical information
- Ganglial cells fire action potential
16
Q
Photoreceptors
A
- Converts electromagnetic radiation to neural signals
- Types of photoreceptors: rods and cones
- Structure:
- Outer segment
- Inner segment (Cell body)
- Synaptic terminal
- Not equally distributed across the retina:
- The fovea has lots of cones
- But the periphery has more rods
- Rods and cones synapse differently to other cells:
- Cones enable high acuity and low senstivity because they synapse 1:1 to bipolar cells which then synapse 1:1 to ganglion cells → Information goes directly to your brain
- Rods enable increasing sensitivity while decreasing acuity because the circuit converges to one ganglion cell.
17
Q
Colour perception
A
- Lights of the same intensity but different wavelengths may not all look as bright
- A spectral sensitivity curve shows the relationship between wavelength and brightness
- There are different spectral sensitivity curves for cones (white lines) and rods (black line)
- Rods don’t give us colour vision, only cones.
- Humans have 3 photopigments: red, green, blue
18
Q
Duplexity theory of vision
A
- Cones and rod mediate different kinds of vision
- Cones
- Photopic (daytime) vision
- Mainly located at the fovea
- Colour vision (3 photopigments)
- High-acuity: 1 cone : 1 ganglion cell (fovea)
- Function: High-acuity (3D) colour information in good lighting
- Rods
- Scotopic (night-time) vision
- Mainly located in the periphery
- Noncolour vision (one photopigment)
- Low-acuity (many rods: 1 ganglion cell)
- Function: low-acuity vision in dim light, movement perception
20
Q
Types of retinal ganglion cells
A
- Differ in appearance, connectivity, and electrophysiological response properties
- M-type (magno) ganglion cells - big: input primarily from rods → good to detect motion
- P-type (parvo) ganglion cells - small: input primarily from cones → good to detect colour vision
21
Q
Retinofugal projection
A
- Optic Nerve
- Optic Chiasm
- Optic Tract
- Most visual information goes to a nuclei in the thalamus lateral geniculate nuclei (LGN.)
- Goes to the primary visual cortex.
- Nonthalamic targets of the
- Optic Tract:
- Hypothalamus: Biological rhythms, including sleep and wakefulness
- Superior colliculus: Orients the eyes in response to new stimuli. Fofiate: move our eyes to the point of interest.
22
Q
Right and left visual hemifields
A
- Left hemifield projects to the right side of the brain
- Nasal retina - close to the nose
- Temporal retina - peripheral to the nose
- These two parts of the retina map slightly differently:
- Information coming from nasal retina crosses at the optic chiasm
- Information from the temporal retina does not cross at the chiasm
- This means lesions at different parts of the chiasm affect vision differently:
- Optic nerve → lose part of the peripheral information on the same eye
- Optic tract → lose information at the contralateral level
- Optic chiasm → lose the periphery
- These two parts of the retina map slightly differently:
30
Q
Extrastriate cortex
A
- Functional Areas of Secondary and Association Visual Cortex (more complex)
- Neurons in each area respond to different visual cues, such as color, movement, or shape
- Lesions of each area results in specific deficits
- Anatomically distinct (about 12 functionally distinct areas identified so far)
- Retinotopically organized
32
Q
Dorsal stream
A
- Criticial area: MT (temporal lobe)
- Most cells: direction-selective; respond more to the motion of objects than their shape
- Arranged into direction-of-motion columns
- Akinetopsia = motion blindness (vision in snapshots)
- associated with damage to the middle temporal (MT) area of the cortex
- deficiency in the ability to see movement
- progress in a normal smooth fashion
- Can also be induced by a high dose of certain antidepressants
36
Q
Auditory pathway stages
A
- Sound waves
- Tympanic membrane (eardrum)
- Ossicles
- Oval window
- Cochlear fluid
- Sensory neuron response
- Primary Auditory Cortex - As it goes into the brain, information from both ears is combined into the brain as one, unlike vision where it’s processed separately
37
Q
Structure of the auditory system
A
- Outer ear – vibration of air molecules
- Pinna: pinna is the only visible part of the ear (the auricle) with its special helical shape. It is the first part of the ear that reacts with sound. The function of the pinna is to act as a kind of funnel which assists in directing the sound further into the ear. Can be moved.
- Goes through auditory canal
- Middle ear – vibration of moveable bones
- Goes to the tympanic membrane which vibrates through the ossicles (small bones)
- Ossicles will vibrate the oval window at the entrance of the inner ear where we have the cochlea
- Inner ear – waves in a fluid
38
Q
Middle ear
A
- Vibration of movable bones
- Sound Force Modification by the Ossicles → 3 bones called the malleus, incus and stapes
- Amplification = greater pressure at oval window than tympanic membrane,
moves fluids
- Attenuation = onset of loud sound causes muscle contraction ⇒ prevents movements of ossicles
- Function: Adapt ear to loud sounds, understand speech better
39
Q
Inner ear
A
- Waves in a fluid
- Cochlea – spiral shape (“snail”)
- Fluid-filled, coiled tunnel that contains the receptors for hearing
- Stapes presses at oval window and pushes liquid around scala vestibuli
- Then round window membrane bulges out ⇒ Hair Cells (Receptors) in the Basilar Membrane respond to sound
- In the middle of scala media chamber, there is the basilar membrane - narrow and stiff base, wide and floppy apex → important to encoding frequency
- High frequencies only excites the initial part of the basilar membrane whereas lower ones will go to the end of the basilar membrane
