7. Sensory Processing 1 Flashcards
The retina is the ___ ___ of vision
Sensory organ
What are the 3 main layers of the retina?
Photoreceptor layer, intermediate layer and the ganglion cell layer
What is found in the photoreceptor layer?
Rods and cones
What is found in the intermediate layer?
Bipolar, horizontal and amacrine cells
What is found in the ganglion cell layer?
Retinal ganglion cells: midget & parasol
What do rods and cones respond to?
Light intensity
In the darkness what do rods and cones release?
A neurotransmitter (glutamate)
Light is absorbed by what in rods and cones?
A pigment
Name the pigments in rods and cones
Rhodopsin
Cone opsin
The change in shape in the shape of photopigment triggers what?
A G-protein cascade that reduces glutamate release
What do bipolar cells do?
They transfer information from rods and cones to retinal ganglion cells
The intermediate layer transforms light information into what?
Contrast information
What are the two types of bipolar cells?
On and off
On bipolar cells are ___ by input
Inhibited
Off bipolar cells are ___ by input
Excited
What are the two types of retinal ganglion cells?
Parasol and midget
Describe parasol ganglion cells
Large dendritic trees
Combine inputs from many bipolar cells
Describe the midget ganglion cells
Combine inputs from few bipolar cells
Dendritic trees larger in periphery for both
What is the term which describes how photoreceptors translate light into neural signals for light intensity?
Signal transduction
What type of cells convert signals for light intensity into signals for contrast?
Bipolar and ganglion cells
Define visual receptive fields
The region of sensory space that evokes a response in a neuron
RFs have a ___ and ___
Position and size
What are the two types of sub-region in RFs?
Excitatory and inhibitory
On RFs respond to an ___ in light intensity
Increase
Off RFs respond to a ___ in light intensity
Decrease
Retinal ganglion cells RFs mostly have what type of organisation?
Centre-surround organisation
Photoreceptors respond to what?
Light intensity
Retinal ganglion cells RFs code for what?
- Differences in light and dark over time (flicker)
- Differences in light and dark over space (contrast)
- Differences in colour
What shape are retinal ganglion cell RFs?
Circular
How many layers does the LGN consist of?
Six
The layers in the LGN differ in terms of what things?
The kind of cells they contain
What type of visual input they receive
Which eye they receive input from
What are the two main visual pathways in the LGN?
Magnocellular (M) pathway
Parvovellular (P) pathway
Which layers are the M pathway?
Inner two layers (1 & 2)
Where does the M pathway receive input from?
Parasol ganglion cells
Which layers are the P pathways?
The outer four (3, 4, 5, 6)
Where does the P pathway receive input from?
Midget ganglion cells
Receptive fields in LGN are similar to those of what?
The retinal ganglion cells
What are the 5 functions of the LGN?
- Relay station between eye and brain
- Response properties similar to retinal ganglion cells
- Receives massive feedback from the cortex
- First site of attentional gating/enhancement
- Sleep-related gating of sensory input to cortex
V1 is also known as what?
The Striate cortex
Most LGN neurons project to where?
V1
V1 consists of how many layers?
Six layers
P pathway projects to where in V1?
VCB
The P pathway splits into 2 new pathways in V1, what are they and what do they do?
P-B pathway: colour (blobs)
P-I pathway: orientation (inter blobs)
Describe how M pathway projects into V1
- Project to layer 4C to 4B
- Cells in layer 4B are sensitive to movement
- Some are binocular and disparity/depth sensitive
Most cells in V1 are ____ (respond to stimulation in either eye)
Binocular
Cells in layer 4 that receive input from LGN are ___ (respond to only one eye)
Monocular
Define ocular dominance
Most cells respond better to stimulation from one eye or the other
What are ocular dominance columns?
Cells preferring each are are clustered into ~1mm thick slabs
What are the 5 functions of V1?
- Topographic organisation
- Contains a map of the visual field
- Detailed maps of orientation, colour, spatial scale, motion direction and 3D depth
- Projects to most higher visual areas in cortex
What 4 things does V1 compute?
- Orientation
- Spatial frequency
- Motion
- Colour
- Depth
V1 cells respond best to a limited range of what?
Temporal frequency (flicker rate; how quickly stimuli change over time)
Cells in M pathway respond better to ___ flicker
Fast
Cells in the P pathway respond best to ___ flicker
Slower
Neurons in V1 project to higher visual cortical areas such as:
V2, 3, 3A, 4, 5…
What do the different higher visual cortical areas respond to?
V5: Motion
V4: Shape and colour
V3/3A: Motion boundaries and textures
Area V2 is divided into multiple what?
Stripes
Describe the features of the thick stripes (M pathway) from V2
Sensitive to orientation and movement
Sensitive to disparity
Describe the features of the thin stripes (P pathway) from V2
Sensitive to colour
Not orientation-selective
Describe the features of the inner-stripes (P pathway) of V2
Orientation-selective
Not direction-selective
Describe the 3 features of V4
- The P pathway projects to V4
- Damage to human V4 impairs colour perception
- Involved in shape discrimination
The M pathways projects to which visual areas?
V3/3A and V5
Describe the features of V3/V3A
Selective for orientation
Respond to motion boundaries
Describe the features of V5 (MT)
Selective for motion, direction and speed
Process information on motion and stereoscopic depth
What does the frequency refer to?
The speed of vibrations
Amplitude refers to what?
The size of the vibrations
A sound at a single frequency is a pure tone, what type of wave does a pure tone look like?
A sine wave
The auditory system works by taking apart what into what?
Sounds into their component frequencies and ‘measuring’ the amplitude of each component
Humans can detect sounds between what measurements of Hz?
20-20,000 Hz
How is the anatomy of the ear divided?
Into outer, middle and inner
Auditory sensory neurons are located in which area of the ear?
The inner ear
What are the two main functions of the outer ear?
- Amplifying sounds around 3kHz
- To help determining the direction of a sound (by allowing through more high frequencies from a high than a low sound source)
What is the function of the middle ear?
To amplify sounds so they can pass from air to water
What are the two mechanisms of the middle ear?
The eardrum and the ear bones
Describe the eardrum (tympanic membrane)
Much larger than the oval window, giving a proportional amplification
Describe what the ear bones (ossicles) do?
Act as levers, magnifying the force of vibrations
The inner ear consists of the cochlea and the semicircular canals, describe the features of these
Semicircular canals are part of the vestibular system
The cochlea is a hollow spiral tube
The cochlea contains what organ?
The Organ of Corti - the sensory organ of hearing
The organ of corti runs along the length of what and sits where?
The length of the cochlea
It sits between two liquid-filled tubes of the cochlea
Hair cells are the ___ ___ of hearing
Sensory neurons
What are the two types of hair cells?
Outer hair cells and inner hair cells
IHCs and OHCs form two sets of rows which run along the length of what?
The cochlea
Describe the 3 stages of how hair cells respond to sound
- Sound vibrations cause the basilar membrane to vibrate
- This causes a ‘shearing’ motion of the BM relative to the tectorial membrane
- This causes hair cells that sit between the BM and TM to bend back and forth
Describe the signal transduction by hair cells
- Bending of the ‘hair’ of hair cells pulls filaments connecting sterocilia
- These filaments (tip links) are believed to connect mechanically to ion channels in the hair cells, opening them
- This causes the hair cells to depolarise and fire APs
Hair cells respond ___ ___
Very fast
Allows hair cells to fire synchrony with sound vibrations up to ___ kHz
3
What are the outer hair cells for?
They receive neural input from the auditory nerve
In response to stimulation, outer hair cells can contract and modify stiffness of basilar membrane - allowing fine tuning of sound sensitivity
What is the purpose of cochlear implants?
To directly stimulate the auditory nerve - to mimic the function of hair cells
Axons from the inner hair cells join to form what?
The auditory nerve
The auditory nerve connects the cochlea with the ____ in the brainstem
Olive
What is the olive involved in?
Sound localisation
Auditory information passes through the MGN into the ___ and the ____
Thalamus and the auditory cortex
Describe the two mechanisms that localise sounds
Time difference between the ears
Processed in the medial superior olive
Intensity differences between the ears
Processed in the lateral superior olive
Where is sound information processed?
In the primary auditory cortex which is located in the superior temporal lobe
