Final exam Flashcards
General senses
Somatic, tactile, thermal, pain, proprioceptive (receptors throughout the body)
Special senses
smell, taste, vision, hearing, balance (receptors located in sense organs such as eye, ear, etc)
Which species sense magnetic fields?
Fish, birds, butterflies, and bats to orient and migrate
All contain magnetite in their brains (sensitive to magnetic fields)
Labeled lines hypothesis
Holds that the CNS determines the type of stimulus receiving input from all sensory cells activated by that stimulus
What is transduction?
Changing a physical stimulus (analog signal) into a neural (digital) signal
Pacinian corpuscle
A free nerve ending surrounds by onion-like structure
Stretching the membrane opens stretch-activated ion channels
Vibrations produce graded potentials
Sensitive range
In general, is wider than the response repertoire of a single cell
- Get the entire range by having multiple parallel neurons with different thresholds - then with higher intensity - get more cells recruited
Range fractionation
Coding intensity - in general, the sensitive range is wider than the response repertoire of a single cell
- Solution - multiple parallel neurons with different thresholds. Higher intensity stimulus - more cells will be recruited (range fractionation)
ie low medium high threshold neurons - if all recruited, neural firing rate is very high
Sensory adaptation
detect initial change, but ignore changing events
This limits the amount of (unnecessary) sensory information to process.
Phasic receptor - change the frequency of firing when there is a constant stimulus (fire with change)
Phasic receptors
Change frequency of firing with constant stimulus
Only fire in response to change in the stimulus
Tonic receptors
Continues to fire as long as the stimulus is present
Thalamus role in sensory pathways
Thalamus receives most of the sensory input (except sometimes olfaction)
- Sends it to the cortex (there are specific cortical regions for each sense)
receptive field
the region of the sensory organ to which a particular neuron will respond.
Neurons at each level of the hierarchy have receptive fields. Progressively more complex
What are the two forms of sensory suppression?
- Use of an accessory organ to decrease input (ie. closing eyes)
- Descending pathways - neural inhibition of the receptor’s activity
What two parts of the brain are involved in focusing?
Cingulate cortex
Posterior parietal (association) cortex
Has polymodal cells
damage is called NEGLECT (causes people to have trouble focusing)
usually contralateral neglect *only on one side of the body
Olfactory receptors
6 million total in 2 cm squared area
Each receptor has a long dendrite that extends to the epithelial layer (many fine cilia along the surface)
Fine UNMYELINATED axons - project through the cribiform plate, synapse in the olfactory bulb.
Constantly replaced throughout life
~1000 receptors but only about 400 are functional (others are spares)
GPCR all!
Olfactory Glomerulus
Where the receptor cells synapse with the mitral cell within the OLFACTORY bulb
Perception of olfaction
We only use 400 R’s but can smell 5000 diff odours –PATTERN CODING
Each particular smell activates an array of receptors - get a specific smell when specific array is activated.
What cells do olfactory receptors innervate?
Mitral cells in particular glomeruli in olfactory bulb
Only one type of olfactory receptor neurons inputs to each glomerulus
Which is the only sense which sensory info does not need to go through the thalamus on the way to the cortex?
Olfaction
What is the prepyriform cortex?
Part of the primary olfactory cortex
The cortical brain regions that receive the mitral cell axon projections
COVID affecting smell
Virus binds ACE2 receptors on support (sustentacular cells) - damages epithelium, major loss of cilia
Taste
The perception of the sensory cells in your taste buds
Flavour (what you understand)
Aroma (what you smell) + what you taste = flavour
Where are taste receptors found?
In special cells called taste cells
Taste bud
Onion like structure formed by many taste cells which are formed from many taste cells
Papillae on the tongue
Upper surface of tongue. thousands of taste buds are found in nipple-like structures called papillae
Each papillae has one or more taste buds… Each taste bud has 50-150 cells
Where are taste receptors found?
In our throat and gut and tongue
Taste receptor types
Sweet, salty, sour, bitter, unami
Each receptor responds to a different chemical components of food
What are the 3 different papillae?
- Fungiform (most numerous (one bud/papillae)
- Foliate
- Circumvallate
Each participate in transduction of all tastes
Fungiform Papillae
Most numerous type
One bud/papillae
Found mostly at the tip of the tongue
Foliate papillae
On the side of the tongue
Circumvallate papillae
On the back of the tongue
Salty taste transduction
Binding of Na+ to the Na+ channel causes opening of the Na+ channel and Na+ enters the cell - cell depolarizes - AP
Sour taste transduction
H+ ions from the food block K+ leak channels - cells depolarizes
Sweet taste transduction
Special GPCR’s cause the closure of K+ channels - get depolarization of cell
Bitter taste transduction (lots of Rs)
GPCR - diff then for sweet though. Reduce K+ channel opening - leading to cell depolarization
(30 diff receptor subtypes)
Umami
Type of GLUTAMATE receptor - GPCR - has a high affinity glutamate binding domain
Responds to certain amino acids
MSG - activates these receptors
What are the cranial nerves involved in taste transduction?
Facial nerve, glossopharyngeal, vagus
Taste transduction
Not as simple as labeled lines - pattern coding (more complex than olfaction) instead.
The relative activity of the different incoming signals will determine the end taste.
What must the retina do?
Must convert (transduce) light energy into APs
Must discriminate different wavelengths
Must work over a wide range of light intensities
Must perceive minute details
Optic disc
Where the blood vessels and axons that make up the optic nerve leave the eye
Blind spot - no photoreceptors here
Fovea
Only cones
Better ratio of photoreceptor cells to ganglion cells in the fovea (1:1)
How many different photopigments are there?
Four
Rhodopsin (496 nm) and one for each type of cone
Each best activated at specific wavelengths
Phototransduction
Opsin = GPCR that is bound to a light - absorbing chromatophore.
G-protein= transducin
Light hits - activates transducin - activates PDE -reduce cGMP - results in the CLOSURE of Na+ channels - causes HYPERPOLARIZATION - less glutamate is released
Glutamate released from photoreceptors
An inhibitory NT
INHIBITS on-centre bipolar cells and activates off-centre bipolar cells
Light - less Glu released - bipolar depol
Dark - more Glu released - bipol hyperpol
Ganglion cells
Don’t see shapes
They have very small dots as receptive fields
centre/surround receptive field
One photoreceptor can contribute to many receptive fields
Detection of edges
Get the largest change in response (largest response) at the edge of the on centre ganglion cell))
Visual field to cortex processing
The right cortex sees the left visual field (left side of both eyes) and the left cortex sees the right visual field (right side coming into either eye)
Corpus callosum connections in the occipital lobe?
Almost no connections!
Except for the cells that lie along the midline of the visual field
What are the two types of retinal ganglion cells?
They project from the retina to the brain
M cells (magnocellular) - receive input from rods
P cells (parvocellular) - receive input from cones
These pathways are segregated throughout the visual system
What are the major targets of the retinal ganglion cells?
Superior colliculus (midbrain - coordinates and detect movements)
Lateral geniculate LGN (thalamus; vision)
Suprachiasmatic nucleus SCN (hypothalamus; circadian clock)
Pretectum (pupil and lens reflexes)
Coding retinal location
Ganglion cells project to the brain in an orderly fashion, preserving their spatial arrangement
What are the main routes to the visual brain?
Tectopulvinar system
Geniculostriate system
Retinohypothalamic tract
Striate cortex
Primary visual cortex = V1
Processes simple forms
Also involved in forming mental images - activated during imagining a visual object
Dorsal visual stream
Visual processing pathway from V1 to parietal lobe - HOW
Ventral visual stream
visual processing pathway from V1 to temporal lobe
WHAT - identifies stimulus
What processing structures are within V1?
- Cortical Columns
- Blobs
- Interblobs
the segregation is preserved from V1 to V2
Blobs
Clusters of cells in the V1 that respond to colour
Interblobs
Clusters of cells that respond to form and motion
V1 simple cells
Act as orientation detectors
Fire more when bars of light are presented in a particular orientation
FOUND IN PRIMARY VISUAL CORTEX
V1 complex cells
Maximally excited by bars of light moving in a particular direction (in a particular orientation)
Hypercomplex cells
like complex cells, but have both excitatory and inhibitory portions of the visual field
Area V2
Extrastriate cortex
Responds to many aspects of vision
Higher order integration - will respond to complex relations among parts of the visual field
Response to illusory contours
Which part of the brain responds to illusory contours?
Extrastriate cortex; area V2
V3A
Dorsal stream - receives inputs from V2 and from the primary visual area
Projects to the posterior parietal cortex
Processing of global motion and form
V3B
Ventral stream
Weaker connections from the primary visual area, stronger connections with the inferior temporal cortex
Colour and dynamic form (forms that change)
Inferior temporal cortex
These neurons receive input from the visual cortex (V3B) from the VENTRAL stream
Maximally excited by complex visual stimuli like hands and faces
Fusiform Gyrus forms part of it
Neurons are very specific in their responses - cells arranged with columns respond to slightly different forms of the object
Fusiform gyrus
Faces, facial expressions
When this area is damaged - called prosopagnosia = face blindness - cannot recognize ppls faces
Found within the inferior temporal cortex
Faceblindness
Prosopagnosia
Results when the fusiform gyrus, a part of the inferior temporal cortex, is damaged.
Area V4
Extrastriate cortex part
Responds to colour and complex sinusoidal stimuli
Area V5
Part of the extrastriate cortex
Responds best to dynamic motion
Damage - akinetopsia - motion blindness - picture motion
Akinetopsia
Motion blindness
Damage to V5 (involved in processing of dynamic form)
See moving stimuli as a series of strobe like images - see visual trails moving behind objects
Difference between robust and feeble dichromatic vision
Both have 2 cones but with feeble, there are less cones (cats)
Nocturnal animals
Often have minimal colour vision - they are active in the dark so they dont really need to see colour
What is the most common type of human colour blindness?
Deuteranopia
Red-green colourblindness is the most common (esp in males)
Can’t distinguish between reds and greens.
3 colours combined in the trichromatic theory?
Red, green and blue
Combination of these three can create the entire range of colour visible to humans
Thought that each is a labeled line into the brain (maintained into primary and secondary cortices)
LEVEL OF THE PHOTORECEPTORS
How to see white light in according to the trichromatic theory?
Full 100% activation of each type of cone
Deep red?
Only 5% activation of long cones
NO activation of the short or medium cones
Opponent process theory
Proposed by Hering that colours are perceived in a balance of 3 pairs
Red/Green, Blue/yellow, and black/white (brightness)
LEVEL OF THE GANGLION CELLS
some of the cells are excited by one of the opponent colours and inhibited by the other
Centre -surround arrangement.
Which part of the extrastriate cortex processes colour?
V4 - Cells in V4 deal with perceived colour
One function: COLOUR CONSTANCY. Objects maintain their colour relative to one another despite change in lighting intensity.
Brain might perceive a certain colour by unconsciously assuming that the object is in a particular type of light.
