PSL300 Term Test 3

what are the 5 special senses?

vision, hearing, equillibrium, taste and smell

what are the 4 somatic senses?

touch, temperature, proprioception and nociception

receptors are

cells which convert stimuli into electrical signals (transduction)

what is a neuron?

vision sensory cell

every sensory system begins with

receptors

receptor potential

a receptor cell converts stimulus energy into a graded change in membrane potential

every type of receptor cell has an

adequate stimulus

adequate stimulus

the form of energy to which a receptor is most responsive (ex thermoreceptors are sensitive to temp)

receptors are classified according to their

adequate stimulus

chemoreceptors

respond to specific molecules/ions

mechanoreceptors

respond to mechanical energy such as pressure, vibration, gravity, sound

thermoreceptors

respond to temperature

photoreceptors

responds to light

receptor threshold

the weakest stimulus that will cause a response in a receptor

perceptual threshold

the weakest stimulus that will cause a conscious perception in the organism

sensory systems involve a series of

neurons

primary sensory neurons synapse onto

secondary sensory neurons

convergence allows

secondary and higher neurons to combine data from multiple receptors

sensory neurons carry info about many aspects of the stimulus, one aspect is

modality (what is the mode/source: light, sound, touch)

groups of neurons can represent intensity in __ ways which are

1. population coding of intensity: # of active neurons
2. frequency coding: stronger stimuli may make individual neurons to fire at a faster rate

both mechanisms can work together

receptors are neurons have

dynamics (changes in stimuli, not in steady levels)

different cells have different dynamics, the 3 types of cells are:

1. phasic cells
2. tonic cells
3. phasic-tonic cells

phasic cells are

cells which respond to a stimulus for a brief moment/change and then stop (FADE AWAY)

tonic cells

are cells that maintain their activity when the stimulus is not changing (at present level)

phasic-tonic cells

are cells that react to change but don't stop/ go to 0 firing when the stimulus is constant. They also carry info about the steady level

many retinal cells are

phasic

example: waving your arm to get a friend's attention will activate the phasic cells in their retina

______ cells make communication more efficient

phasic

since our world is fairly stable, it is more efficient to report changes that occur when there is change between time, this change is called __________

temporal change (change through time)
ex. the weather stations

it is also efficient to report ________ changes, which are:

spatial changes - differences between neighbouring regions in space
ex. darker triangle vs lighter triangle in a square

spatial changes are also known as _________

contrast

locations where there is a strong contrast between two spaces are called _______

edges

sensory systems accentuate edges (make them noticeable) by:

lateral inhibition: cells can inhibit their neighbours or they can inhibit the cells their neighbours excite
ex (an object poking the skin would have an edge between contact and no contact)

away from the edge, __________ and _________ cancel out

excitation and inhibition

most sensory pathways run via the ________ to the _______

thalamus -> cortex

one pathway that does not send signals from the thalamus to the cortex is the:

olfactory (smell) pathway - goes straight from nose -> cortex

equillbrium (balance) pathways project mainly to the _________

cerebellum

sensory processing is ___________

inference (educational guessing) - unconscious and fast

since the brain has to guess, it can be fooled. the brain also ______ coincidences

mistrusts

the eye is divided into __ chambers by the ___ . These chambers are the:

- 2, lens
- anterior chamber, vitreous chamber

the anterior chamber:

is filled with aqueous humor (plasma like fluid)

the vitreous chamber is:

filled with clear jelly that maintains they eyeballs shape

the ______ is a transparent buldge, the outer wall of the eye

cornea

the ____ is a transparent disk that focuses light

lens

the _____ and ____ focus light on the _____, the inner lining of the eye which contains photoreceptors

- cornea
- lens
- retina

light passes from the ____ to the lens through a hole in the ___ called the ____

- cornea
- iris
- pupil

the pupil can change ___

size

in bright light, the pupil _____ to ____ the amount of light reaching the ____

- constricts/shrinks
- reduce
- lens

in the dark, the pupils ____ to _____ the amount of light that reaches the ___

- dilates/expands
- increase
- lens

the pupil is controlled by _____ muscles in the ____

- smooth
- iris

in bright light, _________ signals from the brain contract the ____ _______ muscle, shrinking the pupil

- parasympathetic (long=light)
- pupillary constrictor

in the dark, ___________ signals contract the _____ ______ muscle, _____ the pupil

- sympathetic
- radial pupillary
- dilating

the _____ helps to focus light and control _________________

- pupil
- depth of field (what you can see around you and how much of it)

when the pupil is dilated, we have a ____ depth of field. this means only objects ___ one specific distance are in ____

- shallow
- near
- focus

when the pupil is tightly constricted, we have ____ depth of field, which means everything we see is ____ in _____

- full
- equally
- focus

the problem with using the pupil alone to focus light is that:

- the retinal image is dull
- enlarging the pupil makes the image brighter and blurrier (B&B)

in order to get a retinal image that is both ____ and _____, we rely on ________

- bright
- focus
- refraction

the bending of light is known as:

refraction

light ____ when it enters a medium with a ______ refractive index

- bends
- different

our corneas are made of _______. they bend strongly because there is a big difference between the ____ _____ of air and collagen

- collagen
- refractive index

the cornea is responsible for _____ of the eye's refraction. while the lens accounts for ____

- cornea = 2/3
- lens = 1/3

the lens of the eye is ____. These lenses are flatter in the middle and thinner at the edges. (ex: magnifying glass)

- convex

refraction depends on the:

angle of incidence

a ____ lens bends light more, and so it has a closer _____ _____

- rounder
- focal point

for clear vision, the ____ ____ must fall on the ___

- focal point
- retina

if the objects draws closer, but the lens stays flat, focus falls ___ the ____

- behind
- retina

to bring a closer object into focus, we make the lens ______. This process is called ______ and is an _____ reflex

- rounder
- accomodation, unconscious

what is hyperopia? where does the focal point fall and how can it be solved?

- far-sightedness
- behind the retina
- solved by convex lens (reading glasses)

what is myopia? where does the focal point fall and how can it be solved?

- near-sightedness (MY EYESIGHT)
- in front of the retina (NEAR AND FRONT)
- can be solved with concave lens

a ______ lens causes light rays to ____ ____ more, which is the opposite of a ____ lens

- concave
- spread out
- convex

photoreceptors are found in the

retina

our retina has ___ types of photoreceptors which are:

- rods
- cones

rods and cones are ______, however they do not fire ________ potentials. instead, the respond to ______ with _____ membrane potentials

- neurons, action potentials, stimuli, graded

cones and rods have the ______ basic structure. in the ___ segment, the membrane folds into ___________ layers which contain __________ that respond to light

- same
- outer
- disk-like
- visual pigments

how do photoreceptors detect light?

- they detect light using membrane bound visual pigments

photoreceptors are _______ and more ______ in darkness. this means they release lots of ________

- depolarized
- active
- glutamate

each photoreceptor contains ____ of molecules of its _______. However, each type of photoreceptor has just ____ type of _____.

- millions
- pigments
- one
- pigment

the visual pigment for rods is:

rhodopsin

photoreceptors are not distributed ________. They are most densely packed in the _____, and especially in its central pit called the ______.

- uniformly/equally
- macula
- fovea

we use the ______ for detailed vision

fovea

there are _____ photoreceptors in the ____ spot. The ____ spot is the hole where axons carrying ____ info exit the eyeball to form the ____ nerve.

- no
- blind
- blind
- optic

cones are for _______ and rods are for ________.

- bright light
- dim light

Therefore, _____ are considered to be more sensitive than _____ because they can detect single photons but they only operate in _____ light.

- rods
- cones
- dim

During daylight, ____ are bleached out, which means their _____ is broken down so they can't sense light

- rods
- rhodopsin

cones and rods are distributed differently in the _______. The _____ contains exclusively ______ and the more peripheral ______ contains mainly _____. Therefore, there is a ____ density of _____ in the fovea.

- retina
- fovea
- retina
- rods
- high
- cones

photoreceptors synapse onto ______ cells, which synapse onto _______ cells. up to ______ photoreceptors may converge on a single _______ cell, the BP cells in turn converge on ___.

- bipolar
- ganglion
- 45
- GC

convergence is greatest in the peripheral _____ and least in the ______

- retina
- fovea

everyone neuron in the visual system has a _______________ also called the _____ field. the ______ is the region of the ____ where light affects the cell's activity.

- receptive field/visual field
- visual field
- retina

bipolar cells receptive fields can be on centre or off centre. ___________ are excited by light in the centre of their field and ____________ by light in the surround. These cells respond most when a light spot fills their _____ and the surround is _____.

- on centre cells
- inhibited
- centre
- dark

off centre cells are ___________ by light in the centre, and excited by ______ in the surround. they respond best when a _____ spot fills their centre and the surround is _________.

- inhibited
- light
- dark
- light

both types of bipolar cells react to ___________. when lighting is _________, neither type of _____________ responds. this is because the effects of the centre and surround ___________, which leaves the cell at its ___________ level.

- contrast
- uniform
- bipolar cells
- cancel
- resting

bipolar cells project to ___________ ___________ ______.

- retinal ganglion cells

retinal ganglion cells unlike photoreceptors and bipolar cells, do:

- fire action potentials

ganglion cells in ___________ parts of the retina have different sized ___________. Therefore, a ganglion cell near the ______ gets input from only a few ___________, which are mostly ____.

- different
- receptive fields
- fovea
- photoreceptors, cones

farther out, each ganglion cell gets input from many ________, which are mostly ______.

- receptors
- rods

in the periphery, each ganglion cell is very ___________ to light, but ____ at reporting spatial detail. this is because it blends information from a wide range of ________.

- sensitive
- poor
- receptors

___________ are also classified based on how their signals are used in the brain.

ganglion cells

large ganglion cells are ___________. these cells provide info about ___________ and are ________. they account for about _____ of RGC.

- magnocellular ganglion cells/ M cells
- M = MOVEMENT
- phasic
- ~10%

small ganglion cells are ___________. these cells provide info that is used to infer form and fine detail, like texture. they are less ______ and more ___________. they account for about ___ of RGC.

- parvocellular / P cells
- phasic-tonic
- ~70%

~1 % of ganglion cells are ___________ ganglion cells. there are photoreceptors with their own ________ ___________.

- melanopsin
- visual pigment (melanopsin)

half the optic-nerve fibres cross at the _______ ___________.

optic chiasm.