Sensory neuroscience Flashcards
What are the 5 traditional senses? What are the 4 other extra ones?
Vision, smell. taste, hearing, touch
Balance, proprioception, thermal and pain
What are the four types of information sensory receptors can convery?
Modality, location, intensity, timing
What is the labelled line code?
How stimulus modality is coded
Receptor is selective for one type of stimulus energy
Axons of receptor/afferent neuron acts as a modality specific line of communication
These make connections with specific areas in the CNS
What is a receptive field in the somatic system?
The region of skin innervated by the terminals of the receptor neuron
What is a receptive field in the visual system?
The region of the visual field projected onto a photoreceptor
How is stimulus intensity coded?
Firing frequency of afferent neurons
How is stimulus location coded?
Receptive fields
Different sizes depending on what part of the body
How is onset timing of the stimulus determined?
When the stimulus energy is received by the receptor and causes it to fire
How is the stimulus duration determined? What is adaptation?
By adaptation rates of receptors
When continuous stimuli causes the firing rate of APs to decrease in response
What are tonic receptors?
Slowly adapting receptors responding to prolonged stimulation
What are phasic receptors?
Rapidly adapting receptors responding at the beginning and end of a stimulus
Why do we need divergence in terms of sensory integration?
Allows primary afferent neurons to signal to more than one relay neuron
Why do we need convergence in terms of sensory integration?
Ensures that relay neurons have larger receptive fields than primary afferent neurons
What role do inhibitory neurons play in sensory integration?
They ensure the signal in the most active neuron is propagated- lateral inhibition
When are rods used? What is the photo-pigment in them?
Under conditions of dark adaptation
Rhodopsin
When are cones used? What photo pigments allow them to do this?
Under conditions of light adaptation
Opsins S, M, L
What is the dark current? What property does this give photoreceptors?
An Na+ influx caused by cGMP-gated non-selective cation channels that are open in the dark
Means they are depolarized in the dark
What is the photo pigment in the retinal ganglion? What does it control?
Melanopsin
Doesn’t produce a clear image, only gives idea of light/dark to drive sleep/wake cycle
What happens to photo receptors when there is light?
Light decreases cGMP levels which closes the channels that maintain the dark current
This prevents the Na+ influx so the receptors become hyperpolarised
Phototransduction signal amplification
Rhodopsin is activated by light
Stimulates G-protein Transducin to become transducin GTP
The alpha subunit activates enzyme phosphodiesterase (PDE) which reduces cGMP levels and closes the Na+ channels
What enzyme produces cGMP constantly when in the dark?
Guanylyl cyclase
What are the differences in saturation between rods and cones?
Rods cannot process bright light as they become easily saturated
Cones are not saturated as easily so are used in bright light
Why are rods more easily saturated?
Rhodopsin is bleached
cGMP levels are so low that no additional hyperpolarisation can occur
What role does Ca2+ play in adaptation in the dark?
Ca2+ normally enters cells and blocks guanylyl cyclase
Reduces cGMP production so some channels are closed
What role does Ca2+ play in adaptation in the light?
Channels are shut so Ca2+ cannot enter cells and block guanylyl cyclase
More cGMP is produced so more channels are opened
What happens in terms of neurotransmitters when a photo receptor hyperpolarises in response to light? Why?
Reduced glutamate release
In the dark constant depolarization means constant glutamate release
What are bipolar cells?
Main retinal interneurons that provide a pathway between receptors and ganglion cells
Two types- ON and OFF
How do OFF bipolar cells respond to glutamate?
Hyperpolarise when there is a reduction in glutamate
Switched off by light as they use ionotropic glutamate receptors
How do ON bipolar cells respond to glutamate?
Depolarize when there is a reduction in glutamate
Switched ON by light as they use metabotropic glutamate receptors
How are bipolar cells organised? Why?
Centre-surround organisation
Connected to photo receptors with horizontal cells above
Gives bipolar cells centre-surround receptive fields
Why is the visual system important?
Allows us to detect prey/source food, detect predators/danger, detect mates, communicate
Wavelength
Distance between peaks or troughs
Frequency
Number of waves per second
Amplitude
Difference between wave peak and trough
What three ways do light rays interact with the environment?
Reflection, refraction, absorption
Why does refraction occur?
Speed of light differs between mediums of different densities
What is the function of the pupil and iris?
Pupil- lets light inside the eye
Iris- contains muscles which control amoutn of light entering the eye
What is the function of the cornea?
Glassy transparent covering of pupil and iris that refracts light
What is the function of the sclera?
Continuous with cornea and forms the tough protective wall of the eyeball to give it its shape
What do the extraocular muscles do?
Move the eyeball
What are the two nerves that are involved with the eye?
Optic nerve or cranial nerve II- carries axons from the retina to the brain
Oculomotor nerve or cranial nerve III- controls the extraocular muscles
What is the optic disc?
Origin of blood vessels and optic nerve, cannot sense light (blindspot)
What is the macula?
Region of retina for central vision and is devoid of large blood vessels to improve visual quality
What is the fovea?
Thinnest region of the retina, area of highest visual acuity
Contains most of the cones and no rods
What parts of the eye help the lens to function correctly?
Zonal fibre suspend the lens
Ciliary muscles enable the stretching of the lens for accommodation
Where does refraction onto the retina occur and in what amounts?
80% at the cornea
20% at the lens
What is the degree of refraction determined by
Difference in refractive indices between the two media
The angle at which light hits the interface between these two media
How is light refracted by the cornea?
Light arrives at the cornea by air but the cornea is mainly water so light will travel more slowly through the cornea
Light that hits the cornea directly perpendicular will move straight through onto the retina
What is the focal distance?
Distance from refractive surface to convergence of parallel light rays
When does the lens have to change shape? Why?
When objects are closer up as light rays are not parallel and require additional refraction to focus them on the retina
Eye when focusing on distant objects
Relaxed ciliary muscles
Taut suspensory ligaments
Flattened, weak lens
Eye when focusing on closer objects
Contracted ciliary muscles
Slackened suspensory ligaments
Rounded, strong lens
What is hyperopia and how is it corrected?
Lens is too flat/ eyeball is too short so image is focused behind the retina
Convex lenses
What is myopia and how is it corrected?
Lens is too rounded/ eyeball is too long so image is focused in front of the retina
Concave lenses
In what order does light pass through the retina?
Ganglion cells > bipolar cells > photo receptor cells
What do the nuclear and plexiform cell layers in the retina do?
Nuclear- contain cell bodies
Plexiform- regions where synaptic connections occur
What are retinal ganglion cells and what do they do?
Receive photo sensory information and output this
What do amacrine cells do?
Modulate information transfer between ganglion cells and bipolar cells
What do bipolar cells do?
Connect photo receptors to ganglion cells by either hyperpolarising or depolarising in repsonse to reduced glutamate release from photoreceptors
What do horizontal cells do?
Modulate information transfer between photo receptors and bipolar cells
What is duplicity theory?
You cannot have high sensitivity and high resolution in a single receptor
Separate systems for monochrome and color
Rod structure
Greater number of discs
Higher photo pigment concentration so more sensitive to light than cones
Low visual acuity/ resolution
Cone structure
Fewer discs
Enable color vision, lower sensitivity
High visual acuity/resolution
What are the functions of the chemical senses?
Identify food sources
Avoid noxious substances
Find a mate or mark territories
What are the 5 basic tastes?
Salty, sour, sweet, bitter, umami (savoury)
What are the taste organs?
Primarily tongue, cheeks, soft palate, pharynx, epiglottis
What are lingual papillae? What types are there?
Contain taste buds which are groups of taste cells
Filiform- spiked, no taste buds, sense texture
Foliate- ridges
Fungiform- mushrooms, at sides and front
Circumvallate- pimples, large
How do olfactory receptor cells work?
Odorants must dissolve in the mucus layer to reach olfactory receptor cells
Transduction machinery is found within cilia at the end of the dendrite
The primary afferent neuron = axon of receptor
Characteristics of olfactory receptor cells
Bipolar chemoreceptive neurons
Thin, unmyelinated axons
Regularly replaced
How many odorant receptor proteins do humans have? What kind of receptor are they?
350
G-protein coupled receptors
Odorant receptor Golf pathway
Golf > adenylyl cyclase > cAMP > cyclic nucleotide gated ion channels > depolarisation > Ca2+ gated Cl- channels > further depolarisation
Convergence of olfactory information
Each glomerulus of the olfactory bulb receives input from only one type of olfactory receptor
so there is convergence on secondary neurons
What regulates sleep?
Raphe nucleus, brain stem and the locus coeruleus
What regulates the timing of sleep (not sleep itself)?
Superchiasmatic nucleus in the anterior hypothalamus
What is human’s physiological range of frequency for sound?
20Hz-20,000Hz
What is the high risk threshold? What is the threshold of pain?
120dB
140dB
What are the three ossicles from outer to inner?
Malleus
Incus
Stapes
What is the function of the outer ear/pinna?
Helps the brain to understand where the sound is coming from on the vertical plane
Reason for convoluted shape
What is the tympanic membrane?
Large drum that vibrates backwards and forwards as sound hits it
What structures are in the middle ear?
Tympanic membrane
Ossicles
Oval window
What is the functional significance of the middle ear?
To amplify sound to overcome the greater impedance of cochlea fluid
What is perilymph?
The fluid that the scala vestibuli and scala tympani are filled with- the canals which surround the cochlea
What is endolymph?
Fluid that the scala media is filled with- the inside of the cochlea
What is the difference between perilymph and endolymph in terms of composition? Why?
Perilymph has a composition similar to regular plasma
Endolymph is high in K so cells have a higher potential as this is where the hair cells are
How do the ossicles amplify sound onto the oval window?
The malleus and incus have a rigid connection to each other but the stapes connection is flexible
Acts as a lever system
What happens to the ossicles when the tympanic membrane moves inwards?
Bottom of malleus moves down
Pulls incus inwards which pushes stapes inwards onto the oval window
Where are auditory hair cells located and how are they organised?
Organ of corti
On the basilar membrane
Below the tectorial membrane
3 rows of outer hair cells and 1 row of inner hair cells
Anatomy of the basilar membrane and how this relates to frequencies
Base- narrow, thick, stiff (high)
Apex- wide, thin, floppier (low)
What is the tonotopic map?
Different frequencies of sound cause maximal displacement of the basilar membrane in different regions
High at basal end
Low at apical end
How does basilar membrane displacement affect hair cells when there is sound?
Stapes moves inwards and hits oval window
Basilar membrane moves upwards
Inner hair cell tip links move towards the kinocilium so that TMC1 channels are pulled open
K+ moves into cells from endolymph
Cells depolarise and send signals to primary afferent nerve
How does basilar membrane movement affect hair cells when there is no sound?
Basilar membrane moves downwards
Inner air cell tip links move so that TMC1 channels close
K+ no longer moves in and cells are hyperpolarised so no signal
How do the functions of inner and outer hair cells differ?
Inner- have tip links between steriocillia which allows them to be the mechanoelectrical transducers
Outer- electromotile and act as cochlear amplifiers
What is electromotility?
Changes in electrical profile means they become motile (dance) to amplify the movement of the basilar membrane
What are the three semicircular canals of the vestibular system? What do they control?
Anterior vertical
Posterior vertical
Horizontal
Head rotation (one for each direction)
What are the otolith organs? What do they control?
Utricle- forward and backward movement
Saccule- up and down
How is the vestibular system organised in terms of perilymph and endolymph?
Vestibular labyrinth is filled with endolymph with chambers either side filled with perilymph
What are the ampullas?
Area at the base of each semicircular canal when the mechanotransduction machinery is
How does the movement of hair bundles cause glutamate release?
Hair bundles move towards the kinocilium and subsequent tip links which opens k+ channels
Graded potentials cause Ca2+ channels to open which allow glutamate to be released
Generates EPSPs
What are the differences between the hair cells of the vestibular and auditory systems?
Vestibular- more rows of hairs, respond to lower frequencies, keep their kinocilium throughout life to maintain polarity
What are the two types of vestibular hair cells? What is the difference?
Type 1- calyx which encompasses whole bottom of the cell which means communication is different
Type 2- normal communication
What parts of the saccule and utricle are the hair cells found?
Sensory patches called macula
What is the striola?
A curved line formed from hair cells pointing toward it or away from it
When cells on one side are activated the ones on the other side are inhibited
What is the otolithic membrane?
Membrane resting on top of the hair cells
Gelatinous and has otoconia in it
What is otoconia?
Calcium carbonate crystals which add weight
Weight means the hair cells are pulled in given direction when the otolithic membrane moves
How does the CNS distinguish tilting and moving in a given direction? (same signal output)
Integration of information from the visual system
What is the cupula?
Gelatinous structure penetrated by hair bundles in the ampulla at the base of each semicircular canal
How is angular acceleration (rotation) detected by the semicircular canals?
Inertia of endolymph during rotation displaces the cupula
Hair bundles deflected
Firing of sensory fibres depending on what side of the head- they work in pairs as they are on the same plane
Opposite side is decreased
What is the vestibulo-ocular reflex?
Gaze-stabilizing reflex that allows your eye movements to coordinate with motion so that your vision is stable
What is vestibular nystagmus?
Biphasic eye movement that enables the resetting of eye position during sustained head rotation
Slow phase- eyes rotate in opposite direction to head movement
Quick phase- rapid resetting movement back to centre of gaze
What is the receptor for salty simuli? What kind of receptor is it?
ENaC
Ion channel
What is the receptor for sour simuli? What kind of receptor is it?
OTOP1
Ion channel
What is the receptor for sweet simuli? What kind of receptor is it?
T1R2 and T1R3
GPCR
What is the receptor for umami simuli? What kind of receptor is it?
T1R1 and T1R3
GPCR
What is the receptor for bitter simuli? What kind of receptor is it?
T2Rs
GPCR
Girls and boys hate pedos
Ganglion Amicrine Bipolar Horizontal Photoreceptors
