Sensory systems Flashcards
What is the stimulus receptor and location for the modularity, hearing
Stimulus - mechanical
Receptor - Mechanoreceptor
Location - cochlea
What is the stimulus receptor and location for the modularity, balance
Stimulus - mechanical
Receptor - mechanoreceptor
Location - Vestibular system
What is the stimulus receptor and location for the modularity, vision
Stimulus - light
Receptor - Photoreceptor
Location - retina
What is the stimulus receptor and location for the modularity, Touch
Stimulus - Mechanical
Receptor - Mechanoreceptor
Location - Skin
What is the stimulus receptor and location for the modularity, Temperature
Stimulus - thermal
Receptor - Thermoreceptor
Location - Skin
What is the stimulus receptor and location for the modularity, pain
Stimulus - mechanical,thermal and chemical
Receptor - noiceptor
Location - skin, internal organs
What is the stimulus receptor and location for the modularity, proprioception
Stimulus - mechanical
Recptor - Mechanoreceptor
Location - mucles, tendons, joints
What is the stimulus receptor and location for the modularity, olfaction
Stimulus - chemical
Receptor - Chemoreceptor
Location - nasal cavity
What is the stimulus receptor and location for the modularity, taste
Stimulus - chemical
Receptor - Chemoreceptor
Location - Tongue, Pharynx, palate, epiglottis
How does a stimulus allow for the perception of touch
Stimulus –> sensory receptor activated –> Membrane permeability is altered in the sense cell –> Receptor potential develops in the sense cell –> neurotransmitter is released onto afferent neuron terminals –> AP is generated in Afferent neuron –> AP propagates to the CNS –> CNS integrates the information
What does the proprioception system do
your body’s ability to sense movement, action, and location.
Takes information from Golgi tendon organs and Muscle spindles to tell the CNS how stretched the muscles allowing us not to fall over
What is the difference between a graded receptor potential and an AP
GRP increase in size as a response to increases in stimulus
AP are always the same size but have a threshold for activation
What is an example of direct neuronal activation
Olfactory receptors
Ion influx causes a GRP to develop in cilium
Large enough receptor potentials cause depolarisation in the soma –> APs travel to olfactory bulb
What is an example of neuronal activity using a synapse
Taste receptors
Ion influx causes membrane depolarisation and a GRP develops –> initiates synaptic vesicle to fuse w membrane and neurotransmitter is released –> NT binds to postsynaptic receptors generating an EPSP in the afferent neuron of the dendrite –> big enough EPSPs generate an AP
What is sensory transduction
the translation of the sensory stimulus into neuronal activity
What are the 4 types of information that a sensory receptor can convey
Modality
Location
Intensity
Timing
What is labelled line code
That the receptors are only selective for one type of stimulus energy
Modality specific line of communication
What is synaesthesia
When someone senses one modality but perceive it as another modality
A fault in the labelled line code
“Hear colours”
What is stimulus location
Spatial arrangement of activated receptors within a sense organ which gives information about the stimulus
What is a receptive field in the somatic field
The region of skin innervated by the terminals of the receptor neuron
What is stimulus intensity
The total amount of stimulus energy delivered to the receptor
Lowest stimulus is known as the threshold
When do rapidly adapting receptors respond
At the begging and end of a stimulus
Phasic receptors
When do slowly adapting receptors respond
Respond to prolonged stimulation
Tonic receptors
What is divergence
Allows primary afferent neuron to signal to more than one relay neuron
Allows for redundancy
What is convergence
Ensures that relay neurons have a larger receptive field than primary afferent neurons
What do inhibitory neurons allow throughout sensory integration
Ensures the signal in the most active neuron is propagated
What is the rod photopigment
Rhodopsin
What are the cone photopigments
S - Short wavelength (420)
M - medium (530
L- Long (560)
What is the retinal ganglion photopigment
Melanopsin - plays an important role in non-image-forming visual functions, including hormone secretion, entrainment of circadian rhythms, cognitive and affective processes.
What happens to the membrane potential when photoreceptors are exposed to light
They are hyperpolarised
cGMP - gated non selective cation channels are open in the dark allowing an influx of Na+ (dark current) so cell is depolarised
Light decreases levels of cGMP so closes the channels –> prevents Na+ influx –> K+ still leaves the cell –> hyperpolarised
How many photons allow the sensation of light in humans
5-7
How is rhodopsin activated
Light
What are the two parts of rhodopsin
Opsin and retinal
Opsin varies and retinal can change between cis and trans
Opsin is the GPCR
How does photo transduction occur
Light (photons) enters the retinal pigment causing a change from cis to trans form –> this changes opsin configuration –> activates transducin (GPCR with alpha, beta and sigma subunits) –> Alpha subunit activates Phosphodiesterase –> PDE cleaves cGMP into GMP –> removing cGMP causes Na+ gates to close so Na+ can’t get into the cell and the cell becomes hyperpolarised –> glutamate release decreases –> Light can be seen
Signal amplification as its an enzyme cascade
Why cant rods process bright lights
They become easily saturated and rhodopsin become bleached
What is light adaptation
Photoreceptors initially hyperpolarise greatly, photoreceptors then gradually depolarise with continued bright light
Requires calcium
How does light adaptation occur
in the dark: Ca2+ enters cells and blocks guanylyl cyclase –> reduces cGMP production so closes some ion channels
In the light, channels are shut so Ca2+ cannot enter cells, this causes the block on guanylyl cyclase to be released –> more cGMP produced so more channels open
What does arrestin do
Control GPCR including rhodopsin. Binds to rhodopsin so transducin cant be activated –> stopping the cascade
How are Bipolar cells classified
Based on bipolar response to glutamate
How do Bipolar cells turn on and off
Photoreceptor hyperpolarises to light –> less glutamate release
Bipolar cells hyperpolarise –> OFF bipolar cell
Bipolar cells depolarise –> ON bipolar cell
What receptor does an OFF bipolar cell use
Ionotropic glutamate receptors (positive ions into the cell)
More glutamate released –> binds to receptor which opens K+ channels –> K+ leaves
which hyperpolarises the cell –> releases more glutamate from OFF bipolar cell
What receptor does an ON bipolar cell use
GPCR (metabotropic)
Can be inhibitory
Release glutamate in the dark
In the light –> photo receptor hyperpolarises –> reduction in glutamate –> cell depolarises –> releasing more glutamate from ON bipolar cell
What is the organisation of bipolar cells
Centre-surround receptive field organisation
allows ganglion cells to transmit information not merely about whether photoreceptor cells are exposed to light, but also about the differences in firing rates of cells in the center and surround
Centre –> direct
Surround –> Horizontal
What is wavelength
Distance between peaks or troughs
What is frequency
Waves per second
What is amplitude
Difference between wave peak and trough
What are the 3 ways that light rays interact
Reflection
Absorption
Refraction
What does the pupil do
Lets light inside the eye
What does the iris do
Contains muscles which control the amount of light entering the eye
What does the cornea do
Glassy, transparent covering of the pupil which refracts light
What does the sclera do
Continuous with cornea, forms a tough protective wall that gives the eyes shape
What does the extraocular muscles do
Move the eyeball, controlled by oculomotor nerve (CNIII) (Cranial Nerve)
What does the optic nerve do
Carries axons from retina to brain
What is the optic disk
Origin of blood vessels and optic nerve –> cant sense light
What is the macula
Region of retina for central vision
Has no large blood vessels to improve vision quality
What is the fovea
The highest area of visual acuity
Only cones
What does the retina contain
Sensory receptor cells and afferent neurons
How is stretching and relaxing of the lens enabled
Suspended by zonal fibres (ligaments) which attach to the ciliary muscle
Flattened (distant) - SL contract and cillary muscles relax
Where does refraction take place
Cornea - 80%
Lens - 20%
What is degree of refraction determined by
Angle of the light in the eye
Difference in refractive indices between the two media
How does refraction in the cornea work
Light arrives through air but the cornea is mainly water
Light travels slower through water than air causing refraction
What is the focal distance
The distance from refractive surface to convergence of parallel light rays
How does the lens accommodate to see distant objects
Lines are almost parallel
Cornea provides sufficient refraction to focus the light rays onto the retina
How does the lens accommodate to see close objects
Light rays are not parallel
Requires additional refraction to focus them onto the retina
Caused by the fattening of the lens
CM contract, SL relax
What does the rounded lens do
Increases the refractive power to focus closer objects onto the fovea
What does emmetropic mean
Perfect vision
How is accommodation achieved
Contraction and relaxation of the ciliary muscles to move the lens
How is the retina organised
Laminar organisation
What does the retina do
Converts focussed light into neural activity
What are the 5 cells of the retina
Ganglion cells - output from the retina
Amacrine cells - modulate information between GCs and BCs
Bipolar cells - Connect photoreceptors to ganglion cells
Horizontal cells - modulate information between photoreceptors and BCs
Photoreceptors - sensory transducers, both rods and cones
What are photoreceptors
Membranous disks containing light-sensitive photopigments that absorb light
What is the duplicity theory
Cant have high sensitivity and high resolution in a single receptor
What is the difference between rods and cones
Rods - greater number of disks, higher photopigment concentration, 1000x more sensitive to light, enable vision in low light (scotopic), low visual acuity
Cones - enable colour vision, used in daylight (photopic), high visual acuity and lower sensitivty
What is the difference between the central and peripheral retinal
Central - Low convergence, low sensitivity, high resolution - mainly cones
Peripheral - high convergence, high sensitivity, low resolution - mainly rods
Why do cones have high resolution
Low convergence on retinal ganglion cells
What is the Vitreous humor
colourless substance which provides pressure inside the eyeball to maintain its shape
Why are some people farsighted
The eye is too short
Not enough refraction
Why are people nearsighted
The eye is too long
Rays are more divergent
Increased refraction
What is the chemical sense used for
Identifying food sources
Avoid noxious substances
Finding a mate
What are the 5 basic tastes
Salty - electrolytes - Want high salt content
Sour - H+ content - Avoid high acidity
Sweet - Sugars - High sugar content wanted
Bitter - diverse chemical structures 0 Avoid bitter content
Unami (savoury) - Amino acids - High amino acid preference
What are the taste organs
Tongue, cheek, soft palate, pharynx, epiglottis
2000-5000 taste buds with 100 chemoreceptive taste cells per taste bud
What does the taste pore allow
Sensory transduction by microvilli
Where are taste buds contained
Lingual papillae
What tastes require ligand gate ion channels and which require GPCR
Salty - sour - bitter are ionotropic
Sweet and unami are metabotropic
What is the specificity of taste buds and cells
Taste cells only respond to one stimuli whereas taste buds contain many taste cells which respond to various stimuli
How are gustatory afferents separate from taste cells
Require neurotransmitter release across the synaptic cleft
What is capsaicin
Receptor on the tongue which detects heat in food
What are the 4 parts of the tongue
Filli form papillae - middle tongue - texture
Circumvallate - taste - back of the tongue - taste buds in indentation
Foliate papillae - small area - side of tongue
Fongiform - evaginations - top fo the tongue
How do we taste
100 chemoreceptive taste cells per taste bud
Taste pore allows for sensory transduction by microvilli on apex of taste bud.
Microvilli bind to receptors in the taste cell
Synaptic transmission at base
How do odorants reach the olfactory receptor cells
Dissolve in the mucus layer
Where is transduction machinery found
Within the cilia at the end of the dendrite
What is the primary afferent neuron of the olfactory system
The axon of the receptor cell
What are the characteristics of axons in the olfactory system
They are hin and unmyelinated
What is special about the axons in the olfactory system
They are regularly replaced in adults
How many odorant receptor proteins are in the body
around 350
Olfactory receptor cells only express one odorant receptor
One odorant can recognise multiple odorants
The combination of odorant receptors which recognise an odoront which allows us to recognise a specific odor
How does transduction occur
via G(olfs)
What type of receptor are all ORs
GPCR
What is the downstream pathway of every OR
G(olf) –> adenylyl cyclase –> cAMP –> cyclic nucleotide gated ion channels –> depolarisation –> Ca”+ gated Cl- channels –> further depolarisation
What is the difference between an intense stimulus and a large stimulus in the olfactory system
Large - threshold for AP firing is reached
Intense - Large receptor potential - increased AP firing rate
Where does each glomerulus receive signals from
Each glomerulus receives from only one type of olfactory receptor
Where do second order neurons of the olfactory system project
Olfactory cortex (conscious smell)
Olfactory bulbs
Hypothalamus (sex and neuroendocrine)
Hippocampus (memory)
Amygdala (Emotional response)
Reticular formation (visceral responses)
What scale are decibels measured
Logarithmic
Amplitude is measured in dB
What is the pinna
Outer ear - allows brain to hear where on the vertical plane the sound is loated
What is the tympanic membrane
Middle ear - moves back and forth with ear
TM gets pushed by the compression of a soundwave –> pushes stapes into oval window –> pushes fluid in cochlea –> round window allows for movement of fluid out of tympanic membrane
Movement of fluid stimulates cells to allow them to transfer sound
What is the range of human hearing
20Hz to 20,000 Hz
What are the ossicles of the middle ear
Malleus, incus and the stapes
How are the ossicles arranged
Malleus to incus is a rigid connection
Incus to stapes is a flexible connection
What do the ossicles do
Amplify the sound to cause 20x more pressure on the oval window than on the tympanic membrane
How does the tympanic membrane move
TM pushed by the compression phase of the sound wave and pulled by the refraction phase of a sound wave
What are the 3 compartments of the cochlea
Scala vestibuli - Filled with perilymph and connect slarge end to oval window
Scala tympani - filled with perilymph and connects large end to the round window
Scala media - filled with endolymph - high K+ concentration and high potential
What is the anatomy of the basilar membrane
Runs from base to apex
Moves up and down with frequency
Basal end is narrower and stiffer
Apex is wider and floppier
How does the basilar membrane change with the frequency
High frequency moves basal
Low frequency moves apex
How does the basilar membrane displacement affect hair cells
Stapes moves outward –> basal membrane moves upwards –> hair cells depolarise
Stapes moves inward –> Basal membrane moves downwards –> hair cells hyperpolarise
How are hair bundles connected
Tip links
What are the types of hair cell
Inner HC and Outer HC
What do tip links do
Fine structures, the higher the Db the more stereocilia are firing causing the tip links to be highly stimulated.
In over stimulated hearing loss, Tip links break
Tip links opens a cation channel, scala medium contains lots of potassium –> potassium moves in through tip links –> depolarises –> glutamate released –> afferent neuron activated
What do outer hair cells do
They act as the cochlear amplifier (low sounds)
As the voltage changes the HCs move –> amplifies movement of the BM –> outer hair cells move with the BM –> hear at a low frequency
What is the point of the vestibular system
Tells us direction (which way is up and where we are going)
Helps keep our eyes still as we move
Maintains posture
Our ability to perceive our own movement within space
What is the vestibular labyrinth filled with
Endolymph
What is the difference between hair cells of the auditory and vestibular system
Hair cells of vestibular respond to lower frequencies
Vestibular hair cells keep their kinocilium throughout life (sets polarity of hair bundle and changes direction of hair growth)
More rows of stereocilia in vestibular
What are the two types of vestibular hair cell
Type 1 - calyx (post synaptic region which covers the bottom of the hair cell
Type 2 - afferent dendrite
Allows for different properties for communication
What are the semi circular canals for
Different types of rotation
Horizontal - spinning
Anterior
Posterior - moving up while sitting
What is the ampulla
Where mechanotransduction machinery is (HCs)
One ampulla per semi-circular canal
What are the otolith organs
Detect linear motion
Utriculi - Linear acceleration
Saccule - Up and down
What is the utricle and saccule filled with
Endolymph
What direction do hair cells move to become excitated
To the right, tips tighten, Voltage gated Ca2+ channels at the base cause the release of glutamate. Glutamate activates Glutamate receptors on afferent neurons.
Generates EPSPs –> summate to become APs –> neurotransmitter is released –> increase the frequency of impulses onto the nerve
How do the hair bundles allow for hyperpolarisation
Few channels are open
What is the range of the vestibular system
0-20Hz
Where are hair cells found in the vestibular system
In the macula
What is the otoconia
Part of the vestibular system which moves with gravity to open or close ion channels
What is the orientation of hair cells in the vestibular system
Has a line where hair cells face one way and then the opposite on the other side
Auditory has same orientation throughout
How do you tell if there changes in the vestibular system are due to head tilt or linear acceleration
Vision
Propriosensors - muscle stretch
What is the cupula
A gelatinous structure penetrated by hair bundles used for sensing torsional movements of the head
What do the semicircular canals detect
Angular acceleration (rotation)
The inertia of endolymph during rotation displaces the cupula
How do semicircular canals work
Either side of the head do opposite things
Work in pairs (redundancy)
If head moves to the left, there will be increased firing on the left side and a decreased firing on the right side
Hair bundles move to the shorter stereocilia and get inhibited which decreases the firing
How is the vestibulo-ocular reflex activated
Movement activates hair cells –> brainstem communicates with ocular motor –> pulls eyes in opposite direction to movement
What is nystagmus
The resetting of eye rotation by moving (involuntarily from side to side)
Why do you still feel like you are spinning after stopping
Endolymph takes a while to stop after rotation has finished
What is the purpose of the vestibular ocular reflex
Stabilise gaze by countering the movement of the head
