Lecture 9 - Sensory Systems Flashcards
What are the stimuli potentially available to animals and human and what type are they
Mechanical Chemical Photic Thermal Pain Kinestheia External stimuli
What is receptor for chemical stimuli and what does it detect
Chemoreceptor
Taste, smell
What is receptor for mechanical stimuli and what does it detect
Mechanoreceptors
Touch, hearing, balance and acceleration
What is receptor for photic stimuli and what does it detect
Photoreceptors
Vision
What is receptor for thermal stimuli and what does it detect
Thermoreceptors
Hot/cold
What is receptor for pain stimuli and what does it detect
Nocireceptors Various ( chemical, mechanical etc )
What is receptor for kinestheia stimuli and what does it detect
Proprioreceptors
Various ( muscle spindles etc )
What does stimuli cause
Small depolarisation in receptor
What are the types of internal stimuli
Mechanical - baroreceptors
Chemical - Blood O2, /CO2, glucose etc = control levels of respiration
What are baroreceptors
Stretch receptors in the aoritc arch and cartoid body
What are mechanoreceptors sensitive to
Diameter of arteries = informed of blood pressure
What is magnetoreception and what animals use it and why
Animal like birds and fish percieve the Earth’s magnetic field
Used for navigation ( magnetoreception ) - allows them to migrate, know where abouts in world they are
What non - human animals use mechanoreceptors and why
Aquatic animals such as fish and some amphibia have lateral lines ( side of fish ) to sense water movements
What is electroreception and what animals use it and why
Sharks can detect fish buried in sea by detecting their electric fields - sense electricity/electrical signal - action potentials
- allows them to migrate, know where abouts in world they are
What wavelength of light do we see
We see from about 400nm ( violet ) to 750nm ( red )
What wavelength of light do animals see
Fish, birds and insects see UV
Snakes and beetles sensitive in infrared
What are all these examples of
Sensory receptors - senses
What is role of sensory receptors and what is the term called
Converting sensory stimulus to neurobiological activity
Transduction
What is flow chart of stimulus to CNS
Stimulus - transduction - receptor potential - action potential - CNS
What does a stimulus cause
Change in membrane permeability = receptor potential
What is receptor potential result of
Change in membrane permeability
What does receptor potential cause
Action potential - signal to CNS
Where is action potential carried to
CNS
What happens if threshold reached
Action potential ( opens Na+ channels - small depolarisation )
What is the same here
Receptor cell and sensory neuron
How many cells in each nostril that are sensitive to smelll
5 million
What happens to most sensory cells
Most Die eventually
What is receptor in smell and what is it
Olfactory receptor
Sensory neuron - stimulated directly by odor molecule
What is stimuli in smell and what does it activate
Odour molecule
Sensory neuron
What happens to the odour molecule
Dissolves in nasal mucus
Binds to receptors covering cilia on surface of bipolar olfactory neurons
Opens ion channels
Action potential in receptor - transmitted to brain ( cranial nerve )
What does cranial nerve do
Take information from nose to brain
What happens to olfactory receptors
Regenerate ( replaced ) by epithelial cells - turn into new sensory neurons
Summary of smell
Molecule to nose
Chemicals dissolve in mucus
Sensory cells = bipolar neurons - surface = cilia = increase SA. 2 processes coming out
Molecule onto protein receptor - Na channel - Na into bipolar neuron = action potential - CNS
What doesnt generate action potential
Specialised receptor cell
Which synapses generate action potential
Synapses with sensory neuron
What is gustatory receptor
Specialised receptor cell involving specialised cells
Where are our 10,000 taste buds located
On raised papillae of tongue
What is receptor potential
When a receptor cell produces a small depolarisation only in sensory cell
How many cells is taste bud made of
60 cells
What does a small depolarisation trigger
Action potential in sensory neuron - CNS
What is the base of the receptor cell
Sensory neuron
What do the molecules/food do
Dissolves in saliva
Latches onto protein receptors
What do different regions of the tongue respond to
The four different qualities that make up all tastes
Sensitive to different ones
What does an accessory structure do
Modifies stimulus before it hits receptor cell and determines what receptor cell is sensitive to
Examples of accessory structures
Membrane ( hearing )
Vestibular system e.g. hair
What are tactile receptors/receptor cells associated with
Accessory structures
What does function of sensory receptors of skin depend on
Nature of accessory structure
What is sound
Pressure waves in air / variations in air pressure ( perceived by cells in ear)
Transduction of ear
Ears turn sound into neurobiological signals the brain can interpret
What do ears turn sound into
neurobiological signals the brain can interpret
What produces pure sounds
Tuning fork
What is hearing
Turning sound into electrical activity within ear
When is air moved out
High pressure
When is air moved in
Low pressure
What happens when pressure makes membrane vibrate
Air pushed in and out
What does different notes produce
Different notes/objects - different frequencies
What do pure notes combine to form
More complex sounds ( sound quality )
Which notes are more frequent - higher or lower
Higher
Which notes are less frequent - higher or lower
Lower
What is acuity
Tell 2 sounds apart
What are most sounds
Not pure notes - combination of pure notes forming more complex sounds
What are the 3 regions of ear
- Outer ear
- Middle ear
- Inner ear
What does outer ear consist of
Ear canal
What does middle ear consist of
Stapes
Incus
Malleus
Ear drum
What does inner ear consist of
Cochlea
Semicircular canal
Where is pinna found
Outer ear
What is role of pinna
Serves to channel sound into the external auditory meatus ( tube - you stick your finger in )
Takes sound to tympanic membrane
What is tympanic membrane
Ear drum
What happens when sound impinges on tympanic membrane
Vibrates
These vibrations are transferred by middle ear to cause movement of oval window - movement of fluid in inner ear
What happens to tympanic membrane in areas of high pressure
It moves in
What happens to tympanic membrane in areas of low pressure
It moves out
What happens during beginning of transduction
Turns changes in air pressure into movement of tympanic membrane
What do you need to convert movement of tympanic membrane into and why is this hard
Fluid movement in inner ear
Harder than in air because fluid is resistant to movement
What is oval window
Junction to inner ear
What is middle ear filled with
Air
What are the 3 bones in the middle ear
- Malleus
- Incus
- Stapus
What do the 3 bones of middle ear do
Transfer vibration of tympanic membrane to the oval window
What does the Eustacean tube do
Connect the middle of ear to the Nasopharynx =equalises pressure of middle ear to atmospheric pressure
What is nasopharynx
Back of throat
What can 2 muscles do and how is this done
Freeze the bones of the middle ear = protects against loud sounds = turns off hearing.
When muscles contract = stops being transmitted - ossicles held solid - cant transfer vibrations
What is size of pressure changes in sound
Tiny
What do pressure changes in sound result in
Very small vibrations of tympanic membrane, however….
vibrations of tympanic membrane must cause fluid movement in inner ear - requires much greater pressure change
What is role of middle ear
Amplify movement of tympanic ( sound ) membrane - acts as impedance matching device
Takes small vibrations of tympanic membrane and turns it into large vibrations of oval window
What are 2 ways to amplify movement of tympanic membrane
- Pressure on tympanic membrane is spread over a large SA. The area of the oval window is much smaller, concentrating pressure = more effective ( bigger movements )
- Middle ear ossicle acts as a lever system = small movements amplified
What happens as atmospheric pressure lowers
Tympanic membrane bows out - curves in in higher pressure
What does the valsalva membrane do
Equalises pressure in middle ear and atmosphere
What does Eustacean tube do and why
Equalises pressure
Want pressure outside ear to be same as pressure inside ear otherwise tympanic membrane won’t work properly
What does inner ear do
Subserves both auditory and vestibular functions
Bony systems of tubes
What does inner ear consist of
Bony labyrinth filled with perilymph ( fluid ) suspended in which a membranous labyrinth containing endolymph
Endolymph
- Fluid
- Lots of K+
What is inner ear divided into
Cochlea ( coiled )
Vestibule ( bony )
3 semi - circular canals
What is coiled cochlea
Snailed like structure ( hearing )
What is vestibule
Containing membranous saccule and utricle ( vestibular )
Semi circular canals
Orientated in 3 planes of space - coming of membranous sacs
What is ampulla
Where the semi - circular canals join onto utricle = swelling
How is cochela divided
Internally by membranes that run length of cochlea
What is cochlea divided into
- Upper chamber - Scala Vestibule
- Lower chamber - Scala tympani
- Third chamber - Scala media
What contains organ of corti
Scala media
What is scala media filled with
Endolymph
What is Scala Vestibule and Scala tympani filled with
Perilymph
Where do Scala Vestibule and Scala tympani join
Helicotrema - tip of cochlea
What happens when stapes is pushed in
Movement of perilymph in scala vestibule - transferred to scala tympani = causes round window to bulge out
What does vestibular membrane do
Seperates scala vestibule from scala media
What does organ of corti sit on and what does that do
Basement membrane
Divides scala media from scala tympani
What is organ of corti
4 rows of hair cells ( cells with cilia on top - sensory cells) resting on basilar membrane
What is on top of cilia and what is it known as
Tectorial membrane
Accessory structure
What is the cilia on top known as
Stereocilia
What are stereocilia on surface of hair cells embedded into
Gelatinous membrane - tectorial membrane = accessory structure ( on top of cilia )
What are the superficial stereocilia
Sensory receptors, innervated by sensory neurons
What does sensory neuron do
Produce action potential
What does sensory cell cause
Small depolarisation
Which part of membrane vibrates most to high frequencies and why
Basilar membrane
Smaller and more taut near stapes
What kind of frequencies are produced further from stapes
Wider and looser
What responds to lower frequencies
Basilar membrane
What kind of frequencies are produced closer to stapes
Higher frequencies
Do points on basilar membrane vibrate at same frequencies
No - different
What happens to stereocilia at rest
Embedded in tectorial membrane - unbent - sensory neurons firing few actions potentials
What happens when basilar membrane rise/go up and why
Stereocilia bent
Due to mass of tectorial membrane
Why does basilar membrane rise
Due to travelling wave initiated by a sound
What happens when basilar membrane falls/goes down and why
Stereocilia also subject to shearing force but in opposite direction
Why does stereocilia bend
Due to hair cells pushed against heavy accessory structure
What does bending of hair cells cause
Receptor potential
What happens if stereocilia is bent one way
They depolarise, firing rate of action potential increases, basement membrane goes up
What happens if stereocilia is bent other way
They hyperpolairse, firing rate of action potential decreases, basement membrane goes down
Why do these cells work
Cilia are stuck in accessory structure - if not there - they’d just go up and down - never stimulated
What are stereocilia bathed in
Endolymph
What happens when stereocilia is bent
Opens K+ channels = K+ enters hair cell down its conc gradient and depolarises it
Depolarisation
Summary of depolarisation hair cell
Basement membrane up - cilia bends - opens K+ channels = K+ flows in hair cell - depolarises
How are cilia attached
By threads and the bending physically opens up ion channel
Role of outer ear
Collects the sound and channels it to the tympanic membrane = vibrates
Role of middle ear
Amplifies the sound
Vibrations from tympanic membrane to oval wind
Role of inner ear
Low frequency sound stimulate hair cells distant from the stapes, while high frequency sounds stimulate hair cells close to the stapes. The pattern of hair cells stimulated allows the brain to ‘interpret the sound as any given sound stimulates a specific combination of hair cells.
How can sounds be localised
Time of arrival differences
Intensity differences
What is conduction deafness
Sound not conducted to middle of ear, wax, middle ear inflammation, sclerosis of ossicle etc.
What is sensineural deafness
damage to neural structures such as hair cell damage, damage to 8th nerve etc.
What is sinnitus
Continuous ringing/clicking sound in abscence of auditory stimuli
What is the vestibular system
This forms the basis of our sense of balance and acceleration.
What is the vestibular system
This forms the basis of our sense of balance and acceleration.
What modalities does balance involve
tactile receptors in contact with the floor
vision
but without the information about movement and head position provided by the vestibular system these are insufficient
What happens if vestibular system is not working
Can’t keep balance
Is vestibular system conscious or unconscious
unconscious
What does vestibular system control
aspects of our eye movements
What does vestibular system tell you
Where head is in space and how head is moving
What makes upp vestibular system
The utricle, saccule and semi-circular canals
What is structure of vestibular sensory hair cells
The membranous labyrinth of the vestibular system is lined with epithelial cells.
In some areas these cells are modified into sensory hair cells ( receptor cells )
The surface of the hair cells contain cilia, one of which is at the side of the cell and is larger (kinocilium)
The base of the hair
cell joins a sensory neuron
Morphologically and physiologically polarised ( lobsided )
What happens if stereocilia are bent towards kinocilium
depolarise, and the afferent firing rate increases.
What happens if stereocilia are bent away from kinocilium
kinocilium afferent firing rate decreases
When is sensory neuron tonically active
At rest
What is meant by physiologically polarised
React differently depending which way you bend cilia
What is meant by morphologically polarised
Structurally one side of cell different to other
the kinocillium is always on the edge of the cell
Bid side of cilia
Kinocilium
Other side of cilia
Opposite side to kinocillium
Where are hair cells in semi - circular canals found
in the ampullae
Where do hair cells in semi - circular canals sit
On a ridge/crest
What is cilia embedded in
gelatinous cupula (that completely blocks the canal)
Where are kinocillia on semi - circular hair cells
On the side facing the vestibule
side nearest the utricle
What fills whole ampullae
Cupula
What is bony labyrinth part of and what does that cause
part of the skull, so when the head moves so do the semi-circular canals
What happens when head it still
the hair cells are not bent, as the endolymph and skull are not moving
What happens when we turn head one way
The semi-circular canals will rotate in the same direction. The endolymph, however, will relatively move in the opposite direction (in fact, due to inertia it stays more or less in the same place). This endolymph will push against the cupula and bend the hair cells
What happens if you move head to left
Semi circular canal: to left
Endolymph ( fluid ) to right
They are opposite
The kinocillia in the left semi-circular canal will be bent towards the vestibule (excited), those on the right will be bent away from the vestibule (inhibited).
What can CNS determine
From the relative activity of all 6 semi-circular canals the CNS can determine the direction of movement
What type of acceleration do semi - circular canals respond to
Angular acceleration
Not respond to linear motion or constant speed
What happens in angular acceleration
With constant rotation the endolymph will catch up with the bony labyrinth and hair cells will no longer be stimulated.
When rotation ceases we get dizzy as relative endolymph movement is reversed.
Where are hair cells in vestibule located and what are these areas known as
one area in the utricle and one in the saccule
Maculae
What is utricle and saccule
Two bags in middle of bony labyrinth
What directions is macula in saccule
Vertical
What direction is macula in utricle
Horizontal
What are cilia embedded in
In a dense otolithic membrane = heavy
What do kinocilia in macula face
Striola
What happens if all hair cells are bent in a given direction
some will be excited and some inhibited.
Different directions of bending will stimulate/inhibit different populations of hair cells
Brain figuire out which way cilia is pushed knowing which hair cells is activated/inhibited
What acceleration do otolithic organs respond to
Linear acceleration
What happens when you bend head down
Otolithic membrane moves down = bend cilia = depolarisation in some and inhibited in others
What acceleration detects gravity
Linear
What are causes of vestibular dysfunction
Lesions (either traumatic or by, for example, a tumour or an aneurysm) affecting the 8th cranial nerve. A good example is acoustic neuroma.
Ménière’s disease is an idiopathic condition of the inner ear related to endolymph ‘leakage’ (hydrops).
Labyrinthitis is an inflammation of the inner ear following a viral infection
When is receptor not a depolarisation
Vertebrate vision
