Special Senses Flashcards
1
Q
What is the stimulus for vision?
A
Light
2
Q
What is special about light that results in vision?
A
The only thing special about light is that we have special receptors that can interact with light.
3
Q
What is the units for visual wavelengths?
A
Nanometers
nm
4
Q
What wavelengths are our photoreceptors receptive to?
A
Approximately 400-750nm.
5
Q
What do we perceive variations in wavelength as?
A
Changes in colour
6
Q
What do we perceive variations in amplitude of wavelengths as?
A
Changes in brightness/intensity of light
7
Q
What is the job of the visual system?
A
To detect visible radiation and use it as a basis for formation of visual perceptions of the world to guide behaviour
8
Q
What is the special structure for light?
A
The Eye
9
Q
What makes special senses special?
A
They are all a result of a unique structure that house the particular receptor - whereas other systems have the receptor all over the body.
10
Q
What are the two basic components of the eye and their job?
A
An optical component that has the main job of collecting and focusing light into the plane of the retina.
A neural component that converts energy of light into patterned change of membrane potential that OTHER parts of the brain can decode to generate visual perceptions.
11
Q
What is the retina part of?
A
The Brain / part of the CNS.
12
Q
Why do we have a blind spot?
A
Because there are no photoreceptors on top of the optic disc where the optic nerve opening is (retina is not continuous).
13
Q
Where is the optic nerve located?
A
Back of the eye on the side closest to the nose.
14
Q
What is the sclera?
A
The whites of the eye.
it is a fibrous capsule.
15
Q
What is the pigmented disc of the eye?
A
The iris - what gives eye its colour.
16
Q
What is the black spot in iris?
A
Pupil
Pupil is perceive as a black spot but it is actually a hole in the iris. What we are seeing is black pigment at the back of the eye.
17
Q
What prevents internal reflections?
A
The black pigment at the back of the eye (what we see are the pupil).
Black absorbs all wavelengths and reflects nothing therefore no internal reflections. Because there is no light reflecting off the black pigment it means we can localise where light is coming from = locality.
18
Q
What is the Cornea?
A
The transparent structure in front of the iris.
Transparent because it is avascular (meaning it does not have any blood vessel and gets nutrients via transfusion from surrounding vessels).
19
Q
Draw the major structures of the eye.
A
Refer to slide image.
Should include:
Cornea
Aqueous humor
Anterior chamber
Iris
Lens
Posterior Chamber
Zonule Fibers
Cilary body
Sclera
Viteous humor
Retina
Fovea
Optic disc
Optic nerve
20
Q
What is the anterior chamber?
A
Structure that is filled with aqueous humor fluid.
It keeps pressure in the eye.
21
Q
What continuously produces aqueous humor?
A
Cilary body.
As aqueous humor is continuously produced it is also continuously drained away.
22
Q
What are the characteristics of the lens?
A
A fibrous capsule filled with crystallised cells.
It is avascular.
It is slightly elastic and flexible meaning the shape of the lens can change.
23
Q
What are ligaments attaching the lens to the ciliary body called?
A
Zonule Fibres.
24
Q
What is composition of the ciliary body?
A
Smooth muscle.
25
What is the vitreous humor?
The majority of the eye.
Mostly a solution of transparent protein - no tissues of cells in this area.
26
What is the optic disc?
Head of the optic nerve - where axons leave the back of the eye and go to visual centres in the brain.
27
What is the fovea?
A area of the retina.
It has the highest 2 point discrimination - bit of the brain/retina we use when we focus on something.
28
What is refraction?
Bending of light
29
What does refraction result in?
Upside down and back to front.
30
What is refraction related to?
The difference between the refractive indices of the two media, and to the curvature of the refractive surface.
31
What is the refractive index of water and why is this important?
1.333
Light coming from the air first hits water (tear drops that surround our eye) - the refractive index of air is 1.000. This change means that majority of refraction occurs when light goes from air to water because it is the biggest change in refractive index - most other areas of the eye have about the same refractive index as water.
32
What is refractive power?
Refractive power is the reciprocal of focal length in meters.
33
What is refractive power measured in?
Diopters
34
What is the focal point of a "relaxed" eye?
About 1.7cm (1/60).
Because the relaxed eye has a total refractive power of about 60 diopters.
35
What would the effect of a lens having more diopters be?
The more diopters a lens has, the closer it brings the light to a focus.
36
What are the three process of the "near response" that occur as you shift your gaze from distant to near objects?
(1) Accomodation
(2) Constriction of pupil
(3) Convergence of eyes
37
What is accomodation?
Contraction/relaxation of ciliary muscle to alter lens shape and change refractive power
38
What is happening during convergence of eyes?
(E.g., cross eyed).
Convergence of the eyes refers to the coordinated movement of both eyes towards each other to maintain focus on an object as it moves closer to the observer.
Object remain in register on corresponding parts of the two retinae.
39
What is the autofocus mechanism called?
The near response (it is the way we change refractive power of optical components).
40
What happens to refractive power when the lens becomes more round?
refractive power increases
41
If we want to bring the image forward what do we need to do to refractive power?
Adding refractive power brings the image forward.
When you increase the refractive power of the lens, you're essentially increasing its ability to bend light rays. This means the light rays converge more sharply, bringing the focal point closer to the lens.
42
What shape is the lens when the ciliary muscle is relaxed?
Flat = shallow curvature
43
Is the ciliary muscle relaxed when looking at something close up or looking at something far away?
Far away
44
What is happening to the zonular fibres when the ciliary muscle is relaxed?
They are taut
45
When gaze shifts to close up objects what happens to the parasympathetic activity and beyond that allows you to see close up object?
It increases the parasympathetic activity of the ciliary muscle causing it to contract.
Tension is removed from zonular fibers.
Lens becomes more spherical due to natural elasticity.
Eyes total refractive power increase from about 60 up to about 75 diopters.
46
What happens to the size of the pupil when you look at something close up and why?
Decreases in size because ciliary muscle contracts.
47
What are 5 optical defects?
Myopia
Hypermetropia
Astigmatism
Presbyopia
Cataract
48
What is emmetropia?
Normal vision - 20/20
49
What is myopia?
Short sighted.
Myopia occurs when the eyeball is too long or the cornea is too steep, causing light rays to focus in front of the retina rather than directly on it. As a result, distant objects appear blurry, while close objects can be seen more clearly.
To correct myopia, concave (diverging) lenses are used. These lenses help to diverge light rays before they enter the eye, allowing them to focus correctly onto the retina. This effectively shifts the focus point back onto the retina, improving distance vision.
50
What is hypermetropia?
Far sighted.
Hypermetropia occurs when the eyeball is too short or the cornea is too flat, causing light rays to focus behind the retina rather than directly on it. This results in blurry vision, particularly when looking at close objects, while distance vision may remain relatively clear.
To correct hypermetropia, convex (converging) lenses are used. These lenses converge incoming light rays before they enter the eye, allowing them to focus correctly onto the retina. This brings the focus point forward onto the retina, improving both distance and near vision.
51
What are optical defects?
Abnormalities in the shape and size of the eyeball.
52
What is astigmatism?
Where the eye ball is aspherical (more of a rugby ball than a soccer ball).
The result of this is that there are different amounts of refraction in different planes (different refraction dependant on where the light comes from).
53
What corrects astigmatism?
Cylindrical lens
54
What is presbyopia?
Age related loss of accommodation = caused by lens losing elasticity.
55
What does the elasticity of the lens fall from children --> 45/50 year --> 70 year and the consequence on near point?
Therefore accommodation falls from about 15 diopters in children to 2 diopters at around 45-50 years and essentially 0 at 70.
recedes from 10cm at 20 years to 80cm at 60 years.
56
What lens is required to correct presbyopia?
Convex - restore near vision
57
What is a cataract?
Where the lens becomes opaque due to the lens being broken up inside lens capsule.
Occurs predominately with age but some children (Alice) are born with it.
58
How is a cataract fixed?
Plastic lens - but plastic is not flexible so therefore no accommodation so require convex lens.
59
Where is the neural circuit of the eye?
Retina
60
Where in the neural circuit are photoreceptors (light sensitive cells) located?
Furtherest from the light.
61
What are the three interneurons in the eye neural circuit?
Bipolar cells
Amacrine cells
Horizontal cells
62
What are the retinal ganglion cells?
The only cells within eye neural circuit with axons. They send information from retina to other visual centres in the brain.
63
What cells are pushed out in the Fovea Pitt and what is the effect of this?
Ganglion and interneuron cell bodies pushed out to side.
Means that photons have a more direct path to reaching photoreceptors as less intervening substances that may reflect light.
64
What are the proportion of Rods and Cones in eye?
More Rods than Cones in retina.
But less rods than cones in fovea.
65
What are the two types of photoreceptors?
Rods
Cones
66
Are rod or cones used for night vision?
Rods function in low light
67
Do rods or cones detect colour?
Cones - require relatively hight light levels - day and twilight vision.
68
What are the three colours types that Cone photoreceptors detect?
Red, Green and Blue light
69
Why do rods have bigger surface areas than cones?
Rod are made up of individual free floating discs whereas cones are made up of folding membrane.
70
What are photopigments?
Proteins that are sensitive to different wavelengths of light - I is what gives photoreceptors the capacity to response to light.
71
What are the two components that photopigments consist of?
Opsin (membrane spacing protein)
Retinal (chromophore)
72
What type of opsin do rods have?
Rhodopsin
73
What type of opsin do cones have?
Photopsin
Either Short (Blue), Medium (Green) or Long (Red)
74
What is retinal a derivative of?
Vitamin A
75
Describe phototransduction in the dark:
Phototransduction in the dark is essentially the excitatory process.
The inactive retinal is in its 11-CIS isoform.
We have enzymes in the eye making lots of cyclic GMP.
cGMP gated channels open and there is a influx of cations including Na (sodium).
Positive charge coming in means that photoreceptors are a little depolarised due to the cGMP.
Depolarisation results in releasing lots of neurotransmitter glutamate onto the interneuron terminals.
76
Describe phototransduction in the light:
Phototransduction in the light is essentially the inhibitory process.
Light energy is absorbed and used to convert retinal from CIS to TRANS isomer. TRANS is the active isoform.
cGMP is broken down - this results in less cGMP and gated channels close. Therefore less Na influx, photoreceptors hyperpolarised and less glutamate released.
77
What is the one thing that light does?
Converts retinal from CIS to TRANS form.
Everything else in the eye is all a consequence of this and not because of light itself.
78
What are the only cells in the retina that fire AP?
Retinal ganglia cells.
79
What is the perception of colour created by?
Relative activation of the three cone types of photopigments (S, M, L).
80
How can you become colourblind?
Opsin is a protein which is a product of a gene - therefore colour blindness can be inherited. Can also be acquired due to disease.
81
Why are males more likely to be colour blind than females?
Colourblindness affects 8% of males and 0.5% of females.
This is because the gene encoding production of M and L photopsin are on the X chromosome. Therefore males only get one of them so if have it, it will be expressed.
82
What do electrical responses of ganglion cells depend on for retinal processing?
The spatial and temporal pattern of light stimulation on the retina.
83
What role does receptive fields have in retinal processing?
The input to each ganglion cell arises from neighbouring photoreceptors in a circumscribed area of the retina = the cells receptive fields.
RF are roughly circular and divided into two parts = central and the surround.
Ganglion cells respond optimally to the differential illumination of the centre and the surround.
84
What is light illumination?
Contrast in the light - enables us to see shapes.
85
What are the two types of ganglion cell receptive fields?
On-centre and off-centre.
86
If you have an on-centre RF and light falls on the surround what happens?
If more light on the surround you inhibit AP.
If more light in centre then it is excited.
The opposite is true for off-centre RF.
87
What is the effect of large receptive fields on acuity?
Low acuity (Acuity meaning 2 point discrimination).
88
What is the pathway of information from the eye to the primary visual cortex?
Retina
Optic Chiasm
Optic Tract
Material Geniculate Nucleus
Primary Visual Cortex
89
If someone is in your left visual space where do axons from each eye go?
If in left visual space light reflects to the nasal of left eye and temporal of right eye.
Information is brought together on the same side of the brain due to different crossing pathways at chiasm - ipsilateral (same) projection of axons from right eye and contralateral (opposite) projection from left eye.
Means that information concerning images from visual space falling on equivalent parts of the two retinas are brought together for central processing.
Axons got to the primary visual cortex at the dorsal end of the brain for first visual processing.
90
What are the four subcortical visual nucleus that ganglion cell axons project to?
Superior Colliculus
Lateral Geniculate Nucleus
Pretectum
Suprachiasmatic Nucleus
91
What is the Superior Colliculus?
The subcortical visual nucleus that sends information of head movement to move eyes along with it to give stable vision.
Concerned with eye movements and orientation to visual stimuli.
92
What is the Lateral Geniculate Nucleus?
The subcortical visual nucleus concerned with the sensation of vision.
93
What is the Pretectum?
The subcortical visual nucleus that is concerned with the control of pupils - for focus.
94
What is the Suprachiasmatic nucleus?
The subcortical visual nucleus that controls diurnal rhythms (senses daylight).
95
What is sound?
Pressure waves in the air
96
What determines the pitch of sound?
Frequency of pressure waves (number of cycles per second).
97
What determines the loudness of sound?
Amplitude of pressure waves
98
What is the unit of frequency?
Hertz
99
What is volume of noise measured in?
Decibels (dB)
100
What range of frequency are humans most sensitive to?
200-1000 HZ e.g., we can hear 0dB at these frequencies.
101
What is the special structure that allows us to hear (what is the hearing apparatus)?
The ear
102
What is the human threshold of hearing?
Around 50 Hz
103
What happens to the threshold of hearing curve when someone has a hearing impairment?
The curve moves up - e.g., require higher dB (louder volume) to be able to hear.
104
What dB is normal speech?
60dB
105
At what dB would noise cause pain and immediate permanent hearing damage?
140dB
106
How many components are there in the ear?
Three: External ear, Middle ear and Inner ear.
107
Which component of the ear is not air filled?
Inner ear
108
What is the inner ear filled with?
Fluid
109
What are the two main components of the inner ear?
Cochlea and The Vestibule System.
The inner ear is a network of fluid filled tubes.
110
What is "popping" of the ear drums?
The air pressure equalising across the tympanic membrane.
111
What is the auditory apparatus of the ear?
Cochlea
112
What are the names of the three small bones in the middle ear?
Malleus, incus and the stapes.
Collectively known as the ossicles.
113
What is the function of the ossicles bones?
Delivers vibration caused by pressure waves across the middle ear cavity to stapes which is touching oval window of inner ear.
114
What does the external ear consist of?
Pinna
External auditory canal
Tympanic membrane
115
What is the pinna and why is its structure important?
The folded cartilage covered in skin.
Shape and depth of the pinna is important for reflecting sound waves into external auditory canal.
116
What is the external auditory canal?
The tunnel that leads from external of head to the tympanic membrane (the ear drum).
117
What are both the Scala vestibule and Scala tympani filled with?
Perilymph fluid
118
What is the Scala Media filled with?
Endolymph fluid
119
What is the composition of endolymph fluid?
Like intracellular fluid = high in potassium.
(Fluid of the Scala media)
120
What is the composition of perilymph fluid?
Like extracellular fluid = high in sodium
(Fluid of the Scala tympani and Scala vestibuli)
121
What are the three cross section compartments of the cochlea?
Scala Vestibule
Scala Media
Scala Tympani
122
What are the three membranes in the cochlea and which compartment does each surround?
Scala Vestibule surrounded by Reissner membrane
Scala Media surrounded by Tectorial membrane
Scala Tympani surrounded by baslar membrane
| very rarely, my teeth, turn black
123
What is the Organ of Corti and where is it located?
A collection of cells where signal transduction of the ear occurs.
Located in the middle compartment of cochlea = scarla media.
124
Does potassium or sodium cause depolarisation in the ear and why?
Potassium - because the Organ of Corti is located in scarla media which is filled with endolymph fluid which has a high concentration of potassium.
125
What is significant about the basilar membrane?
The membrane has different flexibility along its length e.g., wide and floppy at one end and narrow and stiff at the other end.
The wide and flopping ends natural frequency of oscillation is lower = it oscillates in time with low frequency sounds.
The narrow and stiff ends natural frequency of oscillation is higher = it oscillates in time with high frequency sounds.
126
What are the steps taken for the ear to transfer pressure waves to AP?
Pressure waves from the air enter external auditory canal > deflects the tympanic membrane > middle ear bones move > staples middle ear bone causes the membrane in oval window to move > basilar membrane moves at the point along it's length that is in tune with the frequency of the pressure waves > deflection of stereocelia on overlying organ of corti (cells in scale media) > opening of mechanoreceptors > influx of K+ > Depolarisation at a location along the Basilar Membrane that corresponds to the pitch of the sound > AP to auditory cortex.
127
What are stereocilia?
The hair cells of the ear
128
What membrane of the cochlea overlies stereocilia cells?
Tectorial membrane
129
What type of ion channels are located on the tips of steocilia?
Mechanically gated K+ ion channels
130
What is the kinocilium?
The specialised single cilia at the end of every row of sterocilia - it is the longest one.
131
What is happening during positive mechanical deformation?
Sterocilia are moving towards the kinocilium causing mechanically gated K+ channels in sterocilia to open = depolarisation.
132
What is happening during negative mechanical deformation?
Sterocilia are moving award from the kinocilium causing mechanically gated K+ channels in sterocilia to close = hyper-polarisation.
133
Is the process of signal transduction faster for hearing or vision?
Hearing - because sound wave directly opens ion channels itself (mechanically gated) - no secondary messengers involved.
134
What are the four sound qualities we can discriminate?
Pitch
Intensity
Duration
Direction
135
What does the frequency of sound waves determine?
Pitch
136
What does the frequency of AP determine?
Loudness
137
How do we discriminate the direction of sound?
The time difference in activation of receptors in each ear and by the intensity (loudness) difference in each ear.
138
What are the four central auditory pathways?
1) Auditory receptors in cochlea
2) Brain stem neuron's
3) Medial Geniculate Nucleus
4) Auditory cortex (each side receives information for both ears)
139
What is deafness?
A raised threshold to sound stimuli
140
What are the two types of deafness?
Conduction Deafness
Sensorineural Deafness
141
What is conduction deafness?
Impair sound transmission through out or middle ear due to blockage or infection.
Can be generated by yourself by sticking fingers in ears which blocks sound waves.
142
What is sensorineural deafness?
Damage to receptors or neural pathways - can be due to exposure to loud noises, some antibiotics, tumour or meningitis.
Arises due to damage to auditory apparatus.
143
What does exposure to loudness damage that leads to deafness?
Hair cells
144
Can damage to hair cells be repaired?
No - once you loose them they don't grow back.
145
What is the importance of the vestibular system?
The sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance e.g., it mediate our sense of balance and gives the brain information about what the head is doing.
Keeps image of the world on the retina stable.
146
Where is the vestibular system?
The other part of the inner ear - that is not the cochlea.
147
What does the vestibular system report?
Acceleration (change in velocity).
148
What are the two types of acceleration that the vestibular system reports?
Linear
Angular (rotational)
149
What is the stimulus for the vestibular system?
Change in head position (typically reliant on gravity).
150
Why can we not rely on visual signalling for balance?
Because visual transduction is slow due to secondary messenger system.
Whereas, vestibular transduction is fast as does not rely on secondary messengers.
151
What are the components of the vestibular system?
Otolith organs for linear acceleration reporting.
Semicircular canals for rotational acceleration reporting.
152
How many semicircular canals do we have in total?
6 (three in each ear).
153
What type of fluid is the semicircular canals filled with?
Endolymph
154
What is the swelling at the based of each semicircular canal called?
Ampulla
155
Where in the ampulla do hair cells sit?
Cupula
156
What part of the vestibular reports on linear acceleration?
Otolith organs (saccule and utricle)
157
What is the hair cell membrane of the ampulla called?
Crista ampullaris
158
During acceleration what does the movement of enclosed endolymph cause?
Pushed against the cupula which displaces the hairs on the hair cells causing the opening of mechanical gated ion channels = influx of K+.
159
At rest are AP firing from vestibular hair cells?
Yes - they have a resting rate of discharge meaning that they can signal in two directors (increase or decrease - if at rest was 0 then wouldn't be able to decrease).
160
What direction do the hair cells go to cause an increase in the frequency of AP?
Towards the longest hair cell (towards the kino)
161
Does the Utricle or Saccule report on vertical linear acceleration?
Utricle = horizontal
Saccule = vertical
162
What makes otolith organs top heavy?
Otoconia - stones of calcium carbonate located onto of fluid.
163
What is information from vestibular system used for in the brainstem and how?
stabilise eyes - through oculomotor nuclei
stabiles the head - via input from neck muscle motoneurons
maintain balance - via pathways to cerebellum and spinal cord
164
What are the three vestibular disorders?
Vertigo
Motion Sickness
Bedspins
165
What is vertigo caused by and its symptoms?
Caused by diseases affecting the vestibule or its afferent fibres.
Causes illusion of movement, dizziness, nausea.
166
What is motion sickness caused by?
Caused by mismatch between visual and vestibular information.
167
What helps motion sickness?
If the horizon is visible
168
What causes 'bed-spins'?
Caused by alcohol - the ethanol infiltrates the cupula, lowers elasticity and causes it to float creating perception of movement when your not actually moving.
169
What are Ototoxic drugs?
Drugs that are known to be harmful to hair cells = can result in temporary or permanent hearing loss and disorders of balance.
170
What type of antibiotics are amongst the worst ototoxic drugs?
Aminoglycoside antibiotics e.g., gentamicin, streptomycin and kanamycin.
171
What helps reduce the effects of ototoxic drugs?
Vestibular rehabilitation
172
What is the Cupula?
A gelatinous matrix
173
What causes mechanically gated ion channels of the semicircular canals to open?
During rotational acceleration the enclosed endolymph (due to cupula blocking) pushes on the cupula which displaces the hair cells that sit within it. The displacement of hair cells opens mechanically gated ion channels and causes depolarisation.
174
Are sterocilia more active on the left or the right if the head turns to the left?
Left
175
What direction does endolymph in the ampulla move if the head accelerates to the left?
right - endolymph moves in opposite direction to head acceleration in the ampulla.
176
What do vestibule-ocular reflexes do?
Promote stable images on the retina during head movements - Nystagmus is a type of vestibule-ocular reflex.
177
Is the semicircular canal in the same plane as acceleration the only canal stimulated?
No - it is just most stimulated by acceleration in its preferred plane.
178
What type of receptors are used to sense taste and smell?
Chemoreceptors
179
What are 5 purposes of having chemical sense (taste and smell)?
Sample the content of food/drunk for nutrient content, palatability and toxicity.
Generate sensory perceptions in response to ingested and inhaled chemicals.
Guide appetite, trigger processes for absorbing nutrients.
Avoid poisons and chemical hazards.
Find a mate.
180
What percent of odours are 'pleasant'?
20%
181
Where are taste buds located?
Within tongue papillae - on upper surface of the tongue.
182
What are the three types of tongue papillae?
Foliate - outside edge
Circumvallate - back of tongue
Fungiform - front/around outside
183
What type of cells are taste bud cells?
Columnar epithelial cells (come in clusters)
184
What type of cells do taste buds sit within?
Epithelia cells
185
Where else other than the tongue are taste buds located?
Palate
Pharynx
Epiglottis
186
What is the turned over half life of sensory cells?
10-14 days
187
What are the three types of cells found in each taste bud?
Type 1 (support)
Type 2 (chemoreceptors = GPCR)
Type 3 (ion channels)
188
What is the role of Type 1 taste bud cells?
They are essentially support cells (glial like role) - they mop up transmitters and K+.
Are not directly involved in taste sensation.
189
What type of receptor do Type 2 taste bud cells have?
GPCR chemoreceptors
190
What are the 5 detectable classes of taste?
Sweet
Sour
Salt
Bitter
Umani (amino acids)
191
How does signal transduction occur in Type 3 taste bud cells?
through ion channels
192
What is sweet taste stimulated by?
Sugars
193
What is sour taste stimulated by?
Acids (esp organic acids like citric and acidic acids)
194
What is salty taste stimulated by?
Sodium (NaCl)
195
What is bitter taste stimulated by?
Typically alkaloids (but complex)
196
What is umani taste stimulated by?
Amino acids esp glutamate
197
What molecules/neurotransmitters are involved in taste signalling in taste buds?
ATP
GABA
Serotonin
ACh
198
What is different about type 2 receptor cell mechanism to sensing taste?
In cases of type 2 receptor cells - release of signalling molecule is via a non-vesicular mechanism (does not involve the formation or transport of vesicles - instead relies on other mechanisms of transport).
199
What tastes are type 2 taste bud cells receptive to?
Sweet, Umani, and Bitter
200
Is insulin released before or after blood sugar rises?
Before
201
As well as indicating sweet substances in the mouth what else does T1R (homodimeric GPCR) activation initiate?
Cephalic Phase Insulin Release
202
What is the name of the G protein complex that is activated by T1R?
Gustducin
203
What does gustducin activate?
PLC
204
What does PLC activation result in?
Release of Ca2+ from the ER --> depolarisation (via TRPM5) --> release of signalling molecule via atypical non-vesicular mechanism.
205
What type of channel is the TRPM5?
Temperature sensitive (why ice cream tastes sweet when it is warmer because results in bigger release of neurotransmitters thought channel and therefore bigger response).
206
What does binding of sweet to sweet receptor cause an increase in?
IP3
207
What is the umani taste?
"savoury, delicious"
208
What is umami sensed by and stimulated by?
Sensed by Type 2 cells, stimulated by amino acids, esp glutamate and asparate
209
What type of T1R is umami detected by?
T1R subtype GPCR heterodimers
210
What does umami promote?
Eating behaviour to ensure uptake of essential amino acids
211
What type of GPCR are involved in bitter taste?
Monomeric GPCR
212
What results in depolarisation for sour taste?
Accumulation of protons via Otop 1 > reduces pH and blocks the leaky K+ channels which normally keep cells at RMP. Therefore, results in depolarisation and the influx of Ca2+ results in release of neurotransmitter.
213
Does salty taste use a G-protein signalling pathway?
No
214
How does Na+ enter cells?
Through ENaC - epithelial Na channel
215
What drug blocks the epithelial Na channels?
Amiloride
216
What makes other 'tastes' such as spiciness not true tastes?
Because the stimulating chemicals do not interact with specific oral taste receptors
217
What senses spiciness?
heat and pain sensitive nerve fibres in the mouth that are stimulated by chemical such as capsaicin and piperine
218
What is capsaicin?
An active component of chili peppers - plants from the genus capsicum
219
What is piperine?
The alkaloid that gives pepper its pungency
220
What nerves innervate anterior tongue taste buds?
Chorda tympani
221
What nerves innervate posterior tongue taste buds?
Glossopharyngeal
222
Where do afferent fibres of central taste pathways synapse?
Medulla
223
Is most gustatory input to the brain crossed or uncrossed?
Uncrossed
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What does hypolglossal mean and how does it relate to the tongue?
Hypolglossal means the area below the tongue - location where the main motor nerve supply of the tongue goes.
225
Where is the taste cortex (gustatory cortex)?
below parental lob and behind somatosensory cortex (nearest to bottom of cortex map that has lips/tongue etc)
226
What are odorant's inhaled and swirled around by?
Nasal conchae
227
What do ordorants dissolve in?
Water mucus in the roof of the nasal cavity - e.g., snot. Then binds to receptors within it.
228
What projects from olfactory receptors?
Non-motile cilia
229
Do olfactory hair cells move?
No - they are non motile.
230
What do odourants interact with?
Receptors (GPCR) on the olfactory cell membrane
231
Once olfactory GPCR are activated what happens?
There is an increase in cAMP which causes the opening of cation channel and cation entry causing depolarisation.
This causes the opening of voltage gated Cl- channels and Cl- to go out of the cell increasing depolarisation.
This carries the AP to olfactory bulb.
232
What is are olfactory cells?
Neurons
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Where are olfactory bulbs?
Underside of frontal lobes
234
What do olfactory axons form?
The first cranial nerve
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Where do olfactory bulb axons pass to?
Olfactory cortex in limbic system - the part of our brain associated with emotion, food-getting and sexual behaviour.
236
What is flavour the sum of?
Input from 5 taste cells
Input from odour receptors
Product temperature
Product texture
Spiciness (pain)
Also influence by appearance
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Can one odorant activate more than one receptor type?
Yes - the combination of activated receptors is interpreted in the brain to give the quality of the odour.
238
What are the three nerves in the central pathway that taste buds can innervate?
Chorda tympani nerve (anterior taste buds)
Glossopharyngeal nerve (posterior taste buds)
Vagus Nerve (some)
