Special Senses Flashcards
1
Q
What is the vestibular system?
A
Special proprioceptive system.
Maintains position of eyes, trunk, limbs in relationship to movements and positioning of head.
Information on position, movement/direction and speed.
2
Q
Where are the receptors for the vestibular system?
A
Inner ear - cause action potential in CNVIII (vestibulocochlear).
3
Q
Describe the vestibular apparatus?
A
Located in bony labyrinth (membranous structure within bony structure); 3 semicircular canals (anterior, lateral, posterior), utricle, saccule.
Canals are filled with endolymph and at the base of each is an ampullae (location of receptors).
4
Q
Which part of the vestibular apparatus detects rotation/acceleration?
A
Semicircular canals.
Anterior/ventral = up/down (nod)
Posterior/dorsal = side to side (ear to shoulder)
Lateral = side to side (saying no)
5
Q
Which part/s of the vestibular apparatus are responsible to detecting linear acceleration?
A
Utricle - forwards/backwards
Saccule - up/down
6
Q
Where are the receptors responsible for detection of movement found?
A
Ampullae of semicircular canals.
7
Q
What is a cupula?
A
Gelatinous area surrounding stereocilia. Separated from endolymph by membrane.
8
Q
What signals do the stereo cilia transmit when upright/at rest?
A
Partial depolarisation.
Low frequency in afferent neuron.
9
Q
Which direction do stereo cilia bend in relation to movement?
A
In the opposite direction.
10
Q
What signal is transmitted when stereocilia bend away from the kinocilium?
A
Hair cells become hyper polarised and the frequency of AP in afferent neuron declines.
11
Q
What signal is transmitted when stereocilia bend towards the kinocilium?
A
Hair cells become depolarised and frequency of AP in afferent neuron increases.
12
Q
What difference is there between hair cells in the utricle and saccule?
A
Utricle - hair cells are in horizontal rows, stereocilia extend vertically.
Saccule - hair cells are in vertical rows, stereo cilia extend horizontally.
13
Q
What is the vestibule-occuar reflex?
A
Allows maintenance of fixed gaze by counteracting head movement.
Fibres originate in semicircular canals, project to medial and lateral vestibular nuclei. One stimulatory motor pathway to lateral rectus muscle of (R) eye, one to (L) eye - initiates contraction.
14
Q
What do the inhibitory pathways of the vestibule-occular reflex do?
A
Cause relaxation of opposite rectus muscles allowing eye movement in opposite direction to head movement.
15
Q
Which descending tract allows the cerebellum to influence movement and posture as well as govern righting reflexes?
A
Vestibulospinal tract
16
Q
What are some of the signs/symptoms of vestibular lesions?
A
Loss of coordination between head, trunk and limbs (imbalance).
Head tilt (ventral ear towards affected side).
Circling towards affected side.
Loss of extensor tone on affected side, increased tone on contralateral side.
Tips/rolls/leans/falls towards affected side.
Nystagmus and strabismus.
Asymmetric ataxia.
17
Q
What determines loudness in sound waves?
A
Amplitude
18
Q
What determines pitch in sound waves?
A
Frequency of waves.
Low frequency=low pitched waves
19
Q
What is the function of the middle ear?
A
Selectively amplifies sound pressure at different frequencies by factor of 30-100.
Translates low impedance signals by amplification by increasing pressure gain around the oval window - this is achieved by focusing sound waves from a large diameter tympanic membrane onto smaller oval window.
20
Q
What is the function of the eustachian/auditory tube?
A
Connects middle ear with pharynx.
Maintains neutral pressure within middle ear.
Equilibrate pressure by swallowing or yawning.
21
Q
Which two muscles regulate sound to the inner ear?
A
Tensor tympani
Stapedius
22
Q
What are the functions of the ossicles?
A
Amplification of the motion produced by initial sound waves.
23
Q
What are the stages of amplification of sound in the middle ear?
A
- Sound waves hit tympanic membrane.
- Tympanic membrane vibrates at same frequency as sound waves and with proportional amplitude.
- Vibrations of tympanic membrane cause malleus to oscillate.
- Ossicles amplify motion produced by initial sound waves.
- Oscillation of stapes transferred through oval window to fluid in cochlea.
24
Q
What is the environment of the middle ear? And inner ear?
A
Middle ear - air
Inner ear - aqueous
25
What occurs in the cochlea?
Sound waves are transformed to neural impulses.
| Amplifies and decomposes sound information into simpler elements.
26
Describe the anatomy of the cochlea?
2 membranes that seperate 3 fluid filled compartments.
Vestibular and basilar membrane seperate cochlea into scala vestibuli, scala tympani and scala media.
Membranes join at helicotrema.
27
What is the cochlea separated from the middle ear by?
Oval and round windows.
28
What is the name of the liquid present within the scala vestibuli and scala tympani?
Perilymph (similar composition to CSF)
29
Describe the transmission of sound through the cochlear?
Vibrations in oval window -> waves in perilymph of scala vestibuli -> travel through scala tympani -> motion in round window (also dissipates sound waves).
30
What is the name of the liquid present within the scala media?
Endolymph (similar composition to intracellular fluid)
31
What is the end-cochlear potential?
Electrical potential difference between peri- and endolymph
32
What is the organ of corti? What is it composed of?
Sensory organ for sound.
Located on top of basilar membrane within scala media.
Contains hair cells, supporting cells and overlying tectorial membrane.
33
Where are stereo cilia tips embedded?
Tectorial membrane
34
What do hair cells contain?
Stereocilia
35
What is the difference between inner and outer hair cells/.
Inner - begin sound transduction when bent.
| Outer - modulate sensitivity of inner hair cells and receive primarily efferent innervation.
36
What is cochlear function dependent on?
Ability of basilar membrane to vibrate in response to sound.
37
What is the name of the specialised epithelial cells that detect sound vibrations?
Hair cells
38
What causes stereo cilia to move? Which portions of the cochlear are the stereo cilia and perilymph in?
Movement of perilymph.
| Perilymph is in scala vestibuli, stereotipia are in scala media.
39
What are the stages of sound transduction throughout the whole auditory canal?
1. Sound waves enter external auditory meatus, hit tympanic membrane and cause it to vibrate.
2. Bony ossicles vibrate in response and transit vibration to oval window.
3. Vibrating oval window creates waves in perilymph within cochlea.
4. Perilymph waves cause vestibular and basilar membranes to deflect/move relative to one another.
5. Causes stereo cilia to bend back and forth.
6. Causes opening and closing of mechanically gated K channels.
40
What are stereo cilia?
Highly specialised cells that contain actin cytoskeleton.
Taper at basal end forming 'pivot' with membrane.
Graded in height and arranged in bilaterally symmetrical manner.
Tips are connected via fine filament called 'tip-link'.
41
Which nerve are hair cells and stereo cilia innervated by?
Afferent branch of vestibulocochlear nerve.
42
What happens when hair cells become depolarised?
Mechanically gated K channels open allowing it to flood into cell.
Causes opening of voltage gated Ca channels because surrounding endolymph is high in K.
Causes release of NT onto nerve terminals.
43
What is the function of 'tip-links'?
Where movement of stereo cilia is translated into receptor potential.
Stretching of the tip links in relation to movement of stereo cilium opens K channels.
44
Describe what is occurring when there are no sound waves present and stereo cilia are extending straight up?
Small amount of tension on tip links holds K channels partially open.
Small influx of K and partial depolarisation.
Opening of some Ca channels into hair cells.
Small amount of NT release by exocytosis communicating with afferent branch of vestibulocochlear nerve.
Low frequency of action potentials.
45
What occurs when the stereo cilia bend towards the kinocilium?
Increased tension on tip links, K channels open more.
More K influx, more depolarisation, more Ca channels open.
Increased NT being released.
Increased frequency of AP in afferent cochlear neuron.
46
What is the kinocilium?
Tallest stereocilium
47
What occurs when the stereo cilia bend away from the kinocilium?
Less tension on tip links causing K channels to close.
Hair cell becomes hyperpolarised compared to resting state and so voltage gated Ca channels close and less NT released.
Decreased AP frequency compared with resting position.
48
High frequency sounds are detected where in the cochlea?
Closer to the oval window, basilar membrane is narrower and stiffer.
49
Low frequency sounds are detected where in the cochlea?
Deeper within cochlear, near helicotrema. Basilar membrane is wider and more flexible here.
50
What is the coding of frequency (pitch) based upon?
Location of hair calls on the basilar membrane that are stimulated.
51
What effect do louder sounds have on stereo cilia?
Cause stereo cilia to bend further in either direction, therefore larger receptor potentials and increased NT release.
52
What is conduction hearing loss?
Damage to external or middle ear (tympanic membrane, ossicles, etc).
Lowers efficiency with which sounds waves are transferred to inner ear.
53
What are the steps of the neural pathway for sound?
1. Afferent signals from hair cells travel in cochlear nerve, branch of vestibulocochlear nerve (CNVIII).
2. Terminate in cochlear nuclei.
3. Second order nerves carry signals to medial geniculate nucleus (thalamus).
4. Third order neurons then carry info to auditory cortex of brain (ascend bilaterally - info from one ear processed on both sides of brain).
5. Organisation within auditory cortex is tonotopic (maps frequency of sound).
54
What is neurosensory deafness?
Damage to inner ear (cochlea, nerve, hair cells).
| Often difficult to determine which exact part is damaged but ultimately transmission of AP to brain is decreased.
55
What is the retina?
Inner most layer of the eye.
| Contains photoreceptors, fovea and optic disk.
56
What do rods detect?
Low levels of light.
| Allow animals to see in black and white.
57
What do cones detect?
Detect colour.
Require more light to be activated.
Provide greater acuity.
58
What is the optic disk?
Area where multipolar ganglion cells merge into optic nerve.
59
What is the fovea?
Central part of retina where light from centre of vision is transmitted to.
High concentration of cones, no rods.
60
What is the macula?
Surrounds fovea, has cones as well as increasing number of rods as distance from fovea increases. No blood vessels.
61
Where is the highest concentration of cones in the eye?
Fovea, sharply decline either side of this.
62
What are the only photoreceptors present in periphery of retina?
Rods
63
What are is the function of photoreceptor cells?
Focus light rays from the environment.
64
Which layer of the retina are rod and cone photoreceptors present in?
Outermost/peripheral layer.
| Furthest from light source and face choroid.
65
What other cell types are present in the retina and which layers do they form?
Bipolar cells - middle layer
Amacrine and horizontal cells - middle layer
Ganglion cells - inner cell layer (deepest)
66
What is the function of bipolar cells?
Intermediary cell that transmits electrical signals from rods and cones to ganglion cells.
67
What is the function of ganglion cells?
They are the cell bodies of the optic nerve.
| Synapse with bipolar cells to transmit electrical signal from rods and cones to CNS.
68
What is the Tapetum lucidum?
Structure that enables nocturnal animals to see in dimly lit situations.
Reflective layer behind retina - reflects light further simulating the rods.
69
What is required for the perception of depth?
Binocular vision
70
What is phototransduction? Where does it occur?
Conversion of light energy into electrical signals.
| Occurs in outer segment of retina.
71
What are the cell layers within the mature retina?
Choroid - retinal pigmented epithelium - photoreceptors outer segment - outer nuclear layer (rods/cones) - outer plexiform layer - inner nuclear layer - inner plexiform layer - retinal ganglion cell layer - vitreous humour.
72
What are the main roles of photoreceptors?
Conversion of light energy into electrical signals.
73
What are the two major classes of photoreceptors?
Rods and cones.
74
In which layer does the synapses of photoreceptor cells, bipolar cells and horizontal cells occur?
Outer plexiform layer.
75
What is the 3 neuron chain of phototransduction?
Photoreceptor - bipolar cell - retinal ganglion cell - lateral geniculate nucleus (thalamus)
76
Where are the cell bodies of amacrine and horizontal cells located?
In inner nuclear layer and processes in outer and inner plexiform layers.
77
What is the role of horizontal cells?
Maintain sensitivity to contrast over wide range of light intensities.
Lateral interaction between photoreceptor and bipolar cells.
78
Amacrine cells are post synaptic to...... and presynaptic to....
Bipolar cells.
| Retinal ganglion cells.
79
What is the role of amacrine cells?
Modulate visual signals in a range of ways.
80
Are there overall more rods or cones?
Rods
81
What are the characteristics of rods?
```
Black and white vision.
Night and dim light vision.
High sensitivity to light.
Low visual acuity (high convergence with bipolar cells).
Located peripheral retina
>100million.
```
82
What are the characteristics of cones?
```
Colour and day vision.
Respond to different wave lengths.
Low sensitivity to light.
High acuity (low convergence with bipolar cells)
located in fovea.
3 million
```
83
What is the first step of phototransduction and what does it involve?
Absorption of light via photopigment.
84
What is photopigment and what are its different forms?
Molecule that absorbs light, it has a light absorbing portion (retinal) and a protein (opsin).
1 type in rods, other 3 in cones.
Each absorbs best at different wavelengths;
Long (L) cones - red
Middle (M) cones - green
Short (S) cones - blue
Rhodopsin - rods
85
What is the function of opsin?
Determines which wavelengths are absorbed by altering the electromagnetic energies to which the retinal is sensitive.
86
What does light activation of photoreceptors cause?
Graded change in membrane potential and a corresponding rate of change in NT release onto postsynaptic neurons.
Light activation causes hyper polarisation of membrane potentials.
87
What electrical state are photoreceptors in when in the dark?
Depolarised.
88
What are the stages of phototransduction of light in rods when it is dark?
1. cGMP levels in cytosol are high.
2. Sodium channels open.
3. Sodium enters cell, causes depolarisation that spreads to terminal.
4. Ca channels open in response to depolarisation.
5. Ca enters cell, triggers exocytosis of NT.
6. NT cases graded potentials in bipolar cell.
89
What are the stages of phototransduction of light in rods when it is light?
1. Light absorbed by rhodopsin.
2. Restinal and opsin dissociate.
3. Transduction is activated.
4. Phosphodiesterase is activated.
5. cGMP levels in cytosol decrease.
6. Na channels close.
7. Hyperpolarisation due to decreased Na levels.
8. Ca channels close.
9. NT release decreased.
10. Graded potential in bipolar cell gets smaller.
90
True or false? Cones are relatively insensitive to light and require increased light levels for activation.
True
91
Do rods or cones have more effective adaptation mechanisms?
Cones.
| Allows them to return to resting state faster.
92
What is the rod threshold for activation?
Scotropic
93
What is the cone threshold for activation?
Mesotropic
94
Do dogs have colour vision?
Minimal, they have poor colour perception
95
How do photoreceptors communicate with bipolar and horizontal cells?
Release glutamate
96
In what order does a signal pass through the retinal cells?
Photoreceptor - bipolar and horizontal cells.
Horizontal cells also communicate to bipolar cells.
Bipolar cells communicate to ganglion and amacrine cells.
Amacrine cells also communicate to ganglion cells.
97
What is convergence?
Each photoreceptor cell communicates with less than one bipolar cell (eg. two photoreceptors both stimulate one bipolar cell).
98
What effect does convergence have on acuity?
Decreased convergence means increased acuity.
| Increased convergence means increased sensitivity to light.
99
Which retinal cells are responsible for lateral modulation?
Horizontal and amacrine cells.
100
What are some features of the macula?
Area of retina that supports high visual acuity.
Free of blood vessels.
Acuity greatest in centre - fovea.
101
Is there any convergence of cells within the fovea?
No, 1 cone communicates with 1 bipolar cell which communicates with 1 ganglion cell.
102
Is there any convergence in the periphery of the macula?
Yes, thousands of rods can converge onto 1 bipolar cell.
103
What gives rise to binocular vision?
Presence of ipsilateral projections.
104
What are the output neurons of the retina?
Ganglion cells - their axons form the optic nerve
105
What is the optic tract?
Once axons pass through optic chiasm they become the optic tract.
106
What is the pathway of visual conduction?
1. Light strikes photoreceptor, AP conducted to optic nerve.
2. Axons pass through optic chiasm, most decussate (nasal half), some stay ipsilateral (temporal half).
3. Optic tract.
4. Axons terminate on lateral geniculate nucleus (thalamus).
5. Axons sent via optic radiations to visual cortex where data is processed for shape, colour, movement, location and spatial organisation.
107
What % of human optic chiasm decussates?
60%
108
Why don't cattle, horses and sheep cross cattle grids?
Poor depth perception (80-90% decussation)
109
What is the main target of all retinal ganglion cells?
Lateral geniculate nucleus (thalamus)
110
What are the other targets of retinal ganglion cells?
Hypothalamus - regulation of circadian rhythms.
Pretectum - reflex control of pupil and lens.
Superior colliculus - orientates movement of head and eyes.
111
Which tract is responsible for mediating motor responses to visual stimuli?
Tectospinal tract.
| Visual cortex connected to superior colliculus where tract begins.
112
Which cranial nerves and subsequent tests can be carried out to evaluate cranial nerve function?
CNII - visual acuity
CNII, III - pupillary light
CNII, VII - menace response
113
Outline the pupillary light reflex pathway.
Ganglion cells second major target is pretectum.
1. Presence of light is communicated along optic nerve to the pretectum.
2. Pretectal neurons project to Edinger-Westphal nucleus (close to nucleus of oculomotor nerve CNIII).
3. E-W nucleus contains preganglionic parasympathetic neurons that send axons via CNIII to terminate on neurons in ciliary ganglion.
4. Neurons in ciliary ganglion innervate the inner circular constrictor muscle which decreases pupil diameter.
114
What does a taste bud consist of?
Many (50-150) taste receptor cells and their support cells.
115
What is a taste receptor cell?
Modified epithelial cells with microvilli that extend into the pore of the taste bud (hole at top to allow access of cells to saliva and dissolved food molecules).
116
For taste to be experienced a chemical must be what in order for it to bind to a receptor?
Dissolved in saliva.
117
Where are taste buds found in human body?
Oral cavity - tongue, pharynx, epiglottis, proximal oesophagus.
118
Which cranial nerves do taste buds synapse with?
Afferent axons of CN VII, IX and X
119
What are the 5 types of taste buds and their tongue location?
```
Sweet - tip of tongue.
Sour - Margins of tongue
Salty - tip and upper front portion
Bitter - back of tongue
Umami - tip of tongue (same as sweet).
Whole tongue can perceive the taste, just more concentrated in certain areas.
```
120
What are the 5 steps of chemoreception?
1. Ligand activates taste cell (bitter, sweet, umami all G protein coupled, sour has H channels, salt has Na channels).
2. Multiple intracellular pathways are activated (signal transduction pathways/K channels closing and depolarisation).
3. Ca channels open, triggers exocytosis of NT.
4. NT released, primary sensory neuron fires.
5. AP sent to brain.
121
Can taste receptor cells respond to all tastes?
Yes, although they usually respond more strongly to one in particular.
122
Describe the process of signal transduction with sour taste?
1. H enters cell via transient receptor potential (TRP) channels, closing of K channels.
2. Receptor cell depolarises.
3. Voltage gated Na channels on basolateral membrane open.
4. Voltage gated Ca channels in plasma membrane and ER membrane open.
5. Influx of Ca ions.
6. NT release by exocytosis from basal aspect of taste receptor cell.
7. AP in afferent fibre.
123
Describe the process of signal transduction with salty taste?
1. Na enters cell (apical aspect) via amiloride-sensitive Na channel.
2. Depolarisation of cell.
3. Voltage gated Na channels on basolateral membrane open.
4. Voltage gated Ca channels in plasma membrane and ER membrane open.
5. Influx of Ca ions.
6. NT release by exocytosis from basal aspect of taste receptor cell.
7. AP in afferent fibre.
124
Describe the process of signal transduction with sweet taste?
1. Organic sugars bind to transmembrane receptor (T1R2).
2. Initiate G-protein mediated signal transduction cascade.
3. Activation of phospholipase C (PLC-beta2)
4. Increased concentrations of inositol triphosphate (IP3).
5. Opening of transient receptor potential channels (TRP)-TRPM5.
6. Entry of Ca into taste receptor cell.
7. Depolarisation of cell - NT release.
Also;
Activation of G-protein stimulates cAMP production.
cAMP catalysed phosphorylation of K channels.
K channels close.
Decreased loss of K from cell, depolarisation, increased Ca and NT release.
125
Describe the process of signal transduction with bitter taste?
2 parts; binding of bitter molecule and then signal of actual taste.
126
Describe the process of signal transduction with bitter molecules?
1. Nitrogenous compounds bind to membrane receptors (protective mechanism as bitter is associated with toxins).
2. Blocks activity of K channels.
3. Decreased loss of K, depolarisation of taste receptor cell.
4. Opening of voltage gated Ca channels in plasma membrane and ER membrane.
5. Influx of Ca ions - NT release by exocytosis from basal aspect of taste receptor cell.
6. AP in afferent fibre
127
Describe the process of signal transduction with bitter taste?
1. Bitter molecule binds to T2R transmembrane receptor.
2. Activates G-protein gustucin.
3. Activates phospholipase C (PLC-beta2).
4. Increased concentration of inositol triphosphate (IP3).
5. Opening of transient receptor potential channels (TRP) - TRPM5.
6. Entry of Ca into cell.
7. Depolarisation and NT release.
128
Which cranial nerves are involved in the neural pathway of taste?
CN VII - facial
CN IX - glossopharyngeal
CNX - vagus
129
What is the pathway for taste perception to the brain?
1. Taste cells depolarise sending AP via afferent branches of the 3 cranial nerves.
2. Synapse on nucleus of solitary tract (brainstem).
3. Axons project to VPM of thamalus, synapse.
4. Project to gustatory cortex (frontal operculum and insula).
130
What do the reciprocal pathways between the nucleus of solitary tract and hypothalamus and amygdala allow?
Association of memory and emotions with taste.
131
Where are olfactory receptor cells located?
In olfactory mucosa along with sustentacular and basal cells.
132
Afferent nerves from olfactory receptor cells travel to where?
Olfactory bulb via the cribriform plate (CN1).
133
What are the 3 main cell types involved in smell?
Olfactory cells - bipolar neurons with cilia.
Sustentacular cells - columnar epithelium, metabolic and physical support, maintain extracellular environment.
Basal cells - replace olfactory cells
Brush cells also present - provide deep olfactory sensation which connects with CNV (trigeminal).
134
Describe the general anatomy and main functions of olfactory cells?
Bipolar neurons with cilia on dendritic end, these project into the mucus lining the nasal cavity.
Cilia contain receptors that bind specific odourant molecules. They are immotile and increase functional surface area.
135
What role does the lamina propria play in smell?
Bowmans gland - produces mucus found in nasal cavity.
| Olfactory neuron axons
136
What is the general anatomy and function of basal cells?
Rounded cell close to basal lamina.
Partly sheath first portion of receptor cell axon.
Precursors for development of new olfactory receptor cells.
137
What are the brain processing pathways for olfaction?
Olfactory receptors - olfactory nerve to olfactory bulb - olfactory tract to olfactory bulb targets (pyriform cortex, olfactory tubercle, amygdala, entorhinal cortex).
Pyriform cortex links to orbitofrontal cortex that communicates with thalamus.
Amygdala (behaviour associations) links with orbitofrontal cortex, thalamus and hypothalamus.
Entorhinal cortex links with hippocampal formation.
138
How many odours do individual olfactory neurons respond to?
1
139
What is the odour code?
Combination of olfactory neurons stimulated giving rise to recognition of different odours.
140
How are olfactory receptors different to other special sense receptors?
Olfactory receptors are specialised nerve endings on the afferent nerves, not seperate cells as in taste, etc.
141
Where do afferent olfactory nerves terminate?
In the olfactory bulb - here they communicate with mitral cells (second order neurons).
142
What forms the olfactory tract?
Mitral cell axons.
143
Where does recognition of odour occur?
Olfactory cortex.
144
What is trigeminal chemoreception?
3rd chemosensory system - CNV polymodal nociceptive neurons (ophthalmic, maxillary and mandibular branches).
Activated by irritant chemicals inhaled/ingested/contact with face.
Receptors located on terminal branches of polymodal nociceptive neurons (pain and temp).
A lot more sensitive than senses such as olfaction and taste to decrease chances of injury/damage. Cause responses such as salivation, vasodilation, tearing etc to dilute irritant and decrease further contact.
Targets trigeminal nucleus, then VPM nucleus (thalamus) and somatosensory cortex.
