18. Sense Organs Flashcards
1
Q
Which cranial nerve supplies the ear?
A
Vestibulocochlear (8th)
2
Q
What are the sections of the ear?
A
Outer ear
Middle ear
Inner ear
3
Q
How is the middle ear connected to the nasopharynx?
A
Eustachian tube
4
Q
What does the outer ear consist of?
A
Auricle/pinna
External auditory canal
Tympanic membrane (ear drum)
5
Q
What is the auricle/pinna?
A
Flap of elastic cartilage
Covered by skin
6
Q
What is the function of the pinna?
A
Traps and directs sounds waves into the external auditory canal
7
Q
What is the tympanic membrane?
A
Ear drum
Thin semi-transparent partition between the external auditory canal and middle ear
8
Q
What is the tympanic membrane lined with?
A
Simple cuboidal epithelium
Elastic fibres
Collagen fibres
9
Q
What is the function of the tympanic membrane?
A
Transmits sound from the outer ear to the auditory ossicles
Converts sound waves into mechanical vibration
10
Q
What is the middle ear?
A
A small air-filled cavity in the temporal bone
11
Q
What does the middle ear consist of?
A
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
12
Q
What is the function of the middle ear?
A
Transmits sound in the form of vibration from the tympanic membrane to the inner ear (cochlea)
13
Q
What does the stapes connect to?
A
Oval window
14
Q
What does the oval window connect to?
A
Cochlea
15
Q
What is the stapedius?
A
Small muscle that dampens large vibrations
Innervated by the facial nerve
16
Q
What is the alternative name for the inner ear?
A
Labyrinth
17
Q
What does the labyrinth consist of?
A
Bony labyrinth (outer) Membranous labyrinth (inner)
18
Q
What does the bony labyrinth consist of?
A
Series of cavities in the temporal bone:
Three semi-circular canals
Vestibule
Cochlea
19
Q
What do the semi-circular canals and vestibule help with?
A
Balance
20
Q
What does the cochlea help with?
A
Hearing
21
Q
Which fluids does the labyrinth contain?
A
Perilymph
Endolymph
22
Q
What is the cochlea?
A
Spiralled, hollowed chamber
Almost 3 turns around a central bony core
23
Q
What does the cochlea contain?
A
Epithelial cells lined with hair cells
24
Q
What are the hair cells in the cochlea called?
A
Stereocilia
25
What is the function of the stereocilia?
Hearing receptors that extend into the endolymph
26
How does the structure of the cochlea aid hearing?
Movement of the endolymph causes stereocilia movement
| This initiates an electrical impulse
27
What does the vestibulocochlear nerve do?
Provides sensory information for hearing and balance
28
What are the two parts of the vestibulocochlear nerve?
Vestibular fibres
| Cochlear fibres
29
What do the vestibular fibres consist of?
Nerve branches that synapse with receptors for balance
30
What do the cochlea nerve fibres do?
Provides hearing
31
Where does the vestibulocochlear nerve terminate?
Brainstem (pons/medulla oblongata)
32
How can the vestibulocochlear nerve get damaged?
Basilar skull fracture
33
How does the outer ear make sound?
1. Sound comes in
2. Pinna concentrates the soundwaves and directs them along the external auditory canal
3. This causes the tympanic membrane to vibrate
34
How does the middle ear make sound?
1. Vibrations from the tympanic membrane are transmitted through the middle ear by movement of the three auditory ossicles (malleus, incus, stapes)
2. The footplate of the stapes rocks at the oval window sending fluid waves into the cochlea perilymph
35
How does the inner ear make sound?
1. Pressure waves are transmitted into the cochlea which causes the round window to bulge into the middle ear
2. This pressure wave is transmitted into the endolymph and vibrates the basilar membrane and stereocilia
3. The bending of the stereocilia creates a receptor potential - generating an action potential to the nerves
4. The nerve impulses move along the vestibulocochlear nerve to the hearing area in the cerebrum
36
What are the properties of sound?
Pitch
| Volume
37
What is pitch?
Frequency of sound waves
38
How is pitch measured?
Hertz (Hz)
39
What is volume?
Amplitude of sound waves
40
How is volume measured?
Decibels (dB)
41
What is the decibel scale?
0 dB - near silence
10 dB - 10x more powerful
20 dB - 100x more powerful
30 dB - 1000x more powerful
42
What is a whisper in decibels?
15 dB
43
What is a normal conversation in decibels?
60 dB
44
What is a lawnmower in decibels?
90 dB
45
What is a car horn in decibels?
110 dB
46
What is a rock concert/jet engine in decibels?
120 dB
47
What is a gunshot in decibels?
140 dB
48
What decibel level can cause hearing loss?
90 dB
49
What decibel level can cause pain/damage?
140 dB
50
What is white noise?
A constant, background noise that contains all the different frequencies of sound
Brain ignores
51
What is white noise used for?
To block out other sounds
| Aid concentration
52
What is the function of the eustachian tube?
Opens for air to equalise pressure between middle ear and atmosphere
Drains mucus
53
What can make the eustachian tube open?
Yawning
| Swallowing
54
Why is it essential that air can escape the middle ear?
Damage could occur with pressure changes
55
What is common in children as a result of the eustachian tube being horizontal?
Infection between middle ear and pharynx
56
What do the semi-circular canals and vestibule provide information about?
Head position
57
What do the semi-circular canals and vestibule contain?
Stereocilia
58
What extends and rests on the stereocilia?
Dense layer of calcium carbonate crystals
59
What is the layer of calcium carbonate crystals also known as?
Otolithic membrane
60
What does a change in head position create?
Movement in the perilymph and endolymph that causes stereocilia to bend
61
What does bending of the stereocilia in the semi-circular canals and vestibule stimulate?
Stimulates the sensory nerve endings, creating action potential via CN8
62
Where does the action potential stimulated in the semi-circular canals and vestibule transmit to?
Cerebellum
63
Where does the cerebellum get information from to help with balance?
```
Vestibular feedback (from inner ear)
Visual feedback (from eyes)
Proprioceptors (skeletal muscles, joints, ligaments)
```
64
How does the cerebellum maintain balance?
```
Co-ordinates:
Vestibular feedback (from inner ear)
Visual feedback (from eyes)
Proprioceptors (skeletal muscles, joints, ligaments)
```
and passes efferent impulses to the cerebrum and skeletal muscles
65
Where is the eye located?
In the orbital cavity
66
Which cranial nerve serves the eye?
Optic nerve (2)
67
What are the layers of the eye?
Sclera & cornea (outer)
Uvea (middle)
Retina (inner)
68
What does the uvea consist of?
Iris
Ciliary body
Choroid
69
What is the iris?
Coloured part of the eye
| Controls the amount of light reaching the retina by adjusting pupil size
70
Where is the lens located?
Behind the pupil
71
What does the lens do?
Focuses light along the cornea
72
What are the accessory structures of the eye?
```
Eyebrows
Eyelids
Eyelashes
Conjunctiva
Lacrimal apparatus
```
73
What function do the eyebrows play?
Prevents sweat/materials entering the eye
74
What function do the eyelids play?
Spread secretions over the eye
| Protection
75
What is the conjunctiva?
Transparent mucus membrane of columnar epithelial cells lining the internal eyelids and anterior eyeball
76
What is the function of the conjunctiva?
Protects the cornea
77
What does the lacrimal apparatus do?
Produces tears
78
What does blinking do?
Spreads tears
| Protects the eyes from injury (when eyelids are closed)
79
What function do tears have?
Protect the eye from infection
Lubricate eye movement
Emotions
80
Which cranial nerve controls the secretion of tears?
Trigeminal nerve (5)
81
What do tears contain?
IgA
| Lysozymes
82
Where are tears produced from?
Lacrimal gland
83
How do tears cover the eye?
Through blinking
84
What is the lacrimal punctum?
Where tears run in to before entering the nose
85
How do tears enter the nose?
Via the nasolacrimal gland
86
What are eyes responsible for?
Detecting visible light
87
What are wavelengths?
Exhibit colours
| 400-700nm
88
How do objects appear?
The colour of the wavelength that is reflected
89
What is white light?
Combination of all the colours of the visible spectrum
90
How is clear vision achieved?
By light focusing on the retina
91
How does light focus on the retina?
Refraction of light rays
Accommodation of the eyes
Changing the size of the pupils
92
What is refraction?
Bending of light rays
93
How does refraction happen?
When light moves from one substance to another which has a different density
94
How do the cornea and lens help with refraction?
They both refract light rays and help focus the image on the retina
95
How do images appear to the retina?
Inverted (upside down)
| Left-right reversed
96
What happens when objects are closer than 6m?
Light rays are refracted more to enable the retina to focus
97
What is the process of light rays refracting more called?
Accommodation
98
What happens during accommodation?
As lens curvature becomes greater, the focusing power increases
99
What are the characteristics of the lens?
Convex on anterior and posterior surfaces
| Allows incoming light to refract
100
What do the lens and ciliary muscles do to project a sharp image on the retina?
Lens changes its refractive power:
1. Close objects - ciliary muscle contracts
2. Distant objects - ciliary muscle relaxes
101
What happens when the ciliary muscle contracts?
Reduces the suspensory ligament tension
| Lens becomes more convex = greater refraction
102
What happens when the ciliary muscle relaxes?
Increases the suspensory ligament tension
| Lens becomes flattened = less refraction
103
What does looking at near objects constantly do to the eyes?
Tires them out
104
What happens to pupil size during sympathetic nervous stimulation?
Radial muscles contract = dilation of pupils
105
What happens to pupil size during parasympathetic nervous stimulation?
Circular muscles contract = constriction of pupils
106
What is meant by convergence?
The medial movement of two eyeballs so that both are directed towards an object
107
Which muscles move the eyes during convergence?
Extra-ocular
108
What happens to eye rotation if an object is near?
More rotation
109
What happens if convergence isn't completed?
Two images are sent to the brain
| Leads to double vision - diplopia
110
What does focusing on one object allow for?
Perception of depth
| 3D
111
What happens in binocular vision?
Two images from the two eyes are fused in the cerebrum so only one image is perceived
112
What is optic chiasma?
Where the optic nerve crosses over in the brain
113
Where is the optic chiasma located?
Next to the pituitary gland
114
What condition can pituitary tumours cause?
Tunnel vision
115
What is the retina?
Inner layer of the eye
Beginning of the visual pathway
Lines the posterior 3/4 of the eyeball
116
How can the retina be viewed?
Through an ophthalmoscope
117
What can be viewed in the retina?
Blood vessels
| Optic nerve
118
What is the optic disc?
Location where the optic nerve exits the eyeball
119
What is the location where the optic nerve exits the eyeball also called?
Blind spot
120
What is the optic nerve bundled with?
Central retinal artery and vein
121
What does the retina contain?
Pigmented layer of melanin-containing epithelial cells
| Layer of photoreceptors
122
What are the photoreceptors called?
Rod cells
| Cone cells
123
How many rod cells are in the eye?
120 million
124
What is the function of rod cells?
Allows us to see in dim light
| Provides black, white and greyscale colour
125
How many cone cells are in the eye?
6 million
126
What is the function of cone cells?
Produce colour vision
127
What are the types of cone cells?
Blue
Red
Green
128
One of the reasons the optic disc is called the blind spot
Contains no rod or cone cells
129
What is the macula lutea?
Yellowish spot at the exact centre of the retina
130
What is the fovea centralis?
Small depression in the centre of the macula lutea that only contains cone cells
Area of highest visual acuity
131
Where are rod cells more plentiful?
Periphery of the retina
132
What do rod and cone cells form?
Invaginations of their cell membrane to create stacks of discs
133
What are photopigments?
Transmembrane proteins within the discs of rod and cone cells
134
What happens when light hits the photopigment?
It changes shape initiating an action potential
135
What are photopigments derived from?
Vit A
136
What happens once a photopigment is activated?
It must then be restored/regenerated
137
What contributes to the regeneration of rod cells?
Vit A
138
What are derivatives of vit A called?
Retinoids
139
What do retinoids include?
Retinol
Retinal
Retinoic acid
140
What does retinal do in the retina?
Binds to a protein called opsin to produce photopigments
141
Which foods contain preformed vit A
Foods of animal origin
Liver
Egg yolks
142
What are carotenoids?
Vit A precursors
| Powerful antioxidants
143
What are carotenoids turned into?
Retinol
144
Where are carotenoids metabolised into retinol?
Intestines
145
Which foods contain carotenoids?
```
Carrots
Sweet potatoes
Squash
Mango
Leafy greens
```
146
How are carotenoids different to preformed vit A?
Not toxic
| Absorption is regulated
147
What happens during light/dark adaptation?
Dark to light = eyes adjust quite quickly
| Light to dark = eyes adjust more slowly
148
Why does light/dark adaptation differ?
Rods and cones must regenerate photopigments
Cones regenerate within 8 mins
Rods take much longer
149
What is the sense of smell called?
Olfaction
150
How many receptors does the nose contain?
10-100 million
151
Where can the nasal receptors be found?
Olfactory epithelium
152
What does the olfactory epithelium contain?
Olfactory receptors
Supporting cells
Basal cells
153
What are olfactory receptors?
Neurons attached to olfactory hairs
154
How do olfactory receptors produce an action potential?
By responding to chemical stimulus of odorants
155
What is the function of supporting cells?
Physical support
Nourishment
Detoxify odorant chemicals
156
What are basal cells?
Stem cells that continually divide to produce new olfactory receptors
157
How long do olfactory receptors live for?
1 month
158
Why are taste and smell 'chemical senses'?
They arise from interaction with molecules
159
Where can the olfactory glands be found?
In the connective tissue supporting the olfactory epithelium
160
What do the olfactory glands do?
Produce mucus that is carried to the surface by ducts
161
What does the mucus secreted by the olfactory glands do?
Moistens the olfactory epithelium
| Helps to dissolve odorants
162
What is affected if the nasal mucosa becomes inflamed?
Olfaction is inhibited
163
Which cranial nerve is involved in the sense of smell?
Olfactory (1)
164
Where do olfactory nerves extend through?
About 20 olfactory foramina in the cribriform plate of the ethmoid bone
165
Where do the olfactory nerves terminate?
Olfactory bulb - olfactory tract - olfactory area in temporal lobe
166
Where do some of the axons in the olfactory tract project in to?
Limbic system
| hence relation between smell and emotion
167
What can a sense of smell also affect?
Appetite
| Mood
168
Why does olfaction have a low threshold?
Only a few molecules are needed for us to detect a smell
169
How do we adapt our sensitivity to odours?
Rapidly
50% in first second
80% less powerful after a few mins of exposure
170
When can olfaction adaptation reach 100%?
When constantly been exposed to an odour
171
Why do we have olfaction adaptation?
To protect us from danger
| If the scent isn't dangerous, olfaction recalibrates to be able to detect other smells which may be harmful
172
What is taste also known as?
Gustation
173
How do we taste?
Food chemicals dissolve in saliva, stimulating chemoreceptors
They encounter gustatory hairs which generates an action potential
174
How many muscles are in the tongue?
8
175
Which cranial nerve innervates the tongue?
Hypoglossal (12)
176
How many taste buds can be found in an adult's mouth?
10,000
177
Where can the taste buds be found?
Tongue
Soft palate
Pharynx
Epiglottis
178
What do taste buds contain?
Gustatory receptor cells
Supporting cells
Basal cells
179
What is the function of the gustatory receptor cells?
Detect taste
180
How long do gustatory receptor cells live for?
10 days
181
What do the basal cells do?
Produce new gustatory receptor cells
182
Where can taste buds on the tongue be found?
In elevations called papillae
183
What are the three types of papillae?
Circumvallate papillae
Fungiform papillae
Foliate papillae
184
What are circumvallate papillae?
Largest papillae
V-shaped
Found at back of tongue
185
What are fungiform papillae?
Mushroom-shaped
Present all over tongue
Contain about 5 taste buds each
186
What can foliate papillae be found?
Small trenches at lateral margins of tongue
| Most degenerate in childhood
187
What are filiform papillae?
Tactile receptors that help the tongue move food
188
What are the 5 tastes we can detect?
```
Sour
Sweet
Bitter
Salty
Unami
```
189
When is taste impaired?
When the mouth is dry
| no saliva to dissolve the chemoreceptors
190
What does a sense of taste trigger?
Salivation
| Gastric juice secretion (in preparation)
191
Which cranial nerve innervates taste in the anterior 2/3 of the tongue?
Facial (7)
192
Which cranial nerve innervates taste and sensation in the posterior 1/3 of the tongue?
Glossopharyngeal (9)
193
Which cranial nerve supplies general sensation to the anterior 2/3 of the tongue?
Trigeminal (5)
194
Which cranial nerve innervates the throat and epiglottis?
Vague nerve (10)
195
Where does all the taste and sensory information go?
To the gustatory nucleus in the medulla oblongata
| Some fibres to the limbic system
