Chapter 17: Special Senses Flashcards
(247 cards)
1
Q
Olfaction.
A
Chemical sense. Stimulating molecules must be dissolved before interacting with smell receptors.
2
Q
Why can certain smells evoke strong emotional responses or memories?
A
These impulses propagate to the limbic system.
3
Q
Is gustation or olfaction more sensitive?
A
Olfaction.
4
Q
Describe adaptation of olfactory receptors.
A
Olfactory receptors adapt quickly by 50% in the first second of stimulation, and then adapt slowly. Complete insensitivity to certain strong odors occurs a minute after exposure.
5
Q
Olfactory receptors are located in the olfactory epithelium. Describe the olfactory epithelium.
A
In superior part of nose. Covers inferior surface of cribriform plate and extends along the superior nasal concha.
6
Q
What 3 cells are part of the olfactory epithelium?
A
Olfactory receptor cells, supporting cells, basal cells.
7
Q
Olfactory receptor cells.
A
The first order neurons of the olfactory pathway. Bipolar neurons. Exposed dendrite. Axon projects through the cribriform plate that ends in the olfactory bulb.
8
Q
What are the sites of olfactory transduction?
A
Nonmotile olfactory cilia, which extend from the dendrites of olfactory receptor cells.
9
Q
Where are olfactory receptor proteins, and what is their purpose?
A
In the plasma membranes of the olfactory cilia. Detect inhaled chemicals.
10
Q
How long do olfactory receptor cells live for, and how are they replaced?
A
Live for 2 months, and then are replaced by basal cell production.
11
Q
Supporting cells (olfaction).
A
Columnar epithelial cells. Located in the mucous membrane lining of the nose. Provide physical support, nourishment, electrical insulation for olfactory receptor cells, and help detoxify chemicals that come into contact with olfactory epithelium.
12
Q
Basal cells (olfaction).
A
Stem cells (neurons). Located between bases of supporting cells. Continually undergo cell division to produce new olfactory receptor cells.
13
Q
Olfactory glands.
A
Bowman’s glands. Located within connective tissue of olfactory epithelium. Produce mucus to moisten surface of olfactory epithelium and dissolve odorants.
14
Q
How are tears and a runny nose produced after inhaling certain substances (pepper, vapours)?
A
Supporting cells and olfactory glands are innervated by parasympathetic neurons within branches of the facial nerve –> impulses of facial nerve stimulate lacrimal glands in eyes and nasal mucous glands in nose.
15
Q
How many olfactory receptors are in the human nose?
A
10 million, with 400 different functional types.
16
Q
Describe the process of olfaction.
A
Odorant binds to olfactory receptor protein in olfactory cilium –> G-protein activates adenylyl cyclase to produce cAMP –> opens a cation channel that allows Na+ and Ca2+ to enter the cytosol –> depolarizing receptor potential forms in olfactory receptor cell –> if depolarization reaches threshold, then an AP is generated along the axon of the olfactory receptor cell.
17
Q
Gustation.
A
Chemical sense. Simpler than olfaction since there are only 5 primary tastes.
18
Q
What are the 5 primary tastes?
A
Salty, sour, sweet, bitter, umami.
19
Q
Salty taste.
A
Caused by Na+ ions.
20
Q
Sour taste.
A
Caused by H+ ions released from acids.
21
Q
Sweet taste.
A
Caused by sugars and artificial sweeteners.
22
Q
Bitter taste.
A
Caused by a wide variety of substances (caffeine, morphine, quinine) and poisonous substances (strychnine).
23
Q
Umami taste.
A
Caused by amino acids. Results in a meaty and savoury taste.
24
Q
What flavour enhancer results in an umami taste?
A
Monosodium glutamate (MSG).
25
Which foods combine all 5 primary tastes?
Chocolate, coffee, pepper.
26
Which taste has the lowest threshold, and why?
Bitter. Protective function for poisons.
27
Which tastes have the highest threshold?
Salty and sweet.
28
Compete adaptation to a specific taste can occur in:
1-5 minutes of continuous stimulation.
29
Where are the receptors for taste sensations located?
In taste buds in tongue, soft palate, pharynx and epiglottis.
30
Taste buds on the tongue are found in:
Papillae, which increase surface area and provide rough texture of tongue.
31
Vallate papillae.
Circumvallate papillae. Very large. Each one contains 100-300 taste buds. 12 papillae form an inverted V-shaped row at the back of the tongue.
32
Fungiform papillae.
Mushroom-shaped. Each one contains 5 taste buds. Scattered over entire tongue.
33
Foliate papillae.
Located in small trenches on lateral margins of tongue. Most of their taste buds degenerate in early childhood.
34
Filiform papillae.
Pointed and threadlike. Contain tactile receptors but no taste buds. Increase friction between tongue and food. Cover the entire tongue.
35
Each taste bud is an oval body consisting of 3 kinds of epithelial cells:
Supporting cells, gustatory cells, basal cells.
36
Supporting cells (gustation).
Surround 50 gustatory receptor cells in each taste bud, and develop into gustatory receptor cells.
37
Gustatory receptor cells.
Gustatory microvilli project from each cell to the external surface through the taste pore. Synapse with dendrites of first order neurons of gustatory pathway, which branch and contact many gustatory receptor cells in several taste buds.
38
How long do gustatory receptor cell live for, and how are they replaced?
10 days. Replaced by supporting cells.
39
Basal cells (gustation).
Stem cells. Located in the periphery of the taste bud. Produce supporting cells.
40
Describe the process of gustation.
Tastant dissolves in saliva --> makes contact with PM of gustatory microvilli --> depolarizing receptor potential --> exocytosis of synaptic vesicles from gustatory receptor cell --> NTs trigger graded potentials that produce nerve impulses in first order sensory neurons that synapse with gustatory receptor cells.
41
Describe the process of gustation for salty taste.
Na+ ions enter gustatory receptor cells via Na+ channels in PM --> accumulation of Na+ inside the cell causes depolarization --> NT release.
42
Describe the process of gustation for sour taste.
H+ ions enter gustatory receptors via H+ channels --> accumulation of H+ inside the cell causes depolarization --> NT release.
43
Describe the process of gustation for sweet, bitter and umami tastes.
Tastants do not enter gustatory receptor cells. Tastants bind to receptors on PM that are linked to G-proteins --> G-proteins activate enzymes that produce IP3 --> IP3 causes depolarization of gustatory receptor cell --> NT release.
44
How can different tastes be detected in all parts of the tongue?
Each taste bud contains gustatory receptor cells for each type of tastant.
45
More than half the sensory receptors in the human body are located:
In the eyes.
46
Wavelength.
Distance between two consecutive peaks of a wave.
47
Eyes detect visible light with wavelengths ranging from:
400-700 nm.
48
How is colour perceived by the eye?
Colour depends on wavelength. The object will appear the colour of the wavelength that is reflected.
49
Functions of the eyelids (palpebrae).
Shade the eyes during sleep, protect the eyes from excessive light and foreign objects, spread lubrication secretions over the eyeballs.
50
Which muscle is in the upper eyelid?
Levator palpebrae superioris.
51
Palpebral fissure.
Space between upper and lower eyelids that exposes the eyeball.
52
Lateral commissure of eye.
Narrow angle of palpebral fissure. Closer to temporal bone.
53
Medial commissure of eye.
Broad angle of palpebral fissure. Closer to nasal bone.
54
Lacrimal caruncle.
Small red elevation in medial commissure. Contains sebaceous glands and sudoriferous glands.
55
Tarsal plate.
Thick fold of connective tissue that gives form and support to eyelids.
56
Tarsal glands.
Meibomian glands. Located in each tarsal plate. Contain modified sebaceous glands. Secrete a fluid that helps the eyelids from adhering to each other.
57
Infection of tarsal glands.
Produces a tumor/cyst in the eyelid, otherwise known as a chalazion.
58
Conjunctiva.
Thin protective mucous membrane. Consists of nonkeratinized stratified squamous epithelium and goblet cells. Supported by areolar connective tissue.
59
Palpebral conjunctiva.
Lines the inner aspect of eyelids.
60
Bulbar conjunctiva.
Passes from the eyelids onto the surface of the eyeball where it covers the sclera (white of eye). It is vascular over the sclera.
61
What causes bloodshot eyes?
Dilation and congestion of blood vessels of bulbar conjunctiva due to local irritation or infection.
62
What lubricates the hairs of the eyelashes?
Sebaceous ciliary glands at the base of the hair follicles.
63
What causes a sty?
Infection of sebaceous ciliary glands at the base of eyelashes.
64
Lacrimal apparatus.
Group of structures that produces and drains lacrimal fluid during lacrimation (crying).
65
Describe the process of lacrimation.
Lacrimal glands secrete lacrimal fluid --> drains into 6-12 excretory lacrimal ducts --> empties onto the surface of the conjunctiva of the upper eyelid --> tears pass medially over the anterior surface of the eyeball to enter lacrimal puncta (2 small openings) --> superior and inferior lacrimal canaliculi --> lacrimal sac --> nasolacrimal duct --> nasal cavity --> mixes with mucus.
66
Describe the size and shape of a lacrimal gland.
Almond-like.
67
Dacryocystitis.
Bacterial infection of lacrimal sacs. Blocks nasolacrimal ducts.
68
What innervates the lacrimal glands?
Parasympathetic fibres of facial nerves.
69
Lacrimal fluid.
Watery solution. Contains salts, mucus, lysosomes. Protects, cleans, lubricates and moistens the eyeball.
70
How is lacrimal fluid spread medially over the eyeball?
Blinking.
71
How much lacrimal fluid does each lacrimal gland produce each day?
1 mL
72
How does an irritating substance making contact with conjunctiva produce watery eyes?
Parasympathetic stimulation --> excessive secretion of lacrimal fluid by lacrimal glands.
73
How does an inflammation of the nasal mucosa produce watery eyes?
Obstructed nasolacrimal ducts --> blocked drainage of tears to nose.
74
Orbits.
Bony depressions of the skull that protect the eyes, stabilize the eyes in 3D space, and anchor the eyes to muscles that produce their essential movements.
75
Extrinsic eye muscles.
Extend from the orbit to the sclera. Are surrounded by periorbital fat.
76
How many extrinsic eye muscles move each eye?
6
77
The wall of the eyeball consists of 3 layers:
1) Fibrous tunic. 2) Vascular tunic. 3) Inner tunic (retina).
78
Fibrous tunic.
Outer layer of the eyeball. Consists of anterior cornea and posterior sclera.
79
Cornea.
Curved transparent coat that covers the coloured iris. Helps focus light onto the retina.
80
Outer surface of cornea consists of which type of cell?
Nonkeratinized stratified squamous epithelium.
81
Middle coat of cornea consists of which cells?
Collagen fibres and fibroblasts.
82
Inner surface of cornea consists of which type of cell?
Simple squamous epithelium.
83
The central part of the cornea is important for what function?
Receiving oxygen.
84
Sclera.
White of eye. Layer of dense connective tissue made of collagen fibres and fibroblasts. Covers entire eyeball except the cornea.
85
What are the functions of the sclera?
Gives the eyeball its shape to make it more rigid. Protects the inner eyeball. Is the site of attachment of extrinsic eye muscles.
86
Scleral venous sinus.
Canal of Schlemm. Opening at junction of sclera and cornea.
87
Which fluid drains into the scleral venous sinus?
Aqueous humour.
88
Vascular tunic.
Middle layer of the eyeball. Composed of choroid, ciliary body and iris.
89
Choroid.
Highly vascular. Posterior part of vascular tunic. Lines internal surface of sclera.
90
What are the functions of the choroid?
Provides nutrients to the posterior surface of the retina. Contains melanocytes that produce melanin. Absorbs stray light rays. Prevents reflection and scattering of light within the eyeball.
91
Ciliary body.
Anterior part of vascular tunic. Appears dark brown due to melanocytes. Consists of ciliary processes and the ciliary muscle.
92
What becomes the ciliary body?
Choroid.
93
Ciliary processes.
Protrusions or folds on the internal surface of the ciliary body. Contain blood capillaries that secrete aqueous humor. Zonular fibres extend from these processes.
94
Ciliary muscle.
Circular band of smooth muscle. Contraction increases the tightness of zonular fibres to alter the shape of the lens for near/far vision.
95
Iris.
Coloured part of eyeball. Flattened-donut shape. Suspended between cornea and lens. Attached to ciliary processes. Consists of melanocytes and circular and radial smooth muscle fibres. Regulates the amount of light entering the eyeball through the pupil.
96
What regulates pupil diameter in response to light levels?
Autonomic reflexes of iris.
97
Why does the pupil appear black?
Heavily pigmented back of eye.
98
Why do eyes look red in some photographs?
If bright light is directed into the pupil, the reflected light is red because of the blood vessels on the surface of the retina.
99
How does the pupil constrict?
Bright light --> parasympathetic fibres of oculomotor nerve stimulate contraction of circular muscles of iris --> pupil constriction.
100
How does the pupil dilate?
Dim light --> sympathetic neurons stimulate radial muscles of iris to contract --> pupil dilation.
101
How much melanin is present in brown, green and blue eyes?
Brown: lots. Green: medium. Blue: low.
102
Retina.
Inner layer of the eyeball. Lines the posterior 3/4 of the eye. Beginning of the visual pathway.
103
Where is the only place in the body that blood vessels can be viewed directly?
Surface of retina.
104
Optic disc.
Where optic nerve exits the eyeball.
105
Why is the optic disc also called the blindspot?
No rods or cones. Images that strike the blindspot cannot be seen.
106
Central retinal artery.
Branch of ophthalmic artery. Bundled with optic nerve. Branches fan out to nourish anterior surface of retina.
107
Central retinal vein.
Bundled with optic nerve. Drains blood from retina through optic disc.
108
Pigmented layer of retina.
Sheet of melanin-containing epithelial cells between choroid and neural layer of retina. Absorbs stray light rays.
109
Neural/sensory layer of retina.
Multilayered outgrowth of the brain that processes visual data before sending nerve impulses into axons that form the optic nerve.
110
Three layers of retinal neurons:
1) Photoreceptor cell layer. 2) Bipolar cell layer. 3) Ganglion cell layer.
111
The 3 layers of retinal neurons are separated by 2 zones:
Outer and inner synaptic layers. This is where synapses are made. Light passes through the ganglion and bipolar cell layers and both synaptic layers before reaching the photoreceptor layer.
112
Which cells are in the bipolar cell layer of the retina?
Horizontal cells and amacrine cells. They form laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells.
113
Photoreceptors.
Specialized cells in the photoreceptor cell layer of the retina. Begin the process of light rays --> nerve impulses. Rods and cones.
114
How many rods and cones are in each retina?
Cones: 6 million. Rods: 120 million.
115
Rods.
Allow us to see in dim light. Do not provide colour vision.
116
Cones.
Stimulated by bright light. Produce colour vision. Blue cones, green cones, and red cones.
117
Describe the flow of visual information from photoreceptors to the optic nerves.
Photoreceptors --> outer synaptic layer --> bipolar cell layer --> inner synaptic layer --> ganglion cell layer --> axons extend posteriorly to optic disc --> exit eyeball as optic nerve.
118
Macula lutea.
Small flat yellow spot in center of posterior retina. At the visual axis of the eye.
119
Fovea centralis.
Small depression in center of macula lutea that contains only cones. Area of highest visual acuity (resolution).
120
What structure contains only cones, but the bipolar and ganglion cell layers do not cover them?
Fovea centralis.
121
What is a main reason for moving your head and eyes while looking at something?
To place images of interest on your fovea centralis.
122
What can you do to see a faint object better?
Gaze slightly to one side rather than looking directly at it. This is because rod vision is more sensitive than cone vision, and there are more rods in the periphery of the retina.
123
Lens.
Behind the pupil and iris. Enclosed by clear connective tissue capsule. Held in position by encircling zonular fibres. Focuses images on the retina for clear vision.
124
Crystallin proteins.
Arranged like layers of an onion. Make up the refractive media of the lens, which is normally transparent and lacks blood vessels.
125
Which structure divides the interior of the eyeball into an anterior cavity and a vitreous chamber?
Lens.
126
Anterior cavity.
Anterior to lens. Consists of an anterior and posterior chamber.
127
Anterior chamber of anterior cavity.
Between cornea and iris.
128
Posterior chamber of anterior cavity.
Behind iris. In front of zonular fibres and lens.
129
Which substance is present in both chambers of the anterior cavity?
Aqueous humour.
130
Aqueous humour.
Transparent watery fluid. Nourishes lens and cornea. Continually filters out of blood capillaries in the ciliary processes --> posterior chamber --> between iris and lens through pupil --> anterior chamber --> scleral venous sinus --> blood).
131
How often is the aqueous humour completely replaced?
Every 90 minutes.
132
Vitreous chamber.
Large posterior cavity between the lens and retina. Contains vitreous body.
133
Vitreous body.
Transparent jellylike substance that holds the retina flush against the choroid. Gives the retina an even surface for clear images. Occupies 4/5ths of the eyeball. Does not undergo constant replacement. Formed during embryonic life.
134
What does the vitreous body contain?
Water, collagen fibres, hydrochloric acid, phagocytic cells to clear debris.
135
Vitreal floaters.
Collections of debris may cast a shadow on the retina and create an appearance of moving specks. Harmless. Do not require treatment. More common in elderly.
136
Intraocular pressure.
Pressure in the eye produced by the aqueous humor and vitreous body. Maintains shape of eyeball and prevents eye from collapsing. 16 mmHg.
137
What 3 processes are required for image formation?
Refraction of light rats, accommodation, and pupil constriction.
138
Refraction of light rays.
As light rays enter the eye, they are refracted at the anterior and posterior surfaces of the cornea so they come into exact focus on the retina --> inverted --> right-to-left reversal.
139
What percentage of light refraction occurs at the cornea, and at the lens?
Cornea: 75%. Lens: 25%.
140
When an object is more than 6 metres away:
The light rays reflecting from the object are nearly parallel to one another.
141
When an object is less than 6 metres away:
The light rays reflecting from the object are divergent, meaning they must be refracted more if they are to be focused on the retina. This additional refraction is accommodation.
142
When the surface of a lens is convex:
The lens will refract light rays toward each other so that they intersect.
143
When the surface of a lens is concave:
The lens will refract light rays away from each other.
144
Which surface of the lens is convex?
Both the anterior and posterior surfaces.
145
The focusing power of the lens increases as:
The curvature of the lens becomes greater.
146
Accommodation.
When the eye is focusing on a close object, the lens becomes more curved causing greater refraction of the light rays.
147
How does the lens become more curved during accommodation?
Parasympathetic fibres of oculomotor nerve --> contraction of ciliary muscle --> pull ciliary processes and choroid toward the lens --> releases tension on lens and zonular fibres --> lens becomes more convex.
148
Near point of vision.
The minimum distance from the eye that an object can be clearly focused with maximum accommodation.
149
What is the near point of vision for a young adult?
10 cm.
150
What occurs simultaneously with accommodation?
Pupil constriction. Prevents light rays from entering the eye through the periphery of the lens.
151
What is another name for a normal eye?
Emmetropic eye.
152
Myopia.
Nearsightedness. Occurs when the eyeball is too long relative to the focusing power of the cornea and lens, or when the lens is thicker than normal so the image converges in front of the retina.
153
Hyperopia.
Farsightedness. Occurs when the eye is too short relative to the focusing power of the cornea and lens, or when the lens is thinner than normal so the image converges behind the retina.
154
Astigmatism.
The cornea or lens has an irregular curvature, causing blurred or distorted vision.
155
Convergence.
The medial movement of the two eyeballs so that both are directed toward the object being viewed. Produced by coordinated extrinsic eye muscles.
156
What happens to the degree of convergence when viewing a close object?
It becomes greater.
157
Binocular vision.
When both eyes focus on one set of objects, allowing for depth perception. Occurs when light rays from an object strike corresponding points on the two retinas.
158
What is the photopigment in rods?
Rhodopsin.
159
Colour vision.
Results from different colours of light selectively activating the different cone photopigments.
160
How many photopigments are in cones?
3.
161
Transduction of light energy into a receptor potential occurs in:
The outer segment of rods and cones.
162
Photopigments.
Integral proteins in the PM of the outer segment of rods and cones that undergo structural changes when they absorb light.
163
How many opsins do rods have?
1.
164
How many opsins do cones have?
3.
165
All photopigments have 2 parts:
1) Opsin: glycoprotein. 2) Retinal: vitamin A derivative.
166
Why is good vision dependent on adequate dietary intake of carotene-rich vegetables?
Because vitamin A derivatives are formed from carotene, which are critical for the retinal component of photopigments.
167
Retinal.
Light-absorbing part of photopigments.
168
Step 1: Isomerization.
In darkness, retinal has a bent shape (cis-retinal) which fits into the opsin part of the photopigment. When cis-retinal absorbs a photon of light, it straightens into trans-retinal. After isomerization, chemical changes occur in the outer segment of the photoreceptor, leading to the production of a receptor potential.
169
Step 2: Bleaching.
Trans-retinal separates from opsin, causing opsin to look colourless.
170
Step 3: Conversion.
Retinal isomerase enzyme converts trans-retinal back to cis-retinal.
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Step 4: Regeneration.
Cis-retinal binds to opsin to reform a functional photopigment.
172
Light adaptation.
Visual system adjusts from dark to light environment in seconds by decreasing its sensitivity.
173
Dark adaptation.
Visual system adjusts from light to dark environment in minutes by increasing its sensitivity slowly.
174
What happens when light level increases?
More photopigment is bleached.
175
Why don't rods contribute to daylight vision?
Regeneration of rhodopsin cannot keep up with the fast bleaching process that occurs in daylight.
176
What happens to the sensitivity of the visual system when the light level decreases abruptly?
Sensitivity increases rapidly at first, and then more slowly.
177
Full regeneration of cone photopigments occurs when in complete darkness?
During the first 8 minutes of dark adaptation.
178
Phototransduction.
Light energy is converted into a receptor potential in the outer segment of a photoreceptor.
179
Is a photoreceptor depolarized or hyperpolarized at rest?
Depolarized.
180
What happens when a photoreceptor is activated?
Causes a hyperpolarizing receptor potential.
181
Processing of visual input in the retina.
Receptor potential in outer segment of photoreceptor --> inner segment --> synaptic terminals --> NT release --> grade potentials in bipolar and horizontal cells.
182
How many rods synapse with a single bipolar cell?
6. Increases light sensitivity of rod vision, but slightly blurs the image.
183
How many cones synapse with a single bipolar cell?
1. Produces a sharper image, even though it is less sensitive.
184
Horizontal cells.
Influence the synaptic activity between photoreceptors (direct) and bipolar cells (indirect).
185
How do horizontal cells improve visual contrast between adjacent areas of the retina?
One photoreceptor excites the horizontal cell, which then inhibits another photoreceptor to decrease the amount of NT released onto a bipolar cell.
186
Amacrine cells.
Influence the synaptic activity between bipolar cells and ganglion cells. They transmit laterally directed inhibitory signals at synapses formed with bipolar cells and ganglion cells.
187
External ear.
Collects sound waves and channels them inward. Consists of the auricle, external auditory canal and tympanic membrane.
188
Auricle.
Pinna. Flap of elastic cartilage shaped like the end of a trumpet. Attached to the head via ligaments and muscles. Helix is the rim part. Lobule is the inferior part.
189
External auditory canal.
Curved tube that lies in the temporal bone and leads to the eardrum.
190
Tympanic membrane.
Eardrum. Thin semitransparent partition between the external auditory canal and middle ear. Lined by simple cuboidal epithelium. Between the epithelial layers is connective tissue composed of collagen, elastic fibres and fibroblasts. Contains hairs and ceruminous glands (earwax). Separates the middle ear and the external ear.
191
Perforated eardrum.
Tearing of tympanic membrane. Heals within a month.
192
Middle ear.
Conveys sound vibrations to oval window. Small air-filled cavity in the petrous part of the temporal bone that is lined by epithelium. Contains the auditory ossicles, tensor tympani muscle and stapedius muscle.
193
What separates the middle ear from the internal ear?
Thin bony partition that contains the oval window and round window.
194
Auditory ossicles.
Three smallest bones in the body. Attach to the middle ear by ligaments. Attach to each other by synovial joints.
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What are the 3 auditory ossicles?
Malleus, incus and stapes.
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Malleus.
Shaped like a hammer. Handle attaches to internal surface of tympanic membrane. Head articulates with incus body.
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Incus.
Middle bone shaped like an anvil. Articulates with head of stapes.
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Stapes.
Shaped like a stirrup. Base fits into the oval window.
199
Tensor tympani muscle.
Skeletal muscle. Supplied by mandibular branch of trigeminal nerve. Limits movement. Increases tension on eardrum to prevent damage to inner ear from loud noises.
200
Stapedius muscle.
Supplied by facial nerve. Smallest skeletal muscle in the human body. Dampens large vibrations of the stapes from loud noises to protect the oval window. Decreases sensitivity of hearing.
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Hyperacusia.
Abnormally sensitive hearing. Association with paralysis of stapedius muscle.
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What can the tensor tympani muscle and stapedius muscle not protect the inner ear from?
Brief loud noises.
203
What connects the middle ear with the nasopharynx?
Auditory tube, which consists of bone and elastic cartilage.
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The auditory tube opens during swallowing and yawning to:
Allow air to enter or exit the middle ear until the pressure in the middle ear equals the atmospheric pressure.
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Internal ear.
Labyrinth. Complicated series of canals. Houses the receptors for hearing and equilibrium.
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Outer bony labyrinth.
Encloses inner membranous labyrinth. Consists of a series of cavities in the petrous part of the temporal bone. Divided into 3 areas: vestibule, semicircular canals, cochlea. Lined with periosteum. Contains perilymph.
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Perilymph.
Fluid that surrounds the membranous labyrinth.
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Vestibule.
Oval ventral part. Membranous labyrinth in the vestibule consists of the utricle and saccule.
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Semicircular canals.
3 bony canals that project superiorly and posteriorly from the vestibule. Ampulla at one end of each canal.
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Semicircular ducts.
Parts of membranous labyrinth that lie inside the semicircular canals.
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Cochlea.
Anterior of vestibule. Bony spiral canal. Resembles a snail shell. Divided into 3 channels: cochlear duct, scala vestibuli, scala tympani.
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Cochlear duct.
Continuation of membranous labyrinth into cochlea. Filled with endolymph.
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Scala vestibuli.
Channel above cochlear duct. Ends at oval window. Part of bony labyrinth of cochlea. Filled with perilymph.
214
Scala tympani.
Channel below cochlear duct. Ends at round window. Part of bony labyrinth of cochlea. Filled with perilymph.
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What separates the cochlear duct from the scala vestibuli?
Vestibular membrane.
216
What separates the cochlear duct from the scala tympani?
Basilar membrane.
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Spiral organ.
Organ of Corti. Rests on basilar membrane. Composed of epithelial cells and 16000 hair cells.
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Inner hair cells.
Arranged in a single row. Hearing receptors. Convert mechanical vibration of sound into electrical signals.
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Outer hair cells.
Arranged in 3 rows. Increase sensitivity of inner hair cells.
220
Stereocilia.
At the apical tip of each hair cell. Extend into endolymph of cochlear duct.
221
What does the basal end of each hair cell synapse with?
First order neurons and motor neurons from cochlear branch of vestibulocochlear nerve.
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Inner hair cells synapse with:
95% of first order sensory neurons in the cochlear nerve that relay auditory input to the brain.
223
Outer hair cells synapse with:
90% of motor neurons in the cochlear nerve.
224
Inner membranous labyrinth.
Series of epithelial sacs and tubes inside the labyrinth that have the same general form as the labyrinth. House receptors for hearing and equilibrium. Contains endolymph.
225
Which substance in the ear contains high amounts of K+?
Endolymph.
226
Sound waves.
Alternating high and low pressure regions travelling in the same direction through a medium.
227
The higher the frequency of the vibration:
The higher the pitch of the sound.
228
Which frequencies are most accurately heard by the human ear?
500-5000 Hz.
229
What is the entire audible range of the human ear?
20-20000 Hz.
230
The higher the intensity of the vibration:
The louder the sound. An increase of 1 dB represents a 10-fold increase in sound intensity.
231
Hearing threshold.
0-1000 Hz.
232
Sound becomes uncomfortable at ____ and painful above ____.
120 dB. 140 dB.
233
Describe the process of hearing.
Auricle directs sound waves into external auditory canal --> sound waves strike tympanic membrane which then vibrates back and forth --> malleus vibrates --> incus vibrates --> stapes vibrates in the oval window --> fluid pressure waves in the perilymph of cochlea are transmitted from scala vestibuli to scala tympani --> round window --> pressure waves deform walls of scala vestibuli and tympani, and push the vestibular membrane back and form --> pressure waves in endolymph of cochlear duct --> basilar membrane vibrates --> hair cells of spinal organ move against tectorial membrane --> stereocilia bend --> nerve impulses generate in first order neurons of cochlear nerve.
234
Receptor organs for equilibrium.
Vestibular apparatus: utricle, saccule, semicircular ducts.
235
Otolithic organs.
Utricle and saccule. Macula is a small thickened region attached to the inner walls of the utricle and saccule. The two maculae contain the receptors for linear acceleration/deceleration and the position of the head. Maculae consist of hair cells and supporting cells.
236
Hair bundle.
Stereocilia and kinocilium.
237
Otolithic membrane.
Thick gel-like glycoprotein layer secreted by columnar supporting cells. Rests on hair cells. Sits on top of macula so it slides downhill with gravity when you tilt your head forward.
238
Otoliths.
Layer of dense calcium carbonate crystals. Extends over entire surface of otolithic membrane.
239
Utricle.
Responds to horizontal linear acceleration/deceleration and forward/backward tilting of the head.
240
Saccule.
Responds to vertical linear acceleration/deceleration.
241
Bending the hair bundles in one direction stretches the tip links and:
Pulls open cation channels to produce depolarizing receptor potentials. Bending the hair bundles in the opposite direction closes the cation channels and produce hyperpolarization.
242
The two vertical semicircular ducts are the:
Anterior and posterior ducts.
243
The horizontal semicircular duct is the:
Lateral duct.
244
Which position do the semicircular ducts detect?
Rotational acceleration/deceleration.
245
What moves and what stays behind when the head rotates?
Moves: semicircular ducts and hair cells. Lags: endolymph within ampulla.
246
The drag of the endolymph causes:
The cupula and the hair bundles that project into it to bend in the direction opposite to that of the head rotation. If the head continues to move at a steady pace, the endolymph begins to move at the same rate and causes the cupula and hair bundles to stop bending and return to rest. Once the head stops moving, the endolymph keeps moving and then eventually stops.
247
When hair cells are depolarized:
There is a greater frequency of APs generated in the vestibulocochlear nerve.
