Chapter 17: The Special Senses Flashcards
1
Q
Define the olfactory epithelium
A
A region in the superior part of the nasal cavity, covering the inferior surface of the cribriform plate and extending along the superior nasal concha that contains receptors
2
Q
List the 3 types of cells in the olfactory epithelium
A
olfactory receptor cells
supporting cells
basal cells
3
Q
Describe olfactory receptor cells
A
First-order neurons of the olfactory pathway
Bipolar neurons with an exposed knob-shaped dendrite and an axon projecting though the cribifrom plate that ends in the olfactory bulb
4
Q
Define olfactory cilia
A
Projections from the dendrite of an olfactory receptor cell which are sites of olfactory transaction - conversion of a stimulus energy into a grated potential in a sensory neuron
Within the membranes of the cilia are olfactory receptors that detect inhaled chemicals
5
Q
Define odorants
A
chemicals that have an odour that bind to and stimulate the olfactory receptors in the olfactory cilia
6
Q
How do supporting cells contribute to olfaction?
A
Columnar epithelial cells of the mucous membrane lining the nose
They provide physical support, nourishment, and electrical insulation for the olfactory receptor cells and help detoxify chemicals
7
Q
How do basal cells contribute to olfaction?
A
Stem cells located between the bases of the supporting cells that continually undergo cell division to produce new olfactory receptor cells, which live for only a month or so before being replaced
8
Q
Define olfactory glands (Bowman’s glands)
A
Located in the connective tissue that supports the olfactory epithelium which produce mucous that is carried to the surface of epithelium by ducts
Moistens the surface and dissolves odourants so that transduction can occur
9
Q
What is the sequence of events from the binding of an odorant molecule to an olfactory cilium to the arrival of a nerve impulse in the orbitofrontal area?
A
Olfactory transaction occurs in the following way:
- odourant binds and stimulates a G protein (membrane protein)
- G protein activates the enzyme adenylate cyclase to produce a substance called cyclic adenosine monophosphate (cAMP)
- cAMP opens a channel that allows Na+ to enter the cytosol, causing depolarizing generator potential to form
- If depolarization reaches threshold an AP is generated along the axon of the olfactory receptor cell
10
Q
Do olfactory receptors adapt slowly or quickly?
A
Quickly but they are very sensitive (low threshold)
11
Q
Define olfactory (I) nerves
A
on each side of the nose ~40 bundles of unmyelinated axons of olfactory cells tend though about 20 olfactory foramina in the cribiform plate of the ethmoid bone, collectively termed the olfactory (I) nerves
12
Q
Where do olfactory (I) nerves terminate?
A
In the brain in paired masses of gray matter called the olfactory bulbs, which are located below the frontal lobes the cerebrum and lateral to the cristina galli of the ethmoid bone
13
Q
Define the olfactory tract
A
Axons of olfactory bulb neurones extend posteriorly to form the tract
- some projecting to the primary olfactory area of the cerebral cortex located at the inferior and medial surface of the temporal lobe
- Others projecting the limbic and hypothalamus for our emotional/memory-evoked responses
Olfactory sensations are the only sensation that reach the cortex without first synapsing with the thalamus
14
Q
Define taste buds
A
An oval body consisting of 3 kinds of epithelial cells: supporting cells, gustatory receptor cells, and basal cells
15
Q
How do supporting cells contribute to gustation?
A
They contain microvilli and surround about 50 gustatory receptor cells in each taste bud
Gustatory microvilli project from each receptor cell to the external surface through the taste pore, and opening in the taste bud
16
Q
How do basal cells contribute to gustation?
A
Stem cells found at the periphery of the taste bud near the connective tissue layer
Produce supporting ells, which then develop into receptor cells - each receptor cell has a life span of about 10 days
17
Q
Define papillae
A
Elevations on the lounge which increase SA and provide a rough texture to the upper surface of the tongue
18
Q
Describe vallate (circumvallate) papillae
A
About 12 form an inverted V shaped row at the back of the tongue- each houses 100-300 taste buds
19
Q
Describe fugiform papillae
A
Mushroom-shaped elevations scattered around the entire surface of the tongue that contain about 5 taste buds each
20
Q
Describe foliate papillae
A
Located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood
21
Q
Describe filiform papillae
A
pointed, threadlike structures on the entire surface of the tongue that contain tactile receptors but no taste buds
They increase friction between tongue and food making it easier for the tongue to move food in the oral cavity
22
Q
Trace the path of a gustatory stimulus from contact of a tastant with saliva to the primary gustatory area in the cerebral cortex.
A
Tastant is dissolve din saliva and makes contact with the gustatory microvilli, which are the sites of taste transaction
A receptor potential stimulates exocytosis of synaptic vesicles from the gustatory receptor cell
The NTs trigger nerve impulses in the first-order sensory neurons that synapse with gustatory receptors
For salty (Na+) and sour (H+) food the accumulation inside the cell causes depolarization which leads to release of NT
Other tastants bind to receptors of the membrane that are linked to G proteins which activate second messages inside the the gustatory cell which cause depolarization and releases of a NT
23
Q
How does taste thresholds differ?
A
Bitterness is the lowest (poisonous), sour is higher and salty and sweet are similar and have the highest thresholds
Complete adaption of a taste can occur in 1-5 minutes
24
Q
Describe the 3 cranial nerves that contain axons of the first-order gustorary neurons that innervate the taste buds
A
Facial (VII) nerve serves taste buds in the anterior two-thirds of tongue
Glossopharyngeal (IX) serves taste buds in the posterior one-third of tongue
Vagus (X) nerve serves taste buds in the through and epiglottis
25
Describe the gustatory pathway
From taste buds nerve impulses propane along the 3 cranial nerves to the gustatory nucleus in the medulla oblongata
From the medulla, some axons project to the limbic system and hypoththlamus and others project to the thalamus
From the thalamus the signals project to the primary gustatory area in the parietal lobe
26
Define the palpebral fissure
The space between the upper and lower eyelids that exposes the eyeball
Its angles are known as the lateral commissure and medial commissure
27
Define lacrimal caruncle
A small reddish elevation in the medial commissure which contains sebaceous glands and sudoriferous glands
28
Define tarsal plate
A thick fold of connective tissue that gives form and support to the eyelids
Embedded in which are rows of modified sebaceous glands known as tarsal glands (meibomian glands) that secrete a fluid that helps keep the eyelids from adhering to each other
29
Define conjunctiva
A think, protective mucous membrane composed on nonkeratinized stratified squamous epithelium with numerous goblet cells that is supported by areolar connective tissue
30
Define the lacrimal apparatus and the flow of tears
A group of structures that produces and drains lacrimal fluid or tears in a processes called lacrimation
Lacrimal glands secrete tears into 6-12 lacrimal ducts that empty onto the surface of the conjunctiva of the upper lid
Tears pass medially and enter two small openings called the lacrimal puncta
Tears then pass into two ducts called the superior and inferior lacrimal canaliculi which lead into the lacrimal sac and then the nasolacrimal duct
Tears then drain into the nasal cavity
31
What is the purpose of lysozyme in lacrimal fluid?
It is a protective bactericidal enzyme
32
What are the 6 extrinsic eye msucles that move each eye?
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Superior rectus
Inferior rectus
Medial rectus
Superior oblique
Inferior oblique
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they are supplied by the oculomotor (III), trochlear (IV), or abducens (VI) nerves
33
Define periorbital fat
It is what surrounds the extrinsic eye muscles
34
List the 3 major layers of the eyeball
Fibrous tunic
Vascular tunic
Retina (inner tunic)
35
Describe the fibrous tunic
The superficial layer of the eyeball and consists of the: anterior cornea and posterior sclera
36
Describe the anterior cornea
transparent coat that covers the coloured iris; helps focus light into retina due to its curve
Outer surface - nonkeratinized stratified squamous epithelium
Middle - collagen fibers and fibroblasts
Inner - simple squamous epithelium
37
Describe the posterior sclera
the white of the eye; layer of dense connective tissue made up mostly of collagen fibers and fibroblasts
Covers the entire eye except the cornea; gives shape to the eye and protects the inner parts; serves as a site of attachment for extrinsic eye muscles
38
Define scleral venous sinus
An opening at the junction of the clear and cornea - aqueous humour (fluid) drains into this
39
Describe the vascular tunic
The middle layer of the eyeball that is composed of 3 parts: choroid, cilary body, and iris
40
Describe the choroid
The posterior portion the the vascular tunic which lines most of the internal surface of the sclera
Its blood vessels provides nutrients to the posterior surface of the retina
It also contains melanin which absorbs light and prevents reflection and scattering of light within the eyeball
41
Describe the ciliary body
the anterior portion of the vascular tunic that extends from the ora strata (jagged anterior margin of the retina) to ta point just posterior to the function of the sclera and cornea
Contains cillarly processes that secrete aqueous humorous
42
What are zonular fibers (suspensory ligaments) and how do they contribute to vision?
processes that extend from ciliary processes in the vascular tunic that attach to the lens
the tightness of these fibres are chanted by contraction or relaxation of the ciliary muscle (smooth muscle) which alters the shape of the lens, adapting for near/far vision
43
Describe the iris
The coloured portion of the eyeball that consists of melanocytes and circular radial smooth muscle fibers - Amount of melanin determines eye colour
A principal function is to regulate the amount of light entering the eyeball through the pupil
44
Which division of the ANS causes pupillary constriction? Which causes pupillary dilation?
Parasympathetic fibers of the oculomotor (III) nerve stimulate circular muscles (sphincter) of the iris to contract, causing pupil constriction
Sympathetic neurons stimulate radial muscles of the iris to contract, causing pupil increase (dilation)
45
Describe the retina
The inner layer of the eyeball that lines the posterior 3/4 of the eyeball and is the beginning of the visual pathway; consists of 2 layers:
Pigmented layer - sheet of melanin-containing epithelial cells located between the choroid and the neural part of the retina
Neural layer - multilayered outgrowth of the brain that processes visual data extensively before seeing impulses into axons that form the optic nerve
46
List the 3 distinct layers of the renal neurons
Photoreceptor layer
Bipolar cell layer
Ganglion cell layer
They are separated by the outer and inner synaptic layers, were synaptic contacts are made
47
Describe horizontal and amacrine cells. Where are they found?
Present in the bipolar cell layer of the retina - they form laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to bipolar cells to ganglion cells
48
Describe the two types of photoreceptors
Rods - allow us to see in dim light but only in black and white as they do not produce colour vision
Cones - allow us to see bright lights and colour; cones are blue, green, and red
49
Define a blind spot
The optic disc as it does not contain rods or cones and thus we cannot see images that strike this blind spot
50
Define macula lutea and central fovea
macula lutea- The exact center of the posterior portion of the teen, at the visual axis of the eye
Central fovea/fovea centralis - a small depression in the center of the macula lutea, containing only cones and is the area of highest visual acuity
51
Describe the lens
Located behind the pupil and iris, within the cavity of the eyeball
Contains proteins called cyrsallins, arranged like layers of an inion, which make up the refractive media of the lends, which is normally perfectly transparent and lacks blood vessels
52
What are the two cavities of the interior eyeball?
Anterior cavity - contains aqueous humour that helps maintain shape of eyeball and supplies oxygen and nutrients to lens & cornea; consists of 2 chambers:
- Anterior chapter lies between the cornea and iris
- Posterior chamber lies behind the iris and in front of the zonular fibers and lens
Vitreous chamber - contains vitreous body that helps maintain shape of eyeball and keeps retina attached to choroid
53
Define vitreous body
Transparent jellylike substance that holds the retina flush against the choroid, giving the retina an even surface for the receptor of clear images
54
Where is aqueous humor produced, what is its circulation path, and where does it drain from the eyeball?
After its secretion by the ciliary process, aqueous humor flows into the posterior chamber, around the iris, into the anterior chamber, and out of the eyeball through the scleral venus sinus
55
Define intraocular pressures
Pressure in the eye process mainly by aqueous humour and partly by vitreous body
It maintains the shape of the eyeball and prevents it from collapsing
56
Describe refraction or being of light by the lens and cornea
As light enters the eye, they are refracted at the anterior and posterior surfaces of the cornea and then both surfaces of the lens further refract so they come into exact focus on the retina
75% of total refraction occurs at cornea and the rest by the lens
Images are inverted and undergo right-to-left reversal
57
Describe accommodation
When the lens is convex the light will be refracted towards each other; When the lens in concave the light will be refracted away from each other
The increase of curvature of the lens for near vision is accommodation
58
Define near point of vision
The minimum distance from the eye that an object can be clearly focused with a maximum accommodation
~10cm in a young adult
59
Describe presbyopia
A condition where the lens loses elasticity and thus its ability to curve to focus on objects that are too close
This is why older people cannot read the same print as younger people
60
Define emmetropic eye
A normal eye which can sufficiently refract light rays from an object 6m away so that a clear image is focused on retina
61
Describe the following refraction abnormalities
Myopia
Hypermetropia or hyperopia
astigmatism
Myopia (nearsightedness) - eyeball is too long relative to the focusing power or the lens is thicker than normal, so an image converges in front of the retina
Hypermetropia or hyperopia (farsightedness) - eyeball is too short or lens is thinner than normal so image covers behind the retina
astigmatism - either the cornea or lens has an irregular curvature and thus parts of the image are out of focus
62
Define convergence
The medial movement of the two eyeballs so that both are directed toward the object being viewed
The nearer the object, the greater degree of convergence needed to maintain binocular vision
63
Define binocular vision
Both eyes focus on only once set of objects that allows for perception of death and appreciation of 3 dimensional nature of objects
Humans have this type of vision
64
What is the first step in visual transduction?
Absorption of light by a photopigment, a colour dprotein that undergoes structural changes when it absorbs light, in thh outer segment of a photoreceptor
65
Differentiate between the types of photopigments in rods and coves
Rods: rhodopsin
Cones: green, red, blue
66
All photopigemetns associated with vision contain two parts: a glycoprotein known as _____ and a derivative of vit A called ______
opsin ; retinal
67
What are the 4 steps in the cyclical bleaching and regeneration of photopigments (the response to light)?
1. cis-retinal (bent shape in darkness) absorbs light and straightens to trans-retinal, a conversation called ismerization
2. trans-retinal separates from opsin - final product looks colourless and thus termed bleaching
3. An enzyme called retinal isomerase coverts trans-retinal back to cis-retinal
4. cis-retinal binds to opsin, reforming a functional photopigment - process called regeneration
68
Differentiate between light and dark adaptation
As the light level increases, more and more photopigment is bleached
In daylight, rhodopsin cannot keep up with the bleaching process so rods contribute little to daylight vision
69
Describe the operation of rod photoreceptors in darkness
1. cAMP-gated Na+ channels open
2. Inflow of Na+ (dark current)
3. Membrane potential of -30mV
4. Glutamate is released at synaptic terminals and inhibits bipolar cell preventing them from transmitting signals to ganglion cells
70
Describe the operation of rod photoreceptors in darkness
1. isomerization of retinal activates enzyme that breaks down cGMP
2. cGMP-gated Na+ channels close
3. Inflow of Na+ slows
4. Hyperpolarizing receptor potential
5. Glutamate release turned off, which exited cipher cells that simulates ganglion cells to form APs
71
Define color blindness
An inherited inability to distinguish between certain colours as a result of absence or deficiency of one of the three types of cones
72
Define night blindness
Inability to see well at low light levels due to a prolonged vit A deficiency resulting in low levels of rhodopsin
73
Describe the visual brain pathway
1. Axons of all retinal ganglion cells in one eye exit the eyeball at the optic disc and form the optic (II) nerve on that side
2. At the optic chasm, axons from the temporal half of each retina do not cross but continue directly to the lateral geniculate nucleus of the thalamus
3. Axons from the nasal half of each retina cross and continue to the opposite thalamus
4. Each optic tract consists of crossed and uncrossed axons that project from the optic chasm to the thalamus on one side
5. Axon collaterals of the retinal ganglion cells project to the midbrain, where they participate in neural circuits that govern contraction and coordination of movements
6. Axons of the thalamic neurons form the optic radiations which project to the primary visual area of cortex on the same side
74
List the 3 main regions of the ear
External ear - collects sound eaves and channels them inward
Middle ear - covers sound vibrations to the oval window
Inner ear - houses receptors for hearing and equilibrium
75
Describe the 3 components external ear
auricle - flat of elastic cartilage (helix & lobe)
external auditory canal - served due that lies in the temporal bone and leads to the eardrum
eardrum (tympanic membrane) - thin, semitransparent partition between the external canal and the middle ear
76
Which glands secrete cerumen (ear wax) and where are they located?
ceruminous glands - located near the exterior opening
77
Describe the middle ear and the auditory ossicles
Middle ear is a small air-filled cavity in the temporal bone that is lined by epithelium
3 auditory ossicles are connected by synovial joints:
- Malleus: attaches to internal surface of ear drum and articulates with the incus
- Incus: the middle bone that articulates with the head of the stapes
- Stapes: fits into the oval window
78
What structures separate the middle ear from internal ear?
The oval and round windows (below the oval window)
79
Describe the auditory tube (eustachian tube)
Consists of both bone and elastic cartilage and connects the middle ear with the nasopharynx
80
What is the clinical signficance of the stapedius muscle?
Supplied by the facial (VII) nerve and is the smallest skeletal muscle in the human body
Paralysis of this muscle is associated with hyperacusia, which is abnormally sensitive hearing
81
Describe the internal ear and its two many structural divisions
Inner ear (labrinth) has 2 divisions:
An outer bony labyrinth - series of cavities in the petrous portion of the temporal love divided into 3 areas (semicircular canals, vestibule, and cochlea)
An inner membranous labyrinth - series of epithelial sacs and tubes inside the bony labyrinth that have the same general form and house the receptors for hearing and equilibrium
82
Define perilymph and endolymph
perilymph - fluid in the bony labyrinth which is chemically similar to CSF
endolymph - fluid in the membranous labyrinth
83
What are the names of the two sacs that lie in the membranous labyrinth of the vestibule?
Utricle and saccule, which are connected by a small duct
84
Define the vestibule and semicircular canals
The oval central portion of the bony labyrinth
Semicircular canals project from the vestibule and based on their position are named anterior, posterior, and lateral
85
Define ampulla
A swollen enlargement at one end of each semicircular canal
86
Describe the cochlea
Located anterior to the vestibule
It is a bony spinal canal that resembles a snail shell and makes almost three turns around central bony core called the modiolus
87
What fluid is in the cochlear duct?
Endolymph as it a continuation of the membranous labyrinth into the cochlea
88
What are the 3 channels within the cochlea?
Cochlear duct - continuation of the membranous labyrinth into the cochlea
Scala vestibuli - above the duct which ends at the oval window
Scala tympani - below the duct which ends at the round window
The scala channels hold perilymph as they are part of the bony labyrinth
89
Define helicotrema
An opening at the apex of the chuckle where the scale vestibule and tympani connect
90
Describe the vestibular and basilar membrane
Vestibular separates the cochlear duct from the scala vestibule
Basilar separates the cochlear duct from the scala tympani
91
Describe the spiral organ (organ or Corti)
Rests on the basilar membrane and is a coiled sheet of epithelial cells, including hair cells which are the receptors for hearing
92
What are sterocilia?
they are at the apical tip of hair cells and extend into the endolymph of the cochlear duct
They are actually long, hairlike micrvolli
93
Define tectorial membrane
A flexible gelatinous membrane, covers the hair cells of the spiral organ
94
What is the difference between frequency and intensity of a sound vibration?
Frequency is its pitch - the higher frequency the higher the pitch
Intensity is its amplitude - the higher intensity the louder the sounds
95
At what decibel does sound become painful?
140dB - exposure to loud noises damages hair cells in the cochlea
normal conversation is 60dB
96
Describe the events involved in hearing
1. Auricle directs sounds waves into external canal
2. When sound strike tympanic membrane, the altering waves of high/low pressure cause it to move back and forth
3. Central area of tympanic membrane connects to malus which transmits vibration to incus and the stapes
4. As stapes moves back and forth it vibrates in the oval window
5. The movement at the oval window sets up fluid pressure waves in the perilymph of cochlea and pushes on the scala vestibuli
6. Presssure waves are transmitted from scala vestibule to scala tympani and eventually to round window causing it to bugle outward
8. Pressure eave in endoylmpth cause basilar membrane to vibrate, moving hair cells of the spiral organ against the tectorial membrane leading to bedinign to sterocilia
9. Bending leads to release of NT which generates nerve impulses in first-order neurons in cochlear nerve fibers
97
How does auditory information travel through the brine?
It is covered along the cochlear branch of the vestibulocohlear (VII) nerve and then to the brain stem, thalamus, and cereal cortex
98
Differentiate between static and dynamic equilibrium
Static - maintenance of the position of the body (mainly head) relative to the force of gravity (tilting the head and linear acceleration or deceleration)
Dynamic - maintenance of the position of the body (mainly head) is response to sudden movements (rotational acceleration or deceleration)
99
What is the vestibular apparatus? What are its components?
The receptor organs for equilibrium; include the saccule, utricle, and semicircular ducts
100
What is a macula?
A thickened regions in the walls of both the utricle and the saccule
They are the receptors for static equilibrium - they provide sensory information on the position of the head in space and are essential for maintaining appropriate posture and balance
101
Maculae consists of which 2 types of cells?
Hair cells - sensory receptors
| Supporting cells
102
Define otolithic membrane and otoliths
Columnar supporting cells that secrete the thick, gelatinous, glycoprotein layer that rests on the hair cells
Otoliths are a layer of dense calcium carbonate crystals that extend over the entire otolithic membrane
103
With which type of equilibrium are the semicircular ducts associated?
Dynamic equilbrium
As head rotates in one direction cupula which covers the crista (small mass of gelatinous material in the ampulla) is dragged through endolymph and bent in the opposite direction
104
Describe the equilibrium pathway
From hair cells of the semisurcal ducts, utricle and saccule, vestibular information is covered along the vestibular branches of the vesibulocochelar (VIII) nerve and then to the brain stem, cerebellum, thalamus, and cerebral cortex
105
Where are the vestibular nuclei located?
In the medulla and ponds
106
Define cataracts
loss of transparency of the lens - it becomes cloudy due to changes in the structure of the lens proteins
107
Define glaucoma
Most common cause of blindness that i due to abnormally high intraocular pressure as a result of a buildup of aqueous humour within the anterior cavity
It is painless and the other eye may compensate so there is significant damage before it is even diagnoses
108
define deadness
sensorineural - Either caused by impairment of hair cells in the cochlea or damage of the cochlear branches of the vesibulocochelar (VIII) nerve
conduction - caused by impairment to the external and middle ear mechanisms for transmitting sounds
109
Define conjunctivitis
Pink eye
| Inflammation of the conjunctiva - if caused by bacteria and not irritant it can be very contagious
110
Define keratitis
Inflammation or infection of cornea
111
Define tinnits
Ringing, roaring or clicking in ears
112
Define vertigo
Sensation of spinning or movement, often associated with nausea
