ch 17: special senses Flashcards
1
Q
what are the three main regions of the ear and what do they do?
A
External (outer) ear
◦ Collects sound waves
-Middle ear
◦ Conveys sound vibrations to oval window
- Internal (inner) ear
◦ Houses receptors for hearing and
equilibrium
- Internal (inner) ear
2
Q
describe the anatomy of the external ear
A
contains the auricle with is the outside of your ear. it is formed of elastic cartilage covered with skin
the external auditory canal channels sound waves to the tympanic membrane
the tympanic membrane (eardrum) vibrates in response to sound waves and passes the vibrations into the middle ear
3
Q
describe the anatomy of the middle ear
A
the auditory ossicles consist of the incus, malleus and stapes. these are connected by synovial joints
4
Q
The auditory ossicles
a) are muscles that transmit sound vibrations from the outer ear to
the middle ear
b) are muscles that transmit sound vibrations from the outer ear to
the inner ear
c) are bones that transmit sound vibrations from the outer ear to
the inner ear
d) transmit sound waves, but they are neither bones nor muscles
A
C
5
Q
how do vibrations pass through the middle ear
A
Vibrations caused by sound waves are passed on from
the tympanic membrane to the malleus (attached to the
tympanic membrane), followed by the incus, and the
stapes (the three auditory ossicles). The stapes
transmits the vibrations to the inner ear.
6
Q
what do the stapedius muscle and tensor tympani muscle of the middle ear do?
A
The stapedius muscle
and tensor tympani
muscle prevent
excessive vibrations of
ossicles and eardrum
in loud noise.
7
Q
what do the vestibular (oval) window and the cochlear (round window do? in middle ear
A
connect the middle ear and the inner ear
8
Q
what is the function of the auditory tube in the middle ear?
A
The auditory tube connects
the middle ear and the
nasopharynx; to equalize
pressure between external
ear and middle ear
9
Q
describe the semicircular canals of the inner ears
what do the contain
A
The semicircular canals as well as the vestibule
contain the receptors for equilibrium
10
Q
what is the function of the cochlea
A
contains receptor cells for hearing
11
Q
what forms the structures of the inner ear
A
The structures of the inner ear
are formed of an outer bony
labyrinth (contains perilymph )
and an inner membranous
labyrinth (contains endolymph)
12
Q
scala tympani of the cochlea vs scala vestibuli of the cochlea
A
The scala tympani is part
of the bony labyrinth; it
contains perilymph (he fluid contained within the bony labyrinth, surrounding and protecting the membranous labyrinth)
The scala vestibuli is part
of the bony labyrinth; it
contains perilymph
The scala tympani and vestibuli are
completely separated, except at
the helicotrema
13
Q
describe the cochlear duct of the cochlea
A
part of the membranous labyrinth; it contains endolymph
14
Q
endolymph vs perilymph
A
Endolymph is rich in potassium and low in sodium and calcium, whereas perilymph is rich in sodium and low in potassium and calcium
15
Q
the spiral organ of the cochlea
A
The spiral organ is the epithelium
that contains the receptors for
hearing → it rests on the basilar
membrane, in the cochlear duct
16
Q
the vestibular membrane vs basilar membrane of cochlea
A
separates the cochlear duct
from the scala vestibule
The basilar membrane
separates the cochlear duct
from the scala tympani: the
spiral organ rests on it
17
Q
describe soundwaves
A
Alternating regions of high/low pressure travelling in same direction
◦ Waves move through a medium (air, water…)
◦ Waves have frequency, wavelength, and amplitude
18
Q
describe the frequency of soundwaves. which frequencies can we hear?
A
Frequency determines pitch of a sound
◦ Higher the frequency → higher the pitch
◦ Measured in cycles per second, or Hertz (Hz)
◦ Audible range = 20-20,000 Hz
19
Q
what is the amplitude of sound?
A
Intensity = VOLUME = amplitude or “size” of the
wave
20
Q
what are the 8 steps in the physiology of hearing?
A
- The auricle directs sound waves into the external acoustic meatus.
- When sound waves strike the tympanic membrane, the alternating waves of high and low pressure in the air cause the tympanic membrane to vibrate back and forth. The tympanic membrane vibrates slowly in response to low-frequency (low-pitched) sounds and rapidly in response to high-frequency (high-pitched) sounds.
- The central area of the tympanic membrane connects to the malleus, which vibrates along with the tympanic membrane. This vibration is transmitted from the malleus to the incus and then to the stapes.
4.As the stapes moves back and forth, its oval-shaped footplate, which is attached via a ligament to the circumference of the vestibular window, vibrates in the vestibular window. . - The movement of the stapes at the vestibular window sets up fluid pressure waves in the perilymph of the cochlea. As the vestibular window bulges inward, it pushes on the perilymph of the scala vestibuli.
- Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the cochlear window, causing it to bulge outward into the middle ear.
- As the pressure waves deform the walls of the scala vestibuli and scala tympani, they also push the vestibular membrane back and forth, creating pressure waves in the endolymph inside the cochlear duct.
- The pressure waves in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the spiral organ against the tectorial membrane. This leads to bending of the stereocilia and ultimately to the generation of nerve impulses in first-order neurons in cochlear nerve fibers.
21
Q
spiral organ vs hair cells
A
The spiral organ is the
epithelium that contains the
receptors for hearing: it rests
on the basilar membrane
Hair cells with stereocilia
(microvilli) are the
receptors for hearing.
They synapse with firstorder neurons (CN VIII)
22
Q
what does movements of basilar membrane cause
A
Movements of the basilar membrane cause the stereocilia of
hair cells to rub against the tectorial membrane. Bending of
stereocilia causes mechanically gated K+ channels to open,
causing K+
to enter the cell (remember, endolymph is high in K+
23
Q
what happens when there is an influx of K+ cells
A
Influx of K+
leads to
depolarization of the hair cells,
which then release
neurotransmitters onto first-order neurons, triggering an EPSP
in the cochlear branch of the
vestibulocochlear nerve (CN VIII)
24
Q
When depolarization takes place in hair cells,
a) sodium channels open, and sodium enters the cell
b) potassium channels open, and potassium enters the cell
c) potassium channels open, and potassium leaves the cell
d) calcium channels open, and calcium enters the cell
A
d
25
simplified steps of physiology of hearing
1.Auricle directs sounds waves into external auditory canal
2.Eardrum vibrates (slowly for low frequency, rapidly for high frequency)
3.Vibration of eardrum causes malleus to vibrate, transmitted to the incus, then to the stapes
4.Stapes makes oval window vibrate in and out of inner ear
5.Fluid pressure waves develop in the perilymph of scala vestibuli in the cochlea
6.Pressure waves transmitted from scala vestibuli to scala tympani through helicotrema,
eventually through round window (#9), which bulges outward in middle ear
7.Pressure waves also push the vestibular membrane back and forth, creating pressure waves
in endolymph inside cochlear duct
8.Pressure waves in endolymph cause basilar membrane to vibrate, which moves the hair cells
of the spiral organ against the tectorial membrane. Bending of hair cell stereocilia produces
receptor potentials leading to action potential in cochlear branch of CN VIII.
26
describe the 5 steps of the auditory pathway
15. from thala. CN VIII to medula
2. some axons go from medulla to pons to locate the source of sounds
3. from medulla and pons to inferior colliculi of midbrain
4. from midbrain to thalamus to primary auditory area of cerebral cortex
27
what are the 2 types of balance
1. Static equilibrium
◦ Maintain the position of the body (head) relative to the force of gravity, or
linear acceleration
2. Dynamic equilibrium
◦ Maintain body position (head) during sudden movement of any type -
rotation, deceleration or acceleration - rotational
28
what role does the vestibule play in static equillibrium
The vestibule contains
the receptors for static
equilibrium
29
what do the utricle and saccule do in static equillibrium
the utricle and the saccule are
sacs (membranous labyrinth)
of the vestibule
Within the wall of the utricle
and the saccule is a small
region called the macula; both
maculae contain the receptors
for static equilibrium.
30
what role do otolithic membraine and hair cells play in static equilibrium?
otolithic membrane covers hair cells
hair cells with stereocilia are the receptors for equilibrium
supporting cells secrete a gelatinous layer called otolithic membrane
31
what happens when you tilt your head
As you tilt your head, otolithic
membrane moves and causes
the bending of stereocilia
Bending of stereocilia causes
mechanically gated K+ channels to
open, followed by K+
influx, leading
to the depolarization of hair cells.
Neurotransmitters released from hair
cells onto first-order neurons triggers
an EPSP in the vestibular branch of the
vestibulocochlear nerve (CN VIII)
32
Just like with the sense of hearing,
a) equilibrium involves mechanically-gated channels
b) equilibrium involves the vestibulocochlear nerve
c) equilibrium involves the entry of potassium into the cell to cause
depolarization
d) All the above
d) all the above
33
what role do the semicircular canals play in dynamic equillibrium
they contain the receptors for dynamic equillibrium
34
describe the role of the ampulla in dynamic equillibrium
the ampulla of semicircular canals
are sacs of membranous labyrinth
Within the wall of the ampullae
is a small region called crista;
cristae contain the receptor
cells for dynamic equilibrium.
35
describe the role of the cupula
the cupula (gelatinous tissue) covers hair cells
hair cells with stereocilia are the receptors for equillibrium
36
what happens when you turn your head (like shaking it)
As you turn your head, fluid in
ampulla causes cupula to move,
followed by bending of stereocilia
Bending of stereocilia causes
mechanically gated K+ channels to
open, followed by K+
influx, leading
to the depolarization of hair cells.
Neurotransmitters released
from hair cells onto first-order neurons triggers an
EPSP in the vestibular branch
of the vestibulocochlear
nerve (CN VIII)
37
describe the equilibrium pathway
1. CN VIII to vestibular nuclei in medulla and pons
2. From vestibular nuclei to the
cerebellum for balance and posture
3. from vestibular nuclei to CN
III, IV, VI and XI for movements
of eyeball, head and neck
4. Impulses also to go primary
somatosensory are of cerebral
cortex via thalamus
38
Which is the correct order of events of sound
transmission through the ear?
1. Sound waves strike the eardrum
2. The ear ossicles vibrate
3. Hair cells of the organ of Corti vibrate
4. The perilymph in the cochlea moves
5. Sound waves enter the external auditory canal
a) 5, 4, 3, 2, 1
b) 1, 2, 3, 4, 5
c) 5, 1, 2, 4, 3
d) 5, 2, 1, 3, 4
C
39
Which structure within the ampulla contains hair
cells that are involved in dynamic equilibrium?
a) Cupola
b) Macula
c) Otolithic membrane
d) Crista
e) Vestibular apparatus
d) crista
40
what is olfaction
The sense of smell is a chemical sense
◦ Interaction of molecules with receptor cells
◦ To be detected, molecules (odorants) must be dissolved
41
where do olfactory impulses project to (in brain) and why?
Impulses project to the cerebral cortex (primary olfactory area, orbitofrontal
area), the limbic system (for emotional reactions) and the hypothalamus (for
memory-triggered reactions)
42
where are the receptors found for the olfactory system
All receptors (> 100 million) for
the sense of smell are found
within the olfactory epithelium,
which covers the superior nasal
cavity and cribriform plate (part
of the ethmoid bone)
43
what kind of neurons are olfactory receptors? Where do they extend to?
Olfactory receptors are first-order neurons; they are bipolar neurons with olfactory cilia. The long dendrite extends into
nasal cavity; the long axon goes through the
cribriform plate and joins other axons to form CN I
44
what do basal cells do?
Basal cells act as stem
cells in the olfactory
epithelium. Replace the
receptors monthly.
45
what do olfactory glands do?
They produce mucus
46
describe what happens in the physiology of olfaction. What is physically happening?
Odorants bind to
olfactory receptors (1st
order neurons).
Sodium channels
open, causing a
depolarizing graded
potential. A nerve
impulse is triggered in
the first-order neuron.
47
what are the 4 steps of transduction (olfaction)
1. axons of first-order neurons pass through about 40 formina in the cribiform plate
2. first-order neurons synapse with second-order neurons in the olfactory bulb
3. axons of second-order neurons form the olfactory tract
4. Second-order neurons synapse
with neurons in the primary
olfactory area of the cerebral cortex.
48
what is special about the olfactory pathway
Note: Olfactory pathway is the only
special sense where sensory information
goes directly to the cortex without first being relayed to the thalamus.
Some axons within the olfactory tract reach the limbic system and the hypothalamus (for emotional and
memory-evoked responses to odor
49
describe gustation
The sense of taste is also a chemical sense
◦ To be detected, molecules (tastants)
must be dissolved
◦ classes of tastants: sour, sweet, bitter,
salty and umami (meaty, savory)
50
where do they impulses for gustation project to?
| think brain
the cerebral cortex (primary and gustatory area) and the limbic system (for emotional reactions)
51
how many taste buds are there, where are they found?
Approx. 10,000 taste buds are found on the
tongue, soft palate & larynx. Taste buds are found
on the papillae: Vallate papillae (V-shaped row on
back of tongue), fungiform papillae (everywhere
on tongue) and foliate papillae (side of tongue)
(papillae = small projecting body part)
52
describe the filiform papillae. What makes them special?
Another type of papillae, filiform papillae, contain tactile receptors (no
taste buds) and increase friction between the tongue and food
53
describe gustatory receptor cells
Gustatory receptor cells (~50
per taste bud) with gustatory
microvilli that projects into a
taste pore, which opens on
the surface of the tongue.
Gustatory receptors cells
synapse with first-order
neurons.
54
describe the supporting cells of the taste buds
surround the receptor cells,
and basal cells act as stem cells; they replace
gustatory receptor cells every 10 days.
55
what are the two steps in the physiology of taste bud
1. Tastants bind to receptors
on hair of gustatory cell
2. A receptor potential is triggered in gustatory cells,
causing the release of neurotransmitters from the
gustatory receptors onto the first-order neurons
(gustatory receptor cells synapse with first-order neurons)
56
Binding of odorant molecules to olfactory
receptors
a) causes a hyperpolarizing graded potential
b) directly opens sodium channels
c) automatically causes an action potential
d) causes a graded potential, but not directly opens sodium channels
d) causes a graded potential, but not directly opens sodium channels
57
Olfactory receptor cells
a) are part of the olfactory bulb
b) synapse with first-order neurons in the olfactory epithelium
c) synapse with second-order neurons in the olfactory epithelium
d) synapse with second-order neurons in the olfactory bulb
d) synapse with second order-neurons in the synapse
58
In olfaction, binding of a dissolved odorant molecule
to a receptor triggers _____, which leads to a _____.
a) Depolarization / generator potential
b) Hyperpolarization / generator potential
c) Depolarization / receptor potential
d) Hyperpolarization / receptor potential
a) depolarization/ generator potential
59
where are first-order gustatory fibers found
1. cranial nerve X (vagus) (soft palate and epiglottis)
2. cranial nerve IX (glossopharangeal) (posterior 1/3 of tongue)
3. first-order gustatory fibers are also found in cranial nerve VII (facial) (anterior 2/3 of tongue)
60
where do first order neurons synapse with second-order neurons in gustatory system
in the pons or medulla
61
how do impulses travel in gustatory system?
| in brain
Impulses travel to the thalamus and then to the primary gustatory area in the cerebral cortex. Some impulses travel to the limbic
system and the hypothalamus for
emotional and memory-evoked
responses to taste
62
When a receptor potential is triggered in a
gustatory receptor cell
a) an action potential is triggered in the cell if threshold is reached
b) an action potential is triggered in the first order neuron if
threshold is reached
c) neurotransmitters are released onto first-order neurons
d) an action potential is automatically triggered in the gustatory
receptor cell
c) neurotransmitters are released on first-order neurons
63
Which cranial nerve contains first-order
neurons for gustation?
a) CN I
b) CN VII
c) CN XI
d) CN X
e) More than one of the above
E
64
Which is NOT an event that occurs during the
process of gustation?
a) Salty foods trigger opening of the sodium ion channels
b) A tastant is dissolved in saliva
c) First and second order neurons synapse in the spinal cord
d) Depolarization causes release of neurotransmitters
C because a receptor cells does not have an action potential
65
what is special about vision?
More than half the sensory receptors in
the human body are in the eyes.
A large part of the cerebral cortex is
devoted to processing visual information.
66
what is the function of eyelashes and eyebrows
protect the eyeballs from foreign objects, perspiration and the sun
67
what is the function of eyelids/ palpebrae?
protects and lubricates the eye
68
what muscle elevates the upper eyelid?
levator palpebrae
superioris muscle
elevates the upper eyelid
69
what does the lacrimal caruncle in the medial commissure contain?
sebaceous and sudoriferous glands
70
describe the eyelid from superficial to deep
epidermis, dermis, CT, obicularis oculi, tarsal plate, palpebral conjunctiva, bulbar conjunctiva
(not sure if right)
71
what is the tarsal plate
tarsal plate (thick CT gives shape/support to eyelid),
tarsal glands (lubricate)
72
where and what is the palpebral conjunctiva
palpebral conjunctiva lines the
inner aspect of eyelids (protective
mucous membrane – stratified
columnar epithelium w/ goblet cells)
73
describe the bulbar conjunctiva
covers the sclera, but not the cornea
74
describe the lacrimal apparatus
About 1 ml of tears produced per day
* Spread over eye by blinking
* Contains bactericidal enzyme called lysozyme
75
describe the cornea. What is the function?
The cornea is a transparent organ that
covers the iris. It is the anterior
extension of the sclera. The superficial layer is formed of nonkeratinized
stratified squamous epithelium, deeper are collagen fibers, and the deepest layer is simple squamous epithelium
The cornea helps focus light
on the retina
76
describe the sclera
The sclera is the “white” of the
eye. It covers the entire eyeball,
except where the cornea is. It is
formed of dense irregular CT and
gives shape to the eyeball
77
describe the choroid
| in the eye
The choroid is a highly vascular
membrane that provides
nutrients to the retina. It is just
deep to the sclera. It contains
melanocytes, of which melanin
pigments absorb scattered light
78
describe the ciliary body
The ciliary body is composed of the ciliary
muscle, which alters the shape of the lens for
far or near vision, and the ciliary processes,
which produce aqueous humor
79
describe the iris and the pupil
The iris is the colored portion of the
eye. It is formed of melanocytes and
rings of smooth muscle that contract to
alter the size of the pupil (hole in the
center of the iris), thereby regulating
the amount of light that enters the eye.
80
how do your eyes react in bright light
In bright light, a parasympathetic
autonomic reflex causes the
inner circular muscle fibers of
the iris to contract; the size of
the pupil decreases, reducing the
amount of light entering the eye
81
what happens to your eyes in dim light
In dim light, a sympathetic autonomic
reflex causes the outer radial muscle
fibers of the iris to contract; the size of
the pupil increases, increasing the
amount of light entering the eye
82
describe the anterior cavity of the eyeball
The anterior cavity is formed of the anterior
chamber (between the cornea and the iris), and the
posterior chamber (between the iris and the lens).
Both are filled with aqueous humor, a clear fluid
produced by the ciliary process from blood filtration
83
describe the vitreous chamber of the eyeball
The vitreous chamber is filled
with vitreous body, a gel-like
substance that holds the
retina against the choroid
84
describe the lens of the eyeball
The lens is an avascular organ; its
function is to focus the light on the
retina. It is filled with layers of thin
transparent cells; the cells do not
contain any organelle, but contain
transparent proteins called crystalline
85
what is the lens of the eyeball enclosed in?
The lens is enclosed in a clear, elastic CT
capsule, and is held in position by zonular
fibers, which attach to the ciliary process
86
what happens when an image is formed (to the light)
When an image is formed, refraction takes
place; the bending of light as it passes from
one substance (e.g., air) into a 2nd substance
with a different density (e.g., cornea)
87
how do your eyes refract the light?
In the eye, light is refracted by the lens and
the cornea; 75% of the refraction is done
by the cornea, and 25% is done by the lens
88
describe the image focused on the retina
The image focused on the retina is inverted & reversed from
left to right – the brain learns to work with that information
89
how do your eyes react to light right more than 6m away?
Light rays from > 6m (distant objects) are
nearly parallel and only need to be bent slightly
to focus on retina (refraction); the lens is nearly
flat due to the pulling of the zonular fibers
90
how do your eyes react to images less than 6m away?
Light rays from < 6m (close objects) are more
divergent & need more refraction. To view objects
that are close, accommodation must take place;
the increase in the curvature of the lens for near
vision. Ciliary muscles (CN III) contract and
decrease the pull of the zonular fibers on the
lens. As the tension is removed, the lens thickens
91
why are people nearsighted (myopic)
Eyeball too long, or
lens too thick (too
much refraction)
92
why are people farsighted (hyperopic)
Eyeball too short, or
lens too thin (need
greater refraction)
93
Which of the following is TRUE?
a) when the circular muscle fibers of the iris contract, the pupil
decreases in size
b) when the circular muscle fibers of the iris contract, the pupil
increases in size
c) when the radial muscle fibers of the iris contract, the pupil
decreases in size
d) circular and radial muscle fibers must contract together in order
for the pupil to decrease in size
A
94
Which of the following is TRUE?
a) The lens is responsible for most refraction of rays
b) The lens is used to view distant objects
c) The lens is necessary to view objects up close
d) A and B
C
95
In order to view an object up close, which of
the following must happen?
a) The ciliary muscle must relax
b) The zonular fibers must relax
c) The circular muscle fibers of the iris must relax
d) The radial muscle fibers of the iris must relax
b) the zonular fivers must relax
96
Put these structures in the correct order
that light passes through them:
1. Lens
2. Vitreous humour
3. Cornea
4. Sclera
a) 1,2,3
b) 3,1,2
c) 3,1,4,2
d) 3,1,2,4
e) 1,3,2,1
b
97
describe the retina
The retina is the innermost layer of the
eyeball; it contains the photoreceptors.
To form clear images, light needs to be
focused on the retina.
98
macula lutea vs central fovea in retina
The macula lutea is the area located at the
center of the retina. At the exact center of the
macula lutea is the central fovea, a small
depression which contains cones
(photoreceptors for daylight and color vision).
99
describe the optic disc of the retina
The optic disc is the where the optic
nerve (CN II) exits the eyeball. Since
there are no photoreceptors in the optic
disc, we can’t see when light strikes the
optic disc → this is our blind spot.
100
Every field of view has a blind spot because
a) There are no photoreceptors in the optic disc
b) There are no first order neurons in the optic disc
c) There is no sclera in the optic disc
d) Light does not hit the optic disc
A
101
what are rods and cones
photoreceptors (receptors for light stimulus)
102
What do bipolar cells do?
assist in the transmission of signal to the first-order neurons
103
what are ganglion cells (in terms of eyes)
| what do they from
first order neurons: their axons form the optic nerve
104
how many rods are there and where are they found
There are 120 million Rods
distributed along the periphery of
the retina
105
what are rods specialized for?
specialized for black and white vision, in dim light
106
how many cones are they and where are they found?
There are 6 million Cones located
in the central fovea: only cones are
found in the fovea.
107
what are cones specialized for?
cones are specialized for color vision, in bright daylight. They are densely packed and offer the highest level of visual acuity
108
Which of the following is TRUE
a) Cones are in the central fovea, and are for daylight vision
b) Cones are in the periphery of the retina, and are for daylight
vision
c) Rods are in the central fovea, and are for daylight vision
d) Rods are in the periphery of the retina, and are for daylight vision
A
109
what are photopigments and what two parts are they made of?
Photopigments are integral membrane
proteins in the plasma membrane of
photoreceptor cells. They absorb light and are
in the outer segment of photoreceptors: in
discs of rods, and folds of cones.
Photopigments are made of two parts: opsin and retinal
110
what is opsin
the protein portion of photopigments
111
what is retinal?
the light-absorbing portion of photopigments. IT is a derivative version of vit A (stored in epithelial cells)
112
describe the regeneration of bleached photopigments
Bleaching and regeneration time are equivalent to the refractory period of an
action potential: retinal needs to reattach to opsin before the photopigment can
respond to light again (just like repolarization needs to take place before repolarization can be triggered again).
Cones regenerate much faster than rods – it takes about 90 sec. to regenerate half of the cones, but it takes about 5 min. to regenerate half of the rods.
It takes 30-40 min. to regenerate all the rods.
113
what are the 4 steps of regeneration of photopigments
1. Isomerization: light causes retinal to change shape,
which leads to the
generation of a
graded potential
2. bleaching: retinal separates from opsin (photopigment is now non-responsive to lights
3. conversion - retinal isomerase converts trans to cis retinal
4. Regeneration:
Retinal binds to
photopigment again – this takes time; it
takes longer in rods
than it does in cones
114
how does the regeneration of bleached photopigments relate to daylight vision?
Since rods regenerate very slowly, they
contribute little to daylight vision
◦ Once the light has struck, the
photopigment must regenerate to
be able to respond to light again
◦ Because they are slow at this, rods are always “out of service” in broad daylight
Since cones regenerate much faster, there always is a cone “ready” to be
struck by light, even in broad daylight
115
what is dark adaptation?
Dark adaptation - adjustments when enter the dark from a bright situation
◦ In the dark, cones are not sensitive enough to perceive dim light, but rods are
sensitive enough (Why? Stay tuned…)
After a few minutes in the dark, rods have
regenerated and can then respond to light
Sensitivity increases slowly over many
minutes
116
describe the convergence of neural networks
There are 126 million photoreceptors that
converge onto 1 million ganglion cells
Direction of light
600 rods synapse on a single bipolar
cell, increasing light sensitivity
(remember spatial summation?)
although a slightly blurry image results
one cone synapses onto one bipolar
the cell produces the best visual acuity,
at the expense of sensitivity
117
Why can rods be used in dim light?
a) Because they can respond to less photons than cones
b) Because they regenerate slower than cones
c) Because they regenerate faster than cones
d) Because of spatial summation, many rods synapse onto one
bipolar cell
D
118
describe the formation of receptor potentials in complete darkness
Na+ channels are held open, and
photoreceptor is always partially
depolarized (-30mV).
The partial depolarization results
in the continuous release of an
inhibitory neurotransmitter onto
bipolar cells, thereby suppressing
the activity of bipolar cells
(remember IPSP?)
119
what happens to the formation of receptor potentials in presence of light
Enzymes cause the closing of Na+
channels producing a hyperpolarized
receptor potential (-70mV).
The release of inhibitory
neurotransmitters is stopped, bipolar
cells become excited and trigger an EPSP
in ganglion cells (first-order neurons).
120
describe the journey from light stimulus to the brain
Light penetrates retina
* Rods & cones transduce light into
receptor potentials
* Rods & cones excite bipolar cells
* Bipolar cells excite ganglion cells
121
describe how visual information travels
| nerves and parts of the brain
Optic nerves cross at the optic chiasm
Visual information travels to the thalamus
Visual information ends in the primary visual area of the cerebral cortex
122
what happens when visual information travels to the hypothalamus vs what happens when visual information travels to the brainstem
Visual information also travels
to the hypothalamus, for sleep
patterns and circadian rhythms
Visual information also travels to
the brainstem, to regulate the
size of the pupil (CN III) and for
coordination of head and eye
movements (superior colliculi)
123
what happens when light from the nasal half of field of view hits the temporal side of the retina
Fibers from the temporal
side of the retina do NOT cross in
the optic chiasm, and go to the
same side of the brain (right eye,
right side of brain)
124
what happens when light from the temporal half of field of view hits the nasal side of the retina?
Light from temporal half of field of
view hits the nasal side of the retina.
Fibers from the nasal side of the
retina cross in the optic chiasm, and
go to the opposite side of the brain
(right eye, left side of brain)
ame for both eyes: peripheral
stimuli cross at the chiasm,
and central stimuli do not
cross at the chiasm (slide 81 ch 17)
125
how does the left occipital lobe receive visual images?
The left occipital lobe receives
visual images from the right side
of an object through impulses
from the medial ½ of the right
eye and lateral ½ of the left eye
The left occipital lobe sees
the right ½ of the world and
the right occipital lobe sees
the left ½ of the world
126
what is retinal detachment
◦ Detachment of the neural portion of the
retina from the pigmented epithelium →
fluid accumulates between layers
◦ Causes distorted vision and blindness in
the corresponding field of vision
◦ Can be reattached by laser surgery
127
what are cataracts
Loss of transparency of the lens that can lead to
blindness
128
what is glaucoma
◦ Abnormally high intraocular pressure, due to a
buildup of aqueous humor inside the eyeball, which
destroys neurons of the retina
◦ Second most common cause of blindness (after
cataracts), especially in the elderly
129
Which of the following does NOT describe
the visual pathway as light enters the eye?
a) Visual information from the right half of the visual field goes to
the left side of the brain
b) All axons from the temporal half of the retina cross in the optic
chiasm
c) All axons of the retina exit the eye at the optic disc
d) Optic axons connect the thalamus to the primary visual area in
the cortex
B
130
The receptor potential in a photoreceptor
(e.g., a rod) is caused by the release of an
inhibitory neurotransmitter.
a) True
b) False
B) false; it's caused by a photon of light
