BIO100 Chptr 12 Nervous System III Senses Flashcards
1
Q
aud-
A
aud-, to hear: auditory
—pertaining to hearing.
2
Q
choroid
A
choroid, skinlike: choroid coat
—middle, vascular layer of the eye.
3
Q
cochlea
A
cochlea, snail: cochlea
—coiled tube in the inner ear.
4
Q
corn-
A
corn-, horn: cornea
—transparent outer layer in the anterior portion of the eye.
5
Q
iris
A
iris, rainbow: iris
—colored, muscular part of the eye.
6
Q
labyrinth
A
labyrinth, maze: labyrinth
—complex system of connecting chambers and tubes of the inner ear.
7
Q
lacri-
A
lacri-, tears: lacrimal gland
—tear gland.
8
Q
lut-
A
lut-, yellow: macula lutea
—yellowish spot on the retina.
9
Q
macula
A
macula, spot: macula lutea
—yellowish spot on the retina.
10
Q
malle-
A
malle-, hammer: malleus
—one of the three bones in the middle ear.
11
Q
ocul-
A
ocul-, eye: orbicularis oculi
—muscle associated with the eyelid.
12
Q
olfact-
A
olfact-, to smell: olfactory—pertaining to the sense of smell.
13
Q
palpebra
A
palpebra, eyelid: levator palpebrae superioris
—muscle associated with the eyelid.
14
Q
photo-
A
photo-, light: photoreceptors
—specialized structures in the eye responsive to light.
15
Q
scler-
A
scler-, hard: sclera
—tough, outer protective layer of the eye.
16
Q
therm-
A
therm-, heat: thermoreceptor
—receptor sensitive to changes in temperature.
17
Q
tympan-
A
tympan-, drum: tympanic membrane
—eardrum.
18
Q
vitre-
A
vitre-, glass: vitreous humor
—clear, jellylike substance in the eye.
19
Q
general senses
A
The general senses are those with receptors widely distributed throughout the body, including the skin, various organs, and joints.
20
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special senses
A
The special senses have more specialized receptors and are confined to structures in the head, such as the eyes and ears.
21
Q
receptor cells
A
Receptors are the cells or structures that detect sensations. A receptor cell is changed directly by a stimulus. A transmembrane protein receptor is a protein in the cell membrane that mediates a physiological change in a neuron, most often through the opening of ion channels or changes in the cell signaling processes.
22
Q
membrane receptors
A
are specialized protein molecules attached to or integrated into the cell membrane. Through interaction with specific ligands (e.g., hormones and neurotransmitters), the receptors facilitate communication between the cell and the extracellular environment.
23
Q
Receptor Types
Five types of sensory receptors are recognized, based on their sensitivities to specific stimuli:
A
Chemoreceptors Pain receptors Thermoreceptors Mechanoreceptors - (Proprioceptors, baroreceptors , stretch receptors) Photoreceptors
24
Q
Chemoreceptors (ke″mo-re-sep′torz)
A
respond to changes in the concentration of chemicals. Receptors associated with the senses of smell and taste are of this type. Chemoreceptors in internal organs detect changes in the blood concentrations of oxygen, hydrogen ions, glucose, and other chemicals.
25
Pain receptors, also called nociceptors (no″se-sep′torz)
respond to tissue damage. Triggering stimuli include exposure to excess mechanical, electrical, thermal, or chemical energy.
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Thermoreceptors (ther″mo-re-sep′torz)
sense temperature change.
27
Mechanoreceptors (mek″ah-no re-sep′torz)
are of several types and respond to mechanical forces by detecting changes that deform the receptors. They include a number of receptors in the skin that respond to physical contact, and several receptors in the ear that provide information about balance and vibrations from sound.
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Proprioceptors (pro″pre-o-sep′torz)
respond to changes in the tensions of muscles and tendons;
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baroreceptors (bar″o-re-sep′torz)
also called pressoreceptors, in certain blood vessels detect changes in blood pressure;
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stretch receptors
in the lungs respond to degree of inflation.
31
Photoreceptors (fo″to-re-sep′torz)
in the eyes respond to light energy of sufficient intensity.
32
membrane potentials (receptor potentials)
also known as a generator potential, a type of graded potential, is the transmembrane potential difference produced by activation of a sensory receptor. - The influx of current will often bring the membrane potential of the sensory receptor towards the threshold for triggering an action potential.
33
A sensation occurs
when sensory neurons reach threshold and the resulting action potentials cause the brain to become aware of that sensory event. "Thus, pain is a sensation, but realizing that you have just stepped on a tack is a perception."
34
A perception occurs
when the brain interprets those sensory impulses. "Thus, pain is a sensation, but realizing that you have just stepped on a tack is a perception."
35
projection
At the same time that a sensation forms the cerebral cortex interprets it as coming from the receptors being stimulated. This process, which is closely related to perception, is called projection, because the brain projects the sensation back to its apparent source. Projection allows a person to pinpoint the region of stimulation. In this way, we perceive that the eyes see an apple, the nose smells it, and the ears hear the teeth crunch into it.
36
sensory adaptation
refers to a reduction in sensitivity to a stimulus after constant exposure to it. While sensory adaptation reduces our awareness of a constant stimulus, it helps free up our attention and resources to attend to other stimuli in the environment around us. - "tuning out"
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exteroreceptive senses
are associated with changes at the body surface. They include the senses of touch, pressure, temperature, and pain.
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interoceptive (visceroceptive) senses
are associated with changes in viscera (blood pressure stretching blood vessels, an ingested meal stimulating pH receptors in the small intestine, and so on).
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Proprioceptive senses
are associated with changes in muscles and tendons and in body position.
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Free nerve endings
the simplest receptors, are common in epithelial tissues, where the ends of dendrites branch and extend between epithelial cells. They are responsible for the sensation of itching and other sensations
41
Tactile (Meissner’s) corpuscles
are small, oval masses of flattened connective tissue cells in connective tissue sheaths. Two or more sensory fibers branch into each corpuscle and end within it as tiny knobs.
Tactile corpuscles are abundant in hairless areas of skin, such as the lips, fingertips, palms, soles, nipples, and external genital organs. They provide the sensation of fine touch, such as distinguishing two points on the skin where an object touches, to judge its texture
42
Lamellated (Pacinian)
corpuscles are nerve endings encased in relatively large, ellipsoidal structures composed of connective tissue fibers and cells. They are common in the deeper dermal tissues of the hands, feet, penis, clitoris, urethra, and breasts and also in the connective tissue capsules of synovial joints.Heavier pressure and stretch stimulate lamellated corpuscles. They also detect vibrations in tissues.
43
referred pain
Visceral pain may feel as if it is coming from some part of the body other than the part being stimulated, in a phenomenon called referred pain. - Referred pain may derive from common nerve pathways that conduct sensory impulses both from skin areas and from internal organs
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fast pain fibers (also known as A-delta fibers)
are myelinated. They conduct impulses rapidly, at velocities up to 30 meters per second. These impulses are associated with the immediate sensation of sharp pain, which typically seems to originate in a local area of skin. This type of pain seldom continues after the pain-producing stimulus stops.
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slow pain fibers (C fibers)
are unmyelinated. They conduct impulses more slowly than fast pain fibers, at velocities up to 2 meters per second. These impulses cause a delayed, dull, aching pain sensation that may be widespread and difficult to pinpoint. Such pain may continue after the original stimulus ceases. Although immediate pain is usually sensed as coming from the surface, delayed pain is felt in deeper tissues as well as in the skin. Visceral pain impulses are typically carried on C fibers.
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enkephalins
either of two compounds that occur naturally in the brain. They are peptides related to the endorphins, with similar physiological effects. - Enkephalins and endorphins are released in response to extreme pain, providing natural pain control.
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monoamine serotonin
These neurotransmitters are involved in mediating a wide range of physiological and homeostatic functions, which vary with the part of the brain being examined.
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endorphins
are another group of neuropeptides with pain-suppressing, morphinelike actions. They are found in the pituitary gland and in regions of the nervous system, such as the hypothalamus, that relay pain information. - Enkephalins and endorphins are released in response to extreme pain, providing natural pain control.
49
Muscle spindles
are located throughout skeletal muscles. Each spindle consists of several small, modified skeletal muscle fibers (intrafusal fibers) enclosed in a connective tissue sheath. Each intrafusal fiber has near its center a specialized nonstriated region with the end of a sensory nerve fiber wrapped around it
50
Golgi tendon organs
are in tendons close to their attachments to muscles. Each Golgi tendon organ connects to a set of skeletal muscle fibers and is innervated by a sensory neuron. Golgi tendon organs have high thresholds, and increased tension stimulates them. Sensory impulses from them produce a reflex that inhibits contraction of the muscle whose tendon they occupy. Therefore, the Golgi tendon organs stimulate a reflex with an effect that is the opposite of a stretch reflex. The Golgi tendon reflex also helps maintain posture, and it protects muscle attachments from being pulled loose by excessive tension.
51
Receptors Associated with General Senses
* Free nerve endings (mechanoreceptors) - Detect changes in pressure - Touch, pressure
* Tactile corpuscles (mechanoreceptors) - Detect objects moving over the skin - Touch, texture
* Lamellated corpuscles (mechanoreceptors) - Detect changes in pressure - Deep pressure, vibrations, fullness in viscera
* Free nerve endings (thermoreceptors) - Detect changes in temperature - Heat, cold
* Free nerve endings (pain receptors) - Detect tissue damage - Pain
* Free nerve endings (mechanoreceptors) - Detect stretching of tissues, tissue spasms - Visceral pain
* Muscle spindles (mechanoreceptors) - Detect changes in muscle length - None
* Golgi tendon organs (mechanoreceptors) - Detect changes in muscle tension - None
52
Olfactory receptor cells
and their membrane receptor molecules, sense odors.
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olfactory bulbs
Once olfactory receptor cells are stimulated, impulses are conducted along their axons through tiny openings in the cribriform plates of the ethmoid bone. These fibers (which collectively form the first cranial nerves) synapse with neurons located in the enlargements called olfactory bulbs, that lie within the cranial cavity on either side of the crista galli of the ethmoid bone
54
olfactory tracts
is a bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cortex, amygdala, and entorhinal cortex.
55
The olfactory organs
are high in the nasal cavity above the usual pathway of inhaled air, so in order to smell a faint odor, a person may have to sniff and force air up to the receptor areas.
56
Taste buds
are the special organs of taste. They resemble orange sections and are located on the surface of the tongue associated with tiny elevations called papillae
57
papillae
a small rounded protuberance on a part or organ of the body.
| "as food touches the tongue it comes into contact with the sensory papillae"
58
taste cells
Each taste bud includes a group of modified epithelial cells, the taste cells (gustatory cells), that function as sensory receptors. Taste cells have vesicles that contain neurotransmitter. Interwoven among and wrapped around the taste cells is a network of sensory fibers whose ends closely contact the receptor cell membranes.
59
five types of taste buds
The different types of taste buds provide at least five primary taste (gustatory) sensations.
sweet, sour, salty, bitter, and umami (oo-mom′ee).
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tongue Sensory impulses come from the facial nerve ...
Sensory impulses from taste receptor cells in the anterior two-thirds of the tongue travel on fibers of the facial nerve (VII)
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tongue impulses from receptors in the posterior -
| come from the nerve ...
impulses from receptors in the posterior one-third of the tongue and the back of the mouth pass along the glossopharyngeal nerve (IX)
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impulses from receptors at the base -
| come from the nerve ...
impulses from receptors at the base of the tongue and the pharynx travel on the vagus nerve (X).
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Types of Smell and Taste Disorders
Type - Smell - Taste
* Loss of sensation - Anosmia - Ageusia
* Diminished sensation - Hyposmia - Hypogeusia
* Heightened sensation - Hyperosmia - Hypergeusia
* Distorted sensation - Dysosmia - Dysgeusia
64
The outer ear consists of
an outer, funnel-like structure called the auricle (pinna), an S-shaped tube, the external acoustic meatus (external auditory canal) that leads inward for about 2.5 centimeters, and the tympanic membrane (eardrum). The meatus terminates with the tympanic membrane.
65
The middle ear, or the tympanic cavity
is an air-filled space in the temporal bone that separates the outer and inner ears. It is bounded by the tympanic membrane laterally and the inner ear medially and houses three small bones called auditory ossicles
66
The three auditory ossicles, called the malleus, the incus, and the stapes (middle ear)
are attached to the wall of the tympanic cavity by tiny ligaments and are covered by mucous membrane.
67
oval window
(or fenestra vestibuli) is a membrane-covered opening that leads from the middle ear to the vestibule of the inner ear. Vibrations that contact the tympanic membrane travel through the three ossicles and into the inner ear.
68
tympanic reflex
helps prevent damage to the inner ear by muffling the transmission of vibrations from the tympanic membrane to the oval window. The reflex has a response time of 40 milliseconds, not fast enough to protect the ear from sudden loud noises such as an explosion or gunshot.
69
auditory (aw′di-to″re) tube (eustachian tube)
connects each middle ear to the throat. This tube allows air to pass between the tympanic cavity and the outside of the body by way of the throat (nasopharynx) and mouth. It helps maintain equal air pressure on both sides of the tympanic membrane. This is necessary for normal hearing
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labyrinth - Inner (Internal) Ear
The inner ear is a complex system of intercommunicating chambers and tubes called a labyrinth (lab′i-rinth). Each ear has two such regions—the bony labyrinth and the membranous labyrinth.
71
bony (osseous) labyrinth
is a cavity within the temporal bone; the membranous labyrinth is a tube of similar shape that lies within the bony labyrinth. Between the bony and membranous labyrinths is a fluid called perilymph, secreted by cells in the wall of the bony labyrinth. In the membranous labyrinth is a slightly different fluid called endolymph.
The parts of the labyrinths include a cochlea (kok′le-ah) and three membranous semicircular ducts within three bony semicircular canals. The cochlea functions in hearing. The semicircular canals and associated structures contribute to the sense of equilibrium. A bony chamber called the vestibule, between the cochlea and the semicircular canals, houses membranous structures that serve both hearing and equilibrium.
72
cochlea
cochlea is a tube, widest at its base and progressively narrower toward its tip, or apex. It is shaped a bit like a snail shell, coiled around a bony core, the modiolus. A thin, bony shelf (spiral lamina) extends out from the core and coils around it within the tube. A portion of the membranous labyrinth in the cochlea, called the cochlear duct (scala media), runs inside the tube opposite the spiral lamina, and together these structures divide the tube into upper and lower compartments.
73
round window
is one of the two openings from the middle ear into the inner ear. It is sealed by the secondary tympanic membrane (round window membrane), which vibrates with opposite phase to vibrations entering the inner ear through the oval window.
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scala vestibuli
The vestibular duct or scala vestibuli is a perilymph-filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the cochlear duct. It is separated from the cochlear duct by Reissner's membrane and extends from the vestibule of the ear to the helicotrema where it joins the tympanic duct.
75
scala tympani
The tympanic duct or scala tympani is one of the perilymph-filled cavities in the inner ear of the human. It is separated from the cochlear duct by the basilar membrane, and it extends from the round window to the helicotrema, where it continues as vestibular duct.
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modiolus
In facial anatomy, the modiolus is a chiasma of facial muscles held together by fibrous tissue, located lateral and slightly superior to each angle of the mouth.
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cochlear duct (scala media)
is an endolymph filled cavity inside the cochlea, located between the tympanic duct and the vestibular duct, separated by the basilar membrane and Reissner's membrane (the vestibular membrane) respectively. The cochlear duct houses the organ of Corti.
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vestibular membrane (Reissner’s membrane)
is a membrane inside the cochlea of the inner ear. It separates the cochlear duct from the vestibular duct.
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basilar membrane
is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani.
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spiral organ (organ of Corti)
is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential.
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hair cells
are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment.
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decibels
Units called decibels (dB) measure sound intensity as a logarithmic scale.
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Sense of Equilibrium
The feeling of equilibrium (balance) derives from two senses—static equilibrium (stat′ik e′kwĭ-lib′re-um) and dynamic equilibrium (di-nam′ik e′kwĭ-lib′re-um).
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Equilibrium meaning
Definition. noun, plural: equilibriums or equilibria. (1) The condition in which all acting influences are balanced or canceled by equal opposing forces, resulting in a stable system. (2) The state of balance or static; the absence of net tendency to change. Supplement.
85
static equilibrium
also known as mechanical equilibrium, means the reaction has stopped. ... In biology, the equilibrium of a system is called homeostasis. Changes in temperature, pressure, the addition of more reactants/products and changes in other variables cause a system to create a new point of equilibrium
86
dynamic equilibrium
is the steady state of a reversible reaction where the rate of the forward reaction is the same as the reaction rate in the backward direction. ... In biology, the equilibrium of a system is called homeostasis.
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organs of static equilibrium
are in the vestibule, a bony chamber between the semicircular canals and the cochlea.
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The membranous labyrinth inside the vestibule consists of two expanded chambers
```
a utricle (u′trĭ-kl) and a saccule (sak′ūl).
The larger utricle communicates with (is continuous with) the saccule and the membranous portions of the semicircular canals; the saccule, in turn, communicates with the cochlear duct
```
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macula
The macula is part of the retina at the back of the eye.
(The utricle and saccule each has a small patch of hair cells and supporting cells called a macula (mak′u-lah) on its wall.)
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ampulla
Any membranous bag shaped like a leathern bottle, as the dilated end of a vessel or duct; especially the dilations of the semicircular canals of the ear.
91
crista ampullaris
is the sensory organ of rotation. They are found in the ampullae of each of the semicircular canals of the inner ear, meaning that there are 3 pairs in total. The function of the crista ampullaris is to sense angular acceleration and deceleration.
92
The muscles that move the eyelids
include the orbicularis oculi and the levator palpebrae superioris.
93
Each eyelid (palpebra) is composed of four layers
skin, muscle, connective tissue, and conjunctiva. The skin of the eyelid, the thinnest of the body, covers the lid’s outer surface and fuses with its inner lining near the margin of the lid
94
conjunctiva
is a mucous membrane that lines the inner surfaces of the eyelids and folds back to cover the anterior surface of the eyeball, except for its central portion (cornea). Although the tissue that lines the eyelids is relatively thick, the conjunctiva that covers the eyeball is very thin. It is also freely movable and transparent, so that blood vessels are clearly visible beneath it. “Pinkeye” is a form of conjunctivitis, or inflammation of the conjunctiva.
95
lacrimal apparatus
consists of the lacrimal gland, which secretes tears, and a series of ducts, which carry the tears into the nasal cavity. The gland is in the orbit, superior and lateral to the eye. It secretes tears continuously, which pass through tiny tubules and flow downward and medially across the eye.
96
Two small ducts (superior and inferior canaliculi)
collect tears, and their openings (puncta) can be seen on the medial borders of the eyelids. From these ducts, the fluid moves into the lacrimal sac, which lies in a deep groove of the lacrimal bone, and then into the nasolacrimal duct, which empties into the nasal cavity.
97
extrinsic muscles of the eye
Superior rectus—rotates the eye upward and toward the midline.
Inferior rectus—rotates the eye downward and toward the midline.
Medial rectus—rotates the eye toward the midline.
Lateral rectus—rotates the eye away from the midline.
Superior oblique—rotates the eye downward and away from the midline.
Inferior oblique—rotates the eye upward and away from the midline.
98
Superior rectus - extrinsic muscles of the eye
Superior rectus—rotates the eye upward and toward the midline.
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Inferior rectus - extrinsic muscles of the eye
Inferior rectus—rotates the eye downward and toward the midline.
100
Medial rectus - extrinsic muscles of the eye
Medial rectus—rotates the eye toward the midline.
101
Lateral rectus - extrinsic muscles of the eye
Lateral rectus—rotates the eye away from the midline.
102
Superior oblique - extrinsic muscles of the eye
Superior oblique—rotates the eye downward and away from the midline.
103
Inferior oblique - extrinsic muscles of the eye
Inferior oblique—rotates the eye upward and away from the midline.
104
sclera (skle′rah)
the white portion of the eye. The sclera makes up the posterior five-sixths of the outer tunic and is opaque due to many large, seemingly disorganized collagen and elastic fibers. The sclera protects the eye and is an attachment for the extrinsic muscles.
105
choroid coat
the pigmented vascular layer of the eyeball between the retina and the sclera.
106
ciliary body
is a circular structure that is an extension of the iris, the colored part of the eye. The ciliary body produces the fluid in the eye called aqueous humor. It also contains the ciliary muscle, which changes the shape of the lens when your eyes focus on a near object
107
The middle, or vascular, tunic of the eyeball (uveal layer)
of tissue surrounding the eye, also known as the vascular tunic or „uvea“, is formed – from behind forward – by the choroid, the ciliary body, and the iris. The choroid takes up the posterior five-sixths of the bulb and is mainly comprised of blood vessels.
108
ciliary processes
are formed by the inward folding of the various layers of the choroid
109
lens
is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina.
110
suspensory ligaments
A suspensory ligament is a ligament that supports a body part, especially an organ.
111
ciliary muscle
the part of the eye that connects the iris to the choroid. It consists of the ciliary muscle (which alters the curvature of the lens), a series of radial ciliary processes (from which the lens is suspended by ligaments), and the ciliary ring (which adjoins the choroid).
112
accommodation in the eye
In medicine, the ability of the eye to change its focus from distant to near objects (and vice versa). This process is achieved by the lens changing its shape. Accommodation is the adjustment of the optics of the eye to keep an object in focus on the retina as its distance from the eye varies.
113
iris
is a thin diaphragm mostly composed of connective tissue, smooth muscle, and specialized contractile epithelial cells. Seen from the outside, it is the colored portion of the eye. The iris extends forward from the periphery of the ciliary body and lies between the cornea and the lens.
114
aqueous humor
the clear fluid filling the space in the front of the eyeball between the lens and the cornea.
115
pupil
is a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.
116
retina
is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.
117
There are five major groups of retinal neurons.
The nerve fibers of three of these groups—the photoreceptors, bipolar neurons, and ganglion cells—provide a direct pathway for impulses triggered in the photoreceptors to the optic nerve and brain. The nerve fibers of the other two groups of retinal cells, called horizontal cells and amacrine cells, pass laterally between retinal cells. The horizontal and amacrine cells modify the pattern of impulses conducted on the fibers of the direct pathway.
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macula lutea
an oval yellowish area surrounding the fovea near the center of the retina in the eye, which is the region of keenest vision.
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fovea centralis
is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.
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optic disc
The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye. The ganglion cell axons form the optic nerve after they leave the eye.
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vitreous humor
the transparent gelatinous tissue filling the eyeball behind the lens.
122
vitreous body
The vitreous body (vitreous meaning "glass-like", from Latin vitreus, equivalent to vitr(um) glass + -eus -ous) is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous humor or simply "the vitreous".
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refraction
Refractions determine the presence of ametropia, an error in the focusing of light rays as they pass through the cornea and retina of the eye. (Eye Dr. test)
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rods
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision.
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cones
Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes (e.g. the human eye). They respond differently to light of different or color vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light.
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Albinism
Albinism is an inherited condition in which an enzyme required to produce pigment is missing, causing very pale, highly sun-sensitive skin. More severe forms of albinism also affect the eyes, making vision blurry and intolerant to light. A person may squint even in very faint light. This separate extra sensitivity arises because light reflects inside the lenses, overstimulating visual receptors.
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rhodopsin
is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR). It belongs to opsins. Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When rhodopsin is exposed to light, it immediately photobleaches.
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iodopsins
a photochemical pigment contained within CONE CELLS present in the retina of most vertebrate eyes. Iodopsin consists of RETINOL and a protein, which is different for each of the three cone pigments and as a result each of the pigments has a different colour.
129
Stereoscopic vision (stereopsis)
simultaneously perceives distance, depth, height, and width of objects. Such vision is possible because the pupils are 6–7 centimeters apart. Consequently, close objects (less than 20 feet away) produce slightly different retinal images. That is, the right eye sees a little more of one side of an object, while the left eye sees a little more of the other side. The visual cortex superimposes and interprets the two images. The result is the perception of a single object in three dimensions
