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2 - Keiser A&P 2 > 0-1 Chapter 16 - sense Organs > Flashcards

0-1 Chapter 16 - sense Organs Flashcards

1
Q

sense organs

A

nerve tissue surrounded by other tissues that enhance response to certain type of stimulus
•added epithelium, muscle or connective tissue

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2
Q

transduction

A

the conversion of one form of energy to another

–fundamental purpose of any sensory receptor

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3
Q

receptor potential

A

small, local electrical change on a receptor cell brought about by an initial stimulus
•results in release of neurotransmitter or a volley of action potentials that generates nerve signals to the CNS

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4
Q

sensation

A

a subjective awareness of the stimulus

–most sensory signals delivered to the CNS produce no conscious sensation

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5
Q

Receptors Transmit Four Kinds of Information

A

Modality
Location
Intensity
Duration

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6
Q

Modality

A

type of stimulus or the sensation it produces

–vision, hearing, taste

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7
Q

labeled line code

A

all action potentials are identical. Each nerve pathway from sensory cells to the brain is labeled to identify its origin, and the brain uses these labels to interpret what modality the signal represents

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8
Q

Location

A

encoded by which nerve fibers are issuing signals to the brain

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9
Q

receptive field

A

area that detects stimuli for a sensory neuron

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10
Q

sensory projection

A

brain identifies site of stimulation

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11
Q

projection pathways

A

the pathways followed by sensory signals to their ultimate destination in the CNS

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12
Q

Intensity

encoded in 2 ways

A

Strength

frequency

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13
Q

Duration

A

how long the stimulus lasts

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14
Q

sensory adaptation

A

if stimulus is prolonged, the firing of the neuron gets slower over time, and we become less aware of the stimulus

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15
Q

phasic receptor

A

generate a burst of action potentials when first stimulated, then quickly adapt and sharply reduce or stop signaling even though the stimulus continues

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16
Q

tonic receptor

A

adapt slowly, generate nerve signals more steadily

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17
Q

Classification of Receptors by

A

modality
origin of stimuli
distribution

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18
Q

by modality

A

–thermoreceptors, photoreceptors, nociceptors, chemoreceptors, and mechanoreceptors

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19
Q

origin of stimuli

A

–exteroceptors -detect external stimuli
–interoceptors -detect internal stimuli
–proprioceptors -sense body position and movements

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20
Q

by distribution

A

–general (somesthetic) senses -widely distributed
–special senses -limited to head
•vision, hearing, equilibrium, taste, and smell

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21
Q

General Senses

A

structurally simple receptors

–one or a few sensory fibers and a little connective tissue

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22
Q

unencapsulated nerve endings

A

•dendrites not wrapped in connective tissue
–free nerve endings
–tactile (Merkel) discs
–hair receptors (peritrichial endings

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23
Q

free nerve endings

A

–for pain and temperature

–skin and mucous membrane

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24
Q

tactile discs

A

–for light touch and texture

–associated with Merkel cells at base of epidermis

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25
Q

hair receptors

A

–wrap around base of hair follicle

–monitor movement of hair

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26
Q

encapsulated nerve endings

A
  • dendrites wrapped by glial cells or connective tissue

* connective tissue enhances sensitivity or selectivity of response

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27
Q

encapsulated nerve endings

types

A 
–tactile (Meissner) corpuscles
–Krause end bulbs
–bulbous (Ruffini) corpuscles
–lamellar (pacinian) corpuscles
–muscle spindles
–golgi tendon organs
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28
Q

tactile (Meissner) corpuscles

A

–light touch and texture

–dermal papillae of hairless skin

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29
Q

Krause end bulb

A

–tactile; in mucous membranes

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30
Q

lamellated (pacinian) corpuscles

A

phasic
–deep pressure, stretch, tickle and vibration
–periosteum of bone, and deep dermis of skin

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31
Q

bulbous (Ruffini) corpuscles

A

tonic

–heavy touch, pressure, joint movements and skin stretching

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32
Q

Sound receptors are

A

mechanoreceptors

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33
Q

Somesthetic Projection Pathways

A

from receptor to final destination in the brain, most somesthetic signals travel by way of three neurons

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34
Q

1st order neuron (afferent neuron)

A

–from body, enter the dorsal horn of spinal cord via spinal nerves
–from head, enter pons and medulla via cranial nerve
–touch, pressure and proprioception on large, fast, myelinated axons
–heat and cold on small, unmyelinated, slow fibers

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35
Q

2nd order neuron

A

–decussation to opposite side in spinal cord, medulla, or pons
–end in thalamus, except for proprioception, which ends in cerebellum

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36
Q

3rd order neuron

A

–thalamus to primary somesthetic cortex of cerebrum

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37
Q

pain

A

discomfort caused by tissue injury or noxious stimulation, and typically leading to evasive action
–important since helps protect us

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38
Q

nociceptors

A

two types providing different pain sensations

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39
Q

fast pain

A

travels in myelinated fibers at 12 -30 m/sec

•sharp, localized, stabbing pain perceived with injury

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40
Q

slow pain

A

travels unmyelinated fibers at 0.5 -2 m/sec

•longer-lasting, dull, diffuse feeling

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41
Q

somatic pain

A

from skin, muscles and joints

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42
Q

visceral pain

A

from the viscera

–stretch, chemical irritants or ischemia of viscera (poorly localized

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43
Q

bradykinin

A

most potent pain stimulus known

–makes us aware of injury and activates cascade or reactions that promote healing

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44
Q

Projection Pathway for Pain

A

two main pain pathways to brain, and multiple subroutes

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45
Q

first-order neuron cell bodies

A

in dorsal root ganglion of spinal nerves or cranial nerves V, VII, IX, and X

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46
Q

spinothalamic tract

A

most significant pain pathway

–carries most somatic pain signals

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47
Q

spinoreticular tract

A

carries pain signals to reticular formation

–activate visceral, emotional and behavioral reactions to pain

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48
Q

referred pain

A

pain in viscera often mistakenly thought to come from the skin or other superficial site

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49
Q

analgesic

A

(pain-relieving) mechanisms of CNS just beginning to be understood

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50
Q

enkephalins

A

two analgesic oligopeptides with 200 times the potency of morphine

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51
Q

endogenous opioids

A

internally produced opium-like substances

•enkephalins, endorphins, and dynorphins

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52
Q

neuromodulators

A

neuromodulators that can block the transmission of pain signals and produce feelings of pleasure and euphoria

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53
Q

spinal gating-

A

stops pain signals at the posterior horn of the spinal cord

SEE DIAGRAM

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54
Q

spinal gating-

rubbing or massaging injury

A

•pain-inhibiting neurons of the posterior horn receive input from mechanoreceptors in the skin and deeper tissues
–rubbing stimulates mechanoreceptors which stimulates spinal interneurons to secrete enkephalins that inhibit second-order pain neurons

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55
Q

gustation

A

(taste) –sensation that results from action of chemicals on taste buds

MUST BE LIQUID TO TASTE

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56
Q

taste buds - location

A

4000 -taste buds mainly on tongue

–inside cheeks, and on soft palate, pharynx, and epiglottis

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57
Q

lingual papillae

4 areas

A

filiform
foliate
fungiform
vallate (circumvallate)

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58
Q

filiform

A

no taste buds

•important for food texture

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59
Q

foliate

A

no taste buds

•weakly developed in humans

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60
Q

fungiform

A

•at tips and sides of tongue

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61
Q

vallate (circumvallate)

A
  • at rear of tongue

* contains 1/2 of all taste buds

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62
Q

taste cells

A

synapse with and release neurotransmitters onto sensory neurons at their base
Have: taste hairs, taste pores,

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63
Q

taste hairs

A

have tuft of apical microvilli(taste hairs) that serve as receptor surface for taste molecules
taste hairs are epithelial cells not neurons

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64
Q

taste pores

A

pit in which the taste hairs project

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65
Q

basal cells

A

stem cells that replace taste cells every 7 to 10 days

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66
Q

supporting cells

A

resemble taste cells without taste hairs, synaptic vesicles, or sensory role

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67
Q

Physiology of Taste

A

to be tasted, molecules must dissolve in saliva and flood the taste pore

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68
Q

five primary sensations

A 
salty
–sweet
–sour
–bitter 
–umami
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69
Q

mouthfeel

A

detected by branches of lingual nerve in papillae

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70
Q

two mechanisms of action

A

activate 2nd messenger systems
depolarize cells directly
either mechanism results in release of neurotransmitters that stimulate dendrites at base of taste cells

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71
Q

activate 2nd messenger systems

A

•sugars, alkaloids, and glutamate bind to receptors which activates G proteins and second-messenger systems within the cell

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72
Q

depolarize cells directly

A

sodium and acids penetrate cells and depolarize it directly

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73
Q

Projection Pathways for Taste

A
  • facial nerve, glossopharyngeal nerve, vagus nerve
  • all fibers reach solitary nucleus in medulla oblongata
  • signals sent two destinations: hypothalamus and amygdala or Thalamus
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74
Q

facial nerve

A

collects sensory information from taste buds over anterior two-thirds of tongue

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75
Q

glossopharyngeal nerve

A

from posterior one-third of tongue

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76
Q

vagus nerve

A

from taste buds of palate, pharynx and epiglottis

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77
Q

hypothalamus and amygdala

A

control autonomic reflexes –salivation, gagging and vomiting

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78
Q

thalamus

A

relays signals to postcentral gyrus of cerebrum for conscious sense of taste

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79
Q

orbitofrontal cortex

A

sent on to orbitofrontal cortex to be integrated with signals from nose and eyes -form impression of flavor and palatability of food

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80
Q

olfaction

A

sense of smell

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81
Q

olfactory mucosa

A

–contains 10 to 20 million olfactory cells, which are neurons, as well as epithelial supporting cells and basal stem cells
–mucosa of superior concha, nasal septum, and roof of nasal cavity covering about 5 cm2

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82
Q

olfactory cells

A

–are neurons
–shaped like little bowling pins
only neurons in the body directly exposed to the external environment
–have a lifespan of only 60 days

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83
Q

olfactory hairs

A

head bears 10 –20 cilia called olfactory hairs
–have binding sites for odorant molecules and are nonmotile
–lie in a tangled mass in a thin layer of mucus

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84
Q

axons collect into small fascicles and leave cranial cavity through

A

the cribriform foramina in the ethmoid bone

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85
Q

fascicles are collectively regarded as

A

Cranial Nerve I

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86
Q

olfactory receptors adapt

A

quickly
–due to synaptic inhibition in olfactory bulbs
PHASIC

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87
Q

Human Pheromones

A

–human body odors may affect sexual behavior

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88
Q

olfactory cells synapse in

A

olfactory bulb

–on dendrites of mitral and tufted cells

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89
Q

glomeruli

A

dendrites meet in spherical clusters called glomeruli
•each glomeruli dedicated to single odor because all fibers leading to one glomerulus come from cells with same receptor type

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90
Q

tufted and mitral cell axons form

A

olfactory tracts

–reach primary olfactory cortex in the inferior surface of the temporal lobe

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91
Q

Hearing and Equilibrium

A

both senses reside in the inner ear, a maze of fluid-filled passages and sensory cells
•fluid is set in motion and how the sensory cells convert this motion into an informative pattern of action potentials

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92
Q

hearing

A

a response to vibrating air molecules

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93
Q

equilibrium

A

the sense of motion, body orientation, and balance

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94
Q

sound

A

any audible vibration of molecules
–a vibrating object pushes on air molecules
–in turn push on other air molecules
–air molecules hitting eardrum cause it to vibration

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95
Q

pitch

A

our sense of whether a sound is „high‟ or „low‟

–determined by the frequency

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96
Q

infrasonic

A

infrasonic frequencies below 20 Hz

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97
Q

ultrasonic

A

ultrasonic frequencies above 20,000 Hz

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98
Q

loudness

A

the perception of sound energy, intensity, or amplitude of the vibration
–expressed in decibels (dB)
–prolonged exposure to sounds > 90dB can cause damage

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99
Q

ear has three sections

A

outer, middle, and inner ear
–first two are concerned only with the transmission of sound to the inner ear
–inner ear –vibrations converted to nerve signals

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100
Q

outer ear

A

a funnel for conducting vibrations to the tympanic membrane (eardrum)

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101
Q

auricle

A

(pinna) directs sound down the auditory canal

•shaped and supported by elastic cartilage

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102
Q

auditory canal

A

passage leading through the temporal bone to the tympanic membrane

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103
Q

external acoustic meatus

A

slightly s-shaped tube that begins at the external opening and courses for about 3 cm

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104
Q

guard hairs

A

protect outer end of canal

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105
Q

cerumen

A

earwax) –mixture of secretions of ceruminous and sebaceous glands and dead skin cells
–sticky and coats guard hairs
–contains lysozyme with low pH that inhibits bacterial growth
–water-proofs canal and protects skin
–keeps tympanic membrane pliable

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106
Q

middle ear

A

located in the air-filled tympanic cavity in temporal bone

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107
Q

tympanic membrane

A

(eardrum) –closes the inner end of the auditory cana
•innervated by sensory branches of the vagus and trigeminal nerves
–highly sensitive to pain

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108
Q

tympanic cavity

A

is continuous with mastoid air cells

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109
Q

auditory (eustachian) tube

A

connects middle ear cavity to nasopharynx

•equalizes air pressure on both sides of tympanic membrane

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110
Q

auditory ossicles

A

malleus
incus
stapes

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111
Q

malleus

A

attached to inner surface of tympanic membrane

112
Q

incus

A

articulates in between malleus and stapes

113
Q

stapes

A

footplate rests on oval window –inner ear begins

114
Q

stapedius and tensor tympani muscles attach to

A

stapes and malleus

115
Q

Otitis media

A

(middle ear infection) is common in children
–auditory tube is short and horizontal
–infections easily spread from throat to tympanic cavity and mastoid air cells

116
Q

tympanostomy

A

lancing tympanic membrane and draining fluid from tympanic cavity
–inserting a tube to relieve the pressure and allow infection to heal

116
Q

bony labyrinth

A

passageways in temporal bone

117
Q

membranous labyrinth

A

fleshy tubes lining the bony labyrinth

118
Q

Inner (Internal) Ear fleshy tubes filled with

A

endolymph-similar to intracellular fluid

120
Q

Inner (Internal) Ear fleshy tubes floating in

A

perilymph-similar to cerebrospinal fluid

121
Q

labyrinth

A

vestibule and three semicircular ducts

122
Q

cochlea

A

organ of hearing
–2.5 coils around an screwlike axis of spongy bone, the modiolus
–threads of the screw form a spiral platform that supports the fleshy tube of the cochlea

123
Q

cochlea has three fluid-filled chambers separated by membranes:

A

scala vestibule
scala tympani
scala media

124
Q

scala vestibuli

A

superior chamber
•filled with perilymph
•begins at oval window and spirals to apex

125
Q

scala tympani

A

inferior chamber
•filled with perilymph
•begins at apex and ends at round window
–secondary tympanic membrane –membrane covering round window

126
Q

scala media

A

(cochlear duct) –triangular middle chamber

•filled with endolymph

127
Q

scala media separated from scala vestibuli by

A

vestibular membrane

128
Q

scala media separated from scala tympani by

A

thicker basilar membrane

129
Q

scala media contains

A

spiral organ -organ of Corti -acoustic organ –converts vibrations into nerve impulses

130
Q

spiral organ

A

spiral organ has epithelium composed of hair cells and supporting cells

131
Q

stereocilia

A

hair cells have long, stiff microvilli called stereocilia on apical surface

132
Q

tectorial membrane

A

gelatinous tectorial membrane rests on top of stereocilia

133
Q

spiral organ has four rows of hair cells spiraling along its length

A

inner hair cells

outer hair cells

134
Q

inner hair cells

A

single row of about 3500 cells

•provides for hearing

135
Q

outer hair cells

A

three rows of about 20,000 cells
•adjusts response of cochlea to different frequencies
•increases precision

136
Q

tympanic membrane

A

–has 18 times area of oval window

–ossicles concentrate the energy of the vibrating tympanic membrane on an area 1/18the size

137
Q

tympanic reflex

A

–during loud noise, the tensor tympani pulls the tympanic membrane inward and tenses it
–stapedius muscle reduces the motion of the stapes

138
Q

vibration of ossicles causes

A

vibration of basilar membrane under hair cells
–as often as 20,000 times per second
–hair cells move with basilar membrane

139
Q

stereocilia of outer hair cells

A

–bathed in high K+fluid, the endolymph
•creating electrochemical gradient
•outside of cell is +80 mV and inside about –40 mV
–tip embedded in tectorial membrane

140
Q

stereocilium on inner hair cells

A

–single transmembrane protein at tip that functions as a mechanically gated ion channel
K+flows in –depolarization causes release of neurotransmitter
•stimulates sensory dendrites and generates action potential in the cochlear nerve

141
Q

Sensory Coding

A

for sounds to carry meaning, we must distinguish between loudness and pitch

142
Q

loudness

A

for sounds to carry meaning, we must distinguish between loudness and pitch
•variations in loudness(amplitude) cause variations in the intensity of cochlear vibrations

143
Q

pitch

A

depends on which part of basilar membrane vibrates

144
Q

at basal end

A

membrane attached, narrow and stiff

•brain interprets signals as high-pitched

145
Q

at distal end

A

5 times wider and more flexible

•brain interprets signals as low-pitched

145
Q

deafness

A

hearing loss

146
Q

conductive deafness

A

conditions interfere with transmission of vibrations to inner ear
•damaged tympanic membrane, otitis media, blockage of auditory canal, and otosclerosis

147
Q

otosclerosis

A

fusion of auditory ossicles that prevents their free vibration

148
Q

sensorineural (nerve) deafness

A

death of hair cells or any nervous system elements concerned with hearing
•factory workers, musicians and construction workers

149
Q

vestibular ganglia

A

visible lump in vestibular nerve

150
Q

spiral ganglia

A

buried in modiolus of cochlea

151
Q

Auditory Projection Pathway

A

sensory fibers begin at the bases of the hair cells
–somas form the spiral ganglion around the modiolus
–axons lead away from the cochlea as the cochlear nerve
–joins with the vestibular nerve to form the vestibulocochlear nerve, Cranial Nerve VIII

152
Q

each ear sends nerve fibers to

A

both sides of the pons
–end in cochlear nuclei
–synapse with second-order neurons that ascend to the nearby superior olivary nucleus
–superior olivary nucleus issues efferent fibers back to the cochlea
•involved with cochlear tuning

153
Q

binaural hearing

A

comparing signals from the right and left ears to identify the direction from which a sound is coming
–function of the superior olivary nucleus

154
Q

fibers ascend to the

A

inferior colliculi of the midbrain
–helps to locate the origin of the sound, processes fluctuation in pitch, and mediate the startle response and rapid head turning in response to loud noise

155
Q

third-order neurons begin

A

in the inferior colliculi and lead to the thalamus

156
Q

fourth-order neurons

A

complete the pathway from thalamus to primary auditory complex
–involves four neurons instead of three unlike most sensory pathways

157
Q

primary auditory cortex

A

lies in the superior margin of the temporal lobe

–site of conscious perception of sound

158
Q

because of extensive decussation of the auditory pathway

A

damage to right or left auditory cortex does not cause unilateral loss of hearing

159
Q

equilibrium

A

coordination, balance, and orientation in three-dimensional space

160
Q

vestibular apparatus

A

constitutes receptors for equilibrium
three semicircular ducts
two chambers

161
Q

three semicircular ducts

A

detect only angular acceleration

162
Q

two chambers

A
  • anterior saccule and posterior utricle

* responsible for static equilibrium and linear acceleration

163
Q

static equilibrium

A

the perception of the orientation of the head when the body is stationary

164
Q

dynamic equilibrium

A

perception of motion or acceleration

165
Q

linear acceleration

A

change in velocity in a straight line (elevator)

166
Q

angular acceleration

A

change in rate of rotation (car turns a corner)

167
Q

macula

A

2 by 3 mm patch of hair cells and supporting cells in the saccule and utricle

168
Q

macula sacculi

A

lies vertically on wall of saccule

•because the macula sacculi is nearly vertical, it responds to vertical acceleration and deceleration

169
Q

macula utriculi

A

lies horizontally on floor of utricle

170
Q

each hair cell has

A

40 to 70 stereocilia and one true cilium -kinocilium embedded in a gelatinous otolithic membrane

171
Q

otoliths

A

calcium carbonate-protein granules that add to the weight and inertia and enhance the sense of gravity and motion

172
Q

static equilibrium

A

when head is tilted, heavy otolithic membrane sags, bending the stereocilia, and stimulating the hair cells

173
Q

dynamic equilibrium

A

in car, linear acceleration detected as otoliths lag behind, bending the stereocilia, and stimulating the hair cells

174
Q

rotary movements detected by the

A

three semicircular ducts
•bony semicircular canals of temporal bone hold membranous semicircular ducts
•each duct filled with endolymphand opens up as a dilated sac (ampulla) next to the utricle
•each ampulla contains crista ampullaris, mound of hair cells and supporting cells

175
Q

crista ampullaris

A
  • consists of hair cells with stereocilia and a kinocilium buried in a mound of gelatinous membrane called the cupula(one in each duct)
  • orientation causes ducts to be stimulated by rotation in different planes
176
Q

Equilibrium Projection Pathways

A

hair cells of macula sacculi, macula utriculi and semicircular ducts synapse on vestibular nerve (part of CN VIII)
•fibers end in a complex of four vestibular nuclei on each side of the pons and medulla
–left and right nuclei receive input from both ears

177
Q

Equilibrium Projection Pathways

information sent to

A

-cerebellum

178
Q

cerebellum

A

integrates vestibular information into its control of head and eye movements, muscle tone, and posture

179
Q

vision

A

(sight) –perception of objects in the environment by means of the light that they emit or reflect

180
Q

light

A

visible electromagnetic radiation

–light must cause a photochemical reaction to produce a nerve signal

181
Q

ultraviolet radiation

A

-< 400 nm; has too much energy and destroys macromolecules

182
Q

infrared radiation

A

-> 750 nm; too little energy to cause photochemical reaction, but does warm the tissues

183
Q

eyebrows

A

provide facial expression

–protect eyes from glare and perspiration

184
Q

eyelids

A

(palpebrae)
–block foreign objects, help with sleep, blink to moisten
–meet at corners (commissures)

185
Q

eyelids consist of

A

–consist of orbicularis oculi muscle and tarsal plate covered with skin outside and conjunctiva inside
–tarsal glands secrete oil that reduces tear evaporation
–eyelasheshelp keep debris from eye

186
Q

conjunctiva

A

a transparent mucous membrane that lines eyelids and covers anterior surface of eyeball, except cornea
•richly innervated and vascular (heals quickly)
–secretes a thin mucous film that prevents the eyeball from drying

187
Q

Lacrimal Apparatus

A
  • tears flow across eyeball help to wash away foreign particles, deliver O2and nutrients, and prevent infection with a bactericidal lysozyme
  • tears flow through lacrimal punctum (opening on edge of each eyelid) to the lacrimal sac, then into the nasolacrimal duct emptying into nasal cavity
188
Q

Extrinsic Eyes Muscles

A

•6 muscles attached to exterior surface of eyeball
–superior, inferior, lateral, and medial rectus muscles, superior and inferior oblique muscles
•innervated by cranial nerves III, IV and VI

189
Q

superior, inferior, medial and lateral rectus muscles move the eye

A 
up, down, medially & laterally
Oculomotor nerve (III)
190
Q

superior and inferior oblique

A

mm. turn the “twelve o‟clock pole” of each eye toward or away from the nose
superior - Trochlear nerve (IV)
lateral - Abducens nerve (VI)

191
Q

orbital fat

A

surrounds sides and back of eye, cushions eye and allows free movement, protects blood vessels, and nerves

192
Q

three principal components of the eyeball

A

–three layers (tunics) that form the wall of the eyeball
–optical component –admits and focuses light
–neural component –the retina and optic nerve

193
Q

Tunics of the Eyeball

A

tunica fibrosa
tunica vasculosa
tunica interna

194
Q

tunica fibrosa

A

outer fibrous layer
–sclera–dense, collagenous white of the eye
–cornea-transparent area of sclera that admits light into eye

195
Q

tunica vasculosa

A

(uvea) –middle vascular layer
–choroid
–ciliary body
–iris

196
Q

choroid

A

highly vascular, deeply pigmented layer behind retina

197
Q

ciliary body

A

extension of choroid that forms a muscular ring around lens
•supports lens and iris
•secretes aqueous humor

198
Q

iris

A

colored diaphragm controlling size of pupil, its central opening
•melanin in chromatophores of iris -brown or black eye color
•reduced melanin –blue, green, or gray color

199
Q

tunica interna

A

retina and beginning of optic nerve

200
Q

Optical Components

A

•transparent elements that admit light rays, refract (bend) them, and focus images on the retina

201
Q

Optical Components 4

A

–cornea
–aqueous humor
–lens
–vitreous body (humor)

202
Q

cornea

A

•transparent cover on anterior surface of eyeball

203
Q

aqueous humor

A
  • serous fluid posterior to cornea, anterior to lens
  • reabsorbed by scleral venous sinus (canal of Schlemm)
  • produced and reabsorbed at same rate
204
Q

lens

A

•lens fibers –flattened, tightly compressed, transparent cells that form lens
•suspended by suspensory ligaments from ciliary body
•changes shape to help focus light
–rounded with no tension or flattened with pull of suspensory ligaments

205
Q

vitreous body

A

(humor) fills vitreous chamber

•jelly fills space between lens and retina

206
Q

Aqueous Humor

A

released by ciliary body into posterior chamber, passes through pupil into anterior chamber -reabsorbed into canal of Schlemm

207
Q

Neural Components

A

includes retina and optic nerve

208
Q

retina

A

–forms as an outgrowth of the diencephalon
–attached to the rest of the eye only at optic disc and at ora serrata
–pressed against rear of eyeball by vitreous humor
–detached retina causes blurry areas in field of vision and leads to blindness

209
Q

examine retina with

A

opthalmoscope

210
Q

macula lutea

A

patch of cells on visual axis of eye

211
Q

fovea centralis

A

pit in center of macula lutea

212
Q

blood vessels

A

of the retina

213
Q

fovea centralis

A

center of macula; finely detailed images due to packed receptor cells

214
Q

optic disk

A

blind spot
–optic nerve exits posterior surface of eyeball
–no receptor cells at that location

215
Q

visual filling

A

brain fills in green bar across blind spot area

216
Q

cataract

A

clouding of lens

–lens fibers darken with age, fluid-filled bubbles and clefts filled with debris appear between the fibers

217
Q

glaucoma

A

elevated pressure within the eye due to obstruction of scleral venous sinus and improper drainage of aqueous humor

218
Q

intraocular pressure measured with

A

tonometer

219
Q

Formation of an Image

A

light passes through lens to form tiny inverted image on retina

220
Q

iris diameter

A

–pupillary constrictor -smooth muscle encircling the pupil
•parasympathetic stimulation narrows pupil
–pupillary dilator -spokelike myoepithelial cells
•sympathetic stimulation widens pupil

221
Q

pupillary constrictor

A

smooth muscle encircling the pupil

222
Q

pupillary dilator

A

spokelike myoepithelial cells

223
Q

pupillary constriction and dilation occurs in two situations

A

–when light intensity changes

–when our gaze shifts between distant and nearby objects

224
Q

photopupillary reflex

A

pupillary constriction in response to light

225
Q

consensual light reflex

A

because both pupils constrict even if only one eye is illuminated

226
Q

refraction

A

the bending of light rays

227
Q

Refraction in the Eye

A
  • light passing through the center of the cornea is not bent
  • light striking off-center is bent towards the center
  • aqueous humor and lens do not greatly alter the path of light
228
Q

cornea refracts light more than

A

lens does
–lens merely fine-tunes the image
–lens becomes rounder to increase refraction for near vision

229
Q

emmetropia

A

state in which the eye is relaxed and focused on an object more than 6 m (20 ft) away
–light rays coming from that object are essentially parallel
–rays focused on retina without effort

230
Q

near response

A

adjustments to close range vision requires three processes
convergence of eyes
constriction of pupil

231
Q

convergence of eyes

A

eyes orient their visual axis towards object

232
Q

constriction of pupil

A

•blocks peripheral light rays and reduces spherical aberration (blurry edges)

233
Q

accommodation of lens

A

change in the curvature of the lens that enables you to focus on nearby objects
•ciliary muscle contracts, lens takes convex shape

234
Q

near point of vision

A

closest an object can be and still come into focus

235
Q

emmetropia

A

distant object
relatively dilated pupil
relatively thin lens
lens flatter

236
Q

Convergence

A

close object
relatively constricted pupil
relatively thick lens
lens thicker

237
Q

Hyperopia

A

(farsightedness)

238
Q

Myopia

A

(nearsightedness)

239
Q

Sensory Transduction in the Retina

A

•conversion of light energy into action potentials occurs in the retina

240
Q

structure of retina

A

pigment epithelium

neural components

241
Q

pigment epithelium

A

most posterior part of retina

•absorbs stray light so visual image is not degraded

242
Q

neural components of the retina from the rear of the eye forward

A

photoreceptor cells
bipolar cells
ganglion cells

243
Q

photoreceptor cells

A

absorb light and generate a chemical or electrical signal
–rods, cones, and certain ganglion cells
–only rods and cones produce visual images

244
Q

bipolar cells

A

synapse with rods and cones and are first-order neurons of the visual pathway

245
Q

ganglion cells

A

largest neurons in the retina and are the second-order neurons of the visual pathway

246
Q

light absorbing cells

A

derived from same stem cells as ependymal cells of the brain
–rod cells
-cone cells

247
Q

rod cells

A

(night -scotopic vision or monochromatic vision)
•outer segment –modified cilium specialized to absorb light
–stack of 1,000 membranous discs studded with globular proteins, the visual pigment, rhodopsin
•inner segment –contains organelles sitting atop cell body with nucleus

248
Q

cone cells

A

(color, photopic, or day vision)
•similar except outer segment tapers
•outer segment tapers to a point
•plasma membrane infoldings form discs

249
Q

neuronal convergence

A

and information processing in retina before signals reach brain
–multiple rod or cone cells synapse on one bipolar cell
–multiple bipolar cells synapse on one ganglion cell

250
Q

rods contain visual pigment

A

rhodopsin (visual purple)
–two major parts of molecule
•opsin -protein portion embedded in disc membrane of rod‟s outer segment
•retinal(retinene) -a vitamin A derivative

251
Q

cones contain

A

photopsin(iodopsin)
–retinal moiety same as in rods
–opsin moiety contain different amino acid sequences that determine wavelengths of light absorbed
–3 kinds of cones, identical in appearance, but absorb different wavelengths of light to produce color vision

252
Q

Rhodopsin Bleaching/Regeneration

A

rhodopsin absorbs light, converted from bent shape in dark (cis-retinal) to straight (trans-retinal)
–retinal dissociates from opsin (bleaching)
–5 minutes to regenerate 50% of bleached rhodopsin
•cones are faster to regenerate their photopsin –90seconds for 50%

253
Q

Generating Optic Nerve Signals

A
  • in dark, rods steadily release the neurotransmitter, glutamate from basal end of cell
  • when rods absorb light, glutamate secretion ceases
  • bipolar cells sensitive to these on and off pulses of glutamate secretion
  • these cells excited by rising light intensities
  • when bipolar cells detect fluctuations in light intensity, they stimulate ganglion cells directly or indirectly
  • ganglion cells are the only retinal cells that produce action potentials
  • ganglion cells respond to the bipolar cells with rising and falling firing frequencies
  • via optic nerve, these changes provide visual signals to the brain
254
Q

light adaptation

A

(walk out into sunlight)
–pupil constriction and pain from over stimulated retinas
–pupils constrict to reduce pain & intensity
–color vision and acuity below normal for 5 to 10 minutes
–time needed for pigment bleaching to adjust retinal sensitivity to high light intensity
–rod vision nonfunctional

255
Q

dark adaptation

A

(turn lights off)
–dilation of pupils occurs
–rod pigment was bleached by lights
–in dark, rhodopsin regenerates faster than it bleaches
–in a minute or two night (scotopic) vision begins to function
–after 20 to 30 minutes the amount of regenerated rhodopsin is sufficient for your eyes to reach maximum sensitivity

256
Q

duplicity theory of vision

A

explains why we have both rods and cones
–a single type of receptor can not produce both high sensitivity and high resolution
•it takes one type of cell and neural circuit for sensitive night vision
•it takes a different cell type and neuronal circuit for high resolution daytime vision

257
Q

Scotopic System

A

Night Vision
rods sensitive –react even in dim light
–extensive neuronal convergence
–600 rods converge on 1 bipolar cell
–many bipolar converge on each ganglion cell
–results in high degree of spatial summation
•one ganglion cells receives information from 1 mm2of retina producing only a coarse image
•edges of retina have widely-spaced rod cells, act as motion detectors
–low resolution system only
–cannot resolve finely detailed images

258
Q

Color Vision Photopic System

A

Day Vision)
•fovea contains only 4000 tiny cone cells (no rods)
–no neuronal convergence
–each foveal cone cell has “private line to brain”
•high-resolution color vision
–little spatial summation so less sensitivity to dim light

259
Q

Color Vision

A

•primates have well developed color vision
–nocturnal vertebrates
have only rods

260
Q

three types of cones

A

are named for absorption peaks of their photopsins
–short-wavelength(S) cones peak sensitivity at 420 nm
–medium-wavelength(M) cones peak at 531 nm
–long-wavelength(L) cones peak at 558 nm

261
Q

color perception

A

based on mixture of nerve signals representing cones of different absorption peaks

262
Q

color blindness

A

have a hereditary alteration or lack of one photopsin or another
•most common is red-green color blindness
–results from lack of either L or M cones

263
Q

stereoscopic vision

A

is depth perception -ability to judge distance to objects

–requires two eyes with overlapping visual fields which allows each eye to look at the same object from different angles

264
Q

panoramic vision

A

has eyes on sides of head (horse or rodents –alert to predators but no depth perception)

265
Q

fixation point

A

point in space in which the eyes are focused
–looking at object within 100 feet, each eye views from slightly different angle
–provides brain with information used to judge position of objects relative to fixation point

266
Q

Visual Projection Pathway

first-order neurons

A

bipolar cells of retina

267
Q

Visual Projection Pathway

second-order neurons

A

retinal ganglion cells are second-order neurons whose axons form optic nerve

268
Q

optic chiasm

A

two optic nerves combine to form optic chiasm

–half the fibers cross over to the opposite side of the brain (hemidecussation) and chiasm splits to form optic tracts

269
Q

optic tracts

A
  • right cerebral hemisphere sees objects in the left visual field because their images fall on the right half of each retina
  • each side of brain sees what is on side where it has motor control over limbs
270
Q

optic tracts pass

A

laterally around the hypothalamus with most of their axons ending in the lateral geniculate nucleus of the thalamus

271
Q

Visual Projection Pathway

third-order neurons

A

third-order neurons arise in geniculate nucleus of the thalamus and form the optic radiation of fibers in the white matter of the cerebrum
-project to primary visual cortex of occipital lobe

272
Q

conscious visual sensation occurs

A

primary visual cortex of occipital lobe

273
Q

Visual Information Processing

A

some processing begins in retina

–adjustments for contrast, brightness, motion and stereopsis

274
Q

primary visual cortex is connected by

A

association tracts to visual association areas in parietal and temporal lobes which process retinal data from occipital lobes
–object location, motion, color, shape, boundaries
–store visual memories (recognize printed words)

2 - Keiser A&P 2 (15 decks)

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