1. Chapter 16
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2. Sense Organs Sensory receptors General senses Chemical senses
properties and types
General senses
Chemical senses
Hearing and equilibrium
Vision

3. Properties of Receptors
Sensory transduction
convert stimulus energy into nerve energy
Receptor potential
local electrical change in receptor cell
Adaptation
conscious sensation declines with continued stimulation

4. Receptors Transmit Information
Modality - type of stimulus
Location
each sensory receptor receives input from its receptive field
sensory projection - brain identifies site of stimulation
Intensity
frequency, number of fibers and which fibers
Duration - change in firing frequency over time
phasic receptor - burst of activity and quickly adapt (smell and hair receptors)
tonic receptor - adapt slowly, generate impulses continually (proprioceptor)

5. Receptive Fields

6. Classification of Receptors
By modality:
chemo-, thermo-, mechano-, photo- receptors and nociceptors
By origin of stimuli
interoceptors - detect internal stimuli
proprioceptors - sense body position and movements
exteroceptors - detect external stimuli
By distribution
general senses - widely distributed
special senses - limited to head

7. Unencapsulated Nerve Endings
Dendrites not wrapped in connective tissue
General sense receptors
for pain and temperature
Tactile discs
associated with cells at base of epidermis
Hair receptors
monitor movement of hair

8. Encapsulated Nerve Endings
Dendrites wrapped by glial cells or connective tissue
tactile corpuscles - phasic
light touch and texture
krause end bulb - phasic
tactile; in mucous membranes
lamellated corpuscles - phasic
deep pressure, stretch, tickle and vibration
ruffini corpuscles - tonic
heavy touch, pressure, joint movements and skin stretching

9. Somesthetic Projection Pathways
1st order neuron (afferent neuron)
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
2nd order neuron
decussation to opposite side in spinal cord or medulla/pons
end in thalamus, except for proprioception (cerebellum)
3rd order neuron
thalamus to primary somesthetic cortex of cerebrum

10. Pain Nociceptors – allow awareness of tissue injuries
found in all tissues except the brain
Fast pain travels in myelinated fibers at 30 m/sec
sharp, localized, stabbing pain perceived with injury
Slow pain travels unmyelinated fibers at 2 m/sec
longer-lasting, dull, diffuse feeling
Somatic pain from skin, muscles and joints
Visceral pain from stretch, chemical irritants or ischemia of viscera (poorly localized)
Injured tissues release chemicals that stimulate pain fibers (bradykinin, histamine, prostaglandin)

11. Projection Pathway for Pain
General pathway – conscious pain
1st order neuron cell bodies in dorsal root ganglion of spinal nerves or cranial nerves V, VII, IX, and X
2nd order neurons decussate and send fibers up spinothalamic tract or through medulla to thalamus
gracile fasciculus carries visceral pain signals
3rd order neurons from thalamus reach primary somesthetic cortex as sensory homunculus
Spinoreticular tract
pain signals reach reticular formation, hypothalamus and limbic
trigger visceral, emotional, and behavioral reactions

12. Pain Signal Destinations

13. Referred Pain Misinterpreted pain
brain “assumes” visceral pain is coming from skin
heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 to T5

14. Referred Pain

15. CNS Modulation of Pain Intensity of pain - affected by state of mind
Endogenous opiods (enkephalins, endorphins and dynorphins)
produced by CNS and other organs under stress
in dorsal horn of spinal cord (spinal gating)
act as neuromodulators block transmission of pain

16. Spinal Gating Stops pain signals at dorsal horn
descending analgesic fibers from reticular formation travel down reticulospinal tract to dorsal horn
secrete inhibitory substances that block pain fibers from secreting substance P
pain signals never ascend
dorsal horn fibers inhibited by input from mechanoreceptors
rubbing a sore arm reduces pain

17. Spinal Gating of Pain Signals

18. Chemical Sense - Taste Gustation - sensation of taste Lingual papillae
results from action of chemicals on taste buds
Lingual papillae
filiform (no taste buds)
important for texture
foliate (no taste buds)
fungiform
at tips and sides of tongue
vallate (circumvallate)
at rear of tongue
contains 1/2 of taste buds

19. Taste Bud Structure Taste cells Supporting cells Basal cells
apical microvilli serve as receptor surface
synapse with sensory nerve fibers at their base
Supporting cells
Basal cells

20. Physiology of Taste Molecules must dissolve in saliva
5 primary sensations - throughout tongue
Sweet - concentrated on tip
Salty - lateral margins
Sour - lateral margins
Bitter - posterior
Umami - taste of amino acids (MSG)
Influenced by food texture, aroma, temperature, and appearance
mouthfeel - detected by lingual nerve in papillae
Hot pepper stimulates free nerve endings (pain)

21. Physiology of Taste Mechanisms of action
activate 2nd messenger systems
sugars, alkaloids and glutamates bind to receptors
depolarize cells directly
sodium and acids penetrate cells

22. Projection Pathways for Taste
Innervation of taste buds
facial nerve (VII) - anterior 2/3’s of tongue
glossopharyngeal nerve (IX) - posterior 1/3
vagus nerve (X) - palate, pharynx, epiglottis

23. Projection Pathways for Taste
To solitary nucleus in medulla
To hypothalamus and amygdala
activate autonomic reflexes
e.g. salivation, gagging and vomiting
To thalamus, then postcentral gyrus of cerebrum
conscious sense of taste

24. Chemical Sense - Smell Olfactory mucosa
contains receptor cells for olfaction
highly sensitive
up to 10,000 odors
on 5cm2 of superior concha and nasal septum

25. Olfactory Epithelial Cells
Olfactory cells
olfactory hairs neurons with 20 cilia
bind odor molecules in thin layer of mucus
axons pass through cribriform plate
survive 60 days
Supporting cells
Basal cells
divide

26. Physiology of Smell Molecules bind to receptor on olfactory hair
hydrophilic - diffuse through mucus
hydrophobic - transport by odorant-binding protein
Activate G protein and cAMP system
Opens ion channels for Na+ or Ca2+
creates a receptor potential
Action potential travels to brain
Receptors adapt quickly
due to synaptic inhibition in olfactory bulbs

27. Olfactory Pathway Olfactory cells synapse in olfactory bulb
on mitral and tufted cell dendrites
in spherical clusters called glomeruli
each glomeruli dedicated to single odor

28. Olfactory Pathway Output from bulb forms olfactory tracts
end in primary olfactory cortex and thalamus
travel to insula and frontal cortex
identify odors
integrate taste and smell into flavor
travel to hypocampus, amygdala, and hypothalamus
memories, emotional and visceral reactions

29. Olfactory Pathway Feedback
granule cells in olfactory cortex synapse in glomeruli
food smells better when hungry

30. Olfactory Projection Pathways

31. The Nature of Sound Sound - audible vibration of molecules
vibrating object pushes air molecules

32. Pitch and Loudness Pitch - frequency vibrates specific parts of ear
hearing range is 20 (low pitch) - 20,000 Hz (cycles/sec)
speech is where hearing is most sensitive
Loudness – amplitude; intensity of sound energy

33. Outer Ear

34. Outer Ear
Fleshy auricle (pinna) directs air vibrations down external auditory meatus
cartilagenous and bony, S-shaped tunnel ending at eardrum
glandular secretions and dead cells form cerumen (earwax)

35. Anatomy of Middle Ear

36. Middle Ear
Air-filled tympanic cavity in temporal bone between tympanic membrane and oval window
continuous with mastoid air cells
Contains
auditory tube (eustachian tube) connects to nasopharynx
equalizes air pressure on tympanic membrane
ear ossicles
malleus
incus
stapes
stapedius and tensor tympani muscles attach to stapes and malleus

37. Anatomy of Inner Ear

38. Inner Ear Bony labyrinth - passageways in temporal bone
Membranous labyrinth - fleshy tubes lining bony tunnels
filled with endolymph (similar to intracellular fluid)
floating in perilymph (similar to cerebrospinal fluid)

39. Details of Inner Ear
Fig c

40. Details of Inner Ear

41. Anatomy of Cochlea Scala media (cochlear duct)
separated from
scala vestibuli by vestibular membrane
scala tympani by basilar membrane
Spiral organ (organ of corti)

42. Spiral Organ

43. Spiral Organ
Stereocilia of hair cells attach to gelatinous tectorial membrane
Inner hair cells
hearing
Outer hair cells
adjust cochlear responses to different frequencies
increase precision

44. SEM of Cochlear Hair Cells

45. Physiology of Hearing - Middle Ear
Tympanic membrane
has 18 times area of oval window
ossicles transmit enough force/unit area at oval window to vibrate endolymph in scala vestibuli
Tympanic reflex – muscle contraction
tensor tympani m. tenses tympanic membrane
stapedius m. reduces mobility of stapes
best response to slowly building loud sounds
occurs while speaking

46. Stimulation of Cochlear Hair Cells
Vibration of ossicles causes vibration of basilar membrane under hair cells
as often as 20,000 times/second

47. Cochlear Hair Cells Stereocilia of OHCs bathed in high K+
creating electrochemical gradient
tips embedded in tectorial membrane
bend in response to movement of basilar membrane
pulls on tip links and opens ion channels
K+ flows in – depolarization causes release of neurotransmitter
stimulates sensory dendrites at base

48. Potassium Gates

49. Sensory Coding
Vigorous vibrations excite more inner hair cells over a larger area
triggers higher frequency of action potentials
brain interprets this as louder sound
Pitch depends on which part of basilar membrane vibrates
at basal end, membrane narrow and stiff
brain interprets signals as high-pitched
at distal end, 5 times wider and more flexible
brain interprets signals as low-pitched

50. Basilar Membrane Frequency Response
Notice high and low frequency ends

51. Cochlear Tuning
Increases ability of cochlea to receive some sound frequencies
Outer hair cells contract reducing basilar membranes freedom to vibrate
fewer signals from that area allows brain to distinguish between more and less active areas of cochlea
Pons has inhibitory fibers that synapse near the base of IHCs
increases contrast between regions of cochlea

52. Innervation of Internal Ear
Vestibular ganglia - visible in vestibular nerve
Spiral ganglia - buried in modiolus of cochlea

53. Auditory Pathway

54. Auditory Projection Pathway
Spiral ganglion formed by cell bodies of sensory neurons
Axons form cochlear nerve portion of CN VIII
Synapse in cochlear nuclei
Binaural hearing
superior olivary nucleus compares sounds from both sides to identify direction
Inferior colliculus helps
locate origin of sound
process fluctuations in pitch during speech
produce startle response; head turning to loud sound
Fibers from inferior colliculus go to primary auditory cortex – temporal lobe

55. Auditory Processing Centers
Damage to either auditory cortex does not cause unilateral deafness (extensive decussation)

56. Equilibrium Control of coordination and balance
Receptors in vestibular apparatus
semicircular ducts contain crista
saccule and utricle contain macula
Static equilibrium – perceived by macula
perception of head orientation
Dynamic equilibrium
perception of motion or acceleration
linear acceleration perceived by macula
angular acceleration perceived by crista

57. Saccule and Utricle Contain macula
hair cells with stereocilia and one kinocilium buried in a gelatinous otolithic membrane
otoliths add to the density and inertia and enhance the sense of gravity and motion

58. Macula
Static equilibrium - when head is tilted, weight of membrane bends the stereocilia
Dynamic equilibrium – in car, linear acceleration detected as otoliths lag behind

59. Crista ampullaris
Consists of hair cells buried in a mound of gelatinous membrane (one in each duct)
Orientation causes ducts to be stimulated by rotation in different planes

60. Crista Ampullaris - Head Rotation
As head turns, endolymph lags behind, pushes cupula, stimulates hair cells

61. Vestibular Projection Pathways

62. Equilibrium Projection Pathways
Hair cells of macula sacculi, macula utriculi and semicircular ducts synapse on vestibular nerve
Fibers end in vestibular nucleus in pons and medulla

63. Equilibrium Projection Pathways
Information sent to 5 targets
cerebellar control of head and eye movements and posture
nuclei of CN III, IV, and VI to produce vestibulo ocular reflex
reticular formation control of blood circulation and posture
vestibulospinal tracts innervate antigravity muscles
thalamic relay to cerebral cortex for awareness of position and movement

64. Vision and Light
Vision - perception of light emitted or reflected from objects in the environment
Visible light
electromagnetic radiation with wavelengths from 400 to 750 nm
must cause a photochemical reaction to produce a nerve signal
radiation below 400 nm; energetic, kills cells
radiation above 750 nm; too little energy to cause photochemical reaction

65. External Anatomy of Eye

66. Eyebrows and Eyelids Eyebrows provide facial expression
Eyelids (palpebrae)
block foreign objects, help with sleep, blink to moisten
meet at corners (commissures)
consist of orbicularis oculi muscle and tarsal plate covered with skin outside and conjunctiva inside
tarsal glands secrete oil that reduces tear evaporation
eyelashes help keep debris from eye

67. Conjunctiva
Transparent mucous membrane lines eyelids and covers anterior surface of eyeball except cornea
Richly innervated and vascular (heals quickly)

68. Lacrimal Apparatus
Tears flow across eyeball help to wash away foreign particles, help with diffusion of O2 and CO2 and contain bactericidal enzyme

69. Extrinsic Eyes Muscles
6 muscles inserting on eyeball
4 rectus, superior and inferior oblique muscles
Innervated by cranial nerves III, IV and VI

70. Innervation of Extrinsic Eye Muscles

71. Tunics of the Eyeball Fibrous layer - sclera and cornea
Vascular layer - choroid, ciliary body and iris
Internal layer - retina and optic nerve

72. Optical Components Structures refract light to focus on retina cornea
transparent cover on anterior surface of eyeball
aqueous humor
serous fluid posterior to cornea, anterior to lens
lens
changes shape to help focus light
rounded with no tension
flattened due to pull of suspensory ligaments
vitreous humor
jelly fills space between lens and retina

73. Aqueous Humor
Produced by ciliary body, flows to posterior chamber through pupil to anterior chamber - reabsorbed into canal of Schlemm

74. Cataracts and Glaucoma
Cataract - clouding of lens
aging, diabetes, smoking, and UV light
Glaucoma
death of retinal cells due to elevated pressure within the eye
obstruction of scleral venous sinus
colored halos and dimness of vision

75. Neural Components Includes retina and optic nerve Retina
forms as an outgrowth of the diencephalon
attached at optic disc and at ora serrata
pressed against rear of eyeball by vitreous

76. Detached retina Blow to head or lack of vitreous
Blurry areas in field of vision
Disrupts blood supply, leads to blindness

77. Ophthalmoscopic Exam of Eye
Macula lutea - cells on visual axis of eye (3 mm)
fovea centralis - center of macula; finely detailed images due to packed receptor cells
Direct evaluation of blood vessels

78. Test for Blind Spot Optic disk = blind spot
optic nerve exits posterior surface of eyeball
no receptor cells
Blind spot - use test illustration above
close eye, stare at X and red dot disappears
Visual filling - brain fills in green bar across blind spot area

79. Formation of an Image
Light passes through lens to form inverted image on retina
Pupillary constrictor - smooth muscle encircling the pupil
parasympathetic stimulation narrows pupil
Pupillary dilator - spokelike myoepithelial cells
sympathetic stimulation widens pupil
Active when light intensity changes or gaze shifts from distant object to nearby object
photopupillary reflex -- both pupils constrict if one eye is illuminated (type of consensual reflex)

80. Principle of Refraction
Light striking the lens or cornea at a 90 degree angle is not bent.

81. Refraction
Bending of light rays occurs when light passes through substance with different refractive index at any angle other than 90 degrees
refractive index of air is arbitrarily set to n = 1
refractive index
cornea is n = 1.38
lens is n = 1.40
Cornea refracts light more than lens does
due to shape of cornea
lens becomes rounder to increase refraction for near vision

82. Near Response
Allows eyes to focus on nearby object (that sends oblique light waves to eyes)
convergence of eyes
eyes orient their visual axis towards object
constriction of pupil
blocks peripheral light rays and reduces spherical aberration (blurry edges)
accomodation of lens
ciliary muscle contracts, lens takes convex shape
light refracted more strongly and focused onto retina

83. Emmetropia and Near Response
Fig a
Distant object
Close object

84. Emmetropia and Near Response

85. Accommodation of Lens

86. Effects of Corrected Lenses
Hyperopia - farsighted (eyeball too short)
correct with convex lenses
Myopia - nearsighted (eyeball too long)
correct with concave lenses

87. Photoreceptor Cells Posterior layer of retina - pigment epithelium
purpose is to absorb stray light and prevent reflections
Photoreceptors
rod cells (night - scotopic vision)
outer segment - stack of coinlike membranous discs studded with rhodopsin pigment molecules
cone cells (color - photopic vision)
outer segment tapers to a point

88. Histology - Layers of Retina

89. Location of Visual Pigments

90. Nonreceptor Retinal Cells
Bipolar cells (1st order neurons)
synapse on ganglion cells
large amount of convergence
Ganglion cells (2nd order neurons)
axons of these form optic nerve
more convergence occurs (114 receptors to one optic nerve fiber)
Horizontal and amacrine cells form connections between other cells
enhance perception of contrast, edges of objects and changes in light intensity

91. Schematic Layers of the Retina

92. Visual Pigments Rod cells have rhodopsin
has absorption peak at wavelength of 500 nm
2 major parts of molecule
opsin - protein portion
retinal - a vitamin A derivative
Cones contain photopsin (iodopsin)
opsin moieties contain different amino acids that determine wavelengths of light absorbed
3 kinds of cones absorbing different wavelengths of light produce color vision

93. Rhodopsin Bleaching/Regeneration
Rhodopsin absorbs light, converted from bent shape (cis-retinal) to straight (trans-retinal)
retinal dissociates from opsin (bleaching)
5 minutes to regenerate 50% of bleached rhodopsin

94. Generating Visual Signals

95. Generating Nerve Signals - Rods
In the dark, rods exhibit a dark signal
flow of Na+ and release of neurotransmitter (glutamate)
depolarization by Na+ stimulates glutamate release
In the light, dark current and glutamate release stops
bleached rhodopsin molecule acts like an enzyme and breaks down cGMP molecules
Na+ gates close and dark current ceases (inhibition stops), nerve signal results

96. Bipolar Cell Function Two kinds of bipolar cells
inhibited (hyperpolarized) by glutamate
excited by rising light intensity
excited (depolarized) by glutamate
excited by falling light intensity
As your eye scans a scene, areas of light and dark cause a changing pattern of bipolar cell responses
Variable pattern of stimulation of ganglion cells and nerve signals sent to the brain

97. Light and Dark Adaptation
Light adaptation (walk out into sunlight)
pupil constriction and pain from over stimulated retinas
color vision and acuity below normal for 5 to 10 minutes
Dark adaptation (turn lights off)
dilation of pupils occurs
20 to 30 minutes required for regeneration of rhodopsin

98. Duplicity Theory Explains why we have both rods and cones
Single type of receptor cell incapable of providing high sensitivity and high resolution
sensitive night vision = one type of cell and neural circuitry
high resolution daytime vision = different cell type and neuronal circuitry

99. Duplicity Theory

100. Scotopic System (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 mm2 of retina producing only a coarse image
Edges of retina have widely-spaced rod cells, act as motion detectors

101. Photopic System (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

102. Color Vision Primates have well developed color vision
nocturnal vertebrates
have only rods
Cones named for absorption
peaks of photopsins
blue cones peak sensitivity at 420 nm
green cones peak at 531 nm
red cones peak at 558 nm (orange-yellow)
Color perception based on mixture of nerve signals

103. Color Blindness Hereditary lack of one photopsin
red-green is common (lack either red or green cones)
incapable of distinguishing red from green
sex-linked recessive (8% of males)

104. Stereoscopic Vision (Stereopsis)
Depth perception - ability to judge distance to objects
requires 2 eyes with
overlapping visual fields
panoramic vision has eyes
on sides of head (horse)
Fixation point
farther away requires image
focus medial to fovea
closer results in image focus lateral to fovea

105. Visual Projection Pathway

106. Visual Projection Pathway
Bipolar and ganglion cells in retina - 1st and 2nd order neurons (ganglion cell axons of form CN II)
Hemidecussation in optic chiasm
1/2 of fibers decussate so that images of all objects in left visual field fall on right half of each retina
each side of brain sees what is on side where it has motor control over limbs
3rd order neurons in lateral geniculate nucleus of thalamus form optic radiation to 1 visual cortex where conscious visual sensation occurs
Few fibers project to superior colliculi and midbrain for visual reflexes (photopupillary and accomodation)

107. Visual Information Processing
Some processing occurs in retina
adjustments for contrast, brightness, motion and stereopsis
Visual association areas in parietal and temporal lobes process visual data
object location, motion, color, shape, boundaries
store visual memories (recognize printed words)