1. Unit 11 Somatic Senses and Special Senses

2. Objectives: Overview of Sensations Definition of Sensation
Characteristics of Sensations
Types of Sensory Receptors

3. General Senses: Somatic and Visceral
Tactile: Touch, Pressure, Vibration
Thermal (warm, cold)
Pain
Proprioception
Visceral: Internal organ conditions

4. Definition of Sensation
Conscious or subconscious awareness of change in external or internal environment
Requires
Stimulus
Sensory receptor
Neural pathway
Brain region for integration

5. Characteristics Perception: Conscious awareness
Occurs in cerebral cortex
Adaptation: Decreased receptor response during prolonged stimulation
Decreased perception
Adaptation speed varies with receptor
Rapid adaptation: Pressure, Touch, Smell
Slow adaptation: Pain, Body position, Chemical levels in blood

6. Sensory Receptors: Structural Types
Free nerve endings
Pain, thermal, tickle, itch, some touch receptors
Encapsulated nerve endings
Touch pressure, and vibration
Separate, specialized cells
Hair cells in inner ear
Photoreceptors in retina of eye

7. Sensory Receptors: Functional Types
Mechanoreceptors
Cell deformation: Stretching or bending
Touch, Pressure, Vibration
Thermoreceptors: Temperature
Nociceptors: Pain
Photoreceptors: Light
Chemoreceptors: Taste, Smell
Osmoreceptors
Osmotic pressure of body fluid

8. Objectives: Somatic Senses Tactile Sensations Thermal Sensations
Pain Sensations
Proprioceptive Sensations

9. Somatic Senses
Somatic receptors in skin, mucous membranes, muscles, tendons, and joints
Distributed unevenly: Dense concentration of receptors in very sensitive areas
Fingertips, Lips, Tip of tongue
Include tactile, thermal, pain, proprioceptive

10. Tactile Sensations Touch, pressure, vibration Itch and tickle
Encapsulated mechanoreceptors
Itch and tickle
Free nerve endings

11. Touch Rapidly adapting receptors for touch
Meissner corpuscles
Hair root plexuses: Detect hair movement
Slowly adapting receptors for touch
Type I Mechanoreceptors: Merkel discs or Tactile discs
Surface receptors: In epidermis
Type I Mechanoreceptors: Ruffini corpuscles
Deep in dermis and tendons

12. Pressure and Vibration
Pacinian (lamellated) corpuscles: Layers like onion
Rapid adapting
Widely distributed: In dermis, subcutaneous, around joints, tendons, muscles, periosteum
Vibration
Response to rapidly repetitive stimuli
Receptors: Meissner and Pacinian

13. Structure and Location of Sensory Receptors
Copyright 2010, John Wiley & Sons, Inc.

14. Itch and Tickle Itch: Chemical stimulation of Free nerve endings
Bradykinin from inflammation response
Tickle: From Free nerve endings and Pacinian corpuscles
Tickle requires stimulus from outside of self
Effects of attempts to tickle oneself are blocked by signals to/from cerebellum

15. Thermal Sensations Two kinds of Thermoreceptors
Cold receptors: 10˚– 40˚ C (50 – 105˚ F)
Located in epidermis
Warm receptors: 32˚– 48˚ C (90 – 118˚ F)
Located in dermis
Both adapt rapidly but continue slow signals during prolonged stimulus
Outside these ranges: Nociceptors detect pain

16. Pain Sensations Nociceptors Types of pain
Free nerve endings in every tissue except brain
Can respond to any excessive stimulus
Minimal adaptation
Types of pain
Fast pain: acute, sharp pain
Well localized
Slow pain: chronic, burning, aching, throbbing
More diffuse (not localized)
Analgesic drugs – Block formation of chemicals that stimulate nociceptors
Referred pain is visceral pain displaced to surface

17. Distribution of Referred Pain
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18. Proprioception (Kinesthesia)
Awareness of
Body position, movements, weight of objects
Sites of receptors
Muscles (muscle spindles)
Tendons (tendon organs)
Joint kinesthetic receptors (synovial joints)
Inner ear (hair cells): head position
Tracts to
Somatosensory area of cerebral cortex and
Cerebellum
Slight adaptation

19. Functional Areas of the Cerebrum
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20. Objectives:
Special Senses
Olfaction: Sense of Smell

21. Special Senses Smell (Olfaction) Taste (Gustation) Vision Balance
Hearing

22. Smell: Olfaction Site of olfactory receptors
In mucosa of superior region of nose
Three types of olfactory cells
Olfactory receptors
Consist of olfactory hairs with chemoreceptors
These are first order neurons of olfactory pathway
Supporting cells
Epithelial cells: Support, Protect
Basal cells: Stem cells that produce new neurons (receptors) throughout life. Rare!

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Smell: Olfaction
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24. Stimulation of Receptors
Genetic evidence: 100’s of primary odors exist
Binding of chemical odorants stimulates receptor
Recognition of 10,000 odors from combination of primary receptor input
Rapid adaptation by 50% in 1 second

25. Olfactory Pathway First-order neurons Second-order neurons
Olfactory receptors are neurons in nasal mucosa
Axons form olfactory nerves (Cranial nerve I)
Extend through cribriform plate into cranium to olfactory bulb
Second-order neurons
Neuron cell bodies in olfactory bulb
Olfactory tract: Axons extend from olfactory bulb to cerebral cortex (Temporal lobe)
Limbic system: Emotional response to odors

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Olfactory Receptors
Copyright 2010, John Wiley & Sons, Inc.

27. Objectives:
Special Senses
Gustation: Sense of Taste

28. Taste: Gustation
Five primary tastes: Salt, Sweet, Sour, Bitter, and Umami
Perception of what is called “Taste” includes olfactory input
Receptors in 10,000 taste buds
Located on tongue, pharynx, epiglottis
In structures called Papillae
Vallate (posterior)
Fungiform (all over)
Filiform: Touch receptors only

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Taste: Gustation
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30. Copyright 2010, John Wiley & Sons, Inc.
Taste: Gustation
Copyright 2010, John Wiley & Sons, Inc.

31. Structure of Taste Bud Contains 3 types of Epithelial cells
Supporting cells that surround
Gustatory receptor cells
Gustatory hair projects from receptor through taste pore
Basal cells
Stem cells that produce supporting cells that develop into receptor cells (10-day life span)

32. Copyright 2010, John Wiley & Sons, Inc.
Taste: Gustation
Copyright 2010, John Wiley & Sons, Inc.

33. Stimulation of Taste Receptors
Sequence of events
Tastant dissolves in saliva 
Enters taste pore  contacts gustatory hair 
Electrical signal produced 
Causes gustatory cell to release neurotransmitter
That activates dendrites of first-order neurons
Adaptation occurs within minutes
Different tastes arise from activation of different groups of taste neurons

34. Gustatory Pathway Cranial nerves transmit impulses
Facial (CN VII) from Anterior of tongue
Glossopharyngeal (CN IX) from Posterior
Vagus (CN X) from Pharynx, Epiglottis
To medulla oblongata
 Thalamus  Primary gustatory area of cerebral cortex
 Limbic system or hypothalamus

35. Objectives:
Special Senses
Vision: Sense of Sight

36. Vision: Eyes Accessory structures Eyebrows, eyelashes: Protection
Eyelids: Protection and Lubrication (blinking)
Extrinsic muscles: Move eyeball
Superior, Inferior, Lateral and Medial rectus
Superior and Inferior oblique
Lacrimal apparatus: Produces tears
Lysozyme – Bacteria killing enzyme in tears
Lacrimal glands  lacrimal ducts  surface of upper eyelid  surface of eye 
Lacrimal canals  lacrimal sac  nasolacrimal duct  nasal cavity

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Vision: Eyes
Copyright 2010, John Wiley & Sons, Inc.

38. Layers of Eyeball First layer: Fibrous tunic
Anteriorly: Cornea (clear, colorless)
Posteriorly: Sclera (“white of eye”)
Second layer: Vascular tunic consists of
Choroid: Lines most of internal surface of eye
Contains blood vessels that nourish the eye
Ciliary body consists of
Ciliary processes: Secrete aqueous humor
Ciliary muscles: Changes lens shape for focusing
Iris: Pigmented part of eye (blue, brown, green)
Smooth muscle that dilates or constricts pupil
Pupil: Hole for passage of light

39. Layers of Eyeball Third layer: Retina—composed of 2 layers
Neural layer: Outgrowth of brain
Photoreceptor layer: Rods and Cones
Bipolar cell layer
Ganglion cell layer: Axons of neurons form optic nerve (CN II) that exits eye at Optic disc (“blind spot” - no rods/cones)
Pigmented layer: Helps absorb stray light
Between choroid and neural layer

40. Pupil Response to Light
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41. Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball
Copyright 2010, John Wiley & Sons, Inc.

42. Photoreceptors: Rods and Cones
Rods: Black-and-white vision; 120 million
Cones: Color sensitive; 6 million cones
Three types: Sensitive to blue, green or red light
Color vision results from combined input
Cones mostly in Central Fovea in center of Macula Lutea
Point of highest visual acuity (sharpness)
Visual pathway
Photoreceptor cells (rods or cones) 
Bipolar layer 
Ganglion cells; their axons form Optic nerve

43. Photoreceptors: Rods and Cones
Copyright 2010, John Wiley & Sons, Inc.

44. Interior of Eyeball Two cavities separated by the lens
Anterior cavity filled with Aqueous humor
Clear, colorless fluid secreted from capillaries in ciliary body
Completely replaced every 90 min
Establishes intraocular pressure, maintains eye shape; nourishes lens and cornea
Drains into blood in scleral venous sinus (canal of Schlemm)
Vitreous chamber: Filled with gel-like vitreous body (not replaced)
Holds retina back against choroid

45. Physiology of Vision: Three Steps
Formation of image on retina
Stimulation of photoreceptors (rods and cones)
Visual pathway: Nerve impulses pass to cerebral cortex

46. A. Formation of Image on Retina: Four Steps
Refraction (bending) of light rays to focus them on retina
Accommodation: Change of lens shape to focus for near (or far) vision
Constriction (narrowing) of pupil to control amount of light entering the eye
Convergence of eyeballs: For binocular vision

47. Step 1: Refraction of Light
Definition: Bending of light rays as they pass from medium of one density to another of different density
75% occurs at cornea; Lens also helps focus light on retina
Image is inverted but brain adjusts and interprets distance and size

48. Step 1: Refraction of Light
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49. Step 1: Refraction of Light
Copyright 2010, John Wiley & Sons, Inc.

50. Step 1: Refraction of Light
Copyright 2010, John Wiley & Sons, Inc.

51. Step 2: Accommodation
Lens adjusts shape for distance to allow image to focus on retina
For distant objects, ciliary muscle relaxes  Flat lens
For closeup vision, ciliary muscle contracts  Fat lens (rounder = more convex)
Visual disorders
Myopia (nearsightedness): Can see near but not far objects
Eyeball is too long so lens cannot accommodate enough to focus images of distant objects onto retina

52. Step 2: Accommodation Visual disorders
Hyperopia (Farsightedness): Can see far but not near
Eyeball is too short so lens cannot accommodate enough to focus images of near objects onto retina
Astigmatism: irregular curvature of cornea or lens
Presbyopia: aging change  loss of elasticity of lens  farsightedness  reading glasses
These disorders can be corrected with lenses or LASIK (laser-assisted in situ keratomileusis)

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Step 2: Accommodation
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54. Steps 3 and 4: Constriction and Convergence
Constriction of pupil
Autonomic (parasympathetic) reflex to prevent excessive light rays from entering eye
By contraction of circular muscles of iris
Convergence
Eyes rotate inward for binocular vision
By contraction of extrinsic eye muscles

55. B. Stimulation of Photoreceptors
Photoreceptors: Light  neural signal
In rods light is absorbed by a photopigment (rhodopsin) which splits into opsin + retinal and leads  receptor potential
Vitamin A deficiency decreases rhodopsin production and leads to night blindness.
In cones light is absorbed by 3 opsins  receptor potential for color vision
In Colorblindness, red or green cones are missing.

56. C. Visual Pathway
Rods or cones  Bipolar cells  ganglion cells (their axons form optic nerve = CN II)
About 50% of these axons cross over to opposite side of brain in optic chiasm
Axons continue on into optic tract 
 Terminate/synapse in Thalamus 
 Occipital lobes of cerebral cortex
Right brain sees left side of object
Left brain sees right side of object

57. Physiology of Vision: Three Steps
Copyright 2010, John Wiley & Sons, Inc.

58. Visual Disease/Disorder
Conjunctivitis – Pinkeye
Cataracts – Loss of transparency of lens
Ophthalmology – Science that focuses on eyes and disorders

59. Objectives:
Special Senses
Hearing & Equilibrium

60. Hearing and Equilibrium: Ear Structure
Outer ear:
Auricle
External auditory canal
Canal contains hairs and ceruminous glands
Tympanic membrane (ear drum)
Middle ear:
Eustachian tube
Ossicles
Malleus, Incus, Stapes

61. Inner ear: Bony labyrinth + Membranous labyrinth filled with endolymph
Cochlea: Sense organ of hearing,
Vestibule and semicircular canals: Organs of balance

62. Hearing and Equilibrium: Ear Structure
Copyright 2010, John Wiley & Sons, Inc.

63. Inner Ear Structure: Three Regions
Vestibule includes
Two sacs: Utricle and Saccule
Semicircular canals: at right angles
Contain membranous semicircular ducts
Each ends in a swelling known as Ampulla
Cochlea: 3 levels
Cochlear duct: Membranous, has Endolymph
Contains Spiral organ (sensory organ for hearing)
Above: Scala Vestibuli: ends at Oval window
Below: Scala Tympani: ends at Round window

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Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.

65. Spiral Organ Sits on Basilar membrane
Floor of cochlear duct
Contains supporting cells + hair cells
Hair cells
Covered with jellylike Tectorial membrane
Receptors for Auditory sensations
Synapse with sensory neurons in cochlear branch of Vestibulocochlear nerve cranial nerve VIII)

66. Copyright 2010, John Wiley & Sons, Inc.
Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.

67. Physiology of Hearing Sound waves in air  Auditory canal
Tympanic membrane  Ossicle movement  Stapes strikes oval window
Creates pressure waves in Perilymph
Conveyed from Scala Vestibuli  Scala Tympani
Pressure waves in Endolymph cause
Hair cells bend against tectorial membrane
Neurotransmitter released to sensory neurons
Pitch (wavelength): Location in cochlea
Volume (loudness): Intensity of waves

68. Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7 8
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7 8 9
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1

69. Auditory Pathway Cochlear neurons (cranial nerve VIII) end in medulla
On same side: R ear  R side medulla
 Midbrain  Thalamus
 Auditory cortex in Temporal lobe
Each side of brain receives input from both ears
Tinnitus – ringing in the ears

70. Physiology of Equilibrium
Static equilibrium: senses position relative to gravity
As when head is tilted or a car is speeding up or slowing down
Dynamic equilibrium: senses position in response to head movement
As in spinning movements

71. Static Equilibrium Sensed in Maculae of Utricle and Saccule Mechanism
Gravity pulls on otoliths in otolithic membrane
Bends hair cells in otolithic membrane
Triggers nerve impulses in vestibular branch of Vestibulochochlear nerve (VIII)

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Static Equilibrium
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73. Copyright 2010, John Wiley & Sons, Inc.
Static Equilibrium
Copyright 2010, John Wiley & Sons, Inc.

74. Dynamic Equilibrium Semicircular canals (3)
At right angles to each other
Cristae in each ampulla contain
Hair cells embedded in jellylike cupula
Supporting cells
Mechanism
When head turns, hair cells move
Endolymph lags and bends hair cells
 Nerve impulses in Vestibular branch

75. Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium
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76. Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium
Copyright 2010, John Wiley & Sons, Inc.

77. Equilibrium Pathways Axons from vestibular branch
 Medulla or Cerebellum
Medulla  motor control: eye, head, neck
 Spinal cord tracts for adjusting muscle tone and postural muscles