1. Chapter 12 Lecture Outline
See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

2. 12.1: Introduction to Sensory Function
Senses maintain homeostasis, by providing information about the outside world and the internal environment
Sensory receptors collect information from the environment, and relay it to the CNS on sensory neurons
Sensory receptors link nervous system to internal and external changes or events
Sensory receptors can be specialized cells or multicellular structures
General senses:
Receptors that are widely distributed throughout the body
Skin, various organs and joints
Special senses:
Specialized receptors confined to structures in the head
Eyes, ears, nose and mouth

3. 12.2: Receptors, Sensation, and Perception
Sensory receptors:
Respond to specific stimuli
Particularly sensitive to a certain type of environmental change, and less sensitive to other stimuli
Sensation:
A feeling that occurs when brain becomes aware of sensory information
Perception:
The way the brain interprets the sensory information

4. Receptor Types 5 types of sensory receptors in the body:
Chemoreceptors:
Respond to changes in chemical concentrations (smell, taste, oxygen concentration)
Pain receptors (nociceptors):
Respond to tissue damage (mechanical, electrical, thermal energy)
Thermoreceptors:
Respond to moderate changes in temperature
Mechanoreceptors:
Respond to mechanical forces that distort receptor (touch, tension, blood pressure, stretch)
Photoreceptors:
Respond to light (eyes)

5. Sensory Impulses
Sensory receptors can take the form of ends of neurons or cells near extensions of the neurons
Stimulation of receptor causes local change in its membrane potential, causing graded potential according to stimulus intensity
If receptor is part of a neuron, the membrane potential may generate an action potential
If receptor is not part of a neuron, the receptor potential must be transferred to a neuron to trigger an action potential
Peripheral nerves transmit impulses to CNS where they are analyzed and interpreted in the brain

6. Sensation and Perception
Sensation occurs when action potentials make the brain aware of a sensory event (such as pain)
Perception occurs when brain interprets sensory impulses (realizing that the pain is a result of stepping on a tack)
Projection:
Process in which cerebral cortex interprets sensation as being derived from certain receptors
Brain projects the sensation back to the apparent source
It allows a person to pinpoint the region of stimulation

7. Information Flow Through the Nervous System

8. Sensory Adaptation Sensory Adaptation:
Ability to ignore unimportant (or continuous) stimuli
Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation)
When sensory adaptation occurs, sensory impulses become less frequent and may cease
Stronger stimulus is then required to trigger impulses
Best accomplished by thermoreceptors and olfactory receptors

9. 12.3: General Senses General Senses:
Senses with small, widespread sensory receptors, associated with skin, muscles, joints and viscera
General Senses are divided into 3 groups:
Exteroceptive senses:
Senses associated with body surface, such as touch, pressure, temperature, and pain
Interoceptive (visceroceptive) senses:
Senses associated with changes in the viscera, such as blood pressure stretching blood vessels
Proprioceptive senses:
Senses associated with changes in muscles, tendons, and joints, as when changing position or exercising

10. Touch and Pressure Senses
3 types of mechanoreceptors provide touch and pressure senses:
Free nerve endings:
Common in epithelial tissues
Simplest receptors
Sense itching
Tactile (Meissner’s) corpuscles:
Abundant in hairless portions of skin and lips
Detect fine touch and texture
Distinguish between 2 points on skin
Lamellated (Pacinian) corpuscles:
Large oval structures
Common in deeper subcutaneous tissues, tendons and ligaments
Detect heavy pressure and vibrations

11. Touch and Pressure Receptors

12. Temperature Senses Temperature receptors (thermoreceptors):
Free nerve endings in skin; 2 types:
Warm receptors:
Sensitive to temperatures above 25°C (77°F)
Unresponsive to temperature above 45°C (113°F)
Cold receptors:
Sensitive to temperatures between 10°C (50°F) and 20°C (68°F)
Pain receptors:
Respond to temperatures below 10°C; produce freezing sensation
Respond to temperatures above 45°C; produce burning sensation

13. Sense of Pain Pain receptors/nociceptors consist of free nerve endings
Widely distributed
Nervous tissue of brain lacks pain receptors
Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature
Adapt very little, if at all

14. Visceral Pain
Pain receptors are the only receptors in viscera whose stimulation produces sensations
Pain receptors in viscera respond differently to stimulation than those of surface tissues
Visceral pain may feel as if coming from some other part of the body; this is called referred pain
Example of referred pain: Heart pain often feels like it is coming from the left shoulder or medial portion of left arm
Referred pain results from common nerve pathways, in which sensory impulses from the visceral organ and a certain area of the skin synapse with the same neuron in the CNS

15. Referred Pain
Referred pain may occur due to sensory impulses from two regions following a common nerve pathway to brain:

16. Referred Pain

17. Pain Pathways
2 types of axons/fibers that conduct impulses away from pain receptors:
Fast pain (A-delta) fibers:
Myelinated
Conduct impulses rapidly (up to 30 m/sec)
Associated with sharp (acute) pain in localized skin area
Usually stops as soon as stimulus stops
Slow pain (C) fibers:
Unmyelinated
Conduct impulses slowly (up to 2 m/sec)
Associated with dull, aching (chronic) pain
Difficult to localize
Pain often continues after stimulus stops
In the brain, most pain fibers synapse in reticular formation, and proceed to the thalamus, hypothalamus, and cerebral cortex

18. Regulation of Pain Pathways
Thalamus:
Begins sensation of pain
Cerebral cortex:
Judges intensity of pain
Locates source of pain
Produces emotional and motor responses to pain
Gray matter in brainstem:
Regulates flow of impulses from spinal cord
Pain-inhibiting substances produced in the body:
Enkephalins
Serotonin
Endorphins

19. Clinical Application 12.1 Treating Pain
About 25% of people have moderate or severe pain. Treatments for pain:
Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen: can cause GI irritation
Opiates: can be addicting
Acetaminophen: non-addicting, no GI irritation, but can damage liver
Reformulation efforts are producing smaller particles, that dissolve faster and relieve pain faster
Chronic pain treatments:
NSAIDs, exercises, injection of anesthetics into cramping muscles, antidepressants, transcutaneous electrical nerve stimulation (TENS), invasive nerve block

20. Proprioception Proprioceptors:
Mechanoreceptors that send information to CNS about body position, and length and tension of skeletal muscles
Main types of proprioceptors:
Lamellated (Pacinian) corpuscles:
Pressure receptors in joints
Muscle spindles:
Stretch receptors in skeletal muscles
Initiate stretch reflexes, in which spindle stretch causes muscle contraction
Golgi tendon organs:
Stretch receptors in tendons
Stimulate reflexes that oppose stretch reflexes
Help maintain posture, protect tearing of muscles away from insertions

21. Stretch Receptors

22. Visceral Senses Visceral senses have receptors in internal organs
Examples of visceral receptors: lamellated corpuscles, free nerve endings
Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack

23. Receptors Associated with General Senses

24. 12.4: Special Senses Special Senses:
Senses that have sensory receptors are within large, complex sensory
organs in the head:
Smell: olfactory organs in nasal cavity
Taste: taste buds in oral cavity
Hearing and equilibrium: inner ears
Sight: eyes

25. Mixed-Up Senses--Synesthesia
Clinical Application 12.2
Mixed-Up Senses--Synesthesia
Synesthesia (joined sensation):
Condition in which brain interprets a stimulus for one sense as coming from another
Example: “The paint smelled blue”
1 in 1,000 people have this condition, and it lasts a lifetime
Common in creative people
Caused by genetic mutation; 4 genes have been identified
Most common form is grapheme-color type synesthesia:
Letters, numbers or time evoke certain colors
Lexical-gustatory synesthesia:
A name evokes perception of strong taste or smell

26. Sense of Smell Olfaction: the sense of smell Olfactory receptors:
Olfactory receptor cells are chemoreceptors
Respond to chemicals dissolved in liquids
Sense of smell provides 75-80% of sense of taste
Olfactory organs:
Contain olfactory receptor cells (bipolar neurons) and supporting epithelial cells
Cover upper parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum
Odorants may bind to any of almost 400 types of olfactory membrane receptors, resulting in depolarization and action potentials

27. Olfactory Receptors

28. Olfactory Pathways
Once olfactory receptors are stimulated, nerve impulses travel through openings in cribriform plates of ethmoid bone
Olfactory nerves → olfactory bulbs → olfactory tracts → limbic system (for emotions) and olfactory cortex (for interpretation)
Olfactory bulbs analyze sensory impulses
Limbic system, center for memory and emotion, provides emotional responses to certain odorant molecules

29. Olfactory Stimulation
Leading hypothesis for encoding specific smells:
Each olfactory receptor cell contains only 1 type of membrane protein
Each type of membrane protein can bind several types of odorants
Brain interprets binding as an olfactory code
Olfactory organs located high in the nasal cavity, above the pathway of inhaled air
Olfactory receptors undergo sensory adaptation rapidly
Sense of smell drops by 50% within 1 second after stimulation
Olfactory receptor neurons are the only ones in direct contact with environment, and can be damaged
Receptors are replaced regularly (very unusual for neurons to be replaced in the human adult)

30. Gustation: Sense of Taste
Gustation is the sense of taste.
Taste buds:
Organs of taste
Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx
About 10,000 taste buds, each with taste cells
Taste receptors:
Chemoreceptors
Taste cells: modified epithelial cells that function as receptors
Taste hairs: microvilli that protrude from taste cells through pores of taste buds; sensitive parts of taste cells
Taste cells are replaced every 3 days

31. Taste Receptors

32. Taste Sensations 5 primary taste sensations:
Sweet: stimulated by carbohydrates
Sour: stimulated by acids (H+)
Salty: stimulated by salts (N a+ or K+)
Bitter: stimulated by many organic compounds, Mg and C a salts
Umami: stimulated by some amino acids, MSG
Each flavor results from 1 primary taste sensation or a combination
Spicy foods activate pain receptors
Taste receptors undergo rapid adaptation

33. Taste Pathways
Sensory impulses from taste receptor cells travel on fibers of 3 different cranial nerves, according to the location of the taste cells:
Facial nerve (VII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Cranial nerves conduct impulses into medulla oblongata
Impulses then proceed to the thalamus
Impulses are interpreted in the gustatory cortex in the insula

34. Smell and Taste Disorders
Clinical Application 12.3
Smell and Taste Disorders
Disorders of smell and taste can be caused by colds, flu, allergies, nasal polyps, swollen mucous membranes in the nose, head injury, toxic chemical exposure, nutritional or metabolic problem, a disease
Often, cause cannot be identified
Drugs and medications can also alter smell or taste

35. Sense of Hearing Ear: Organ of hearing 3 sections of the ear:
Outer/external ear
Middle ear
Inner/internal ear

36. Outer (External) Ear Parts of the Outer Ear: Auricle (Pinna):
Funnel-shaped
Collects sounds waves
External acoustic meatus:
S-shaped tube
Lined with ceruminous glands
Carries sound to tympanic membrane
Terminates at tympanic membrane
Tympanic membrane (Eardrum):
Vibrates in response to sound waves

37. Middle Ear Parts of the Middle Ear: Tympanic cavity:
Air-filled space in temporal bone
Auditory ossicles:
3 tiny bones
Vibrate in response to tympanic membrane vibrations; amplify force
Malleus, incus and stapes
Hammer, anvil and stirrup
Oval window:
Opening in wall of tympanic cavity
Stapes vibrates against it to move fluids in inner ear

38. Middle Ear: Tympanic Reflex
Muscle contractions that occur during loud sounds, to lessen the transfer of sound vibrations to inner ear, and prevent damage to hearing receptors
Muscles involved are tensor tympani and stapedius

39. Middle Ear: Auditory Tube
Auditory (eustachian) tube:
Connects middle ear to throat
Helps maintain equal pressure on both sides of tympanic membrane
Usually closed by valve-like flaps in throat

40. Inner (Internal) Ear Inner ear is a complex system of labyrinths:
Osseous (bony) labyrinth:
Bony canal in temporal bone
Filled with perilymph fluid
Membranous labyrinth:
Tube within osseous labyrinth
Filled with endolymph fluid

41. Inner Ear 3 parts of labyrinths: Cochlea: Functions in hearing
Semicircular canals:
Function in dynamic equilibrium
Vestibule:
Functions in static equilibrium

42. Cochlea Cochlea: Spiral, snail-shaped tube
Coiled around bony core, the modiolus
Spiral lamina is a bony shelf that coils around the cochlea

43. Windows of the Inner Ear
There are 2 membrane-covered “windows” in the wall of the bony labyrinth:
Oval window:
Opening in the wall of the tympanic cavity, through which the stapes transfers vibrations to the fluid of the inner ear; these vibrations stimulate hearing receptors
Round window:
Window in the wall of the inner ear facing the tympanic cavity, through which excess vibrations dissipate into the tympanic cavity

44. Cochlea The cochlea contains 3 compartments: Scala vestibuli:
Upper compartment
Leads from oval window to apex of spiral
Part of bony labyrinth
Scala tympani:
Lower compartment
Extends from apex of the cochlea to round window
Cochlear duct:
Middle compartment
Portion of membranous labyrinth in cochlea

45. Cochlea The cochlea contains these membranes: Vestibular membrane:
Separates scala vestibuli from cochlear duct
Basilar membrane:
Separates cochlear duct from scala tympani
Tectorial membrane:
Extends partially into cochlear duct; part of the hearing receptor organ, the Spiral Organ

46. Getting a Cochlear Implant
Clinical Application 12.4
Getting a Cochlear Implant
Hearing aids amplify sound, but cochlear implants directly stimulate auditory nerve
Enables a person to hear certain sounds
Best time is before age 3, as brain is rapidly processing speech and hearing

47. Spiral Organ (Organ of Corti)
Organ for sense of hearing
Sits on upper surface of basilar membrane
Contains hearing receptor cells, called hair cells
Hair cells contain stereovilli (or stereocilia)
Tectorial membrane passes like a roof over the hair cell stereovilli
Sound vibrations cause stereocilia to contact and bend against the tectorial membrane
Different frequencies of vibration move different parts of basilar membrane
Nerve impulses are generated

48. Spiral Organ (Organ of Corti)
Sound reception occurs as the basilar membrane vibrates, vibrating the hair cells of the spiral organ, and putting them in contact with the tectorial membrane.

49. Spiral Organ (Organ of Corti)
This is a “straightened out” view of the cochlea. Receptor cells in different regions of the cochlear duct detect different frequencies of vibration (cycles/sec or cps).

50. Auditory Pathways Cochlear branch of vestibulocochlear nerve ↓
Medulla oblongata
Midbrain
Thalamus
Auditory cortex in temporal lobe of cerebrum

51. Clinical Application 12.5 Hearing Loss
About 8% of people have some decree of hearing loss
2 major types of hearing loss: Conductive and Sensorineural
Conductive Deafness:
Interference with conduction of sound vibrations to inner ear
95% of cases of hearing loss
Caused by accumulation of ear wax, hardening or injury of tympanic membrane, injury to auditory ossicles, otosclerosis
Diagnostic tests: Rinne test and Weber test
Sensorineural Deafness:
Damage to cochlea, auditory (vestibulocochlear) nerve, or nerve pathways
Can be caused by long-term exposure to very loud sounds, such as factory noise, loud music, explosions
Also caused by CNS tumors, brain damage resulting from a stroke, use of certain drugs

52. Steps in Generation of Sensory Impulses from the Ear

53. Sense of Equilibrium
Feeling of equilibrium/balance is derived from 2 senses:
Static equilibrium:
Senses position of head when body is not moving
Receptors are found in vestibule of inner ear
Dynamic Equilibrium:
Senses rotation and movement of head and body
Receptors are found in semicircular canals

54. Static Equilibrium
Utricle and saccule are expanded chambers of the membranous labyrinth of the vestibule
Each contains a Macula, an organ of static equilibrium
A macula is a patch of hair cells and supporting cells

55. Static Equilibrium
A macula has hair cells embedded in gelatinous material, with otoliths (calcium carbonate crystals) on its surface
Gravity pulls on gelatinous mass when head changes position
Otoliths shift position, and pull on gelatinous mass and cilia of hair cells
Bending of hairs results in generation of nerve impulses in vestibular branch of the vestibulocochlear nerve

56. Dynamic Equilibrium
Receptors for dynamic equilibrium are found in 3 semicircular canals
3 canals sit at right angles to each other
Each canal contains an ampulla: a swelling of the membranous labyrinth that communicates with the vestibule
Crista ampullaris:
Sensory organ for dynamic equilibrium
Hair cells and supporting cells
Located in ampulla of each semicircular canal
Consists of hair cells whose hairs extend upward into dome-shaped gelatinous mass (cupula)
Rotation of head or body bends cupula, stimulates hair cells
Nerve impulses are sent over vestibular branch of vestibulocochlear n.

57. Dynamic Equilibrium: Crista Ampullaris

58. Sense of Sight Visual receptors are found in the eye
Accessory organs for sense of sight:
Eyelids (palpebrae, protection)
Eyelashes (protection)
Lacrimal apparatus (tear production)
Extrinsic eye muscles (eye movement)

59. Visual Accessory Organs: Eyelids
Eyelids = Palpebrae
Composed of 4 layers:
Skin
Muscle
Connective tissue
Conjunctiva
Orbicularis oculi muscle closes eyelid
Levator palpebrae superioris muscle opens eyelid
Tarsal glands secrete oil onto eyelashes
Conjunctiva: mucous membrane; lines eyelid and covers portion of eyeball

60. Visual Accessory Organs: Lacrimal Apparatus
Lacrimal gland:
In orbit, lateral to eye
Secretes tears
Canaliculi:
2 ducts that collect tears
Lacrimal sac:
Collects tears from canaliculi
Lies in groove in lacrimal bone
Nasolacrimal duct:
Collects from lacrimal sac
Empties tears into nasal cavity
Lysozyme:
Antibacterial component of tears

61. Visual Accessory Organs: Extrinsic Eye Muscles
Superior rectus:
Rotates eye up and medially
Inferior rectus:
Rotates eye down and medially
Medial rectus:
Rotates eye medially
Lateral rectus:
Rotates eye laterally
Superior oblique:
Rotates eye down and laterally
Inferior oblique:
Rotates eye up and laterally

62. Structure of the Eye Hollow, spherical organ of sight
Wall has 3 layers:
Outer (fibrous) tunic
Middle (vascular) tunic
Inner (nervous) tunic

63. The Outer (Fibrous) Tunic
Cornea + Sclera
Cornea:
Anterior sixth
Transparent
Helps focus light rays
Transmits and refracts light
Sclera:
Posterior five sixths
White, opaque
Protects eye, attaches muscles
Pierced by optic nerve and blood vessels

64. Middle (Vascular) Tunic
Middle (vascular) tunic: Choroid coat + Ciliary body + Iris
Choroid coat:
Posterior five-sixths
Provides blood supply
Contains melanocytes
Melanin absorbs extra light
Ciliary body:
Anterior portion
Thickest portion, pigmented
Forms ring to hold lens
Changes lens shape for focusing
Iris:
Anterior to ciliary body
In front of lens
Pigmented
Controls light entering eye

65. Anterior Portion of the Eye
Anterior cavity of eye, between cornea and lens, is filled with a watery fluid, aqueous humor
Lens: Transparent, biconvex, lies behind iris, elastic, held in place by suspensory ligaments of ciliary body; helps focus light rays, and changes shape for long-distance or close vision

66. Ciliary Body and Lens
Ciliary body forms internal ring around the front of the eye
Ciliary processes are the radiating folds
Ciliary muscles contract and relax to move lens
Suspensory ligaments hold lens in position
Lens lies just behind iris and pupil

67. Accommodation Accommodation:
A change in the shape of the lens, to view close objects
Lens thickens and becomes more convex when focusing on close object
Lens thins and becomes flatter when focusing on distant objects

68. Iris Iris controls amount of light entering the eye
Iris consists of connective tissue and smooth muscle (colored portion of eye)
Pupil is window or opening in center of iris
Dim light stimulates radial muscles and pupil dilates
Bright light stimulates circular muscles and pupil constricts
Amount and distribution of melanin determines eye color

69. Aqueous Humor Aqueous Humor: Fluid in anterior cavity of eye
Secreted by epithelium on inner surface of the ciliary body
Provides nutrients and maintains shape of anterior portion of eye
Leaves cavity through scleral venous sinus

70. Inner (Nervous) Tunic Inner tunic consists of retina
Retina contains visual receptors (photoreceptors)
Continuous with optic nerve in back of eye
Ends just behind margin of the ciliary body toward front of eye
Composed of several layers
Macula lutea: yellowish spot in retina
Fovea centralis: center of macula lutea; produces sharpest vision
Optic disc: blind spot; contains no visual receptors; found where nerve fibers from retina leave eye to become optic nerve
Vitreous humor: thick gel that holds retina flat against choroid coat

71. Posterior Cavity
Posterior cavity: space enclosed by lens, ciliary body, and retina
Contains vitreous humor: thick gel that supports internal structures and maintains shape of eye

72. Major Groups of Retinal Neurons
Photoreceptor cells, bipolar cells, and ganglion cells: provide pathway for impulses triggered by photoreceptors to reach the optic nerve
Horizontal cells and amacrine cells: modify, integrate impulses

73. Summary: Layers of the Eye

74. Light Refraction Refraction:
Bending of light, which occurs when light waves pass at an angle between mediums of different densities

75. Types of Lenses Convex lenses cause light waves to converge
Concave lenses cause light waves to diverge

76. Focusing on the Retina As light enters eye, it is refracted by:
Convex surface of cornea
Convex surface of lens
Image focused on retina is upside down and reversed from left to right
Visual cortex corrects the reversals

77. Clinical Application 12.6 Refraction Disorders
Concave lens corrects nearsightedness
Convex lens corrects farsightedness

78. Photoreceptors
Photoreceptors are modified neurons of retina that sense light:
Rods:
Long, thin projections
Contain light sensitive pigment, called rhodopsin
Hundreds of times more sensitive to light than cones
Provide vision in dim light
Produce colorless vision
Produce outlines of objects
Cones:
Short, blunt projections
Contain light sensitive pigments, called erythrolabe, chlorolabe, and cyanolabe
Provide vision in bright light
Produce sharp images
Produce color vision
Fovea centralis contains only cones

79. Rods and Cones
Rods and cones are named for shape of receptive ends: rods are cylindrical and cones are conical

80. Visual Pigments
Rods and cones contain light-sensitive pigments that decompose upon absorption of light:
Rhodopsin (Visual purple):
Light-sensitive pigment in rods
In presence of light, decomposes into Opsin and Retinal
Triggers a complex series of reactions that initiates nerve impulses
Impulses travel along optic nerve
Iodopsins (pigments in cones):
Each type of cone contains different light-sensitive pigment
Each type of cone is sensitive to different wavelengths
Color perceived depends on which types of cones are stimulated
Erythrolabe: responds to red light
Chlorolabe: responds to green light
Cyanolabe: responds to blue light

81. Rhodopsin in a Rod
Rhodopsin is embedded in the many discs of membrane at the end of the rod.

82. Stereoscopic Vision
Provides perception of distance, depth, height and width of objects
Results from formation of two slightly different retinal images from eyes

83. Visual Pathways
The visual pathway proceeds from the ganglion cells of the retina to the optic nerve, optic chiasma, optic tracts, the thalamus, optic radiations, and visual cortex in occipital lobe of cerebrum.
A few fibers branch off before reaching the thalamus, and enter nuclei for visual reflexes

84. 12.5: Life-Span Changes Age-related hearing loss due to:
Damage to hair cells in spiral organ
Degeneration of nerve pathways to the brain
Tinnitus
Age-related visual problems include:
Dry eyes
Floaters (crystals in vitreous humor)
Loss of elasticity of lens, decreasing accommodation (presbyopia)
Glaucoma
Cataracts
Macular degeneration
Age-related smell and taste problems due to:
Loss of olfactory receptors (anosmia)