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Chapter
12
12-1
Somatic and Special Senses
Chapter 12Somatic and Special Senses
Sensory Receptors• specialized cells or multicellular structures that collect information• stimulate neurons to send impulses along sensory fibers to the brain
12-2
Receptor Types
Chemoreceptors• respond to changes in chemical concentrations
Nociceptors (Pain receptors)• respond to tissue damage
Thermoreceptors• respond to changes in temperature
Mechanoreceptors• respond to mechanical forces
Photoreceptors• respond to light 12-3
Sensation and Adaptation
Sensation feeling that occurs when brain interprets sensory impulse
Sensory Adaptation•adjustment of sensory receptors from continuous stimulation• stronger stimulus required to activate receptors• smell and temperature receptors undergo sensory adaptation
12-1
Somatic Senses
• senses associated with skin, muscles, joints, and viscera
• three groups• exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain• proprioceptive senses – senses associated with changes in muscles and tendons• visceroceptive senses – senses associated with changes in viscera
12-6
Touch and Pressure Senses
Free nerve endings• common in epithelial tissues• detect touch and pressure
Meissner’s corpuscles• abundant in hairless portions of skin• detect light touch• detect motion on skin• detect texture
Pacinian corpuscles• common in deeper subcutaneous tissues, tendons, and ligaments• detect heavy pressure
12-7
Touch and Pressure Senses
12-8
Temperature Senses
Warm receptors• sensitive to temperatures between 25oC (77o F) and 45oC (113oF)
Cold receptors• sensitive to temperature between 10oC (50oF) and 20oC (68oF)
•In between – brain interprets impulses from both•Pain receptors
• respond to temperatures below 10oC (50 F)• respond to temperatures above 45oC (113 F)
12-9
Sense of Pain
• free nerve endings • widely distributed • nervous tissue of brain lacks pain receptors• stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature• do not adapt
Visceral Pain• may exhibit referred pain• not well localized
12-10
Referred Pain
• may occur due to sensory impulses from two regions following a common nerve pathway to brain
12-11
Stretch Receptors
• proprioceptors• send information to CNS concerning lengths and tensions of muscles• 2 main kinds of stretch receptors
• muscle spindles – in skeletal muscles• Golgi tendon organs – in tendons
12-14
Stretch Receptors
12-15
Special Senses
• sensory receptors are within large, complex sensory organs in the head• smell in olfactory organs• taste in taste buds• hearing and equilibrium in ears (hair cells)• sight in eyes (rods and cones)
12-16
Smell
Olfactory Receptors• chemoreceptors• respond to chemicals dissolved in liquids
Olfactory Organs• contain olfactory receptors and supporting epithelial cells• cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum • small patch of tissue (12 million cells) on the roof of nasal cavity• smells start as a gas, but must be dissolved in watery fluid that surrounds the cilia of the receptors (each receptor has 10-12) to be detected 12-17
Olfactory Receptors
12-18
Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses travel through
• olfactory nerves to • olfactory bulbs to • olfactory tracts to • limbic system (for emotions) and olfactory cortex (for interpretation)
12-19
Taste
Taste Buds• organs of taste• located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx
Taste Receptors• chemoreceptors• taste cells – modified epithelial cells that function as receptors• taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells
12-20
Taste Receptors
12-21
Taste SensationsFour Primary Taste Sensations (or are there five?)
• sweet – stimulated by carbohydrates• most plentiful near tip
• sour – stimulated by acids• most plentiful at margins
• salty – stimulated by salts• most plentiful at tip and upper front
• bitter – stimulated by many organic compound• most plentiful at back• may be protective – spit out
• umami (?)– stimulated by amino acids (meat, cheese)
Spicy foods activate pain receptors12-22
What does food REALLY Taste like?
Taste is affected by:
• Smell
• Temperature
• Texture
• Psychological impacts such as color
Taste Nerve Pathways
Sensory impulses from taste receptors travel along• cranial nerves to • medulla oblongata to• thalamus to • gustatory cortex (for interpretation)
12-23
Hearing
Ear – organ of hearing
3 Sections• External• Middle• Inner
12-24
External Ear
• auricle• collects sounds waves
• external auditory meatus• lined with ceruminous glands• carries sound to tympanic membrane• terminates with tympanic membrane
• tympanic membrane • vibrates in response to sound waves
12-25
Middle Ear
• tympanic cavity• air-filled space in temporal bone• auditory ossicles (bones)
• vibrate in response to tympanic membrane• malleus, incus, and stapes
• oval window • opening in wall of tympanic cavity (cochlea)• stapes vibrates against it to move fluids in inner ear
12-26
Auditory Tube
• 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
12-27
Inner Ear
• complex system of labyrinths• osseous (bony) labyrinth
• bony canal in temporal bone• filled with perilymph
• membranous labyrinth• tube within osseous labyrinth• filled with endolymph
12-28
Inner Ear
3 Parts of Labyrinths• cochlea
• functions in hearing• semicircular canals
• functions in equilibrium
• vestibule• functions in equilibrium
12-29
Cochlea
Scala vestibuli• upper compartment
Scala tympani• lower compartment
Cochlear duct **• portion of membranous labyrinth in cochlea
• contains Organ of Corti
12-30
Organ of Corti
• group of hearing receptor cells (hair cells)• on upper surface of basilar membrane• different frequencies of vibration move different parts of basilar membrane• particular sound frequencies cause hairs of receptor cells to bend• nerve impulse generated
12-32
Organ of Corti
12-33
Auditory Nerve Pathways
12-34
Summary of the Generation of Sensory Impulses from the Ear
12-35
Equilibrium
Static Equilibrium• vestibule• sense position of head when body is not moving
Dynamic Equilibrium• semicircular canals• sense rotation and movement of head and body
12-36
Vestibule
• Macula **(sensory organ)• hair cells of utricle and saccule sense static balance
12-37
Macula
• responds to changes in head position• bending of hairs results in generation of nerve impulse
12-38
Semicircular Canals
• three canals at right angles• ampulla
• swelling of membranous labyrinth
• crista ampullaris (in ampulla)• sensory organ of dynamic balance• hair cells and supporting cells• rapid turns of head or body stimulate hair cells
12-39
Crista Ampullaris
12-40
Sight
Visual Accessory Organs• eyelids• lacrimal apparatus• extrinsic eye muscles
12-41
Eyelid
•palpebra (eyelid)•composed of four layers
• skin• muscle • connective tissue• conjunctiva
• orbicularis oculi - closes• levator palpebrae superioris – opens• tarsal glands – secrete oil onto eyelashes• conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball
12-42
Lacrimal Apparatus
• lacrimal gland• lateral to eye• secretes tears
• canaliculi (superior, inferior)• collect tears
• lacrimal sac• collects from canaliculi
• nasolacrimal duct• collects from lacrimal sac• empties tears into nasal cavity
12-43
Extrinsic Eye Muscles
Superior rectus• rotates eye up and medially
Inferior rectus• rotates eye down and medially
Medial rectus• rotates eye medially
12-44
Extrinsic Eye Muscles
Lateral rectus• rotates eye laterally
Superior oblique• rotates eye up and laterally
Inferior oblique• rotates eye down and laterally
12-45
Structure of the Eye
• hollow• spherical• wall has 3 layers
• (outer) fibrous tunic• (middle) vascular tunic• (inner) nervous tunic
12-46
Outer Tunic
Cornea• anterior portion• transparent• light transmission• light refraction
Sclera• posterior portion• opaque• protection
12-47
Middle Tunic
Iris • anterior portion• pigmented• controls light intensity
Ciliary body (muscle)• anterior portion• pigmented• holds lens• moves lens for focusing
Choroid coat• provides blood supply• pigments absorb extra light
12-48
Anterior Portion of Eye
• filled with aqueous humor
12-49
Lens
• transparent• biconvex• lies behind iris• largely composed of lens fibers• elastic• held in place by suspensory ligaments of ciliary body
12-50
Accommodation• changing of lens shape to view objects
12-52
Iris
• composed of connective tissue and smooth muscle• pupil is hole in iris• dim light stimulates radial muscles and pupil dilates• bright light stimulates circular muscles and pupil constricts
12-53
Inner Tunic
• retina• contains visual receptors• continuous with optic nerve• ends just behind margin of the ciliary body• composed of several layers• macula lutea – yellowish spot in retina , center, 1 mm• fovea centralis – center of macula lutea; produces sharpest vision, where lens tries to focus light**• optic disc – blind spot; contains no visual receptors• vitreous humor – thick gel that holds retina flat against choroid coat
12-55
Focusing On 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
12-59
Visual Receptors
Rods• long, thin projections• contain light sensitive pigment called rhodopsin• hundred 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
12-60
Rods and Cones
12-61
Visual Pigments
Rhodopsin• light-sensitive pigment in rods• decomposes in presence of light• triggers a complex series of reactions that initiate nerve impulses• impulses travel along optic nerve
Pigments on Cones• each set contains different light-sensitive pigment• each set is sensitive to different wavelengths• color perceived depends on which sets of cones are stimulated• erythrolabe – responds to red• chlorolabe – responds to green• cyanolabe – responds to blue
12-62
Stereoscopic Vision• provides perception of distance and depth• results from formation of two slightly different retinal images
12-63
Visual Pathway
12-64
Life-Span Changes
Age related hearing loss due to • damage of hair cells in organ of Corti• 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• glaucoma• cataracts• macular degeneration 12-65
Clinical Application
Refraction Disorders• concave lens corrects nearsightedness (myopia) when eye is too long or lens focuses light in front of retina
• convex lens corrects farsightedness (presbyopia or hyperopia) when eye is too short or lens focuses light behind retina
12-66