Somatic and Special Senses

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Somatic and Special Senses
Chapter 12
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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

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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

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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

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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

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Touch and Pressure Senses

• Free nerve endings
• common in epithelial tissues
• detect touch and pressure

• Meissners 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

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Touch and Pressure Senses
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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)

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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

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Referred Pain

• may occur due to sensory impulses from two
  regions following a common nerve pathway to brain

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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

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Stretch Receptors
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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)

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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

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Olfactory Receptors
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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)

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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

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Taste Receptors
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Taste Sensations

• Four 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 receptors
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What does food REALLY Taste like?

• Taste is affected by
• Smell
• Temperature
• Texture
• Psychological impacts such as color

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Taste Nerve Pathways

• Sensory impulses from taste receptors travel
  along
• cranial nerves to
• medulla oblongata to
• thalamus to
• gustatory cortex (for interpretation)

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Hearing
Ear organ of hearing

• 3 Sections
• External
• Middle
• Inner

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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

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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

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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

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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

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Inner Ear

• 3 Parts of Labyrinths
• cochlea
• functions in hearing
• semicircular canals
• functions in equilibrium
• vestibule
• functions in equilibrium

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Cochlea

• Scala vestibuli
• upper compartment
• Scala tympani
• lower compartment
• Cochlear duct
• portion of membranous labyrinth in cochlea
• contains Organ of Corti

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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

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Organ of Corti
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Auditory Nerve Pathways
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Summary of the Generation of Sensory Impulses
from the Ear
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Equilibrium

• Dynamic Equilibrium
• semicircular canals
• sense rotation and movement of head and body

• Static Equilibrium
• vestibule
• sense position of head when body is not moving

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Vestibule

• Macula (sensory organ)
• hair cells of utricle and saccule sense static
  balance

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Macula

• responds to changes in head position
• bending of hairs results in generation of nerve
  impulse

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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

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Crista Ampullaris
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Sight

• Visual Accessory Organs
• eyelids
• lacrimal apparatus
• extrinsic eye muscles

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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

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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

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Extrinsic Eye Muscles

• Superior rectus
• rotates eye up and medially

• Inferior rectus
• rotates eye down and medially

• Medial rectus
• rotates eye medially

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Extrinsic Eye Muscles

• Lateral rectus
• rotates eye laterally

• Superior oblique
• rotates eye up and laterally

• Inferior oblique
• rotates eye down and laterally

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Structure of the Eye

• hollow
• spherical
• wall has 3 layers
• (outer) fibrous tunic
• (middle) vascular tunic
• (inner) nervous tunic

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Outer Tunic

• Cornea
• anterior portion
• transparent
• light transmission
• light refraction

• Sclera
• posterior portion
• opaque
• protection

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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

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Anterior Portion of Eye

• filled with aqueous humor

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Lens

• transparent
• biconvex
• lies behind iris
• largely composed of lens fibers
• elastic
• held in place by suspensory ligaments of ciliary
  body

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Accommodation

• changing of lens shape to view objects

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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

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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

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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

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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

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Rods and Cones
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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

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Stereoscopic Vision

• provides perception of distance and depth
• results from formation of two slightly different
  retinal images

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Visual Pathway
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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

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Clinical Application
Refraction Disorders

• convex lens corrects farsightedness (presbyopia
  or hyperopia) when eye is too short or lens
  focuses light behind retina

• concave lens corrects nearsightedness (myopia)
  when eye is too long or lens focuses light in
  front of retina

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