Chapter 12

Somatic 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

Pain receptors

• respond to tissue damage

Thermoreceptors

• respond to changes in temperature

Mechanoreceptors

• respond to mechanical forces

Photoreceptors

• respond to light 12-3

Sensory Impulses

• stimulation of receptor causes local change in its membrane

• a graded electrical current is generated that reflects intensity

of stimulation

• 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 actin potential

• peripheral nerves transmit impulses to CNS

Sensation

• feeling that occurs when brain interprets sensory impulse

12-4

Sensory Adaptation

• adjustment of sensory receptors from continuous

stimulation

• stronger stimulus required to activate receptors

• smell 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

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 above 25oC (77o F)

• unresponsive to temperature above 45oC (113oF)

Cold receptors

• sensitive to temperature between 10oC (50oF) and 20oC

(68oF)

Pain receptors

• respond to temperatures below 10oC

• respond to temperatures above 45oC 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

Pain Nerve Fibers

Acute pain fibers

• thin, myelinated

• conduct impulses

rapidly

• associated with

sharp pain

• well localized

Chronic pain fibers

• thin, unmyelinated

• conduct impulses more

slowly

• associated with dull,

aching pain

• difficult to pinpoint

12-12

Regulation of Pain Impulses

Thalamus

• allows person to be aware

of pain

Cerebral Cortex

• judges intensity of pain

• locates source or pain

• produces motor response to

pain

• produces emotions to pain

Pain Inhibiting Substances

• enkephalins

• serotonin

• endorphins

12-13

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

• sight in eyes

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

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 Sensations

Four Primary Taste Sensations

• sweet – stimulated by carbohydrates

• sour – stimulated by acids

• salty – stimulated by salts

• bitter – stimulated by many organic compound

Spicy foods activate pain receptors

12-22

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 • vibrate in response to tympanic

membrane

• malleus, incus, and stapes

• oval window • opening in wall of tympanic

cavity

• 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 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

• 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

• part of bony labyrinth

12-30

Cochlea

Cochlear duct

• portion of membranous

labyrinth in cochlea

Vestibular membrane

• separates cochlear duct

from scala vestibuli

Basilar membrane

• separates cochlear duct

from scala tympani

12-31

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

• Utricle

• communicates with

saccule and

membranous portion of

semicircular canals

• Saccule

• communicates with

cochlear duct

• Mucula

• hair cells of utricle and

saccule

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 that communicates

with the vestibule

• crista ampullaris

• sensory organ of ampulla

• 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

• composed of four layers • skin

• muscle

• connective tissue

• conjunctiva

• orbicularis oculi - closes

• levator palperbrae 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

• 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 down and

laterally

Inferior oblique

• rotates eye up 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


• pigmented

• controls light intensity

Ciliary body


• 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

Ciliary Body

• forms internal ring around front of eye

• ciliary processes – radiating folds

• ciliary muscles – contract and relax to move lens

12-51

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

Aqueous Humor

• fluid in anterior cavity of eye

• secreted by epithelium on inner surface of the ciliary body

• provides nutrients

• maintains shape of anterior portion of eye

• leaves cavity through canal of Schlemm

12-54

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

• fovea centralis – center of macula lutea; produces

sharpest vision

• optic disc – blind spot; contains no visual receptors

• vitreous humor – thick gel that holds retina flat against

choroid coat

12-55

Layers of Retina

• receptor cells, bipolar cells, and ganglion cells - provide

pathway for impulses triggered by photoreceptors to reach the

optic nerve

• horizontal cells and amacrine cells – modify impulses

12-56

Light Refraction

Refraction

• bending of light

• occurs when light waves pass at an oblique angle into

mediums of different densities

12-57

Types of Lenses

Convex lenses cause

light waves to converge

Concave lenses cause

light waves to diverge

12-58

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

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

• convex lens corrects

farsightedness

12-66

PowerPoint to accompany - Lone Star College...

Documents

Transcript of PowerPoint to accompany - Lone Star College...