chapter 12 the senses. 2 introduction general senses receptors are widely distributed throughout the...

Chapter 12

The Senses

Introduction

• General senses• Receptors are widely distributed throughout the body• Skin, various organs and joints• Touch, pain, temperature, pressure, ect.

• Special senses• Specialized receptors confined to structures in the head • Vision, Taste, Smell, Hearing

Receptors, Sensation, and Perception

• Sensory receptors• Specialized cells or multicellular structures that collect information from the environment

• Stimulate neurons to send impulses along sensory fibers to the brain

• Sensation• A feeling that occurs when brain becomes aware of sensory impulse

• Perception• A person’s view of the stimulus; the way the brain interprets the information

Receptor Types

• Chemoreceptors• Respond to changes in chemical concentrations (smell, taste, pH)

• Pain receptors (nociceptors)• Respond to tissue damage

• Thermoreceptors• Respond to changes in temperature

• Mechanoreceptors• Respond to mechanical forces• Stretch receptors, proprioceptors, baroreceptors

• Photoreceptors• Respond to light

• Projection• Process in which the brain projects the sensation back to the apparent source• It allows a person to pinpoint the region of stimulation

Sensations and Perception

• Ability to ignore unimportant 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)

• Sensory impulses become less frequent and may cease

• Stronger stimulus is required to trigger impulses

Sensory Adaptation

12.3: General Senses

• Senses associated with skin, muscles, joints and viscera

• Three (3) groups:• Exteroceptive senses (exteroceptors)

• Senses associated with body surface such as touch, pressure, temperature, and pain

• Visceroceptive senses (interoceptors)• Senses associated with changes in the viscera such as blood pressure stretching blood vessels and ingestion of a meal

• Proprioceptive senses• Senses associated with changes in muscles and tendons such as at joints

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; distinguish between two points on the skin

Lamellated (Pacinian) corpuscles• Common in deeper subcutaneous tissues, tendons and ligaments• Detect heavy pressure and vibrations

Touch and Pressure Receptors

Epidermis

Dermis

Section ofskin

Free nerveendings

Epithelialcells

Sensorynerve fiber

Epithelialcells

Tactile (Meissner’s) corpuscle(touch receptor)

Sensory nervefiber

Lamellated(Pacinian) corpuscle(pressure receptor)

Connective tissuecells

Sensory nervefiber

b, c: © Ed Reschke

Temperature Senses

• Warm receptors• Sensitive to temperatures above 25oC (77o F)• Unresponsive to temperature above 45oC (113oF)

• Cold receptors• Sensitive to temperatures between 10oC (50oF) and 20oC (68oF)

• Pain receptors• Respond to temperatures below 10oC• Respond to temperatures above 45oC

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

• Adapt very little, if at all

Visceral Pain

• Pain receptors are the only receptors in viscera whose stimulation produces sensations• Pain receptors respond differently to stimulation• Pain receptors are not well localized• Pain receptors may feel as if coming from some other part of the body• Known as referred pain…

Referred Pain• May occur due to sensory impulses from two regions following a common nerve pathway to brain

Appendix

Ureter

Lung and diaphragm

Stomach

Pancreas

Kidney

Urinary bladder

Liver andgallbladder

Smallintestine

Ovary(female)

Liver andgallbladder

Pain Nerve Pathways

• Acute pain fibers• A-delta fibers • Thin, myelinated• Conduct impulses rapidly• Associated with sharp pain• Well localized

• Chronic pain fibers• C fibers • Thin, unmyelinated• Conduct impulses more slowly• Associated with dull, aching pain• Difficult to pinpoint

Regulation of Pain Impulses

• Thalamus • Allows person to be aware of pain

• Cerebral cortex • Judges intensity of pain • Locates source of pain• Produces emotional and motor responses to pain

• Pain inhibiting substances:• Enkephalins• Serotonin• Endorphins

Proprioception

• Mechanoreceptors

• Send information to spinal cord and CNS about body position and length, and tension of muscles

• Main kinds of proprioceptors:• Pacinian corpuscles – in joints• Muscle spindles – in skeletal muscles*• Golgi tendon organs – in tendons*

*considered to be stretch receptors

Stretch Receptors

Muscle spindleSkeletal muscle fiber

Golgi tendon organ

Tendon

Sensorynerve fiber

Sensorynerve endings

Sensorynerve fiber

Connectivetissue sheath

Intrafusalfiber

Skeletal musclefiber

Visceral Senses

• Receptors in internal organs

• 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

Summary of Receptors of the General Senses

End of Section 1, chapter 12

section 2, chapter 12 Smell, Taste, and Hearing

• 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

Sense of Smell

• Olfactory receptors• Bipolar Chemoreceptors• Respond to chemicals (called odorants) dissolved in liquids

• Olfactory organs• Olfactory epithelium - contain olfactory receptors and supporting epithelial cells

• Cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

Olfactory Receptors

Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. The olfactory receptors pass through olfactory foramina in the cribriform plate and synapse with the olfactory bulb in the brain.

(b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae.

Olfactory Nerve Pathways

• Once olfactory receptors are stimulated, nerve impulses travel through• •Olfactory nerves olfactory bulbs olfactory tracts

limbic system (for emotions) & olfactory cortex (for interpretation)

The limbic system, which is involved with emotions and memory is strongly effected by smell.

Olfactory Stimulation

• Olfactory code• Hypothesis • Odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins

• Olfactory organs located high in the nasal cavity above the usual pathway of inhaled air• Olfactory receptors undergo sensory adaptation rapidly• Sense of smell drops by 50% within a second after stimulation

Sense of 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

Taste Receptors

Papillae

Connectivetissue

Sensorynerve fibers

Epitheliumof tongue

Supportingcell

Tastepore

Taste hair

Taste cell

Taste buds

Taste Sensations

• Four primary taste sensations• Sweet – stimulated by carbohydrates• Sour – stimulated by acids• Salty – stimulated by salts• Bitter – stimulated by many organic compounds

• Spicy foods activate pain receptors

Taste Nerve Pathways

• Sensory impulses from taste receptors travel along:• Cranial nerves to… • Medulla oblongata to…• Thalamus to… • Gustatory cortex (for interpretation)

Sense of Hearing

• Ear• Organ of hearing

• Three (3) sections:• External ear• Middle ear• Inner ear

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

Round window

PharynxAuditory tube

Auricle

Oval window (under stapes)

Cochlea

Malleus

Incus Stapes

External acousticmeatus

Semicircularcanals

Vestibulocochlearnerve

Tympanic cavity

Tympanicmembrane

Round window

Auricle

Cochlea

Malleus

Incus Stapes

Semicircularcanals

Tympanic cavity

Tympanicmembrane

• Tympanic cavity• Air-filled space intemporal bone

• Auditory ossicles• Vibrate in response to tympanic membrane• 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

Auditory Tube

• Also known as the 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

Round window

Auricle

Cochlea

Malleus

Incus Stapes

Semicircularcanals

Tympanic cavity

Tympanicmembrane

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

Cochlear nerve

Maculae

Utricle

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous labyrinth

Bony labyrinth

Vestibular nerve

Scalavestibuli (cut)

Scalatympani (cut)

Cochlearduct (cut)containingendolymph

VestibuleOvalwindow

Roundwindow

Semicircularcanals

Bony labyrinth(contains perilymph)

Membranous labyrinth(contains endolymph)

Inner Ear

• Three (3) parts of labyrinths:• Cochlea

• Functions in hearing• Semicircular canals

• Functions in equilibrium

• Vestibule• Functions in equilibrium

Cochlear nerve

Maculae

Utricle

Cochlea

Saccule

Ampullae

Endolymph

Perilymph

Membranous labyrinth

Bony labyrinth

Vestibular nerve

Scalavestibuli (cut)

Scalatympani (cut)

Cochlearduct (cut)containingendolymph

VestibuleOvalwindow

Roundwindow

Semicircularcanals

Bony labyrinth(contains perilymph)

Membranous labyrinth(contains endolymph)

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

Stapes vibrating inoval window

Scala vestibulifilled with perilymph

Vestibularmembrane

Basilarmembrane

Scala tympanifilled withperilymph

Round window

Helicotrema

Membranouslabyrinth

Cochlear ductfilled with endolymph

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

Spiral organ (organ of Corti)

Basilar membrane

Scala vestibuli(contains perilymph)Vestibular membrane

Cochlear duct(contains endolymph)

Scala tympani(contains perilymph)

Branch ofcochlearnerve

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

Spiral organ (organ of Corti)

Hair cells

Basilar membrane

Scala vestibuli(contains perilymph)

Cochlear duct(contains endolymph)

Scala tympani(contains perilymph)

Branch ofcochlearnerve

Tectorialmembrane

Basilarmembrane

Supportingcells

Nervefibers

Branch ofcochlear nerve

Vestibular membrane

Organ of Corti

Cochlear duct

Scala tympani Hair cells

Basilarmembrane

Tectorial membrane

a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited

Auditory Nerve Pathways

Midbrain

Thalamus

Auditory cortex(temporal lobe)

Medial geniculatebody of thalamus

Superiorolivarynucleus

Medullaoblongata

Cochlearnuclei

Summary of the Generation of Sensory Impulses from the Ear

Sense of Equilibrium

• Static equilibrium• Vestibule• Senses position of head when body is not moving

• Dynamic Equilibrium• Semicircular canals• Senses rotation and movement of head and body

Vestibule

• Utricle• Communicates with saccule and membranous portion of semicircular canals

• Saccule• Communicates with cochlear duct

• Macula• Hair cells of utricle and saccule

Saccule

UtricleCochlea

Maculae

Ampullae ofsemicircularcanals

Cochlearduct

Vestibule

Macula

• Responds to changes in head position• Bending of hairs results in generation of nerve impulse

Hair cells

Sensory nerve fiber Supporting cells

Otoliths

(a) Head upright (b) Head bent forward

Maculaof utricle

Hairs ofhair cells bend

Gelatinousmaterial sags

Gravitationalforce

Semicircular Canals

• Three (3) 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

Saccule

Utricle Cochlea

Maculae

Ampullae ofsemicircularcanals

Cochlearduct

Vestibule

Crista Ampullaris

Hair cell

Supporting cells

Sensory nerve fibers

Cupula Cristaampullaris

(a) Head in still position

(b) Head rotating

Crista ampullaris

Semicircular canal

Endolymph

Ampulla

End of section 2, chapter 12

section 3, chapter 12

vision

ivyanatomy.com

Sense of Sight

• Visual accessory organs• Eyelids• Lacrimal apparatus• Extrinsic eye muscles

Eyelid• Palpebra• Composed of four (4) layers:

• Skin• Muscle • Connective tissue• Conjunctiva

• Orbicularis oculi – closes eyelid• Levator palpebrae superioris – opens eyelid• Tarsal glands – secrete oil onto eyelashes• Conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball

Eyelash

Cornea

Conjunctiva

Eyelid

Tendon of levatorpalpebrae superioris

Superiorrectus

Orbicularisoculi

Inferiorrectus

Tarsal glands

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

Lacrimal gland

Lacrimal sac

Superior andinferior canaliculi

Nasolacrimalduct

Extrinsic Eye Muscles

Inferior rectus Inferior oblique

Medialrectus

Superiorrectus

Superioroblique

Lateralrectus(cut)

• Superior rectus• Rotates eye up and medially

• Inferior rectus• Rotates eye down and medially

• Medial rectus• Rotates eye medially

Extrinsic Eye Muscles

Inferior rectus Inferior oblique

Medialrectus

Superiorrectus

Superioroblique

Lateralrectus(cut)

• Lateral rectus• Rotates eye laterally

• Superior oblique• Rotates eye down and laterally

• Inferior oblique• Rotates eye up and laterally

Structure of the Eye

The eye has three distinct layers “tunics”1.Fibrous tunic 2.Vascular tunic3.Nervous tunic

Outer Tunic

• Sclera• Posterior portion• Opaque• Protection

• Cornea• Anterior 1/6th of eye• “window of the eye”• Transparent• Light transmission

Middle Tunic

• Iris “rainbow”• Anterior portion• Pigmented• Controls light intensity

• Ciliary body• Anterior portion• Pigmented• Suspensory ligaments holds lens• Ciliary muscles moves lens for focusing

• Choroid coat• Provides blood supply• Pigments absorb extra light

Anterior Portion of Eye

• Filled with aqueous humor

Lens• The lens is an elastic, biconvex, and transparent structure largely composed of epithelial cells, called lens fibers.

•The lens lies behind the iris and is held in place by suspensory ligaments of ciliary body

Accommodation

• Changing of lens shape to view objects

Lens thick

Lens thin

Ciliary musclefibers contracted

Suspensoryligaments relaxed

Ciliary musclefibers relaxed

Suspensoryligaments taut

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

Sclera

Aqueous humor

Cornea

Vitreous humor

Ciliary process

Ciliary muscles

Posteriorchamber

Ciliarybody

Scleral venous sinus(canal of Schlemm)

Anteriorchamber

Ciliary Body

• Forms internal ring around the front of the eye• Ciliary processes – radiating folds• Ciliary muscles – contract and relax to move lens

Figure 12.28 Lens and ciliary body viewed from behind.Figure 12.28 Lens and ciliary body viewed from behind.

• 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

Inner Tunic

• Retina• Contains visual receptors• Continuous with optic nerve

• Fovea centralis – center of macula lutea; produces sharpest vision

•Macula lutea – yellowish spot in retina

• Optic disc – blind spot; contains no visual receptors

• Vitreous humor – thick gel that holds retina flat against choroid coat

Posterior Cavity

• Contains vitreous humor – thick gel that holds retina flat against choroid coat

Ciliary body

Retina

Choroid coat

Sclera

Fovea centralis

Optic nerve

Cornea

Lateral rectus

Medial rectus

Optic disc

Posterior cavity

Vitreous humor

Posteriorchamber

Anteriorchamber

Aqueoushumor

Suspensoryligaments

Anteriorcavity

Layers of the Eye

Light Refraction

• Refraction • Bending of light• Occurs when light waves pass at an oblique angle into mediums of different densities

Light wave

Perpendicular line

Refractedlight wave

Types of Lenses

• Convex lenses cause light waves to converge

• Concave lenses cause light waves to diverge

(a) (b)

Diverginglight waves

Convexsurface

Lightwave

Converginglight waves

Concavesurface

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

Light waves

ObjectCornea

Retina

Major Groups of Retinal Neurons

• 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

Figure 12. Notice that photoreceptors (rods and cones) are the posterior most cells in this circuit. Light waves stimulate the photoreceptors, which send impulses forward to horizontal cells and ganglion cells before leaving the eye

through the optic disc.

• Rods• Long, thin projections• Contain light sensitive pigment called rhodopsin• Hundred times more sensitive to light than cones• Provide vision in dim light• Produce outlines of objects

• Cones• Short, blunt projections• Provide vision in bright light• Produce sharp images• Produce color vision• Pigments include:

• Erythrolabe – responds to red• Chlorolabe – responds to green• Cyanolabe – responds to blue

Visual Receptors

Color perceived depends on which sets of cones are stimulated

Figure 12.38 Rods and cones. (a) Several rods converge onto a single sensory nerve fiber to the brain (b) separate sensory nerve fibers transmits impulses from the cones to the brain. (c) Scanning electron micrograph of

rods and cones.

Figure 12.38 Rods and cones. (a) Several rods converge onto a single sensory nerve fiber to the brain (b) separate sensory nerve fibers transmits impulses from the cones to the brain. (c) Scanning electron micrograph of

rods and cones.

12.6 Clinical Application

Refraction Disorders• Concave lens corrects nearsightedness

• Convex lens corrects farsightedness

Light waves

CorneaLens

Retina

(a) Eye too long (myopia)

(b) Normal eye

(c) Eye too short (hyperopia)

Pointof focus

Light waves

Concave lens

Convex lens

Uncorrectedpoint of focus

Correctedpoint of focus

Uncorrectedpoint of focus

Correctedpoint of focus

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

Stereoscopic Vision

• Provides perception of distance and depth• Results from formation of two slightly different retinal images

Lightwaves

Right eyeLeft eye

Visual Nerve Pathways

Axons from ganglion cells in retina leave the eyes to form the optic nerves.

Some of the fibers decussate at the optic chiasm.• Fibers from the nasal (medial) half of retina cross over• Fibers from temporal half (lateral) of retina do not cross over

Most fibers of the optic tract continue to the lateral geniculate nucleus of the thalamus, which relays impulses towards the visual cortex.

Figure 12.41 The visual pathway includes the optic nerve, optic chiasma, optic tract, and optic radiations.

End of Chapter 12

chapter 12 the senses. 2 introduction general senses receptors are widely distributed throughout the...

general senses senses

ph pain receptors nociceptors

cold receptors sensitive

visceral pain pain rece

blood pressure

joints touch

brain sensation

heavy pressure

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