The General and Special Senses The General and Special Senses.

The General and

Special Senses

The General and

Special Senses

The General Senses

Sensory Basics•Sensory receptors—Specialized

cells or cell processes that monitor external or internal conditions. Simplest are free nerve endings.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The General Senses

More Sensory Basics•Receptive field—The area monitored

by a single receptor cell

•Adaptation—Reduction in sensitivity at a receptor or along a sensory pathway in the presence of a constant stimulus.


The General Senses

General versus Special Senses•General senses—Temperature, pain,

touch, pressure, vibration, and proprioception. Receptors throughout the body

•Special senses—Smell, taste, vision, balance, and hearing. Receptors located in sense organs (e.g., ear, eye).


The General Senses Receptors and Receptive Fields

Figure 9-1

Key Note

Stimulation of a receptor produces action potentials that propagate along the axon of a sensory neuron. The frequency or pattern of action potentials contains information about the stimulus. A person’s perception of the nature of that stimulus depends on the path it takes inside the CNS.


The General Senses

The General Senses

Pain Definitions•Nociceptors—Receptors for tissue damage

to lead to the sensation of pain•Referred pain—Perception of pain in a part

of the body not actually stimulated•Fast (prickling) pain—Localized pain carried

quickly to the CNS on myelinated axons•Slow (burning) pain—Generalized pain

carried on slow unmyelinated axons


The General Senses

Referred Pain

Figure 9-2

The General Senses

Temperature•Thermoreceptors detect temperature

change• Free nerve endings• Found in dermis, skeletal muscle, liver,

hypothalamus• Fast adapting• Cold receptors greatly outnumber warm

receptors


The General Senses

Touch, Pressure, and Position•Mechanoreceptors—Receptors that respond

to physical distortion of their cell membranes.• Tactile receptors—Sense touch, pressure, or

vibration• Baroreceptors—Sense pressure changes in

walls of blood vessels, digestive organs, bladder, lungs

• Proprioceptors—Respond to positions of joints and muscle


The General Senses

Tactile Receptors•Fine touch or pressure receptors

• Highly detailed information about a stimulus

•Crude touch or pressure receptors• Poorly localized information about a

stimulus• Important types: root hair plexus, tactile

disks, tactile corpuscles, lamellated corpuscles, Ruffini corpuscles


The General Senses

Tactile Receptors in the Skin

Figure 9-3

The General Senses

Baroreceptors•Provide pressure information essential

for autonomic regulation• Arterial blood pressure• Lung inflation• Digestive coordination• Bladder fullness


The General Senses Baroreceptors and the Regulation of

Autonomic Functions

Figure 9-4

The General Senses

Proprioceptors•Monitor joint angle, tension in

tendons and ligaments, state of muscular contraction

• Include:• Muscle spindles• Golgi tendon organs


The General Senses

Chemical Detection•Chemoreceptors respond to chemicals

dissolved in body fluids that surround them and monitor the chemical composition of blood and tissues

•Chemicals that can be sensed include:• Carbon dioxide• Oxygen• Hydrogen ion


The General Senses

Locations and Functions of Chemoreceptors

Figure 9-5

The Special Senses—Smell

Olfactory Organs•Olfactory epithelium

• Olfactory receptor cells•Neurons sensitive to odorants

• Supporting cells• Basal (stem) cells

•Olfactory glands• Mucus-secreting cells



Figure 9-6(a)

The Olfactory Organs


The Olfactory Organs

Figure 9-6(b)


The Olfactory Pathways•Axons from olfactory receptors

penetrate cribriform plate of ethmoid bone

•Synapse in olfactory bulb•Olfactory tract projects to:

• Olfactory cerebral cortex• Hypothalamus• Limbic System


The Special Senses—Taste

Taste (Gustatory) Receptors•Taste buds

• Found within papillae on tongue, pharynx, larynx

• Contain gustatory cells, supportive cells

• Taste hairs (cilia) extend into taste pores

• Sense salt, sweet, sour, bitter•Also sense umami, water

• Synapse in medulla oblongata


The Special Senses—TasteGustatory Receptors

Figure 9-7(a)

The Special Senses—Taste

Figure 9-7(b)

Gustatory Receptors

The Special Senses—TasteGustatory Receptors

Figure 9-7(c)

The Special Senses

Key Note

Olfactory information is routed directly to the cerebrum, and olfactory stimuli have powerful effects on mood and behavior. Gustatory sensations are strongest and clearest when integrated with olfactory sensations.


The Special Senses—Vision

Accessory Structures of the Eye•Eyelids (palpebra) and glands•Superficial epithelium of eye

• Conjunctiva

•Lacrimal apparatus• Tear production and removal

•Extrinsic eye muscles



The Lacrimal Apparatus•Lacrimal gland produce tears

• Bathe conjunctiva• Contain lysozyme to attack bacteria• Tears drain into nasal cavity

•Pass through lacrimal canals, lacrimal sac, nasolacrimal duct



Figure 9-8(a)

The Accessory Structures of the Eye


The Accessory Structures of the Eye

Figure 9-8(b)


Extrinsic Eye Muscles•Move the eye•Six muscles cooperate to

control gaze• Superior and inferior rectus• Lateral and medial rectus• Superior and inferior oblique



Figure 9-9(a)

The Extrinsic Eye Muscles


Figure 9-9(b)

The Extrinsic Eye Muscles


Layers of the Eye•Fibrous tunic

• Outermost layer

•Vascular tunic• Intermediate layer

•Neural tunic• Innermost layer



Figure 9-10(a)

The Sectional Anatomy of the Eye


Figure 9-10(b)

The Sectional Anatomy of the Eye

The Special Senses—VisionThe Sectional Anatomy of the Eye

Figure 9-10 (c)


Layers of the Eye•Fibrous tunic

• Sclera•Dense fibrous connective

tissue•“White of the eye”

• Cornea•Transparent•Light entrance

The Eye: Light PathCopyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

PLAYPLAY


Layers of the Eye•Vascular tunic

• Iris•Boundary between anterior and

posterior chambers• Ciliary body

•Ciliary muscle and ciliary process•Attachment of suspensory ligaments

• Choroid•Highly vascular



Functions of the Vascular Tunic•Provide a route for blood vessels•Control amount of light entering eye

• Adjust diameter of pupil

•Secrete and absorb aqueous humor•Adjust lens shape for focusing


The Special Senses—VisionThe Pupillary Muscles

Figure 9-11


Layers of the Eye•Neural tunic (Retina)

• Outer pigmented part•Absorbs stray light

• Inner neural part•Detects light•Processes image•Communicates with brain



Organization of the Retina•Photoreceptor layer•Bipolar cells•Amacrine, horizontal cells

modify signals•Ganglion cells•Optic nerve (CN II)



Retinal Organization

Figure 9-12(a)


Figure 9-12(b)



Figure 9-12(c)



Chambers of the Eye•Two cavities

• Ciliary body, lens between the two• Anterior cavity

•Anterior compartment

Between cornea and iris

•Posterior compartment

Between iris and lens

• Posterior cavity•Vitreous body



The Aqueous Humor•Secreted by ciliary processes into

posterior chamber•Flows into anterior chamber•Maintains eye shape•Carries nutrients and wastes•Reabsorbed into circulation•Leaves at canal of Schlemm•Excess humor leads to glaucoma



Figure 9-14

Eye Chambers and the Circulation of Aqueous Humor


The Lens•Supported by suspensory

ligaments•Built from transparent cells•Surrounded by elastic capsule•Lens and cornea focus light on

retina• Bend light (refraction)

•Accommodation changes lens shape



Figure 9-15(a)

Focal Point, Focal Distance, and Visual Accommodation



Figure 9-15(b)


Figure 9-15(c)



Figure 9-15(d)



Figure 9-15(e)



Figure 9-16(a)

Image Formation


Figure 9-16(b)

Image Formation


Figure 9-17(a)

Visual Abnormalities


Figure 9-17(b)



Figure 9-17(c)



Figure 9-17(d)



Figure 9-17(e)



Key NoteLight passes through the cornea, crosses the anterior cavity to the lens, transits the lens, crosses the posterior chamber, and then penetrates the retina to stimulate the photoreceptors. Cones, most abundant at the fovea and macula lutea, provide detailed color vision in bright light. Rods, dominant in the peripheral retina, provide coarse color-free vision in dim light.



Visual Physiology•Photoreceptors—Cells specialized to

respond to photons, packets of light energy•Two types of photoreceptors

• Rods•Highly sensitive, non-color vision•In peripheral retina

• Cones•Less sensitive, color vision•Mostly in fovea, center of macula lutea

Site of sharpest vision



Photoreceptor Anatomy•Outer segment

• Discs with visual pigments• Light absorption by rhodopsin

•Opsin + retinal

• Inner segment• Synapse with bipolar cell• Control of neurotransmitter release• Effect on bipolar cells


The Special Senses—VisionThe Structure of Rods and Cones

Figure 9-19


Figure 9-201 of 7

Retinal andopsin are

reassembledto form

rhodopsin

Photon

Retinal changes shape

Bleaching(separation)enzyme

ADP ATP

Opsin Opsin

Opsininactivated

Regeneration

Retinalrestored


Figure 9-202 of 7


reassembledto form

rhodopsin


Figure 9-203 of 7


reassembledto form

rhodopsin

Photon


Figure 9-204 of 7


reassembledto form

rhodopsin

Photon



Figure 9-205 of 7


reassembledto form

rhodopsin

Photon



ADP ATP

Retinalrestored


Figure 9-206 of 7


reassembledto form

rhodopsin

Photon



ADP ATP

Opsin Opsin

Opsininactivated

Retinalrestored


Figure 9-207 of 7


reassembledto form

rhodopsin

Photon


RegenerationBleaching

(separation)enzyme

ADP ATP

Retinalrestored

Opsin Opsin

Opsininactivated


The Visual Pathway•Ganglion cells axon converge at optic disc•Axons leave as optic nerve (CN II)•Some axons cross at optic chiasm•Synapse in thalamus bilaterally•Thalamic neurons project to visual cortex

• Located in occipital lobes• Contains map of visual field



Figure 9-21

The Visual Pathway

Equilibrium and Hearing

Sensory Functions of the Inner Ear•Dynamic equilibrium•Static equilibrium•Hearing



Overview of the Ear•Chambers, canals filled with fluid

endolymph•Bony labyrinth

• Surrounds membranous labyrinth• Surrounded by fluid perilymph• Consists of vestibule, semicircular canals,

cochlea

•External, middle ear feed sound to cochlea



Anatomy of the Ear•External ear

• Pinna (auricle)• External acoustic canal• Tympanic membrane (eardrum)

•Middle ear• Auditory ossicles

•Connect tympanic membrane to inner ear• Auditory tube

•Connection to nasopharynx



Anatomy of the Inner Ear•Vestibule

• Membranous sacs•Utricle•Saccule

• Receptors for linear acceleration, gravity

•Semicircular canal with ducts• Receptors for rotation

•Cochlea with cochlear duct• Receptors for sound



Receptors of the Inner Ear•Hair cells

• Mechanoreceptors• Stereocilia on cell surface

•Bending excites/inhibits hair cell•Information on direction and strength

of mechanical stimuli


Equilibrium and HearingThe Anatomy of the Ear

Figure 9-22

Equilibrium and HearingThe Structure of the Middle Ear

Figure 9-23


Figure 9-24(a,b)

The Anatomy of the Ear


Figure 9-24(c)

The Anatomy of the Ear

The Ear: Ear AnatomyPLAYPLAY


Equilibrium•Semicircular ducts

• Connect to utricle• Contains ampulla with hair cells• Stereocilia contact cupola

•Gelatinous mass distorted by fluid movement

• Detects rotation of head in three planes•Anterior, posterior, lateral ducts



Equilibrium (continued)•Saccule and utricle

• Hair cells cluster in maculae

• Stereocilia contact otoliths (heavy mineral crystals)

• Gravity pulls otoliths

• Detect tilt of head

•Sensory axons in vestibular branch of CN VIII



The Vestibular Complex

Figure 9-25(a-c)


The Vestibular Complex

Figure 9-25(a, d)


Figure 9-25(e)1 of 4

Gravity

Gravity

Head in horizontal position

Head tilted posteriorly

Receptoroutput increases

Otolith moves

“downhill,”distorting

hair cell processes



Gravity




Gravity

Gravity



Otolith moves


hair cell processes



Gravity

Gravity



Receptoroutput increases

Otolith moves


hair cell processes

The Ear: BalancePLAYPLAY


Overview of Hearing•Sound waves vibrate tympanic membrane•Ossicles transfer vibration to oval window•Oval window presses on perilymph in

vestibular duct•Pressure wave distorts basilar membrane•Hair cells of organ of Corti press on

tectorial membrane



The Cochlea and the Organ of Corti

Figure 9-26(a)


Figure 9-26(b)

The Cochlea and the Organ of Corti


Figure 9-271 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

StapesOval

window

Cochlear branch ofcranial nerve VIII

Vestibular duct(perilymph)

Vestibular membrane

Cochlear duct(endolymph)Basilar membraneTympanic duct(perilymph)

Tympanicmembrane

Roundwindow

Sound waves arrive at tympanic membrane.

Movement of tympanic membrane causes displacement of the auditory ossicles.

Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct.

The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct.

Vibrations of the basilar membrane causes vibration of hair cells against the tectorial membrane.

Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII.


Figure 9-272 of 7

Externalacoustic

canal

Movementof sound

waves


Tympanicmembrane


Figure 9-273 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

Stapes

Tympanicmembrane




Figure 9-274 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

StapesOval

window

Tympanicmembrane





Figure 9-275 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

StapesOval

window

Tympanicmembrane

Roundwindow






Figure 9-276 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

StapesOval

window


Vestibular membrane


Tympanicmembrane

Roundwindow






The Ear: Receptor ComplexesCopyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

PLAYPLAYFigure 9-277 of 7

Externalacoustic

canal

Movementof sound

waves

Malleus

Incus

StapesOval

window

Cochlear branch ofcranial nerve VIII


Vestibular membrane


Tympanicmembrane

Roundwindow






Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII.


Auditory Pathways•Hair cells excite sensory neurons•Sensory neurons located in spiral

ganglion•Afferent axons form cochlear branch of

vestibulocochlear nerve (CN VIII)•Synapses in cochlear nucleus in medulla•Neurons relay to midbrain•Midbrain relays to thalamus•Thalamus relays to auditory cortex

(temporal lobe) in a frequency map



Pathways for Auditory Sensations

Figure 9-28


Key NoteBalance and hearing both rely on hair cells. Which stimulus excites a particular group depends on the structure of the associated sense organ. In the semicircular ducts, fluid movement due to head rotation is sensed. In the utricle and saccule, shifts in the position of otoliths by gravity is sensed. In the cochlea, sound pressure waves distort the basilar membrane.


Aging and the Senses

Impact of Aging on Sensory Ability•Gradual reduction in smell and taste

sensitivity as receptors are lost•Lens changes lead to presbyopia

(loss of near vision)•Chance of cataract increases•Progressive loss of hearing

sensitivity as receptors are lost (presbycusis)


The General and Special Senses The General and Special Senses.

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