7. the sense organs

Chapter 7Sense Organs

CHARACTERISTICS OF SENSATIONS

1. Projection- projecting sensation to source of stimulation2. After-image- sensation persists in consciousness after

cessation of stimulation3. Adaptation- continuous stimulus- one gets used to it or

ignores it4. Local Sign- ability to recognize point of application of

stimulus5. Contrast- sensation is affected by events which preceded

or accompany it6. Intensity- dependent on number of receptors stimulated

and rate of transmission

TasteSmellVisionHearingBalance

General Senses General Senses vs.vs. _ _ Special SensesSpecial Senses•Produce the somatic senses•Widely distributed receptors

•Produce the special senses•Grouped in localized areas

Sensory Receptors• Receptor is any structure specialized to detect a

stimulus (simple nerve ending or sense organ)

• All receptors are transducers converting one form of energy to another

Types of Sensory Receptors

• By modality:– chemoreceptors, thermoreceptors, nociceptors (pain),

mechanoreceptors and photoreceptors

• By distribution– general (somesthetic) sense --- widely distributed– special senses --- limited to head

• By origin of stimuli– interoceptors = detect internal stimuli– proprioceptors = sense position & movements of body– exteroceptors = sense stimuli external to body

General Senses

skin, bones, internal organs, joints

Naked nerve endings surrounded by one or more layers

Pacinian corpuscle

Free nerve endings

Encapsulated Nerve Encapsulated Nerve

EndingsEndingsvs

Unencapsulated Unencapsulated

Nerve EndingsNerve Endings

Deeper tissue, muscles

Somatic senses1. Pain and temperature- receptors are free nerve

endings; respond to a variety of stimuli as mechanical stretching, extremes in temperature to produce pain

characteristics of Heat and Cold sensation:

successive contrast, adaptation, after-image

pain, light touch, and temperature

• Free nerve endings include– warm, cold & pain

• Tactile discs are associated with cells at base epidermis

• Hair receptors monitor the movement of hairs

2. Touch and Pressure Receptors-respond to stimuli that ‘deform’ or change their shape and placement and that more hair

– ruffini corpuscles• heavy touch, pressure, joint movements

& skin stretching

– tactile (meissner) corpuscles• light touch & texture

– krause end bulb• tactile corpuscles in mucous membranes

– lamellated (pacinian) corpuscles• deep pressure, stretch, tickle, itch &

vibration

Char: adaptation, local sign

Muscle Spindles - Skeletal Muscle Stretching

Golgi Tendon Organs - Tendon Stretching

3. Stretch Sensations

4. Organic sensations

• Hunger- projected to stomach

-associated with rhythmic contractions and weakness, trembling, nausea, headache

- NS is hyperexcitable

• Thirst- projected to pharynx

- due to low water levels

- extreme thirst leads to mental anguish

5. Visceral Sensations

three groups of stimuli

• Dilation/distension

• Spasm/strong contraction

• Chemical irritation

Referred pain occurs because of the common nerve pathways leading from skin and internal organs.

• Referred pain is misinterpreted pain

– Visceral impulse and cutaneous impulse share the same neurons to brain

– Results in confusion

– ex. Angina pectoris- spasm of smooth muscle in coronary arteries of heart

– brain “assumes” pain is coming from skin not heart– Pain in left shoulder and left arm instead of heart

– ex. pneumonia- pain in abdomen

Referred Pain-felt on the body surface

The Special Senses

Taste- GustationSmell- Olfaction

VisionHearingBalance

The Chemical Sense -- Taste

respond to chemicals in an aqueous solution

food dissolved in saliva

Closely-linked with olfaction and nutrition

•Taste and smell are involved with specific receptor cells called chemoreceptors  

THE TONGUE

• Gustation is the sensation of taste resulting from the action of chemicals on the taste buds

• Lingual papillae– filiform (no taste buds)

• most abundant

– foliate (no taste buds)– fungiform

• at tips & sides of tongue

– circumvallate• at rear of tongue

• contains 1/2 of taste buds

Circumvallate Papilla

Filiformpapilla

Fungiformpapilla

Connective tissue Tongue epithelium

Taste Bud structure

• Lemon-shaped groups of 3 kinds of cells– taste cells, supporting cells, and basal cells

• taste cells with a apical microvilli serving as a receptor surface

• taste cells synapse with sensory nerve fibers at their base

• Lemon-shaped groups of 3 kinds of cells– taste cells, supporting cells, and basal cells

• taste cells with a apical microvilli serving as a receptor surface

• taste cells synapse with sensory nerve fibers at their base

Taste BudsTaste Buds

taste buds

papilla

taste pores

Five Basic Tastes

Salty- metallic ions (NaCl)

Sweet- sugarSweet- sugar

UmamiUmami

Sour- HSour- H++

Bitter- alkaloidsBitter- alkaloids

Why are they important?

Physiology of Taste

• To be tasted, molecules must dissolve in saliva

• 5 primary sensations: salty, sweet, sour, bitter & umami (taste of amino acids such as MSG)

• Taste is also influenced by food texture, aroma, temperature, and appearance.

– hot pepper stimulates free nerve endings (pain)

GUSTATION- TASTEacids cause strong salivary reflexbad tasting food causes gagging or reflexive vomitingtaste can change over timetaste is 80% smell-depends heavily on olfactory receptors

Taste also dependent on thermoreceptors, nociceptors, mechanoreceptors

Projection Pathways for Taste

• Innervation of the taste buds (gustatory cells)– facial nerve for the anterior 2/3’s of the tongue– glossopharyngeal nerve for the posterior 1/3– vagus nerve for palate, pharynx & epiglottis

• Medulla oblongata

• thalamus

• postcentral gyrus of the cerebrum– conscious sense of taste

THE SENSE OF SMELL

Smell in man not as good as animals’; however, some people are wine tasters, perfumers

If you smell a particular odor all day, you won’t recognize its presence, you become accustomed, ex. garbage men

Old people lose sense of smell- lots of perfume

Humans can distinguish 10,000 or so chemicals

What we really smell is pain: ex. chili, ammonia, menthol (cold)

Olfaction-some featuresOlfaction-some features

The Chemical Sense -- Smell

• Receptor cells for olfaction form olfactory mucosa– smell is highly sensitive (more so in

women than men)– distinguish as many as 10,000 odors

• Characteristics : memory

adaptation

•Stimuli in gaseous form•Less impt in man than animals

7 PRIMARY ODORS• Floral- roses

• Musky- perfume/aftershave

• Camphoric- mothballs

• Pepperminty- mint gum

• Ethereal- dry cleaning fluid

• Pungent- vinegar

• Putrid-rotten eggs

Physiology of Smell• Odor molecules bind to a receptor on an olfactory hair

triggering the production of a second messenger– opens the ion channels & creates a receptor potential

• olfactory nerves in olfactory bulbs• olfactory tracts• Olfactory centers in thalamus

– lead to temporal lobe, amygdala, hypothalamus

• emotional responses to odors

• cough, salivate, sneeze or vomit in response to odors

• cerebral cortex sends feedback to bulb cells• changing quality & significance of odors when hungry

Olfactory Epithelial Cells

• Olfactory cells– neurons with 20 cilia

called olfactory hairs• binding sites for odor

molecules in thin layer of mucus

– Live for 60 days

• Supporting cells

• Basal cells divide

Olfactory PathwayOlfactory Pathway

olfactory hairs

olfactory receptor cell

bone

olfactory bulb

Nasal conchae

Olfactory Projection Pathways

Olfactory auras- prior to epileptic attack

May be genetic or a cold (mucus), allergy, zinc deficiency, smoking, aging and growth of nasal polyps

Anosmias- loss of sense of smell

Lose sense of smelllose taste

Uncinate- olfactory hallucinations; may be psychological ex. rotting meat smell

From head injuries that destroy olfactory nerves

THE SENSE OF HEARING AND BALANCE

SENSE OF HEARING• the ‘watchdog’ of the senses•Stimulus- sound waves•Sound- an audible vibration of molecules •Receptors- hair cells in Organ of Corti

Molecules collide with eardrum & make it vibrate.

Pitch and Loudness

• The frequency at which parts of the ear vibrate give us sense of Pitch (high or low pitched sounds)– hearing range is 20 - 20,000 Hz (cycles/sec)

• Loudness is perception of intensity of sound energy– how much the air molecules are compressed in decibels

Sounds 90 dB can cause damage.

Auditory Pathway

auricle External auditory canal

Tympanic membrane

Malleus, incus stapesCochlear fluid is

disturbed

Ripple disturbs hair cells in Organ of Corti

Cochlear nerve

Brain stemthalamusAuditory nerve of temporal lobe

Eustachian Tube• Tympanic cavity filled with air by auditory tube

(Eustachian tube) connected to nasopharynx– opens during swallowing or yawning to equalize air pressure on

both sides of eardrum

Anatomy of Middle Ear

• Middle ear is cavity containing ear ossicles.

Inner Ear

• Passageways in temporal bone = bony labyrinth

• Endolymph-filled tubes floating in perilymph inside the bony labyrinth = membranous labyrinth

vestibular apparatus

cochlea

Anatomy of the Cochlea

• Stereocilia of hair cells attached to tectorial membrane.

• Hearing comes from inner hair cells -- outer ones adjust cochlear responses to different frequencies

2.5 coils

3 fluid-filled chambers

Organ of Corti

Stimulation of Cochlear Hair Cells

• Sound is produced by vibration of ossicles and then vibration of basilar membrane under hair cells

• Can happen as often as 20,000 time per second

Balance and Equilibrium

• Receptors in vestibular apparatus– semicircular ducts contain crista– saccule & utricle contain macula

• Static equilibrium is perception of head orientation when one is not moving– perceived by macula

• Dynamic equilibrium is perception of motion or acceleration – linear acceleration perceived by macula– angular acceleration perceived by crista

The Saccule and Utricle

• Saccule & utricle chambers containing macula– patch of hair cells in macula embedded in a gelatinous

otolithic membrane weighted with granules called otoliths ( CaCO3 crystals)

– otoliths add to density & inertia and enhance the sense of gravity and motion; aka ‘ear stones’

Otoliths

Macula Saccule and Macula Utricle

• With the head erect, stimulation is minimal, but when the head is tilted, weight of membrane bends the stereocilia (static equilibrium)

• When car begins to move at green light, linear acceleration is detected since heavy otolith lags behind (one type of dynamic equilibrium)

Crista ampullaris of Semicircular Ducts

• Crista ampullaris consists of hair cells buried in a mound of gelatinous membrane (one in each duct)

• Orientation of ducts causes different ducts to be stimulated by rotation in different planes

Crista Ampullaris & Head Rotation

• As head turns, the endolymph lags behind pushing the cupula and stimulating its hair cells

• Vision is perception of light emitted or reflected from objects in the environment

• Stimulus- light waves

VISION

THE SENSE OF SIGHT

The Optical Apparatus

THE PROCESS OF SEEING1. Formation of

retinal image

Processes involved:

a. refraction of light rays- due to cornea, aqeous humor, lens, vitreous humor

b. accomodation of lens

Accommodation of Lens

SEEING cont.2. Constriction of pupil-directs light rays to retina

3. Convergence of eyes- eyeballs converge so that visual axes come together at the object viewed

•Neural apparatus includes the retina & optic nerve•Retina forms as an outgrowth of the brain

attached only at optic disc where optic nerve begins

•Detached retinablow to head or lack of sufficient vitreous bodyblurry areas in field of visionleads to blindness due to disruption of blood supply

Test for Blind Spot

• Optic disk or blind spot is where optic nerve exits the posterior surface of the eyeball– no receptor cells are found in optic disk

• Blind spot can be seen using the above illustration– in the right position, stare at X and red dot disappears

• Visual filling is the brain filling in the green bar across the blind spot area

blind spot macula

The RetinaThe Retina

Effects of Corrected Lenses

• Hyperopia is farsighted (eyeball too short)– correct with convex lenses

• Myopia is nearsighted (eyeball too long)– correct with concave lenses

Retinal Cells• Posterior layer of retina is pigment epithelium

– purpose is to absorb stray light & prevent reflections

• Photoreceptors cells are in next layer• Rod cells (night vision)

-with rhodopsin pigment molecules (light-sensitive)

-w/light= breaks down into opsin and retinal

-sensitive to movement of objects

• Cone cells (color vision in bright light)– Detail and color

– Less sensitive to light

– Needs brighter light to break down pigments

and generate action potential

Details of the Retina

lightlight

photoreceptive cells

ChoroidSchlera

Ganglion

Amacrine

Bipolar neuron

Horizontal cells