7. the sense organs
DESCRIPTION
Credits: Ed Cabalang JrTRANSCRIPT
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