ANS 331: Sensory Organs
I. Sensations
1. Result from stimuli that initiate
afferent impulses
A. Conscious--Cerebral Cortex
2. Types of Senses
A. Visceral
B. Touch
C. Pressure
D. Temperature
E. Pain
F. Proprioception
F. Special Senses
a. Sight
b. Hearing
c. Taste
d. Smell
e. Equilibrium
3. All sensations involve a receptor organ
A. Sensory Receptors convert different types
of energy to action potentials
a. Sound
b. Light
c. Chemical
d. Thermal
e. Mechanical
B. Receptor responses are specific
II. Specific Senses
1. Visceral Senses
A. Hunger
a. Hypothalamus senses low metabolites (hypoglycemia)
b. Causes conscience desire for food
--Stimulates digestive tract (stomach growl)
B. Thirst
a. Dehydration
i. Immediate loss of extracellular fluid, followed by
intracellular fluid loss by Osmosis
ii. 10% loss is severe
iii. Electrolytes (ions) are depleted too
iv. Rehydration requires water + electrolytes
--Water poisoning can occur without
electrolytes
--Hypotonic blood may cause hemolysis
b. Stimulus for Thirst
i. Hypothalamus
1. Thirst cells stimulated by increase in cell
osmoconcentration
--Consequence of Dehydration
--Causes a conscience desire for
water
2. Anti-diuretic Hormone (Vasopressin) produced
--Released from Pituitary
--Acts on kidney tubule cells to
absorb water
ii. Kidney
1. Kidney will conserve water when possible
2. Angiotensin II causes thirst
A. Renin produced by kidney causes
production
B. Stimulated by Low Blood Pressure
a. Dehydration
b. Hemorrhage
C. Also causes salt retention and
vasoconstriction
c. Relief of Thirst
i. Enough is taken in to bring cell osmoconcentration
to normal
ii. Temporary relief
1. Wetting of mouth and Pharynx
2. Distension of stomach
3. Prevent over ingestion
d. Thirst is an important mechanism for maintenance
of water balance
C. Hollow organ fullness
a. Body senses fullness digestive and parts of urinary tract
b. Over fullness can cause pain
c. Interaction with Hunger and Thirst responses
D. Visceral Pain
a. Pleuritis and Peritonitis
i. Inflamation of Pleura and/or Perintoneum
ii. Caused by injury
b. Pain can be severe
2. Touch and Pressure
A. Touch (Tactile Sense)
a. Sensation of something being in contact
with the surface of the body
b. Receptor is called Meissner's Corpuscle
--Modified dendritic process
B. Pressure
a. Sensation of something pressing on the body surface
b. Receptor is called Vater-Pacinian Corpuscle
--Modified dendritic process
C. Modified receptors sense light contact, deep pressure,
vibration, and hair movement.
3. Temperature
A. Physiological Responses to Heat
a. Hypothalamic thermoreceptors
i. Cause reflexes
b. Skin Receptors
i. Heat: Corpuscles of Ruffini
ii. Cold: Krause's End Bulb
iii. Also cause reflexes
c. Circulatory Adjustments
i. Heat is lost when blood is brought to the skin
surface
1. Vasodilation
2. Inhibit sympathetic vasoconstrictors
ii. Reflex
d. Evaporative Heat Loss
i. Evaporation of water results in cooling
ii. Sweating
1. Importance varies among species
2. Less effective in domestic animals than
humans
--horse>cattle>sheep>dogs>cats>swine
iii. Panting
1. Inhaled air is cooled by moist tongue
2. Increase dead space ventilation without
change in alveolar ventilation
--Prevents hyperventilation
iv. Sweating and panting are reflexes
--Skin and Hypothalamic receptors
B. Physiological Responses to Cold
a. Cold activates heating mechanisms
i. Skin and hypothalamic receptors
b. Reduction of Heat Loss
i. Animals curl up when they lie down
ii. Piloerection
1. Hair made more erect with by arrector pili
muscle of hair follicle
2. Increases insulation value of hair or fur
--Goose bumps
iii. Vasoconstriction of peripheral blood vessels to skin
iv. Countercurrent heat exchange in extremities
1. Veins and Arteries in close proximity
to exchange heat
c. Increase of Heat Production
i. When heat reduction isn't efficient, heat production
is necessary
1. Critical temperature is point where heat
production starts
2. Cattle and Sheep have lowest critical
temperature of farm animals
--Withstand cold better
ii. Shivering
1. Muscle contractions converted to heat
iii. Epinephrine and Norepinephrine release
--Increase metabolism of fat
iv. Thyroid hormone
--Increase metabolism
C. Hypothermia and Hyperthermia
a. Hypothermia
i. Reduction of deep body temperature below normal
in nonhibernating animals
ii. Result of prolonged exposure to cold, coupled with
inability of heat-conserving and heat generating
mechanisms to keep pace
iii. Life threatening unless environmental temperatures
improve or external heat is provided
b. Hyperthermia
i. Increase in body temperature above normal
ii. Fever
1. Body uses to fight microorganisms
A. Immunological mechanisms are
accelerated
B. High temp. detrimental to microbes
2. Can be damaging to body tissues if it goes
to high
--Brain, Testis, Heart Valves
3. Set point in hypothalamus is increased
A. Body senses blood is too cold
4. Heat conserving and generating
mechanisms are turned on
A. Usually self limiting
5. Shivering and a feeling of cold
characteristic of beginning of fever
ii. Heat stroke
1. Heat production exceed evaporative
capacity of the environment
4. Pain
A. Pain Reception--Nociception
a. Protective Mechanisms
b. Nociceptor
--Bare Nerve Endings
--Respond to all intense stimuli
B. Fibers are Myelinated and Unmyelinated
a. Myelinated
i. Short lag between stimulus
and reaction
ii. More intense, sharp pain
b. Unmyelinated
i. Long Lag time
ii. Aching and Throbbing Quality
C. Threshold variable among individuals
D. Diversion can reduce pain perception
--Example: Horse Twitch
5. Proprioceptions
A. Sense of body position and movement
B. Proprioceptors
a. Found in Skeletal M., Tendons,
Ligaments, and Joint Capsules
b. Examples
i. Muscle Spindles
--Sensitive to stretch
--Provide muscle tone
ii. Golgi Tendon Organ
--Sensitive to stretch
iii. Joint Receptors
--Sensitive to position and angle
of joints
c. Most heavily myelinated nerve fibers
--Need to be fast
6. Taste
A. Gustation--Sense of Taste
a. Function
--Discrimination
--Healthful vs. Harmful
B. Taste Bud
a. Receptor Organ
b. Located on Tongue Papillae
--Some on palate, pharynx, and
larynx
c. Components
i. Taste Pore and Pit
--Substance in solution
(gland of von Ebner)
ii. Gustatory Cells
--Contain taste hairs
--Stimulate Cranial Nerves
(VII and IX)
C. Taste Sensations
a. Humans
i. Salty
ii. Sweet
iii. Bitter
iv. Sour
b. Animals
--Sensations not known for sure
--Probably different between animals
7. Smell
A. Olfaction--Sense of Smell
a. Important Functions in Animals
i. Protection
ii. Reproduction
iii. Communication
b. Macrosmatic
--Greatly developed sense of smell:
Larger area
--Most Domestic and Wild Animals
c. Microsmatic
--Lesser developed sense of smell:
Smaller area
--Humans, Monkeys, some Aquatic
Animals
d. Anosmatic
--No Sense of Smell
--Many Marine Mammals
B. Olfactory Region
a. Found in mucous membrane of nasal
cavity
b. Olfactory receptor cell
i. Dendritic Process
--Olfactory cilia
--Olfactory vesicle
ii. Lie between sustentacular cells
--Support cells
--Simple Columnar Epithelium
iii. Lubricated by glands of Bowman
--Subepithelial glands
--Substance goes into solution by
air movement
c. Stimulate Cranial Nerve I
C. Odor Perception
a. Unlikely specific type of cell for each
smell
b. Probably smells combine for
sensation
c. An odor can overcome another
D. Pheromones
a. A chemical secreted by one animal
that influences the behavior of another animal
--Chemical Communication
b. Functions
a. Mating
b. Marking Trails or Boundaries
c. Recognizing individuals from
same herd or nest
d. Marking Food Sources
e. Emitting Alarms
8. Hearing and Equilibrium
A. Ear
--Auditory Organ
a. External ear
i. Pinna (Auricle)
--Outer visible Part
--Funnel-Shaped Cartilage
--Hairless inside
--Varying degrees of musculature
ii. External Acoustic Meatus
--Tube to middle ear
iii. Tympanic Membrane
(Ear drum)
--Sensitive to vibrations of sound
waves
--Stimulate Auditory Ossicles
b. Middle ear
i. Auditory ossicles
--Malleus (Hammer)
--Incus (Anvil)
--Stapes (Stirrup)
ii. Vestibular (oval) window
--Transmits signal from ossicles
to inner ear
iii. Cochlear (round) window
--Terminal end of Cochlea
ii. Auditory (Eustachian) tube
--Pressure equalization with
pharynx
c. Inner ear
I. Vestibular apparatus
--Position and Equilibrium
ii. Cochlea
--Sound
iii. Form a Labyrinth
--Osseous & Membranous
B. Vestibular Structure and Function
a. Fluids
i. Endolymph
--Fluid inside the membranous
--Similar to intracellular fluid
ii. Perilymph
--Fluid between membranous
and osseous
--Similar to cerebral spinal fluid
b. Three semicircular canals
i. Anterior, Lateral, Posterior
ii. Different Geometric Planes
(Right Angles)
iii. Ampulla
--Dilated portion of canals
--Contain sensory receptors for
equilibrium
--Crista ampullaris
--Hair cells sense movement/inertia of
endolymph through canals
c. Utricle and Saccule
I. Utricle
--Connects semicircular canals
ii. Saccule
--Connects cochlear region
and endolymph duct
iii. Both contain macula regions
--Spacial equilibrium receptors
--Hair cells sense weight
(gelatinous endolymph)
--No movement needed to respond
C. Cochlear Structure and Function
a. Cochlea
--Snail shell shaped labyrinth
b. Three cochlear ducts (Scala)
i. Vestibuli, Media, Tympani
ii. Contain endolymph
--Sound waves move
c. Organs of Corti
i. Located along Scala media
ii. Convert sound waves to nerve
impulses
iii. Hair cells resonate basilar
membrane
--Causes depolarization
iv. Organs at base
--Recognize highest frequency
sounds
v. Organs at apex
--Recognize lowest frequency sounds
d. Cochlear (Round) Window
i. Absorbs movement of perilymph
D. Sound Reception Path
a. Pinna (Auricle)
b. External Auditory Meatus
c. Tympanic Membrane
d. Auditory ossicles
c. Vestibular (Oval) Window
d. Endolymph through scala media of cochlea
e. Organ of Corti (Frequency Dependent)
f. Cranial nerve (VII) impulse
to Cerebral Cortex
g. Perilymph stopped by cochlear window
h. Pressure equalized by Eustachian Tube
9. Vision
A. General Information
a. Eye--Receptor Organ for Vision
b. Stimulus--Light
B. Structure and Functions of the Eye
and Eyeball
a. Tunics
--Three Layers or Coats
i. Fibrous Tunic (External Coat)
--Supportive Layer
--Cornea, Sclera
ii. Vascular Tunic (Middle Coat) also called uvea
--Choroid, Ciliary Bodies, Iris
iii. Nerve Tunic (Inner Coat)
--Retina
b. Cornea
i. Transparent to allow entrance
of light
--Light transmission proportional
to cornea surface area
ii. Nocturnal animals have larger
corneas
iii. Avascular
iv. Innervated by nonmyelinated
nerve fibers
--One of most sensitive tissues
in body
c. Sclera
i. White of Eye
ii. Vascular
iii. Makes up majority of outside of eye
iv. Junction between Sclera and Cornea
is called the Limbus
d. Lens
i. Positioned between cornea
and retina
ii. Convex structure
--Converges light rays to retina
iii. Avascular
iv. Accommodation
--Adjustment of focal lengths for
near and far objects:
Refraction=Bending of Light
--Ciliary muscles controls:
More convex=Short distance
Less convex=Long distance
--Domestic animals don't
accommodate well
--Auxiliary Accommodation:
e.g. Horse:
Ramp Retina perceives
light at different planes
e. Iris
i. Controls amount of light entering
the eye
ii. Colored Part
iii. Pupil--Opening
iv. Two Smooth Muscles Innervated
by Autonomic Nerves
Parasympathetic--Circular,
Decrease size
Sympathetic--Radial,
Increase size
f. Humors
i. Aqueous Humor
--In front of lens
--3 functions
1. Nutrition
2. Waste Removal
3. Occupy Space
ii. Vitreous Humor
--Behind lens
--Gelatinous mass
(Vitreous Body)
--Occupies space
g. Retina
i. Composed of ten layers
--Mostly nerve tissue
ii. Photoreceptors:
--Rods
--Cones
--Convert light to nerve impulses
iii. Black in color
--Melanin
--Absorbs light and prevents
reflection
iv. Rods
--Black and White Vision
--Make up majority of retina in
domestic animals
--Very sensitive to light,
Night vision
v. Cones
--Color Vision
--High concentration in birds
--Day vision
C. Chemistry of Vision
a. Light causes biochemical reactions in
the rods and cones
b. Rhodopsin
--Light sensitive chemical in rods
--Vitamin A derivative;
Deficiency=Night Blindness
D. Adaption to Varying Light
a. Autonomic Visual Reflexes
b. Rhodopsin
c. Tapetum
--Light reflecting layer of cells of the
inner choroid
--Present in cats, dogs, horses, and
ruminants in varying degrees
--Allow photoreceptor cells to be
restimulated from same light
--Causes eyes to glow in the dark--
eyeshine
E. Field of Vision
a. The more lateral the eyes the larger
the field of vision
i. Herbivores
ii. Gives greater protection from
predators
b. The more forward placed has better
depth perception
i. Binocular Vision
ii. Carnivores
iii. All Domestic animals have some
degree of binocular vision
directly in front of them
F. Eyeball Movement
a. Skeletal Muscles innervated by
Cranial nerves
b. Up/Down, Side/Side, Rotational,
Inward (Retraction)
G. Accessory Structures
a. Conjunctiva
--The mucous membrane that lines
the inner surface of the eyelid
and the exposed surface of the
eyeball
b. Precorneal film
--Three Layers
i. Mucin Layer
--Innermost layer produced by
Conjunctiva
--Lubrication
--Lysozyme
--Digests bacterial walls
--Wetability
--Surface tension
ii. Lacrimal Layer
--Tear secretions
--Hydration
iii. Oily Layer
--Reduces evaporation
--Surface tension
c. Eyelid
i. Protect Eye
ii. Upper and Lower folds of Skin
iii. Lateral and medical corners are called canthus
iv. Third Eyelid
1. Found in domestic animals
2. Also called nictitating membrane
3. T-Shaped plate of cartilage covered
by conjunctiva on medial side of eye
v. Eyelashes also protect eye
--Camels have long eyelashes to keep
sand out of eye.
~~~~~Revised 9/24/03~~~~~ TAW