Transcript Sensory Organs

Sensory Organs
Tada Obert
Dept of Livestock & Wildlife Management
Sensations
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Result from stimuli that initiate afferent impulses
Types of Senses:
 Visceral
 Touch
 Pressure
 Temperature
 Pain
 Proprioception
 Special Senses:
 Sight, Hearing, Taste, Smell, Equilibrium
All sensations involve a receptor organ
 Sensory Receptors convert different types of energy to action
potentials:
 Sound, Light, Chemical, Thermal, Mechanical
 Receptor responses are specific.
Visceral Senses
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A. Hunger
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Hypothalamus senses low metabolites (hypoglycemia)
Causes conscience desire for food
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Stimulates digestive tract (stomach growl)
B. Thirst
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Dehydration
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Immediate loss of extracellular fluid, followed by intracellular fluid loss by
Osmosis
10% loss is severe
Electrolytes (ions) are depleted too
Rehydration requires water + electrolytes
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Water poisoning can occur without electrolytes
Hypotonic blood may cause hemolysis
Visceral Senses > Thirst
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Stimulus for Thirst
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Hypothalamus
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Thirst cells stimulated by increase in cell osmoconcentration
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Anti-diuretic Hormone (Vasopressin) produced
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Released from Pituitary
Acts on kidney tubule cells to absorb water
Kidney
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Consequence of Dehydration
Causes a conscience desire for water
Kidney will conserve water when possible
Angiotensin II causes thirst
Renin produced by kidney causes production
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Relief of Thirst
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Enough is taken in to bring cell osmoconcentration to normal
Temporary relief
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Stimulated by Low Blood Pressure (dehydration, hemorrhage)
Also causes salt retention and vasoconstriction
Wetting of mouth and Pharynx
Distension of stomach
Prevent over ingestion
Thirst is an important mechanism for maintenance of water balance
Visceral Senses cont’d
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Hollow organ fullness
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Body senses fullness digestive and parts of urinary tract
Over fullness can cause pain
Interaction with Hunger and Thirst responses
Visceral Pain
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Pleuritis and Peritonitis
 Inflamation of Pleura and/or Perintoneum
 Caused by injury
Pain can be severe
Touches and Pressure
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A. Touch (Tactile Sense)
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Sensation of something being in contact with the surface of
the body
Receptor is called Meissner's Corpuscle
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B. Pressure
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Sensation of something pressing on the body surface
Receptor is called Vater-Pacinian Corpuscle
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Modified dendritic process
Modified dendritic process
C. Modified receptors sense light contact, deep
pressure, vibration, and hair movement.
Temperature
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A. Physiological Responses to Heat
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Hypothalamic thermo-receptors
Skin Receptors also cause reflexes
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Heat:
Cold:
Corpuscles of Ruffini
Krause's End Bulb
Circulatory Adjustments
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Heat is lost when blood is brought to the skin surface
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cause reflexes
Vasodilation
Inhibit sympathetic vasoconstrictors
Reflex
Evaporative Heat Loss
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Evaporation of water results in cooling
Sweating
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Importance varies among species
Less effective in domestic animals than humans
 horse>cattle>sheep>dogs>cats>swine
Panting
 Inhaled air is cooled by moist tongue
 Increase dead space ventilation without change in alveolar ventilation
 Prevents hyperventilation
Sweating and panting are reflexes
 Skin and Hypothalamic receptors
Physiological Responses to Cold
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Cold activates heating mechanisms
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Skin and hypothalamic receptors
Reduction of Heat Loss
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Animals curl up when they lie down
Piloerection
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Vasoconstriction of peripheral blood vessels to skin
Countercurrent heat exchange in extremities
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Hair made more erect with by arrector pili muscle of hair follicle
Increases insulation value of hair or fur (goose bumps)
Veins and Arteries in close proximity to exchange heat
Increase of Heat Production
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When heat reduction isn't efficient, heat production is necessary
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Shivering
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Muscle contractions converted to heat
Epinephrine and Norepinephrine release
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Critical temperature is point where heat production starts
Cattle and Sheep have lowest critical temperature of farm animals (withstand cold better)
Increase metabolism of fat
Thyroid hormone
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Increase metabolism
Hypothermia & Hyperthermia
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Hypothermia
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Reduction of deep body temperature below normal
in non-hibernating animals
Result of prolonged exposure to cold, coupled with
inability of heat-conserving and heat generating
mechanisms to keep pace
Life threatening unless environmental
temperatures improve or external heat is provided
Hyperthermia
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Increase in body temperature above normal
Fever
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Body uses to fight micro-organisms
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Can be damaging to body tissues if it goes to high
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Body senses blood is too cold
Heat conserving and generating mechanisms are turned on
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Brain, Testis, Heart Valves
Set point in hypothalamus is increased
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Immunological mechanisms are accelerated
High temp. detrimental to microbes
Usually self limiting
Shivering and a feeling of cold characteristic of beginning of fever
Heat stroke
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Heat production exceed evaporative capacity of the environment
Pain
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Pain Reception  Nociception
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Protective Mechanisms
Nociceptor
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Fibers are Myelinated and Unmyelinated
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Myelinated
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Short lag between stimulus and reaction
More intense, sharp pain
Unmyelinated
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Bare Nerve Endings
Respond to all intense stimuli
Long Lag time
Aching and Throbbing Quality
Threshold variable among individuals
Diversion can reduce pain perception
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Example: Horse Twitch
Proprioceptions
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Sense of body position and movement
Proprioceptors
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Found in Skeletal Muscles, Tendons, Ligaments, and Joint Capsules
Examples
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Muscle Spindles
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Golgi Tendon Organ
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Sensitive to stretch
Joint Receptors
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Sensitive to stretch
Provide muscle tone
Sensitive to position and angle of joints
Most heavily myelinated nerve fibers
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Need to be fast
Taste
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Gustation  Sense of Taste
Function
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Discrimination (healthful vs harmful)
Taste Bud
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Receptor Organ
Located on Tongue Papillae
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Components
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Some on palate, pharynx, and larynx
Taste Pore and Pit
 substance in solution  (gland of von Ebner)
Gustatory Cells
 Contain taste hairs--Stimulate Cranial Nerves VII and IX (Facial Sensory Nerve
& Glossopharyngeal Sensory Nerve)
Taste Sensations
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Humans (salty, sweet, bitter, sour)
Animals
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Sensations not known for sure
Probably different between animals
Smell
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Olfaction  Sense of Smell
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Important Functions in Animals
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Macrosmatic
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Lesser developed sense of smell: Smaller area
Humans, Monkeys, some Aquatic Animals
Anosmatic
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Greatly developed sense of smell: Larger area
Most Domestic and Wild Animals
Microsmatic
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Protection, Reproduction, & Communication
No Sense of Smell
Many Marine Mammals
Olfactory Region
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Found in mucous membrane of nasal cavity
Olfactory receptor cell
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Dendritic Process
Lie between sustentacular cells
Lubricated by glands of Bowman
Stimulate Cranial Nerve I (Olfactory/Smell Sensory Nerve).
Smell cont’d
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Odour Perception
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Unlikely specific type of cell for each smell
Probably smells combine for sensation
An odour can overcome another
Pheromones
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A chemical secreted by one animal that influences the behaviour of another
animal
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Chemical Communication
Functions
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Mating
Marking Trails or Boundaries
Recognizing individuals from same herd or nest
Marking Food Sources
Emitting Alarms
Hearing & Equilibrium
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Ear  Auditory Organ
External ear
Middle ear
Inner ear
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Vestibular apparatus for position and equilibrium
Cochlea for sound
Sound Reception Path
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Pinna (Auricle)
External Auditory Meatus
Tympanic Membrane
Auditory ossicles
Vestibular (Oval) Window
Endolymph through scala media of cochlea
Organ of Corti (Frequency Dependent)
Cranial nerve (VIII) [Auditory] impulse to Cerebral Cortex
Perilymph stopped by cochlear window
Pressure equalized by Eustachian Tube
Vision
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General Information
 Eye  Receptor Organ for Vision
 Stimulus  Light
Structure and Functions of the Eye and Eyeball
 Tunics (fibrous, vascular, nerve)
 Cornea (transparent to allow entrance of light, nocturnal animals have
larger corneas, avascular, also innervated by non-myelinated nerve
fibers, one of most sensitive tissues in body.
 Sclera (white of eye)
 Lens (convex structure, converges light rays to retina, avascular,
accommodation, refraction, ciliary muscles controls)
 Domestic animals don't accommodate well.
 Iris (controls amount of light entering the eye)
 Humors
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Aqueous Humor (nutrition, waste removal, occupy space)
Vitreous Humor (occupies space)
Retina
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Composed of ten layers, mostly nerve tissue
Photoreceptors: rods & cones (convert light to nerve impulses)
Black in colour (melanin - absorbs light and prevents
reflection
Rods - black and white vision
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make up majority of retina in domestic animals
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Very sensitive to light,
Night vision
Cones - colour vision
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High concentration in birds
Day vision
Chemistry of Vision
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Light causes biochemical reactions in the rods and cones
Rhodopsin  Light sensitive chemical in rods, Vitamin A
derivative; Deficiency = Night Blindness
Adaption to Varying Light
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Autonomic Visual Reflexes
Rhodopsin
Tapetum
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Light reflecting layer of cells of the inner choroid
Present in cats, dogs, horses, and ruminants in varying degrees
Allow photoreceptor cells to be re-stimulated from same light
Causes eyes to glow in the dark  eyeshine
Field of Vision
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More lateral eyes, larger field of vision (herbivores)
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More forward placed, better depth perception
(binocular vision)  carnivores
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Gives greater protection from predators
All domestic animals have some degree of binocular vision
directly in front of them
Eyeball Movement
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Skeletal muscles innervated by Cranial nerves
Up/Down, Side/Side, Rotational, Inward (Retraction)
Accessory Structures
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Conjunctiva
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Pre-corneal film
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mucous membrane lining the inner surface of the eyelid and the exposed
surface of the eyeball
Three Layers
 Mucin  lubrication, lysozyme, digests bacterial walls, wetability, surface
tension
 Lacrimal  tear secretions, hydration
 Oily  reduces evaporation, surface tension
Eyelid
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Protect Eye
Upper and Lower folds of Skin
Lateral and medical corners are called canthus
Third Eyelid (also called nictitating membrane)
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Found in domestic animals
T-Shaped plate of cartilage covered by conjunctiva on medial side of eye
Eyelashes also protect eye
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Camels have long eyelashes to keep sand out of eye.