Sense organs Flashcards
Four general stimuli of sensory system
- Mechanical (touch, hearing, balance)
- Thermal (hot, cold)
- Electromagnetic (vision)
- Chemical (taste, smell)
Visceral sensations
Miscellaneous category of interior body sensations
Vague and poorly localized
Include hunger, thirst, full bladder and sexual
With hollow organs, such as those seen in the GIT, stretching causes feelings of severe pain
Many internal can be handled, cut, or crushed without perception of pain
The pleura and peritoneum have lots of sensory receptors
Touch sense
Also known as the tactile sense
The sensation of something being in contact with the body
Different types of touch sensors within the skin produce various sensations including touch and pressure (you will be mapping these receptors during physiology labs.)
We can adapt to continuous touch or pressure, so we are often unaware of it unless it changes (e.g. are you aware of the pressure of your chair against you – or of the pen in your hand)
Temp sense
Temperature receptors detect changes in body temperature and transmit this information to the CNS
Activates mechanisms to correct and maintain homeostasis
Temperature receptors may be superficial or central (thermostat)
Superficial temp
are located within the skin and detect its temperature changes
When extremes are detected, the heat or cold receptors increase impulse generation to the CNS
Impulses are recognized at a conscious level, cause a change in behavior to correct
If temperature is normal, impulse frequency is low and steady – no conscious recognition
Central temp
monitors the core temperature of the body via the blood
Receptors are in the hypothalamus (the thermostat center)
Core temperature can be assessed with a rectal thermometer
Fever
Fever (pyrogenic hyperthermia) is centrally mediated
Thermostat is set higher
Animlas shivers and vasoconsticts to raise temp
Non-pyrogenic hyperthermia is the result of exertion or teh envirpnment
Animal tries to cool to compensate
panting and weating
Can be much higher temps than in fever
Monitoring both superficial and central temp
allows the CNS to correct fluctuations through changes in:
Blood flow to skin and extremities
Sweating/panting
Hairs standing up (piloerection)
Shivering
Hormone production of the thyroid
Behavior e.g. huddling in piglets and puppie
Heatstroke
Is shock due to severe hyperthermia caused by a hot external environment or exertion.
Body initially tries to compensate by losing heat
Shock is due to fluid loss, vasodilation and direct heat damage to organs.
High temperatures can also directly impair brain function (weakness, convulsions and unconsciousness may occur).
Many species have mechanisms to cool blood supplying brain for extra protection
Maximum survivable temp above normal is about 5˚C
Hypothermia
Subnormal body temp
Often a problem during/ following anesthasis
especially in smaller animals
Causes decreased HR, RR, weakness, confusion, coma and death
pain is
Pain receptors (nociceptors) are the most abundant and widely distributed sensory receptors
The only place on the body where they are not found is within the brain
Headaches are caused by swelling of surrounding tissues including the dura mater or spasms in the muscles of the face, scalp and neck
Are simple nerve endings whose purpose is to alert the body to prevent further damage to body
Sensitive to all types of stimuli
The process of pain perception
Transduction
Transmission
Modulation
Perception
Trasnduction
conversion of stimuli into a nerve impulse (nociceptor)
Example - can increase sensitivity of pain receptors (e.g. sunburn)
Transmission
moves signal up the axon of the sensory nerve fiber
Example - local block of peripheral nerve (e.g. declaw block)
Modulation
information is integrated at level of spinal cord
Example - analgesics like opioids (alter transmission of pain signals)
Perception
pain is processed by the brain
Example - General anesthesia – alters consciousness
Pain can be classified
Superficial (skin and subcutaneous areas), deep (muscles and joints) or visceral (internal organs)
Note that visceral pain is often ‘referred’, or interpreted by the body as originating from somewhere else
Example in humans is how heart pain is often felt down the left arm
In dogs is when a ‘pinched nerve’ in the neck causes them to hold up a front leg
Happens because a neuron in pain center can receive inputs from nerves from different parts of the body so → confuses location where pain si coming from
Acute (sharp and intense) or chronic (dull and aching)
Animals do not worry about pain
The amount of pain an animal feels is affected by
The amount of pain an animal feels in various situations is difficult to determine by simple observation
May be due to the survival instinct
An animal that show signs of weakness may be signaling others, including predators, to attack
Threshold for pain varies from species to species and between individual animals
Sensation of pain is often much greater if the pain is anticipated
Animals that tend to be high strung and more excitable are less able to endure pain
Animals that are more complacent and easy-going react less intensely to the same painful stimulus
Diverting the animal’s attention reduces pain perception
Twitching a horse’s lip
Tapping on a cats frontal bone
Watching TV!
Interestingly, pain receptors do not diminish their signal of the sensation, and may even continue to signal pain once the source has been removed
Proprioception
Also called body sense
Sensory receptors are located within the skeletal muscles, tendons ligaments and joint capsules
Generally stretch receptors keep track of the amount of tension on each area
Cerebellum creates the overall sense of position by integrating the info
Coordinates movement – aligns intent with actual position
Test assessing knuckling response, observing for ataxia
Taste is
Also called gustatory sense
Detected by chemoreceptors on the tongue and lining the mouth and pharynx.
Receptors occur in groups called taste buds
Most are located on the tongue in elevated structures called papillae
Have tiny openings called taste pores
Allow substances that are dissolved in saliva to stimulate sensory cells
Send impulses to taste centers in brain
Linked to smell
Helps animals select foods that contain nutritional substances that are required for health
Smell is
The olfactory sense
Carried by cranial nerve I, he olfactory nerve
Very important for animal communication
Olfactory cells act as chemoreceptors
Organized in 2 patches of olfactory epithelium found high in the nasal passagesCombination of olfactory cells and supporting epithelium
Covered with a layer of mucus
“Sniffing” brings the odor molecules deeper and higher into nasal cavity
Odor molecules dissolve in mucus and contact the sensory processes of the olfactory cells
Generate an electrical signal
Each olfactory cell is a neuron specialized to detect a specific chemical
Helps us to differentiate smells
Doesn’t require very many molecules of the substance to stimulate the receptors
Receptors can adapt, so sensitivity to an odor decreases over time
Remain sensitive to new odors
Vomeronasal organ
A diverticulum of the nasal cavity into the hard palate
Olfactory receptor there are sensitive to pheromones
Especially important for reproductive signaling and behaviour
Sensation from the vomeronasal organ relayed to the cerebral cortex and the hypothalamus
Incisive papilla leads to incisive ducts than into vomeronasal organ
Flehmen response
Hearing is
Also called auditory sense
Aural refers to the ear
Mechanical sense (rather than chemical sense)
Converts air vibrations into nerve impulses, which are interpreted by the brain as sound
Equilibrium
The sense of balance
Mechanical sense
Outer ear is and pinna
Extends from the exterior to the eardrum
Pinna - fleshy part of ear
Functions to catch sound
Cartilage covered with skin
Very mobile
Varies widely depending on species and breed (especially in dogs)
External auditory canal
Transmits sound
Soft membrane-lined passageway from pinna to eardrum
In most domestic species, it is a L-shaped tube
Has a vertical and horizontal component
Ends blindly at the eardrum or tympanic membrane
In some dog breeds, like poodles, it can be full of hair
Has ceruminous glands which secrete wax – protects against infection
Tympanic membrane
(eardrum) - thin, semitransparent membrane
Tightly stretched across the opening between the external auditory canal and the middle ear cavity
Thin and delicate
Vibrates with the same frequency as sound waves that strike it.
Middle ear
Transmits and amplifies sound
A hollowed-out area of the temporal bone, lined by soft tissue membranes
Separated from the external ear by the tympanic membrane
Separated from the inner ear by the membranes of the oval and round windows of the cochlea
Filled with air
Connected to pharynx by the EUSTACHIAN or AUDITORY tube
Sympathetic fibers of middle ear
Middle ear infections can cause Horner’s syndrome
Signs are
Ptosis
Miosis
Enophthalmos
Auditory ossicles
a system of levels that transmit and amplify sound vibrations of the tympanic membrane to the cochlea
Malleus (hammer) - attached to the tympanic membrane
Incus (anvil) – forms synovial joints to link other 2 bones
Stapes (stirrup) - attach to membrane of the oval window of the cochlea (don’t MISs the order)
Eustachian tube
(auditory tube) functions to equalize pressure on both sides of the tympanic membrane, protecting it from rupture
Ears pop when changing altitude- air moving through auditory tube
Swallowing or yawning opens auditory tube allowing air to middle ear and equalizes pressure
Guttural pouch
diverticulum of auditory tube found in equine only
Large, air-filled space
Dorsocaudal to the nasopharynx
Contains a branch of the carotid artery
A heat regulation device to cool the horse’s brain during exercise
CN VII and IX to XII pass along the wall of the pouch
Inner ear is and the three parts
Functions as site where hearing and balance is sensed
Three parts
Cochlea (hearing)
Vestibule (equilibrium)
Semicircular canals (equilibrium)
Cochlea
The cochlea contains a tube called the cochlear duct, filled with a fluid(endolymph)
The duct divides, but does not fill, the bony cavity.
There is a fluid filled channel on either side of the cochlear duct.
The two arms communicate at the apex to form a U shaped tube
The U-shaped tube has 2 openings – one at either end, both covered by membranes:
The oval window attaches to the staoes
The round window bulges in and out as fluid moves within the U-shaped tube
