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
Cochlear duct houses
The cochlear duct houses the sensory cells called the Organ of Corti
Houses hair cells
The receptors for hearing
Have cilia (hairs) on their surface and nerve endings at their base
The hair cells are covered by a gelatin-like tectorial membrane
Sound perception
Sound waves (changes in air pressire) cause the tympanic membrane and the ossicles of the middle ear to vibrate
Loud sounds cause greater displacement of the membranes than soft sounds
As the stapes vibrates back and forth it pushes and pulls on the membrane covering the oval window of the cochlea
Vibrates the fluid surrounding the cochlear duct
Vibrations are transferred to the organ of Corti
This bends the sensory hairs
Generates nerve impulses that travel to the brain via the vestibulocochlear nerve (CN VIII) and are interpreted as sound
Different frequencies are felt at different locations along the organ of Corti so the brain differentiate frequencies
Partly due to the different lengths of the ‘hairs’ on the hair cells.
The slight asymmetry to ears helps localize sound better
Equilibrium sensors
Receptors are in portions of the inner ear called the vestibule and semicircular canals
Sensory inputs also come from proprioceptors and vision
Conflicting signals from vision and vestibular system cause motion sickness.
Vastibule
Static Equilibrium
Usually gravity to determine position on a linear plane (like walking)
Part of the inner ear between the cochlea and the semicircular canals
Gelatinous matrix containing crystals of calcium carbonate, called otoliths, sits above hair cells in a path of equilibrium
Tilting the head shifts the otoliths due to the pull of gravity, which bends the cilia on the hair cells
Generates nerve impulses which are sent to the brain
2 sacs of vestibule
Made up of 2 saclike spaces
Utricle
Saccule
Semicircular canal of inner ear
Dynamic Equilibrium
Consists of three semicircular canals, at right angles to each other
Sense head rotation by their different planes of orientation:
Horizontal
Frontal
Sagittal
Work like the vestibule but there are no otoliths
Hair cells occur in patches
The hairs stick up into a gelatinous, free-floating structure which moves with the fluid in the canals
As the head rotates the fluid lags due to inertia
Causes the sensory hairs to bend, generating nerve impulses which are sent to the brain
Nystagmus normal position
Normal (Positional)
Jerky movement of the eyes that occurs when the head is rotated from side to side
During head rotation, the eye moves slowly in the opposite direction, remaining “fixed” on a stationary object
After the head has rotated a considerable distance, the eyes move rapidly in the direction of rotation and then become fixed again
Abnormal nystagmus
Nystagmus when there is no head movement
Slow and fast phases (like positional)
Usually in the horizontal plane
Seen during certain stages of general anesthesia and with vestibular disease
Animals with vestibular problems also have head tilt and circle or fall (may even roll) in one direction
Pendular nystagmus is a lifelong condition of minor significance
The eye is
Organ of sight: consists of the eyeball and its accessory structures
Vision
Electromagnetic stimulus is used to generate an image that is transmitted to the brain
Cornea is
transparent anterior part that lets light into the eyeball
No blood vessels, but lots of sensitive nerves
Very painful to have a scratch!
Becomes opaque if it dries out or becomes edematous
Sclera is composed of
- the white of the eye
Gives shape and protects the inner structures
The limbus is
The junction of the cornea and sclera
Choroid is
pigment and blood vessels between sclera and retina
Some species have a reflective tapetum
Allows light to bounce back through the retina a second time for better night vision
Not in pigs or humans
Iris is
colored, donut shaped part of eye
pupil is
central opening of iris which lets light in, can constrict or dilate to regulate light entry
Ciliary body is and does what
holds and helps focus the lens
Muscles of the ciliary body attach by processes to the lens
Focuses the lens by contraction or relaxation of the ciliary muscle
Produces aqueous humor that fills the eye
Retina is and does
functions to collect image
Contains the photoreceptors, rods and cones
optic disc is and does
origin of optic nerve, which goes to the brain to interpret visual images
Optic disc is the point at which the nerve leaves the eye to transmit visual information to the brain
Has no photoreceptors, so any light hitting it will not contribute to the image
Creates a blind spot in vision
Normally the brain fills in the gap in detail
The artery and vein also enter and leave the eye at this point
Aqueous compartment is
between cornea and lens. Subdivided into a large anterior chamber in front of the iris and a small posterior chamber between the iris and the lens.
Filled with a clear watery fluid called aqueous humor that is produced by the ciliary body
Fluid circulates through aqueous compartment then is reabsorbed into blood stream
Excess accumulation of fluid= high intraocular pressure
Primarily responsible for maintaining internal pressure of the eye
Vitreous compartment
located between lens and retina
Filled with a jelly-like substance called vitreous humor
Maintains the shape of the eye and holds the retina in place
Lens of the eye
Soft, transparent, elastic, biconvex
Composed of layers of tiny protein fibers
Lacks blood vessels and nerves
Accommodation- ciliary muscles adjust the shape of the lens to focus light on the retina depending on distance of images
Ciliary muscles are contracted for close-up vision- test them by looking at a distance objects to prevent eye strain
Retina of the eye
Innermost sensory layer of the eye
Composed of several layers of cells
The actual photoreceptor cells are near the outside (towards the choroid)
The inner layer is nerve fibers that converge on the optic disc to form the optic nerve
The surface of the retina is sometimes called the FUNDUS of the eye
Photoreceptors two types and do what
Rods: function well in dim light, but do not detect color and have poor sensitivity to detail
Cones: function well in bright light, see color, and have excellent sensitivity to detail
-Our domestic animals have few cones. Therefore, they see washed-out colors with poor detail
-Macula/fovea in primates- high density of cones allows precise vision
Formation of a visual iamge
Refraction is the bending of light rays as they pass from one medium to another at an oblique angle
Occurs in the eye to focus light on the retina
Air → cornea → aqueous humor → lens → vitreous humor → RETINA
Cornea most important refraction point
Image is upside down- the brain interprets it as right side up!
Visual pathway
Impulses form the retina travel on the optic nerves (CN II) and merge at a place in the brain called the optic chiasm
Some fibers cross over to the other side of the brain
Others continue to the same side
Processing of image form different sides on the same part of the brain allows for stereoscopic (biocular) vision
The visual image is and why are they that way
The visual image may be 2-dimensional, or 3-dimensional
Depends on the field of vision
Need binocular vision to see 3-D images
Predatory animals tend to have good binocular vision
Allows them to stalk and calculate distances for attack
Prey animals tend to have a narrower area of binocular vision
Instead, emphasis is on wider RANGE of vision, even if it is monocular
Conjunctiva is and does what
Special mucous membrane lining eyelid and eyeball
Palpebral - lines inner surface of eyelid
Bulbar - reflection of palpebral conjunctiva onto eyeball
Blood vessels are close to the surface of the area
Checked during PE
Pale = anemia , shock
Yellow/orange = jaundice
Eyelids are and do what
Upper, lower, and third
Lateral junction
Lateral Canthus
Medial junction
Medial canthus
Meibomian (tarsal) glands line the lid margins
Secrete waxy substance to contain tears in eye
Can become plugged and enlarge, or may become cancerous
Can sometimes relieve plugging with hot compresses or by pulling associated eyelash
Third-eyelid is and does what
Third eyelid (nictitating membrane) - fold of conjunctiva, reinforced by T-shaped cartilage located at medial canthus of eye between upper and lower eyelids and eyeball.
retraction of eyeball, by muscle or pressing on the eyeball, causes the 3rd eyelid to passively move across the cornea to protect it
Lacrimal apparatus is ad does what
Group of structures that produce and drain tears
Lacrimal glands - pink glands located on dorsolateral aspect of eyeball,
Releases tears onto surface of eye
Tears are made from what layers
Inner mucous layer: from the conjunctiva
Has antibacterial substances to fight infection
Middle tear layer: from the lacrimal glands
Moisturize the cornea
Outer oily layer: from the tarsal glands
Minimizes tear evaporation and spillage over lid
Lacrimal punctum
openings which drain away excess tears
On the upper and lower eyelid near medial canthus
Drain into the lacrimal canaliculi → lacrimal sac → nasolacrimal duct → nasal cavity
Eye muscles are
Six muscles attach to the sclera and control delicate eye movement
4 straight (rectus) muscles – on 4 sides of eye
2 oblique – dorsal and ventral
Often a 7th – the retractor bulbi which pulls the eye deeper into the socket and protrudes the third eyelid.
Entropion
An inversion of the lid margins
Eyelashes irritate the corneal and conjunctival surfaces
Ectropion
An eversion of the lid margins causing chronic conjunctival exposure
Cherry eye is and caused by
Genetic weakness in attachment of gland to third eyelid
Inflammation and/or prolapse of the accessory lacrimal land of the third eyelid and associated nictitating membrane
Common in young dogs, particularly the “droop-eyed” breeds - spaniels, basset hounds etc
Prolapse of the eye
Acute prolapse of the eye is a result of trauma and is most common in the canine and feline
An emergency
Prognosis for retention of vision is poor (50% in dogs, much less in cats) but prognosis retention of globe is good
Cancer eye
Ocular Squamous Cell Carcinoma (Cancer eye)
Most common in white faced, outdoor, animals (exposed to sun more).
White faced cattle and horses
Has a hereditary basis
Usually occurs in older animals
Tumour may originate from eyelids, conjunctiva or 3rd eyelid
The cancerous or precancerous lesions can be multiple and present in one or both eyes
Corneal ulcers
Many, MANY causes
Often start as trauma and then become infected
Often become infected, which leads to deep ulcer or ruptured cornea
Diagnosed with fluorescein stain
A corneal ulcer means the epithelium is destroyed
Shallow ulcers heal rapidly by epithelialization
Deep ulcers granulate in – needs blood vessels to grow in from limbus
Keratitis
Inflammation of the cornea with resulting edema, vascularization, scarring and pigmentation
May include ulceration of the cornea
Seen in all species because of mechanical damage, keratoconjunctivitis sicca, entropion, ectropion, and bacterial and viral infections such as pinkeye in cattle
Conjunctivitis
Inflammation and/or infection of the conjunctiva
Eyes are red, have discharge and are squinting (blepharospasm)
Common in all species
Associated with a multitude of conditions from physical irritation to bacterial and viral infection
Dry eye
Keratoconjunctivitis sicca (The disease “Dry Eye”)
Mainly seen in SA
Due to a tear deficiency
Usually results in conjunctivitis,cloudiness of the cornea (=corneal edema), corneal ulceration and/or corneal scarring
Glaucoma
Increased intraocular pressure that damages the retina and optic nerve, leading to blindness
Damages the retina and optic nerve, leading to blindness
Painful - often the only presenting complaint is a behavioural change
Genetic or secondary to other ocular disease
Cataracts
White opacity of the lens, any species
May cause blindness
Can develop in younger animals due to heredity or disease such as
Infection or trauma to the eye/lens
Diabetes mellitus
Treat through surgical lens removal (can place a prosthesis)
Lenticular/nuclear sclerosis
The lens may become opaque with age
Old fibers harden and lose transparency
Gives a blue haze to lens
Doesn’t interfere with vision much
Progressive retinal atrophy
An inherited disease complex seen in Irish Setters and Collies as young as 4-6 months and in Miniature Poodles as old as 5 years
Night blindness leading to total blindness
Otitis externa
Inflammation and/or infection of the pinna and external auditory meatus (auditory canal)
May be caused by ALLERGIES, trauma, excessive amounts of wax, moisture and hair, or the presence of ear mites
Most common in “flop-eared” breeds of dogs and in cats infested with mites
Ears are painful, itchy and “smelly”
Otitis media or/and interna
Usually progressing from otitis externa or from an infection tracking via the auditory tube from the nasopharynx
Animals exhibit head shaking, head tilt, circling and loss of balance, Horners syndrome
May lead to meningitis and death
Aural hematoma
A soft swelling of the pinna
Seen in dogs, cats and pigs
The result of trauma (bite wounds), may be self-inflicted from scratching and rubbing in association with otitis
Guttural pouch mycosis
Equine disease
Can get infected by fungi
These like to grow on the carotid artery
Can damage adjacent nerves or cause massive blood loss
