3.2 Sense Organs (Book)
How might examination of the bulbar and palpebral portions of the conjunctiva be useful as part of the overall physical examination of an animal? 10-7
The transparency of the conjunctiva allows the underlying tissues to show through, so it can be used as a window to see the blood vessels that are hidden elsewhere in the body by opaque structures, such as the skin. By looking through the conjunctiva at the lining of the eyelid, we can often detect abnormalities such as anemia (pale color caused by decreased blood flow), jaundice (yellowish color), and cyanosis (dark purplish color).
What are the two most important senses in birds? 21-4
vision and hearing
Where are the bird's ears located? 21-4
A bird's ears are located on the sides of its head, behind and slightly below its eyes.
tympanic membrane
eardrum connect-tissue membrane
Describe the structure and function of the components of the ear.
external ear: funnel to collect sound wave vibrations and direct them to eardrum middle ear: amplifies and transmits vibrations from eardrum to inner ear inner ear: contains sensory receptors that convert mechanical vibrations to nerve impulses along with receptors for equilibrium sense most ear structures are housed w/in temporal bone of skull lined with soft tissue membranes
3 major layers of the eye
fibrous layer: outermost. fxn: admits light to interior and gives strength and shape to eye - consists of cornea and sclera (limbus = conjunction b/w the two) vascular layer (uvea): middle layer - consists of choroid, iris, ciliary body nervous layer: retina. image sensor in camera of eye. contains sensory receptors for vision
layers of the retina
from outside in... pigment layer photoreceptor layer bipolar cell layer ganglion cell layer nerve fiber layer
List and describe the visceral senses.
hunger and thirst: detect deficiencies in nutrients and water hollow organ fullness: have stretch receptors
conus papillaris
in lizards; analogous to avian pecten extends into vitreous humor from optic disc and involved in providing nutrition and removing waste from eye
Describe the origin of tears and explain how tears flow onto and drain from the eye.
lacrimal apparatus: includes structures that produce and secrete tears, and structures that drain tears away from surface of eye. - tears produce by lacrimal glands and accessory lacrimal glands of third eyelids - several small ducts from each gland deposit tears into dorsal conjunctival sacs; tears wash down over eyes, aided by blinking movements of eyelids drainage: - two openings (lacrimal puncta) in upper and lower eyelid margins drain tears away from surface of eye - tears flow down ducts to lacrimal sacs --> then to nasolacrimal ducts --> nasal cavity * why you sniffle when your eyes water
Describe the structure of the taste buds
majority are on sides of papillae tiny, rounded structures made of gustatory cells and supporting cells taste pores allow dissolved substances to enter taste buds and contact sensory receptors chemical substances dissolved in saliva come into contact with receptors; nerve impulses are generated and travel to brain to be interpreted as tastes
hearing in nocturnal owls
operculum: fleshy flap of skin at each external ear opening that helps funnel sound into ears ears are asymmetric to help with vertical location of sound large eardrums, columellae, and cochleas; well-developed acoustic center in hindbrain
pinna
outer ear flap fxn: collects sound wave vibrations and directs the into external auditory canal
nociceptors
pain receptors most widely distributed sensory receptors inside and on surface of body alert CNS to potentially harmful stimuli NOT found in brain
Where is aqueous humor produced? Where is it drained from the aqueous compartment of the eye? 10-6
posterior chamber by cells of the ciliary body. It is drained by the canal of Schlemm, and the fluid is returned to the bloodstream. The canal of Schlemm is a ringlike structure located at the edge of the anterior chamber at the angle where the iris and the cornea meet.
What is nociception and what roles do transduction, transmission, modulation, and perception play in it? (10-1)
process of experiencing pain. 1. Transduction is the conversion of the painful stimulus to a nerve impulse that occurs at the sensory nerve ending. 2. Transmission of the nerve impulse up the sensory nerve fibers to the spinal cord is the next step. 3. Modulation (changing) of the sensory nerve impulses can occur in the spinal cord, and this can significantly influence the information the brain receives, particularly in cases of chronic and/or severe pain. This modulation process can amplify (make more severe) or suppress (make less severe) sensory impulses through synapses between neurons in the dorsal horns of the spinal cord. 4. perception of the painful impulses by several areas of the brain occurs. Conscious perception occurs in the cerebral cortex, but other areas of the brain are also involved. These include areas involved with the autonomic nervous system (fight or flight), fear and anxiety, memory, arousal, and behavior and emotion.
avian cornea
protected by 3 eyelids - upper - lower - nicitating membrane (3rd eyelid)
formation of a visual image
refraction: bending of light rays that occurs as rays pass into medium of different optical density, which affects speed of light transmission refractive media: cornea, aqueous humor, lens, vitreous humor - cornea does most of the work
rods and cones
rods: thin sensitivity to light: high sensitivity to detail: low sensitivity to color: absent - produce a somewhat coarse image in shades of gray - main receptors for low-light conditions cones: thick sensitivity to light: low sensitivity to detail: high sensitivity to color: high - do not fxn well in dim light - perceive color and detail
proprioception
sense of body position and movement operates at subconscious level vet testing "righting reflex"
visual spectrum in birds
wide spectrum of light wavelengths - many species can see UV light
The cornea and sclera are both made up substantially of collagen fibers. Why is the cornea transparent, but the sclera opaque? 10-5
The cornea contains no blood vessels, and the amount of water it contains is carefully controlled
What is the main refractive structure of the eye? Why? 10-6
The cornea is the main refractive structure because of its curvature and the extreme difference between its optical density and that of the air in front of it
What is the function of the iris? 10-5
The iris controls the amount of light that enters the posterior part of the eyeball. The pupil enlarges in low light conditions and gets smaller in bright light.
Why is the optic disc the blind spot of the eye? 10-6
The optic disc contains only nerve fibers and a few blood vessels but no photoreceptor cells, so no visual images are formed there.
How is the physical concept of inertia important to the functioning of the semicircular canals? 10-4
When the head moves in the plane of one of the semicircular canals, inertia causes the endolymph to lag behind the movement of the canal itself. The relative movement of the endolymph pulls on the cupula, which bends the hairs. This generates nerve impulses that give the brain information about the rotary motion of the head.
importance of hearing in birds
- finding food - hiding from predators - defending territories - communication amongst flock
Photoreception in birds
- have rods and cones similar in fxn to that of mammals - nocturnal birds have more rods than cones for night vision
avian vision
- optic lobe takes up majority of midbrain - large portion of skull devoted to housing and protecting eyes
How is the functioning of the vestibule and the semicircular canals similar? How is it different? 10-4
. Both have endolymph- and perilymph-filled structures. The crista of the semicircular canals is similar to the macula of the vestibule. Both have supporting cells and hair cells with their processes (modified dendrites) sticking up into a gelatinous structure. However, there are no otoliths in the semicircular canals to weigh down the cupula. Instead, it functions as a float that moves with the endolymph in the membranous canal. Whereas the vestibular system senses rotary motion of the head with the semicircular canals, the vestibule senses linear motion and position of the head
How would arthritis in the tiny joints of the ossicles affect hearing? Could this possibly affect the hearing of older animals? 10-3
. Yes, arthritis could affect hearing in older animals. Arthritis could decrease the conduction of sound waves from the tympanic membrane to the oval window. The force of the vibrations would be decreased and the animal's hearing might be impaired.
List the four general types of stimulus that can trigger a response from sensory receptors.
1. mechanical (touch, hearing, balance) 2. thermal (hot and cold) 3. electromagnetic (vision) 4. chemical (taste and smell)
anatomical features responsible for bird's visual acuity
1. retina is lightly vascularized - decreases interruption of image reaching back of eye 2. retina packed with photoreceptor cells (more image clarity) 3. connection b/w photosensitive cells and nerve fibers - each cone has single connection with bipolar nerve cell (individual representation in the brain)
Sense of touch in birds
2 types of sensory nerve endings grandry's corpuscle: located in tongue and palate of many species that dig for food herbst corpuscle: located in areas of mouth, palate, mouth folds of young birds; cloaca, legs, wings, uropygial gland and bases of many feathers
general structure of avian eye
3 layers of tissue: - fibrous tinuc (outermost): sclera and cornea (formed by small ring of bones call sclerotic ring - uveal tunic (middle): vascular, pigmented. consists of choroid, iris, ciliary (striated) muscles - neural tunic (innermost): consists of retina (photreceptor cells and neural cells that transmit light images to brain pecten: highly vascular, ribbonlike structure attached to retina - floats in vitreous humor in direction of lens and distributed nutrition to eye
How does the tapetum aid low-light vision? 10-5
After light has passed through the photoreceptors (the rods and cones) in the retina, it reflects off the tapetum and passes back through the photoreceptors again, stimulating them a second time. Therefore, most animals can see better in dim light than we can
Why do you suppose mild to moderate pain often does not appear to affect the mood or behavior of domestic animals significantly? (10-1)
Animals do not seem to have the same kind of emotional reaction to pain that humans do. They often seem to hide it well. Hiding signs of pain is a survival instinct for most animals. An animal that shows signs of pain is showing signs of weakness that might encourage other animals, including predators, to attack it.
how are the senses of taste and smell similar? how are they different? (10-2)
Both are chemical senses. Whereas many nonhuman animals have less perceptive eyesight but a highly acute sense of smell, humans have a less perceptive sense of smell and a highly acute sense of taste.
Describe the structure and function of the components of the eyeball.
Components: eyelids: covers cornea: "window" that admits light to interior of eye. pain receptors make it one of the most sensitive tissues in body sclera: white of eye. makes up majority of eye's fibrous layer choroid: consists of pigment and blood vessels that rupply retina. forms highly reflective area in rear of eye (tapetum lucidum) iris: colored part of eye. pigmented muscular diaphragm that controls amt of light enters posterior part of eyeball pupil: opening in center of iris. enlarges in low-light conditions and gets smaller in bright light. consists of radially arranged fibers and circulatory arranged fibers ciliary body: ring-shaped, located immediately behind iris. contains tiny muscles that adjust shape of of lens to allow near and far vision retina: inner nervous layer that lines back of eye. contains rods and cones - where image is formed, sensed, and converted to nerve impulses that are decoded in the brain - lines most of vitreous compartment lens: soft, transparent; made of microscopic fibers arranged in layers - elastic and biconvex. lies between aqueous humor and vitreous humor - helps to focus a clear image on retina (with help of muscles of ciliary body) optic disc: where nerve fibers leave eye to form optic nerve. contains only nerve fibers and a few blood vessels but no photoreceptor cells - blind spot of the eye optic nerves: carries visual information to the brain
How might repeated exposure to loud sounds lead to progressive hearing loss? 10-3
Everything up to the generation of an auditory nerve impulse by the hair cells (sensory cells) in the organ of Corti of the cochlea involves movement: the tympanic membrane, the ossicles, the round and oval windows, the endolymph and perilymph in the cochlea, the tectorial membrane, and the microvilli of the hair cells. Loud noises cause exaggerated movements of all those structures. In the short term, irreparable damage rarely results. Over long periods of time, however, loud noises can cause damage to these mechanical structures that the body may not be able to fully repair. Some examples might include damage to the microvilli of the hair cells, thickening or displacement of the tectorial membrane, thickening of the membranes covering the round and oval windows, and damage to the delicate joints between the bony ossicles.
Which type of vision requires more muscular effort: close-up vision or far-away vision? Why? 10-6
For close-up vision, the ciliary muscles must contract to take tension off the suspensory ligaments
An animal has an area of inflammation located at the dorsal limbus of its right eye. Where is the lesion located? 10-5
If the iris is compared with the face of a clock, this lesion would be at approximately 12 o'clock, at the junction of the cornea and the sclera (white) of the eye.
If the medial rectus muscle of an animal's eye was damaged and lost its ability to contract, what would the effect be on the positioning of the affected eye? Why? 10-7
If the medial rectus muscle were unable to contract, the pull of the lateral rectus muscle would cause the eyeball to deviate (move abnormally) laterally. Also the animal would not be able to rotate that eyeball toward the midline, because this muscle originates from a small area around the optic canal and fissure and inserts on the medial side of the sclera (near the 9 o'clock position if you are standing in front of the animal).
How would an animal with a plugged nasolacrimal system appear? Why? 10-7
If the nasolacrimal system were plugged, tears would be "spilling" out of the eyes because they would have nowhere to drain
Why would keen hearing be important to the survival of a potential prey animal? Why would it be important to a predator? 10-3
Keen hearing allows a potential prey animal to hear movements caused by its predator and escape. Keen hearing allows a predator to hear the slightest movements made by its potential prey so that it can track and find it.
An animal can intentionally blink its eyelids. Can it intentionally cover its eye with its third eyelid? Why or why not? 10-7
No muscles attach to the third eyelid. Its movements are entirely passive.
What is the difference between ossicles and otoliths? 10-4
Ossicles are small bones in the middle ear that conduct sound waves from the tympanic membrane to the oval window of the cochlea. Otoliths are tiny calcium carbonate stones in the vestibule that respond to gravity to provide information about the position of the head.
What are otoliths and why are they important to the equilibrium sense? 10-4
Otoliths are tiny crystals of calcium carbonate in a gelatinous matrix that covers hair cells and supporting cells of the macula. The hair cells are similar to the hair cells of the organ of Corti in the cochlea. Gravity causes the otoliths and the gelatinous matrix to put constant pressure on the hairs as long as the head stays still. Movement of the head bends the sensory hairs, which generate nerve impulses that give the brain information about the position and linear movement of the head. Otoliths are important to the sense of equilibrium because information sensed by the vestibule (which contains the otoliths) regarding linear motion and head position is integrated with information about rotary motion of the head gained by the semicircular canals so that the brain can form a picture of what is happening to the animal's head, and by extension, to its body as a whole. Together, the vestibule and semicircular canals provide the total picture of equilibrium to the brain.
List and describe the processes that contribute to nociception.
Process of experiencing pain; includes 4 processes 1. transduction: conversion of pain stimulus to nerve impulse, which occurs at sensory nerve ending 2. transmission: nerve impulse in transmitted up sensory nerve fibers to spinal cord 3. modulation: changing of sensory nerve impulses - can occur in spinal cord; can significantly influence information brain receives (esp. with chronic or severe pain) - can suppress of amplify sensory impulses through synpases between neurons in dorsal horns on spinal cord - can be influenced by several different classes of drugs 4. conscious perception: by several areas of brain - conscious perception occurs at cerebral cortex but other areas are involved (areas involved with autonomic nervous system, fear/anxiety, memory, arousal, behavior, emotion)
Why is the proprioceptive sense so important to the maintenance of balance and an upright posture? (10-1)
Proprioception allows animals to perform such basic functions as procuring food and escaping danger so they can survive. Maintenance of balance and an upright posture is essential to these activities
Which layer of the eyeball contains the photoreceptors? 10-5
Retina (the inner nervous layer)
What kind of vision do the rods in the retina perceive? What do cones perceive? 10-6
Rods are more sensitive to light than cones, but they produce a somewhat coarse image in shades of gray. The cones are more sensitive to color and detail than are the rods, but they do not function well in dim light. So rods are the main receptors for dim light vision, and cones perceive color and detail.
How would the rupture or perforation of an eardrum affect hearing? 10-3
Rupture or perforation of an eardrum would decrease the tension of the structure. This would decrease the force of the vibrations that move along the ossicles to the inner ear, impairing hearing.
How would an animal probably feel if they had a middle ear infection that caused the opening of the Eustachian tube to swell closed? 10-3
The purpose of the eustachian tube is to equalize the air pressure on the two sides of the tympanic membrane. With an infection that closes it off, this could not happen and would cause pain as the membrane bulges in and out, because the tympanic membrane has many pain receptors.
What is the basic cause of motion sickness? 10-4
There is a disagreement among the sensory receptors for the vestibular system, eyes, and proprioception, which can result in the unpleasant sensations of motion sickness, such as headache, nausea, and vomiting. The eyes look around the interior of the vehicle and see that nothing is apparently moving, but the equilibrium receptors and proprioceptors detect motion.
why do nonhuman animals often greet each other by sniffing? (10-2)
They live in more of a smell-oriented world. They communicate and understand information by their sense of olfaction. For example, dogs obtain a huge amount of information from sniffing the air or an object where other animals have been.
Why do touch and pressure sensations fade so rapidly from the conscious mind unless they change or are severe? (10-1)
Touch and pressure sensations are not threats to the well-being of the animal and tend to fade from the conscious mind, allowing the CNS to focus on other more important sensations.
Why are visceral sensations important to the survival of an animal? (10-1)
Visceral sensations keep the CNS informed about the overall prevailing conditions inside and outside the body. The result is the initiation of behaviors designed to ensure the well-being of the animal.
major compartments of the eyeball
aqueous: in front of lens and ciliary body - contains clear, watery fluid called aqueous humor - humor constantly being drained and produced. produced by cells of ciliary body - drained by canal of schlemm and fluid is returned to bloodstream vitreous: behind lens and ciliary body - contains clear, gelatinous fluid called vitreous humor posterior chamber: space behind iris and in front of lens anterior chamber: space in front of iris and lens
extraocular muscles of eye
attach to sclera fxn: hold eyes in place and delicately and accurately move them in humans... - 4 straight muscles (rectus muscles -- dorsal, ventral, medial, lateral) - 2 oblique muscles (dorsal and ventral oblique muscles) many animals have 7th ocular muscle called retractor bulbi
why is "bird brain" inaccurate?
avian brain is large in proportion to body size vision and hearing centers are relatively large - taste, touch, smell are relatively small
Which category of temperature receptors is most critical to the long-term survival of an animal in very hot or very cold environmental conditions: the superficial receptors or the central receptors? (Hint: Which is more critical to an animal's survival—keeping its skin and extremities from getting too hot or cold or keeping the core of its body from getting too hot or cold?) (10-1)
central receptors
The nasolacrimal duct system is absent in what order of reptiles? 22-3
chelonians
inner ear
cochlea: spiral-shaped
Describe the structure of the conjunctiva and eyelids.
conjunctiva: thin, transparent membrane that covers front portion of eye and lines interior surface of eyelids - bulbar covers eyeball; palpebral covers eyelids (space between the two is called conjunctival sac fxn: allows underlying tissues to show through so we can see blood vessels that are hidden elsewhere in body by opaque structures eyelids: upper and lower folds lined by thin, moist conjunctiva - corners: lateral and medial canthi - tarsal glands (dots allong eyelid margin): produce waxy substance that helps prevent tears from overflowing onto face - third eyelid (nicitating membrane): located medially b/w eyelids and eyeball. T-shaped plate of cartilage covered by conjunctiva. contain lymph nodules and accessory lacrimal (tear-producing) gland. no muscles; passive movement
middle ear
contains ossicles (small bones) malleus (hammer): outermost; attached to tympanic membrane; forms synovial joint w/ incus incus (anvil): middle bone that forms joint with stapes stapes (stirrup): innermost containts eustachian tube: connects middle ear with pharynx
Which reptiles have a tapetum? 22-3
crocodilians
Describe the processes that contribute to the sense of equilibrium.
mechanical sense helps animal maintain balance by keeping track of position and movements of the head balance involves equilibrium receptors and eyes and proprioceptors around body receptors: vestibule: b.w cochlea and semicircular canals. made of two saclike spaces (utricle and saccule) filled with endolymph fluid - macula: sensory epithelium. - gravity causes otoliths and gelatinous matrix to put constant pressure on hairs as long as head stays still. movement of head bends sensory hairs which generates nerve impulses that give brain info about head position - linear motion semicircular canals: on other side of vestibule from cochlea - ampulla contains receptor structure (crista ampullaris) - when head moves in plane of one of semicircular canals, inertia causes endolymph to lag behind movement of canal itself - generates nerve impulses that give brain info about motion of head, particularly rotary motion -
what is the temperature sense?
monitoring half of body's temp control system receptors detect increases or decreases in body temperature and transmit information to CNS; CNS can activate mechanisms to correct conditions such as hypothermia or hyperthermia
glands in the reptile eye
most posses lacrimal glands and harderian glands both produce secretions that combine to form tear film
globe and intraocular structures in reptiles
most possess scleral bones (ossicles) which help eye maintain shape and provide protection from trauma lens is more fluid in chelonians. lens is squeezed through pupil lens is more rigid in snakes and ciliary bodies are very closely associated with root of iris. lens moves back and forth as result of pressure change within aqueous and vitreous humors all reptiles have avascular retinas. all nutrition and waste removal is performed by choroidal vessels or modified vessels that protrude into vitreous humor
importance of superficial and central temperature receptors
nervous system can initiate corrective actions if things become too hot or cold: - sweating - shivering - piloerection (hair standing up) - thyroid hormone production can also initiate actions for animal to correct temperature: - seeking shade - seeking out warmth Goal: bring body temperature back to a balance
periocular structures in reptiles
nictitans (third eyelid): well-developed and mobile in variety of species spectacle/brille: in snakes and some species of lizard; clear, fused scale that covers and protects eye most reptiles have poorly-developed extraocular muscles making the globe relatively immobile
avian ear anatomy
on sides of head, behind and slightly below eyes 3 chambers: external: funnels sound to eardrum. often protected by auricular feathers. separated from middle ear by tympanic membrane middle: consists of single boned (columella) which connects to inner ear and acts as funnel to transmit sound - cochlear window located adjacent to where columella connects with inner ear (protects inner ear from pressure damage) inner: fxns to maintain balance and equilibrium (labyrinth) and converts sound waves into nerve impulses sent to the brain (cochlea)
If a dog walks out of an air-conditioned house and lies in the sun on a hot summer day, which of its temperature receptors will signal the brain first that the dog is getting hot: superficial receptors or central receptors? (10-1)
superficial receptors
Differentiate between superficial and central temperature sensors
superficial: located in skin fxn: detect upward/downward changes in skin temperature - heat receptors increase generation of nerve impulses when temp increase, and cold receptors increase theirs when temp falls - impulses alert conscious mind central: located in hypothalamus fxn: keep track of core body temp by monitoring temp of blood
classifications of pain
superficial: skin and subcutaneous areas deep: muscles and joints visceral: internal organs acute: sharp and intense chronic: dull and aching
what is touch?
tactile sense sensation of something being in contact with surface of body
In terms of eye structures, crocs have a ___ whereas other reptiles don't
tapetum
List and describe the special senses.
taste (gustatory sense): chemical sense receptor location: in mouth on taste buds; majority on sides of papillae smell (olfactory sense): chemical sense location: 2 patches of olfactory epithelium up high in both nasal passages how it works: odor molecules dissolve in mucus and contact sensory processes, nerve impulses are generated and travel to brain to be interpreted as smells hearing (auditory sense): mechanical sense location: how it works: converts vibrations of air molecules into nerve impulses interpreted as sound vision
Which skull bone houses the middle and inner ear structures? 10-3
temporal bone
Which layer of the eyeball are the iris and ciliary body part of? 10-5
uvea
general senses
visceral, touch, temperature, pain, proprioception transmit information to CNS through peripheral and autonomic nerve fibers