A&P 2 - Ch 16 Sense Organs
Taste buds have 40 to 60 taste cells on them. Describe the anatomy of taste cells.
- Have tufts of apical microvilli (taste hairs) that serve as receptor surface for taste molecules - Taste pores: pit in which the taste hairs project - Taste cells are epithelial cells, not neurons - Synapse with and release neurotransmitters onto sensory neurons at their base
What are the actions of the extrinsic eye muscles?
- Rectus muscles move the eye up, down, medially and laterally - Superior and inferior obliques turn the "twelve o'clock pole" of each eye toward or away from the nose *for a more precise understanding, search YouTube for "Actions of the ocular muscles"
Describe some of the key characteristics of olfactory cells
- They're neurons shaped like bowling pins - head bears 10 to 20 cilia (olfactory hairs) with binding sites for odorant molecules - olfactory hairs lie in a tangled mass in thin layer of mucus - basal ends of cells become axons, which collect into fascicles, pass through cribiform foramina in ethmoid bone, and are collectively regarded as cranial nerve I
In what three ways do human pheromones affect sexual behavior?
1) A person's sweat and vaginal secretions affect sexual physiology 2) Presence of men influences female ovulation 3) Ovulating women's vaginal secretions raise men's testosterone levels
What are mechanisms of action of taste cells? What is the common end result of these?
1) Activate second-messenger systems 2) Depolarize cells directly Either mechanism results in neurotransmitter stimulation of dendrites at base of taste cell.
Describe the auditory projection pathway. *Very complicated, does not include cochlear tuning or reflex. Recommend reviewing Saladin and pray this is not tested.
1) Axons lead away from cochlea as cochlear nerve and join with vestibular nerve to form vestibulocochlear nerve (VIII). 2) First-order neurons synapse in cochlear nuclei of pons 3) Second order neurons synapse with superior olivary nucleus of pons and inferior colliculus of midbrain. 4) Third-order neurons begin in inferior colliculi and lead to thalamus 5) Fourth-order neurons complete the pathway from thalamus to primary auditory complex in temporal lobe of cerebrum
What are the two most common causes of blindness and their mechanisms?
1) Cataract - clouding of lens as lens fibers darken with age, also caused by diabetes mellitus. 2) Glaucoma - elevated pressure within the eye that applies pressure to the retina causing retinal cell death and optic nerve damage.
What three cranial nerves transmit taste sensation?
1) Facial nerve (VII) - collects taste from anterior two-thirds of tongue 2) Glossopharyngeal nerve (IX) - from posterior one-third of tongue 3) Vagus nerve (X) - from taste buds of palate, pharynx and epiglottis
What are the four types of lingual papillae and their characteristics?
1) Filiform - no taste buds, important for food texture 2) Foliate - no taste buds, weakly developed in humans 3) Fungiform - at tips and sides of tongue, has taste buds 4) Vallate - at rear of tongue, contain half of all taste buds
Provide two examples of unencapsulated nerve endings and their functions
1) Free nerve endings - for pain and temperature 2) Tactile discs - for light touch and texture
All nerve fibers of taste send sensation to the solitary nucleus in the medulla oblongata. From here, to what two destinations in the brain are signals sent?
1) Hypothalamus and amygdala - control autonomic reflexes: salivation, gagging and vomiting 2) Thalamus relays to postcentral gyrus of cerebrum - conscious sense of taste (yummy!)
What are the two categories of acceleration determined by dynamic equilibrium?
1) Linear acceleration - change in velocity in a straight line 2) Angular acceleration - change in rate of rotation
What are the three classifications of receptors?
1) Modality - thermo-, photo-, chemoreceptors 2) Origin of stimuli - extero-, intero-, proprioreceptors 3) Distribution - general v. special senses (vision, hearing, equilibrium, taste and smell)
What are the four kinds of information transmitted by sensory receptors?
1) Modality - type of sensation (vision, taste, hearing) via labeled line code 2) Location - area of the body detecting the stimulus 3) Intensity - which nerve fibers, how many and how fast 4) Duration - how long stimulus lasts
List the five primary taste sensations and the chemicals which produce them
1) Salty - metal ions (sodium, potassium) 2) Sweet - sugars, carbohydrates 3) Sour - acids, citrus 4) Bitter - spoiled foods, alkaloids, nicotine, caffeine 5) umami - "meaty" taste of amino acids, meat broth
What are the three chambers of the cochlea? Describe their relative positions and the fluids that fill them.
1) Scala vestibuli - superior chamber; begins at oval window and spirals to apex; filled with perilymph 2) Scala tympani - inferior chamber; begins and apex and ends at round window; filled with perilymph 3) Scala media (cochlear duct) - triangular middle chamber between previous two; filled with endolymph
What are the two forms of equilibrium?
1) Static equilibrium - perception of the orientation of the head when the body is stationary 2) Dynamic equilibrium - perception of motion or acceleration
What are the six extrinsic muscles attached to the surface of the eyeball?
1) Superior rectus muscle 2) Inferior rectus muscle 3) Lateral rectus muscle 4) Medial rectus muscle 5) Superior oblique muscle 6) Inferior oblique muscle
What are the three principle components of the eyeball?
1) Three layers (tunics) that form the wall 2) Optical component admits and focuses light 3) Neural component, retina and optic nerve
What are the three tunics of the eyeball?
1) Tunica fibrosa - outer fibrous layer 2) Tunica vasculosa (uvea) - middle vascular layer 3) Tunica interna - retina and beginning of optic nerve
Describe the projection pathway for somesthetic signals from below the head? (three orders of neurons)
1) first order neuron enters dorsal horn of spinal cord via spinal nerves 2) second-order neuron decussates to opposite side, ends in thallamus 3) third-order neuron terminates in primary somesthetic cortex of cerebrum
Describe the projection pathway for somesthetic signals from the head? (three orders of neurons)
1) first order neuron enters pons and medulla via cranial nerve 2) second-order neuron decussates to opposite side, ends in thallamus 3) third-order neuron terminates in primary somesthetic cortex of cerebrum
What are the two key functions of the ciliary body?
1) supports lens and iris 2) secretes aqueous humor
The olfactory mucosa contains how many olfactory cells? What kinds of cells are these?
10 to 20 million neurons.
How many odors can we distinguish on average?
2,000 to 4,000
What is the audible range of pitch for humans? *not tested
20 to 20,000 Hz. Speech is between 1,500 to 5,000 Hz
Prolonged exposure to sound above what amplitude causes hearing damage? *probably not tested
>90 dB
What are receptive fields and what is their significance?
A sensory neuron detects stimuli within an area called its receptive field. Multiple stimuli within a single receptive field are interpreted as a single stimulus. Receptive fields come in many sizes and affect multiple types of sensation.
What is a sensory receptor?
A structure specialized to detect a stimulus. Includes sense organs and bare nerve endings.
How does sound or vibration travel from the middle ear to the inner ear?
Air vibration causes the tympanic membrane to vibrate. This vibration is carried by the ossicles (malleus, incus and stapes) to the oval window. The footplate of the stapes rests on the oval window and transmits vibration into the inner ear.
What is the dilated sac at the end of each semicircular duct next to the utricle?
Ampulla
Define sound
Any audible vibration of molecules. Vibrating air molecules cause the eardrum to vibrate, which produces sound.
The spaces anterior and posterior to the lens are filled with a liquid and gel respectively. What are these?
Aqueous humor - serous fluid filling the anterior chamber between the iris and the cornea Vitreous body (vitreous humor) - transparent jelly filling the large space behind the lens
How does the crista ampullaris detect rotation?
As the head turns, endolymph lags behind, pushes the cupula, bends the stereocilia, and stimulates hair cells *after 25 to 30 seconds of continual rotation, the endolymph catches up with the movement and stimulation ceases
In middle ear, what anatomy connects the middle ear cavity to the nasopharynx, equalizes pressure on both sides of tympanic membrane?
Auditory tube, aka eustachian tube, aka pharyngotympanic tube
What are the three components of the tunica vasculosa?
Choroid - highly vascular, deeply pigmented layer behind retina Ciliary body - extension of choroid that forms muscular ring around lens Iris - colored diaphragm controlling size of pupil
Contrast rods and cones
Cones - bright light, color, high visual acuity, concentrated in the center of retina Rods - dim light, monochromatic, produces contrast, concentrated along the sides of the retina
The transparent mucous membrane that lines the eyelids and covers the anterior surface of the eyeball, except the cornea, is called...
Conjunctiva
What is the lacrimal apparatus and how does it work?
Consists of the lacrimal (tear) gland and a series of ducts that drain tears into the nasal cavity. Tears cleanse, lubricate and nourish the eye, then flow into the lacrimal punctum (pore) near the medial commissure, and eventually into the nasal cavity.
Each ampulla contains a mound of hair cells and supporting cells called a...
Crista ampullaris
What is the gelatinous cap that extends from the crista to the roof of the ampulla containing the stereocilia of the hair cells?
Cupula
Some (not all) of the second order neurons of the visual projection pathway decussate at what point? Why is the location of this point significant?
Decussate at the optic chiasm, near the pituitary gland. A pituitary adenoma or aneurism could adversely affect vision.
How do hair cells depolarize and trigger action potentials of their associated sensory neurons?
Each stereocilium has a potassium gate at its tip that is linked to the potassium gate of the adjacent stereocilium. Vibrations cause the each stereocilium to bend and pull open the potassium gate of the adjacent stereocilium. This causes potassium to rush in, depolarize the hair cell, and release neurotransmitter that triggers action potential of the sensory neuron.
Rotary movements are detected by the semicircular ducts. What fluid fills these?
Endolymph
What kind of cells make up the organ of Corti?
Epithelium, composed of hair cells and supporting cells
The membranous labyrinth is filled with _______ (fluid) and floats in ______ (fluid). These fluids are similar to what other fluids?
Filled with endolymph (similar to intracellular fluid) and floats in perilymph (similar to cerebrospinal fluid) endo=inner peri=around
How does fluid in the inner ear relate to hearing and equilibrium?
Fluid is set in motion, and the sensory cells convert this motion into an informative pattern of action potentials
Which two types of lingual papillae ore most important?
Fungiform and vallate
What are two protective anatomical structures of the outer ear?
Guard hairs and cerumen (ear wax)
How does the organ of Corti differentiate between high and low pitched sounds?
High-pitch, short wavelength vibration displaces the basilar membrane closer to the oval window. Low-pitch, long wavelength vibration displaces the basilar membrane further from the oval window.
What is sensory adaptation as it relates to duration?
If stimulus is prolonged, the firing of the neuron gets slower over time, and we become less aware of the stimulus
How is dynamic equilibrium produced?
In a car, linear acceleration is detected as otoliths lag behind, bending the stereocilia and stimulating the hair cells
What is unique about the auditory projection pathway?
Involves four neurons instead of three like most sensory pathways
Second-order optic nerve fibers have three potential destinations. What are these?
Lateral geniculate nucleus of the thalamus (filtering by reticular formation). Pretectal nucleus and Superior colliculus of the midbrain (for reflexes).
Surface protrusions on the tongue are called...
Lingual papillae
The saccule and utricle each contain a 2 to 3 mm patch of hair cells and supporting cells called a what? Where are their respective patches of hair cells located?
Macula Macula sacculi - lies vertically on wall of saccule Macula utriculi - lies horizontally on floor of utricle
What are the three auditory ossicles? What is their function?
Malleus, incus and stapes. These transmit vibrations from the tympanic membrane in the inner ear to the oval window in the inner ear.
There are 130 million rods and 6.5 million cones in the retina, but only 1.2 million nerve fibers in the optic nerve. With is the significance of this discrepancy?
Neuronal convergence and information processing occurs in the retina before signals reach the brain. Multiple rods or cones synapse with one bipolar cell, and multiple bipolar cells synapse on one ganglion cell.
Which cranial nerve enervates the olfactory mucosa?
Olfactory (I) der
3 mm medial to the macula lutea is a region where nerve fibers converge and exit the eye, along with blood vessels. What is this region?
Optic disc
The retina is an extension of what cranial nerve?
Optic nerve (II)
What is the spiral organ within the scala media that converts acoustic vibration into nerve pulses?
Organ of Corti
The optic disc contains no receptor cells and produces a blind spot in our vision. Why don't we have a black spot in our vision?
Our fancy brain fills in the blank space with the surrounding image through a process called visual filling.
What are the three sections of the ear? What are their functions?
Outer, middle and inner. Outer and middle transmit sound to the inner, where vibration is converted to nerve signals -> sound
What is referred pain?
Pain in the viscera mistakenly thought to come from the skin. Brain mistakes where pain is coming from.
What is the technical term for the eyelids? What are their functions?
Palpebrae Block foreign objects, help with sleep, blink to moisten
In adapting to duration, receptors are divided into what two categories?
Phasic receptors - generate burst of action potentials, then reduce or stop signalling Tonic receptors - adapt slowly, generate nerve signals more steadily
Third order neurons project to what region of the brain, where conscious visual sensation occurs?
Primary visual cortex of the occipital lobe
What are the functions of the eyebrows?
Provide facial expression, protect eyes from glare and perspiration
Color blindness is the hereditary alteration or lack of one photopsin or another. What is the most common form of color blindness and what is its cause?
Red-green color blindness resulting from a lack of either L or M cones.
What are the three photoreceptor cells?
Rods, cones and certain ganglion cells. Only rods and cones produce visual images.
What's the mnemonic to remember cranial nerve enervation of the extrinsic eye muscles?
SO 4 (sup oblq) LR 6 (lat rect) AO 3 (all others)
What are the two components of the tunica fibrosa?
Sclera - dense, collagenous white of the eye Cornea - transparent area of sclera that admits light
What is the primary purpose of the conjunctiva?
Secrete thin mucous film that prevents the eyeball from drying
Pain transmission can be blocked by pharmacology, which blocks neurotransmission along the pain pathway. What's another way to ease pain utilizing its projection pathway?
Send other stimuli that competes along the same pathway, such as temperature (ice or heat), light touch or tickle (probably not).
What is the definition of sensation? To what extent do humans experience sensation?
Sensation is the subjective awareness of stimulus. Most sensory signals delivered to the CNS produce no conscious sensation.
Cones come in three flavors. How are they classified and what does each do?
Short-wavelength (S), medium-wavelenght (M), and long-wavelength (L). Somewhat inaccurately referred to as blue, green and red respectively (BGR=SML).
Glands within the tarsal plates which secrete oils that reduce tear evaporation are called...
Tarsal glands
The palpebrae contain a supportive fibrous section which thickens along their margins called...
Tarsal plates
The gelatinous membrane resting on top of the stereocilia is called...
Tectorial membrane
What is the difference between the bony labyrinth and the membranous labyrinth?
The bony labyrinth is the series of passageways in the temporal bone. The membranous labyrinth is the series of fleshy tubes which line the bony labyrinth.
What is transduction and why is this important?
The conversion of stimulus energy (light, heat, touch, sound) into nerve signals. This is the fundamental purpose of any sensory receptor.
The projection pathway for pain also runs through the hypothalamus and limbic system. Why is this significant?
The hypothalamus could trigger an autonomic response (?). The limbic system is responsible for emotion and memory, will remember not to do that again.
The lens focuses light on what structure of the retina?
The macula lutea, a 3 mm patch of cells with a tiny pit in the middle, the fovea centralis, that has the highest concentration of cones producing the most finely detailed images.
The projection pathway for pain runs through the reticular formation. Why is this significant?
The reticular formation is the origin of the descending analgesic pathway and can block pain. It is also capable of ignoring repetitive or inconsequential stimuli.
What anatomy of the inner ear senses equilibrium? What are its components?
The vestibular apparatus, consisting of three semicircular ducts and two chambers, the anterior saccule and posterior utricle
What do taste cells and olfactory cells have in common?
They both require taste or odorant molecules to be dissolved in a solution, e.g. olfactory mucus.
Which cranial nerves enervate the extrinsic eye muscles?
Trochlear (4) -> superior oblique Abducens (6) -> lateral rectus Oculomotor (3) -> all others
In the middle ear, what anatomy closes the inner end of the auditory canal and separates it from the middle ear?
Tympanic membrane (eardrum)
What two membranes separate the scala vestibuli and tympani from the scala media?
Vestibular membrane separates scala vestibuli from scala media. Basilar membrane separates scala media from scala tympani.
What three major pieces of anatomy reside in the bony labyrinth and what are their general functions?
Vestibule, semicircular ducts and cochlea. Cochlea contains the organ of hearing. Vestibule and semicircular ducts are responsible for equilibrium.
Describe how vibrations that reach the oval window produce sound sensation
Vibration travels through the scala vestibuli and causes displacement of the basilar membrane. This displacement is sensed by the hair cells, which are depolarized and produce action potentials in their associated sensory neurons. Vibration that displaces the basilar membrane travels through the scala tympani to the round window where they are dampened or dispersed.
How is static equilibrium produced?
When head is tilted, otolithic membrane sags, bending the stereocilia and stimulating the hair cells
The lens is made of cartilage that that changes shape when stretched. How does the ciliary body change the shape of the lens, and how does this affect vision?
When the ciliary body is relaxed, there is tension on the suspensory ligaments of the lens causing it to flatten for distance viewing. When the ciliary body flexes, suspensory ligaments become relaxed and the lens bulges for close-up viewing.
The points where the eyelids meet at the corner of the eyes are called...
commissures
What else influences taste?
food texture, aroma, temperature and appearance
Middle ear infection common in children is called...
otitis media
Each hair cell has 40 to 70 stereocilia and one true cilium embedded in a gelatinous material called...
otolithic membrane
The calcium carbonate-protein granules that add to the weight and inertia of this membrane are called...
otoliths
How are action potentials in olfactory cells generated?
second-messenger system
Hair cells have long, stiff microvilli on their apical surface called...
stereocilia
How do we taste hot pepper?
stimulates free nerve endings and produces pain, not taste
Hearing and equilibrium both reside in...
the inner ear
