T/F: One olfactory receptor can respond to several types of stimuli.
True
Olfactory neurons are imbedded in this.
Olfactory epithelium
How do we physically percieve odors?
Odorants are dissolved in the olfactory mucus and stimulate the neurons imbedded there
What makes olfactory neurons different from other types of neurons?
They regenerate periodically
How often do olfactory neurons regenerate?
About every 2 months
What cells replace/regenerate olfactory neurons?
Basal cells
T/F: Olfaction is a G-protein-mediated mechanism involving a complex with Polypeptide C.
False, the complex involves adenylate cylase
This G-protein subunit dissociates and activates adenylate cyclase in olfaction.
Alpha unit
After activation, adenylate cyclase catalyses the conversion of __________ into ___________.
ATP ; cAMP
What triggers the release of the G-protein from the receptor?
Binding of a dissolved odorant
T/F: After adenylate cyclase is activated, it converts cAMP into ATP which binds to cation channels and allows the influx of cations into the cell causing depolarization.
False, it converts ATP into cAMP
Fix the errors in this list of steps in the perception of olfaction:
1.Odorant dissolves in the extracellular fluid of the olfactory neuron
2.Odorant binds to receptor
3. G-protein attaches to the receptor and dissociates
4. Beta subunit attaches to Phospholipase C
5. Phopholipase C catalyzes the conversion of cAMP into ADP
6. ADP binds to anion channels, which allow the influx of Cl- ions
7. Influx of Cl- ions depolarizes the cell and triggers an action potential
1.Odorant dissolves in the nasal mucus
2.Odorant binds to receptor
3. G-protein detachesfrom the receptor and dissociates
4. Alpha subunit attaches to adenylate cyclase
5. Adenylate cyclase catalyzes the conversion of ATP into cAMP
6. cAMP binds to cation channels, which allow the influx of various cations
7. Influx of cations depolarizes the cell and triggers an action potential
Olfactory neurons in the olfactory epithelium pass through what feature in what bone?
Cribiform plate of the Ethmoid bone
Olfactory neurons pass through the bone and synapse with __________ or __________ in the __________.
Mitral cells
Tufted cells
Olfactory bulbs
T/F: Mitral and Tufted cells extend to the thalamus where they synapse with association neurons.
False, they extend to the olfactory tract. Olfaction does not pass through the thalamus!
This lobe of the brain is associated with olfaction.
Frontal lobe
T/F: Olfactory neurons from the olfactory tract synapse directly with neurons in the olfactory cortex (in the frontal lobe) without passing through the thalamus.
True
T/F: Olfactory neurons are imbedded in the olfactory epithelium and are unipolar cells.
False, they are bipolar cells. One side extends dendrites down into the mucus, the other is an axon extending into the olfactory bulb through the cribiform plate
What does the medial olfactory area do?
Associates visceral and emotonal reaction to odors (makes you recoil from or seek out the smells)
What does the intermediate olfatory area do?
It moderates the olfactory neurons (acclimates you to smells by attenuating consistent inputs))
What does the lateral olfactory area do?
Consciously percieves smells (detects and identifies smells)
T/F: The intermediate olfactory area receives inputs from the medial and lateral areas, then projects neurons back into the olfactory bulbs.
True (these are the pathways it uses to regulate olfactory activity)
What are the types of tongue papillae?
Filiform
Vallate
Fungiform
Foliate
What are the types of taste papillae?
Vallate
Fungiform
Foliate
Where are filiform papillae found?
All over the tongue
Where are vallate papillae found?
8 - 12 of them in a V-shape near the posterior aspect of the tongue
Where are fungiform papillae found?
All over the tongue
Where are foliate papillae found?
Lateral folds of the tongue
What do filiform papillae look like?
In situ: Shredded meat (give the tongue its "fuzzy" appearance
Cross-section: Filamentous
What do vallate papillae look like?
In situ: raised bumps or buttons
Cross-section: large knob or wedge
What do fungiform papillae look like?
In situ: Little red or pink spots scattered over the surface of the tongue
Cross-section: Mushroom cap cross-section
What do foliate papillae look like?
In situ: can't see them in the lateral folds
Cross-section: leaf-shaped
T/F: Tastes must be dissolved in saliva to be percieved.
True
How are taste buds held in place?
They are surrounded by supporting cells
T/F: Taste buds have microvilli that extend into a pore to percieve taste.
True (this is why flavors must be dissolved in saliva to be percieved)
How often are taste buds replaced?
About every 10 days
What is the only papilla that is not associated with taste?
Filiform
What type of papilla is most numerous on the tongue?
Filiform
T/F: The microvilli on taste bud cells are also called gustatory cilia.
False, they are called gustatory hairs
The tip of the tongue has the highest concentration of receptors for these tastes.
Salt
Sweet
Salt receptors are located here.
Tip of the tongue
Sweet receptors are located here.
Tip of the tongue
Sour receptors are located here.
Lateral aspects of the tongue
Bitter receptors are located here
Posterior of the tongue
This is the taste humans are most sensitive to.
Bitter
The sensation of this taste is produced directly through the influx of metal cations.
Salt
These tastes are craved by humans.
Salt
Umami
The sensation of this taste is produced by the effect of H+ ions on channel proteins.
Sour
The sensation of these tastes is produced via a G-protein complex involving adenylate cyclase.
Sweet
Umami
The sensation of this taste is produced via a G-protein complex involving Phospholipase C.
Bitter
These tastes are sensed directly due to cations in the substance being tasted.
Salt
Sour
These tastes involve a G-protein complex of some sort.
Umami
Sweet
Bitter
The receptors for this taste are scattered all about the tongue.
Umami
Umami receptors are located here.
All about the tongue
T/F: Bitter is a taste produced through a G-protein complex involving adenylate cyclase.
False, the complex involves phospholipase C
In what ways can H+ ions effect the sour taste?
Direct diffusion of the H+ into the cell via a H+ ion channel protein
Binding to K+ channel proteins which close and prevent K+ from leaving the cell
Binding to and opening ligand-gated channels that permit other cations to enter the cell
These tastes depend on the influx of some cation(s) into the cell from outside.
Salt
Sour
Umami
This taste results from the release of intracellular stores of Ca2+.
Bitter
This taste results from phosphorylation of K+ channels, which causes them to close and prevent K+ from leaving the cell.
Sweet
T/F: Sweet and sour can both be triggered by the phosphorylation of K+ ion channels.
False, sweet is triggered this way but sour is triggered through the binding of H+ to K+ gated channel proteins.
What compounds trigger the bitter taste?
Alkaloids
Why is bitter the most sensitive taste in humans?
Many alkaloid compounds are poisonous and high sensitivity to them would prevent us from ingesting them
In the Bitter taste, what does activated phospholipase C do?
It converts phosphoinositol (PIP2) into inositol triphosphate (IP3), which then triggers the release of intracellular Ca2+ stores causing depolarization.
What compounds can trigger the sweet taste?
Sugars
CHO
Some proteins (ex: aspartame)
What compound trigger the umami taste?
Amino acids
What compounds trigger the sour taste?
Acids
What compounds trigger the salt taste?
Salts (anything with a metal cation component that dissociates in saliva)
The chorda tympani is a portion of what nerve?
CN VII (Facial)
The chorda tympani carries sensation from what portion of the tongue?
Anterior 2/3
This nerve carries sensation from the anterior 2/3 of the tongue.
Chorda tympani portion of CN VII (Facial)
This nerve carries sensation from the posterior 1/3 of the tongue.
CN IX (Glossopharyngeal)
CN IX (Glossopharyngeal) carries sensation from what portion ofthe tongue?
Posterior 1/3
Sensation on the base of the tongue is carried by what nerve?
CN X (Vagus)
CN X (Vagus) carries sensation from what portion of the tongue?
Base
T/F: Sensation from the posterior 2/3 of the tongue is carried on CN IX (Glossopharyngeal).
False, CN IX (Glossopharngeal) carries sensation from the posterior 1/3 of the tongue
T/F: The chorda tympani carries sensation from the anteior 2/3 of the tongue.
True
This is the region of the brainstem that all taste sensation nerves synapse with.
Tractus solitarius
Nerves in the tractus solitarius synapse with other neurons where?
Thalamus
External structures of vision.
Eyebrow
Eyelids
Eyelashes
Conjunctiva
Another name for eyelids.
Palpebrae
What is the palpebral fissure?
The opening between the top and bottom eyelids
What are the Canthi and what flavors do they come in?
Canthi are the corners of the eyes where the palpebrae meet and they come in medial & lateral flavors
How is the medial canthus different from the lateral canthus?
The medial canthus has the caruncle
What is a caruncle?
It is a collection of modified sweat and sebaceous glands in the medial canthus
What gives the palpebra its shape?
A layer of dense connective tissue called the tarsal plate
What do ciliary glands do?
Modified sweat glands for the eyelashes
These glands produce sebum at the inner margins of the eyelids.
Meibomian glands
The layer of transparent mucous membrane that covers the inner aspect of the eyelids is called the __________.
Palpebral conjunctiva
The transparent mucous membrane lining the sclera of the eye is called the __________.
Bulbar conjunctiva
T/F: Although they abut, the palpebral and bulbar conjunctiva are not actually connected to each other.
False, the conjunctiva is a solid sheet of transparent mucous membrane and the two sections are so named based on their location only.
The turn where the conjunctiva folds back on itself to line the inner surface of the eyelid is called the __________.
Conjunctival fornix (inferior or superior)
Where is the lacrimal gland located?
Superolateral margin of the eyelid
What is the function of the lacrimal gland?
Secretes tears to flush the eyes
Why does your nose run when you cry?
Tears enter the puncta near the medial canthus and drain through the lacrimal canaliculi to the lacrimal sac, which empties into the nasolacrimal duct and finally into the nasal cavity causing your nose to run
What are the extrinsic muscles of the eye and what is their action?
Superior rectus (elevates eye)
Inferior rectus (depresses eye)
Lateral rectus (helps abduct eye)
Medial rectus (adducts eye)
Superior oblique (depress and abduct eye)
Inferior oblique (elevate and abduct eye)
What nerve innervates each extrinsic muscle of the eye?
SO4LR6AL3
Superior oblique - CN IV (Trochlear)
Lateral rectus - CN VI (Abducens)
All the others - CN III (Oculomotor)
What are the three layers of the eye called?
Tunica
What are the three tunica named?
Fibrous tunic
Vascular tunic
Nervous tunic
What comprises the tunica?
Fibrous tunic = sclera and cornea (this is the outermost tunic)
Vascular tunic = choroid, ciliary body, and iris
Nervous tunic = retina (this is the innermost tunic)
What is the ciliary body comprised of?
Ciliary muscle
Ciliary ring
Ciliary processes
What is the sclera made of?
Dense collagenous connective tissue with some elastic fibers thrown in
What is the cornea made of?
A matrix of transparent connective tissues containing collagen, elastic fibers, and proteoglycans with a layer of stratified squamous epithelium on the exterior surface
What is the function of the sclera?
Maintain the shape of the eye and provide muscle attachment
What is the function of the cornea?
Allows light to enter the eye and also refracts that light into the lens
T/F: The sclera is vascular (since you can see the arteries in the whites of your eyes)
False, the fibrous tunic is avascular
T/F: The cornea and sclera are contiguous
True
T/F: The choroid is associated with the sclera.
True
Why would the choroid be pigmented?
Prevents scattering of light rays in the eye to enhance visual acuity
What does the ciliary body do (as a whole)
Produces the aqueous humor
T/F: Aqueous humor is produced by the ciliary body and fills only the anterior chamber.
False, it fills both the anterior and posterior chambers
What do the ciliary muscles do?
Control the shape of the lens
What muscle consticts the pupil?
Sphincter pupillae muscles (encircle the iris)
What muscles dialate the pupil?
Technically, none. While not exactly muscles, a modified form of epithelial cells (called myoepithelial cells) form the dilator pupillae and they are arranged around the iris like spokes on a wheel.
T/F: The sphincter pupillae muscles are innervated by neurons of the sympathetic nervous system.
False, during sympathetic stimulation the pupils will dilate, not consrict
T/F: The sphincter pupillae muscles have parasympathetic innervation.
True, because the dilators are controlled by smpathetic innervation
T/F: Pupillary muscles are a modified type of skeletal muscle.
False, they are smooth muscle (you have no conscious control of them)
What are the two layers of the nervous tunic?
Pigmented retina (outer layer)
Neuronal retina (inner layer)
Which layer of the nervous tunic houses the sensory cells?
Nervous retina
Why is the outer layer of the nervous tunic pigmented?
For the same reason as the choroid: it prevents light rays from scattering in the eye
Name the order of the structures that light hits as it enters the eye
Stratified squamous epithelium of cornea
Connective tissue layer of cornea
Passes through the aqueous humor in the anterior chamber
Passes through the pupillary opening of the iris
Lens
Vitreous humor
Nerve fibers of the optic nerve
Neuronal retina
Ganglionic cell layer
Inner plexiform cell layer
Bipolar layer
Outer plexiform layer
Photoreceptor layer
Pigmented retina
T/F: When light strikes the retina, the photoreceptors are the first thing it hits.
False, the light rays must pass through the optic nerve fibers and then through 4 layers of cells before they even have a chance to be detected by the photoreceptors
T/F: Light rays detected by the photoreceptors and the action potentials they create travel in opposite directions within the sensory retina.
True, the action potential travels toward the pupil while the light rays travel toward the wings of the sphenoid bone behind the eye
What do rods do?
Provide low-acuity, non-colored vision in low-light conditions and detect motion
What do cones do?
Provide high acuity, colored vision
What is the main distribution of rods in the retina?
Cover most of the retina (except the macula and the fovea centralis)
What is the main distribution of the cones in the retina?
The macula and the fovea centralis
What is the fovea centralis?
A pit in the center of the macula lutea where your vision is the most acute.
What are the boundaries of the anterior chamber of the eye?
Between the iris and cornea
What are the boundaries of the posterior chamber?
From the lens to the iris
This is an abnormal increase in intraocular pressure.
Glaucoma
Where is the aqueous humor produced?
Ciliary body of the vascular tunic
Where is the aqueous humor reabsorbed?
It is absorbed into the bloodstream through the canal of Schlemm (scleral venous sinus) located where the cornea and sclera meet
What are the functions of the vitreous humor?
Maintains shape of eye
Refracts light
Keeps lens and retina in place
This is clouding of the normally transparent lens.
Cataract
T/F: Rods have little or no convergence while cones exhibit spatial summation (convergence) of synapses down to ganglion cells.
False, Rods spatially sum while cones do not (that's why cones have greater acuity)
T/F: The medial portion of either visual field will always cross over contralateral at the optic chiasm.
False, they remain ipsilateral because this information is carried on the lateral retina
T/F: The medial portion of the retina will always cross over contralateral at the optic chiasm.
True, the retinal input crosses because it carries information about the lateral visual field
T/F: The lateral portion of either visual field will always cross contralateral at the optic chiasm.
True, because this information is carried on the medial retina
T/F: The lateral portion of the retina will always cross contralateral at the optic chiasm.
False, they always stay ipsilateral
T/F: Action potentials generated by the photoreceptors travel contra to the incoming light rays and exit the eye via ganglionic cell axons, which form CN II (Optic).
False, photoreceptors do not generate action potentials, ganglionic cells do that
Decribe the path of the "visual" action potential when the eye is struck by light from the medial visual field.
AP is generated by ganglionic cell on lateral retina
AP travels down ganglionic axon (which becomes part of the optic nerve)
This axon travels to optic chiasm, but does not cross
This axon becomes part of the ipsilateral optic tract carrying the AP to the ipsilateral lateral geniculate nucleus of the thalamus
Here the AP crosses a synapse, entering the ipsilateral optic radiations that carry it to the ipsilateral visual cortex
Decribe the path of the "visual" action potential when the eye is struck by light from the lateral visual field.
AP is generated by ganglionic cell on the medial retina
AP travels down ganglionic axon (which becomes part of the optic nerve)
This axon travels to the optic chiasm and crosses over to the contralateral side
This axon becomes part of the contralateral optic tract carrying the AP to the contralateral lateral geniculate nucleus of the thalamus
Here the AP crosses a synapse, entering the contralateral optic radiations that carry it to the contralateral visual cortex
Why do axons carrying visual input to the geniculate nuclei also have collateral branches that synapse in the superior colliculi of the midbrain?
The colliculi control reactions based on visual input, but do not process visual information. They do not cause you to "see," they cause you to duck when something is coming at you.
What is the visual pigment in rods?
Rhodopsin (visual purple)
What is the visual pigment in cones?
Iodopsin (photopsin)
What is the inevitable consequence to our vision of the photoreceptors only producing local graded potentials (rather than AP's)?
Because spatial summation from hundreds of rods can converge on one ganglion cell it is possible for very weak input (low light) to trigger an action potential, but because hundreds of cells are involved the image is 'grainy.' Since cones in the fovea centralis do not converge it takes a much higher amount of input (daylight) to trigger an action potential in the ganglion cell it synapses with, but because only one cone cell is involved the image is much more distinct.
What is the definition of refraction?
Bending light
What is the defnition of convergence (with respect to light rays)?
Light striking a convex surface
What is the definition of focal point?
The point where light rays meet and cross
Is emmetropia a good thing?
Yes, it refers to focusing on objects far enough away that you do not need to flatten the lens (normal, relaxed vision)
What is meant by the far point of vision?
The distance from the eye (~20 ft) that an object must be to be in focus without thickening the lens (minimum distance of emmetropic vision)
What is meant by the near point of vision?
The minimum distance from the eye that an object can still be focused on (shortest distance to an object where the eye can still focus on it)
T/F: When relaxed, the ciliary muscles are not pulling tension on the lens and it is a more rounded shape for near vision.
False, relaxation of the ciliary muscles pulls tension on the suspensory ligaments and flattens the lens for far vision
What is accomodation?
When the ciliary muscles contract the ciliary body shrinks in diameter, which reduces tension on the suspensory ligaments and allows the lens to bulge into a more rounded shape. This is how you focus on objects lying between the far point and near point of vision.
What is convergence?
When the eyes "cross" to keep a near object in sight (due to reflex contraction of the medial recti)
When you focus on near objects, your eyes exhibit miosis. What is it and why does it occur?
Miosis is the involuntary constriction of the pupil and it occurs to 'filter' out distracting input so you can focus more exclusively on the near object.
What is myopia?
What causes it?
How is it corrected?
Myopia is 'nearsightedness'
It is caused by the eye being too long (increase in distance from lens to retina), which causes the light rays to converge in front of the retina
It is corrected with a concave lens that refracts the light rays away from each other before they enter the eye, moving the focal point posteriorly in the eye
What is hyperopia?
What causes it?
How is it corrected?
Hyperopia is 'farsightedness'
It is caused by the eye being too short (reduction in the distance from the lens to the retina), which causes the light rays to converge somewhere behind the retina
It is corrected with a convex lens that refracts the light rays toward each other before entering the eye, moving the focal point anteriorly in the eye
What is presbyopia?
What causes it?
How is it corrected?
Presbyopia is a reduction in the eye's ability to accomodate
It is caused by stiffening of the eye-lens wih age
It is corrected with reading glasses or bifocal lenses
What is the cause of astigmatism?
Cornea or lens not curved properly
What constitutes the outer ear?
Auricle, external auditory canal, outer surface of the tympanic membrane
What constitutes the middle ear?
Inner surface of tympanic membrane, auditory (Eustacian) tube, malleus,incus, and stapes
What constitutes the inner ear?
Cochlea and semi-circular canals
T/F: the middle ear is fluid-filled.
False, it is air-filled
What are the auditory ossicles?
Small bones in the middle ear (malleus, incus, stapes)
What muscle attaches to the stapes and what nerve innervates it?
The stapedius, innervated by CN VII (Facial)
What muscle attaches to the malleus and what nerve innervates it?
The tensor tympani muscle, innervated by CN V (Trigeminal)
What is the function of the middle ear muscles?
During loud noises, they contract to try to brace the ossicles and prevent damage
These are the two labyrinths of the inner ear.
Bony and Membranous
What constitutes the bony labyrinth?
The passageways in the bone that house the hearing/balance organs
What constitutes the membranous labyrinth?
The hearing/balance organs housed in the bony labyrinth
This senses changes in static balance
Vestibule
This macula of the vestibule is parallel to the floor of the skull.
Utricle
This macula of the vestibule is perpedicular to the floor of the skull.
Saccule
This senses changes in kinetic (dynamic) balance.
Semi-circular canals
This is the fluid that fills the non-sensory canals in the membranous labyrinth.
Perilymph
This is the fluid that fills the sensory canal in the membranous labyrinth.
Endolymph
The sensory canal in the membranous labyrinth has two names. What are they?
Cochlear duct and scala media
The superior non-sensory canal in the membranous labyrinth is called what?
Scala vestibuli
The inferior non-sensory canal in the membranous labyrinth is called what?
Scala tympani
The wall of the scala vestibuli is called what?
Vestibular membrane
T/F: The hair cells in the Organ of Corti perceive sound by vibrating against the vestibular membrane.
False, they vibrate against the tectoral membrane
The wall of the scala tympani is called what?
Basilar membrane
The sensory organ of hearing is called what?
Organ of Corti (Spiral organ)
How does hearing actually occur?
Vibrations are detected by the tympanic membrane
Tympanic membrane transmits vibrations to the ossicles
Stapes transmits vibrations to the oval window
Oval window transmits vibrations to the perilymph of the scala vestibuli
The perilymph transmits vibrations to the vestibular membrane
Vestibular membrane transmits vibrations to the endolymph of the scala media (cochlear duct)
Endolymph of the scala media transmits vibratons to the basilar membrane
Hair cells in the Organ of Corti are attached to the basilar membrane and they begin to vibrate, rubbing against the tectoral membrane
Voila! Sound.
How do we detect pitch in sound?
The sound's perceived pitch depends on the position of the hair cells that vibrate. High-pitched sounds have a short wavelength and will vibrate hair cells near the oval window. Low-pitched sounds have a longer wavelength and will vibrate hair cells farther from the oval window.
Where is the auditory cortex located?
Temporal lobes
T/F: Hearing is the only sense that does not synapse in the thalamus on its way to its cortex.
False, the only sense that does not go through the thalamus is smell
T/F: The balance organs detect position
False, they detect changes in the rate of motion
The sensory portion of the utricle and saccule are called what?
Macula
Describe the macula in the utricle and saccule.
Specialized epithelium of columnar hair cells with many stereocilia (microvilli) and one true cillium emedded in a gelatinous goo studded with otoliths that stimulate the hair cells with varying frequencies.
T/F: Kinetic balance is perceived via the use of otoliths in a gelatinous mass stimulating hair cells.
False, this is how static (vestibular) balance is perceived
What are the bulges in the semi-circular canals called?
Ampullae
What is in the semi-circular canals?
Endolymph
What is the crista ampullaris?
A bulge in the epithelium of the ampullae that houses the sensory hair cells
What structure stimulates the hair cells of the crista ampullaris?
A gelatinous cap called the cupula
T/F: Balance structures sense motion.
False, they sense changes in the rate of motion, not motion itself
T/F: Vestibular neurons send information to the motor nuclei for the extrinsic eye muscles.
