Which part of an olfactory receptor cell detects an odorant molecule?



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Chapter 16

  1. Which part of an olfactory receptor cell detects an odorant molecule?

Ans: pg. 572 – olfactory hairs


  1. What is the function of the supporting cells of the nasal epithelium?

Ans: pg. 573 – to provide physical support, nourishment, and electrical insulation for the olfactory receptor cells, and to help detoxify chemicals that come in contact with the olfactory epithelium



  1. How do basal cells contribute to olfaction?

Ans: pg. 573 – they produce new olfactory receptor cells


  1. Olfactory receptor cells are unique among neurons because they can undergo what process?

Ans: pg. 573 – cell division


  1. Why must the olfactory epithelium have a coating of mucus?

Ans: pg. 573 – to moisten the surface of the olfactory epithelium and dissolve odorants


  1. What is the sequence of events from the binding of an odorant molecule to an olfactory hair to the arrival of a nerve impulse in an olfactory bulb?

Ans: pg. 573 – odorant binds to a receptor protein (odorant binding protein) and activates adenylate cyclase resulting in the production of cyclic adenosine monophosphate → sodium ion channels open → inflow of Na+ → depolarizing generator potential → action potential triggered → nerve impulses propagate along axon of olfactory receptor cell


  1. How long would it take for your olfactory receptor cells to adapt to the smell of something very rotten?

Ans: pg. 574 – about one minute



  1. What is the difference between the olfactory nerves, olfactory bulbs, and olfactory tract in the olfactory pathway?

Ans: pg. 574 – olfactory nerves: formed by bundles of unmyelinated axons of olfactory receptor cells, first-order neurons; olfactory bulbs: distal ends of the olfactory nerves, site of synapse of olfactory nerves with dendrites and cell bodies of second-order neurons (olfactory bulb neurons); olfactory tract: formed by axons of second-order olfactory bulb neurons, project to the limbic system and hypothalamus



  1. For each of the primary tastes, give an example of a food that strongly represents that taste.

Ans: pg. 576 – sweet (sugar), sour (sour pickle), salty (potato chips), bitter (coffee), umami (meat)


  1. Why does a cold or allergy reduce your sense of taste?

Ans: pg. 576 – it reduces the sense of smell which is the major part of taste


  1. Where on the tongue are each of the four types of papillae located?

Ans: pg. 577 – 1) circumvallate: form an inverted V-shaped row at the back of the tongue; 2) fungiform: scattered over the entire surface of the tongue; 3) foliate: located in small trenches on the lateral margins of the tongue; 4) filiform: over the entire surface of the tongue


  1. What is the function of supporting cells in taste buds?

Ans: pg. 577 - insulate the receptor cells from each other and from the surrounding tongue epithelium


  1. What must happen to odorant and tastant molecules before they can be sensed?

Ans: pg. 576 – they must be dissolved in an aqueous solution (saliva or fluids coating nasal membranes)


  1. Which type of receptors are olfactory and gustatory receptor cells?

Ans: pg. 576 – chemoreceptors


  1. How do the receptor cells for olfaction and gustation differ in structure and function?

Ans: pg. 572, 577 –structure: olfactory receptor cells are bipolar neurons with a nonmotile cilia that projects from the dendrite; whereas, gustatory receptor cells have a single, long microvillus (gustatory hair) that projects from the receptor cell to the external surface; function: olfactory cells are receptors for the sense of smell; whereas, gustatory cells are receptors for the sense of taste


  1. What is the sequence of events from the binding of a tastant molecule to a gustatory hair to the generation of an action potential in a first-order gustatory neuron?

Ans: pg. 577 – release of neurotransmitter molecules from the gustatory receptor cell with the neurotransmitter triggering action potentials in the first-order neurons


  1. Why is the low threshold of bitter substances a survival advantage?

Ans: pg. 577- because poisonous substances often are bitter


  1. How do the olfactory and gustatory pathways differ?

Ans: pg. 578 – gustatory nerve impulses are propagated in first-order neurons through three cranial nerves


  1. Give the name and function of each muscle of the eyelids.

Ans: pg. 580 – 1) levator palpebre superioris: raises upper eyelid; 2) orbicularis oculi: closes eyelid


  1. Why do eyelids of healthy eyes not stick together?

Ans: pg. 580 – Meibomian glands secrete a fluid that keeps the eyelids from adhering to each other


  1. Which structure shown in Figure 16.6 is continuous with the inner lining of the eyelids?

Ans: pg. 580 - conjunctiva


  1. What protective functions would be compromised if a person lost his or her eyelashes and eyebrows?

Ans: pg. 580 – protection from foreign objects, perspiration, and direct rays of the sun


  1. What is lacrimal fluid, and what are its functions?

Ans: pg. 580 – a watery solution containing salts, mucus, and lysozyme and functions to protect, clean, lubricate, and moisten the eyeball


  1. Why would someone with reduced lacrimal fluid production (dry eyes) be more prone to an eye infection?

Ans: pg. 580 – the protective bactericidal enzyme, lysozyme, would be absent in sufficient amount to protect against bacteria


  1. Why does your nose run when you cry?

Ans: pg. 582 – the lacrimal glands produce excessive lacrimal fluid that may spill over the edges of the eyelids and even fill the nasal cavity with fluid


  1. What are the components of the fibrous tunic and vascular tunic?

Ans: pg. 583 – fibrous tunic: cornea and sclera; vascular tunic: choroids, ciliary body, iris


  1. Through which part of the eye does light enter?

Ans: pg. 583 – cornea


  1. What produces differences in pupil color?

Ans: pg. 583 – pigmentation in iris


  1. Which division of the autonomic nervous system causes papillary constriction? Which causes papillary dilation?

Ans: pg. 585 – a) parasympathetic; b) sympathetic


  1. How does melanin assist vision?

Ans: pg. 585 – it absorbs stray light rays which prevents reflection and scattering of light within the eyeball


  1. Through which structures does light pass as it travels through the neural layer of the retina? How does visual information pass from photoreceptors to the optic nerve?

Ans: pg. 585 – a) ganglion cell, bipolar cell, photoreceptors; b) photoreceptors, bipolar cells, ganglion cells, optic nerve


  1. Which part of the retina produces the sharpest vision when light falls on it?

Ans: pg. 585 – central fovea


  1. Where is aqueous humor produced, what is its circulation path, and where does it drain from the eyeball?

Ans: pg. 587 – 1) from blood capillaries in the ciliary processes; 2) from blood capillaries in the ciliary processes into the posterior chamber, then forward between the iris and lens, through the pupil, and into the anterior chamber; 3) into the scleral venous sinus (canal of Schlemm) and then into the blood


  1. What is the function of the aqueous humor? The vitreous body?

Ans: pg. 587 – a) nourishes the lens and cornea; b) contributes to intraocular pressure holding the retina flush against the choroids


  1. What separates the anterior and posterior chambers of the eyeball? The anterior cavity from the vitreous chamber?

Ans: pg. 587 – a) iris and ciliary process; b) suspensory ligaments and lens



  1. Which characteristics allow the lens to transmit light?

Ans: pg. 587 – proteins (crystallins) arranged like the layers of an onion


  1. Why are we unable to see an image that strikes the blind spot?

Ans: pg. 587 – it contains no rods or cones


  1. What is refraction? Which components of the eye are primarily responsible for refracting light?

Ans: pg. 590 – a) bending of light rays; b) cornea, lens


  1. If you were looking at the horizon, trying to determine where you were (focusing on the distance), then looking down to read a map (focusing up close), which process must your eyes accomplish to keep your vision focused?

Ans: pg. 591 – accommodation


  1. Which sequence of events occurs when you look at a distant object? When you look at a close object?

Ans: pg. 591 – a) ciliary muscle is relaxed and lens is flattened due to being stretched in all directions; b) ciliary muscle contacts, the ciliary muscle is pulled toward the lens which pulls the ciliary process forward the lens, ciliary process moves forward toward the lens which releases tension on the lens and suspensory ligaments, which allows the lens to become more spherical


  1. Which refraction abnormality do you likely have if both near and far objects are out of focus?

Ans: pg. 591 – astigmatism


  1. What is convergence? Why is it important for human vision?

Ans: pg. 592 – a) the medial movement of the two eyeballs so that both are directed toward the object being viewed; b) it allows for binocular vision



  1. What are the functional similarities between rods and cones?

Ans: pg. 593 – transduction of light energy into a receptor potential occurs in the outer segment of both rods and cones; both contain photopigments; both synapse with bipolar neurons


  1. What is the conversion of cis-retinal to trans-retinal called? What is the conversion of trans-retinal to cis-retinal called?

Ans: pg. 594 – a) isomerization; b) regeneration


  1. Why do you see an after-image after staring at a bright light?

Ans: pg. 595 – because regeneration has not yet occurred


  1. How do photopigments respond to light and recover in darkness?

Ans: pg. 595 – in light, more and more photopigment is bleached; whereas, in darkness, more and more photopigment regenerates


  1. What is the function of cGMP in photoreceptors?

Ans: pg. 595 – to allow Na+ to flow into photoreceptor outer segments so that the photoreceptor can continue to release neurotransmitter


  1. Why does a decreased release of glutamate by photoreceptors generate a receptor potential in bipolar cells?

Ans: pg. 596 – the glutamate is an inhibitory neurotransmitter



  1. What is the composition of the optic nerve?

Ans: pg. 596 – axons of the ganglion cells


  1. Light rays from an object in the temporal half of the visual field strike which half of the retina?

Ans: pg. 596 – nasal half


  1. By which pathway do nerve impulses triggered by an object in the nasal half of the visual field of the left eye reach the primary visual area of the cortex?

Ans: pg. 596 – axons of the nasal half of the retina cross at the optic chiasma and continue to the opposite side of the thalamus, then to the primary visual area of the cortex on the same side


  1. If you lost your auricles (common in severe burns of the head), how would your hearing be affected?

Ans: pg. 599 – sound waves could not be directed to the external auditory canal

  1. Why do small particles such as dust from a dirt trail, normally not travel to the interior of your external auditory canal?

Ans: pg. 599 – hairs and cerumen in the external auditory canal prevent dust and foreign objects from entering the ear


  1. Which structures separate the middle ear from the external ear and from the internal ear?

Ans: pg. 600 – 1) tympanic membrane; 2) oval window and round window


  1. List the auditory ossicles in order of sound wave transmission through the middle ear. For each ossicle, name two structures to which it is attached.

Ans: pg. 600 – a) malleus, incus, anvil; b) malleus: tympanic membrane and incus; incus: malleus and stapes; stapes: incus and oval window


  1. An infection of the throat can lead to a secondary infection of the middle ear (otitis media). How are these structures connected?

Ans: pg. 601 – via the auditory (pharyngotympanic) tube


  1. What are the three subdivisions of the bony labyrinth?

Ans: pg. 601 – semicircular canals, vestibule, cochlea


  1. What are the names of the two sacs that lie in the vestibule?

Ans: pg. 601 – saccule and utricle


  1. Which component of the cochlea contains the receptors for hearing?

Ans: pg. 602 – organ of Corti (spiral organ)


  1. Why might loud noises cause dizziness?

Ans: pg. 602 – because the membranous labyrinth connects the vestibule and cochlea


  1. Which nerve innervates the inner ear? Which branch of that nerve transmits equilibrium signals? Which branch transmits auditory signals?

Ans: pg. 602 – a) vestibulocochlear; b) vestibular; c) cochlear


  1. Would strongly blowing through a whistle produce sound waves of high or low frequency?

Ans: pg. 606 – high frequency


  1. Why would excess cerumen in the external auditory canal muffle incoming sounds?

Ans: pg. 600 – it would prevent sound waves from traveling easily through the external auditory canal and striking the tympanic membrane


  1. How are sound waves transmitted from the auricles to the spiral organ?

Ans: pg. 606 – from auricles into external auditory canal to tympanic membrane to ear ossicles to oval window setting up fluid pressure waves in the cochlea in the scala vestibule to the scala tympani which pushes the vestibular membrane back and forth creating pressure waves in the in the endolymph inside the cochlear duct which causes the basilar membrane to vibrate, which moves the hair cells of the spiral organ against the tectorial membrane, which binds the hair cell microvilli, which produces receptor potentials


  1. How does the tympanic membrane respond to quieter sounds? To low-pitched sounds?

Ans: pg. 606 – it moves more slowly


  1. If fluid waves in the cochlea bounced back and forth, sounds would echo inside your cochlea. What stops fluid waves from traveling more than once through the cochlea?

Ans: pg. 606 – the round window


  1. Which part of the basilar membrane vibrates most vigorously in response to banging on a bass drum (low-frequency sounds)? How would the basilar membrane respond to someone quietly whispering (low-intensity sounds)?

Ans: pg. 606 – a) the portion of the basilar membrane toward the apex of the cochlea near the helicotrema; b) with smaller vibrations


  1. How is the human ear able to identify the origin of a sound?

Ans: pg. 607 – via slight differences in the timing of impulses arriving from the two ears to the pons


  1. What is the pathway for auditory impulses from the cochlea to the cerebral cortex?

Ans: pg. 607 – cochlea to cochlear nerve to vestibulocochlear nerve to medulla oblongata to pons to midbrain to thalamus to primary auditory area in the superior temporal lobe of the cerebral cortex


  1. What is the difference between static and dynamic equilibrium?

Ans: pg. 610 – static equilibrium refers to the maintenance of the position of the body relative to the force of gravity; whereas, dynamic equilibrium is the maintenance of body position in response to sudden movements such as rotation, acceleration, and deceleration


  1. How are the receptors for hearing and equilibrium structurally similar?

Ans: pg. 610 – they both involve hair cells as the sensory receptors


  1. If you were blindfolded, would maculae or cristae sense that you were hanging upside-down? Where are maculae and cristae each found?

Ans: pg. 610 – a) macula; b) maculae are in the saccule and utricle of the vestibule and the cristae are in the semicircular canals

  1. What function is served by the otoliths?

Ans: pg. 610 – add weight to the otolithic membrane, amplifying the pull of gravity during movements


  1. Why do we need three, rather than one or two, semicircular canals?

Ans: pg. 610 – the ducts lie at right angles to one another allow them to respond to virtually any rotation movement of the head


  1. With which type of equilibrium are the semicircular ducts, the utricle, and the saccule associated?

Ans: pg. 610 – 1) semicircular ducts: rotational movements; 2) utricle and saccule: straight-line changes in speed and direction


  1. Where do axons in the vestibular branch of the vestibulocochlear nerve terminate? What purposes are served by the transmission of equilibrium input to these locations?

Ans: pg. 610 – a) medulla oblongata and pons; b) axons from the medulla and pons extend to the nuclei of cranial nerves that control eye movement and to the nucleus of the accessory nerve that helps control head and neck movements






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