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Questions and Answers
Which of the following is a primary class of odor?
Which of the following is a primary class of odor?
Where do olfactory sensory neurons synapse after passing through the cribiform plate?
Where do olfactory sensory neurons synapse after passing through the cribiform plate?
Which cranial nerve is responsible for the olfactory sensory pathway?
Which cranial nerve is responsible for the olfactory sensory pathway?
Which structure is NOT involved in the secondary processing of olfactory information?
Which structure is NOT involved in the secondary processing of olfactory information?
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Which type of gustatory papillae is the most numerous but does not contain taste buds?
Which type of gustatory papillae is the most numerous but does not contain taste buds?
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Which area of the brain is involved in the emotional responses to smells?
Which area of the brain is involved in the emotional responses to smells?
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What role do supporting cells play in taste buds?
What role do supporting cells play in taste buds?
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What is a characteristic of the olfactory pathway in relation to thalamic processing?
What is a characteristic of the olfactory pathway in relation to thalamic processing?
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What is the primary cause of myopia or nearsightedness?
What is the primary cause of myopia or nearsightedness?
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What effect does glaucoma have on eye health?
What effect does glaucoma have on eye health?
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Which part of the ear is primarily involved in balance?
Which part of the ear is primarily involved in balance?
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How is presbyopia corrected?
How is presbyopia corrected?
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What is the function of the auditory or eustachian tube?
What is the function of the auditory or eustachian tube?
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Which disorder is characterized by the clouding of the lens?
Which disorder is characterized by the clouding of the lens?
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What role do ossicles play in the ear?
What role do ossicles play in the ear?
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Which part of the visual field projects to the right side of the brain?
Which part of the visual field projects to the right side of the brain?
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What is the primary function of rods in the retina?
What is the primary function of rods in the retina?
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Where do ganglion cell axons converge before exiting the eye?
Where do ganglion cell axons converge before exiting the eye?
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Which type of ganglion cell generates more action potentials when light is focused on the center of its receptive field?
Which type of ganglion cell generates more action potentials when light is focused on the center of its receptive field?
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What is the role of interneurons in the retina?
What is the role of interneurons in the retina?
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Which part of the retina does the optic nerve primarily transmit axons from?
Which part of the retina does the optic nerve primarily transmit axons from?
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What happens to the axons from the nasal part of the retina at the optic chiasm?
What happens to the axons from the nasal part of the retina at the optic chiasm?
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Which structure consists of axons from the thalamic neurons projecting to the visual cortex?
Which structure consists of axons from the thalamic neurons projecting to the visual cortex?
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How are visual fields projected to the brain?
How are visual fields projected to the brain?
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What is the primary function of the tensor tympani muscle?
What is the primary function of the tensor tympani muscle?
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Which cranial nerve innervates the stapedius muscle?
Which cranial nerve innervates the stapedius muscle?
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What type of fluid fills the cochlear duct (scala media)?
What type of fluid fills the cochlear duct (scala media)?
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What is the role of the basilar membrane in the cochlea?
What is the role of the basilar membrane in the cochlea?
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Where are the sensory cells (hair cells) located within the cochlea?
Where are the sensory cells (hair cells) located within the cochlea?
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What feature distinguishes the width of the basilar membrane near the oval window from its width near the helicotrema?
What feature distinguishes the width of the basilar membrane near the oval window from its width near the helicotrema?
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What is the primary communication pathway between the oval window and the cochlea?
What is the primary communication pathway between the oval window and the cochlea?
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What is the primary function of the attenuation reflex?
What is the primary function of the attenuation reflex?
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What is the main role of inner hair cells in the auditory system?
What is the main role of inner hair cells in the auditory system?
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How do outer hair cells contribute to hearing sensitivity?
How do outer hair cells contribute to hearing sensitivity?
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What determines the pitch of a sound wave?
What determines the pitch of a sound wave?
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What effect do tensor tympani and stapedius muscles have on hearing?
What effect do tensor tympani and stapedius muscles have on hearing?
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Which statement about sound wave vibrations in the cochlea is correct?
Which statement about sound wave vibrations in the cochlea is correct?
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What role do tip links play in hair cells of the inner ear?
What role do tip links play in hair cells of the inner ear?
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Which part of the brain processes the action potentials from cochlear nerve fibers?
Which part of the brain processes the action potentials from cochlear nerve fibers?
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What is the function of K+ gates in the hair cells of the cochlea?
What is the function of K+ gates in the hair cells of the cochlea?
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Study Notes
Olfactory Epithelium
- Basal cells are replaced every 2 months
- There may be as many as 50 primary odors
- Camphorous (mothballs), musky, floral, pepperminty, ethereal (fresh pears), pungent, putrid
Olfactory Sensory Pathway
- Olfactory neurons pass through the cribiform plate to the olfactory bulbs
- Olfactory neurons synapse with tufted cells or mitral cells
- Association neurons receive input from the brain
- Information is delivered to the olfactory cortex of the frontal lobe
- Information does not go through the thalamus
Olfactory Processing
- Majority of neurons in the olfactory tracts project to the central olfactory cortex areas in the temporal and frontal lobes
- Includes the piriform cortex, amygdala, and orbitofrontal cortex
- Secondary olfactory areas involved with emotional and autonomic responses to smell
- Includes the hypothalamus, hippocampus, and limbic system
Gustatory/Taste
- Taste bud: supporting cells surround taste cells
- Taste cells have microvilli (gustatory hairs) extending into taste pores
- Types of gustatory or glossal papillae:
- Filiform: Most numerous, no taste buds
- Vallate: Largest, have taste buds
- Foliate: Leaf-shaped, contain most sensitive taste buds, decrease in number with age
- Fungiform: Mushroom-shaped, overlap in response to light
### Inner Layers of the Retina
- Rods and cones synapse with bipolar cells that synapse with ganglion cells in all areas except the fovea
- Except in fovea centralis, ganglion cell axons converge at optic disc, exit via optic nerve, then impulses travel to visual cortex
- Fovea centralis: highest visual acuity
- Rods: spatial summation. One bipolar cell receives input from numerous rods, one ganglion cell receives input from several bipolar cells
- Cones exhibit little or no convergence
- Receptive Fields
- Area from which a ganglion cell receives input
- Those in fovea centralis smaller than in other parts of retina
- On-center ganglion cells: generate more action potentials when light is directed onto the receptive field. Respond to intensity of light
- Off-center ganglion cells: more action potentials when light is off or when light does not hit center of field. Respond to contrasts in light
- Interneurons present in inner layers and modify signal before signal leaves retina. Enhance borders and contours, increasing intensity at borders. Horizontal, amacrine, and interplexiform cells
Visual Pathways
- Each visual field is divided into a temporal and a nasal half.
- After passing through the lens, light from each half of a visual field projects to the opposite side of the retina.
- An optic nerve consists of axons extending from the retina to the optic chiasm.
- In the optic chiasm, axons from the nasal part of the retina cross and project to the opposite side of the brain. Axons from the temporal part of the retina do not cross.
- An optic tract consists of axons that have passed through the optic chiasm to the thalamus.
- The axons synapse in the lateral geniculate nuclei of the thalamus. Collateral branches of the axons in the optic tracts synapse in the superior colliculi.
- An optic radiation consists of axons from thalamic neurons that project to the visual cortex.
- The right part of each visual field projects to the left side of the brain, and the left part of each visual field projects to the right side of the brain.
- Binocular vision: visual fields partially overlap yielding depth perception.
Eye Disorders
- Myopia (nearsightedness) Focal point too near lens, image focused in front of retina. Corrected by concave lenses
- Hyperopia (farsightedness) Image focused behind retina. Corrected by convex lenses.
- Presbyopia: Degeneration of accommodation, corrected by reading glasses.
- Astigmatism: Cornea or lens not uniformly curved.
- Cataract: Clouding of lens.
- Macular degeneration: Common in older people, loss in acute vision.
- Retinal detachment: Can result in complete blindness.
- Glaucoma: Increased intraocular pressure by aqueous humor buildup.
- Ptosis: Drooping of the upper eyelid due to paralysis or disease, or as a congenital condition.
Hearing and Balance
- Divided into external, middle, and inner ear.
- External and middle: hearing.
- Internal: hearing and equilibrium.
- External Ear: Auricle or pinna: elastic cartilage covered with skin. External auditory canal: lined with hairs and ceruminous glands. Produce cerumen. Tympanic membrane: Thin membrane of two layers of epithelium with connective tissue between. Sound waves cause it to vibrate. Border between external and middle ear.
Auditory Structures and Their Functions
- Middle ear: Separated from the inner ear by the oval and round windows.
- Auditory or eustachian tube: opens into pharynx, equalizes pressure. Passage to mastoid air cells in mastoid process.
- Ossicles: malleus, incus, stapes: transmit vibrations from eardrum to oval window.
- Oval window: connection between middle and inner ear. Foot of the stapes rests here and is held in place by annular ligament.
Muscles of the Middle Ear
- Tensor tympani: inserts on malleus; innervated by cranial nerve V
- Stapedius: inserts on stapes and innervated by cranial nerve VII
- Attenuation reflex: muscles contract during loud noises and prevent damaging vibrations
Inner Ear
- Bony labyrinth: tunnels and chambers in the temporal bone
- Cochlea: hearing
- Vestibule: balance
- Semicircular canals: balance
- Membranous labyrinth: membranous tunnels and chambers suspended in the bony labyrinth
- Fluids:
- Endolymph: in membranous labyrinth
- Perilymph: in spaces between membranous labyrinth and periosteum of bony labyrinth
Inner Ear, Bony and Membranous Labyrinths
- Oval window communicates with vestibule, which communicates with the scala vestibuli of the cochlea
- Scala vestibuli extends from oval window to helicotrema at cochlear apex
- Second cochlea chamber (scala tympani) from helicotrema to round window
- Scala vestibuli and scala tympani filled with perilymph
Cochlea
- Wall of scala vestibuli is vestibular membrane
- Wall of scala tympani is basilar membrane
- Cochlear duct (scala media): space between vestibular and basilar membranes
- Filled with endolymph
- Width of basilar membrane increases from 0.04 mm near oval window to 0.5 mm near helicotrema
- Near oval window basilar membrane responds to high-frequency vibrations
- Near helicotrema responds to low-frequency vibrations
- Spiral organ (organ of Corti): cells in cochlear duct. Contain hair cells (sensory cells) with hair-like projections at the apical ends. These are microvilli called stereocilia.
- Tips of inner hair cells embedded in tectorial membrane
- Basilar region of hair cells covered by synaptic terminals of sensory neurons.
- Cell bodies of afferent neurons grouped into cochlear (spiral) ganglion.
- Afferent fibers form the cochlear nerve.
Cochlea
- Hair cells arranged in rows of inner hair cells (responsible for hearing) and outer hair cells (regulate tension on basilar membrane).
- Hair bundle: stereocilia of one inner hair cell. Tip link (gating spring) attaches tip of each stereocilium in a hair bundle to the side of the next longer stereocilium.
- As stereocilia bend, they open K+ gates (mechanically gated ion channel).
- Vibrations produce sound waves.
- Volume or loudness: function of wave amplitude
- Pitch: function of wave frequency
- Timbre: resonance quality or overtones of sound
The Process of Hearing
- External ear: Collects sound waves, conducts through external auditory canal.
- Middle ear: Tympanic membrane vibrates, ossicles vibrate, vibrations transferred to oval window. Tensor tympani and stapedius muscles reflexively dampen excessively loud sounds (sound attenuation reflex).
- Inner ear: Vibration of perilymph causes vestibular membrane to vibrate, which causes vibrations in endolymph. Basilar membrane displaced, detected by hair cells. Vibrations in scala tympani dissipated by movement of round window.
Effect of Sound Waves on Points Along the Basilar Membrane
- Different frequency sounds cause maximum vibrations of different regions of basilar membrane. High pitch near base. Low pitch near apex.
- Sensitivity of Hearing: More than 90% of afferent axons of the cochlear ganglion synapse with inner hair cells. Only 10 to 30/hair cells. Outer hair cells receive efferent input causing them to shorten. Tuning hair cells to specific frequencies. Actin filaments in hair cells attach to K+ gated channels and can move them along the cell membrane and tighten or loosen the spring. Hair cells are tuned to very specific frequencies.
Central Nervous System Pathways for Hearing
- Sensory axons from the cochlear ganglion terminate in the cochlear nucleus in the brainstem.
- Afferent cochlear nerve fibers send action potentials to superior olivary nucleus in medulla oblongata. These are compared to one another and strongest is taken as standard. Efferent action potentials inhibit other action potentials. Action potentials from maximum vibration go to cortex and are perceived.
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Description
Test your knowledge on the olfactory and gustatory systems, including the structure and function of olfactory epithelium, sensory pathways, and processing. Explore how smells are perceived and processed in the brain, alongside the basics of taste perception.
