Chapter 17 - Special Senses Flashcards
Olfaction
The sense of smell
Olfactory Epithelium
Epithelial cells found in the roof of the nasal cavity
3 Cell Types Found in Olfactory Epithelium
- Supporting (Sustentacular) Cells
- Basal (Stem) Cells
- Olfactory Receptors
Supporting (Sustantecular) Cells
Provide support, insulation, nourishment, and detoxification to the olfactory epithelium
Basal (Stem) Cells
Layer that constantly divides to form new olfactory/gustatory receptors
Olfactory Receptors
- Pseudostratified bipolar sensory neurons sensitive to odorants
- Have 1 olfactory hair + 1 unmyelinated axon
- Bowman’s Glands = secrete mucous
Olfactory Transduction (6 Steps)
- Odorant binds to receptors on olfactory hairs
- G-protein linked activation of adenyl cyclase
- cAMP activation
- Na+ influx
- Generator potential
- Action potential
Olfactory Pathway
Olfactory receptors -> RIght & left olfactory nerves (penetrates cribiform plate) -> Olfactory bulbs (synapses w/ 2nd order relay neurons) -> Olfactory tracts -> Primary olfactory area
- Projections to limbic system & hypothalamus = visceral/emotional responses to smell & memory evoked responses
- Projection to thalamus = odor identification & discrimination area of frontal lobe
Primary Odors
- Hundreds in total
- Nose can recognize approx. 10,000 different odor combinations
- 10 to 100 million olfactory receptors present in epithelium
Odor Thresholds & Adaptation
- Smell threshold may be very low
- Adaptation to odors occurs quickly
- With age, decreased olfactory receptor no. = hyposmia/ anosmia
Gustation
The sense of taste
5 Primary Taste Sensations
- Bitter
- Sour
- Salty
- Sweet
- Savory (Umami)
* Complex flavors = combinations of primary tastes + smell + tactile sensations
* Lowest sensitivity threshold = bitter
* Highest sensitivity threshold = savory
Adaptation
Decreased sensitivity due to constant stimulation
Tastants
Chemical substances that cause gustatory (taste bud) stimulation, as well as olfactory stimulation
Odorants
Chemical substances that cause olfactory stimulation, also affects gustation
3 Types of Epithelial Cells in Taste Buds
- Basal (Stem) Cells
- Supporting Cells
- Gustatory Receptors
Supporting Cells (Gustatory)
Provide nutritional support to other cells in taste buds
Gustatory Receptors
Have 1 gustatory hair (microvillus) which project from the taste pore which synapses w/ the 1st order sensory neuron
Taste Transduction (Ionic Tastes)
Dissolved tastants bind gustatory hairs -> Salty (Na+) and Sour (H+) enter cell via ion channels of different gustatory receptors -> Ca+2 influx -> Exocytotic release of neurotransmitter -> EPSPs in 1st order sensory neuron -> Firing of action potentials
Taste Transduction (Organic Tastes)
Dissolved tastants bind gustatory hairs -> Sweet, bitter, umami bind surface protein receptors of different gustatory receptors -> 2nd messenger release -> Closing of K+ channels, depolarizing cell -> Ca+2 influx + release of stored ER Ca+2 -> Increased cytosolic Ca+2 -> Exocytotic release of neurotransmitter -> EPSPS -> Action potential
4 Different Locations of Taste Buds
- Tongue
- Soft Palate
- Pharynx
- Epiglottis
* More taste buds associated w/ lingual papillae, located on dorsal/lateral tongue surface
4 Papillae Types
- Vallate Papillae
- Fungiform Papillae
- Foliate Papillae
- Filiform Papillae
Vallate Papillae
V-shaped row near back of tongue
Fungiform Papillae
Scattered over dorsal tongue surface
Foliate Papillae
Located on sides of tongue
Filiform Papillae
Most numerous on tongue; no taste buds, contain tactile receptors
Gustatory Pathway
Cranial nerves 7, 9, & 10 carry taste info -> Gustatory nucleus in medulla (synapse w/ 2nd order relay neurons) -> Limbic system & hypothalamus (emotional response) + Thalamus -> Primary gustatory area of parietal lobe & nearby association areas
3 Different Accessory Structures of the Eye
- Extrinsic Muscles
- Eyelids + Eyelashes
- Lacrimal Apparatus
3 Pairs of Extrinsic Eye Muscles
- Superior + Inferior Rectus: Elevation + Depression of eyeball
- Lateral + Medial Rectus: Abduction + Adduction of eyeball
- Superior + Inferior Oblique: Intorsion + Extorsion of eyeball
3 Cranial Nerves that Control Extrinsic Eye Muscles
- Oculomotor (3) nerve
- Trochlear (4) nerve
- Abducens (6) nerve
* Brainstem & cerebellum control eyeball movements
Functions of the eyelids
To provide shade, protection & lubrication to the eyball
Surface Anatomy of Eyelid (3 Parts)
- Palpebral Fissure = Space between upper & lower eyelids
- Lateral & Medial Commisures = Corners where the upper & lower eyelids meet
- Lacrimal Caruncle = Small, pink, globular nodule at the corner of the eyeball
Palpebral Layers of the Eyelid
- Epidermis
- Dermis
- SubQ tissue
- Orbicularis oculi
- Tarsal plate
- Tarsal gland
- Tarsal plate
- Areolar CT
- Palpebral conjunctiva
2 Eyelid Muscles
- Orbiculars Oculi = Closes eyelids
2. Levator Palpebrae Superioris = Opens eyelids
Tarsal Glands
- Embedded in tarsal plate
- Responsible for lipid-rich secretions
Chalazion
Cyst in the eyelid due to a blocked oil gland
2 Types of Conjuctiva
- Palpebral = Continuous w/ Bulbar Conjunctiva
- Bulbar Conjunctiva = Covers sclera, but not cornea
* Blood shot eyes caused by vasodilation due to irritation of bulbar conjunctiva
Eyelashes
- Blink reflex allows eyelashes to brush off dirt
- Sebaceous ciliary glands secrete oil which lubricates the eyes
- Sty = infection of sebaceous ciliary glands
2 Parts of the Lacrimal Apparatus
- Lacrimal Gland + Excretory Lacrimal Ducts
2. Lacrimal Sac + Superior & Inferior Lacrimal Canaliculi + Nasolacrimal Duct
Lacrimal Gland
- Secretes fluid (tears), contains salt, mucus & lysozyme
- Functions to protecct, clean & lubricate the eyes
- Parasympathetic innervation via Facial (7) nerve
- Tears -> Lacrimal puncta -> Superior & inferior lacrimal canaliculi -> Lacrimal Sac -> Nasolacrimal duct -> Nose
Dacrocystitis
Infection of the lacrimal sac; usually bacterial
3 Coats (Tunics) of the Eyeball
- Fibrous Tunic
- Vascular Tunic
- Retina
Fibrous Tunic (2 Main Parts)
- Sclera
2. Cornea
Sclera
White, dense CT, surrounds eyeball except at cornea
Cornea
Transparent cover over iris
Canal of Schlemm (AKA “Scleral Venous SInus”)
Drains aqueous humor
Vascular Tunic/Uvea (3 Main Parts)
- Choroid
- Ciliary Body
- Iris
Choroid
- Middle, dark brown layer of vascular tunic
- Has many blood vessels
- Absorbs stray light
Ciliary Body
- Runs from ora serrata to corneal/scleral junction
- Contains ciliary muscle (controls shape of lens)
- Ciliary process -> Aqueous humor & attach zonular fibers
- Accommodation for near vision = contraction of ciliary muscle; leads to decreased tension on zonular fibers, which leads to rounding up of lens
Iris
- Circular pigmented diaphragm, which regulates size of pupil
- Eye color = type & amount of melanin
- Eumelanin = black-brown pigment
- Pheomelanin = reddish-yellow pigment
2 Pupillary Responses to Light Intensity
- Miosis
2. Mydriasis
Miosis
Contraction of sphincter pupillae due to bright light (Parasympathetic)
Mydriasis
Contraction of dilator pupillae due to dim light (Sympathetic)
Retina/Inner Tunic (2 Layers)
- Pigmented Layer
2. Neural Layer
Pigmented Layer
Contains melanin
*Ocular melanoma = Eye cancer
Neural Layer (3 Parts)
- Photoreceptor Layer
- Bipolar Cell Layer
- Ganglion Cell Layer
Photoreceptor Layer
Contains rods & cones
Bipolar Cell Layer
Contains bipolar neurons
Ganglion Cell Layer
Contains ganglion cells whose fibers -> Optic (2) nerve
Outer Synaptic Zone
Area between photoreceptor & bipolar layer
Inner Synaptic Zone
Area between bipolar & ganglion cell layer
2 Photoreceptors Found in Retina
- Rods
- Cones
- Both contain light-sensitive pigments
- Light striking photoreceptors permits bipolar cells to stimulate ganglion cells to fire APs along their axons, which form the optic (2) nerve.
Rods
- Photoreceptors for low illumination (i.e. night vision)
- Cause mydriasis in dim light
- Only rods (located in periphery of retinae) are sensitive to faint light
- Do not detect fine detail/color
- Very sensitive in low illumination
- High neural convergence = electrical activity of many rods converges on a single ganglion cell
Cones
- Photoreceptors reponsible for color vision & visual acuity
- Outer segment is cone-like
- Cone photopigment = iodopsin = cis-retinal + different opsin
- 3 Types: Blue, red & green; respond to different wavelengths of light
- Perception of many colors = mixing inputs of 3 different cone types
- Most visual images are focused on fovea centralis
2 Other Retinal Cell Types
- Horizontal Cells
- Amacrine Cells
*Both modify passing signals between the 3 cell layers
Neural Cell Convergence
- 120 mil. rods/retina & 6 mil. cones/retina, but only 1 mil. ganglion cells
- Up to 600 rods synapse w/ each bipolar cell (Leads to high sensitivity w/ poor resolution)
- 1 cone synapses w/ each bipolar cell (Leads to low sensitivity w/ high resolution)
*Signal integration occurs before APs sent to lateral geniculate nucleus of thalamus & then to primary visual area of occipital lobes
Optic Disc
- AKA “Blind Spot”
- Space where optic nerve & central retinal artery & vein pass through retina
Ophthalmoscope
Device used to examine the eye grounds
Macula Lutea
- Oval, yellowish retinal area w/ depression (Fovea Centralis)
- Fovea Centralis has the highest resolution
- Visual acuity/Resolution = due to greatest concentration of cones
Age-related Macular Disease (2 Types)
- Defined as gaps in central vision (Causes distortion of images)
1. Dry form: Pigment layer atophy
2. Wet form: Leaky blood vessels, progression of dry form
Retinal Detachment
- Caused by accumulation of fluid between retina & choroid
- Treatment: Pneumatic retinopexy or scleral buckle
Interior of Eyeball (2 Parts)
- Crystalline Lens
2. Anterior & Posterior Cavities
Crystalline Lens
- Attached to ciliary processes by zonular fibers (suspensory ligaments)
- Composed of crystallin protein, arranged in laminae
Cataracts
Opacity in lens, causing blurred vision
Posterior Cavity
- AKA “Vitreous Chamber”
- Filled w/ vitreous humor (AKA “Vitreous Body”)
- Vitreal Floaters = Small spots that drift throught the field of vision
- Hyaloid Canal = Site of hyaloid artery
Anterior Cavity
- Located between cornea & lens
- Subdivided into anterior & posterior chambers
- Filled w/ aqueous humor made by ciliary processes
Intraocular Pressure
- Fluid pressure inside the eye
- Normal range = 12 -22 mmHg
- Average = 16 mmHg
Glaucoma
- Increased intraocular pressure due to blockage of canal of Schlemm/scleral venous sinus; causes compression of renal areries
- Can lead to ischemic damage, which can cause partial/complete blindness
Visible Light
Wavelengths of electromagnetic spectrum (400 - 700 nanometers)
*Vision = Presence of retinal photoreceptors capable of recording these energy wavelengths
Refraction of Light Rays
- Bending of light as it passes from one translucent medium to another of different density
- Concave surfaces cause light to bend outward/diverge
- Convex surfaces cause light to bend inward/converge
- Converging light rays meet at the focal point
- Images on retina inverted & reversed
- Eye parts that refract light: cornea, aqueous humor, lens, vitreous humor
Changing Shape of Lens (2 Ways)
- Flattening = Relaxation of ciliary muscles, increasing tension on zonular fibers (For far vision)
- Rounding = Contraction of ciliary muscles, decreasing tension on zonular fibers (For near vision)
Accommodation
Contraction of ciliary muscles to enable near vision
Near Point of Vision
- Minimum distance from eye that an object can be clearly focused
- Changes w/ age due to decreased lens elasticity
Presbyopia
Loss of lens elasticity due to advancing age
3 Processes of Image Formation on Retina
- Light refraction by cornea & lens
- Accommodation of lens, for near vision
- Constriction of pupil to prevent extraneous light from entering eye
*Functions 2 & 3 result parasympathetic motor innervation -> contraction of intrinsic eye muscles
Convergence (Other Meaning)
Medial movement of eyeballs to a single image of near object
3 Types of Refraction Abnormalities
- Myopia
- Hyperopia
- Astigmatism
Emmetropia
Normal vision
Myopia
- Nearsightedness; only near objects can be seen clearly
- Causes: Focus isn’t directed to retinal screen, but vitreous humor
- Treatment: Concave corrective lens
Hyperopia
- Farsightedness; only far objects can be seen clearly
- Causes: Focus goes farther than the retinal screen
- Treatment: Convex corrective lenses
Astigmatism
Irregular curvature of lens/cornea
Mechanism for Light Transduction
- Rod outer segment = Disc-like membrane stacks w/ embedded rhodopsin
- Light splits rhodopsin into retinal & opsin (called bleaching)
- Cis -> trans isomerization causes trans-retinal to seperate from opsin
- Isomerization step -> chemical reactions-> receptor potential
- Retinal isomerase converts trans-retinal -> cis-retinal which re-associates w/ opsin (called regeneration)
Isomerization Process
Activation of an enzyme (PDE) that degrades c-GMP -> Closes c-GMP-gated Na+ channels -> Decreased Na+ influx (dark current) -> Hyperpolarizing receptor potential -> Cessation of tonic glutamate inhibitory neurotransmitter release
*Permits EPSPs in bipolar neuron -> activation of amacrine cell -> firing action potentials by ganglion cell axon
Regeneration Process
Retinal Isomerase converts trans-retinal -> cis-form, which re-attaches opsin -> Inhibition of PDE -> c-GMP accumulation in rod cell -> Re-opening of c-GMP- gated Na+ channel -> Na+ influx -> Membrane depolarization -> Tonic glutamate inhibitory neurotransmitter release (Which prevents activation of bipolar neuron due to IPSPs causing hyperpolarization)
Retinal
- Vitamin A derivative
- Vitamin A found in vegetables w/ carotenes, such as carrots
Light Adaptation
- Rods switch “off” due to decreased rhodopsin & cones switch “on”
- In strong light, rod bleaching is much faster than regeneration
- Rods hardly contribute to visual signal
- Cones do contribute to visual signal, because they cycle faster
- Rapid regeneration in strong light happens because some photopigment in cones always in cis-form
- Bright lights cause miosis, which also reduces rod participation
Dark Adaptation
- Rods switch “on” & cones switch “off”
- Takes several minutes due to need to synthesize more rhodopsin
- Cones insensitive to weak light
- Dim lights cause mydriasis, which also increases rod participation
Color Blindness
- Condition caused by deficiency in a particular cone type
- Red-green color blindness: Red & green are seen as the same color
Nyctalopia
- “Night Blindness”
- Caused by chronic vitamin A deficiency
Visual Pathway
Ganglion cell action potentials -> Optic (2) nerve -> Optic chiasm -> Optic tract -> Lateral geniculate nucleus of thalamus -> Optic radiations -> Primary visual area
Stereoscopic (AKA “Binocular”) Vision
- Each eye sends info to brain about object, but from a slightly different angle
- Integration of the signals -> steroscopic vision
Depth Perception
Ability to perceive relative distance of objects in a visual field
2 Steps of Stereoscopic Vision
- Since optic nerves cross at optic chiasm, each half of brain receives info from both eyes about same part of an object
- 1a. Neurons carrying info about the nasal visual field of one eye & temporal visual field of opposite eye project to the same cerebral hemisphere
- 1b. Axons from two medial halves of the retinae cross in optic chiasm
- 1c. Axons from two lateral halves of the retinae remain uncrossed - Two halves of the brain communicate -> 3D interpretation of object
2 Locations Ganglion Cell Axons Travel To
- Midbrain
- 1a. Pretectal Nuclei: Pupillary accommodation reflexes
- 1b. Superior Colliculi: Head + eye movements regarding sight sound - Suprachiasmatic Nucleus (Circadian Rhythm)
2 Sensory Functions Located in Inner Ear
- Equilibrium (AKA “Balance”)
- Hearing (AKA “Audition”)
*Mechanoreceptors = hair cells w/ stereocilia that respond to mechanical stimulation
3 Major Parts of the Ear
- External (Outer) Ear
- Middle Ear
- Internal (Inner) Ear
External (Outer) Ear (3 Parts)
- Auricle (AKA “Pinna”): Consists of helix & lobule
- External Auditory Canal: Lined w/ epidermis & derivatives (fine hairs, sweat glands & ceruminous glands)
- Tympanic Membrane: The eardrum
Middle Ear
- Space within temporal bones
- Begins just medial to tympanic membrane
- Extends to bony wall w/ oval window & round window
- Opening duct leads to mastoid sinuses
3 Auditory Ossicles in Middle Ear
- Malleus (Hammer)
- Incus (Anvil)
- Stapes (Stirrup)
- Footplate rests on oval window’s membrane
Otitis Media
Infections of the middle ear
Auditory (Eustachian) Tube
- Runs from middle ear to nasopharynx
- Equalizes air pressure on both eardrum surfaces
- Ensures sound waves striking eardrum are not attenuated
Protection Against Loud Noises (2 Ways)
- Tensor Tympani muscle contraction = Decreased motion of eardrum
- Stapedius muscle contraction = Decreased motion of stapes
Hyperacusia
- Abnormally sensitive hearing
- Caused by paralysis of either the tensor tympani, or stapedius or both
Internal (Inner) Ear (2 Divisions)
- Bony Labyrinth: Contains perilymph
2. Membranous Labyrinth: Contains endolymph
3 Main Components of the Inner Ear
- Vestibule
- Semicircular Canals
- Cochlea
Vestibule
- Chamber between semicircular canals & cochlea
- Function: Maintain static balance
- Contains the utricle & saccule
- Mechanoreceptors contained in the macula of the utricle & saccule
- Stereocilia of hair cells stick to gelatinous otolithic membrane
- Mechanoreceptors provide info on position of head + linear acceleration/deceleration
Otoliths
- CaCO3 granules located on the utricle & saccule
- Embedded on top of otolithic membrane
- Motion -> sagging of otolithic membrane -> bending of hair cell’s stereocilia
Semicircular Canals
- Found in anterior, posterior & lateral forms
- Function: Maintain dynamic balance
- Semicircular Ducts: Inner portion of the canals
- Ampulla: Swellings of the semicircular ducts
- Stereocilia of hair cells stick to gelatinous cupula (which are located within the ampullae)
- Crista: Contains supporting + hair cells for dynamic balance
- Vestibular branch of vestibulocochlear (8) nerve is composed of ampullary nerves, utricular nerve & saccular nerve
Cochlea
- Function: Conduct hearing
- Spirals around modiolus
- Contains organ of Corti, which -> info to cohclear nuclei of medulla via cochlear branch of cranial nerve 8 -> thalamus -> temporal lobe
3 Channels of the Cochlea
- Cochlear Duct (AKA “Scala Media”): Found in membranous labyrinth
- Vestibular Canal (AKA “Scala Vestibule”): Found in bony labyrinth
- Tympanic Canal (AKA “Scala Tympani”): Also found in bony labyrinth
Organ of Corti
- AKA “Spiral Organ”
- Sends info to cochlear nuclei of medulla via cochlear branch of cranial nerve 8 -> thalamus -> temporal lobe
- Basilar Membrane = Lower wall of cochlear duct
- Vestibular Membrane = Upper wall of cochlear duct
- Hair cells of the tectorial membrane rest on the basilar membrane
- Inner hair cells (90-95% sensory) = Transduce sound vibrations into electrical impulses
- Outer hair cells (90% motor) = Regulate sensitivity of inner hair cells
Dynamic Equilibrium
- Maintenance of body position in response to angular/rotational movement
- Sense organs = cristae in ampullae of 3 semicircular ducts
- During movement, endolymph within semicircular ducts displaces cupulas causing stereocilia of hair cells to bend, initiating APs in 1st order sensory neurons, which -> brain
Transduction for Mechanical Vibrations into APs
- Hair cell’s stereocilia membrane has mechanically-gated K+ channel
- Bending of stereocilia in one direction -> tip-link protein opens mechanically-gated K+ transduction channel -> K+ influx -> depolarization of hair cell
- Hair cell depolarization -> opening of voltage-gated Ca+2 channels -> Ca+2 influx -> exocytotic release of neurotransmitter by hair cell -> EPSPs in 1st order sensory neuron -> increased AP firing rate of 1st order neuron -> brain via vestibular branch of cranial nerve 8
- When stereocilia are bent in the opposite direction -> closing of K+ transduction channel -> decreased AP firing by 1st order sensory neuron
Static Equilibrium
- Maintain orientation of body relative to gravity
- Necessary for posture & balance
- Sense organs = maculae of utricle & saccule
Kinocilium
A true cilium, present in stereocilium hair bundles of mechanoreceptors for both static & dynamic balance
Vestibular Ganglion
Contains cell bodies of 1st order sensory neurons (for hearing + equilibrium)
Vestibular Nuclei
- Termination point of most vestibular branch fibers of cranial nerve 8
- Sends motor commands to cranial nerve nuclei 3, 4, 6, and 11 (coordinates eye + head movement)
- Also sends motor commands to vestibulospinal tract (regulates muscle tone)
- Conveys sensory info to ventral posterior nucleus of thalamus, then -> vestibular area of somatosensory cortex
2 Characteristics of Sound
- Intensity of Vibration (AKA “Amplitude”/”Loudness”); measured in decibels (dB)
- Frequency of Vibration (AKA “Pitch”); audible range = 20 -20,000 Hertz
Audition
- AKA “Hearing”
- Cochlear hair cells register a sound’s intensity & frequency
- Sound waves strike eardrum -> vibrations conveyed to ossicles
- Ossicles convey vibrations to oval window membrane
- Vibrations of oval window membrane -> pressure waves in perilymph of vestibular canal
- Loudness = Distance of eardrum travel
- Pitch = Speed of vibration
Helicotrema
Connection between the vestibular canal and tympanic canal
Oval Window Membrane Vibration
- Causes pressure waves toward round window
- When oval window membrane moves inward, round window membrane moves outward to prevent sound attentuation
Perilymph Fluid Movement
- Causes up & down movement of vestibular membrane at certain points (depending on sound frequency) -> increases pressure in endolymph in cochlear duct -> vibration of basilar membrane
- Some stereocilia of hair cells pushed against tectorial membrane -> bending -> receptor potential -> neurotransmitter release -> EPSPs in 1st order sensory neurons -> APs
- Cell bodies of 1st order sensory neurons in spiral organ/organ of Corti
- APs carried by cochlear branch of cranial nerve 8 -> brainstem
Recognition of Sound Intensity
The higher the sound intensity, the larger the vibrations, the greater number of APs fired per second
Recognition of Sound Frequency
- High pitch sounds cause the vestibular & basilar membranes to resonate near to oval window
- Low pitch sounds cause the vestibular & basilar membranes to resonate near to helicotrema
- Intermediate pitch sounds are registered at intermediate positions along the length of the organ of Corti
Otoacoustic Emission
- Motor neuron stimulation of outer hair cells -> rhythmic shortening/lengthening of hair cells -> oscillation of basilar membrane -> increased signal by inner hair cells
- Diagnosis of deafness in newborn
Cochlear Implants
Devices that translate sounds into electrical signals for interpretation by the brain; meant to help deaf people w/ destroyed hair cells
Meniere’s Disease
- Increased endolymph in membranous labyrinth
- Endolymphatic sac maintains cosntant pressure & volume of endolymph
- Causes tinnitus, vertigo & possible deafness
