1/19 Britton Special Senses I Flashcards
What are the five special senses?
- taste
- smell
- vision
- hearing
- equilibrium
HVEST
Taste
Sensory receptor:
Sensory organ:
Taste receptor; Taste bud
Hearing
Sensory receptor:
Sensory organ:
- Hair cell
- cochlea
Vision
Sensory receptor:
Sensory organ:
- rods and cones
- retina
Equilibrium
Sensory receptor:
Sensory organ:
- hair cell
- vestibular aparatus
Smell
Sensory receptor:
Sensory organ:
- olfactory cell
- olfactory epithelium
Gustation
Action of tasting
How many taste buds does a typical adult have
3,000-10,000
Children have more taste buds than adults
Taste buds are found on 3 types of ______ distributed on the ______ surface of the tongue
Papillae; dorsal surface of the tongue
What taste buds are found on the anterior 2/3s of the tongue
Fungiform
Where do fungiform taste buds have the highest density
At the tip of the tongue
What taste buds are large papillae arranged in a chevron (V-line) at the rear of tongue
Circumvallate
What taste buds are present on the posterolateral surface of the tongue
Foliate
Additional taste buds are found on:
oral mucosa of the palate, pharynx, epiglottis
Components of taste bud
- Each taste bud is composed of ______
- 50-100 ______
- numerous _____ cells and support cells
- all arranged around a ______ on the dorsal surface of the tongue
- epithelial cells
- taste cells - receptors
- basal cells
- central taste pore
Taste receptor is stimulated by:
Tastant
In taste buds, epithelial cells are all arranged around _____ on the _____ of the tongue
central taste pore; dorsal surface
Each taste bud is composed of:
Epithelial cells (taste cells/receptors, basal cells, support cells)
- _______ in the taste receptors project into the taste pore
- _______ provide the receptor surface for taste
- are exposed to _______ dissolved in saliva
- microvilli
- microvilli
- chemicals
How often are taste receptor cells replaced and by differentiation of what cells?
Every 10 days via differentiation of basal cells
A branching terminal network of ____ are interwoven around the taste receptor cells
Nerve fibers
Taste bud receptors are afferent or efferent?
Afferent sensory fibers
Taste receptors are modified ______ cells that respond to ______ stimuli
epithelial; chemical (tastants)
Taste receptors are _____ receptors
chemoreceptors
Taste receptors are the site of:
Sensory transduction
Taste receptors are innervated by ____ sensory nerve fibers penetrating the ______
afferent; basal lamina
Taste Bud Innervation
- the nerve fibers branch extensively and receive synaptic input from the ______ receptors
- each taste bud is innervated by how many sensory nerve fibers?
- each nerve fiber receives Input from how many taste buds?
1) Taste receptors
2) 50 sensory nerve fibers
3) 5 taste buds
What are the 5 different taste modalities?
- sweet
- salty
- bitter
- sour
- umami
What is the common stimulus for sweet sensation?
Sucrose
What is the common stimulus for salty sensation?
NaCl
What is the common stimulus for sour sensation?
Acid
What is the common stimulus for bitter sensation?
Quinine
What is the common stimulus for umami sensation?
Monosodium glutamate (MSG)
What do salty and sour chemicals activate what channel?
Ligand gated channels
Salt is sensed by _____ ions
sour taste is triggered by ______
mediated via _______
Na+ ions; protons (H+ ions); epithelial sodium channel (ENaC)
Sweet, Bitter, and Umami chemicals activate what channel?
GPCR’s
Sweet sensation activates _____
T1R family (GPCR)
Bitter activates ______ (GPCR)
T2R family
_____ is coupled to a Gs protein, called ______
T2R; gustducin
Umami activates _____ (GPCR)
Glutamate receptor (mGluR4)
When stimulated, each of the taste receptor ion channels/GPCRs generate a:
Receptor potential
______ of taste receptor contains various ion channels and GPCRs
Apical membrane
Sensory Transduction in Taste Receptors
Explain the steps of sensory transduction
- Stimulation by chemical tastants
- Ion channel or GPCR signaling pathway generates receptor potential (depolarization)
- Intracellular Ca2+ increases through opening of voltage gated Ca2+ channels or release from intracellular stores
- Vesicles fuse to basolateral membrane for synaptic transmission (mediated by serotonin)
- Serotonin binds to receptors on primary sensory neurons and AP is elicited
What do taste receptors synapse with?
_____ from fungiform papillae
_____ from posterior 1/3 of the tongue
_____ from palate, pharynx, elsewhere
- primary afferent sensory neurons (1st order) from branches of 3 cranial nerves
- CN 7
- CN 9
- CN 10
All primary sensory nerves for taste synapse with ____ order neurons in the ____ in the _______
2nd; nucleus of the tractus solitarius (NTS) in the medulla
NTS relays information to the ______
Thalamus (3rd order)
Thalamus projects to the ______ _______
Gustatory cortex
Sensory Coding for Taste
Taste is coded in the sum of ____ in each cranial nerve in response to a specific ______
neural activity; taste modality
Each taste has its own distinct _____
Nerve response patterns
The response of different ______ and the subsequent integrations of the ______ generated encode taste
taste receptors; AP’s
Ageusia
Absence of taste
Hypogeusia
Diminished taste sensitivity
Dysgeusia
Unpleasant perception of taste (metallic, foul, rancid)
Abnormalities in taste detection can be caused by damage to what nerves?
CN 7 and 9 (due to neurological disorders such as Bell’s palsy, multiple sclerosis, infections)
Abnormalities in taste detection can be caused by ______ deficiency
Vitamin B3, zinc
Problems in taste detection can be caused by ______ (4)
- poor oral hygiene
- adverse side effect of drugs which cause xerostomia
- aging
- tobacco use
Olfactory epithelium is a specialized portion of:
Nasal mucosa
What are the 3 structures of the olfactory epithelium?
- olfactory sensory neurons
- supporting columnar cells
- basal stem cells
- OSN’s are the ____ receptors for olfactory ____
- Each OSN is a _ nerve cell
- Each OSN projects a ________ which terminates in ____ into the mucus layer of the nasal cavity epithelium
- What are present on the cilia?
- OSN axons pass through the ____ to the ____
- sensory, transduction
- bipolar
- dendrite, olfactory cilia
- membrane odorant receptors (GPCR’s)
- cribriform plate, olfactory bulb
Supporting columnar cells secrete _____ that proves the appropriate environment for ____ detection
Mucus; odor
______ generate new olfactory sensory neurons as needed
Basal stem cells
Structure of the Olfactory Bulb
1. _____ are primary sensory afferents (1st order)
2. the _____ is the site where OSN synapse with dendrites of ____
3. _____ cells are 2nd order sensory neurons whose axons enter the olfactory tract and (ascend/ descend) to the olfactory cortex
- Olfactory sensory nerves
- glomerulus, mitral cells
- mitral cells-ascend (synapse with 3rd order to gustatory center in brain)
- there are _______ human genes for olfactory receptors= 3% of the human genome
- the olfactory system is an extremely discriminative and sensitive _______ system
- # of distinct odors
- 1000, olfactory
- chemosensory system
- > 1 million
All olfactory receptors are _____
G-Protein Coupled Receptors (GPCR’s)
What is a smell?
Chemical in the air dissolved in the mucus
Perceiving an odor begins with the _______ and transport of ______ to the olfactory mucosa
Inhalation, aromas
Odorants bind to ______ on the _____ and initiate the sensory transduction cascade, leading to generation of ______ in the sensory ______ nerve
GPCR’s, cilia, APs in the sensory olfactory nerve
Sensory Transduction in Olfactory Receptors
1) odorants bind to diverse ______ which are coupled to Gs proteins called _____
2) ______ dissociate
3) Alpha subunit activates:
4) _____ acts as a second messenger to open ____ channels
5) Inward diffusion of Na+ produces a depolarization, which is a ____
1) GPCR’s; Golf
2) alpha, beta, and gamma subunits
3) Adenylyl cyclase to catalyze cAMP production
4) cAMP; Na+ ion channels
5) action potential
In sensory transduction in olfactory receptors, ____ are specific to different types of odors
G proteins (of GPCRs)
Sensory Transduction in Olfactory Receptors
1. Action potentials are ______ ______ depending on the concentration of ______
2. Action potentials can be ______ to produce specific patterns of activity for each stimulating odorant
3. contributes to _____ ____ of odors
4. Action potentials in the ____ are generated and propagated to synapses in the _____ within the ______
1) graded responses, odorants
2) summated
3) neural coding
4) olfactory nerve (CN I); glomeruli; olfactory bulb
Sensory Transduction in Olfactory Receptors
AP frequency is proportional to:
AP can be ______ by rapidly adapting receptors
1) concentration of odorants
2) attenuated
-receptors have adaptation; stimulated and sustained smells will ‘switch off’ after a long exposure
Sensory Transduction in Olfactory Receptors
1) the ______ is the site where axons of olfactory nerves synapse with numerous dendrites from ______ cells and ______ cells
2) the mechanism of _______ of olfactory neurons with mitral cells generate ______ APs
3) this complex pattern of neuronal integration _______ the various odorant molecules
4) the axons of ______ cells (2nd order neurons) enter the olfactory tract and (ascend/descend) to the olfactory cortex
1) glomeruli; mitral cells; tufted cells
2) convergence/divergence, subsequent
3) discriminates
4) mitral cells; ascend
Sensory coding for smells created from activation of:
Multiple receptors and neurons
Anosmia
Inability to smell
Hyposmia
Diminished olfactory sensitivity
Hyperosmia
Enhanced olfactory sensitivity (common in pregnancy)
Dysosmia
Distorted sense of smell
Causes of Abnormalities in Odor Detection can be caused by:
1) damage to olfactory nerves (head trauma, tumors)
2) sinus infections
3) nasal congestion
4) nasal polyps
5) poor dental hygiene
Basic Mechanism of Vision
The eyes convert _____ energy into AP’s in the _____ nerve that are conducted to the _______ cortex, where they produce the sensation of vision
photon; optic; cerebral
2 components of vision
Optical and neuronal
Visual image is focused on _______ on the retina
Photoreceptors
the visual component is transduced by the _______ into a pattern of ______
Photoreceptors; graded receptor potentials
What are the layers of tissue present in the eye?
Outer layer; middle layer; inner layer
What is the outer layer of the eye made up of
Sclera and cornea
Protective white layer of the eyeball, no light can pass
Sclera
Transparent anterior portion through which light rays enter the eye
Cornea
What is the fluid part of the eye made up of
Aqueous humor and vitreous humor
What is the middle layer of the eye made up of?
Iris, ciliary body, choroid
Colored portion of the eye, in front of the lens
Iris
Adjusts the refractive power of the lens
Ciliary body
Nourishing vascular layer of the eye
Choroid
What is the inner layer of the eye made up of
Retina
Neural tissue containing photoreceptor cells, lines the posterior 2/3rds of the choroid
Retina
Formation of Images on the Retina
1) light rays ______ in all directions from their source
2) light rays that reach the _____ must be focused to a point on the _____ for optimal vision
- diverge
- pupil, retina
During refraction, light waves ____ as they pass through transparent materials of different densities
Bend
What is the mechanism that allows the formation of focused images on the retina?
Refraction
What structures in the eye allow refraction to occur?
cornea and lens
Properties of Light
1) on a concave surface: light waves striking the surface ______
2) on a convex surface: light waves striking the surface ______ at a single point called the ______ ______
1) diverge
2) converge, focal point
Formation of Images on the Retina
1) the cornea and lens both have ______ surfaces and help to focus light rays on the retina
2) the _______ is responsible for most of the refraction
3) however, the curvature of the _____ can be adjusted for near and far vision-termed _______
1) convex
2) cornea
3) lens; accomodation
________ is the process by which the curvature of the lens is adjusted
accommodation (focusing)
The lens is suspended by ______ _____ extending from _______ that control tension on the lens
Zonular fibers; ciliary muscles
Ciliary muscle is _____ muscle and is controlled almost entirely by _____
Smooth; parasympathetic nerves
When focusing distant objects, tension on the lens is ______. The lens ______ and has (more/less curvature)
increased; flattens; less curvature
when focusing near objects, tension on the lens is ______. The lens rounds up and curvature (increases/decreases)
Released; curvature increases
The refractive power of the lens is greatest when:
Curvature is the greatest
Emmetropia
Correct focus
Myopia
Nearsightedness
Hyperopia
Farsightedness
Myopia:
1) Where do light rays focus?
2) Are far or near objects blurry?
3) How is this corrected?
1) in front of the retina
2) far/distant objects are blurry
3) with biconcave lens- cause light rays to diverge so rays are brought to focus on the retina
Hyperopia
1) Where do light rays focus?
2) near or far objects are blurry?
3) corrected with what type of lens?
1) beyond the retina
2) near objects are blurry
3) biconvex lens-add to the refractive power of the lens
What regulates the amount of light entering the eye
Pupil
Pupil size is controlled by the _____
Iris
What are the 2 muscles of the iris
- circular muscle layer
- radial muscle layer
What muscle layer of the iris is controlled by parasympathetic neurons of the ANS
Circular muscle layer
The _____ of the iris constricts the pupil in bright light, termed ____
Circular muscle layer; miosis
What muscle layer of the iris is controlled by sympathetic neurons of the ANS
Radial muscle layer
The _____ of the iris dilates the pupil in dim light, termed ____
Radial muscle layer; mydriasis
The _____ is the neural portion of the eye
Retina
What are the 5 types of neurons in the retina?
- photoreceptors (rods and cones)
- bipolar cells
- ganglion cells
- horizontal cells
- amacrine cells
What are the 3 distinct layers of the retina and what is present in each layer?
- outer: contains rods and cones
- middle: contains bipolar, horizontal, and amacrine cells
- inner: contains ganglion cells
Rods are the receptors for _____
Cones are the receptors for _____
Night vision; color vision
Photoreceptors: Rods and Cones
Outer Segment
1) composed of ______ ______ shaped in either regular stacks of discs (?) or flattened sacs(?)
2) contain the _______ _____ that react to light to initiate receptor potentials
1) membranous disks-(rods) and (cones)
2) photosensitive pigment
Photoreceptors: Rods and Cones
Inner Segment contains cell nucleus that synthesizes:
photosensitive compounds
Photoreceptors: Rods and Cones
Synaptic Terminal
region of synaptic contact with _____ or ______ cells
bipolar or horizontal cells
Each photosensitive compound is a compound molecule that contains:
- light absorbing retinal
- opsin protein
What are the 2 configurations retinal exists in?
In the dark; 11-cis retinal
In the light; 11-trans retinal
What determines which wavelengths of light are optimally absorbed by the photoreceptor
The type of opsin present
______ is needed for the synthesis of retinal
Vitamin A (deficiency leads to visual abnormalities)
Rods contain a single photopigment called:
Rhodopsin
How many pigments do cones contain?
3 (blue, green, red)
Cones differ in the _____ they contain
Types of photopigments (opsins)
1) Each opsin type has a sensitivity to light of ______ wavelengths
2) referred to as what color cones?
3) what are the wavelengths of the cones, respectively?
- different
- blue, green, red cones
- short, medium, long
Color vision is:
Trichromatic
What is color sensation determined by?
The relative AP frequencies generated from each of the 3 colored cones (red, green, and blue)
Any spectral color can be produced by:
Mixing various proportions of these colors
blue, green, red
The photosensitive pigment of rods is
Rhodopsin
1) Rhodopsin is coupled with a G protein called ______
2) when the G protein is stimulated, what subunits dissociate?
3) G-alpha activates ______, which catalyzes cyclic GMP degradation
- transducin
- alpha, beta, gamma
- phosphodiesterase adenylyl cyclase
1) light stimulation of _____ in the rods leads to a structural change in ____ _____ and a conformational change in ______
2) activation of the Gs-protein ______, in turn activates phosphodiesterase (PDE)
3) PDE hydrolyzes _____, reducing its concentration and leading to the closure of ______ _____ ____ channels in the membrane
4) produces a _______ receptor potential
1) rhodopsin, 11-retinal (cis-to trans-); opsin
2) transducin
3) cGMP, cGMP-gated Na+ channels
4) hyperpolarizing
What channels are present in the outer segment membrane of both rod and cone photoreceptors?
Cyclic GMP-gated ion channels
What is responsible for the light induced changes in electrical activity of photoreceptors?
Cyclic GMP gated ion channels
1) leads to a _____ in cGMP levels
2) closing of the ____ permeable channels
3) photoreceptor produces a _____ receptor potential
- decrease
- Na+
- hyperpolarizing
In the Dark
1) cGMP levels are _____
2) cGMP binds to and opens _____ permeable channels
3) ____ enter
4) _______ receptor potential is generated in photoreceptor cells
1) high
2) Na+
3) Na+ (or other cations)
4) depolarization
Explain the steps of response of photoreceptor to light
1) light is absorbed by photopigment
2) Retinal and Opsin dissociate
3) Transducin is activated
4) Phosphodiesterase is activated
5) cGMP levels in cytosol decrease
6) Na+ channels close
7) With less sodium entering the cell, the cell hyperpolarizes
8) Ca2+ channels close
9) Transmitter release is decreased
10) Graded potential in bipolar cell gets smaller
Explain the steps of the state of photoreceptor in the dark
1) cGMP levels are high
2) sodium channels are open
3) Sodium enters the cell, causing a depolarization that spreads from the outer segment to the terminal
4) Ca2+ open in response to depolarization
5) Calcium enters the cell, triggering exocytosis of transmitter
6) Transmitter causes graded potentials in bipolar cell
Vision
1) _____ ______ formed by the axons of ganglion cells of the retina
2) CN ____ exits each eye and combines in front of the brainstem to form the _____ ______
1) Optic Nerve (CN II)
2) CN II, optic chiasm
What does light from the left visual field strike?
the nasal retina of the left eye and the temporal retina of the right eye
The ganglion axons from the left eye retina _____ to the right brain at the optic chiasm while ganglion axons from the right eye retina stay on?
decussate; ganglion axons from the right eye stay on the same side
2 _____ ____ emerge from the optic chiasma to the associated lateral geniculate nucleus (LGN) of the ______
Optic tracts; thalamus
Where does the neural pathway terminate
Primary visual cortex
Anatomic Distribution of Rods and Cones
___ density throughout the retina, with a sharp peak in the ______
Low; fovea
Fovea
Small depression within the retina where visual acuity is the greatest
Anatomic Distribution of Rods and Cones
Rods
_____ density throughout the retina but absent in the _____
____ _____ is the region on the retina where the optic nerve leaves the eye. There are no photoreceptors in this area so does not respond to light, forming a ______
High; fovea; optic disk; blind spot
Visual acuity
- Degree to which details of objects are perceived
- defined as the shortest distance by which 2 lines can be separated and still be perceived as 2 lines
Visual acuity is often determined by using _____ viewed from a distance of 20 ft
Snellen Letter Charts
What is a disease in which there is gradual deterioration of visual acuity
Age-related macular degeneration
What causes color blindness genetically
Inherited abnormality
inherited as recessive and X-linked
8% males, 0.4% females
What is the most common color blindess
Red/green color blindness
Transient blue-green color weakness occurs as a side effect in individuals taking ___
Viagra for the treatment of ED because the drugs inhibit retinal phosphodiesterase
What charts are used to test for color blindess
Isihara Charts
