Gustation and Taste Buds Overview
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Questions and Answers

What is the primary function of gustatory cells?

  • Detect texture of food
  • Regenerate taste receptor cells
  • Transduce taste signals (correct)
  • Support taste bud structure

    • Which cranial nerve innervates the anterior two-thirds of the tongue?

  • Facial nerve (CN VII) (correct)
  • Glossopharyngeal nerve (CN IX)
  • Trigeminal nerve (CN V)
  • Vagus nerve (CN X)

    • Which type of papillae is primarily involved in tasting and is found on the anterior margin of the tongue?

  • Circumvallate papillae
  • Filiform papillae
  • Fungiform papillae (correct)
  • Foliate papillae

    • Which type of gustatory cell responds specifically to sour stimuli?

    <p>Type III cells</p> Signup and view all the answers

    What is the life span of a taste receptor cell approximately?

    <p>10 days</p> Signup and view all the answers

    How do tastants interact with gustatory receptor cells?

    <p>Via taste pores in taste buds</p> Signup and view all the answers

    Which of the following tastes is specifically stimulated by chemical salts?

    <p>Salty</p> Signup and view all the answers

    What structural feature distinguishes circumvallate papillae from other types?

    <p>They form an inverted 'V' shape</p> Signup and view all the answers

    What role do basal cells serve in taste buds?

    <p>Regenerate taste receptor cells</p> Signup and view all the answers

    Which cranial nerve innervates the epiglottis and lower pharynx?

    <p>Vagus nerve (CN X)</p> Signup and view all the answers

    Which type of gustatory cells are responsible for sensing salty tastes?

    <p>Type I cells</p> Signup and view all the answers

    What primarily causes the perception of sour taste?

    <p>Free H+ ions blocking K+ channels</p> Signup and view all the answers

    Which type of taste receptor is activated by amino acids, especially glutamate?

    <p>Umami receptors</p> Signup and view all the answers

    Which gustatory cells respond to bitter tastes and how many differing receptors do they contain?

    <p>Type II cells; ~50-100 receptors</p> Signup and view all the answers

    Which taste is influenced by olfactory receptors in addition to primary taste receptors?

    <p>Overall taste perception</p> Signup and view all the answers

    What is the myth associated with the taste bud tongue map proposed in 1901?

    <p>Different regions of the tongue are solely responsible for specific tastes</p> Signup and view all the answers

    Which cell type is NOT associated with the activation of GPCR for taste perception?

    <p>Type I cells</p> Signup and view all the answers

    Which layer of the eye includes the iris, ciliary body, and choroid?

    <p>Vascular tunic</p> Signup and view all the answers

    What flavor does the chemical group linked to alkaloids represent?

    <p>Bitter</p> Signup and view all the answers

    Which of the following is NOT a function of the protective structures of the eye?

    <p>Lubricating the eye with tears</p> Signup and view all the answers

    What is the primary role of the conjunctiva?

    <p>To form a protective layer over the eye</p> Signup and view all the answers

    Which component of visible light is defined as the distance between two wave peaks?

    <p>Wavelength</p> Signup and view all the answers

    What structure is responsible for producing sebum to prevent tear overflow?

    <p>Tarsal glands</p> Signup and view all the answers

    Which part of the eye does the conjunctiva NOT cover?

    <p>The cornea</p> Signup and view all the answers

    What is the anatomical term for the space between the eyelids?

    <p>Palpebral fissure</p> Signup and view all the answers

    What type of epithelium makes up the conjunctiva?

    <p>Stratified squamous epithelium</p> Signup and view all the answers

    Which characteristic of a photon is represented by the amplitude of light waves?

    <p>Intensity of the light</p> Signup and view all the answers

    What is the primary role of lacrimal fluids?

    <p>To lubricate the anterior surface of the eye</p> Signup and view all the answers

    What is the primary function of the ciliary body?

    <p>To produce aqueous humor</p> Signup and view all the answers

    Which structure is responsible for the intake of light into the eye?

    <p>Cornea</p> Signup and view all the answers

    What happens to the lens when the ciliary muscles are contracted?

    <p>The lens thickens.</p> Signup and view all the answers

    Where are rods primarily located within the retina?

    <p>Throughout the peripheral retina</p> Signup and view all the answers

    Which of the following best describes the function of the iris?

    <p>Controls the amount of light entering the eye</p> Signup and view all the answers

    What is the role of the retinal pigment epithelial cells?

    <p>Store and recycle vitamin A</p> Signup and view all the answers

    What is the effect of high convergence in terms of visual acuity?

    <p>Lower acuity due to larger receptive fields</p> Signup and view all the answers

    During accommodation, what occurs for distant vision?

    <p>Ciliary muscles relax, lens becomes flat</p> Signup and view all the answers

    Which type of light does rhodopsin in rods primarily respond to?

    <p>A wide range of wavelengths from 400 nm to 600 nm</p> Signup and view all the answers

    Which of the following accurately describes the blind spot in the retina?

    <p>Contains no photoreceptors</p> Signup and view all the answers

    What is the primary reason for differences in color perception?

    <p>The ratio of stimulation among cone types</p> Signup and view all the answers

    What physiological process allows the eye to adjust to low light conditions?

    <p>Dark adaptation</p> Signup and view all the answers

    Which structure acts as the gelatinous fluid filling the posterior cavity of the eye?

    <p>Vitreous humor</p> Signup and view all the answers

    What occurs in the neural layer of the retina?

    <p>Conversion of light energy into nerve signals</p> Signup and view all the answers

    Which type of papillae is primarily responsible for texture perception rather than taste?

    <p>Filiform</p> Signup and view all the answers

    What type of gustatory cell serves as the stem cell within the taste buds?

    <p>Type IV</p> Signup and view all the answers

    What is the structural feature of circumvallate papillae that distinguishes them from other types?

    <p>Deep, narrow depression surrounding them</p> Signup and view all the answers

    Which cranial nerve is responsible for innervating the posterior one-third of the tongue?

    <p>Glossopharyngeal nerve (CN IX)</p> Signup and view all the answers

    What is the lifespan of a taste receptor cell?

    <p>10 days</p> Signup and view all the answers

    What activates the depolarization in Type II gustatory cells responsible for sweet taste?

    <p>Specific configuration of glucose</p> Signup and view all the answers

    Which gustatory cell type is primarily responsible for sensing salty tastes?

    <p>Type I cells</p> Signup and view all the answers

    Which type of cell in the gustatory system transduces sweet and umami tastes?

    <p>Type II</p> Signup and view all the answers

    Which mechanism is involved in the perception of sour flavors?

    <p>Blocking of K+ channels by H+ ions</p> Signup and view all the answers

    What phenomenon do gustatory signals primarily add dimensions to, influencing our taste experience?

    <p>Pleasantness</p> Signup and view all the answers

    What taste receptor cell type is associated with a diverse range of bitter taste stimuli?

    <p>Type II cells</p> Signup and view all the answers

    Which papillae type functions mostly during infancy and early childhood but is less developed in adults?

    <p>Foliate</p> Signup and view all the answers

    Where do axons of gustatory sensory neurons project after contacting the gustatory cells?

    <p>Medulla Oblongata</p> Signup and view all the answers

    What misconception was popularized by D. Hänig's 1901 publication regarding taste perception?

    <p>Specific regions of the tongue are solely responsible for different tastes</p> Signup and view all the answers

    What do the gustatory microvilli of gustatory cells primarily interact with?

    <p>Saliva and tastants</p> Signup and view all the answers

    What role do olfactory receptors play in taste perception?

    <p>They contribute additional flavor information.</p> Signup and view all the answers

    Which taste is specifically linked to amino acids like glutamate?

    <p>Umami</p> Signup and view all the answers

    Which statement is true regarding Type III gustatory cells?

    <p>They respond to free H+ ions causing sour taste perception.</p> Signup and view all the answers

    What is the main purpose of the tarsal glands located in the eyelids?

    <p>To produce sebum and prevent tear overflow</p> Signup and view all the answers

    Which layer of the eye is responsible for providing structural support and includes the sclera and cornea?

    <p>Fibrous tunic</p> Signup and view all the answers

    How does the conductive path of light affect our vision?

    <p>By controlling the intensity of light hitting the retina</p> Signup and view all the answers

    What role do goblet cells play in the conjunctiva?

    <p>Lubricating and moistening the eye</p> Signup and view all the answers

    What is the primary function of the lacrimal apparatus?

    <p>To produce, collect, and drain tears</p> Signup and view all the answers

    What characteristic of visible light is determined by its wavelength?

    <p>The color perception</p> Signup and view all the answers

    Which two parts make up the conjunctiva?

    <p>Ocular and palpebral</p> Signup and view all the answers

    What does the amplitude of light waves represent?

    <p>The intensity of light</p> Signup and view all the answers

    Which structures primarily cushion the eye within the orbit of the skull?

    <p>Orbital fat</p> Signup and view all the answers

    What forms the continuous lining over the external surface of the eye?

    <p>Conjunctiva</p> Signup and view all the answers

    What is the role of the lacrimal gland in eye function?

    <p>Produces tears that cleanse and moisten the eye surface</p> Signup and view all the answers

    Which structure provides the main protective function for the eye?

    <p>Sclera</p> Signup and view all the answers

    What is the principal function of the ciliary body?

    <p>To produce aqueous humor</p> Signup and view all the answers

    What is the significance of the fovea centralis?

    <p>It is the area of sharpest vision due to a high concentration of cones</p> Signup and view all the answers

    Which type of muscle regulates the size of the pupil?

    <p>Sphincter pupillae and dilator pupillae</p> Signup and view all the answers

    What process occurs when the ciliary muscles contract?

    <p>The lens becomes round to accommodate near vision</p> Signup and view all the answers

    Which statement accurately describes the relationship between rods and cones in the retina?

    <p>Rods are responsible for low light vision and are concentrated in the peripheral retina</p> Signup and view all the answers

    How does the process of refraction affect light as it enters the eye?

    <p>Light bends when passing through different media, focusing on the retina</p> Signup and view all the answers

    What occurs during dark adaptation in the eyes?

    <p>Rods adjust to low light conditions more slowly than cones</p> Signup and view all the answers

    What determines the color perception in human vision?

    <p>The stimulation ratios of different cone types in response to light</p> Signup and view all the answers

    What is the primary function of photosensitive ganglionic cells in the retina?

    <p>Regulate the release of melatonin from the pineal gland</p> Signup and view all the answers

    Which of the following best describes the optic disc?

    <p>Area devoid of photoreceptors where the optic nerve exits the retina</p> Signup and view all the answers

    What characterizes the anterior chamber of the anterior cavity of the eye?

    <p>Serves as a space between the cornea and iris filled with aqueous humor</p> Signup and view all the answers

    What happens when light transitions from air into the cornea?

    <p>It slows down, leading to light bending (refraction)</p> Signup and view all the answers

    Study Notes

    Gustation

    • Sense of taste
    • Chemicals detected by chemoreceptors in the oral cavity
    • Allows sampling of food and drink consumed
    • Aided by the olfactory sense

    Organization of Gustatory System

    • Papillae possess taste buds
    • Found on the anterior surface of the tongue and the soft palate
    • Taste buds house gustatory cells (various types) and support cells
    • Gustatory cells are the taste receptor cells

    Papillae of the Tongue

    • Foliate: Leaf-like, less developed in humans, functions mostly in infancy and early childhood
    • Filiform: Thread-like, short and spiky, found on anterior 2/3rds of tongue, don't have taste buds, detect texture and manipulate food
    • Circumvallate: Mushroom-shaped, about 10-12, create a boundary between anterior and posterior aspects, great concentration of taste buds
    • Fungiform: Mushroom-shaped, about 300, primarily on anterior margin of tongue, contain a few taste buds

    Taste Buds

    • Taste pores open to oral cavity
    • Dissolved taste-producing chemicals (tastants) come into contact with gustatory cells
    • Gustatory cells are packaged in taste buds
    • Basal cells are stem cells
    • Transitional cells are support cells
    • Nerve fibers are found between cells
    • Life span of a taste receptor cell is ~10 days

    Gustatory Cells

    • Specialized neuroepithelium
    • Dendritic ending is formed by gustatory microvilli
    • Tastants interact with receptors on microvilli
    • Four types of cells
    • Type I: Respond to Na+ ions (salt)
    • Type II: Transduce sweet, umami, and bitter; use GPCRs to detect tastants
    • Type III: Respond to sour stimuli
    • Type IV: Serves as the stem cell

    Gustatory Pathway

    • Gustatory cells contact sensory neurons of the facial nerve (CN VII) and glossopharyngeal nerve (CN IX)
    • CN VII innervates anterior 2/3rds of tongue
    • CN IX innervates posterior 1/3rd of tongue
    • CN X innervates epiglottis and lower pharynx
    • Axons project to medulla oblongata to 2° neurons projecting to thalamus
    • Tertiary neurons to cortical gustatory area
    • Other neurons project from thalamus to hypothalamus and limbic system
    • Processes behavioral aspects associated with taste and smell

    Five Primary Tastes

    • Salty: Stimulated by chemical salts, Na+ enters through ENaC channels, found on Type I gustatory cells
    • Sour: Caused by free H+, H+ binds to and blocks K+ channels, reducing passive movement of K+, found on Type III gustatory cells
    • Sweet: Specific configuration of glucose, activates a GPCR to cause depolarization via second messenger cascade, found on Type II gustatory cells
    • Umami: Triggered by amino acids (esp. glutamate), activates a GPCR to cause depolarization via second messenger cascade, found on Type II gustatory cells
    • Bitter: Chemically diverse group (including alkaloids), activates a GPCR to cause depolarization via second messenger cascade, found on Type II gustatory cells

    Other Taste Receptors

    • Taste perception influenced by other receptors (especially olfactory)
    • Carbon Dioxide receptor (Car4)
    • Fatty receptors

    The Taste Bud Tongue Map Myth

    • 1901 D. Hänig published paper containing data on taste sensitivity in different regions of the tongue
    • Data misinterpreted, leading to the "tongue map" myth

    Eye Structure

    • Almost spherical organ
    • Located within the orbit of the skull
    • Cushioned by orbital fat
    • Three principal layers (outside to inside): fibrous, vascular, and nervous

    Protective Structures of the Eye

    • Eyebrows: Thick hairs preventing sweat from entering the eyes
    • Eyelashes: Protect the front of the eye from foreign objects
    • Eyelids: Movable coverings of the eye, including the conjunctiva, tarsal glands, and palpebral fissure; prevent tear overflow
    • Lacrimal caruncle: Region medial to eyelids, contains ciliary glands producing a gritty substance

    Conjunctiva

    • Specialized stratified squamous epithelium
    • Continuous lining of the external anterior surface of the eye and internal eyelids
    • Two parts (ocular & palpebral conjunctiva)
    • Contains numerous goblet cells and is highly vascular and innervated
    • Doesn't cover cornea

    Lacrimal Apparatus

    • Produces, collects, and drains tears
    • Lacrimal fluid lubricates and cleanses the eye surface
    • Contains antibacterial lysozyme
    • Lacrimal gland located in superolateral depression of the orbit, continuously produces tears
    • Blinking washes tears towards lacrimal caruncle
    • Tears pass through lacrimal puncta, canaliculi, into the lacrimal sac, and then through the nasolacrimal duct into the nasal cavity

    Fibrous (External) Tunic

    • Sclera: Posterior structure, "white" of the eye, continuous with the dura mater that surrounds the optic nerve, providing eye shape and protection; attachment point for extrinsic eye muscles
    • Cornea: Anterior structure, convex transparent structure, composed of epithelium, avascular, supplied nutrients from lacrimal gland (anteriorly) and aqueous humor (posteriorly), allows light passage and refracts light

    Extrinsic Eye Muscles

    • Allow eye movement, keeping eyes stable in the orbit
    • Attached to the fibrous tunic

    Vascular Tunic

    • Highly vascularized, contains intrinsic muscles of the eye
    • Three parts (Choroid, Ciliary body, and Iris)
    • Choroid: Posterior vascular region; provides nutrients to the retina; many melanocytes to absorb extraneous light
    • Ciliary Body: Anterior to the choroid, contains ciliary muscles that alter the shape of the lens, smooth muscle connected to suspensory ligaments, produces aqueous humor
    • Iris: Anterior structure, colored portion of eye, controls light entering the eye, has two smooth muscles (sphincter and dilator pupillae)-- both with sympathetic innervation

    Iris

    • Thin pigmented smooth muscle
    • Controls amount of light entering the eye (through the pupil)
    • Pupil is opening in the center of iris through which light passes
    • Two smooth muscles:
      • Sphincter pupillae—circular, contractile; parasympathetic innervation
      • Dilator pupillae—radial, dilating; sympathetic innervation

    Retina

    • Innermost tunic, two layers
    • Pigmented Layer: Adjacent to the choroid, provides Vitamin A to the neural layer, absorbs light before it reaches the neural layer
    • Neural Layer: Innermost layer, contains photoreceptor cells and associated neurons, transduces light energy into nerve signals

    Cells of the Neural Layer

    • Photoreceptor Cells: Rods and cones; convert light energy to nerve signals, generate graded potentials
    • Bipolar Cells: Lie between photoreceptors and ganglion cells. Fewer cells than photoreceptors; converge visual input onto the ganglion cells; generate graded potentials
    • Ganglion Cells: Innermost layer of neurons; axons to CNS via optic nerve; generate action potentials
    • Other Cells: Horizontal cells, amacrine cells (integrate visual input between photoreceptors/bipolar/ganglion cells; generate graded potentials

    Other Cells

    • Photosensitive ganglionic cells: Found in neural layer, light-sensitive, possess melanopsin, help reset internal circadian clock, regulate pupil size, and regulate melatonin production
    • Retinal pigment epithelial cells: In pigmented layer to capture light, contain melanin

    Components of the Retina

    • Distribution of Rods and Cones: Not uniform; cones concentrated in fovea; rods concentrated in periphery
    • Optic Disc: Contains no photoreceptors; point where ganglion axons exit retina to form optic nerve; also known as the "blind spot."
    • Macula Lutea: Directly in line with the pupil, lateral to the optic disc; contains fovea centralis—high concentration of cone cells, area of sharpest vision
    • Peripheral Retina: Contains mostly rods, effective in low light

    The Lens

    • Transparent structure focusing light onto the retina
    • Shape determines the degree of refraction
    • Modified by suspensory ligaments and ciliary muscles
    • Accommodation: Flattened lens for distant vision; rounded lens for near vision

    Refraction

    • Different mediums affect light speed
    • Light bends (refracts) when transitioning between mediums
    • Lens shape determines the direction of refracted light:
      • Concave lenses cause light to bend away from a focal point
      • Convex lenses cause light to bend toward a focal point

    Cavities of the Eye

    • Posterior Cavity: Posterior to the lens and anterior to the retina; filled with vitreous humor (gelatinous fluid); maintains eye shape, holds retina against choroid, transmits light
    • Anterior Cavity: Contains aqueous humor, anterior to the lens and posterior to the cornea; filtrate from blood plasma; produced by ciliary bodies; subdivided into posterior and anterior chambers; provides nutrients to cells of lens and cornea.

    Focusing Light on the Retina

    • Bending of light (refraction) to focus on light-sensitive cells of the retina
    • Each structure (and liquid) that the light passes through affects its course
    • Cornea is the initial focusing structure
    • Lens modification (accommodation) adjusts for near or far vision; shapes the lens
    • Focal point of collected light is the fovea centralis—high density of cones

    Rods and Cones

    • Rods: One type; outer segment with membrane-bound discs; concentrated in periphery; high sensitivity, low acuity; responsible for vision in dim light; high convergence on ganglion cells
    • Cones: Three types; outer segment with folds of plasma membrane; concentrated in fovea centralis; low sensitivity, high acuity; responsible for color vision; low convergence on ganglion cells

    Photopigment

    • Light-absorbing photoreceptor responsible for initiating light energy transduction
    • Found in the membranes of the discs
    • Two parts:
      • Opsin: G-protein coupled receptor; several types, each stimulated over a range of light wavelengths (Rhodopsin in rods, Photopsins in cones)
      • Retinal: Vitamin A derivative; ligand to opsin; two states dependent on light absorption

    Color Perception

    • Dependent on the ratio of stimulation of the various types of cones in response to different wavelengths of light
    • Example: Wavelength of 560 nm stimulates red cones maximally, green cones to a lesser degree, and blue cones do not stimulate

    Receptive Fields

    • Area where a photon can stimulate a single ganglion cell
    • Larger receptive fields when more photoreceptors converge on a single ganglion cell.
    • Smaller receptive fields when fewer photoreceptors converge on a single ganglion cell.

    Convergence and Acuity

    • Acuity is dependent on the number of photoreceptors converging on a single ganglion cell
    • Low convergence yields more acuity
    • High convergence yields less acuity
    • Low convergence yields smaller receptive fields and greater acuity
    • High convergence yields larger receptive fields and reduced acuity

    Dark Adaptation

    • Eyes' ability to adjust to low light
    • Dependent on rods and cones
    • Cones adapt quickly, requiring more light
    • Rods adapt slowly, requiring less light
    • Gives rise to photopic (cone-dependent) and scotopic (rod-dependent) vision

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