Visual Systems and Photoreceptors
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Questions and Answers

What effect does light have on photoreceptors?

  • It leads to hyperpolarization (correct)
  • It induces a release of calcium ions
  • It causes depolarization
  • It creates an excitatory response in bipolar cells

    • What is the role of less released glutamate in bipolar cells?

  • It opens special ion channels in bipolar cells (correct)
  • It causes an excitatory response in bipolar cells
  • It increases the action potential in ganglion cells
  • It inhibits phototransduction entirely

    • Which structure in the visual system is responsible for crossing visual information from the contralateral side?

  • Optic nerve fibers
  • Retinal ganglion cells
  • Optic chiasm (correct)
  • Visual cortex

    • What happens if enough EPSP is generated in a ganglion cell?

    <p>Action potentials are sent along the optic nerve</p> Signup and view all the answers

    In the visual pathway, where does visual information finally reach?

    <p>Occipital lobe</p> Signup and view all the answers

    What is the primary function of the lateral rectus muscle?

    <p>Abduction of the eye</p> Signup and view all the answers

    Which structure of the eye acts as a protective, transparent covering?

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

    What triggers the pupils to constrict during close vision?

    <p>Bright light</p> Signup and view all the answers

    What is the primary role of the retinal pigmented layer?

    <p>Absorbs stray light rays</p> Signup and view all the answers

    During which state do pupils dilate as a response to emotional changes?

    <p>Appealing subject matter</p> Signup and view all the answers

    Which layer of the eye contains the blood vessels and is darkly pigmented?

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

    What is the main function of the lacrimal glands?

    <p>Produce aqueous tear film</p> Signup and view all the answers

    Which part of the eye is responsible for light sensing?

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

    What is the primary function of rods in the visual system?

    <p>They enable night vision and peripheral vision.</p> Signup and view all the answers

    Which type of cell in the retina primarily responds to bright light and produces color vision?

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

    What neurotransmitter is released by horizontal cells upon depolarization?

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

    What occurs to retinal in the rods when they absorb light?

    <p>It changes to all-trans-retinal.</p> Signup and view all the answers

    What is the main purpose of the amacrine cells in the retina?

    <p>To connect bipolar cells and ganglion cells with inhibitory feedback.</p> Signup and view all the answers

    Which photopigment is associated with rods for vision in low light?

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

    What distinguishes color blindness in terms of the types of cones affected?

    <p>Absence or dysfunction of one or more cone types.</p> Signup and view all the answers

    What role do bipolar cells play during light and dark conditions?

    <p>They switch between an ON state in light and an OFF state in dark.</p> Signup and view all the answers

    What is the metabolic role of the inner segment of photoreceptors?

    <p>Maintains the health and function of the receptor.</p> Signup and view all the answers

    How do the three types of cones contribute to color vision?

    <p>Each cone type senses a unique wavelength, combining to create color.</p> Signup and view all the answers

    Which of the following accurately describes the role of taste receptors?

    <p>They respond to substances dissolved in saliva.</p> Signup and view all the answers

    What is the primary function of the tympanic membrane?

    <p>To vibrate in response to sound waves.</p> Signup and view all the answers

    Which statement is true about the process of dynamic equilibrium?

    <p>It involves the bending of hair cells in response to angular movements.</p> Signup and view all the answers

    Which of the following statements about smell receptors is accurate?

    <p>Sniffing helps bring odors into contact with them.</p> Signup and view all the answers

    What distinguishes sensorineural deafness from conduction deafness?

    <p>Sensorineural deafness involves impairment in hair cells or the auditory pathway.</p> Signup and view all the answers

    Which of the following structures is part of the inner ear?

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

    How do otoliths contribute to static equilibrium?

    <p>They roll in response to gravitational changes.</p> Signup and view all the answers

    Which nerve is primarily involved in transmitting taste impulses to the brain?

    <p>Facial nerve</p> Signup and view all the answers

    The organ responsible for detecting sound waves in the cochlea is known as:

    <p>The Organ of Corti</p> Signup and view all the answers

    What role does the pharyngotympanic tube serve?

    <p>To equalize pressure in the middle ear.</p> Signup and view all the answers

    Which of the following best explains the mechanics of hearing?

    <p>Sound waves cause the eardrum to vibrate, transmitting motion through ossicles to the cochlea.</p> Signup and view all the answers

    Which component of balance and equilibrium primarily responds to gravity?

    <p>Maculae in the vestibule</p> Signup and view all the answers

    What is the function of the semicircular canals?

    <p>To sense angular and rotational movements.</p> Signup and view all the answers

    How does motion sickness occur according to the equilibrium system?

    <p>It arises from conflicting sensory inputs between vestibular and visual systems.</p> Signup and view all the answers

    Which of the following tastes is NOT considered one of the five basic tastes?

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

    Study Notes

    Lecture 4: Special Senses

    • This lecture covers the special senses, including the visual, chemical (taste and smell), auditory, and vestibular systems. It draws on Sherwood Chapter 5 for detailed information.

    Objectives

    • The lecture will cover the visual system, including the eye itself and its accessory structures.
    • It will look at chemical senses (taste and smell).
    • The auditory system will be explored.
    • Finally, the vestibular system will be discussed.

    Visual System: The Eye

    • 70% of all sensory receptors are located in the eye.
    • The eye is largely sheltered by fat and bony orbit.
    • Accessory structures include:
      • Eyebrows: shade the eye and prevent perspiration.
      • Eyelids: protect the eye, and have glands that secrete oil.
      • Eye lashes: initiate reflexive blinking.
      • Eye muscles: control eye movement.

    Visual System: Extraocular Muscles

    • Lateral Rectus Muscle: abducts the eye.
    • Medial Rectus Muscle: adducts the eye.
    • Superior Rectus Muscle: moves the eye upward.
    • Inferior Rectus Muscle: moves the eye downward.
    • Superior Oblique Muscle: moves the eye downward.
    • Inferior Oblique Muscle: moves the eye upward.

    Visual System: Structures of the Eye

    • Cornea: transparent, protective covering of the iris and pupil.
    • Sclera: protective, white, connective tissue covering.
    • Conjunctiva: epithelial layer connecting the sclera to the eyelids.
    • Lacrimal glands: secrete aqueous tear film which lubricates the eye.

    Visual System: Structures of the Eye

    • Iris: the colored part of the eyeball, regulates the amount of light entering the eye.
    • Pupil: central opening of the iris. -Pupil constrict in bright light and close vision -Pupils dilate in dim light and during emotional states
    • Lens: clear, flexible tissue responsible for focusing.
    • Retina: light-sensing tissue at the back of the eye.
      • A delicate, two-layered membrane with photoreceptors

    Visual System: Retinal Layers

    • Pigmented Layer: absorbs stray light rays.
    • Neural Layer: processes visual data.

    Visual System: Cells of the Retina

    • Photoreceptors:
      • Rods: numerous (~120 million), used for dim light and peripheral vision, do not detect colour, see grayscale.
      • Cones: less numerous (~6 million), detect colour in bright light.
    • Ganglion Cells: receive visual information from photoreceptors and send signals to the optic nerve, ON and OFF responses associated with light/dark.
    • Bipolar Cells: receive signals from photoreceptors and transmit signals to ganglion cells.
    • Horizontal Cells: modulate signaling between photoreceptors and bipolar cells.
    • Amacrine Cells: modulate signaling between ganglion and bipolar cells.

    Visual System: Cells of the Retina (more detailed)

    • Outer Segment: detects light, contains photopigments.
    • Inner Segment: metabolic area of the receptor.
    • Synaptic Terminal: transmits signals to bipolar cells.

    Visual System: Light Sensitive Photopigment

    • Photopigments are present in the rods and cones.
    • Rhodopsin (rods): absorbs all wavelengths of light.
    • Photopsin (cones): three types (red, green, blue) for colour vision.

    Visual System: Dark Vision (Rods)

    • 11-cis-retinal in the dark.
    • All-trans-retinal in the light.
    • Light stimulus causes retinal to change shape.
    • That starts the conversion of energy (photon) into a nerve impulse
    • Conversion of 11-cis-retinal to all-trans-retinal in response to light initiates the process of transduction.
    • The conversion of 11-cis-retinal to all-trans-retinal in response to light initiates the process of transduction.

    Visual System: Colour Vision (Cones)

    • Three types of photoreceptors:
    • Photopsin I (red)
    • Photopsin II (green)
    • Photopsin III (blue)
    • Colour vision is the result of combinations of these cone stimulations
    • Colour blindness is related to lack of one or more cone types.

    Chemical Senses (Taste and Smell):

    • Their chemoreceptors respond to chemicals dissolved in solutions.
      • Taste – dissolved in Saliva
      • Smell – dissolved in nasal fluids
      • 5 basic tastes: Sweet, Sour, Salty, Bitter and Umami
    • Taste and smell are closely related; smell contributes substantially to taste experience.

    Taste Receptors (Gustation)

    • Located along edges of small, depressed areas called fissures (on the tongue)
    • Stimulated when substance is dissolved in solution
    • Taste receptors are often G-protein coupled receptors.
    • Taste is sent to the brain via CN VII (facial nerve) and CN IX.

    Smell Receptors (Olfaction)

    • Located in the olfactory epithelium (upper part of nasal cavity)
    • Chemicals detected must be dissolved in solution
    • Must "sniff" to bring odors upward.

    Hearing:

    • The ear (inner, outer, and middle ear) contains hearing and balance receptors.
    • The outer and middle ear are involved in hearing only.
    • Receptors for hearing and balance respond to different stimuli independently.

    The Ear (overall summary of structures):

    • Houses hearing and equilibrium
    • The three parts of the ear: external (outer), middle and inner ear; and receptors for hearing and balance.
    • Hearing and balance receptors respond to separate stimuli.
    • They are activated independently

    Anatomy of the Ear

    • External ear (outer): pinna and external auditory meatus, lined with ceruminous glands that secrete cerumen
    • Middle ear (tympanic membrane): sound waves cause vibration that moves the auditory ossicles
    • Inner ear (bony labyrinth): vestibule, semicircular canals and cochlea,
    • These structures have hair cells -In the inner ear, hair cells are mechanoreceptors.

    Internal Ear

    • Comprised of bony chambers in the temporal bone that house parts for hearing and balance -The vestibule and semicircular canals are used for balance
      • The cochlea contains hair cells, mechanoreceptors for hearing

    The Cochlea (of the Inner Ear)

    • Contains the spiral organ of Corti.
    • The spiral organ of Corti contains thousands of hair cells.
    • These hair cells are receptors for hearing.

    Organ of Corti (detailed look at the cochlea)

    • Contains hair cells that are the hearing receptors.
    • Sound waves, travelling through the ear, causes vibration in fluids of the cochlea.
    • These vibrations stimulate hair cells which then transmit signals through the cochlear nerve and onto the auditory cortex.

    Sound Transduction:

    • Sound waves vibrate the eardrum.
    • These vibrations are transmitted across the middle ear and vibrate the oval window (of inner ear).
    • Vibrations cause fluid movement in the cochlea.
    • This movement causes bending of hairs on inner hair cells located on the basilar membrane which leads to transduction of vibrations into electrical signals to be sent further along.

    Auditory Pathway

    • The auditory pathway includes the cochlea, vestibulocochlear nerve, medulla, midbrain and the medial geniculate body of the thalamus and the primary auditory cortex.
    • Vibrations are transduced and carried to the auditory cortex in the temporal lobe.

    Deafness

    • Sensorineural deafness: issues with hair cells, cochlear nerve or neurons.
    • Could be caused by prolonged drug exposure, loud noise.
    • Conduction deafness: sound vibrations cannot reach inner ear due to buildup of earwax or injury to eardrum.

    The Vestibular System

    • Responds to head movements.
    • Equilibrium receptors in the inner ear.
      • Static equilibrium - Vestibule (responds to head position relative to gravity)
      • Dynamic equilibrium - Semicircular canals (responds to head position/movement relative to body motion)

    Anatomy of the Vestibular Apparatus

    • Consists of the bony and membranous labyrinths. -Bony labyrinth – filled with perilymph, -Membranous labyrinth - suspended within the perilymph and filled with endolymph.

    Static Equilibrium

    • Macula: patches of hair cells embedded in otolithic membrane w/ tiny stones (otoliths)
    • Otoliths' movement in response to head position pulls on the gel, bending hair cells, sending impulses to the cerebellum.

    Dynamic Equilibrium

    • Cristae ampullaris: Hair cells in semicircular canals covered by the cupula.
    • When the head moves, endolymph lags behind causing the cupula to deflect, stimulating hair cells, sending vestibular nerve impulses to cerebellum.

    Balance and Orientation Pathways

    • Three input modes: vestibular receptors, visual receptors, and somatic receptors.
    • These receptors allow the body to respond reflexively to maintain balance and orientation.

    Input and output of the Vestibular Nuclei

    • Visual, cutaneous, and proprioceptive inputs are used in coordination

    Homeostatic Imbalance: Motion Sickness

    • Sensory mismatch between vestibular and visual inputs from movement results in motion sickness

    Lecture 4 Pop Quiz Questions

    • These are questions for a quiz. The questions are about the different special senses. -Function of middle and inner ear -Process of transmission of impulses to auditory cortex -Difficulties differentiating between conduction and sensorineural deafness -Static and dynamic equilibrium differences -Description of how dynamic equilibrium works -Case study examining vertigo, semicircular canals and how the brain processes conflicting impulses to generate motion sickness

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    Lecture 4 - Special Senses (Vision, Hearing) PDF

    Description

    Explore the intricate details of photoreceptors and their role in the visual system through this quiz. Dive into topics such as the effect of light on photoreceptors, the function of glutamate in bipolar cells, and the crossing of visual information. Test your understanding of the visual pathway and its components.

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