Anatomy: The Cochlea
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Anatomy: The Cochlea

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Questions and Answers

Which fluid is secreted by epithelial cells within the cochlear duct?

  • Endolymph (correct)
  • Plasma
  • Perilymph
  • Interstitial fluid

    • What is the main role of the cochlear nerve in the auditory system?

  • Transmit action potentials from hair cells to auditory cortex (correct)
  • Transmit pressure changes from the oval window
  • Transduce sound waves into electrical signals
  • Regulate endolymph composition

    • In terms of ionic composition, which fluid in the cochlea has a high concentration of potassium ions?

  • Intercellular fluid
  • Plasma
  • Perilymph
  • Endolymph (correct)

    • Which structure serves as a receptor for sound vibrations in the cochlea?

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

    What is the anatomical location of the vestibular duct within the cochlea?

    <p>Above the cochlear duct</p> Signup and view all the answers

    Which membrane acts as a support structure for the hair cells in the cochlea?

    <p>Tectorial membrane</p> Signup and view all the answers

    What is the primary function of the tympanic duct in the cochlea?

    <p>Contains perilymph fluid</p> Signup and view all the answers

    Which component is NOT part of the cochlear anatomy?

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

    What is the primary role of the cochlea in auditory pathways?

    <p>Converting sound waves into electrical signals</p> Signup and view all the answers

    Which structures are targeted by secondary sensory neurons in the auditory pathway?

    <p>Cochlear nuclei in the medulla</p> Signup and view all the answers

    In which structure does the main auditory pathway synapse after the cochlear nuclei?

    <p>Midbrain and thalamus</p> Signup and view all the answers

    Which type of hearing loss results from damage to the structures of the inner ear?

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

    What is the function of the 'maculae' found in the otolith organs?

    <p>Sensing linear acceleration and head position</p> Signup and view all the answers

    What type of fluid is found within the vestibular apparatus chambers?

    <p>High K+, low Na+ endolymph</p> Signup and view all the answers

    What does the auditory cortex primarily process?

    <p>Electrical signals from the cochlea</p> Signup and view all the answers

    Which part of the auditory pathway is responsible for transmitting sound information to the cerebral cortex?

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

    What initiates the bending of the hair cells in the cochlear duct?

    <p>Fluid waves in the cochlear duct</p> Signup and view all the answers

    Which structure plays a crucial role in transmitting sound vibrations from the outer ear to the inner ear?

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

    What is the primary function of the neurotransmitters released by hair cells in the cochlear duct?

    <p>To generate action potentials in sensory neurons</p> Signup and view all the answers

    What type of fluid is found within the cochlear duct?

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

    Which of the following structures is NOT involved in the auditory transduction process?

    <p>Vestibular duct</p> Signup and view all the answers

    What happens to the energy from sound waves as it travels through the cochlear duct?

    <p>It is dissipated back into the middle ear</p> Signup and view all the answers

    Which component of the ear helps in amplifying sound before it reaches the cochlea?

    <p>Tympanic membrane</p> Signup and view all the answers

    Which of the following best describes the role of the cochlear nerve?

    <p>To transmit action potentials to the brain</p> Signup and view all the answers

    What role does the tectorial membrane play in the function of the cochlea?

    <p>It causes the movement of cilia on hair cells when displaced.</p> Signup and view all the answers

    What happens to hair cells when they are excited?

    <p>They bend toward the kinocilium.</p> Signup and view all the answers

    What is the function of tip links in hair cells?

    <p>To act as springs that open ion channels during excitation.</p> Signup and view all the answers

    Which component is involved in signal transduction within the cochlea?

    <p>Cochlear nerve fibers</p> Signup and view all the answers

    During inhibition of hair cells, what occurs?

    <p>Tip links pull apart, closing ion channels.</p> Signup and view all the answers

    Which part of the cochlea contains the specialized hair cells?

    <p>Basilar membrane</p> Signup and view all the answers

    What initiates the process of auditory signal transduction in hair cells?

    <p>Bending of hair cells towards the kinocilium.</p> Signup and view all the answers

    What happens to ion channels in hair cells during excitation?

    <p>They open, allowing influx of ions like potassium.</p> Signup and view all the answers

    What effect does the opening of ion channels in hair cells have on cell membrane potential and neurotransmitter release?

    <p>It opens voltage-gated Ca2+ channels and increases neurotransmitter release.</p> Signup and view all the answers

    How does the sensitivity of the basilar membrane vary with sound wave frequency?

    <p>It shows variable sensitivity to sound wave frequencies along its length.</p> Signup and view all the answers

    What happens when cation channels in hair cells are closed?

    <p>Cell hyperpolarization occurs, resulting in no action potentials.</p> Signup and view all the answers

    What initiates action potentials in primary sensory neurons related to hair cell excitation?

    <p>The neurotransmitter release from hair cells.</p> Signup and view all the answers

    What role do voltage-gated Ca2+ channels play in hair cell function?

    <p>Their opening leads to neurotransmitter release in response to depolarization.</p> Signup and view all the answers

    What is the consequence of increased action potentials in primary sensory neurons?

    <p>It enhances sensitivity to sound and signal transmission.</p> Signup and view all the answers

    How does excitation and inhibition affect ion channels in hair cells?

    <p>Excitation opens ion channels, while inhibition closes them.</p> Signup and view all the answers

    What is indicated by action potentials being generated in primary sensory neurons?

    <p>Depolarization of hair cells has occurred.</p> Signup and view all the answers

    The release of neurotransmitters occurs at the ______ terminal.

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

    In the absence of light, rhodopsin is ______, maintaining high levels of cGMP.

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

    During phototransduction, ______ cells synapse with bipolar cells.

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

    The process of converting light into electrical signals is known as ______.

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

    Bipolar cells can be classified into ______ types based on their response to light.

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

    The recovery phase of rhodopsin after it has been activated by light involves ______ of the pigment.

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

    The hyperpolarization of photoreceptor cells is essential for the release of ______.

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

    Transducin plays a crucial role in the amplification of the ______ signal during phototransduction.

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

    The ______ cell is crucial for visual signal processing in the retina and can be activated or inhibited by light.

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

    During the ______ phase, rhodopsin molecules regenerate after being bleached by light exposure.

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

    The type of bipolar cell is determined by the ______ nature of the glutamate receptors they express.

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

    Hyperpolarization of photoreceptors leads to a decrease in ______ release.

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

    The ______ mechanism involves the activation of transducin to amplify the phototransduction response.

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

    Bipolar cells can have an on-center or off-surround receptive ______ that influences their response to light.

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

    In response to light stimulus, ganglion cells exhibit an ______ rate of firing of action potentials.

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

    Adjacent photoreceptors converge to form the visual ______ for one ganglion cell.

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

    Bipolar cells can be classified into two types: ______ and ______ cells.

    <p>on-center, off-center</p> Signup and view all the answers

    After light exposure, the process that leads to hyperpolarization in photoreceptors is primarily due to the activation of ______.

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

    The release of neurotransmitters in response to light occurs at the ______ of the bipolar cells.

    <p>axon terminals</p> Signup and view all the answers

    Rhodopsin undergoes a recovery phase after being exposed to light, during which it converts back to ______.

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

    In response to light, on-center ganglion cells increase their firing rate while ______ cells decrease their activity.

    <p>off-center</p> Signup and view all the answers

    The signaling pathways involving ______ lead to the enhancement of contrast in visual receptors.

    <p>lateral inhibition</p> Signup and view all the answers

    During the recovery phase of rhodopsin, the conversion of all-trans retinal back to 11-cis retinal is crucial for ______.

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

    The mechanism whereby activated transducin amplifies the response to light is known as ______.

    <p>signal amplification</p> Signup and view all the answers

    The opening of cation channels in hair cells leads to ______ of the cell.

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

    When hair cells are inhibited, ion channels ______ which leads to less cation entry.

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

    In the hyperpolarization mechanism, the influx of ______ ions decreases, leading to decreased neurotransmitter release.

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

    The primary sensory neuron sends a ______ signal in response to action potentials generated by hair cells.

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

    Voltage-gated ______ channels open in response to depolarization, promoting neurotransmitter release.

    <p>Ca2+</p> Signup and view all the answers

    The recovery phase of rhodopsin involves the conversion of ______ back to its inactive form after stimulation.

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

    There are different types of bipolar cells, including those that mediate ______ and those that mediate inhibition.

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

    In the cochlea, the release of neurotransmitters is crucial for transmitting signals to the ______ sensory neurons.

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

    In the light, photoreceptors ______ - decreased release of neurotransmitter, glutamate.

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

    LIGHT-ON bipolar cells has ______ glutamate receptors.

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

    In the dark, photoreceptors are ______ and continuously release their neurotransmitter, glutamate.

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

    OFF bipolar cells have ______ glutamate receptors.

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

    In the light, OFF bipolars ______ as the receptors are inhibited.

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

    The ______ type of bipolar cells is activated in the light.

    <p>light-on</p> Signup and view all the answers

    The increase in the rate of firing of action potentials is determined by the type of ______ cells.

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

    Inhibitory glutamate receptors on ON bipolar cells lead to their ______ when activated by light.

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

    What role does hyperpolarization of photoreceptor cells play in light signal processing?

    <p>It decreases neurotransmitter release to bipolar cells.</p> Signup and view all the answers

    Which component is critical for the amplification of the visual signal during phototransduction?

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

    During which phase does rhodopsin regenerate after being bleached by light exposure?

    <p>Recovery phase</p> Signup and view all the answers

    What determines the excitatory or inhibitory nature of bipolar cells?

    <p>The rate at which glutamate receptors are activated or inhibited.</p> Signup and view all the answers

    What is the primary mechanism that leads to the release of neurotransmitters from photoreceptor cells?

    <p>Increased calcium ion concentration.</p> Signup and view all the answers

    What characterizes on-center bipolar cells in response to light?

    <p>They are activated when the center is illuminated.</p> Signup and view all the answers

    Which factor is crucial for determining whether a ganglion cell will respond strongly to light?

    <p>The contrast in light intensity between the center and the surround.</p> Signup and view all the answers

    Which type of bipolar cell is primarily activated by the decrease in glutamate levels during light exposure?

    <p>On-center bipolar cells</p> Signup and view all the answers

    What mechanism is responsible for the hyperpolarization of photoreceptor cells?

    <p>Closure of sodium channels</p> Signup and view all the answers

    Which statement accurately describes the role of transducin during phototransduction?

    <p>Transducin activates phosphodiesterase, leading to reduced cGMP levels.</p> Signup and view all the answers

    What effect does the hyperpolarization of photoreceptor cells have on neurotransmitter release?

    <p>Decreases neurotransmitter release</p> Signup and view all the answers

    During the recovery phase of rhodopsin after activation, what main process occurs?

    <p>Regeneration of 11-cis-retinal</p> Signup and view all the answers

    Which types of bipolar cells respond oppositely to light and contribute to contrast detection?

    <p>Off-center bipolar cells</p> Signup and view all the answers

    What function do horizontal cells serve in the processing of light signals?

    <p>Inhibit lateral signals from bipolar cells</p> Signup and view all the answers

    How are ganglion cells categorized based on their receptive fields?

    <p>On-center and off-center</p> Signup and view all the answers

    What role do color opponent ganglion cells play in vision?

    <p>Process colors antagonistically</p> Signup and view all the answers

    What is the primary effect of hyperpolarization in photoreceptors when exposed to light?

    <p>Decrease in neurotransmitter release</p> Signup and view all the answers

    What role does transducin play in the phototransduction process?

    <p>It amplifies the light signal after phototransduction begins.</p> Signup and view all the answers

    How does the release of glutamate change in dark conditions for photoreceptors?

    <p>Glutamate is continuously released at high levels.</p> Signup and view all the answers

    During the recovery phase of rhodopsin, which of the following occurs?

    <p>Rhodopsin is regenerated and returns to its active state.</p> Signup and view all the answers

    What type of receptors do LIGHT-ON bipolar cells express?

    <p>Inhibitory receptors that hyperpolarize the cell.</p> Signup and view all the answers

    What determines the response of OFF bipolar cells to changes in light conditions?

    <p>The activation of excitatory glutamate receptors.</p> Signup and view all the answers

    Which statement accurately describes the signaling changes of ON bipolar cells when light is introduced?

    <p>They undergo depolarization due to receptor activation.</p> Signup and view all the answers

    Which condition leads to OFF bipolar cells hyperpolarizing?

    <p>Increased levels of glutamate release.</p> Signup and view all the answers

    What effect does hyperpolarization of a hair cell have on neurotransmitter release?

    <p>It decreases neurotransmitter release due to reduced cation entry.</p> Signup and view all the answers

    Which best describes the role of transducin in signal amplification during phototransduction?

    <p>Transducin mediates the activation of phosphodiesterase to reduce cGMP levels.</p> Signup and view all the answers

    What occurs during the recovery phase of rhodopsin after light activation?

    <p>Rhodopsin undergoes phosphorylation, leading to its inactivation.</p> Signup and view all the answers

    Which type of bipolar cell is known for its direct response to light intensity changes?

    <p>On-bipolar cells, which depolarize in response to light.</p> Signup and view all the answers

    Which neurotransmitter is primarily released in response to hair cell depolarization?

    <p>Glutamate, which acts as an excitatory signal.</p> Signup and view all the answers

    How does the mechanism of inhibition in hair cells function?

    <p>It leads to the closure of cation channels, reducing neurotransmitter release.</p> Signup and view all the answers

    Which characteristic is true regarding the sensitivity of the basilar membrane?

    <p>It is more sensitive to high frequencies at its base than at its apex.</p> Signup and view all the answers

    What is the result of an increase in action potentials in primary sensory neurons?

    <p>The perception of sound intensity increases.</p> Signup and view all the answers

    What occurs in photoreceptor cells that is essential for the release of neurotransmitters when light is absent?

    <p>Depolarization of the cells</p> Signup and view all the answers

    Which component plays a crucial role in amplifying the signal during phototransduction?

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

    What is the effect of light exposure on rhodopsin during the recovery phase?

    <p>It regenerates after being bleached</p> Signup and view all the answers

    What distinguishes different types of bipolar cells in relation to light?

    <p>Their response direction to light stimuli</p> Signup and view all the answers

    In the mechanism of rod phototransduction, what maintains high levels of cGMP in the absence of light?

    <p>Open cyclic nucleotide-gated channels</p> Signup and view all the answers

    What is the primary consequence of hyperpolarization in photoreceptor cells during light exposure?

    <p>Reduced neurotransmitter release</p> Signup and view all the answers

    What role does the signaling pathway involving transducin primarily play in the visual system?

    <p>Amplifying the visual signal</p> Signup and view all the answers

    During the phototransduction process, what happens to bipolar cells when photoreceptors are hyperpolarized?

    <p>They become depolarized</p> Signup and view all the answers

    What is the membrane potential of a rod cell in darkness?

    <p>–40mV</p> Signup and view all the answers

    How does light influence the opening of channels in rod cells?

    <p>It closes a large number of channels.</p> Signup and view all the answers

    What role does transducin play in the phototransduction pathway?

    <p>It amplifies the light signal.</p> Signup and view all the answers

    What occurs to Ca2+ levels in the rod cells when the light bleaches rhodopsin?

    <p>Ca2+ levels decrease.</p> Signup and view all the answers

    What is the primary signaling molecule involved in maintaining high levels in rod cells before photon absorption?

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

    How does phototransduction affect the tonic release of glutamate in rod cells?

    <p>It decreases the release of glutamate.</p> Signup and view all the answers

    What triggers exocytosis in rod cells during phototransduction?

    <p>Ca2+ influx through voltage-gated channels.</p> Signup and view all the answers

    What initiates the signal that light is present in the visual field for rod cells?

    <p>The specific absorption of photons through rhodopsin.</p> Signup and view all the answers

    What effect does opsin activation have on cGMP levels in the cell?

    <p>It decreases cGMP levels.</p> Signup and view all the answers

    What is the primary ion channel that closes when cGMP levels decrease?

    <p>Cyclic nucleotide-gated (CNG) channels.</p> Signup and view all the answers

    How does the hyperpolarization of the cell affect neurotransmitter release?

    <p>It decreases neurotransmitter release.</p> Signup and view all the answers

    During the hyperpolarization process, what is the membrane potential typically shifted to?

    <p>-70 mV</p> Signup and view all the answers

    What initiates the second messenger cascade during phototransduction?

    <p>The activation of opsin by light.</p> Signup and view all the answers

    What role does transducin play in the process following opsin activation?

    <p>It amplifies the signal for subsequent cellular responses.</p> Signup and view all the answers

    What occurs to retinal during the bleaching process?

    <p>It is released from opsin.</p> Signup and view all the answers

    What is the primary outcome of one photon of light activating rhodopsin?

    <p>Activation of multiple transducin molecules.</p> Signup and view all the answers

    What happens to the ON bipolar cells in the presence of light?

    <p>They depolarize and increase neurotransmitter release.</p> Signup and view all the answers

    How do the OFF bipolar cells respond to light?

    <p>They hyperpolarize in the presence of light.</p> Signup and view all the answers

    What type of receptors do LIGHT-ON bipolar cells possess?

    <p>Inhibitory glutamate receptors.</p> Signup and view all the answers

    What occurs in photoreceptors when exposed to light?

    <p>They hyperpolarize and reduce neurotransmitter release.</p> Signup and view all the answers

    What is the primary neurotransmitter released by photoreceptors in darkness?

    <p>Glutamate.</p> Signup and view all the answers

    How do ON bipolar cells behave in darkness?

    <p>They are inhibited which leads to hyperpolarization.</p> Signup and view all the answers

    What determines the signal sent to the brain regarding light conditions?

    <p>The type and response of bipolar cells to glutamate.</p> Signup and view all the answers

    In what way do OFF bipolar cells differ from ON bipolar cells?

    <p>OFF bipolar cells depolarize in light while ON hyperpolarize.</p> Signup and view all the answers

    What effect does hyperpolarization have on hair cell function?

    <p>It decreases action potentials in neurons.</p> Signup and view all the answers

    What is the primary consequence of cation channels being closed in hair cells?

    <p>Hyperpolarization of the cell.</p> Signup and view all the answers

    During what condition does the cell membrane of a hair cell hyperpolarize?

    <p>When neurotransmitter release decreases.</p> Signup and view all the answers

    What is a key role of voltage-gated Ca2+ channels in the context of hair cell activity?

    <p>They initiate neurotransmitter release.</p> Signup and view all the answers

    What is the result of increased action potentials in primary sensory neurons?

    <p>Enhanced tonic signaling.</p> Signup and view all the answers

    What occurs when hair cells are excited?

    <p>Opening of ion channels.</p> Signup and view all the answers

    What effect does increased concentration of cations (K+, Ca2+) have on the hair cell?

    <p>It leads to cell depolarization.</p> Signup and view all the answers

    What is the main effect of inhibitory signals on ion channels in hair cells?

    <p>They close ion channels.</p> Signup and view all the answers

    What happens to cGMP levels in rods when there is no light present?

    <p>cGMP levels increase</p> Signup and view all the answers

    What is the effect on the membrane potential of rods when light is absent?

    <p>Membrane potential remains depolarized</p> Signup and view all the answers

    Which ion channels remain open in the absence of light?

    <p>Cyclic nucleotide-gated channels</p> Signup and view all the answers

    What occurs to the state of rhodopsin in rods when light is not present?

    <p>Rhodopsin is inactive and unable to respond to light</p> Signup and view all the answers

    What is the primary difference in ion flow in rods when light is present compared to when it is absent?

    <p>Na+ and Ca2+ influx decreases, leading to hyperpolarization</p> Signup and view all the answers

    Which type of cellular response is essential for the transmission of visual signals by bipolar cells?

    <p>Depolarization in the presence of light</p> Signup and view all the answers

    What role does the pigment epithelium cell play during the phototransduction process?

    <p>It aids in the regeneration of rhodopsin</p> Signup and view all the answers

    What is the consequence of high cGMP levels in the context of rod cell function?

    <p>Opening of cyclic nucleotide-gated channels</p> Signup and view all the answers

    Study Notes

    Anatomy of the Cochlea

    • The cochlea has three main ducts: vestibular duct, cochlear duct, and tympanic duct.
    • The cochlear duct contains endolymph, which is secreted by epithelial cells and has a high potassium concentration.
    • Perilymph in vestibular and tympanic ducts is similar to plasma.
    • The organ of Corti, located in the cochlear duct, houses hair cell receptors responsible for sound detection.

    Auditory Pathways

    • Sound waves create electrical signals in the cochlea, which are transmitted via the cochlear nerve.
    • The primary sensory neurons relay signals to the cochlear nuclei in the medulla oblongata.
    • Secondary sensory neurons project to two nuclei in the pons, both ipsilateral and contralateral to the side of the stimulus.
    • Auditory signals pass through nuclei in the midbrain and thalamus before reaching the auditory cortex.

    Hearing Loss

    • Hearing loss can be classified into three types: conductive, central, and sensorineural.
    • Conductive hearing loss occurs when there is no transmission through the external or middle ear.
    • Central hearing loss involves damage to neural pathways between the ear and cerebral cortex.
    • Sensorineural hearing loss results from damage to inner ear structures and may require a cochlear implant.

    Components of Equilibrium

    • Equilibrium is defined as a state of balance, which includes dynamic (movement) and static (upright position) components.
    • The vestibular apparatus consists of semicircular canals and otolith organs that detect head position and motion.
    • Equilibrium pathways primarily project to the cerebellum.

    Anatomy of the Vestibular Apparatus

    • The vestibular apparatus comprises interconnected fluid-filled chambers filled with endolymph rich in potassium.
    • Semicircular canals provide information about rotational acceleration, while otolith organs detect linear acceleration and head position.
    • Sensory receptors, including cristae in the semicircular canals and maculae in the otolith organs, play key roles in balance.

    Signal Transduction in Hair Cells

    • Hair cells contain kinocilium, which is the longest cilium and is embedded in the tectorial membrane.
    • Hair cell bending towards the kinocilium results in depolarization and increased neurotransmitter release.
    • Bending away from the kinocilium leads to hyperpolarization and decreased neurotransmitter release, impacting signal transmission.

    Sensory Coding for Pitch

    • The basilar membrane varies in sensitivity to sound wave frequencies along its length, allowing for pitch discrimination.
    • Specific regions of the basilar membrane respond to different frequencies, forming the basis of auditory perception.

    Processing of Light Signals

    • The excitatory or inhibitory nature of glutamate receptors determines the type of bipolar cell.
    • Ganglion cells are organized into on-center and off-surround fields, enhancing contrast detection.
    • Multiple photoreceptors converge onto a single ganglion cell, creating a shared visual field.
    • Horizontal cells inhibit the signals of nearby bipolar cells, enhancing contrast through lateral inhibition.

    Types of Bipolar Cells

    • Light-On Bipolar Cells:
      • Possess inhibitory glutamate receptors.
      • Activated in light, leading to depolarization; hyperpolarized in the dark.
    • Light-Off Bipolar Cells:
      • Have excitatory glutamate receptors.
      • Activated in the dark, resulting in depolarization; hyperpolarized in light.

    Ganglion Cell Activity

    • Ganglion cells generate action potentials that signal the brain based on input from bipolar cells and photoreceptors.
    • Action potential firing rates vary:
      • Increased rate with a strong signal (high contrast).
      • Decreased rate with weak signals or uniform light conditions.

    Visual/Receptive Fields

    • Each ganglion cell corresponds to a specific area of the retina, integrating signals from multiple photoreceptors.
    • On-center/Off-surround Field:
      • Strongly responds to light in the center while being inhibited by light in the surround.
    • Off-center/On-surround Field:
      • Strongly responds to light in the surround while being inhibited by light in the center.
    • Visual fields aid in detecting movement and object edges rather than absolute light intensity.

    Edge and Contrast Detection

    • At boundaries, excitation and inhibition are unbalanced, enhancing the perception of transitions between dark and bright areas.
    • This sharpens the detection of changes in luminance.

    Color Opponent Cells

    • Color opponent ganglion cells have distinct color properties in their center and surround, contributing to color perception.

    Phototransduction in Rods

    • In the absence of light, rhodopsin remains inactive, leading to high cGMP levels and open ion channels.
    • Sodium and calcium ions enter rods, maintaining depolarization, while potassium efflux is lower.
    • When light is present, channels close, hyperpolarizing the cell and inhibiting neurotransmitter release.

    Sensory Coding for Pitch

    • The basilar membrane in the cochlea demonstrates variable sensitivity to different sound wave frequencies, coding for pitch based on the location along its length.

    Processing of Light Signals

    • The excitatory or inhibitory nature of glutamate receptors determines the type of bipolar cell.
    • Ganglion cells are organized into on-center and off-surround fields, enhancing contrast detection.
    • Multiple photoreceptors converge onto a single ganglion cell, creating a shared visual field.
    • Horizontal cells inhibit the signals of nearby bipolar cells, enhancing contrast through lateral inhibition.

    Types of Bipolar Cells

    • Light-On Bipolar Cells:
      • Possess inhibitory glutamate receptors.
      • Activated in light, leading to depolarization; hyperpolarized in the dark.
    • Light-Off Bipolar Cells:
      • Have excitatory glutamate receptors.
      • Activated in the dark, resulting in depolarization; hyperpolarized in light.

    Ganglion Cell Activity

    • Ganglion cells generate action potentials that signal the brain based on input from bipolar cells and photoreceptors.
    • Action potential firing rates vary:
      • Increased rate with a strong signal (high contrast).
      • Decreased rate with weak signals or uniform light conditions.

    Visual/Receptive Fields

    • Each ganglion cell corresponds to a specific area of the retina, integrating signals from multiple photoreceptors.
    • On-center/Off-surround Field:
      • Strongly responds to light in the center while being inhibited by light in the surround.
    • Off-center/On-surround Field:
      • Strongly responds to light in the surround while being inhibited by light in the center.
    • Visual fields aid in detecting movement and object edges rather than absolute light intensity.

    Edge and Contrast Detection

    • At boundaries, excitation and inhibition are unbalanced, enhancing the perception of transitions between dark and bright areas.
    • This sharpens the detection of changes in luminance.

    Color Opponent Cells

    • Color opponent ganglion cells have distinct color properties in their center and surround, contributing to color perception.

    Phototransduction in Rods

    • In the absence of light, rhodopsin remains inactive, leading to high cGMP levels and open ion channels.
    • Sodium and calcium ions enter rods, maintaining depolarization, while potassium efflux is lower.
    • When light is present, channels close, hyperpolarizing the cell and inhibiting neurotransmitter release.

    Sensory Coding for Pitch

    • The basilar membrane in the cochlea demonstrates variable sensitivity to different sound wave frequencies, coding for pitch based on the location along its length.

    Phototransduction Process

    • Photoreceptors hyperpolarize in the presence of light, leading to decreased release of glutamate.
    • Two types of bipolar cells: LIGHT-ON (inhibitory) and LIGHT-OFF (excitatory).
    • LIGHT-ON bipolar cells depolarize when activated by light and hyperpolarize in the dark.
    • LIGHT-OFF bipolar cells hyperpolarize when activated by light and depolarize in the dark.

    Mechanism of Action

    • Activation of the On-bipolar cell occurs through the opening of inhibitory glutamate receptors.
    • LIGHT-OFF bipolar cells activate excitatory receptors leading to depolarization in low light and hyperpolarization in bright light.
    • Rhodopsin activation by light triggers a second messenger cascade through the G protein Transducin.

    Ionic Changes

    • Light exposure decreases levels of cGMP leading to the closure of cyclic nucleotide-gated (CNG) channels.
    • Photon absorption by rhodopsin activates retinal, releasing it from opsin, a process called bleaching.
    • Membrane potential changes: In darkness, potential is approximately –40 mV due to continuous glutamate release; light exposure hyperpolarizes the cell to about –70 mV.

    Signal Processing

    • The amplitude of neurotransmitter glutamate release is proportional to light levels.
    • The rod system prevents random channel opening from affecting membrane potential, ensuring accurate signaling.
    • Tonic release of glutamate constantly signals bipolar neurons, influencing their activation state.

    Importance of Phototransduction

    • Rods are crucial for low-light vision and signal processing.
    • Depolarization and hyperpolarization of photoreceptors directly affect action potentials in upstream sensory neurons.
    • No action potentials occur when photoreceptors are hyperpolarized under bright conditions.

    Cochlea and Sensory Coding

    • Basilar membrane responds variably to sound frequencies along its length, encoding pitch.
    • The release of neurotransmitter glutamate from sensory neurons modulates signal transmission to bipolar cells.
    • The cochlear system aligns with visual systems in processing external stimuli to maintain sensory perception.

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    Neuro Physiology - Spec Senses ENG NOTES_Dr E Marais.ppt

    Description

    This quiz explores the anatomy of the cochlea, focusing on its various parts such as the vestibular apparatus, windows, and ducts. It helps in understanding the structure and function of the cochlea in the auditory system. Perfect for students of anatomy and biology.

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