MD137 Lecture 5: Nerve Impulse and Synapse
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Questions and Answers

What is the process called when sensory receptors decrease their sensitivity to a constant strength stimulus?

  • Action potential modulation
  • Stimulus habituation
  • Neurotransmitter release
  • Sensory adaptation (correct)

    • Which type of receptor is responsible for signaling changes in stimulus intensity?

  • Rapidly adapting receptors (correct)
  • Slowly adapting receptors
  • Constant receptors
  • Intermittent receptors

    • Which statement best describes slowly adapting receptors?

  • They stop firing action potentials after a short duration.
  • They release neurotransmitters only during motion.
  • They respond exclusively to sudden changes in stimuli.
  • They continue to signal the presence of a stimulus. (correct)

    • What happens to the action potential frequency of primary sensory neurons in response to a constant stimulus?

    <p>It decreases as long as the stimulus is present.</p> Signup and view all the answers

    What allows primary sensory neurons to respond differently to ongoing stimuli?

    <p>Adaptation mechanisms in sensory receptors</p> Signup and view all the answers

    What distinguishes rapidly adapting receptors from slowly adapting receptors?

    <p>Rapidly adapting receptors respond quickly to the onset of a stimulus and then stop firing.</p> Signup and view all the answers

    Which best describes the role of afferent neurons in sensory perception?

    <p>They carry signals from receptors to the central nervous system.</p> Signup and view all the answers

    What is the relationship between the receptor potential and action potentials in afferent neurons?

    <p>Receptor potential must exceed a threshold to generate action potentials.</p> Signup and view all the answers

    What happens to the response of slowly adapting receptors when a constant stimulus is applied?

    <p>They continue to respond as long as the stimulus is present.</p> Signup and view all the answers

    What best describes the overall function of receptors in the context of afferent pathways?

    <p>They convert stimuli into electrical signals to be communicated by afferent neurons.</p> Signup and view all the answers

    What is defined as the stimulus to which a specific receptor is specifically sensitive?

    <p>Adequate stimulus</p> Signup and view all the answers

    Which of the following best describes the process of stimulus transduction?

    <p>Transformation of stimulus energy into receptor potential</p> Signup and view all the answers

    What occurs when the receptor potential reaches the threshold for activation of sodium channels?

    <p>Action potentials are generated</p> Signup and view all the answers

    Which mechanism is responsible for increased stimulus intensity at the receptor level?

    <p>Activation of a larger number of receptors and increased firing frequency</p> Signup and view all the answers

    In sensory physiology, what role do ion channels play during the mechanism of stimulus transduction?

    <p>They allow current flow leading to receptor potential changes</p> Signup and view all the answers

    What is the primary effect of a larger receptor potential in sensory receptors?

    <p>Higher firing frequency in afferent neurons</p> Signup and view all the answers

    Which statement accurately describes the response of neighboring receptor units during strong stimulus conditions?

    <p>They may also be activated in response to the larger stimulus</p> Signup and view all the answers

    Which of the following correctly outlines the sequence in the generation of a sensation from a stimulus?

    <p>Stimulus → Receptor potential → Current flow → Action potential generation</p> Signup and view all the answers

    What initiates the spike in action potential propagation in unmyelinated neurons?

    <p>Local current spread causing depolarization of nearby membrane</p> Signup and view all the answers

    What is the effect called when a postsynaptic potential (PSP) causes an increase in firing?

    <p>Excitatory postsynaptic potential (EPSP)</p> Signup and view all the answers

    Which ion primarily contributes to excitatory transmission in neurons?

    <p>Sodium (Na+)</p> Signup and view all the answers

    What characterizes inhibitory postsynaptic potentials (IPSPs)?

    <p>Increased chloride ion permeability</p> Signup and view all the answers

    In the context of synaptic transmission, what role does calcium (Ca2+) play?

    <p>It triggers the release of neurotransmitters.</p> Signup and view all the answers

    How does a local current spread influence action potential propagation?

    <p>It depolarizes adjacent areas, potentially initiating new action potentials.</p> Signup and view all the answers

    What is the primary effect of an excitatory transmission at the synapse?

    <p>It increases the likelihood of an action potential.</p> Signup and view all the answers

    What happens during an inhibitory synaptic transmission?

    <p>The postsynaptic potential becomes more negative.</p> Signup and view all the answers

    What is the primary function of sensory receptors in the sensory system?

    <p>They convert physical stimuli into nerve action potentials.</p> Signup and view all the answers

    Which of the following receptor types is specifically responsible for light detection?

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

    What does the term 'sensory adaptation' refer to?

    <p>The phenomenon of decreasing sensitivity to constant stimuli.</p> Signup and view all the answers

    What is the main role of afferent pathways in the sensory system?

    <p>Carry sensory information to the central nervous system.</p> Signup and view all the answers

    Which type of receptor is responsible for detecting pain?

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

    What is the significance of the brain having a map of the location of each receptor?

    <p>To determine the specific type and location of sensory stimuli.</p> Signup and view all the answers

    Which sensory receptors respond to cold and warmth?

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

    What is the role of the transducer in the sensory system?

    <p>To convert different forms of energy into neuronal activity.</p> Signup and view all the answers

    Which of the following is NOT a function of the somatosensory pathway?

    <p>Facilitating synaptic transmissions.</p> Signup and view all the answers

    Which statement is true about the receptors within a sensory unit?

    <p>They can only respond to the same stimulus modality.</p> Signup and view all the answers

    Study Notes

    Course Information

    • Course: MD137
    • Introduction to Physiology
    • Lecturer: Dr. Leo Quinlan
    • Email: [email protected]

    Lecture 5: Nerve Impulse and the Synapse

    • Topic: Sensory system and nerve impulse
    • Synapse: Collects data and passes it on
    • Learning Outcomes:
      • Describe the basic role of neurons in sensory physiology
      • Explain examples of how physical stimuli are translated to nerve APs
      • Classify stimuli
      • Explain sensory adaptation
      • Define and explain the function of a synapse
      • Distinguish between EPSPs and IPSPs

    General Properties of Sensory Systems

    • Stimulus type: Internal or external
    • Energy source
    • Receptors: Sense organs act as transducers
    • Afferent pathway conveys information
    • CNS integration processes information

    Receptor Types

    • Various receptor types exist, including:
      • Mechanoreceptors (respond to stretch/pressure)
      • Thermoreceptors (respond to temperature)
      • Photoreceptors (respond to light)
      • Chemoreceptors (respond to chemicals)
      • Nociceptors (respond to stimuli causing tissue damage)

    Somatic Senses

    • Enables body to feel sensations (ache, chill)
    • Responsible for touch and pain
    • Receptors: Widely distributed throughout body
    • Responds to many kinds of stimuli
    • Receptors have receptive fields that overlap
    • Examples: Merkel's disk, free nerve endings etc

    Somatosensory Pathway

    • Sensory pathways convey the type and location of stimuli
    • Type of stimuli determined by the receptor activated
    • Location determined by the location map in the brain

    Somatic Senses - Internal Stimuli

    • Include touch, temperature, pain, itch, and proprioception
    • Pathways transmit sensory signals to the thalamus

    Stimulus Type

    • Each receptor is sensitive to a specific stimulus modality
    • Mechanoreceptors - stretch/pressure
    • Thermoreceptors - temperature
    • Photoreceptors - light
    • Chemoreceptors - chemicals
    • Nociceptors - tissue damage
    • Receptor fields frequently overlap.

    Adequate Stimulus

    • Each stimulus has a specific receptor type
    • Examples: taste buds -> taste, rods/cones -> light

    Stimulus Intensity - Encoding

    • Intensity increased by:
      • Larger receptor potentials
      • More receptors activated
      • Neighboring units activated
    • Increased firing frequency in primary unit
    • Increased firing frequency in higher order neurons

    Generating a Sensation

    • Stimulus opens/closes ion channels
    • Current flows across receptor membrane creating a graded receptor potential
    • If this potential surpasses threshold, action potentials are generated to propagate along the afferent neuron
    • Neurotransmitters are released

    Stimulus Duration

    • Some neurons fire action potentials as long as the stimulus is present, others don't
    • Adaptation: Receptors decrease sensitivity.
    • Rapidly adapting: Signal changes in stimulus intensity
    • Slowly adapting: Signal continuous stimulus presence

    Adaptation

    • Quickly adapting receptors - signal onset and offset only
    • Slowly adapting receptors - respond continuously

    AP Propagation

    • APs travel along neurons
    • Includes unmyelinated and myelinated axons

    AP Propagation Unmyelinated

    • Continuous conduction: depolarization of each segment to initiate the next

    AP Propagation Myelinated

    • Saltatory conduction: APs jump between Nodes of Ranvier

    Chemical Synapse

    • Action potential triggers neurotransmitter release
    • Neurotransmitter binds to receptor
    • Synapsing of presynaptic and postsynaptic cells

    Postsynaptic Potential (PSP)

    • EPSP: Increases firing rate
    • IPSP: Decreases firing rate
    • PSPs combine in the axon hillock

    Excitatory transmission

    • Action potential causes depolarization
    • Release of neurotransmitters

    Inhibitory transmission

    • Action potential causes hyperpolarization
    • Release of neurotransmitters

    Learning Outcomes (Repeated)

    • Describe basic role of neurons
    • Explain translation of physical stimuli to nerve APs
    • Classify stimuli
    • Explain sensory adaptation
    • Define and explain synapse function
    • Distinguish EPSPs and IPSPs

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    Lecture 5: Nerve Impulse and Synapse 2024-2025 PDF

    Description

    This quiz focuses on Lecture 5 of the Introduction to Physiology course, covering essential concepts regarding nerve impulses and synapses. Students will explore the role of neurons in sensory physiology, classify different stimuli, and understand sensory adaptation and synaptic functions. Prepare to test your comprehension of sensory systems and receptor types.

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