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. (B)</p> Signup and view all the answers

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

<p>Adaptation mechanisms in sensory receptors (B)</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. (D)</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. (B)</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. (A)</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. (D)</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. (B)</p> Signup and view all the answers

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

<p>Adequate stimulus (D)</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 (B)</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 (D)</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 (C)</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 (C)</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 (A)</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 (D)</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 (C)</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 (B)</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) (D)</p> Signup and view all the answers

Which ion primarily contributes to excitatory transmission in neurons?

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

What characterizes inhibitory postsynaptic potentials (IPSPs)?

<p>Increased chloride ion permeability (B)</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. (C)</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. (D)</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. (B)</p> Signup and view all the answers

What happens during an inhibitory synaptic transmission?

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

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

<p>Photoreceptors (C)</p> Signup and view all the answers

What does the term 'sensory adaptation' refer to?

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

Which type of receptor is responsible for detecting pain?

<p>Nociceptors (A)</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. (C)</p> Signup and view all the answers

Which sensory receptors respond to cold and warmth?

<p>Thermoreceptors (D)</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. (C)</p> Signup and view all the answers

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

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

Flashcards

Rapidly Adapting Receptor

A receptor that responds strongly to a change in stimulus, but quickly decreases its firing rate even if the stimulus continues.

Slowly Adapting Receptor

A receptor that continues to fire action potentials as long as the stimulus is present, even if it is constant.

Receptor Potential

A change in membrane potential of a sensory receptor in response to a stimulus.

Afferent Neuron

A neuron that conducts signals from sensory receptors to the central nervous system.

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Action Potentials

Electrical impulses that travel along the axon of a neuron.

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Action Potentials and Stimulus Duration

Some sensory neurons fire action potentials continuously as long as a stimulus is present, while others only fire at the start and end of the stimulus.

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Adaptation in Sensory Receptors

Sensory receptors decrease their sensitivity to a stimulus of constant strength over time. This means the frequency of action potentials decreases.

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Sensory Receptors Signal Presence and Change

Sensory receptors are designed to detect changes in the environment and signal the presence of a stimulus.

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Adequate Stimulus

The specific type of stimulus that a receptor is most sensitive to.

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Example: Taste Buds

Taste buds are specialized receptors that are most sensitive to chemical stimuli, specifically those that dissolve in saliva.

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Example: Rods and Cones

Rods and cones are light-sensitive receptors found in the retina. Rods are more sensitive to low light, while cones are responsible for color vision.

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Stimulus Intensity

The strength or magnitude of a stimulus, which can be encoded by the nervous system to represent different levels of sensation.

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Encoding Stimulus Intensity

The nervous system encodes stimulus intensity by using several mechanisms, including the frequency of action potentials, the number of receptors activated, and the activation of neighboring receptors.

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Stimulus Transduction

The process by which a stimulus is converted into a neural signal that the brain can interpret.

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What is the basic role of neurons in sensory physiology?

Neurons act as the communication pathways for sensory information. They receive signals from sensory receptors and transmit these signals to the central nervous system (CNS) for processing.

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How are physical stimuli translated into nerve action potentials (APs)?

Sensory receptors convert physical stimuli into electrical signals. This process involves a change in the receptor's membrane potential, which can trigger an action potential that travels along the neuron.

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What are sensory receptors?

Specialized cells or endings of neurons that detect specific types of stimuli, such as light, sound, pressure, or temperature.

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What is sensory adaptation?

The gradual decrease in the firing rate of a sensory neuron when exposed to a constant stimulus. This allows us to focus on changing stimuli rather than constant ones.

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What is a synapse?

A specialized junction where communication occurs between neurons or between a neuron and a muscle or gland. It allows for the transmission of signals from one cell to another.

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What is an excitatory postsynaptic potential (EPSP)?

A depolarizing potential in the postsynaptic neuron that increases the likelihood of an action potential being fired.

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What is an inhibitory postsynaptic potential (IPSP)?

A hyperpolarizing potential in the postsynaptic neuron that decreases the likelihood of an action potential being fired.

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What is a stimulus?

Any change in the internal or external environment that can be detected by sensory receptors.

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What is a transducer?

A specialized structure in a sensory receptor that converts a physical stimulus into an electrical signal.

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What is a somatosensory pathway?

A pathway that carries sensory information from the body to the brain. It's responsible for processing information about touch, pain, temperature, and proprioception.

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Local Current Spread

The flow of electrical charge within a neuron, caused by the movement of ions across the membrane. This current spreads along the axon, causing depolarization of adjacent areas.

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Electrotonic Conduction

The passive spread of electrical charge along a neuron's membrane, without generating action potentials. It's influenced by factors like membrane resistance and capacitance.

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Action Potential Propagation in Unmyelinated Axons

The process where action potentials travel along an unmyelinated axon, involving continuous depolarization and repolarization at each point of the axon.

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Chemical Synapse

A specialized junction between two neurons where communication happens through the release of neurotransmitters. It involves a presynaptic neuron releasing neurotransmitters that bind to receptors on the postsynaptic neuron.

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Post-Synaptic Potential (PSP)

The change in membrane potential of the postsynaptic neuron in response to the binding of neurotransmitters. Can be excitatory (EPSP) or inhibitory (IPSP).

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Excitatory Postsynaptic Potential (EPSP)

A depolarizing PSP that makes the postsynaptic neuron more likely to fire an action potential. It's caused by the influx of positive ions.

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Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarizing PSP that makes the postsynaptic neuron less likely to fire an action potential. It's caused by the influx of negative ions or the outflow of positive ions.

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How are stimuli classified?

Stimuli, which are physical events that trigger a response in a sensory receptor, can be classified based on their modality (e.g., light, sound, pressure), intensity (e.g., weak, strong), and duration (e.g., short, long).

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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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