Touch and Mechanoreceptors: L18
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Questions and Answers

What is the primary function of sensory systems in relation to stimuli?

  • To amplify sensory signals for better perception
  • To eliminate irrelevant sensory information
  • To discriminate different properties of stimuli (correct)
  • To generate emotions based on external stimuli

    • What differentiates tonic receptors from phasic receptors?

  • Tonic receptors provide continuous information, while phasic receptors respond to changes (correct)
  • Tonic receptors adapt rapidly, while phasic receptors do not
  • Tonic receptors are only activated by light stimuli
  • Tonic receptors are situated in the skin, while phasic receptors are situated in the organs

    • What is a generator potential?

  • A type of sensory hormone released during transduction
  • A feedback mechanism that enhances sensory perception
  • A potential that creates a reflexive movement in response to stimuli
  • An electrical signal generated as a result of transduction of a stimulus (correct)

    • Which of the following is NOT a specialized sense organ involved in touch?

    <p>Rods and cones</p> Signup and view all the answers

    In the context of sensory systems, what is meant by 'transduction'?

    <p>The conversion of stimulus energy into an electrical signal</p> Signup and view all the answers

    What is the relationship between receptive field size and spatial acuity?

    <p>Smaller receptive fields lead to higher spatial acuity.</p> Signup and view all the answers

    In which cortex is the primary somatosensory cortex located?

    <p>Postcentral gyrus</p> Signup and view all the answers

    What system is responsible for transmitting tactile information from the body to the somatosensory cortex?

    <p>Dorsal Column-Medial Lemniscal System</p> Signup and view all the answers

    Which of the following pathways transmits touch information from the face?

    <p>Trigeminal System</p> Signup and view all the answers

    What type of mechanoreceptor is Merkel Disk’s classified as?

    <p>Slow adapting</p> Signup and view all the answers

    What key function do mechanoreceptors perform?

    <p>Transduce mechanical stimuli into neural signals</p> Signup and view all the answers

    Which of the following provides the highest sensitivity for two-point discrimination?

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

    What structure is involved in processing tactile information before it reaches the somatosensory cortex?

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

    Which sensory nerve is responsible for a rash in the mandibular region?

    <p>Mandibular branch of the trigeminal nerve</p> Signup and view all the answers

    What is the conduction velocity range for touch sensory receptors?

    <p>35-75 m/s</p> Signup and view all the answers

    Which factor determines the size of the receptive field in somatosensory afferents?

    <p>The size of the branching of sensory afferents within the skin</p> Signup and view all the answers

    What does 2-point discrimination measure?

    <p>The ability to distinguish two closely applied stimuli as distinct</p> Signup and view all the answers

    Which sensory receptors are associated with proprioception?

    <p>Muscle spindles</p> Signup and view all the answers

    What is the correct diameter range for free nerve endings responsible for pain and temperature sensation?

    <p>1-5 micrometer</p> Signup and view all the answers

    Which scenario is an example of low spatial acuity?

    <p>Identifying a single point of touch</p> Signup and view all the answers

    What aspect of somatosensory afferents varies with the density of receptors?

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

    What factors are involved in encoding the stimulus strength in the sensory systems?

    <p>Amplitude of generator potential and frequency of action potentials</p> Signup and view all the answers

    How do phasic receptors respond to stimuli over time?

    <p>They rapidly decrease their response after the initial stimulus</p> Signup and view all the answers

    What is a receptive field in the context of the somatosensory system?

    <p>The region of skin innervated by a single spinal nerve</p> Signup and view all the answers

    What type of neurons convey fine touch information to central circuits?

    <p>Pseudounipolar neurons in the DRG</p> Signup and view all the answers

    What does the concept of a dermatome represent in the somatosensory system?

    <p>A region of skin innervated by a single DRG spinal nerve</p> Signup and view all the answers

    Which mechanoreceptor is primarily responsible for detecting pressure and vibration?

    <p>Pacinian corpuscle</p> Signup and view all the answers

    How does touch transduction occur in sensory receptors?

    <p>By causing depolarization of the receptor cell membrane</p> Signup and view all the answers

    What distinguishes tonic receptors from phasic receptors?

    <p>Tonic receptors respond continuously and adapt slowly</p> Signup and view all the answers

    In the somatosensory system, how does spatial acuity vary across the body?

    <p>It is higher in areas with smaller receptive fields</p> Signup and view all the answers

    What physiological change occurs in response to a strong stimulus?

    <p>Increased frequency of action potentials</p> Signup and view all the answers

    What is the primary function of Meissner's corpuscles?

    <p>Motion detection</p> Signup and view all the answers

    Which mechanoreceptor is characterized by being slow-adapting?

    <p>Merkel disks</p> Signup and view all the answers

    Where are Pacinian corpuscles primarily located?

    <p>In the subcutaneous layer</p> Signup and view all the answers

    Which receptor is responsible for detecting skin stretch?

    <p>Ruffini's corpuscles</p> Signup and view all the answers

    What property distinguishes Merkel disks from other mechanoreceptors?

    <p>They detect edges and texture.</p> Signup and view all the answers

    Which mechanoreceptors are classified as fast-adapting?

    <p>Meissner's and Pacinian</p> Signup and view all the answers

    Which mechanoreceptor has the highest spatial acuity?

    <p>Merkel disks</p> Signup and view all the answers

    What type of stimuli do Pacinian corpuscles respond to?

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

    Which statement correctly describes the receptive field of Meissner's corpuscles?

    <p>They have a small and precise receptive field.</p> Signup and view all the answers

    Which mechanoreceptor type is primarily involved in grip control?

    <p>Meissner's corpuscles</p> Signup and view all the answers

    Study Notes

    Sensory Systems Overview

    • Sensory systems relay information from the environment to the brain for processing.
    • Sensory input is received, integrated, and generates a motor output.
    • Sensory input travels through the peripheral nervous system (PNS) to the central nervous system (CNS) for processing.

    Types of Sensory Systems

    • Hearing
    • Balance
    • Touch
    • Thermoreception (temperature)
    • Nociception (pain)
    • Proprioception (body position)
    • Vision
    • Smell
    • Taste

    Sensory Receptors

    • Molecules and cells are involved in sensory reception within the CNS.
    • Specialized cells (e.g., rods and cones in the retina) detect specific stimuli.
    • Receptors transduce energy from a stimulus to an electrical signal.
    • This signal is processed through transduction, encoding, and processing.

    CNS Disorders & Treatment

    • Central nervous system (CNS) disorders can affect sensory systems.
    • Treatments for such disorders vary according to the specific disorder.

    Aims

    • Students should be able to describe specialized sense organs for touch, as well as their molecular and cellular structures.
    • Students should be able to describe the specific neural circuits in the CNS related to touch and similar senses.

    Structure of the Sensory Lecture

    • General features of sensory systems will be covered, followed by touch and mechanoreception.

    Learning Outcomes

    • Understanding the distinct levels of organization within sensory systems to discriminate different stimuli's features.
    • Understanding how generator potentials work during the processing of sensory input.
    • Recognizing the general organization and cell structure within the sensory systems.
    • Distinguishing the difference between tonic and phasic receptors (and examples).

    Sensory Systems: General Features

    • Energy stimuli (chemical, light, mechanical) activates sensory receptors:   - Transduction: converting stimuli into electrical signals.   - Encoding: representing different aspects of a stimulus (modality, intensity, duration, location) as code.   - Processing: interpreting the encoded sensory input into sensation and perception.

    Functional Categories of Sensory Receptors

    • Exteroceptors: detect stimuli from the external environment.
    • Proprioceptors: detect the body's position.
    • Interoceptors: detect internal conditions (e.g., blood pressure).
      • Categories include mechanoreceptors (pressure, stretch, movement), thermoreceptors (temperature), nociceptors (pain), photoreceptors (light), chemoreceptors (chemicals), osmoreceptors (water).
      • Different receptors respond to specific stimuli, like light, chemicals or tactile pressure.
    • General and specialized categories exist within each.

    Signal Transduction

    • The process of converting stimulus energy into an electrical signal.
    • Begins with stimuli of varying strengths.
    • Graduated/graded responses to different stimulus strengths lead to different generator potentials, up to the threshold for action potentials.
    • Action potentials are all- or-none electrical signals that are generated if the generator potential reaches the threshold.

    Encoding and Transmission

    • Encoding represents features of the stimuli, including modality (types), intensity (strength), duration (how long), and location (localization).
    • Different nerve fibers within the PNS have varying conduction velocities with this response to stimulus that affect the timing.
    • The frequency of action potentials carries the information about intensity. This frequency is directly related to the amplitude of the generator potential.

    Types of Sensory Neurons

    • Specialized sensory neuron: the stimulus activates the receptor protein on the receiving end of the neuron, causing depolarization of the trigger zone to create an action potential.
    • Specialized receptor epithelial: the stimulus activating the receptor protein leads to depolarization of the epithelial sensory cell, which triggers the release of neurotransmitters that induce a graded potential on the dendrite of an afferent neuron that leads to an action potential.

    Sensory System Adaptation

    • Tonic receptors: slowly adapting, fire steadily as long as the stimulus is present (important for constant information like pain).
    • Phasic receptors: rapidly adapting, fire only when the stimulus changes (important for information about the onset and offset of stimuli, e.g., touch).

    Somatic Sensory System - Fine Touch

    • Learning objectives cover organization, receptive fields, different properties, neural pathways, transductive mechnoreceptors.

    The Somatic Sensory System - Fine Touch

    • Somatosensory afferents convey fine touch information to central circuits via distinct pathways for the body and face.
    • Spinal cord and trigeminal ganglia are involved.
    • Pseudounipolar neurons in DRG (dorsal root ganglion) have peripheral and central processes involved.

    Dermatomes

    • Dermatomes are regions of skin innervated by the spinal nerve of a single dorsal root ganglion.
    • These structures are crucial for understanding nerve distribution and diagnosing neurological conditions.

    Shingles

    • The rash from shingles is confined to a dermatomal region that depends on the infected sensory nerve.
    • Understanding the distribution of shingles is important for diagnosing and treating affected patients.

    Functional Properties of Sensory Systems

    • Different criteria are used to subdivide somatosensory afferents linking peripheral sensory receptors to the CNS.

    Receptive Fields

    • Receptive fields are areas of skin surface over which stimuli change the rate of action potentials.
    • Receptor density affects receptive field size.
    • High receptor density leads to smaller receptive fields, improving spatial acuity (finer touch discrimination).

    Two-Point Discrimination

    • 2-point discrimination measures spatial acuity (ability to distinguish two separate points).
    • Differences in spatial acuity exist across body parts due to receptive field size and density.

    Mechanoreceptors:

    • Morphological and Functional Differences. These include superficial and deep locations. Examples include Meissner's corpuscles, Merkel disks, Pacinian Corpuscles, Ruffini corpuscles.
      • Spatial acuity and receptive field size are related.

    Touch: Mechanoreceptors

    • These receptors are categorized into superficial receptors and deep receptors based on location within the skin.
    • Each mechanoreceptor type (e.g., Meissner's corpuscles, Pacinian corpuscles) has different adaptive properties (fast or slow adapting).
    • They also respond to different stimulus types and have varying receptive field sizes.

    Touch: Transmission Pathways

    • Two different pathways transmit touch information from the body and face to the brain.
    • Dorsal column-medial lemniscal system (body): 1/2/3 order neurons that synapse in the thalamus to arrive at the somatosensory cortex.
    • Trigeminothalamic system (face): similar to the dorsal pathway, but with different nuclei in the brainstem and thalamus.

    Touch: Mechanoreceptor Overview

    • Different touch related receptors have different properties, including different locations within the skin, function (e.g. shapes, locations), etc.

    Mechanoreceptor Transduction

    • Stimulus causes mechanical deformation of the mechanoreceptor, affecting ion channels, leading to a receptor potential & depolarization of the afferent neuron.

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    Description

    Test your knowledge on sensory systems focusing on touch and mechanoreceptors. This quiz explores key concepts such as receptor types, tactile information transmission, and the brain's processing of sensory input. Understand how these systems contribute to our perception of stimuli.

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