Physiology of Touch: Receptors and Pathways, Animation

00:03:56
https://www.youtube.com/watch?v=udzhuFz3HKw

Résumé

TLDRThe sense of touch, or tactile sense, is the ability to perceive contact with the skin through mechanical stimuli. Tactile receptors, which are nerve endings in the skin, respond to pressure, vibration, and movement. These receptors can be classified as encapsulated or unencapsulated, and are functionally either rapidly-adapting or slowly-adapting. Rapidly-adapting receptors respond quickly to initial stimuli but adapt quickly, while slowly-adapting receptors continue to send signals for longer durations. The sensitivity of these receptors varies across body regions; smaller receptive fields are more sensitive to touch. The sensory pathway involves three neurons: first-order neurons from receptors, second-order neurons in the spinal cord, and third-order neurons that transmit signals to the thalamus and then to the sensory cortex, which is organized according to body regions' receptor density. Sensitive areas like fingers have larger cortical representation than less sensitive areas like the trunk.

A retenir

  • 🖐️ Touch perception is crucial for interacting with our environment.
  • 🔍 Tactile receptors are classified as encapsulated or unencapsulated.
  • ⚡ Rapidly-adapting receptors respond to changes; slowly-adapting to steady pressure.
  • 🏷️ Sensitive regions like fingers have a higher density of receptors.
  • 🧠 The sensory cortex maps body regions based on receptor density.
  • 🔗 A touch sensory pathway involves three types of neurons.
  • 📦 Receptive fields determine how we perceive touch.
  • 👂 Sensory signals cross to the opposite side of the brain.
  • 📏 Size of the cortical area represents sensory receptor density.
  • 🌍 Different body parts have varying sensitivity due to receptor distribution.

Chronologie

  • 00:00:00 - 00:03:56

    The sense of touch, known as the tactile sense, involves the perception of objects through contact with the skin. Mechanical stimuli like pressure and vibration deform tactile receptors, which are sensory nerve endings. This deformation opens ion channels, leading to cellular depolarization and, if strong enough, action potentials sent to the brain. There are various types of tactile receptors classified as encapsulated or unencapsulated, and functionally as rapidly-adapting or slowly-adapting, with different sensitivities to touch stimuli. A touch sensory pathway involves three types of neurons: first-order neurons (touch receptors), second-order neurons (intermediate synapses), and third-order neurons (transmit to sensory cortex), with a complex relationship between receptive fields and sensitivity determined by receptor density in different body areas.

Carte mentale

Vidéo Q&R

  • What is the tactile sense?

    The tactile sense is the perception of objects in contact with the skin, triggered by mechanical stimuli like pressure and vibration.

  • How do tactile receptors function?

    Tactile receptors respond to mechanical stimuli, causing cellular depolarization and generating action potentials sent to the brain.

  • What types of tactile receptors exist?

    Tactile receptors can be classified into encapsulated or unencapsulated, and functionally as rapidly-adapting or slowly-adapting.

  • What is a receptive field?

    A receptive field is the specific area of skin that stimulates a single sensory neuron; touch in this area transmits one signal to the brain.

  • Why do different body parts have different sensitivity to touch?

    Sensitivity varies due to the density of sensory receptors; areas like fingers have a higher density than the trunk, resulting in greater sensitivity.

  • How is sensory information transmitted to the brain?

    Sensory information travels through a pathway involving three neurons: first-order from receptors, second-order in the spinal cord, and third-order to the cortex.

  • What is the role of the thalamus in touch perception?

    The thalamus acts as a relay station, conducting sensory information from the spinal cord to the sensory cortex.

  • What happens when two points touch a receptive field?

    If touched at two points within one receptive field, it feels like a single touch; sensitivity varies by body region.

  • What are the characteristics of rapidly-adapting receptors?

    Rapidly-adapting receptors detect changes and movements but quickly reduce signal generation if the stimulus remains constant.

  • What are slowly-adapting receptors responsible for?

    Slowly-adapting receptors maintain signals for longer, indicating steady pressure and helping to detect texture and shape.

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  • 00:00:03
    The sense of touch, or tactile  sense, is the perception of
  • 00:00:07
    objects that come into contact with the skin. Basically, mechanical stimuli such as pressure,
  • 00:00:13
    stretch, vibration or movement, cause physical  deformation in tactile receptors, which are
  • 00:00:19
    essentially nerve endings of sensory neurons.  The deformation typically leads to opening of
  • 00:00:25
    ion channels, allowing ions to flow in or out of  the cells, resulting in cellular depolarization.
  • 00:00:33
    If the stimulus is strong enough, action  potentials are generated and sent to the brain.
  • 00:00:40
    There are several types of tactile  receptors, located in different
  • 00:00:43
    layers of the skin and deeper tissues. Anatomically, they can be encapsulated or
  • 00:00:49
    unencapsulated, meaning they are wrapped or  not wrapped in connective tissue, respectively.
  • 00:00:56
    Functionally, they can be  rapidly-adapting, or slowly-adapting:
  • 00:01:00
    - Rapidly-adapting receptors generate action  potentials when first stimulated, then quickly
  • 00:01:06
    adapt and reduce or stop generating signals  even if the stimulus continues. They respond
  • 00:01:13
    to changes and therefore detect movements and  sequence of events, rather than static objects.
  • 00:01:19
    - Slowly-adapting receptors, on the other hand,  keep generating signals for a longer time.
  • 00:01:26
    They carry messages about steady pressure on the  skin and sense object’s texture, edges and shapes.
  • 00:01:34
    Touch receptors also differ in their sensitivity  - some respond to light touch, others sense only
  • 00:01:40
    heavy pressures. A sensory neuron receives signals  from an area called its receptive field. Any
  • 00:01:48
    touch within a receptive field stimulates one  sensory neuron, transmitting one single signal
  • 00:01:54
    to the brain. Being touched at 2 points within a  receptive field would feel like a single touch. On
  • 00:02:01
    the skin of the back, 2 points of contact several  centimeters apart may feel like 1 touch, while on
  • 00:02:07
    a finger, 2 contact points just 2 millimeters  apart can be felt separately. Receptors with
  • 00:02:14
    small receptive fields are more sensitive,  they respond to lower frequencies of vibration;
  • 00:02:20
    receptors with large receptive fields typically  respond to higher frequencies of vibration.
  • 00:02:27
    A touch sensory pathway involves 3 neurons: - Touch receptors are first-order neurons.
  • 00:02:33
    Their axons form sensory fibers  that enter the spinal cord
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    via the dorsal root of spinal nerve. - Inside the cord, first-order neurons synapse
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    with second-order neurons either near the point  of entry, or in the medulla of the brainstem.
  • 00:02:50
    Second-order neurons then cross over to the  other side of the cord, before ascending to
  • 00:02:54
    the thalamus. This is how sensory information  from the left side of the body is transmitted
  • 00:03:00
    to the right side of the brain, and vice versa. - Third-order neurons conduct the information
  • 00:03:05
    from the thalamus to the sensory cortex. Sensory neurons from the face and head
  • 00:03:12
    follow several cranial nerves, mainly  the trigeminal nerve, to the brainstem,
  • 00:03:16
    where they synapse with second-order neurons,  which decussate and continue to the thalamus.
  • 00:03:24
    The sensory cortex is spatially organized so  that its adjacent areas represent neighboring
  • 00:03:30
    regions of the body. The size of the cortical area  representing a certain body region is proportional
  • 00:03:37
    to the number of sensory receptors it has. Thus,  sensitive regions with high density of receptors,
  • 00:03:43
    such as fingers or face, have a larger cortical  representation than the less sensitive trunk.
Tags
  • tactile sense
  • touch receptors
  • sensory neurons
  • action potentials
  • receptive fields
  • cortical representation
  • sensory pathways
  • rapidly-adapting receptors
  • slowly-adapting receptors
  • mechanical stimuli