General Sensory Receptors Overview

Introduction to General Sensory Receptors

  • Focus on understanding general sensory receptors and their functions.

Nociceptors (Pain Receptors)

  • Definition: Receptors that detect noxious stimuli (pain).
  • Function: Always send a standard rate of firing of action potentials, even when not stimulated (tonic).
  • Location: Found throughout the body with large receptive fields; difficult to pinpoint exact pain location.
  • Types of Pain Detected:
  • Extreme Temperature: Respond to harmful heat or cold.
  • Mechanical Stimuli: Detect damage from cuts, bruises, etc.
  • Chemical Pain: Resulting from tissue damage (e.g., inflammation).
  • Axon Types:
  • Myelinated Axons: Transmit sharp, immediate pain rapidly (e.g., a cut on the finger).
  • Unmyelinated Axons: Transmit dull, aching pain more slowly (e.g., background pain).

Thermoreceptors (Temperature Receptors)

  • Definition: Receptors sensitive to temperature changes.
  • Function: Generally inactive and become active in response to temperature extremes (phasic).
  • Types:
  • Cold Receptors: Active at temperatures between 10-20 °C.
  • Warm Receptors: Active at temperatures between 25-45 °C.
  • Significance: More cold receptors than warm receptors, important for detecting dangerous low temperatures due to endothermic nature of humans.

Mechanoreceptors (Mechanical Stimuli Receptors)

  • Definition: Receptors that respond to mechanical stimuli like touch and pressure.
  • Function: Contain mechanically gated ion channels; respond to twisting, stretching, or physical contact.
  • Types:
  • Tactile (Touch) Receptors: Detect texture, shape, and pulsation; exist in low and high densities across different body regions.
  • Baroreceptors (Pressure Receptors): Respond to pressure within blood vessels and hollow organs like lungs and bladder.
  • Proprioceptors: Detect position of limbs and joints — crucial for coordination; include:
    • Muscle Spindles: Monitor muscle stretch.
    • Golgi Tendon Organs: Monitor tension in tendons.
    • Joint Capsule Sensory Receptors: Detect pressure and stretch in joints.

Tactile Mechanoreceptors

  • Types of Receptors: Includes free nerve endings, tactile corpuscles, Merkel cells, Ruffini corpuscles, laminated corpuscles, and root hair plexus.
  • Function: Each type has different structures and locations, leading to varying response characteristics and sensitivities to touch.
  • Special Features:
  • Some tactile receptors have small receptive fields for fine touch (e.g., fingertips).
  • Larger receptive fields found in less sensitive areas (e.g., center of the back).

Baroreceptors (Pressure Sensors)

  • Role: Detect pressure changes and prevent overstretching in various body systems (e.g., blood vessels, lungs).
  • Function: Mostly subconscious processing; except bladder receptors which send signals to the central nervous system when stretched, alerting to the need for behavioral response.

Proprioceptors (Position Sensors)

  • Function: Inform the central nervous system about the position and movement of body parts.
  • Types:
  • Muscle Spindles: Detect muscle length changes.
  • Golgi Tendon Organs: Monitor tension in tendons to prevent excessive force.
  • Joint Capsule Receptors: Monitor joint pressure and position.

Chemoreceptors (Chemical Sensors)

  • Definition: Detect concentrations of chemicals in the body (e.g., pH levels, carbon dioxide, oxygen).
  • Function: Constantly sample blood and cerebrospinal fluid; inactive most of the time but active under certain conditions to ensure homeostasis.

Conclusion

  • Understanding these receptors is crucial for comprehending how the body senses and responds to internal and external stimuli.