SENSORY RECEPTORS | Anatomy2Medicine
Sensory Receptors,Functions,Skin

SENSORY RECEPTORS

    • TYPES OF SOMATOSENSORY RECEPTORS
    • Mechanoreceptors

 

  • “very rapidly adapting” (MCQ)

 

        • pacinian corpuscle

 

  • “rapidly adapting” (MCQ)

 

        • Meissner’s corpuscle and hair follicles

 

  • “slowly adapting” (MCQ)

 

        • Ruffini’s corpuscle
        • Merkel’s receptors
        • tactile discs
      • Very rapidly and rapidly adapting receptors

 

  • detect changes in the stimulus

 

        • detect changes in velocity
      • Slowly adapting receptors
        • respond to intensity and duration of the stimulus.

 

  • Pacinian corpuscles (MCQ)

 

        • encapsulated receptors
        • found in the subcutaneous layers of nonhairy and hairy skin and in muscle
        • They are the most rapidly adapting of all mechanoreceptors.
        • Because of their very rapid on-off response, they can (MCQ)

 

  • detect changes in stimulus velocity

 

          • encode the sensation of vibration.
      • Meissner’s corpuscles (MCQ)
        • encapsulated receptors
        • found in the dermis of nonhairy skin
        • most prominently on the fingertips, lips (MCQ)
        • locations where tactile discrimination is especially good.
        • They have small receptive fields
        • can be used for two-point discrimination. (MCQ)

 

  • rapidly adapting receptors that encode point discrimination, precise location, tapping, and flutter.
  • Hair-follicle receptors

 

        • arrays of nerve fibers surrounding hair follicles in hairy skin.
        • When the hair is displaced, it excites the hair-follicle receptors. (MCQ)
        • rapidly adapting
        • detect velocity and direction of movement across the skin.

 

  • Ruffini’s corpuscles(MCQ)

 

        • located in the dermis of nonhairy and hairy skin and in joint capsules
        • have large receptive fields (MCQ)
        • stimulated when the skin is stretched.
        • stimulus may be located some distance from the receptors it activates.
        • slowly adapting receptors. (MCQ)
        • When the skin is stretched, the receptors fire rapidly, then slowly adapt to a new level of firing that corresponds to stimulus intensity.

 

  • Ruffini’s corpuscles detect stretch and joint rotation. (MCQ)

 

      • Merkel’s receptors
        • slowly adapting receptors (MCQ)
        • found in nonhairy skin and have very small receptive fields.
        • These receptors detect vertical indentations of the skin
        • response is proportional to stimulus intensity.

 

  • Tactile discs (MCQ)
  • similar to Merkel’s receptors but are found in hairy, rather than nonhairy, skin. (MCQ)
  • Thermoreceptors

 

      • slowly adapting receptors (MCQ)
      • two classes – cold receptors and warm receptors

 

  • at 36C, both receptors are active

 

      • When the skin is warmed above 36C, the cold receptors become quiescent(MCQ)

 

  • when the skin is cooled below 36C, the warm receptors become quiescent.

 

      • If skin temperature rises to damaging levels (above 45C)

 

  • warm receptors become inactive

 

        • polymodal nociceptors will be activated.
      • extremely cold (freezing) temperatures also activate nociceptors.
    • Nociceptors
      • respond to noxious stimuli that can produce tissue damage.
      • two major classes of nociceptors
        • thermal or mechanical nociceptors (MCQ)
          • supplied by finely myelinated A-delta afferent nerve fibers (MCQ)
          • respond to mechanical stimuli such as sharp, pricking pain.
        • polymodal nociceptors.
          • supplied by unmyelinated C fibers (MCQ)

 

  • respond to high-intensity mechanical or chemical stimuli and hot and cold stimuli.
  • Damaged skin releases a variety of chemicals, including bradykinin, prostaglandins, substance P, K+, and H+(MCQ)

 

      • initiate the inflammatory response.
      • The blood vessels become permeable,
      • there is local edema and redness of the skin.
    • Mast cells near the site of injury  release histamine that activates nociceptors(MCQ)