Sensory Receptors Overview

Sensory Receptors

• Sensory perception involves receiving and interpreting information from both the internal (e.g., movement, pain) and external (e.g., vision, hearing) environments.
• Receptors act as energy transducers, converting various forms of energy into signals the body can understand.

Types of Sensory Receptors

• Classification by energy type:

  • Mechanoreceptors: respond to mechanical pressure or distortion
  • Thermoreceptors: respond to temperature changes
  • Photoreceptors: respond to light

• Classification by complexity:

  • Free nerve endings: simple structures, often involved in pain and temperature detection
  • Sensory bodies (or encapsulated nerve endings): more complex structures with specialized coverings, frequently involved in touch and pressure
  • Sensory cells: cells specialized for particular sensory functions (e.g., taste, smell)

• Classification by location of stimuli:

  • Exteroreceptors: receive stimuli from outside the body (e.g., touch, sight, hearing)
  • Interoreceptors: receive stimuli from within the body (e.g., pain in internal organs)
  • Proprioreceptors: receive info about body position and movement (e.g., muscles, tendons)
  • Telereceptors: detect stimuli from a distance (e.g., sight, hearing, smell)

Receptor Cells and Their Features

• Sensory receptors consist of two segments: an outer segment, which receives the stimulus, and an inner segment with mitochondria responsible for energy production.
• When a stimulus activates the outer segment, ion channels open or close, causing changes in membrane potential in the cell. This change, called receptor potential, is a graded potential.
• If the receptor potential reaches a threshold level, it triggers an action potential.
• The intensity of the stimulus is directly proportional to the magnitude of the receptor potential and the frequency of action potentials.

Weber-Fechner and Steven's Law

• Weber-Fechner Law: Stimulus intensity and sensation intensity are not directly proportional. A larger change in the stimulus is required to detect a difference in sensation as stimulation levels increase.
• Stevens' Law: The relationship between stimulus intensity and perceived intensity of a sensation is not linear but follows a power law. This means that perceived magnitude increases at a slower rate than the intensity of the stimulus.
• Adaptation: Receptors can adapt, meaning their sensitivity to a constant stimulus decreases over time. Different sensory systems exhibit different levels of adaptation (e.g., pain receptors adapt slowly).