General Sensory Receptors

Overview

General sensory receptors are specialized structures that detect changes in the environment and transmit sensory information to the central nervous system. They are classified based on the type of stimulus they detect.

• Thermoreceptors: Detect changes in temperature. These receptors are found in the skin and help maintain homeostasis by sensing heat and cold.

• Proprioceptors: Monitor the position and movement of skeletal muscles and joints. They provide information about body position and movement, essential for coordination and balance.

  • Muscle spindles: Detect changes in muscle length and contribute to the stretch reflex.

  • Stretch receptors: Respond to stretching of tissues, such as in muscles and tendons.

• Nociceptors: Detect pain resulting from physical or chemical damage to tissues. They are important for protective reflexes.

• Mechanoreceptors: Respond to mechanical forces such as pressure, vibration, and touch.

  • Tactile (Meissner's) corpuscle: Sensitive to light touch and located in the dermal papillae of hairless skin (e.g., fingertips, lips).

  • Lamellar (Pacinian) corpuscle: Detects deep pressure and high-frequency vibration. Found deeper in the dermis and in subcutaneous tissue.

  • Baroreceptors: Monitor changes in pressure within body structures, such as blood vessels.

• Chemoreceptors: Respond to chemical stimuli, such as changes in blood pH, oxygen, and carbon dioxide levels.

Example: When you touch a hot surface, thermoreceptors and nociceptors in your skin are activated, sending signals to your brain to withdraw your hand.

Two-Point Discrimination

Definition and Importance

Two-point discrimination is the ability to distinguish two separate points of contact on the skin. It is a measure of tactile acuity and varies across different body regions.

• Key Point: Areas with a high density of tactile receptors (e.g., fingertips) have a smaller two-point discrimination threshold, allowing for finer sensory resolution.

• Application: The two-point discrimination test is used clinically to assess the integrity of sensory pathways.

Example: The minimum distance at which two points are felt as separate on the fingertip is much less than on the back.

Adaptation of Receptors

Overview

Adaptation refers to the decrease in response of a sensory receptor to a constant stimulus over time. This allows the nervous system to ignore unimportant stimuli and focus on changes in the environment.

• Phasic receptors: Rapidly adapt to a constant stimulus and stop responding. They are specialized for detecting changes in stimuli.

  • Example: Olfactory receptors quickly adapt to persistent odors.

• Tonic receptors: Adapt slowly or not at all, providing continuous information about a stimulus.

  • Example: Nociceptors (pain receptors) are tonic, ensuring that pain is continuously perceived as long as the stimulus persists.

Additional info: Adaptation is essential for preventing sensory overload and allowing organisms to detect new or changing stimuli more effectively.