Lecture on Sensory Receptors and Special Senses

Introduction

• Overview of sensory receptors: tactile, gustation, olfaction.
• Vision and anatomy of the eye and inner ear reserved for lab.

Common Terminology

• Stimuli: Sensory information our bodies are exposed to.
• Sensation: Activation of receptors for stimuli.
• Perception: Central processing of sensory stimuli into meaningful patterns.
• Not all sensations are perceived, e.g., ticking clock sound fades with time.
• Attention: Influences perception and sensation, e.g., tuning out background noise when focused.

Sensory Receptors

• General senses: Temperature, pain, touch, stretch, and pressure.
• Special senses: Gustation, olfaction, vision, equilibrium, and hearing.

Sensory System Model

• External stimulus changes a receptor.
• Sensory neurons send signals to CNS, causing relay neuron changes, resulting in actions.

Properties of Sensory Receptors

• Adaptation: Decrease in action potential firing with constant stimulus.
  • Tonic receptors: Constant stimulus processing, e.g., balance receptors.
  • Phasic receptors: Detect new or changed stimulus, e.g., tactile receptors.

Classification of Receptors

• Distribution
  • General sense receptors: Throughout skin and organs (somatic and visceral).
  • Special sense receptors: Complex organs in the head for smell, taste, vision, hearing, equilibrium.
• Origin of Stimulus
  • Exteroreceptors: External environment stimuli.
  • Interoreceptors: Internal organ stimuli.
  • Proprioceptors: Body position stimuli.
• Modality of Stimulus
  • Chemoreceptors: Chemical molecules.
  • Thermoreceptors: Temperature changes.
  • Photoreceptors: Light changes.
  • Mechanoreceptors: Plasma membrane shape changes.
  • Nociceptors: Painful stimuli.

Tactile Receptors

• Most numerous, detecting touch, pressure, vibration.
• Unencapsulated tactile receptors: Light touch response, e.g., free nerve endings.
• Encapsulated receptors: Complex, require more pressure/vibration, e.g., Meissner's and Pacinian corpuscles.

Proprioception

• Sense of movement and body position.
• Muscle spindle: Senses muscle length and stretch.
• Golgi tendon organ: Senses tension and load on limbs.

Visceral Senses

• Mechanoreceptors and interoreceptors.
• Referred Pain: Perception of pain on skin surface from internal organ issues, e.g., heart attack, brain freeze.
  • Hypothesis: Convergence of skin and visceral receptors at spinal cord, leading to brain confusion.

This lecture outlines the essential concepts of sensory receptors, including various types and their functions in detecting and processing external and internal stimuli.