Understanding the Human Senses

Jan 27, 2025

Anatomy & Physiology 2: Introduction to Senses

Key Concepts

  • Homeostasis: Central theme in physiology, maintaining a balanced internal environment despite external changes.
  • Senses: Link the external environment to the internal body, crucial for maintaining homeostasis.

Types of Senses

  • General Senses: Simple and distributed throughout the body.

    • Touch, Pressure, Vibration, Pain, Temperature, Proprioception.
    • Proprioception: Awareness of body position (e.g., knowing arm position with eyes closed).
    • Somatic vs Visceral Senses:
      • Somatic: Surface-level senses (skin, muscles).
      • Visceral: Senses from organs (stomach fullness, heart rate).

  • Special Senses: Located in specific head regions, complex structures.

    • Olfaction (Smell), Gustation (Taste), Vision, Hearing and Equilibrium (Balance).
    • Complex anatomy, specific locations in the head.

Neural Pathways

  • Information travels to and from the brain through nerve pathways.
    • Corticospinal Tract: Efferent pathway from brain (cortex) to spinal cord, related to motor responses.
    • Spinothalamic Tract: Afferent pathway bringing sensory information to the brain.

Action Potentials & Nerve Impulses

  • Action Potentials: Activation of nerves due to stimuli reaching threshold.
  • Receptors: Gather stimuli (light touch, temperature, pain) and convert to action potentials.

Types of Sensory Receptors

  • Mechanoreceptors: Respond to mechanical changes (touch, pressure, vibration).
  • Thermoreceptors: Detect temperature changes.
  • Photoreceptors: Light detection (vision).
  • Chemoreceptors: Chemical detection (smell, taste).
  • Nociceptors: Pain receptors, respond to harmful stimuli.

Sensory Processing

  • Sensory info is processed in specific brain regions (e.g., occipital lobe for vision, temporal lobe for hearing).
  • Postcentral Gyrus: Primary region receiving sensory input before relaying to other brain areas.

Sensory Adaptation

  • The brain adjusts to continuous stimuli to prevent overload.
  • Sensory adaptation occurs when receptors decrease firing rates over time if the stimulus is constant.
  • Examples include getting used to odors, background noise, and temperature.

Classification of General Senses

  • Exteroceptive: External stimuli (pressure, touch, temperature, pain).
  • Proprioceptive: Awareness of body position and movement.
  • Visceroceptive: Internal organ stimuli.

Specific Sensory Receptors

  • Free Nerve Endings: Basic neuron structures for touch and pain.
  • Meissner's Corpuscles: Light touch, located on hairless skin areas (fingertips, lips).
  • Pacinian Corpuscles: Deep pressure, located in deeper skin layers.

Additional Notes

  • Thermoreceptors respond to temperatures between specific ranges and adapt quickly.
  • Sensory adaptation allows focus on important changes rather than constant stimuli.
  • Extreme temperatures (below 32°F or above 212°F) are not adaptable, emphasizing the protective role of pain.

These notes provide an overview of the lecture on senses within the context of maintaining homeostasis and the nervous system's role in processing sensory stimuli.