Sensation, Perception, and Cranial Nerves

Sensation and Perception

• Sensation: The process where environmental or internal stimuli are converted into electrochemical signals (action potentials).
• Perception: The processing and interpretation of these signals within the central nervous system (CNS), leading to conscious awareness of the stimulus.

Sensory Receptors

• Sensory receptors convert stimuli into action potentials.
• Categorized by location:
  • General Receptors: Spread throughout the body tissues.
    • Examples: Touch/pressure, heat, pain.
  • Special Receptors: Located in specific organs.
    • Examples: Sight, smell, hearing, taste.

Categories of Receptors Based on Stimulus Type

• Chemoreceptors: Detect the presence and/or concentration of chemicals.
• Pain Receptors (Nociceptors): Detect tissue damage.
• Thermoreceptors: Detect changes in temperature.
• Mechanoreceptors: Detect changes in pressure or movement.
• Photoreceptors: Detect changes in light energy.

Categories of Receptors Based on Structure

• Free Nerve Endings:
  • Dendrites of neurons that act as receptors.
• Encapsulated Nerve Endings:
  • Nerve endings enclosed in a connective tissue capsule.
• Specialized Receptor Cells:
  • Cells with distinct structures, like rods in the eye.

Sensory Processing Pathway

• The general sensory processing pathway is as follows:
  • Peripheral sensation → Nerve pathway → CNS → Spinal cord or brainstem → Thalamus → Primary sensory cortex → Association areas

Touch and Related Senses

• Touch/Pressure Receptors:
  • Free Nerve Endings: Detect general touch and pressure.
  • Meissner’s Corpuscles (Tactile Corpuscles): Detect light touch and low-frequency vibrations, especially in the skin of fingertips and lips.
  • Pacinian Corpuscles (Lamellated Corpuscles): Detect deep pressure and high-frequency vibrations.

Pain Receptors

• Pain Receptors:
  • Free Nerve Endings: Detect tissue damage.
  • Transmembrane receptors:
    • Bind to chemicals released when tissue is damaged.
    • Triggered by extremes in temperature, pressure/movement and chemicals.

Thermoreceptors

• Thermoreceptors:
  • Free Nerve Endings: Detect temperatures different from body temperature.
    • Different receptors for hot and cold.

Sensory Processing Pathway (Repeated)

• The general sensory processing pathway is as follows:
  • Peripheral sensation → Nerve pathway → CNS → Spinal cord or brainstem → Thalamus → Primary sensory cortex → Association areas

Cranial Nerves

The following is a summary table of the 12 cranial nerves:

Brain Lobe Diagram.

• Frontal Lobe
  • Includes the precentral gyrus (area 4), which is the primary motor cortex, and Broca's area (areas 44, 45).
• Parietal Lobe
  • Contains the postcentral gyrus (areas 1, 2, 3), which is the primary somatosensory cortex, the angular gyrus (area 39), and the supramarginal gyrus (area 40).
• Occipital Lobe
  • Located at the back.
• Temporal Lobe
  • Features the primary auditory cortex (area 22).
• Other Structures
  • Includes the midbrain, pons, medulla, hypothalamus, pituitary gland, and thalamus.