Lecture Notes: General and Special Senses

Overview

• General Senses: Simple structure; receptor is the first-order neuron.
• Special Senses: Complex setup; involves special receptor cells communicating with first-order neurons.

Neuronal Structure

• General Senses:
  • First-order neuron acts as the receptor.
  • Some modifications near the end may occur.
• Special Senses:
  • Involves an extra receptor cell synapsing onto the first-order neuron.
  • Allows for more complex signaling pathways.

Receptor Distribution

• General Senses:
  • Receptors distributed over body surfaces (e.g., pain, temperature, touch).
  • Examples: Fine touch, thermal receptors found all over the body.
• Special Senses:
  • Located in special sensory organs.
  • Examples: Photoreceptors in retina, auditory receptors in cochlea, gustatory receptors on tongue.

Central Processing

• General Senses:
  • Processed in the primary sensory cortex (postcentral gyrus).
  • Right side of body monitored by left brain and vice versa.
• Special Senses:
  • Processed in specialized cortical regions.
  • Locations: Occipital lobe for vision, temporal lobe for olfaction and gustation.

Receptive Field

• General Senses: Larger receptive fields, sometimes with specialized tissue.
• Special Senses: Small receptive fields, require direct stimulus.

Labelled Line and Sensory Coding

• Labelled Line: Pathway from receptor to cerebral cortex; tells stimulus type and location.
• Sensory Coding: Describes intensity and duration of stimulus; similar to Morse code.

Types of Receptors

• Tonic Receptors: Always on, release neurotransmitters; allows complex signaling.
• Phasic Receptors: Have on/off phases, respond to specific stimuli.

Adaptation

• Peripheral Adaptation: Decrease in sensitivity at receptor cell.
• Central Adaptation: Decrease in sensitivity at a sensory nucleus along the pathway.

Additional Concepts

• Referred Pain: Pain perceived at a location other than the stimulus site (e.g., heart attack pain in the arm).
• Sensory Coding and Intensity: How the brain interprets the strength and duration of a stimulus.

Conclusion

• The lecture concludes with a promise to discuss different sensory receptors in detail in the next video.
• Emphasis on the complexity and ongoing research in sensory reception and neurobiology.