chp 16

Classification by Stimulus

• Mechanical stimuli

  • Senses: touch, pressure, vibration, proprioception

  • Receptors: mechanoreceptors (e.g., Meissner's corpuscles, Pacinian corpuscles, Merkel discs, Ruffini endings); hair follicle receptors; muscle spindles; Golgi tendon organs

• Thermal stimuli

  • Senses: cold, warmth

  • Receptors: thermoreceptors (cold and warm)

• Nociceptive stimuli

  • Senses: pain

  • Receptors: nociceptors (mechanical, thermal, chemical)

Somatic Receptors

• Mechanoreceptors

  • Examples: Meissner's corpuscles, Pacinian corpuscles, Merkel discs, Ruffini endings

• Proprioceptors

  • Examples: muscle spindles, Golgi tendon organs, joint receptors

• Thermoreceptors

  • Examples: cold receptors, warm receptors

• Nociceptors

  • Function: respond to potentially damaging stimuli (mechanical, thermal, chemical)

Brain Interaction with Somatic Senses

• Transduction

  • Stimulus $\to$ receptor potential $\to$ action potentials in afferent neurons

• Ascending pathways

  • Dorsal column–medial lemniscus: discriminative touch, vibration, conscious proprioception

  • Spinothalamic tract: pain and temperature

• Relay and processing

  • Thalamus (ventral posterior nucleus) relays to primary somatosensory cortex (S1)

  • S1 provides somatotopic map of the body surface

  • S2 and association areas integrate to perception and interpretation

• Modulation and integration

  • Descending pathways