Neuroscience of Touch and the Dorsal Columns-Medial Lemniscus Pathway

Introduction

• Somatosensation: Refers to sensations from the body, collected by cutaneous receptors in the skin.
• Types of sensations include pressure, pain, and vibration.
• Focus of this lecture: Fine touch and vibration.
• Pain will be discussed separately.

Dorsal Columns-Medial Lemniscus Pathway

• Primary Pathway: Carries touch information to the brain.
• Also carries proprioception (body position in space) signals.

Origin and Initial Pathway

• Signals originate from:
  • Cutaneous receptors for touch.
  • Proprioceptors in muscles and joints for proprioception.
• Signals enter the spinal cord via dorsal roots.
• Travel up the spinal cord to the medulla.

Fiber Bundles

• Fasciculus Gracilis: Carries information from the lower body.
• Fasciculus Cuneatus: Carries information from the upper limbs and torso.

Synapses in Medulla

• Nucleus Gracilis: Fasciculus gracilis synapses here.
• Nucleus Cuneatus: Fasciculus cuneatus synapses here.

Medial Lemniscus Pathway

• Medial Lemniscus: Arises from the dorsal column nuclei.
• Decussates (crosses over to the other side) before traveling to the thalamus.
• Synapses in the ventral posterolateral nucleus (VPL) of the thalamus.

Final Pathway to Somatosensory Cortex

• From the thalamus, fibers travel to the postcentral gyrus in the cortex.
• The postcentral gyrus contains the somatosensory cortex, the main sensory area for touch.

Somatosensory Cortex

• Somatotopic Arrangement: Specific parts of the somatosensory cortex receive signals from specific body parts.
• Integration: Nature and location of the sensation are integrated here, leading to conscious perception of touch.

Key Concepts

• Cutaneous Receptors: Diverse receptors responding to specific touch sensations.

• Proprioception: Awareness of body position and movement, essential for coordination.

• Crossing Over (Decussation): Critical feature of the pathway for processing touch information.

• Understanding this pathway is essential for comprehending how the brain processes touch and body position signals.