Somatosensory Pathways: Dorsal Column (Medial Meniscal Pathway)

Overview

• Focus: Dorsal column, also known as the medial meniscal pathway
• Function: Carries touch, vibratory sense, and proprioception sensations to the cerebral cortex

Spinal Cord Anatomy

• Dorsal Root: Carries sensory neurons from periphery to CNS
• Ventral Root: Carries motor neurons from CNS to PNS
• Dorsal Column Tract: Located at the back of the spinal cord
  • Divided into two parts:
    • Fasciculus cuneatus (lateral)
    • Fasciculus gracilis (medial)
• Function: Carries sensory information on touch, pressure, vibration, and proprioception to the somatosensory cortex

Somatosensory Cortex and Pathways

• Location: Perception of somatic sensory information
• Thalamus: Important relay station in the ascending pathway
• Brainstem Components: Midbrain, pons, medulla

Mechanoreceptors and Sensory Cells

• Types of Mechanoreceptors:
  • Merkel Cells: Touch and pressure (superficial skin)
  • Ruffini Endings: Sustained pressure
  • Meissner Corpuscles: Tap and flutter sensations
  • Pacinian Corpuscles: Deep pressure and vibration
• Function: Detect changes and send sensory information to CNS

Neural Pathway Details

• First-order Neuron:
  • Travels up the dorsal column (fasciculus cuneatus or gracilis)
• Second-order Neuron:
  • Synapses at nucleus cuneatus or gracilis in the medulla
  • Crosses midline at medulla, travels up the medial meniscal tract
  • Synapses at ventral posterior lateral nucleus of the thalamus
• Third-order Neuron:
  • Carries sensory information to primary somatosensory cortex in a specific manner

Sensory Information Processing

• Left vs. Right Processing:
  • Sensation on the left perceived by right brain, and vice versa
• Fasciculus Cuneatus: Upper body information (cervical spinal cord)
• Fasciculus Gracilis: Lower body information (lumbar spinal cord)

Proprioception

• Definition: Sense of position and movement of the body
• Proprioceptors: Located in muscles, tendons, and joints
  • Muscle Spindles: Provide info on muscle length
  • Golgi Tendon Organs: Provide info on muscle tension
• Pathway: Similar to touch and pressure pathways, travels through dorsal column

Recap

• Structures Involved: Somatosensory cortex, midbrain, pons, medulla (nucleus gracilis and cuneatus)
• Neural Pathway: First-order neuron travels up dorsal column, synapses in medulla, second-order neuron crosses midline and synapses in thalamus, third-order neuron relays to cortex

Important Concepts

• Sensory Pathways: Involves first, second, and third-order neurons
• Body Coordination: Proprioception allows for balance and spatial orientation
• Specific Sensory Regions: Different regions in the somatosensory cortex correspond to different body parts.