123. Sensory Cortex – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• The sensory cortex is responsible for the perception, analysis, and interpretation of somatic sensations. It receives sensory information from the thalamus and enables conscious awareness of touch, pain, temperature, and proprioception. Body parts requiring fine sensory discrimination, especially the hands and face, occupy larger cortical areas.
• The major somatosensory cortical areas are:
  • Primary somatosensory cortex (SI): Located in the postcentral gyrus (Brodmann areas 3, 1, and 2). It is the principal cortical area for processing somatic sensations.
  • Secondary somatosensory cortex (SII): Located in the parietal operculum along the superior wall of the lateral sulcus.
  • Somatosensory association cortex: Mainly Brodmann area 5, responsible for integrating sensory information and higher sensory functions.
  • Supplementary sensory area: Participates in sensory integration.
• Connections of the sensory cortex:
  • Receives third-order sensory fibers from the ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei of the thalamus.
  • Sensory information is processed sequentially from area 3b → areas 1 and 2 → association cortex.
  • Extensive reciprocal connections exist between SI, SII, the association cortex, thalamus, and motor cortex, allowing sensorimotor integration.
• The primary somatosensory cortex is functionally organized into:
  • Area 3a: Receives mainly proprioceptive input from muscles, tendons, and joints.
  • Area 3b: Main cortical area for cutaneous sensations.
  • Area 1: Integrates cutaneous and proprioceptive information for detailed tactile perception.
  • Area 2: Processes mainly deep sensations and contributes to proprioception.
• The body is represented in an orderly sensory homunculus. The face, lips, tongue, and hands occupy disproportionately large cortical areas because of their high receptor density and need for precise sensory discrimination, whereas the trunk has a smaller representation.
• The cortex has a columnar organization, where each vertical column processes a specific sensory modality from a particular body region. This arrangement allows parallel processing and precise sensory analysis.
• Functions of the primary somatosensory cortex:
  • Identifies the site, intensity, quality, and direction of sensory stimuli.
  • Performs tactile discrimination, localization, and perception of movement.
  • Transfers processed information to higher cortical areas for interpretation.
• Effects of lesions of SI:
  • Contralateral impairment of sensation.
  • Greater loss of fine touch and proprioception than pain and temperature.
  • Impaired two-point discrimination, tactile localization, stereognosis, and kinesthesia.
  • Area-specific lesions produce characteristic deficits, such as impaired texture discrimination (area 1) and astereognosis (area 5).
• Secondary somatosensory cortex (SII) contributes to tactile learning, sensory integration, and recognition of complex tactile stimuli. Lesions mainly impair tactile learning with minimal effect on primary sensory perception.
• The parietal association cortex integrates sensory information from multiple modalities and is essential for hand-eye coordination, spatial orientation, language functions (dominant hemisphere), and spatial awareness (nondominant hemisphere). Lesions may cause constructional apraxia, visuospatial deficits, and hemispatial neglect.