Lecture on the Parietal Lobe

Introduction

• Focus on the cerebral cortex, primarily the parietal lobe

Anatomy of the Parietal Lobe

• Boundaries: Three main boundaries
  • Anterior boundary: Central Sulcus (separates parietal lobe from the frontal lobe)
  • Inferior boundary: Lateral Sulcus (Sylvian Fissure; separates parietal lobe from the temporal lobe)
  • Posterior boundary: Parietal Occipital Sulcus (separates occipital lobe from the parietal lobe)

Functional Areas

• Primary Somatosensory Cortex
  • Located in the post-central gyrus
  • Involved in conscious awareness of somatic sensations (touch, pain, temperature, vibrations, pressure, proprioception)
• Somatosensory Association Cortex
  • Located just posterior to the primary somatosensory cortex
  • Involved in analyzing sensations, recognition, and memory storage of somatic sensations
  • Provides meaning to the sensations; helps identify objects and spatial positioning
• Posterior Association Area
  • Overlaps with occipital and temporal lobes
  • Multi-modal association area; integrates somatic, visual, and auditory sensations
  • Involved in spatial coordination and communication with the pre-frontal cortex for thought, executive function, memory, and motor activity

Detailed Functions of Primary Somatosensory Cortex

• Broadman areas 3, 1, 2
• Involved in conscious awareness and perception of somatic sensations via two main pathways:
  • Dorsal Column-Medial Lemniscus Pathway: Carries fine/discriminative touch, proprioception, and vibration
  • Spinothalamic Tracts: Carries pain, temperature, crude/light touch, and pressure sensations
• Sensations from the right side of the body go to the left primary somatosensory cortex and vice versa
• Surprisingly, contributes about 40% to motor pathways via corticospinal and corticobulbar tracts

Somatotopic Arrangement (Sensory Homunculus)

• Sensory Homunculus: Represents somatotopic arrangement of the primary somatosensory cortex
• Medial part: Represents lower limbs
• Lateral part: Represents upper limbs, head, and neck
• Clinical relevance:
  • Anterior Cerebral Artery occlusion: Causes contralateral lower extremity sensory loss
  • Middle Cerebral Artery occlusion: Causes contralateral upper extremity and head/neck sensory loss
  • Larger body parts on homunculus indicate increased sensitivity

Somatosensory Association Cortex

• Analyzes, recognizes, and provides meaning to somatic sensations
• Functions involve determining size, texture, weight, position; object recognition
• Clinical tests:
  • Asteriognosis: Inability to identify objects by touch
  • Graphesthesia: Inability to identify numbers/letters drawn on skin
  • Statognosis: Inability to identify body part positions
  • Barognosis: Inability to distinguish differences in weight

Posterior Association Area

• Multi-modal association integrating visual, auditory, and somatic sensory information
• Communicates with prefrontal cortex and motor cortex for thought, executive function, memory, and movement
• Example: Response to dropping a beaker of hydrochloric acid (integration of auditory, visual, and somatic sensory inputs)

Conclusion

• Reviewed anatomy, functional areas, and clinical relevance of the parietal lobe
• Emphasized importance of multimodal association areas and their role in sensory integration and motor coordination

Thanks for attending!