Parietal Lobe

Aka: Parietal Lobe, Parietal Lobe Function, Cerebral Parietal Lobe, Homunculus, Primary Somatosensory Cortex, Primary Somesthetic Area, Brodmann Area 3 1 2, Secondary Somatosensory Cortex, Secondary Somesthetic Area, Brodmann Area S2, Superior Parietal Lobule, Brodmann Area 5, Visuo-Motor Coordination Area, Brodmann Area 7, Angular Gyrus, Brodmann Area 39, Supramarginal Gyrus, Brodmann Area 40, Brodmann Areas of Parietal Lobe, Posterior Paracentral Gyrus, Precuneus, Post Central Gyrus

1. Definitions
   1. Parietal Lobe
      1. Parietal Lobe receives sensory input and performs language processing
      2. As with motor centers in the Frontal Lobe, the Parietal Lobe is organized in the form of the cortical humunculus
         1. Disproportionately large region devoted to the face and hands, in contrast with the torso and legs
      3. Sensory functionality is primarily contained in Brodmann Areas 3,1,2
         1. Also in adjacent seconday somatic area (for pain and TemperatureSensation)
      4. Brain Lesions result in Receptive Aphasia, sensory loss, hemianopia and and spatial Disorientation.
2. Anatomy: Brodmann Areas of Parietal Lobe
   1. Images
      1. 
      2. 
   2. Primary Somatosensory Cortex or Somesthetic Area (Area 3,1,2)
      1. Lesions in this region affect contralateral sensory loss in light touch, pressure and proprioception
      2. Pain and Temperature sense are received in a region inferior to Area 3,1,2, known as the Secondary Somesthetic Area.
   3. Secondary Somatosensory Cortex or Somesthetic Area (Area S2)
      1. Lesions in this region affect pain and Temperature sense
      2. These fibers are inferior to Primary Somesthetic Area (Area 3,1,2)
   4. Superior Parietal Lobule (Anterior, Area 5)
      1. Involved in spatial orientation
   5. Visuo-Motor Coordination (Posterior, Area 7)
      1. Involved in spatial orientation
   6. Angular Gyrus (Area 39)
      1. When in the dominant hemisphere, a lesion in the Angular Gyrus affects the ability to read (alexia) and write (agraphia).
   7. Supramarginal Gyrus (Area 40)
      1. Dominant hemisphere lesions in the Supramarginal Gyrus cause Agnosia of tactile Sensation and proprioception
      2. The patient may have difficulty with left-right discrimination and Apraxia (difficulty with skilled movement)
      3. It also affects the interpretation of gestures made by other people.
3. Physiology: Homunculus
   1. Homunculus is a graphical representation of sensory and motor control
   2. Man standing at the midline between the two Cerebral Hemispheres
      1. Legs are above the falx cerebri at the medial Parietal Lobe (Anterior Cerebral Artery)
      2. Legs are relatively small compared to arms and head
         1. Represents fewer overall Neurons dedicated to leg motor and sensory control
   3. Man is bending at the waist over the top of the Parietal Lobe
      1. Legs and head extend over the lateral Parietal Lobe (Middle Cerebral Artery)
      2. Arms and head are relatively large
         1. Represents greater overall Neurons dedicated to arm/head motor and sensory control
4. Signs: Brain Lesions
   1. Receptive Aphasia (Area 39)
   2. Sensory loss (Area 3,1,2 and Area S2 following Homunculus distribution)
   3. Spatial Disorientation (Area 5, 7)
   4. Hemianopia (loss of half of Visual Field in each eye)
   5. Agnosia of tactile Sensation and proprioception (Area 40, dominant hemisphere)
   6. Apraxia (difficulty with skilled movement) and altered left-right discrimination (Area 40)
5. Exam
   1. Cognitive Dominant
      1. Names fingers
      2. Knows left and right
      3. Performs calculations on paper
      4. Reading
   2. Cognitive Non-Dominant
      1. Constructs copy of matchstick figure made by examiner
6. References
   1. Newton (1994) Am Fam Physician 49(4): 787-97 [PubMed]