SOMATOSENSORY
CORTEX
Learning Objectives
• SOMATOSENSORY CORTEX
• Homunculus
• SOMATOSENSORY AREA I
• SOMATOSENSORY AREA II
• Somatosensory association area
Cerebral Cortex
• Brodmann’s areas
• Fifty
• Histological ---- Functional
• General Scheme
– Central fissure
– Sensory signals from all modalities - Posterior
– Anterior half parietal Lobe – Somatosensory
signals – Reception and Interpretation
– Posterior half – Still higher levels of interpretation
Posterior half of frontal Lobe
Muscle contraction & Body movements
Sensory
signals
from all
modalities
- Posterior
Anterior half
parietal Lobe –
somatosensory
signals –
reception and
interpretation
Auditory signals Temporal Lobe
Visual signalsOccipital Lobe
Somatosensory cortex
SOMATOSENSORY AREA I
SOMATOSENSORY AREA II
• Post central gyrus cerebral cortex
• High degree of
localization
• Extensive and more
studied - more
important
• Areas 3,1,2
• Poor localization
• Less studied
• Signals enters here:
– From brainstem
– From somatosensory
cortex
– From visual area
– From auditory area
Receive information from opposite side of body
Structural layers of cerebral cortex
I Molecular
II Ext Granular
III Small Pyramidal cells
IV Int Granular cells
V Large Pyramidal Cells
VI Fusiform/Polymorphic
cells layer
• Incoming signal excite neuronal Layer IV
• Layers I and II receive diffuse, nonspecific input
signals from lower brain centers
• The neurons in Layers II and III send axons the cerebral cortex
• Layer V - Generally larger and project to more
distant areas, such as to the basal ganglia, brain
stem and spinal cord.
• Layer VI, especially large numbers of axons
extend to the thalamus, providing signals from
the cerebral cortex
Functions of somatosensory area I
1. Localize discretely - different sensations
2. Critical degrees of pressure
3. Weights of objects
4. Shape or form of objects -- Stereognosis
5. Texture of objects
6. Localize pain and temperature sensations
Somatosensory association area
• Brodmann’s area 5 and 7
• Parietal cortex - behind somatosensory area I
• Decipher sensory information entering
somatosensory area I
• Receives signals from:
– Somatosensory area I
– Ventrobasal nuclei of thalamus
– Other nuclei of thalamus
– Visual and auditory cortices
Effect of removing somatosensory
association area
 Unable to recognize complex objects/complex
forms by feeling them on opposite side
 Loses sense of form of his/her own body / body
parts on opposite side
 Oblivious to opposite side
 Forgets to use opposite side for motor functions
 Tends to recognize one side of object and
forgets other side - Amorphosynthesis