Post on 11-Feb-2016
description
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
Visual signals- Occipital Lobe
Auditory signals -Temporal Lobe
Posterior half of frontal Lobe
Muscle contraction & Body movements
Sensory signals from all modalities- Posterior
Anterior half parietal Lobe – somatosensory signals – reception and interpretation
Somatosensory cortexSOMATOSENSORY AREA I• Post central gyrus -
cerebral cortex• High degree of
localization• Extensive and more
studied - more important
• Areas 3,1,2
SOMATOSENSORY AREA II• 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