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