SOMATOSENSORY CORTEX

Dr. Ayisha QureshiProfessor

MBBS, MPhil

Cerebral Cortex is the most ventral and superior part of the brain, located in the anterior area of the skull and consisting of 2 hemispheres. It is responsible for the

integration of complex sensory information and initiation and coordination of motor activity.

Difference b/w GYRUS & SULCUS?

Identify Longitudinal

Fissure?

Name the Lobes of the

Cerebral Cortex.

Identify the Central Sulcus?

What is it’s significance?

How are the Rt & Lt lobes connected?

Difference b/w Sulci & Gyri:

FACTS ABOUT CEREBRAL CORTEX

Cerebrum forms 80% of the total

brain.

It weighs 1200 g in females & 1400 g in

males.

Larger brains are associated with

larger bodies NOT with greater

intelligence!!!

It looks like a much-folded

walnut & feels like butter!!

Cerebral dominance OR Lt Brain- Rt Brain

Dominance.

SOMATOSENSORY CORTEX

It is the area of the cerebral cortex that receives sensory impulses directly from the relay centers in thalamus. It has 3 parts: 1. Somatosensory Area –I 2. Somatosensory Area- II3. Association Cortex

The term somesthetic cortex is reserved for Somatosensory Area-I only.

Cererbral cortex is divided into structurally distinct areas (based on cryoarchitecture & organization of cells). These areas are

called the Brodmann’s areas and are app. 50 in no.

THE HOMUNCULUS (Little man)A Sensory Homunculus is a

“neurological map” of space given to the various anatomical parts of the

body. It depicts what humans would look like if our parts grew in

proportion to how much we sensed them.

Somatosensory cortex- I • It is also called the Primary

Somesthetic area.• It comprises of area 3,1,2.• The body areas are represented

by a sensory homunculus which is a small figure of a man showing the size of the various parts of the body in proportion to the extent of sensation felt.

• Lips occupy the greatest area followed by the face and the thumb. This is because many more receptors lie in the lips than in any other part of the body.

Somatosensory cortex- II• Its function is not well

known.• It seems to be concerned

more with the spinothalamic tract and pain sensibility.

• It further elaborates the sensory input received by Somatosensory Area I.

Layers of the Somatosensory Cortex & Their Functions.

WHAT WILL HAPPEN IF THE SENSORY CORTEX IS DAMAGED?

FUNCTIONS OF SOMATOSENSORY CORTEXIf bilateral excision of somatosensory area I is done, then the

following effects take place:1. Person is unable to localize precisely the different

sensations in the different parts of the body but can do so crudely. Tactile discrimination is lost.

2. Sensation of pressure persists but its intensity is decreased and localization is poor. Light pressure changes are not appreciated.

3. Person is unable to judge the weight of object. 4. Astereognosis (inability to recognize shape or form of

subjects with eyes closed). 5. Person is unable to judge texture of an object. 6. Fine grade changes in temperature are not appreciated. 7. The ability to recognize the orientation of various parts of

the body in relation to each other is lost (proprioception).8. Pain is least affected but pain is poorly graded and poorly

localized.

SENSORY ASSOCIATION AREAS

Somatosensory Association Areas

The Association areas are concerned with recognition, perception and interpretation of stimuli.

Brodmann’s areas 5 & 7.It receives information from:1. Somatosensory cortex I2. Ventrobasal nucleus of Thalamus & other areas of Thalamus3. Visual cortex4. Auditory cortex

What will happen when it is removed?Amorphosynthesis- person loses ability to recognize complex

objects & forms on the opposite side of the body. Person forgets that the other side of his/her body is even there. Same is true for feeling objects: person forgets that the other side of the object is exists.

PHANTOM LIMB PAIN

In 1551, a military surgeon, Ambroise Pare wrote:

“… the patients, long after the amputation is made, say they still feel pain in the amputated part. Of this they complain strongly.”

CAUSE OF PHANTOM LIMB

PAINIt is defined as pain felt by an amputee that seems to be located in the missing limb. The area of the brain that once received input from the leg and foot now responds to stimulation of the stump, in exactly the same way it did when the limb was attached. Other theories suggest remapping of the somatosensory cortex. Mirror box therapy is used for treatment of Phantom limb pain.

DERMATOMES

DERMATOMES

• Dermatomes: It is the area of the skin that is supplied with sensory innervation by a pair of spinal nerves.

• There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these nerves relay sensations (including pain) from a particular region of skin to the brain.

What is the significance of a Dermatomal Map?

• Important in clinical considerations of nerve damage. Loss of sensation in a dermatomal pattern can provide information about the location of nerve damage.

• They are of major importance when a clinician needs to anesthetize a particular portion of the body.

• Dermatomes have clinical significance, especially in the diagnosis of certain diseases. Symptoms that follow a dermatome, such as pain or a rash, may indicate a pathology that involves the related nerve root. Examples include dysfunction of the spine or a viral infection. Viruses that remain dormant in nerve ganglia, such as the Varicella zoster virus, which causes both chickenpox and shingles, often cause either pain, rash or both in a pattern defined by a dermatome