Somatosensory Cortex: The main somatosensory cortex is part of the somatosensory system and is located in the postcentral gyrus. It was first characterized by Wilder Penfield’s surface stimulation investigations, as well as related surface potential studies by Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1, and 2, recent work by Kaas suggests that only area 3 should be referred to as “primary somatosensory cortex” for homogeneity with other sensory fields, as it receives the majority of the thalamocortical projections from the sensory input fields.

Tactile representation is organized (inverted) from the toe (at the top of the cerebral hemisphere) to the mouth in the primary somatosensory cortex (at the bottom). Parts of the cortex may, however, be regulated by partially overlapping regions. The primary somatosensory cortex of each brain hemisphere only carries a tactile representation of the opposing (contralateral) side of the body. The quantity of primary somatosensory cortex dedicated to a body part is proportional to the relative density of cutaneous touch receptors on that body part, not to the absolute size of the body surface. The density of cutaneous tactile receptors on a body part is a good indicator of the sensitivity of tactile stimulation at that body part. As a result, the human lips and hands have a higher representation than the rest of the body.

Somatosensory Cortex Primary


What is the somatosensory cortex’s function?


Processing somatic feelings is handled by the main somatosensory cortex. Touch, proprioception (the position of the body in space), nociception (pain), and temperature are all detected via receptors located throughout the body.






What is the somatosensory system’s purpose?


The somatosensory system is the part of the sensory system that is responsible for the conscious awareness of touch, pressure, pain, temperature, position, movement, and vibration, all of which are emitted by the muscles, joints, skin, and fascia.


What is the location of the somatosensory cortex?


The primary somatosensory cortex is housed in the parietal lobe, in a ridge of cortex known as the postcentral gyrus. The central sulcus, a large fissure that runs down the side of the cerebral cortex, is located right posterior to it.


Somatosensory Cortex Primary


The brain is the body’s command and control center. The corpus colossum connects the right and left sides of the brain, or lobes, in the middle. Each lobe is responsible for a distinct function. The cerebral cortex is the brain’s outermost layer. Consider it as the skin of a fruit, with the skin representing the cerebral cortex and the fruit representing the apple’s white inside. Processing and higher-order thinking skills like reasoning, language, and comprehending the world are aided by the cerebral cortex. The cerebral cortex is seen as the dark contour in this image of a cross-section of the brain.


Function of the Somatosensory Cortex


The somatosensory cortex is positioned in the middle of the brain and is a portion of the cerebral cortex. The somatosensory cortex is outlined in red in this picture of the brain.


Processing somatic feelings is handled by the main somatosensory cortex. Touch, proprioception (the position of the body in space), nociception (pain), and temperature are all detected via receptors located throughout the body. The information is conveyed to the thalamus and subsequently to the primary somatosensory cortex when such receptors detect one of these sensations.


Somatosensory Cortex Primary


According to the delineations of German neuroscientist Korbinian Brodmann, the primary somatosensory cortex is divided into many sections. Brodmann discovered 52 separate brain regions based on cellular composition differences; these divisions are still extensively used today, and the areas they form are known as Brodmann’s areas. Brodmann classified the primary somatosensory cortex into three areas: 3 (which is subdivided into 3a and 3b), 1 (which is subdivided into 3a and 3b), and 2 (which is subdivided into 3a and 3b).


Brodmann’s numbers for the somatosensory cortex are based on the sequence in which he studied the postcentral gyrus and are hence unrepresentative of any important ranking. Area 3 of the somatosensory cortex is widely regarded as the major area. The majority of somatosensory input is received straight from the thalamus in Area 3, and this information is processed here first. Area 3b is responsible for the basic processing of touch sensations, whereas area 3a is responsible for responding to input from proprioceptors.


Areas 1 and 2 are heavily connected to Area 3b.


As a result, while area 3b is the principal location for touch data, it is also routed to areas 1 and 2 for more complex processing. For example, region 1 appears to be vital for experiencing an object’s texture, whereas area 2 appears to be important for perceiving size and shape. Proprioception is also a function of Area 2. Specific lesions to any of these areas of the somatosensory cortex support the roles indicated above; for example, lesions to area 3b cause general tactile sensation deficits, but lesions to area 1 cause texture discrimination impairments.


Each of the primary somatosensory cortex’s four areas is organized so that a specific place in that area receives information from a specific part of the body. The complete body is represented in this way in each of the four divisions of the somatosensory cortex, which is referred to as somatotopic. Because some parts of the body are more sensitive than others (e.g., the lips and hands), they require more circuitry and brain to process sensations. As a result, the somatotopic maps in the somatosensory cortex are skewed, and the highly sensitive portions of the body occupy a disproportionate amount of space (see image to the right).


Function of the Primary Somatosensory Cortex


All sensory input from the body is received by the somatosensory cortex. Neurons are cells that are found in the brain or in nerves that extend into the body. Neurons that detect skin sensations, pain, visual, or auditory inputs all transmit their data to the somatosensory cortex to be processed. The graphic below depicts how skin sensations are transmitted to the brain via neurons for processing.


Some neurons are extremely critical, and a large portion of the somatosensory cortex is dedicated to deciphering their data. Our analyst receives the most critical information from the senior scientist, and he spends considerable time deciphering it. Our younger scientists or volunteers, on the other hand, collect less relevant data, so our analyzer, or somatosensory cortex, spends less time on it. The input from each neuron is sent to a specific location in the somatosensory cortex. The somatosensory cortex then goes to work trying to figure out what the information means. Consider it as if scientists were transmitting information to a data analyst. Each scientist collects data and delivers it to a master analyzer or the somatosensory cortex, just like a neuron.


The Somatosensory Cortex is in charge of processing sensory information.


The primary somatosensory cortex (areas 1, 2, and 3) is a key receptor of general bodily sensation and is located on the postcentral gyrus. The primary somatosensory cortex receives sensory data from the skin, muscles, tendons, and joints of the body via thalamic radiations. Partial sensory loss (paresthesia) results from lesions of this brain; total sensory loss (anesthesia) is rare. On the other side of the body, a lesion causes numbness and tingling. Gross sensory loss and an inability to localize feeling result from widespread damaging lesions.


S1 is the name of the primary somatosensory cortex. Sensory information from the somatic senses, as well as proprioceptive and visceral senses, is received in this part of the cerebral cortex. It is found on the parietal lobe’s postcentral gyrus, as seen in Figure 4.3.6. The somatic senses’ topological order is intact as they enter the spinal cord, travel up the dorsal column tracts to the nucleus gracilis or nucleus cuneatus, and then through the thalamus to imprint onto the cortex. As a result, the body’s surface corresponds to the brain’s surface.


Definition of Somatosensory Cortex, Location of Somatosensory Cortex


The neurons in a somatosensory pathway represent the contralateral (opposite) side of the body or face at the level of decussation. It’s crucial to understand the decussation site because it’ll help with clinical diagnosis. When an afferent route is injured below the decussation location, sensory loss occurs on the ipsilateral side of the lesion (i.e., the loss is on the same side as the lesion or ipsilesional). When an afferent route is injured above the decussation location, the sensory loss occurs on the side opposite the lesion (i.e., the loss is on the side opposite the lesion or contralesional).


The axons of the gracile and cuneate nuclei decussate in the medulla along the medial lemniscal route. The axons of the posterior marginal nucleus are involved in the decussation of the neospinothalamic pathway in the spinal cord. The axons of the spinal trigeminal nucleus decussate as they leave the nucleus in the medulla and lower pons, whereas the axons of the major sensory trigeminal nucleus decuss as soon as they leave the nucleus in the mid pons.