The somatosensory cortex is a region of the brain responsible for receiving and processing sensory information from around the body, such as touch, temperature, and pain.
This cortex is in what is in the postcentral gyrus of theLobo parietaland is behind the primarymotor cortexmake lobo frontal.
The somatosensory cortex receives tactile information from the body, including sensations such as touch, pressure, temperature, and pain. This sensory information is then carried to the brain via neural pathways to the spinal cord, brainstem, and thalamus.
This information is then projected to the somatosensory cortex, which in turn has numerous connections with other areas of the brain to process the sensory information.
The somatosensory cortex uses sensory information to initiate important movements that may be required to deal with specific situations.
Somatosensory pathways typically consist of three neurons: primary, secondary, and tertiary.
Primary neurons are the sensory receptors in the periphery of the somatosensory cortex that can perceive various stimuli such as touch or temperature. Secondary neurons are located in the spinal cord and brainstem and act as a relay station.
Afferent pathways (which carry signals to the central nervous system) in the spinal cord and brainstem function by relaying information from the periphery and rest of the body to the brain. These end in the thalamus or cerebellum.
Tertiary neurons, located in the thalamus and cerebellum, project to the somatosensory cortex. This will help form a sensory homunculus, a representative map of the body.
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Function of the somatosensory cortex
It consists of the primary somatosensory cortex and the secondary somatosensory cortex.
primary somatosensory cortex
The primary somatosensory cortex, also known as S1, is located at a crest of the cerebral cortex known as the postcentral gyrus.
The primary somatosensory cortex is located just behind the central sulcus, a slit that runs along the side of the cerebral cortex, and includes Brodmann areas 3a, 3b, 1, and 2.
The primary somatosensory cortex receives projections from nuclei of thebrain thalamus.
These nuclei receive fibers from the contralateral half of the body, i.e. the opposite side of the body from which the area in the brain is located. Overall, the primary somatosensory cortex is responsible for processing bodily sensations.
These sensations are received through receptors throughout the body that are responsible for sensing sensations such as touch, pain, temperature, and proprioception (the body's ability to sense its own position in space).
Brodmann's area 3 is responsible for receiving most of the somatosensory input from the thalamus, with initial information processing occurring here.
Brodmann-Areal 3bis responsible for processing the basic sensations of touch, while area 3a responds to information from the proprioceptors (receptors responsible for proprioception). Area 3b is also connected to areas 1 and 2, where more complex processing takes place.(Video) Somatosensory cortex organization and function
Area 1 is particularly important for recognizing the texture of an object. However, area 2 plays a role in the perception of the shape and size of objects and is involved in addition to proprioception.
An important function of the primary somatosensory cortex is its ability to localize where particular sensations arise in the body. For example, we can pinpoint the exact location of touch, pain, and pressure.
This region is also responsible for the perception of pressure by judging the level of pressure exerted on the body. Another function of this range is that it can help us determine the weight of an object by looking at it.
This is useful to determine if we are capable of carrying something and to better assess if carrying it requires extra effort. Likewise, the primary somatosensory cortex can help us judge the shapes of objects with our eyes closed and identify objects by touch.
For example, you might hold a book in your hands and be able to identify the object with your eyes closed based on the feel of that object. Likewise, this region would help us to judge the texture of objects, which would depend on the movement of fingers and hands across an object's surface.
So you could run your fingers over the book and the pages in it and tell by the texture what that object was.
Secondary somatosensory cortex
Behind the primary somatosensory cortex is the secondary somatosensory cortex. This region of the parietal lobe appears to serve as an association area for sensory input. It is associated with episodic memory, visuo-spatial processing, self-reflection, and aspects of consciousness.
The secondary somatosensory cortex, also known as S2, is not as well understood as the primary somatosensory cortex and many fibers in this area are thought to originate from the primary somatosensory area.
The secondary somatosensory cortex is adjacent to the primary somatosensory cortex at the apex of the lateral sulcus, a fissure in the cortex that separates the frontal and parietal lobes from the temporal lobes.
In addition to being connected to the primary somatosensory cortex, this region is believed to receive direct projections from the thalamus.
The secondary somatosensory cortex is thought to be involved in tactile object recognition and memory. It is suggested that although the primary area receives peripheral sensory information, the secondary area needs to store, process, and retain that information.(Video) 2-Minute Neuroscience: Cerebral Cortex
This area has been shown to contain many somatotopic representations of the body that are complex and indicative of multiple sub-regions of this area. S2 is also believed to represent the sensory discriminatory aspects of pain.
Neuroimaging studies have found that bilateral activation in the secondary somatosensory cortex is related to perceived pain intensity (Coghill, 2009).
Finally, the secondary somatosensory cortex connects to the hippocampus and theAmygdala. This allows it to absorb information from the environment and make decisions about how we act on that information through past experiences and how we think about the information.
Within the somatosensory cortex, body parts are represented on a homunculus sensory map. This means that there are areas within the somatosensory cortex that are organized in such a way that a specific location receives information from a specific part of the body.
Thus, the surface area of the cortex devoted to a body part correlates with the amount of sensory information from that area. Some body regions are more sensitive than others and are therefore shown distorted in the Homunculus map, so that these body regions take up a disproportionately large amount of space.
For example, the hands and lips are very sensitive to sensations. So there is a large area of the somatosensory cortex dedicated to sensation in these areas. In contrast, body parts like the back are less sensitive to sensation and would therefore represent a much smaller area in the cortex.
Typically, the medial portions of the sensory homunculus represent body parts, such as the hips and below, that are less sensitive to sensation. At the same time, the sides have more surface area that would be where the areas of the fingers, lips, eyes and face that would be more sensitive to sensation would be.
Somatosensory dysfunction of the cortex
Damage to the somatosensory cortex can result in mild deficits, and the symptoms of damage depend on which area is damaged.
Damage to this can result from injury to one or more areas, sometimes from a stroke. Another type of injury is multiple sclerosis (MS), which results in a loss of proprioception or exteroception (sensation of stimuli outside the body).
Below are descriptions of some of the symptoms that can occur as a result of damage:
Damage to the somatosensory cortex can cause numbness or sometimes paresthesia, which is a tingling sensation in certain parts of the body. Deafness can result from damage to the cerebral cortex, which then affects the body's receptors for certain areas.
Because the most sensitive areas, such as the hands and face, have the most receptors and occupy most of the surface area of the cerebral cortex, they are more prone to numbness.
This numbness as a result of damage can also lead to difficulty sensing the temperature of something, which can pose a safety issue if a person cannot tell when a surface might be too hot, for example.
Inability to localize sensations
Damage can result in people being unable to identify where in their body a sensation occurred. They can localize to some extent and identify the general region where a sensation occurred, e.g. B. pointing to the back or a specific leg.
This identification is possible because other brain regions can also localize in the cerebral cortex. Likewise, someone with damage to this area would have difficulty seeing things traced on their skin, e.g. B. not being able to identify which letter was traced on a hand.
This inability is called tactile agnosia, and people with the condition may also have difficulty identifying objects by touch alone.
Therefore, when they close their eyes and are asked to identify an object, they may have a hard time recognizing whether they are holding a book or a cup because they can feel the same thing.
Inability to assess weight and pressure
Another possible damage symptom is the inability to judge the weight of items. These people could not tell if an object is heavy or light after carrying it. Likewise, people with this damage would have difficulty assessing the physical strain.
These individuals may know that pressure was being applied to their body, but would not be able to identify the level or severity of the pressure being applied.
Phantom pain in the limbs
It is relatively common for people who have had a limb amputated to experience sensation in their amputated limb. This is called a phantom limb and it can cause pain in people who have it.
Studies have found that this pain correlates with changes in the primary somatosensory cortex, which is no longer receiving the expected information from the amputated limb (Flor, 2003).
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