How Many Neurons Are In The Somesthetic Pathway From The Skin To The Postcentral Gyrus

Somatosensory Cortex

By Olivia Guy-Evans, published June 11, 2021

past Saul Mcleod, PhD

The somatosensory cortex is a region of the encephalon which is responsible for receiving and processing sensory information from beyond the torso, such as bear on, temperature, and pain.

This cortex is located within the which is located in the postcentral gyrus of the parietal lobe, and lies behind the master motor cortex of the frontal lobe.

Neurons Firing

The somatosensory cortex receives tactile information from the torso, 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 data is then projected to the somatosensory cortex, which in plow has numerous connections with other brain areas in social club to procedure the sensory information.

The somatosensory cortex uses sensory information to initiate of import movements that may be required to deal with particular situations.

Somatosensory Pathway

Somatosensory pathways are typically comprised of three neurons: primary, secondary, and third.

The primary neurons are the sensory receptors within the periphery of the somatosensory cortex which are able to notice various stimuli such as touch or temperature. The secondary neurons are located within the spinal string and brainstem and deed as a relay station.

Afferent pathways (which carry signals to the central nervous system) in the spinal cord and brainstem working past passing information from the periphery and the rest of the body to the encephalon. These will then terminate in either the thalamus or the cerebellum.

The tertiary neurons, which are located within the thalamus and cerebellum, will then project to the somatosensory cortex. This will then aid in forming a sensory homunculus, which is a representational map of the body.

Somatosensory Cortex Area Function

It comprises the primary somatosensory cortex and the secondary somatosensory cortex.

Primary Somatosensory Cortex

The primary somatosensory cortex, also referred to as S1, is plant in a ridge of the cerebral cortex known as the postcentral gyrus.

Located just posterior of the central sulcus, a crack that runs down the side of the cerebral cortex, the primary somatosensory cortex comprises of Brodmann's areas 3a, 3b, 1, and 2. The main somatosensory cortex receives projections from nuclei of the thalamus of the brain.

These nuclei receive fibers from the contralateral half of the body, meaning the opposite side of the torso from which the area is located in the brain. Overall, the chief somatosensory cortex is responsible for the processing of sensations from the body.

These sensations are received through receptors located throughout the body that are responsible for detecting sensations such as touch, pain, temperature, and proprioception (the torso's power to perceive its own position in space).

Brodmann'south expanse 3 is responsible for receiving near of the somatosensory input from the thalamus, with the initial processing of information occurring hither.

Brodmann expanse 3b is responsible for processing the basics of bear on sensations, whilst area 3a responds to information from proprioceptors (receptors responsible for proprioception). Expanse 3b is also connected to areas i and 2 which is where more complex processing takes identify.

Area 1 specifically is important in sensing the texture of an object. Area 2 all the same has a role in perceiving shape and size of objects as well equally existence involved with proprioception.

An of import function of the chief somatosensory cortex is the ability for information technology to locate where specific sensations arise in the body. This allows united states to pinpoint the exact location of touch, pain, and pressure level for instance.

This region is also responsible for being able to perceive force per unit area, through judging the degrees of pressure put on the body. Another office of this area is that it can assistance us determine the weight of an object by looking at it.

This is useful so that we are able to decide if we are able to carry something, and to gage a better idea of whether extra endeavor is required to acquit it. Too, the primary somatosensory cortex can help u.s.a. judge the shapes of objects with our optics closed and be able to identify objects through bear on.

For instance, yous could agree a volume in your hands and be able to identify the object with your eyes closed, based on how this object feels. Similarly, this region would help us judge the texture of objects, which would be dependant on the motility of the fingers and easily over the surface of an object.

Therefore, you could run your fingers over the book and the pages within and know what this object was by the texture.

Secondary Somatosensory Cortex

Posterior to the main somatosensory cortex lies the secondary somatosensory cortex. This region of the Parietal lobe seems to be serve as an association area for sensory input. It is involved with episodic retention, visuospatial processing, reflections upon self, and aspects of consciousness.

The secondary somatosensory cortex, also referred to every bit S2 is not as well understood equally the chief somatosensory cortex and it is believed that a lot of the fibers in this area come from the primary somatosensory area.

The secondary somatosensory cortex is located adjacent to the primary somatosensory cortex in the upper part of the lateral sulcus, a cleft in the cortex that separates the frontal and parietal lobes from the temporal lobes.

This region is believed to not just exist continued to the primary somatosensory cortex, only too receives directly projections from the thalamus.

The secondary somatosensory cortex is believed to be involved in tactile object recognition and memory. Information technology is suggested that whilst the primary surface area receives peripheral sensory information, it requires the secondary area to store, procedure, and retain this information.

This expanse has been shown to contain many somatotopic representations of the body which are complex and propose multiple subregions of this area. S2 is also thought to represent the sensory discriminative aspects of pain.

Neuroimaging studies have found that bilateral activation inside the secondary somatosensory cortex relate to the perceived intensity of hurting (Coghill, 2009).

Finally, the secondary somatosensory cortex has connections to the hippocampus and the amygdala. This allows information technology to receive information from the environment and make decisions on how to deal with this information through using by experiences and how nosotros feel about the information.

Homunculus Map

Within the somatosensory cortex, parts of the body are represented onto a sensory homunculus map. This means that there are areas within the somatosensory cortex which are arranged as such that a particular location receives data from a particular part of the body.

Thus, the surface area of the cortex dedicated to a part of the trunk correlates with the amount of sensory information from that area. Some areas of the body are more sensitive than others and are therefore represented in the homunculus map in a distorted way, so those areas of the trunk accept up a disproportionate corporeality of space.

For instance, the hands and the lips are very sensitive to sensations and then there is a large area of the somatosensory cortex which is dedicated to sensation in these areas. Whereas body parts such as the back are less sensitive to sensations and would therefore have a much smaller expanse in represented in the cortex.

Typically, the medial portions of the sensory homunculus tend to represent trunk parts such every bit the hips and beneath, those being the ones less sensitive to sensation. Whereas, the lateral sides have a larger surface area which would be where the areas for fingers, lips, optics, and face would be, those which would be more sensitive to sensations.

Somatosensory Cortex Dysfunction

Impairment to the somatosensory cortex can upshot in mostly balmy deficits, and symptoms of damage are dependant upon which surface area was damaged.

Damage to this could result from lesions to one or more than areas, sometimes as a effect of a stroke. Another type of lesion is multiple sclerosis (MS) which results in loss of proprioception or exteroceptive (sensations from stimuli outside of the trunk).

Below are descriptions of some of the symptoms that may exist experienced as a result of impairment:

Numbness

Harm to the somatosensory cortex can produce numbness or sometimes paraesthesia, which is a tingling sensation in certain parts of the body. Numbness can result due to impairment in the cortex which then affects the receptors on the body for certain areas.

As more sensitive areas such as the hands and confront have the most receptors and accept up the largest amount of surface area on the cortex, these are most susceptible to numbness.

This numbness as a result of damage can also outcome in difficulties with existence able to detect the temperature of something, which could be a safety effect if an individual is unable to recognize when a surface may be scolding hot for instance.

Inability to Localize Sensations

Damage could result in individuals beingness unable to pinpoint where on their torso a sensation has taken place. They can localize to an extent past identifying the general region a awareness occurred, such as stating the back or a certain leg.

This identification is possible due to other brain regions in the cerebral cortex being able to localize besides. Similarly, someone with impairment to this area would have difficulty being able to recognize things being traced onto their pare, such as beingness unable to identify what letter has been traced on a manus.

This disability is called tactile agnosia, and people with this condition may likewise accept difficulties identifying objects by bear on alone.

Therefore, if they are closing their optics and are asked to identify an object, they may find it difficult to identify whether they were holding a book or a cup, as these may feel the same to them.

Inability to Gauge Weight and Pressure

Another possible symptom of damage is the inability to gauge the weight of objects. These individuals would non be able to identify whether an object was heavy or light after carrying information technology. Besides, people with this harm would notice difficulty in judging physical pressure.

These individuals may exist able to know that pressure level has been applied to their trunk only would non be able to identify the degree or severity of the pressure applied.

Phantom Limb Pain

It is relatively mutual for people who have had a limb amputated to experienced sensations in their amputated limb. This is called phantom limb and information technology can crusade some pain to individuals who suffer from this.

Studies have found that this pain shows correlations to changes in the principal somatosensory cortex which is no longer receiving expecting input from the amputated limb (Flor, 2003).

Most the Author

Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master's degree in Psychology of Didactics from the University of Bristol in 2019. Olivia has been working every bit a back up worker for adults with learning disabilities in Bristol for the last four years.

How to reference this article:

How to reference this commodity:

Guy-Evans, O. (2021, June eleven). Somatosensory cortex. Simply Psychology. www.simplypsychology.org/somatosensory-cortex.html

References

Coghill, R. R. (2009). Pain: Neuroimaging. Encyclopedia of Neuroscience, 409-414.

Flor, H. (2003). Remapping somatosensory cortex after injury. Advances in neurology, 93, 195-204.

Neuroscientifically Challenged. (2016, March 10). Know your brain: Master somatosensory cortex. https://www.neuroscientificallychallenged.com/blog/know-your-encephalon-primary-somatosensory-cortex

Purves, D., Augustine, Thousand., Fitzpatrick, D., Katz, L., LaMantia, A., McNamara, J., & Williams, Southward. (2001). Neuroscience 2nd edition. sunderland (ma) sinauer associates. Types of Eye Movements and Their Functions.

Raju, H., & Tadi, P. (2020). Neuroanatomy, Somatosensory Cortex. StatPearls [Internet]. The Homo Retentiveness. (2020, November, 25). Somatosensory Cortex. https://homo-memory.internet/somatosensory-cortex/

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