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The sensory areas of the cerebral cortex or somatosensory cortex

The sensory areas of the cerebral cortex or somatosensory cortex

The somatosensory cortex is an area of ​​the brain located in the parietal lobe, responsible for processing the sensory information of the skin, muscles and joints. This area detects and interprets information about touch, temperature, pain and pressure and allows us to perceive the size, shape and texture of an object through touch. In addition, the somatosensory cortex is responsible for helping us control the position of our own body in the space. The specific areas of the somatosensory cortex correspond to specific parts of the body.

Content

  • 1 Primary somesthetic area
  • 2 Somesthetic association cortex
  • 3 Primary visual cortex
  • 4 Auditory cortex
  • 5 Olfactory Bark
  • 6 Taste Bark
  • 7 Vestibular cortex

Primary Somesthetic Area

The primary somatosensory cortex is responsible for the somatic sensation processing. These sensations arise from the receptors located throughout the body that are responsible for detecting touch, proprioception (that is, the position of the body in space), nociception (that is, pain) and temperature. When these receptors detect a sensation, it sends the information to the thalamus and then to the primary somatosensory cortex.

It is divided into multiple areas described by German neuroscientist Korbinian Brodmann. Brodmann identified 52 different regions of the brain according to differences in cell composition; These divisions are still used today and the regions they form are known as Brodmann areas. Brodmann divided the primary somatosensory cortex into areas 3 (which is subdivided into 3a and 3b), 1 and 2, occupies the postcentral gyrus both laterally and medially.

Most afferences come from the posterior ventral nucleus of the thalamus. These axons reach the cortex through the internal capsule.

Each of the areas of the primary somatosensory cortex is arranged so that it receives information from a specific area of ​​the body. This arrangement is known as somatotopic, and the entire body is represented in this way in each of the somatosensory cortex divisions. Because some areas of the body (e.g., lips or hands) are more sensitive than others, we can see that they require more circuits and cortex area to devote to the processing of their sensations. Therefore, somatotopic maps found in the somatosensory cortex appear distorted because the most sensitive areas of the body occupy a much larger amount of space.

There is a topographic or somatotopic representation of the body. Each contralateral half is inverted (down, feet at the top of the cortex and head at the bottom). This representation of the human body in the cortex called sensory homunculus.

Thus, the representations of the various parts of the body on the map do not keep the same proportions as in the body. That is, the size of the cortical area dedicated to a certain part of the body does not depend on its actual size, but on the functional importance of this part and the need for sensitivity of this area.

The space that occupies a part of the body in the cortex is not fixed or static and it does not simply reflect the density of the receptors in the periphery. If a part of the body cannot be used, its cortical representation decreases in size, and also vice versa.

The electrical stimulation of this region produces sensations of tingling or setting in a contralateral area of ​​the body, the location of which is related in an orderly manner with the stimulated point.

Injury to the primary somesthetic area

Dysfunctions in this area cause:

  • Deterioration of discriminative touch (judge the exact location or intensity of a stimulus).
  • Deficits of conscious proprioception (sense of position and movement).
  • Partial loss of pain and temperature sensation.

Association Somesthetic Bark

It is found mainly in the upper part of the parietal lobe along the lateral and medial part (areas 5 and 7 of Brodmann).

Receive fibers from the primary somesthetic area.

Data related to general sensations are integrated. It allows the assessment and global understanding of the characteristics and identification of an object by the touch and sense of the position, that is, the recognition of this object.

Association somesthetic cortex lesion

When an injury occurs in this area, the person is able to perceive the general sensations of the body, but not to interpret the information you receive based on previous experience. These problems in the recognition of objects through a certain sense, although the meaning is basically intact, are generally called agnosias. In the case of extensive injury to areas 5 and 7, tactile agnosias occur; of these there are several types and one of these is asterognosia or inability to identify a common object by touch without the help of sight.

Primary visual cortex

The primary visual cortex is found in the occipital lobe (Brodmann area 17) in both cerebral hemispheres. It is a small portion of the visible surface of the cortex in the occipital lobe, but as it extends to the calcarine groove, it constitutes a significant portion of the cortical surface in general. The primary visual cortex is sometimes also called striated cortex due to the presence of a large band of myelinated axons that extends along the ends of the calcarine groove. These axons, known as the Gennari line In reference to the first researcher who noted his presence at the end of the 18th century, the primary visual cortex appears scratched (the striatum comes from Latin and implies a striped appearance).

Primary visual area

The primary visual cortex is essential for the conscious processing of visual stimuli. Its importance for visual perception is highlighted by the cases in which people have suffered damage in this area, in these cases patients generally have interruptions in visual perception that can range from the loss of specific aspects of vision (for example, depth perception), until the complete loss of awareness of visual stimuli.

The main source of entries is the lateral geniculate body of the thalamus. The primary visual cortex of each hemisphere receives information from the contralateral visual field, which comes from both eyes.

There is a topographic representation of the contralateral visual field from both eyes. This representation is called retinotopic: Small concrete regions of the retina are represented in small concrete regions of the cortex, and adjacent areas in the retina are represented in adjacent cortical areas.

Injury of the primary visual area

The lesion of the primary visual cortex of a hemisphere causes appearance of blind areas (scotomas) in the visual field contralateral to the injured cortex.

Visual bark of association

It contains the following two regions:

  • The region surrounding the primary visual area in the occipital lobe (areas 18 and 19)
  • A large part of the temporal lobe (Areas 20, 21 and 37) called the inferotemporal visual area.

The bark of visual association Taken together to relate the current visual experience with the past, recognize what you see and appreciate the meaning.

Electrical stimulation causes very live hallucinations of scenes from the past, this indicates that it has a role in the storage or recall of visual memories.

Association lesion of the visual cortex

Injuries produce visual agnosias, or difficulty interpreting the stimuli.

An injury to the medial part of the lower temporal lobe causes prosopagnosia, an inability to recognize faces, even those of very familiar people.

An injury in areas 18, 19 and 37 causes achromatopsia, a deficit to distinguish colors.

Auditory cortex

The primary auditory cortex is the part of the temporal lobe that processes auditory information in humans and other vertebrates. It is a part of the auditory system, which performs basic and superior functions in hearing.

The auditory cortex is divided into three parts: the primary, secondary and tertiary auditory cortex. The primary auditory cortex, located between the other two, is found primarily in areas 41 and 42 of Brodmann. It is located in the temporal lobe, just above the ears. The function of the primary auditory cortex is to process the sound. It processes information such as the tone, volume and location of a sound, and it is crucial to understand the language.

Primary auditory cortex

Most of it is found in the ventral wall of the Silvio fissure, that is, in the upper surface of the temporal lobe. It corresponds to areas 41 and 42 of Brodmann.

The primary auditory cortex receives most of its afferences from the medial geniculate nucleus of the ipsilateral thalamus (which receives information mainly from the opposite ear, although it also receives several ipsilateral fibers). There is a tonotopic projection, that is, the range of audible frequencies is represented in an orderly manner in the auditory cortex.

The primary auditory cortex is located in the temporal lobe, receives information from the medial geniculate nucleus of the thalamus and has a tonotopic organization.

Lesion of the primary auditory cortex

If the entire primary hearing area is damaged, the person you will not realize what you hear. However, the ability to react reflexively to sounds remains. There are connections ranging from both ears to the left and right primary auditory cortices. That is why a person who has suffered an injury on one side of the auditory cortex alone is able to discriminate sound frequencies quite well. However, he will suffer great difficulties locating sounds. This is because each primary auditory cortex is primarily responsible for locating sounds on the opposite side.

Association auditory cortex

It is located in the back of Brodmann area 22, in the temporal lobe. It allows a more elaborate perception of acoustic information.

Association auditory cortex lesion

The lesion of this area in the dominant hemisphere (usually the left), which is called Wernicke's area, results in serious language comprehension problems. Thus, the interpretation of language is one of the functions of the auditory cortex of association.

Olfactory bark

The olfactory cortex is the area of ​​the cortex in the anterior brain and receives a direct input from the olfactory bulb. In most mammals there are several areas in this cortex: The main region is the piriformis bark.

It is the only part of the vertebrate anterior brain that receive a direct sensory input. It is present even in the most primitive fish, which suggests that it is a central element of the vertebrate brain. Since smell is the dominant sensory modality in most species, olfactory cortical mechanisms give us an idea of ​​the basic behavioral patterns that largely underlie the behavior of mammals and primates. The olfactory system is also one of the first sensory systems to differentiate and become functional during fetal life.

The olfactory system has the following characteristics:

It is the only one that does not highlight the thalamus. It is the only primary sensory cortex is paleocortical rather than neocortical. It is ipsilateral (each hemisphere receives information from the nostril on the same side).

The primary olfactory cortex is at the base of the brain and is projected on the olfactory association cortex that occupies Brodmann area 28 and is called the entorhinal cortex.

The olfactory system receives information from the olfactory bulbs, which receive fibers directly from the olfactory epithelium.

Olfactory stimuli produce emotional and visceral responses, and evoke memories because olfactory areas connect with areas of the limbic system, such as the amygdala and the hippocampus.

Taste bark

The primary taste bark is a brain structure responsible for the perception of taste. It is divided into two substructures: the anterior insula in the insular lobe and the frontal opercle in the lower frontal gyrus of the frontal lobe. Here are the neurons that encode the stimuli and the intensity of the flavors such as sweet, salty, bitter and acid.

I know located at the bottom of the parietal lobe, adjacent to the representation of the tongue in the somatosensory cortex (area 43).

The posterior ventral nucleus of the thalamus receives information from the gustatory core of the trunk and is projected to the taste bark.

Injury to the taste bark

Bilateral injury causes alteration or loss of taste sensitivity.

Vestibular cortex

The vestibular cortex is the part of the brain that is at the entrance of the vestibular system. The vestibular system, in most mammals, it is the sensory system that provides the sense of balance and spatial orientation in order to coordinate movement with balance. It sends signals mainly to the neuronal structures that control eye movements, and to the muscles that keep us upright.

It is found in the parietal lobe, next to the primary somesthetic cortex, although it is also thought that there might be a secondary vestibular area in the temporal lobe.

References

Carpenter, M.B. (1994). Neuroanatomy Fundamentals Buenos Aires: Panamerican Editorial.

Diamond, M.C .; Scheibel, A.B. i Elson, L.M. (nineteen ninety six). The human brain Work book. Barcelona: Ariel.

Guyton, A.C. (1994) Anatomy and physiology of the nervous system. Basic Neuroscience Madrid: Pan American Medical Editorial.

Kandel, E.R .; Shwartz, J.H. and Jessell, T.M. (eds) (1997) Neuroscience and Behavior. Madrid: Prentice Hall.

Martin, J.H. (1998) Neuroanatomy. Madrid: Prentice Hall.

Netter, F.M. (1987) Nervous System, Anatomy and Physiology. A Ciba Collection of Medical Illustrations (volum 1) Barcelona: Salvat.

Nolte, J. (1994) The human brain: introduction to functional anatomy. Madrid: Mosby-Doyma.

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