Postcentral gyrus
Encyclopedia
The lateral postcentral gyrus is a prominent structure in the parietal lobe
of the human brain
and an important landmark. It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch
. Like other sensory areas, there is a map of sensory space in this location, called the sensory homunculus
.
The primary somatosensory cortex was initially defined from surface stimulation studies of Wilder Penfield
, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann area
s 3, 1 and 2, more recent work by Kaas
has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of the thalamocortical projections from the sensory input fields.
(or S1). Because Brodmann
sliced the brain
somewhat obliquely, he encountered area 1 first; however, from rostral to caudal the Brodmann
designations are 3, 1 and 2, respectively.
Brodmann area 3 is subdivided into area 3a and 3b. Where BA 1 occupies the apex of the postcentral gyrus, the rostral border of BA 3a is in the nadir of the Central sulcus, and is caudally followed by BA 3b, then BA 1, with BA 2 following and ending in the nadir of the postcentral sulcus. BA 3b is now conceived as the primary somatosensory cortex because 1) it receives dense inputs from the NP nucleus of the thalamus; 2) its neurons are highly responsive to somatosensory stimuli, but not other stimuli; 3) lesions here impair somatic sensation; and 4) electrical stimulation evokes somatic sensory experience. BA 3a also receives dense input from the thalamus; however, this area is concerned with proprioception
.
Areas 1 and 2 receive dense inputs from BA 3b. The projection from 3b to 1 primarily relays texture information; the projection to area 2 emphasizes size and shape. Lesions confined to these areas produce predictable dysfunction in texture, size, and shape discrimination.
Somatosensory cortex, like other neocortex, is layered. Like other sensory cortex (i.e. visual and auditory) the thalamic inputs project into layer IV, which in turn project into other layers. Also like other sensory cortices, S1 neurons are grouped together with similar inputs and responses into vertical columns that extend across cortical layers (e.g. As shown by Vernon Mountcastle, into alternating layers of slowly adapting and rapidly adapting neurons; or spatial segmentation of the vibrissae on mouse/rat cerebral cortex).
This area of cortex, as shown by Wilder Penfield
and others, is organized somatotopically, having the pattern of a homunculus. That is, the legs and trunk fold over the midline; the arms and hands are along the middle of the area shown here; and the face is near the bottom of the figure. While it is not well-shown here, the lips and hands are enlarged on a proper homunculus
, since a larger number of neuron
s in the cerebral cortex
are devoted to processing information from these areas.
The positions of Brodmann area's 3, 1 and 2 are - from the nadir of the central sulcus towards the apex of the postcentral gyrus - 3a, 3b, 1, and 2 respectively.
These areas contain cells that project to the secondary somatosensory cortex
.
, astereognosia, loss of vibration
, proprioception
and fine touch
(because the third-order neuron of the medial-lemniscal pathway cannot synapse in the cortex). It can also produce hemineglect, if it affects the non-dominant hemisphere.
It could also reduce nociception
, thermoception
and crude touch
, but since information from the spinothalamic tract
is interpreted mainly by other areas of the brain (see insular cortex
and cingulate gyrus), it is not as relevant as the other symptoms.
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
of the human brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and an important landmark. It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...
. Like other sensory areas, there is a map of sensory space in this location, called the sensory homunculus
Cortical homunculus
A cortical homunculus is a pictorial representation of the anatomical divisions of the primary motor cortex and the primary somatosensory cortex , i.e., the portion of the human brain directly responsible for the movement and exchange of sense and motor information of the rest of the body.There...
.
The primary somatosensory cortex was initially defined from surface stimulation studies of Wilder Penfield
Wilder Penfield
Wilder Graves Penfield, OM, CC, CMG, FRS was an American born Canadian neurosurgeon. During his life he was called "the greatest living Canadian"...
, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann area
Brodmann area
A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...
s 3, 1 and 2, more recent work by Kaas
Jon Kaas
Jon Kaas is a professor at Vanderbilt University and a member of the United States National Academy of Sciences. He has made discoveries about the organization of the mammalian brain, including the description of many areas of the cerebral cortex and their neuroplasticity.Work from the Kaas's...
has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of the thalamocortical projections from the sensory input fields.
Postcentral gyrus
The lateral postcentral gyrus is bounded by:- medial longitudinal fissureMedial longitudinal fissureThe great longitudinal fissure is the deep groove which separates the two hemispheres of the vertebrate brain....
mediallyAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
(to the middle) - central sulcusCentral sulcus-External links:* via the Neuroscience Information Framework...
rostrallyAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
(in front) - postcentral sulcusPostcentral sulcusThe postcentral sulcus of the parietal lobe lies parallel to, and behind, the central sulcus in the human brain....
caudallyAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
(in back) - lateral sulcusLateral sulcus-External links:* * * http://www.uams.edu/radiology/education/residency/diagnostic/pdf/sylvian_cistern_RSNA2003.pdf...
inferiorlyAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
(underneath)
Brodmann areas 3, 1 and 2
Brodmann areas 3, 1 and 2 make up the primary somatosensory cortex of the human brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
(or S1). Because Brodmann
Korbinian Brodmann
Korbinian Brodmann was a German neurologist who became famous for his definition of the cerebral cortex into 52 distinct regions from their cytoarchitectonic characteristics.-Life:...
sliced the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
somewhat obliquely, he encountered area 1 first; however, from rostral to caudal the Brodmann
Brodmann area
A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...
designations are 3, 1 and 2, respectively.
Brodmann area 3 is subdivided into area 3a and 3b. Where BA 1 occupies the apex of the postcentral gyrus, the rostral border of BA 3a is in the nadir of the Central sulcus, and is caudally followed by BA 3b, then BA 1, with BA 2 following and ending in the nadir of the postcentral sulcus. BA 3b is now conceived as the primary somatosensory cortex because 1) it receives dense inputs from the NP nucleus of the thalamus; 2) its neurons are highly responsive to somatosensory stimuli, but not other stimuli; 3) lesions here impair somatic sensation; and 4) electrical stimulation evokes somatic sensory experience. BA 3a also receives dense input from the thalamus; however, this area is concerned with proprioception
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
.
Areas 1 and 2 receive dense inputs from BA 3b. The projection from 3b to 1 primarily relays texture information; the projection to area 2 emphasizes size and shape. Lesions confined to these areas produce predictable dysfunction in texture, size, and shape discrimination.
Somatosensory cortex, like other neocortex, is layered. Like other sensory cortex (i.e. visual and auditory) the thalamic inputs project into layer IV, which in turn project into other layers. Also like other sensory cortices, S1 neurons are grouped together with similar inputs and responses into vertical columns that extend across cortical layers (e.g. As shown by Vernon Mountcastle, into alternating layers of slowly adapting and rapidly adapting neurons; or spatial segmentation of the vibrissae on mouse/rat cerebral cortex).
This area of cortex, as shown by Wilder Penfield
Wilder Penfield
Wilder Graves Penfield, OM, CC, CMG, FRS was an American born Canadian neurosurgeon. During his life he was called "the greatest living Canadian"...
and others, is organized somatotopically, having the pattern of a homunculus. That is, the legs and trunk fold over the midline; the arms and hands are along the middle of the area shown here; and the face is near the bottom of the figure. While it is not well-shown here, the lips and hands are enlarged on a proper homunculus
Homunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
, since a larger number of neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s in the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
are devoted to processing information from these areas.
The positions of Brodmann area's 3, 1 and 2 are - from the nadir of the central sulcus towards the apex of the postcentral gyrus - 3a, 3b, 1, and 2 respectively.
These areas contain cells that project to the secondary somatosensory cortex
Secondary somatosensory cortex
The human secondary somatosensory cortex is a region of cerebral cortex lying mostly on the parietal operculum.Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only represented in the previously described primary somatosensory cortex but also in a...
.
Clinical significance
Lesions affecting the primary somatosensory cortex produce characteristic symptoms including: agraphesthesiaAgraphesthesia
Agraphesthesia is a disorder of directional cutaneous kinesthesia or a disorientation of your skin's sensation across its space. It is a difficulty recognizing a written number or letter traced on the palm of one's hand after parietal damage....
, astereognosia, loss of vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
, proprioception
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
and fine touch
Fine touch
Fine touch, , is a sensory modality which allows a subject to sense and localise touch. The form of touch where localisation is not possible is known as crude touch....
(because the third-order neuron of the medial-lemniscal pathway cannot synapse in the cortex). It can also produce hemineglect, if it affects the non-dominant hemisphere.
It could also reduce nociception
Nociception
Nociception is defined as "the neural processes of encoding and processing noxious stimuli." It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue...
, thermoception
Thermoception
Thermoception or thermoreception is the sense by which an organism perceives temperature. The details of how temperature receptors work are still being investigated. Ciliopathy is associated with decreased ability to sense heat, thus cilia may aid in the process...
and crude touch
Crude touch
Crude touch is a sensory modality which allows the subject to sense that something has touched them, without being able to localise where they were touched...
, but since information from the spinothalamic tract
Spinothalamic tract
The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch...
is interpreted mainly by other areas of the brain (see insular cortex
Insular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...
and cingulate gyrus), it is not as relevant as the other symptoms.