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A part of the brain positioned superior to the occipital lobe and posterior to the frontal lobe, that integrates sensory information from different modalities, particularly determining spatial sense and navigation.
A prominent structure in the parietal lobe of the human brain and an important landmark that is the location of the primary somatosensory cortex, the main sensory receptive area for the sense of touch.
A somatosensory pathway will typically have three long neurons: primary, secondary and tertiary. The first always has its cell body in the dorsal root ganglion of the spinal nerve . The second has its cell body either in the spinal cord or in the brainstem; this neuron's ascending axons will cross to the opposite side either in the spinal cord or in the brainstem. The axons of many of these neurones terminate in the thalamus, others terminate in the reticular system or the cerebellum. In the case of touch and certain types of pain, the third neuron has its cell body in the ventralposteriornucleus of the thalamus and ends in the postcentral gyrus of the parietal lobe.
In the periphery, the somatosensory system detects various stimuli by sensory receptors, e.g., by mechanoreceptors for tactile sensation and nociceptors for pain sensation. The sensory information (touch, pain, temperature, etc.,) is then conveyed to the central nervous system by afferent neurones, of which there are a number of different types which vary in their size, structure and properties. Generally, there is a correlation between the type of sensory modality detected and the type of afferent neurone involved. For example, slow, thin, unmyelinated neurones conduct pain whereas faster, thicker, myelinated neurones conduct casual touch.
In the spinal cord, the somatosensory system includes ascending pathways from the body to the brain . One major target within the brain is the postcentral gyrus in the cerebral cortex. This is the target for neurons of the Dorsal Column Medial Lemniscal pathway and the Ventral Spinothalamic pathway. Note that many ascending somatosensory pathways include synapses in either the thalamus or the reticular formation before they reach the cortex. Other ascending pathways, particularly those involved with control of posture, are projected to the cerebellum, including the ventral and dorsal spinocerebellar tracts. Another important target for afferent somatosensory neurons which enter the spinal cord are those neurons involved with local segmental reflexes.
The primary somatosensory area in the human cortex is located in the postcentral gyrus of the parietal lobe. This is the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space called a homunculus at this location. For the primary somatosensory cortex, this is called the sensory homunculus. Areas of this part of the human brain map to certain areas of the body, dependent on the amount or importance of somatosensory input from that area. For example, there is a large area of cortex devoted to sensation in the hands, while the back has a much smaller area. Somatosensory information involved with proprioception and posture also targets an entirely different part of the brain, the cerebellum.
This 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 sensory and motor information of the body.
The cortical homunculus is a visual representation of the concept of "the body within the brain" -- that one's hand or face exists as much as a series of nerve structures or a "neuron concept" as it does in a physical form. This concept relates to many neuro-biological phenomena including "phantom limb" and "body integrity identity disorder".
The thalamus is a midline symmetrical structure within the brain of vertebrates including humans, situated between the cerebral cortex and midbrain . Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness.
Sensory neurons route directly from the limb to the cortex., Sensory neurons route directly to the thalamus from the limb., Sensory neurons route through spinal cord ascending tracts to the cortex and then the thalamus., and Sensory neurons route through spinal cord ascending tracts to the thalamus and then cortex.