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The somatosensory system is a diverse sensory system
Sensory system

A sensory system is a part of the nervous system responsible for processing sense information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception....
 comprising the receptors and processing centres to produce the sensory modalities such as touch, temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 perception, 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....
 (body position), and 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....
 (pain). The sensory receptors cover the skin
Skin

The skin is the outer covering of the body, also known as the epidermis. It is the largest organ of the integumentary system made up of multiple layers of epithelial biological tissue, and guards the underlying muscles, bones, ligaments and organ s....
 and epithelia, skeletal muscle
Skeletal muscle

They generally contract voluntarily , although they can contract involuntarily through Reflex action. The whole muscle is wrapped in a special type of connective tissue, epimysium....
s, bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
s and joint
Joint

A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally....
s, internal organ
Organ (anatomy)

In biology, an organ is a biological tissue that performs a specific function or group of functions. Usually there is a main tissue and sporadic tissues....
s, and the cardiovascular system. While touch is considered one of the five traditional sense
Sense

Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception....
s, the impression of touch is formed from several modalities; In medicine, the colloquial term touch is usually replaced with somatic senses to better reflect the variety of mechanisms involved.

The system reacts to diverse stimuli
Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. When a stimulus is applied to a sensory receptor, it elicits or influences a Reflex action via Transduction ....
 using different receptors: thermoreceptors, mechanoreceptors and chemoreceptors.






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The somatosensory system is a diverse sensory system
Sensory system

A sensory system is a part of the nervous system responsible for processing sense information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception....
 comprising the receptors and processing centres to produce the sensory modalities such as touch, temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 perception, 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....
 (body position), and 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....
 (pain). The sensory receptors cover the skin
Skin

The skin is the outer covering of the body, also known as the epidermis. It is the largest organ of the integumentary system made up of multiple layers of epithelial biological tissue, and guards the underlying muscles, bones, ligaments and organ s....
 and epithelia, skeletal muscle
Skeletal muscle

They generally contract voluntarily , although they can contract involuntarily through Reflex action. The whole muscle is wrapped in a special type of connective tissue, epimysium....
s, bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
s and joint
Joint

A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally....
s, internal organ
Organ (anatomy)

In biology, an organ is a biological tissue that performs a specific function or group of functions. Usually there is a main tissue and sporadic tissues....
s, and the cardiovascular system. While touch is considered one of the five traditional sense
Sense

Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception....
s, the impression of touch is formed from several modalities; In medicine, the colloquial term touch is usually replaced with somatic senses to better reflect the variety of mechanisms involved.

The system reacts to diverse stimuli
Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. When a stimulus is applied to a sensory receptor, it elicits or influences a Reflex action via Transduction ....
 using different receptors: thermoreceptors, mechanoreceptors and chemoreceptors. Transmission of information from the receptors passes via sensory nerves, along the spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
 and into the brain. Processing primarily occurs in the primary somatosensory area
Postcentral gyrus

The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It was initially defined from surface stimulation studies of Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall....
 in the parietal lobe
Parietal lobe

The parietal lobe is a lobe in the brain. It is positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different sensory modality, particularly determining spatial sense and navigation....
 of the cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
.

At its simplest, the system works when a sensory neuron
Neuron

Neurons are responsive cell in the nervous system that process and transmit information by electrochemical Signal . They are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves....
 is triggered by a specific stimulus such as heat; this neuron passes to an area in the brain uniquely attributed to that area on the body—this allows the processed stimulus to be felt at the correct location. The mapping of the body surfaces in the brain is called a homunculus
Homunculus

The concept of a homunculus is, most generally, any representation of a human being. It is often used to illustrate the functioning of a system....
 and is essential in the creation of a body image
Body image

Body image is a term which may refer to a person's perception of their own physical appearance, or the internal sense of having a body which is interpreted by the brain....
.

Anatomy

The somatosensory system is spread through all major parts of a mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
's body (and other vertebrates). It consists both of sensory receptors and sensory (afferent
Afferent

Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney....
) neurones in the periphery (skin, muscle and organs for example), to deeper neurones within the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
.

General somatosensory pathway


A somatosensory pathway typically has two long neurons: primary, secondary and tertiary (or first, second, and third).
  • The first neuron always has its cell body in the dorsal root ganglion
    Dorsal root ganglion

    In anatomy and neurology, the dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent nerve spinal nerves....
     of the spinal nerve
    Spinal nerve

    The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord....
     (if sensation is in head or neck, it will be the trigeminal nerve ganglia
    Trigeminal ganglion

    The trigeminal ganglion is a sensory ganglion of the trigeminal nerve which occupies a cavity in the dura mater covering the trigeminal impression near the apex of the petrous part of the temporal bone....
     or the ganglia of other sensory cranial nerves
    Cranial nerves

    Cranial nerves are nerves that emerge directly from the brain stem in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in human anatomy fit this description, twelve are conventionally recognized....
    ).
  • The second neuron has its cell body either in the spinal cord or in the brainstem. This neuron's ascending axons will cross (decussate) to the opposite side either in the spinal cord
    Spinal cord

    The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
     or in the brainstem. The axons of many of these neurones terminate in the thalamus
    Thalamus

    The thalamus is a pair and symmetric part of the brain. It constitutes the main part of the diencephalon....
     (for example the ventral posterior nucleus
    Ventral posterior nucleus

    The ventral posterior nucleus is the somato-sensory relay nucleus in thalamus of the brain....
    , VPN), others terminate in the reticular system or the cerebellum
    Cerebellum

    The cerebellum is a region of the brain that plays an important role in the integration of perception, coordination and motoneuron control. In order to coordinate motor control, there are many neural pathways linking the cerebellum with the cerebrum motor cortex and the spinocerebellar tract ....
    .
  • In the case of touch and certain types of pain, the third neuron has its cell body in the VPN of the thalamus and ends in the postcentral gyrus
    Postcentral gyrus

    The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It was initially defined from surface stimulation studies of Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall....
     of the parietal lobe
    Parietal lobe

    The parietal lobe is a lobe in the brain. It is positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different sensory modality, particularly determining spatial sense and navigation....
    .


Periphery

In the periphery, the somatosensory systemn 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
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
 by afferent
Afferent

Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney....
 neurones. There are a number of different types of afferent
Afferent

Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney....
 neurones 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. So for example slow, thin unmyelinated neurones conduct pain whereas faster, thicker, myelinated neurones conduct casual touch.

Spinal cord

In the spinal cord, the somatosensory system includes ascending pathways from the body to the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
. One major target within the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
 is the postcentral gyrus
Postcentral gyrus

The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It was initially defined from surface stimulation studies of Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall....
 in the cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
. This is the target for neurones 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
Posture

Posture or posturing may refer to:In humans* Neutral spine or good posture* Human position* Abnormal posturing, in neurotrauma* Posturography, in neurology...
 are projected to the cerebellum
Cerebellum

The cerebellum is a region of the brain that plays an important role in the integration of perception, coordination and motoneuron control. In order to coordinate motor control, there are many neural pathways linking the cerebellum with the cerebrum motor cortex and the spinocerebellar tract ....
. These include the ventral
Ventral spinocerebellar tract

The ventral spinocerebellar tract conveys proprioception information from the body to the cerebellum. It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract....
 and dorsal spinocerebellar tract
Dorsal spinocerebellar tract

The dorsal spinocerebellar tract conveys proprioception information from the body to the cerebellum.It is part of the somatosensory system and runs in parallel with the ventral spinocerebellar tract....
s. Another important target for afferent
Afferent

Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney....
 somatosensory neurones which enter the spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
 are those neurones involved with local segmental reflexes.

Brain

The primary somatosensory area in the human cortex is located in the postcentral gyrus
Postcentral gyrus

The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It was initially defined from surface stimulation studies of Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall....
 of the parietal lobe
Parietal lobe

The parietal lobe is a lobe in the brain. It is positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different sensory modality, particularly determining spatial sense and navigation....
. The postcentral gyrus is the location of the primary somatosensory area, the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space called a homunculus
Homunculus

The concept of a homunculus is, most generally, any representation of a human being. It is often used to illustrate the functioning of a system....
 at this location. For the primary somatosensory cortex, this is called the sensory homunculus. Areas of this part of the human brain
Human brain

The human brain is the center of the human nervous system and is a highly complex organ. It has the same general structure as the brains of other mammals, but is over five times as large as the "average brain" of a mammal with the same body size....
 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. Interestingly, one study showed somatosensory cortex was found to be 21% thicker in 24 migraine sufferers, on average than in 12 controls, although we do not yet know what the significance of this is. Somatosensory information involved 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 posture also targets an entirely different part of the brain, the cerebellum
Cerebellum

The cerebellum is a region of the brain that plays an important role in the integration of perception, coordination and motoneuron control. In order to coordinate motor control, there are many neural pathways linking the cerebellum with the cerebrum motor cortex and the spinocerebellar tract ....
.

Physiology


Initiation of probably all "somatosensation" begins with activation of some sort of physical "receptor". These somatosensory receptors tend to lie in skin, organs or muscle. The structure of these receptors is broadly similar in all cases, consisting of either a "free nerve ending
Free nerve ending

A free nerve ending is an unspecialized, afferent nerve ending, meaning it brings information from the body's periphery to the brain. They function as cutaneous receptors and are essentially used by vertebrates to detect nociception....
" or a nerve ending embedded in a specialised capsule. They can be activated by movement (mechanoreceptor
Mechanoreceptor

A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel nerve ending, and Ruffini corpuscles....
), pressure (mechanoreceptor
Mechanoreceptor

A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel nerve ending, and Ruffini corpuscles....
), chemical (chemoreceptor) and/or temperature. In each case, the general principle of activation is similar; the stimulus causes depolarisation of the nerve ending and then an action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
 is initiated. This action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
 then (usually) travels inward towards the spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
.

Technology

The new research area of haptic technology can provide touch sensation in virtual and real environments. This new discipline has started to provide critical insights into touch capabilities.

See also

  • Cell signalling
  • Special senses
    Special senses

    The traditional five senses in human kind are the senses of Visual perception, Hearing , taste, and olfaction, and touch. In medicine, the special senses are the first four of these; touch is specifically excluded as a special sense....
  • Cellular Cognition
  • Muscle spindle
    Muscle spindle

    Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons....


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