Spinothalamic tract
Encyclopedia
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. The pathway decussates at the level of the spinal cord
, rather than in the brainstem like the posterior column-medial lemniscus pathway
and corticospinal tract
.
. This means that the sensation is accompanied by a compulsion to act. For instance, an itch is accompanied by a need to scratch, and a painful stimulus makes us want to withdraw from the pain.
Pseudounipolar neuron
s (those with only one long process) in the dorsal root ganglion
have axons that lead from the skin
into the dorsal spinal cord
where they ascend or descend one or two vertebral levels via Lissauer's tract and then synapse
with secondary neurons in either the substantia gelatinosa
or the nucleus proprius
. These secondary neurons are called tract cells.
The axons of the tract cells cross over (decussate) to the other side of the spinal cord via the anterior white commissure
, and to the anterolateral corner of the spinal cord (hence the spinothalamic tract being part of the anterolateral system
). The axons travel up the length of the spinal cord into the brainstem, specifically the rostral ventromedial medulla
.
Traveling up the brainstem, the tract moves dorsally. The neurons ultimately synapse with third-order neurons in several nuclei of the thalamus -- including the medial dorsal, ventral posterior lateral, and ventral medial posterior nuclei. From there, signals go to the cingulate cortex
, the primary somatosensory cortex, and insular cortex
respectively.
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
about pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, itch
Itch
Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response...
and crude touch. The pathway decussates at the level of the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
, rather than in the brainstem like the posterior column-medial lemniscus pathway
Posterior column-medial lemniscus pathway
The posterior column-medial lemniscus pathway is the sensory pathway responsible for transmitting fine touch, vibration and conscious proprioceptive information from the body to the cerebral cortex; as well as tactile pressure, barognosis, graphesthesia, stereognosis, recognition...
and corticospinal tract
Corticospinal tract
The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
.
Tracts
There are two main parts of the spinothalamic tract (STT):- The lateral spinothalamic tractLateral spinothalamic tractThe lateral spinothalamic tract , which is a part of the Anterolateral system, is a bundle of sensory axons ascending through the white matter of the spinal cord, carrying sensory information to the brain. It carries pain and temperature sensory information to the thalamus of the brain...
transmits painPainPain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
and temperatureTemperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
. - The anterior spinothalamic tractAnterior spinothalamic tractThe ventral spinothalamic fasciculus situated in the marginal part of the anterior funiculus and intermingled more or less with the vestibulo-spinal fasciculus, is derived from cells in the posterior column or intermediate gray matter of the opposite side...
(or ventral spinothalamic tract) transmits crude touch.
Information transmitted
The types of sensory information transmitted via the spinothalamic tract are described as affective sensationAffective sensation
An affective sensation is a sensation accompanied with a strong compulsion to act on it, causing reflex actions such as the scratch reflex or the withdrawal reflex. Affective sensations are transmitted via the spinothalamic tract through the spinal cord....
. This means that the sensation is accompanied by a compulsion to act. For instance, an itch is accompanied by a need to scratch, and a painful stimulus makes us want to withdraw from the pain.
Sub-systems
There are two sub-systems identified:- Direct (for direct conscious appreciation of pain)
- Indirect (for affective and arousal impact of pain). Indirect projections include
- Spino-Reticulo-Thalamo-Cortical (part of the ascending reticular arousal system, aka ARAS)
- Spino-Mesencephalic-Limbic (for affective impact of pain).
Path of sensation
The Spinothalamic Tract, like the Dorsal Column-Medial Lemniscus Tract, use three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex.Pseudounipolar 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 (those with only one long process) in the dorsal root ganglion
Dorsal root ganglion
In anatomy and neuroscience, a dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.-Unique unipolar structure:...
have axons that lead from the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
into the dorsal spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
where they ascend or descend one or two vertebral levels via Lissauer's tract and then synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
with secondary neurons in either the substantia gelatinosa
Substantia gelatinosa
Substantia gelatinosa can refer to:* Substantia gelatinosa of Rolando * Substantia gelatinosa centralisSubstantia gelatinosa is a structure involved in pain transmission....
or the nucleus proprius
Nucleus proprius
The Nucleus proprius is a layer of the spinal cord adjacent to the substantia gelatinosa. Nucleus proprius constitutes the bulk of the dorsal horn and receives inputs from the dorsal root ganglions that carry sensory information, such as light touch, as well as pain and temperature information...
. These secondary neurons are called tract cells.
The axons of the tract cells cross over (decussate) to the other side of the spinal cord via the anterior white commissure
Anterior white commissure
The anterior white commissure, also known as the alba anterior medullae spinalis, is a bundle of nerve fibers which cross the midline of the spinal cord just anterior to the gray commissure...
, and to the anterolateral corner of the spinal cord (hence the spinothalamic tract being part of the anterolateral system
Anterolateral system
In the nervous system, the anterolateral system is an ascending pathway that conveys pain, temperature , and crude touch from the periphery to the brain. It comprises three main pathways:-External links:*...
). The axons travel up the length of the spinal cord into the brainstem, specifically the rostral ventromedial medulla
Rostral ventromedial medulla
The rostral ventromedial medulla , is a group of neurons located close to the midline on the floor of the medulla . The rostral ventromedial medulla sends descending inhibitory and excitatory fibers to the dorsal horn spinal cord neurons.There are 3 categories of neurons in the RVM. On-cells,...
.
Traveling up the brainstem, the tract moves dorsally. The neurons ultimately synapse with third-order neurons in several nuclei of the thalamus -- including the medial dorsal, ventral posterior lateral, and ventral medial posterior nuclei. From there, signals go to the cingulate cortex
Cingulate cortex
The cingulate cortex is a part of the brain situated in the medial aspect of the cortex. It includes the cortex of the cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus...
, the primary somatosensory cortex, and 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...
respectively.