The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direction ...

. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the

somatosensory cortex In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch ( haptic perception), as well as temperature ( thermoception), body position ( proprioception), and pain. It ...

of the postcentral gyrus. The spinothalamic tract consists of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries information about crude touch. The lateral spinothalamic tract conveys

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

and

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

. In the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...

, the spinothalamic tract has somatotopic organization. This is the segmental organization of its cervical, thoracic, lumbar, and sacral components, which is arranged from most medial to most lateral respectively. The pathway crosses over ( decussates) at the level of the spinal cord, rather than in the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

like the dorsal column-medial lemniscus pathway and lateral corticospinal tract. It is one of the three tracts which make up the anterolateral system.

Structure

There are two main parts of the spinothalamic tract: * The lateral spinothalamic tract transmits

and

. * The anterior spinothalamic tract (or ''ventral'' spinothalamic tract) transmits crude touch and firm pressure. The spinothalamic tract, like the dorsal column-medial lemniscus pathway, uses three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex. Pseudounipolar

neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...

s in the

dorsal root ganglion A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dor ...

have axons that lead from the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

into the dorsal

where they ascend or descend one or two vertebral levels via Lissauer's tract and then

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses fr ...

with secondary neurons in either the substantia gelatinosa of Rolando or the

nucleus proprius The nucleus proprius is a layer of the spinal cord adjacent to the substantia gelatinosa. The nucleus proprius can be found in the gray matter in all levels of the spinal cord. It constitutes the first synapse of the spinothalamic tract carrying ...

. 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). Decussation usually occurs 1-2 spinal nerve segments above the point of entry. The axons travel up the length of the spinal cord into the

, 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 posterior medial nuclei. From there, signals go to the cingulate cortex, the primary somatosensory cortex, and

insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal and frontal lobes) within each hemisphere of the mammalian ...

respectively.

Anterior spinothalamic tract

The anterior spinothalamic tract, (Latin: ''tractus spinothalamicus anterior'') or ventral spinothalamic fasciculus situated in the marginal part of the anterior funiculus and intermingled more or less with the vestibulospinal tract, is derived from cells in the posterior column or intermediate gray matter of the opposite side. Aβ fibres carry sensory information pertaining to crude touch from the skin. After entering the spinal cord the first order neurons synapse (in the nucleus proprius), and the second order neurons decussate via the anterior white commissure. These second order neurons ascend synapsing in the VPL of the thalamus. Incoming first order neurons can ascend or descend via the Lissauer tract. This is a somewhat doubtful fasciculus and its fibers are supposed to end in the

and to conduct certain of the touch impulses. More specifically, its fibers convey crude touch information to the VPL ( ventral posterolateral nucleus) part of the thalamus. The fibers of the anterior spinothalamic tract conduct information about pressure and crude touch (protopathic). The fine touch (epicritic) is conducted by fibers of the medial lemniscus. The medial lemniscus is formed by the axons of the neurons of the gracilis and cuneatus nuclei of the medulla oblongata which receive information about light touch, vibration and conscient proprioception from the gracilis and cuneatus fasciculus of the spinal cord. This fasciculus receive the axons of the first order neuron which is located in the dorsal root ganglion that receives afferent fibers from receptors in the skin, muscles and joints.

Lateral spinothalamic tract

The lateral spinothalamic tract (or lateral spinothalamic fasciculus), is a bundle of

afferent nerve fiber Afferent nerve fibers are the axons (nerve fibers) carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections ''arrive'' at a particular brain region. Efferent nerve fibers ...

s ascending through the white matter of the

, in the spinothalamic tract, carrying sensory information to the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

. It carries pain, and temperature sensory information ( protopathic sensation) to the

. It is composed primarily of fast-conducting, sparsely

myelinated Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

A delta fibers and slow-conducting, unmyelinated C fibers. These are secondary sensory neurons which have already

d with the primary sensory neurons of the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain a ...

in the posterior horn of the spinal cord (one of the three grey columns). Together with the anterior spinothalamic tract, the lateral spinothalamic tract is sometimes termed the ''secondary sensory fasciculus'' or ''spinal lemniscus''.

Anatomy

The neurons of the lateral spinothalamic tract originate in the spinal dorsal root ganglia. They project peripheral processes to the tissues in the form of free nerve endings which are sensitive to molecules indicative of cell damage. The central processes enter the spinal cord in an area at the back of the posterior horn known as the posterolateral tract. Here, the processes ascend approximately two levels before synapsing on second-order neurons. These secondary neurons are situated in the posterior horn, specifically in the Rexed laminae regions I, IV, V and VI. Region II is primarily composed of Golgi II interneurons, which are primarily for the modulation of pain, and largely project to secondary neurons in regions I and V. Secondary neurons from regions I and V decussate across the anterior white commissure and ascend in the (now contralateral) lateral spinothalamic tract. These fibers will ascend through the

, including the medulla oblongata,

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

and

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal ( alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

, as the spinal lemniscus until synapsing in the ventroposteriorlateral (VPL) nucleus of the

. The third order neurons in the thalamus will then project through the internal capsule and corona radiata to various regions of the cortex, primarily the main

, Brodmann areas 3, 1, and 2.

Function

The types of sensory information 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. 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 The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation ...

, aka ARAS) ** Spino-Mesencephalic-Limbic (for affective impact of pain).

Anterolateral system

In the

nervous system In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...

, the anterolateral system is an ascending pathway that conveys

( protopathic sensation), and crude touch from the periphery to the

. It comprises three main pathways:

Clinical significance

In contrast to the axons of second-order neurons in dorsal column-medial lemniscus pathway, the axons of second-order neurons in the spinothalamic tracts cross at every segmental level in the spinal cord. This fact aids in determining whether a lesion is in the brain or the spinal cord. With lesions in the brain stem or higher, deficits of pain perception, touch sensation, and proprioception are all contralateral to the lesion. With spinal cord lesions, however, the deficit in pain perception is contralateral to the lesion, whereas the other deficits are ipsilateral. See Brown-Séquard syndrome. Unilateral lesions usually cause contralateral anaesthesia (loss of pain and temperature). Anaesthesia will normally begin 1-2 segments below the level of lesion, due to the sensory fibers being carried by dorsal-lateral tract of Lissauer up several levels upon entry into the spinal cord, and will affect all caudal body areas. This is clinically tested by using pin pricks.

References

External links

*
Diagram at mfi.ku.dk

{{Authority control Spinal cord tracts Sensory systems Thalamic connections