Spinothalamic tract where is crossover

The anterolateral pathway consists of three tracts: the spinal thalamic tract, best known for and mediates discriminative aspects of pain and temperature, such as location and intensity; the spinoreticular tract, which is thought to participate in the emotional and arousal aspects of pain; and the spinomesencephalic tract in the periaqueductal gray participates in the central modulation of pain.

The spinothalamic and spinomesencephalic tracts arise mainly from the spinal cord laminae 1 through 5, while the spinoreticular arises diffusely from the intermediate zone to the ventral horn laminae 6 through 8. In addition to pain and temperature, some crude touch sensations can be conveyed by the anterolateral pathways when the posterior column is damaged. To summarize, if you step on a thumbtack with your left foot, your spinothalamic tract enables you to realize "something sharp is puncturing the sole of my foot.

Remember that the somatotopic organization preserves the spatial orientation of the central nervous system. Here you can visualize, attempt to draw, or trace the pathway of the DCML, which will transmit sensations of fine touch, proprioception, and vibration entering the spinal cord via the dorsal root on the same side of the sensation into the posterior columns.

It is helpful if you picture fibers, again adding on the lateral aspects as you ascend higher into the posterior column. So if we begin in the lower extremity and ascend in the cord, we see upper trunk to arm to neck is added as we rise. The anterolateral pathways, which carry pain, temperature, and crude touch, also have somatotopic organization in which the feet are mostly laterally represented. If we use the left side of the body as the location for the sensory stimulation, you can picture fibers coming into the DRG and decussating at the cord level in the anterior commissure and adding on medially, as the anterolateral pathway ascends in the spinal cord.

Slide 8: Spinal Cord Sensory and Motor Pathways Here on slide 8, we can see both ascending pathways in blue and descending pathways in red. Let's use this slide to review some of the concepts in the lecture series. Stop and take time to answer the following questions: - At what level does the decussation occur for the dorsal column medial lemniscal pathway?

Answers to these questions will be related in the case at the end of the lecture series. Slide 9: Somatosensory Cortex Somatosensory information that arrives at the thalamus is brought to the primary somatosensory cortex.

The information is somatotopically organized with the face most lateral and the legs most medial. This information is also carried to the association areas, specifically Brodmann areas 5 and 7. Remember that association areas assist with higher level sensory function and store information related to past experiences.

Both the primary and association areas have extensive connections with the motor cortex. Lesions in a somatosensory cortex produce deficits referred to as cortical sensory loss.

Slide Central Pain Modulation One of the most important findings in pain research was the discovery that the brain has modulatory circuits whose main function is to regulate the perception of pain. Because pain is highly dependent on experience and therefore varies from person to person, it is difficult to treat clinically. Advances in pain research have led to some important pain therapies. The initial side of modulation is the spinal cord, which is pictured here, where inner connections between nociceptive and non-nociceptive pathways can control the transmission of pain to higher centers in the brain.

This interaction was discovered in the s and is called the Gate Control Theory, which is the basis for the use of transcutaneous electrical nerve stimulation TENS.

In TENS, electrodes are used to stimulate large-diameter afferent fibers that overlap the area of injury. Stimulation of the dorsal columns via surface electrodes presumably relieves pain because it activates large numbers of type A-beta fibers synchronously.

This would be analogous to rubbing your shin after hitting it against a hard object, thus modulating your pain. The periaqueductal gray receives inputs from the hypothalamus, amygdala, and cortex, and it inhibits pain transmission. In research animals, it was found that direct stimulation of the periaqueductal gray produces a profound and selective analgesia.

This stimulation was very specific in that the animal can still respond to touch, pressure, and temperature within the body area that was in analgesic, but simply had less pain. Since the discovery that opiates applied directly to the spinal cord produce a potent analgesic effect, this has led to the administration of opiates in certain conditions by means of intrathecal or epidural roots.

Injection of opiates, such as morphine, into specific regions of the brain also produces powerful analgesic by inhibiting the firing of nociceptive neurons in the dorsal horn. The periaqueductal gray region is among the most sensitive sites for eliciting such analgesics.

It is an essential link in the transfer of sensory information, other than olfaction, from receptors in the periphery to sensory processing regions in the cerebral hemispheres.

It was previously thought to be only a relay station, but it is now clear that it plays a gating and modulatory role in relaying sensation.

The thalamus is divided into a medial nuclear group, a lateral nuclear group, and a ventral anterior nuclear group, which is separated by a Y-shaped white matter structure called the internal medullary lamina. Nuclei located within the internal medullary lamina itself are called intralaminar nuclei. The midline thalamic nuclei are an additional thin collection of nuclei lying adjacent to the third ventricle, several of which are continuous and functionally very similar to the intralaminar nuclei.

Finally, the thalamic reticular nucleus forms an extensive but thin sheet enveloping the lateral aspect of the thalamus. Slide Three Categories of Thalamic Nuclei The thalamic nuclei that make up the relaying nuclei are the anterior group, thought to play a role in memory and emotion; the medial group, which is implicated in memory; the ventral group, which conveys somatosensory information; and the posterior group, which conveys auditory and visual information.

The intralaminar nuclei project to limbic structures in the basal ganglia and receive inputs from the spinal cord, brain stem, and cerebellum and are thought to mediate cortical arousal and integration of sensory submodalities. The reticular nucleus is not interconnected with the cortex, but their axons terminate on the other nuclei of the thalamus. The reticular nucleus modulates activity in other thalamic nuclei.

Slide Specific Thalamic Relay Nuclei Here is a table of the most well-known and clinically relevant thalamic nuclei with main inputs, main outputs, and functions. Cover the right side and name the major nuclei that are responsible for visual inputs, limbic inputs, and inputs to the basal ganglia. Slide Clinical Sensory Dysfunction Sensory dysfunction can be caused by lesions anywhere in the somatosensory pathways. We are now going to take a look at some of the clinical manifestations that may occur as part of your clinical practice.

We will explore sensory loss, paresthesia, spinal cord lesions, and bowel, bladder, and sexual dysfunction. Slide Sensory Loss: Patterns and Locations Again, sensory loss can be caused by lesions anywhere in the somatosensory pathways, and if we review that pathway, it can include peripheral nerves, nerve roots, the posterior column medial lemniscal and anterolateral pathways, the thalamus, thalamocortical white matter, and the primary somatosensory cortex.

Over the next few slides, we will look in detail at lesions in each of these locations listed here on slide Slide Lesion of Primary Sensory Cortex or Thalamic In the following illustrations, lesions are shown in red, and sensory loss is shown in green. With the pathways drawn, we can see that the deficit is contralateral to the lesion, and the clinical manifestations can vary depending on the lesion size and exact location. This left-sided cortical lesion can potentially affect the sensory modalities related to the posterior column medial lemniscal system including touch, joint position, and vibration, as well as the anterolateral and trigeminothalamic systems for pain, temperature, and touch on the right side of the body.

Large lesions may affect adjacent cortical areas that involve higher order abilities such as recognition of objects by touch, motor deficits such as hemiparesis, or corticobulbar function. Slide Lateral Pontine or Medullary Lesions Here on slide 17 the lesion is in the lateral pons or medulla, and we can see that it involves the anterolateral pathways and the spinal trigeminal nucleus on the ipsilateral side, causing loss of pain and temperature sensation in the body opposite the lesion and loss of pain and temperature sensation in the face on the same side as the lesion.

Slide Medial Medullary On this slide, we haHere on slide 18 we are looking at sensory loss in a lesion of the medial medulla. The lesion will therefore involve the medial lemniscus and will cause contralateral loss of vibration and proprioception. Slide Nerve Roots or Peripheral Nerves Lesions in nerve roots or peripheral nerves can cause sensory disturbances.

Distal symmetrical polyneuropathies can cause bilateral sensory loss in a stocking and glove pattern in all modalities. Associated deficits of lesions in the peripheral nerves often include lower motor neuron weakness and other reflex changes. Slide Isolated Nerve Root Lesions In isolated nerve root lesions, the sensory loss is in specific territories related to the nerves' innervation. Log In. Sign Up. Become a Gold Supporter and see no ads.

Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Citation, DOI and article data. Palipana, D. Anterior spinothalamic tract. Reference article, Radiopaedia. Central Nervous System , Spine.

Anterior spinothalamic tracts Ventral spinothalamic fasciculus. URL of Article. Gross anatomy Peripheral connections First-order neurons, whose cell bodies are in the dorsal root ganglion and whose axons extend from peripheral receptors, enter the cord via dorsal nerve roots.

Central course The aforementioned first-order neurons synapse with second-order neurons whose bodies are located in the ipsilateral dorsal horn of the cord. Sensory Dissociation video. Crossed Findings video. Exam Tests video. Traps video. Pearls video. Introduction Clinically, there are 2 major somatosensory pathways that are examined. The first is the spinothalamic ST part of the anterolateral system and the second is the dorsal column-medial lemniscus DCML system.

The principle sensory modalities for the ST system are pain and temperature. The principle sensory modalities for DCML system are vibratory, position sense and discriminatory or integrative sensation. Spinothalamic The anatomical pathways for the 2 major sensory systems is as follows: ST - the axons from the 1st order neuron located in the dorsal root ganglion enter the dorsal root entry zone and within several segments synapse with 2nd order neurons in the dorsal horn.

Axons from the 2nd order neuron cross immediately via the ventral white commissure to the anterolateral quadrant of the spinal cord then ascend as the spinothalamic tract to the ventral posterior lateral nucleus VPL of the thalamus. The axons of the 3rd order neurons project to the postcentral gyrus or somatosensory cortex there are also projections to the insular and anterior cingulate cortex but we are mainly focusing on the primary somatosensory cortex.

Dorsal Column-Medial Lemniscus The axons from the 1st order neurons located in the dorsal root ganglion enter the dorsal root entry zone and then ascend in the dorsal columns on the same side of the cord until they reach the 2nd order neurons in the medulla.

Axons from the 2nd order neurons cross at the level of the medulla and then travel near the midline in the medial lemniscus. By the time the medial lemniscus reaches the rostral pons it has moved laterally and at this point it is in close proximity to the spinothalamic tract as it ascends to the VPL of the thalamus. The 3rd order neuron projects to the primary somatosensory cortex in the postcentral gyrus.

Trigeminal System The trigeminal system is the somatosensory system for the face, which is clinically tested in the cranial nerve exam.