Author: Lorenzo Crumbie MBBS, BSc•Reviewer: Francesca Salvador MScLast reviewed: October 05, 2021Reading time: 24 minutes


*
*
*
*
*
*
*
*

As the overseer that the bulk of the body physiological processes, the mind has numerous connections through extracranial structures. The spinal cord acts as one of the major conduits with which the body and also the mind exchanges information. The spinal cord is the caudal continuation of the brainstem. The commences at the foramen magnum and also traverses the vertebral foramen come the reduced border of the first lumbar vertebra (L1) in one adult, and the lower border that the second or upper border of the third lumbar vertebra (L2/L3) in a cultivation child.

You are watching: Ascending and descending tracts of spinal cord pdf

The spinal cord has many groups that nerve yarn going towards and coming indigenous the brain. These have been jointly called the ascending and also descending tracts the the spinal cord, respectively. The tracts room responsible for transporting sensory and motor stimuli to and from the perimeter (respectively).

Key facts around the ascending and descending tracts of the spinal cord
Lateral spinothalamicPain and temperature
Ventral spinothalamicPressure and also crude touch
Dorsal columnVibration, proprioception, two-point discrimination
SpinocerebellarProprioception in joints and muscles
CuneocerebellarProprioception in joints and muscles (like the spinocerebellar)
SpinotectalTactile, painful, and thermal stimuli
SpinoreticularIntegration of stimuli from joints and muscles right into the reticular formation
Spino-olivaryAdditional details to the cerebellum as an accessory pathway
CorticospinalVoluntary, discrete, expert motor activities
ReticulospinalRegulation come voluntary movements and also reflexes
RubrospinalPromotion the flexor and inhibition that extensor muscle activity
VestibulospinalInhibition the flexor and also promotion of extensor muscle activity
TectospinalPostural movements from intuitive stimuli

The objective of this write-up is to give review of the tracts of the spinal cord. Much more detailed discussions about the pathways of the tracts and some connected disorders can be uncovered in the respective write-ups for the ascending and also descending tracts.


Contents
Cross-sectional check out of the spinal cord outline of spinal tractsSummary
+ present all

synopsis of spinal cord anatomy

The spinal cord is a cylindrical fixed of neural tissue expanding from the caudal facet of the medulla oblongata of the brainstem to the level the the first lumbar vertebra (L1). When the size of the spinal cord different from one separation, personal, instance to another, the is usually longer in males (approximately 45 cm) than it is in females (approximately 42 cm). The spinal cord is circumferentially and also longitudinally enclosed in all three meningeal layers (i.e. dura, arachnoid and pia mater) and is rely in cerebrospinal fluid. It is securely encased in ~ the vertebral canal of the vertebral spine. For this reason, the spinal cord likewise has the same locations of lordosis (forward curvature) in the cervical and also lumbar regions, and also kyphosis (backward curvature) in the thoracic and sacral regions as the vertebral column.

*
structure of the spinal cord (coronal view)

The spinal cord have the right to be equally split along the midline dorsoventral axis by drawing a line through the depression known as the dorsal and also ventral median sulci. ~ above each half of the spinal cord, a ventrolateral and dorsolateral sulcus is appreciated at the sites native which the ventral and also dorsal nerve roots leave and enter the spinal cord, respectively. These paired spinal nerve roots also carry out a basis for segmentation the the spinal cord, together they correspond to the vertebra who intervertebral foramina they take trip through.

has actually the spinal cord anatomy gained you feeling a small overwhelmed? Ease you yourself into learning around the anatomy the the Nervous system with our free practice tests, quizzes and flashcards.

together the spinal cord ideologies its most inferior limit, the tapers off to type the conus medullaris. At the inferior border that L1, a filamentous expansion of the spinal cord known as the filum terminale is constant caudally, to the allude of insertion in ~ the coccyx. In ~ the lumbar enlargement, the spinal nerves arborize to form the cauda equina, which exits the vertebral canal via the particular foramina. 


Cross-sectional check out of the spinal cord

Cross-sectional analysis of the spinal cord reveals the it is comprised of a main area of cabinet bodies, referred to as grey matter, and also a peripheral area the myelinated axons well-known as the white matter

Grey column of the spinal cord

The grey issue is a butterfly-shaped collection of neuronal cell bodies. That is subdivided into the dorsal (posterior), intermediate (lateral), and ventral (anterior) grey columns (horns). The columns are likewise further functionally subdivided based on Rexed’s group such that the dorsal shaft (Rexed laminae i – VI, and also Clarke’s nucleus, also known together the cell nucleus dorsalis) processes sensory stimuli. On the other hand, the ventral grey tower (Rexed laminae VIII & IX, and component of VII) contains the cell bodies the the alpha (α) engine fibers the relay details to that suit. The intermediate column (containing component of Rexed VII and also VIII) dwellings cells that create the preganglionic sympathetic tracts.

*
Cross-sectional see of the spinal cord

Each fifty percent of the grey obelisk is joined by a horizontal grey commissure through which the central canal runs. The main canal is the caudal continuation of the fourth ventricle and as such communicates cranially v the intracranial ventricular systems and cisterns. It also serves as a reference point so the anatomists have the right to identify the grey commissure right into anterior and also posterior divisions. The slither the grey issue that overcome dorsally is the posterior grey commissure, if the component that passes ventrally is the anterior grey commissure

White shaft of the spinal cord

The white matter is the repertoire of myelinated nerve yarn that take trip to and also from the brain. Like the grey matter, it can be subdivided right into anterior (ventral), posterior (dorsal), and lateral segments called funiculi (s. Funiculus). However, unlike the functional department of the grey matter, the department of the white matter into the particular funiculi is done using anatomical landmarks:

The anterior funiculus is restricted medially by the ventral median sulcus, and also laterally by the ventrolateral sulcus.  The lateral funiculus is minimal ventrally and dorsally by the ventrolateral and dorsolateral sulci.  The posterior funiculus is located lateral to the dorsal typical sulcus, and medial the dorsolateral sulcus.

The dorsal funiculus is specifically unique in that it deserve to be subdivided right into two fasciculi. The gracile fasciculus (fasciculus gracilis) is closer come the dorsal median sulcus, when the cuneate fasciculus (fasciculus cuneatus) is closer come the dorsolateral sulcus. Fan to the reality that over there is a somatotopic arrangement the this funiculus, both fasciculi might not be current at every spinal levels. However, once they are both present, they space separated native each various other by the dorsal intermediate sulcus. 

Cross-sectional evaluation of the spinal cord is a yes, really tricky topic, so don’t fret if friend don’t acquire it right away! usage our spinal cord diagrams and also quizzes to exercise until you’re emotion confident. 

synopsis of spinal tracts

the is necessary to know the jargon linked with the spinal cord tracts in order to evaluate the anatomy and physiology linked with the tracts. The tracts are described according to the funiculus within which they room located. Additionally, a an ext precise location have the right to be given based upon the proximity that the tract to the midline. These descriptions are used in conjunction with the name of the street to help in localizing the neuronal pathway. The prefix spino- suggests that the tract is originating within the spinal tract. Therefore, the lateral spinothalamic tract refers come a swarm of nerve fibers traveling within the lateral funiculus that the spinal cord, i beg your pardon originated within the cord and also will terminate in ~ the thalamus.

In contrast, the bundle the fibers well-known as the rubrospinal tract originates indigenous the red nucleus of the midbrain and travels to the spinal cord. However, the reader have to bear in mind that although the tracts are described as being confined to a certain region, over there is far-ranging overlap that the tracts in real life; therefore they might not always obey the prescribed group systems.

*
summary of the pyramidal tracts (ventral view)

The white matter of the spinal cord has a mixture that ascending (sensory or afferent) and descending (motor or efferent) tracts. These tracts room bilaterally combine structures; few of which might cross the midline (decussate) at various levels come relay info to the next of the body, or from the next of the brain, on the side opposite to the point of origin. An example of this is the corticospinal tract, where fibers originating native the left cerebral cortex decussate in ~ the level the the pyramids in the caudal medulla oblongata to supply muscles the the ideal side of the body. 

Ascending tracts that the spinal cord

growing up, the impression was given that there were only five senses the humans have the right to detect. These were sight, smell, sound, taste, and also touch. However, that is clear that touch can be further broadened to incorporate pain, heat changes, pressure, light (crude) touch, vibration, two-point discrimination, and also proprioception. Sight, sound, smell, and also taste are special afferent stimuli that space conveyed through their particular cranial nerves. However, the various other tactile modalities space transmitted with the ascending tracts that the spinal cord. There are eight recognized ascending tracts send a range of sensory stimuli that are debated below.

recognition of this stimuli is provided by a range of mechanoreceptors distributed throughout the body. This mechanoreceptors are complimentary nerve endings that space responsive come several species of stimuli. Castle include:


*
*
*

Pacinian corpuscles (for vibration and also pressure sensation) Meissner’s corpuscles (light touch) Merkel’s discs (pressure receptors) Golgi tendons (for proprioception) joint receptors nociceptors (for noxious stimuli) muscle spindles (stretch receptors) Lateral spinothalamic tract

Cutaneous sensory receptors transmit painful and varying thermal stimuli through the dorsal nerve root. The fibers climate synapse the dorsal horn that the grey matter. The yarn of the second-order neurons decussate to the contralateral side and ascend in the lateral spinothalamic tract. These fibers pass v the medulla oblongata, posterior part of the pons, and enter the tegmentum that the midbrain.

The lateral spinothalamic tract contents then synapse top top third-order neurons in the thalamus. As the stimuli because that pain and also temperature transforms are processed here, they pass this info through the posterior limb of the inner capsule, v the corona radiata to reach the postcentral gyrus (Brodmann 3, 1, 2).

*
Post main gyrus (coronal view) Ventral (anterior) spinothalamic tract

Cutaneous mechanoreceptors that space sensitive to crude (non-discriminative) touch and pressure alters transmit stimuli through the dorsal root ganglion. They synapse in the substantia gelatinosa (Rexed II) after ascending or descending for one or two segments in the posterolateral tract of Lissauer. Succeeding fibers pass to the other side via the anterior grey commissure to emerge in the anterior funiculus.

Here, the fibers form the ventral (anterior) spinothalamic tract and ascend with the medulla oblongata alongside the lateral spinothalamic and spinotectal tracts. Choose the lateral spinothalamic tract, the ventral spinothalamic tract additionally synapses ~ above neurons in the thalamus. The remainder the the course of the third-order neurons the this street is analogous to that of the lateral spinothalamic tract. 

Dorsal column: Medial lemniscus pathway and cuneocerebellar tracts

countless cutaneous receptor detect and also transmit sensory modalities such together light (discriminative) touch, vibration sense, proprioception, and also two-point discrimination. Proprioception describes the brain’s capacity to discern the actual spatial location of each part of the body. Two-point discrimination refers to the accuracy through which one deserve to detect that a component of the body is gift touched and that two relatively close points space being concurrently stimulated. The receptors send impulses with the dorsal root ganglion and also directly into the dorsal funiculus to type the dorsal column. 


The fibers split to kind short descending and long ascending yarn that participate in local reflex arcs. This enables unconscious efferent treatment in situations where a economic stimulation (i.e. Overextension that a limb) becomes harmful. Many of the lengthy ascending fibers walk on to kind the fasciculus gracilis (throughout the size of the spinal cord) and also the fasciculus cuneatus (at and over the level the the sixth thoracic vertebra). Both set of fibers travel ipsilaterally, with the gracile fasciculus carrying stimuli from the reduced limbs and lower six thoracic segment (T7 – T12) and the cuneate fasciculus conveying stimuli from the top 6 (T1 – T6) and every one of the cervical vertebrae.


*
*

They every terminate in ~ their particular nucleus (gracile and cuneate) within the medulla oblongata. The 2nd order neurons produce the internal arcuate fibers the pass contralaterally with the sensory decussation, to form the medial lemniscus pathway. The fibers proceed towards the thalamus and then to Brodmann’s areas 3, 1, 2

the note, the fibers occurring from the cuneate nucleus kind the posterior external arcuate fibers the travel through the inferior cerebellar peduncle, to get in the cerebellum. This is known as the cuneocerebellar tract, i beg your pardon carries joint position and proprioception come the cerebellum.

Ventral (anterior) spinocerebellar 

The mechanoreceptors bring sensory information from the upper and lower limbs and also trunk come the dorsal source ganglion the the eighth cervical v to the third lumbar (C8 – L3) segments. They get in the dorsal grey horn and also synapse on the nucleus dorsalis (Clarke’s nucleus). Keep in mind that Clarke’s nucleus is only found between C8 – L3. Because of this fibers arising over or listed below that level will travel through the dorsal white shaft until they come at the nearest level.

*
Anterior spinocerebellar tract (axial view)

no all the yarn of this tract proceed toward the cerebellum on the same side. Just a decimal of fibers will continue in the ipsilateral lateral funiculus; if the bulk of the fibers will decussate to kind the ventral spinocerebellar tract that the contralateral lateral funiculus. Both tracts will certainly ascend with the medulla oblongata, and accessibility the cerebellar cortex through their corresponding superior cerebellar peduncle. However, it has been theorized the the bulk of the contralateral fibers travel with the middle cerebellar peduncle, to cross back to the initial side. 

Dorsal (posterior) spinocerebellar 

The dorsal spinocerebellar tract also carries unconscious proprioception come the cerebellum yet from the lower limbs and also trunk. Choose the ventral spinocerebellar tract, this info is relayed come Clarke’s nucleus after ~ passing through the dorsal source ganglion. 

*
Dorsal spinocerebellar street (axial view)

However, unequal the ventral counterpart, axons of the second-order neurons native Clarke’s cell core pertaining to this tract get in the posterolateral aspect of the ipsilateral lateral funiculus. Together it forms the dorsal spinocerebellar tract, the fibers ascend come the medulla oblongata and enter the inferior cerebellar peduncle. Castle then integrate with the mossy yarn of the rostral and caudal cerebellar vermis.

descending tracts that the spinal cord

Muscular contraction versus a relatively fixed skeletal device is the principal attribute of the musculoskeletal system that facilitates locomotion. However, muscle fibers room dependent on action potentials produced by the spinal engine neurons the the anterior grey horn in stimulate to create a movement. Both conscious and also unconscious regulation of these lower engine neurons the the anterior grey horn is accomplished by many upper engine neuron pathways the originate over the level of speak (i.e. Cerebral cortex, cerebellum, etc.). The actions of the upper motor neurons administer stimulatory and also inhibitory modulation of the task of the anterior horn cells, and by extension, the activity of the motor system. 

unlike the sensory pathways, whereby the first-order neurons to be at the level that the spinal cord and also the third-order neurons to be in the brain, the motor system has first-order neurons within the brain and third-order neurons at the anterior grey column.

Corticospinal tracts

The huge pyramidal cells that the lamina pyramidalis interna (the internal pyramidal layer; fifth histological layer) of the cerebral cortex are the first-order neurons of the corticospinal tract. While the majority of yarn arise from the precentral areas (Brodmann’s areas 4, and also 6), the postcentral gyrus likewise contributes to its formation as well. However, those developing from the postcentral gyrus do not add to motor regulation. Just the motor component of the corticospinal tract will get involved in regulation voluntary movement. Also, note that over there is a somatotopic arrangement of the corticospinal tract the is best understood through reviewing the engine homunculus.


*
*
*
*

The corticospinal tract travels in opposing direction to the terminal components of the spinothalamic and medial lemniscus tracts. It pipeline the cortex with the corona radiata and internal capsule prior to passing through the basis pedunculi. Importantly, it develops the great pyramidal decussation in the caudal facet of the medulla oblongata, whereby a bulk of the fibers overcome to the opposite side. As a result, fibers originating in the ideal hemisphere will travel in the left lateral funiculus, as the lateral corticospinal tract. The few fibers that did not decussate continue caudally in the ventral funiculus together the ventral (anterior) corticospinal tract. While the lateral corticospinal tract synapses in the anterior grey horn of all spinal segments follow me the size of the spinal cord, the ventral corticospinal tract only regulates the proximal thoracic and also cervical segments.

Vestibulospinal tract

The vestibular nuclei space chiefly responsible for handling special afferent signals from the semicircular canal device of the inside ear , via the vestibular department of the vestibulocochlear nerve (CN VIII). It provides this information (in addition to visual and cerebellar cues) to recognize the spatial relationship of the human body to the environment. The lateral vestibular nucleus sends out ipsilateral efferent fibers referred to as the vestibulospinal tract. As they continue into the anterior funiculus, they ultimately synapse top top the ventral grey horn cells. The effect of this innervation is come inhibit flexor and also promote extensor, muscle task to maintain balance.

*
Vestibulospinal street (axial view) Rubrospinal tract

in ~ the level that the superior colliculus in the tegmentum of the midbrain is a bilaterally paired set of oval nuclei well-known as the red nucleus. The nucleus itself is under constant regulation through corticorubral and also cerebellorubral pathways. Together the fibers emerge from the nucleus, lock decussate to form the rubrospinal tract. These fibers eventually get in the lateral funiculus, wherein they combine with the reflex cells the the anterior grey horn. Therefore, the rubrospinal street indirectly dead regulatory signals from the cerebrum and also cerebellum to inhibit extensor and promote flexor, muscle activity.

*
Rubrospinal street (axial view) Reticulospinal tracts

additionally originating in ~ the red nucleus, the reticular formation is a varied tract the runs follow me the pontomedullary axis. The reticular formation – i beg your pardon principally deals with arousal and maintaining consciousness – forms synapses ~ above nuclei whose fibers that will become the reticulospinal tracts. There room pontine and also medullary divisions of this tract; which also have components that decussate, and those that continue ipsilaterally.

The reticulospinal tracts eventually carry out regulatory impulses come the spinal reflex centers and voluntary movement. It has actually been provided that the pontine reticulospinal tract provides rise to the ventral reticulospinal tract in the ventral funiculus, if the medullary reticulospinal tract descends in the lateral funiculus to form the lateral reticulospinal tract.


*
*

Tectospinal tract

an extremely often individuals respond by jumping far from an object that unexpectedly moves or is viewed as hazardous in ~ the time. This solution is mitigated partially by the tectospinal tract. Intuitive impulses passing through the optic tract gains access to the superior colliculus. The majority of this fibers conveniently decussate to sign up with the medial longitudinal fasciculus soon after leave the premium colliculus. The fibers of the tectospinal tract then enter the ventral funiculus (close to the ventral median sulcus), before terminating in the anterior grey horn the the proximal cervical segments. They incorporate with the reflex centers to produce the postural movements in an answer to visual stimuli.

To end up up your learning, take a deeper look at at some of the particular white matter tracts or take it a quiz on every the tracts and nuclei covered in this article!


Summary

Ascending tracts

Just to recap the ascending spinal tracts:

Lateral spinothalamic carries pain and thermal stimuli.Ventral spinothalamic is responsible because that pressure and also crude touch sensations.Dorsal column is the area the vibration sensation, proprioception, and two-point discriminationSpinocerebellar tracts (anterior and posterior divisions) command unconscious stimuli because that proprioception in joints and also muscles.Cuneocerebellar carries the same info as the spinocerebellar tracts.Other ascending tracts in the spinal cord the are debated in much more detail in other posts include:Spinotectal offer an accessory pathway because that tactile, painful, and thermal stimuli to reach the midbrain.Spino-olivary is an accessory pathway the carries extr information come the cerebellum.

Descending tracts

In summary, the diminish tracts of the spinal cord are:

Lateral and also ventral (anterior) corticospinal tracts attend to voluntary, discrete, skilled motor activities.Lateral and also ventral (anterior) reticulospinal tracts provide excitatory or inhibitory regulation of voluntarily movements and reflexesRubrospinal tract promotes flexor and also inhibit extensor muscle activityVestibulospinal tract disclosure extensor and also inhibit flexor muscle activity. It likewise supports balance and posture.Tectospinal tracts facilitate postural movements arising from visual stimuli.

Sources

References:

Kiernan, J. A, Murray Llewellyn Barr, and Nagalingam Rajakumar: Barr"s The human being Nervous System. 10th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.Moore, Keith together et al. The emerging Human. 9th ed., Elsevier-Saunders, 2013.Sadler, T. W, and also Jan Langman. Langman"s clinical Embryology. 12th ed., Philadelphia, PA, Lippincott Williams & Wilkins, 2012Snell, Richard S. Clinical Neuroanatomy: 7th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2010.

Illustrators:

Structure that the spinal cord (coronal view) - Rebecca BettsCross-sectional check out of the spinal cord - Paul KimOverview the the pyramidal tracts (ventral view) - Paul KimPost central gyrus (coronal view) - Paul KimAnterior spinocerebellar tract (axial view) - Paul KimDorsal spinocerebellar street (axial view) - Paul KimVestibulospinal tract (axial view) - Paul KimRubrospinal street (axial view) - Paul KimTectospinal tract (axial view) - Paul Kim

Ascending and also descending tracts the the spinal cord: desire to learn more about it?

Our engaging videos, interactive quizzes, thorough articles and also HD atlas are here to get you top results faster.

See more: Outlook Has Run Into An Error That Is Preventing It From Working Correctly

What perform you prefer to discover with?


“I would honestly say the rwandachamber.org cut my research time in half.”–Read more.

*
Kim Bengochea, Regis University, Denver