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 brain has plenty of connections with extracranial structures. The spinal cord acts as one of the primary conduits v which the body and the brain exchanges information. The spinal cord is the caudal continuation of the brainstem. It commences at the foramen magnum and traverses the vertebral foramen come the lower border that the first lumbar vertebra (L1) in one adult, and the reduced border of the second or upper border the the third lumbar vertebra (L2/L3) in a growing child.
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The spinal cord has numerous groups the nerve fibers going towards and also coming indigenous the brain. These have been jointly called the ascending and descending tracts the the spinal cord, respectively. The tracts space responsible for delivering sensory and also motor stimuli to and also from the periphery (respectively).
|Lateral spinothalamic||Pain and temperature|
|Ventral spinothalamic||Pressure and crude touch|
|Dorsal column||Vibration, proprioception, two-point discrimination|
|Spinocerebellar||Proprioception in joints and also muscles|
|Cuneocerebellar||Proprioception in joints and also muscles (like the spinocerebellar)|
|Spinotectal||Tactile, painful, and thermal stimuli|
|Spinoreticular||Integration that stimuli native joints and also muscles right into the reticular formation|
|Spino-olivary||Additional info to the cerebellum together an accessory pathway|
|Corticospinal||Voluntary, discrete, experienced motor activities|
|Reticulospinal||Regulation to voluntary movements and also reflexes|
|Rubrospinal||Promotion of flexor and inhibition that extensor muscle activity|
|Vestibulospinal||Inhibition of flexor and promotion of extensor muscle activity|
|Tectospinal||Postural movements from visual stimuli|
The function of this write-up is to give an introduction of the tracts the the spinal cord. An ext detailed discussions around the pathways of the tracts and also some associated disorders deserve to be found in the respective posts for the ascending and descending tracts.
Cross-sectional watch of the spinal cord synopsis of spinal tractsSummary
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summary of spinal cord anatomy
The spinal cord is a cylindrical mass of neural tissue prolonging from the caudal aspect of the medulla oblongata of the brainstem come the level the the first lumbar vertebra (L1). When the size of the spinal cord different from one individual to another, that is usually longer in males (approximately 45 cm) than it is in females (approximately 42 cm). The spinal cord is circumferentially and longitudinally enclosed in all three meningeal layers (i.e. dura, arachnoid and pia mater) and also is exposed in cerebrospinal fluid. That is securely encased in ~ the vertebral canal that the vertebral spine. Because that this reason, the spinal cord additionally has the same locations of lordosis (forward curvature) in the cervical and also lumbar regions, and also kyphosis (backward curvature) in the thoracic and also sacral regions as the vertebral column.
The spinal cord can be equally separated along the midline dorsoventral axis by illustration a line v the depression known as the dorsal and ventral median sulci. Top top each fifty percent of the spinal cord, a ventrolateral and also dorsolateral sulcus is evaluate at the sites from which the ventral and also dorsal nerve roots leave and also enter the spinal cord, respectively. These paired spinal nerve roots also administer a basis because that segmentation the the spinal cord, together they correspond to the vertebra whose intervertebral foramina they take trip through.
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as the spinal cord approaches its most inferior limit, the tapers off to kind the conus medullaris. At the worse border the L1, a filamentous expansion of the spinal cord well-known as the filum terminale is consistent caudally, to the point of insertion in ~ the coccyx. At the lumbar enlargement, the spinal nerves arborize to type the cauda equina, which exit the vertebral canal via the particular foramina.
Cross-sectional see of the spinal cord
Cross-sectional evaluation of the spinal cord reveals that it is comprised of a main area of cell bodies, referred to as grey matter, and a peripheral area the myelinated axons well-known as the white matter.
Grey obelisk of the spinal cord
The grey issue is a butterfly-shaped repertoire of neuronal cell bodies. It is subdivided into the dorsal (posterior), intermediate (lateral), and ventral (anterior) grey columns (horns). The columns are additionally further functionally subdivided based on Rexed’s category such that the dorsal shaft (Rexed laminae ns – VI, and also Clarke’s nucleus, likewise known as the cell nucleus dorsalis) procedures sensory stimuli. ~ above the other hand, the ventral grey pillar (Rexed laminae VIII & IX, and component of VII) includes the cell bodies of the alpha (α) motor fibers the relay info to the suit. The intermediate shaft (containing component of Rexed VII and also VIII) houses cells that create the preganglionic sorry tracts.
Each half of the grey column is united by a horizontal grey commissure with which the central canal runs. The main canal is the caudal extension of the 4th ventricle and thus communicates cranially with the intracranial ventricular systems and cisterns. It additionally serves as a reference allude so the anatomists can identify the grey commissure right into anterior and posterior divisions. The slither that grey matter that overcome dorsally is the posterior grey commissure, if the component that overcome ventrally is the anterior grey commissure.
White column of the spinal cord
The white issue is the repertoire of myelinated nerve fibers that travel to and from the brain. Like the grey matter, it have the right to be subdivided right into anterior (ventral), posterior (dorsal), and also lateral segments dubbed funiculi (s. Funiculus). However, unequal the functional department of the grey matter, the department of the white matter into the corresponding funiculi is done using anatomical landmarks:The anterior funiculus is limited medially by the ventral typical sulcus, and laterally by the ventrolateral sulcus. The lateral funiculus is minimal ventrally and also dorsally by the ventrolateral and dorsolateral sulci. The posterior funiculus is situated lateral to the dorsal mean sulcus, and also medial the dorsolateral sulcus.
The dorsal funiculus is specifically unique in that it can be subdivided into two fasciculi. The gracile fasciculus (fasciculus gracilis) is closer to the dorsal average sulcus, if the cuneate fasciculus (fasciculus cuneatus) is closer to the dorsolateral sulcus. Owing to the fact that there is a somatotopic arrangement the this funiculus, both fasciculi might not be existing at all spinal levels. However, when they space both present, they room separated from each other by the dorsal intermediate sulcus.
Cross-sectional analysis of the spinal cord is a yes, really tricky topic, so don’t stress if you don’t gain it directly away! use our spinal cord diagrams and also quizzes to exercise until you’re emotion confident.
rundown of spinal tracts
the is important to know the jargon associated with the spinal cord tracts in bespeak to evaluate the anatomy and physiology linked with the tracts. The tracts are described according to the funiculus in ~ which they room located. Additionally, a an ext precise location can be given based on the proximity that the tract to the midline. This descriptions are provided in conjunction v the surname of the street to aid in localizing the neuronal pathway. The prefix spino- shows that the street is originating within the spinal tract. Therefore, the lateral spinothalamic tract refers to a swarm of nerve yarn traveling in ~ the lateral funiculus of the spinal cord, which originated within the cord and will terminate within the thalamus.
In contrast, the bundle of fibers well-known as the rubrospinal tract originates indigenous the red nucleus of the midbrain and travels to the spinal cord. However, the reader need to bear in mind that although the tracts are explained as gift confined come a particular region, over there is significant overlap that the tracts in actual life; therefore they may not always obey the prescribed classification systems.
The white matter of the spinal cord contains a mixture the ascending (sensory or afferent) and also descending (motor or efferent) tracts. This tracts room bilaterally combine structures; few of which might cross the midline (decussate) at different levels come relay information to the side of the body, or native the side of the brain, top top the next opposite come the point of origin. An example of this is the corticospinal tract, where fibers originating native the left cerebral cortex decussate at the level that the pyramids in the caudal medulla oblongata to it is provided muscles of the right side of the body.
Ascending tracts that the spinal cord
farming up, the impression was given that there were only 5 senses that humans deserve to detect. These to be sight, smell, sound, taste, and touch. However, that is clear that touch deserve to be further broadened to encompass pain, heat changes, pressure, light (crude) touch, vibration, two-point discrimination, and proprioception. Sight, sound, smell, and taste room special afferent stimuli that room conveyed v their respective cranial nerves. However, the various other tactile modalities room transmitted v the ascending tracts the the spinal cord. There space eight well-known ascending tracts send a selection of sensory stimuli that are discussed below.
acknowledgment of these stimuli is listed by a selection of mechanoreceptors distributed throughout the body. These mechanoreceptors are complimentary nerve endings that are responsive come several species of stimuli. Lock include:
Pacinian corpuscles (for vibration and also pressure sensation) Meissner’s corpuscles (light touch) Merkel’s discs (pressure receptors) Golgi tendons (for proprioception) share receptors nociceptors (for noxious stimuli) muscle spindles (stretch receptors) Lateral spinothalamic tract
Cutaneous sensory receptor transmit painful and also varying thermal stimuli v the dorsal nerve root. The fibers then synapse the dorsal horn that the grey matter. The fibers of the second-order neurons decussate to the contralateral side and also ascend in the lateral spinothalamic tract. This fibers pass with the medulla oblongata, posterior component of the pons, and enter the tegmentum of the midbrain.
The lateral spinothalamic tract contents then synapse top top third-order neurons in the thalamus. Together the stimuli for pain and temperature transforms are handle here, they happen this info through the posterior body of the inner capsule, v the corona radiata to reach the postcentral gyrus (Brodmann 3, 1, 2).
Cutaneous mechanoreceptors that space sensitive to crude (non-discriminative) touch and also pressure transforms transmit stimuli through the dorsal root ganglion. They synapse in the substantia gelatinosa (Rexed II) ~ ascending or descending because that one or 2 segments in the posterolateral tract of Lissauer. Subsequent fibers pass to the various other side via the anterior grey commissure to emerge in the anterior funiculus.
Here, the fibers form the ventral (anterior) spinothalamic tract and also ascend through the medulla oblongata alongside the lateral spinothalamic and spinotectal tracts. Like the lateral spinothalamic tract, the ventral spinothalamic tract likewise synapses ~ above neurons in the thalamus. The remainder the the food of the third-order neurons the this tract is analogous to that of the lateral spinothalamic tract.Dorsal column: Medial lemniscus pathway and cuneocerebellar tracts
plenty of cutaneous receptors detect and also transmit sensory modalities such together light (discriminative) touch, vibration sense, proprioception, and two-point discrimination. Proprioception describes the brain’s ability to discern the actual spatial place of each part of the body. Two-point discrimination refers to the accuracy with which one have the right to detect that a component of the human body is being touched and also that two reasonably close points room being concurrently stimulated. The receptor send impulses v the dorsal root ganglion and directly right into the dorsal funiculus to form the dorsal column.
The fibers break-up to form short descending and long ascending yarn that take part in local reflex arcs. This allows unconscious efferent treatment in instances where a economic stimulation (i.e. Overextension the a limb) becomes harmful. Most of the lengthy ascending fibers go on to type the fasciculus gracilis (throughout the size of the spinal cord) and the fasciculus cuneatus (at and over the level of the sixth thoracic vertebra). Both set of fibers travel ipsilaterally, through the gracile fasciculus carrying stimuli from the reduced limbs and lower 6 thoracic segments (T7 – T12) and also the cuneate fasciculus send stimuli from the upper 6 (T1 – T6) and all of the cervical vertebrae.
They each terminate at their particular nucleus (gracile and also cuneate) in ~ the medulla oblongata. The second order neurons produce the internal arcuate fibers that pass contralaterally with the sensory decussation, to kind the medial lemniscus pathway. The fibers continue towards the thalamus and also then come Brodmann’s areas 3, 1, 2.
the note, the fibers arising from the cuneate nucleus form the posterior outside arcuate fibers the travel with the worse cerebellar peduncle, to go into the cerebellum. This is known as the cuneocerebellar tract, which carries joint position and also proprioception to the cerebellum.Ventral (anterior) spinocerebellar
The mechanoreceptors lug sensory information from the upper and lower limbs and trunk to the dorsal source ganglion the the eighth cervical through to the 3rd lumbar (C8 – L3) segments. They go into the dorsal grey horn and also synapse ~ above the nucleus dorsalis (Clarke’s nucleus). Keep in mind that Clarke’s nucleus is only found in between C8 – L3. Thus fibers arising over or listed below that level will travel through the dorsal white column until they arrive at the nearest level.
no all the fibers of this tract continue toward the cerebellum on the same side. Just a decimal of fibers will proceed in the ipsilateral lateral funiculus; while the bulk of the fibers will certainly decussate to type the ventral spinocerebellar tract of the contralateral lateral funiculus. Both tracts will certainly ascend v the medulla oblongata, and accessibility the cerebellar cortex through their particular superior cerebellar peduncle. However, it has been theorized that the bulk of the contralateral fibers travel through the middle cerebellar peduncle, to cross back to the initial side.Dorsal (posterior) spinocerebellar
The dorsal spinocerebellar tract additionally carries unconscious proprioception come the cerebellum but from the reduced limbs and also trunk. Choose the ventral spinocerebellar tract, this information is relayed to Clarke’s nucleus after ~ passing with the dorsal root ganglion.
However, unequal the ventral counterpart, axons of the second-order neurons indigenous Clarke’s cell core pertaining to this tract go into the posterolateral element of the ipsilateral lateral funiculus. As it creates the dorsal spinocerebellar tract, the fibers ascend to the medulla oblongata and also enter the inferior cerebellar peduncle. Castle then combine with the mossy fibers of the rostral and caudal cerebellar vermis.
diminish tracts that the spinal cord
Muscular contraction versus a fairly fixed skeletal system is the principal attribute of the musculoskeletal system that facilitates locomotion. However, muscle fibers space dependent on activity potentials produced by the spinal engine neurons that the anterior grey horn in stimulate to develop a movement. Both conscious and unconscious regulation of these lower engine neurons that the anterior grey horn is completed by countless upper motor neuron pathways the originate above the level of speak (i.e. Cerebral cortex, cerebellum, etc.). The action of the upper motor neurons carry out stimulatory and inhibitory modulation the the activity of the anterior horn cells, and by extension, the activity of the engine system.
unlike the sensory pathways, whereby the first-order neurons were at the level the the spinal cord and also the third-order neurons to be in the brain, the engine system has actually first-order neurons in ~ the brain and third-order neurons in ~ the anterior grey column.Corticospinal tracts
The large pyramidal cells that the lamina pyramidalis interna (the internal pyramidal layer; fifth histological layer) of the cerebral cortex room the first-order neurons of the corticospinal tract. If the majority of yarn arise indigenous the precentral areas (Brodmann’s locations 4, and also 6), the postcentral gyrus also contributes to its formation as well. However, those developing from the postcentral gyrus perform not add to engine regulation. Just the motor component of the corticospinal tract will get involved in regulating voluntary movement. Also, note that over there is a somatotopic arrangement of the corticospinal tract the is finest understood by reviewing the engine homunculus.
The corticospinal street travels in the contrary direction to the terminal parts of the spinothalamic and medial lemniscus tracts. It pipeline the cortex v the corona radiata and internal capsule prior to passing v the basis pedunculi. Importantly, it develops the great pyramidal decussation in the caudal element of the medulla oblongata, where a bulk of the fibers cross to opposing side. As a result, fibers originating in the best hemisphere will travel in the left lateral funiculus, as the lateral corticospinal tract. The couple of fibers that did no decussate continue caudally in the ventral funiculus as the ventral (anterior) corticospinal tract. While the lateral corticospinal tract synapse in the anterior grey horn of all spinal segments along the length of the spinal cord, the ventral corticospinal tract only regulates the proximal thoracic and cervical segments.Vestibulospinal tract
The vestibular nuclei are chiefly responsible for handling special afferent signals from the semicircular canal device of the inside ear , via the vestibular division of the vestibulocochlear nerve (CN VIII). It uses this information (in addition to visual and also cerebellar cues) to identify the spatial relationship the the human body to that environment. The lateral vestibular nucleus sends out out ipsilateral efferent fibers referred to as the vestibulospinal tract. As they proceed into the anterior funiculus, they ultimately synapse ~ above the ventral grey horn cells. The effect of this innervation is come inhibit flexor and also promote extensor, muscle task to maintain balance.
at the level that the premium colliculus in the tegmentum that the midbrain is a bilaterally paired set of oval nuclei known as the red nucleus. The nucleus itself is under constant regulation by corticorubral and cerebellorubral pathways. As the fibers arise from the nucleus, lock decussate to kind the rubrospinal tract. This fibers eventually get in the lateral funiculus, whereby they combine with the reflex cells that the anterior grey horn. Therefore, the rubrospinal tract indirectly tote regulatory signals from the cerebrum and also cerebellum come inhibit extensor and promote flexor, muscle activity.
also originating in ~ the red nucleus, the reticular formation is a diverse tract the runs along the pontomedullary axis. The reticular formation – i m sorry principally encounters arousal and maintaining awareness – develops synapses top top nuclei whose fibers the will end up being the reticulospinal tracts. There space pontine and medullary divisions of this tract; which likewise have contents that decussate, as well as those that continue ipsilaterally.
The reticulospinal tracts eventually provide regulatory impulses come the spinal reflex centers and voluntary movement. It has been detailed that the pontine reticulospinal tract provides rise come the ventral reticulospinal tract in the ventral funiculus, while the medullary reticulospinal tract descends in the lateral funiculus to type the lateral reticulospinal tract.
very often individuals respond by jumping far from an item that suddenly moves or is regarded as hazardous at the time. This solution is mitigated partially by the tectospinal tract. Visual impulses passing through the optic tract gains accessibility to the superior colliculus. The majority of this fibers conveniently decussate to sign up with the medial longitudinal fasciculus soon after leave the exceptional colliculus. The yarn of the tectospinal street then go into the ventral funiculus (close to the ventral typical sulcus), prior to terminating in the anterior grey horn of the proximal cervical segments. They combine with the reflex centers to develop the postural movements in response to visual stimuli.
To end up up your learning, take a deeper look at at several of the specific white issue tracts or take it a quiz on all the tracts and also nuclei spanned in this article!
Just to recap the ascending spinal tracts:Lateral spinothalamic carries pain and thermal stimuli.Ventral spinothalamic is responsible for pressure and crude touch sensations.Dorsal column is the area of vibration sensation, proprioception, and also two-point discrimination. Spinocerebellar tracts (anterior and also posterior divisions) conduct unconscious stimuli for proprioception in joints and muscles.Cuneocerebellar tote the same details as the spinocerebellar tracts.Other ascending tracts in the spinal cord the are discussed in an ext detail in other write-ups include:Spinotectal serves an accessory pathway because that tactile, painful, and also thermal stimuli to with the midbrain.Spino-olivary is an accessory pathway that carries added information come the cerebellum.
In summary, the descending tracts that the spinal cord are:Lateral and ventral (anterior) corticospinal tracts deal with voluntary, discrete, skilled motor activities.Lateral and also ventral (anterior) reticulospinal tracts provide excitatory or inhibitory regulation of voluntary movements and reflexesRubrospinal tract disclosure flexor and also inhibit extensor muscle activityVestibulospinal tract promotes extensor and inhibit flexor muscle activity. It also supports balance and posture.Tectospinal tracts facilitate postural movements developing from intuitive stimuli.
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 developing Human. Nine ed., Elsevier-Saunders, 2013.Sadler, T. W, and Jan Langman. Langman"s medical 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 of the spinal cord (coronal view) - Rebecca BettsCross-sectional check out of the spinal cord - Paul KimOverview of 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 tract (axial view) - Paul KimTectospinal street (axial view) - Paul Kim
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