What is the difference between a descending tract and an ascending tract

These cells are located at all levels of the spinal cord and are grouped into three main categories: root cells, column or tract cells and propriospinal cells. The root cells are situated in the ventral and lateral gray horns and vary greatly in size.

The root cells contribute their axons to the ventral roots of the spinal nerves and are grouped into two major divisions: 1 somatic efferent root neurons, which innervate the skeletal musculature; and 2 the visceral efferent root neurons, also called preganglionic autonomic axons, which send their axons to various autonomic ganglia.

The column or tract cells and their processes are located mainly in the dorsal gray horn and are confined entirely within the CNS. The axons of the column cells form longitudinal ascending tracts that ascend in the white columns and terminate upon neurons located rostrally in the brain stem, cerebellum or diencephalon. Some column cells send their axons up and down the cord to terminate in gray matter close to their origin and are known as intersegmental association column cells.

Other column cell axons terminate within the segment in which they originate and are called intrasegmental association column cells. Still other column cells send their axons across the midline to terminate in gray matter close to their origin and are called commissure association column cells. The propriospinal cells are spinal interneurons whose axons do not leave the spinal cord proper.

Some of these fibers also are found around the margin of the gray matter of the cord and are collectively called the fasciculus proprius or the propriospinal or the archispinothalamic tract. The prominent nuclear groups of cell columns within the spinal cord from dorsal to ventral are the marginal zone, substantia gelatinosa, nucleus proprius, dorsal nucleus of Clarke, intermediolateral nucleus and the lower motor neuron nuclei. The axons of its neurons contribute to the lateral spinothalamic tract which relays pain and temperature information to the diencephalon Figure 3.

Substantia gelatinosa is found at all levels of the spinal cord. Located in the dorsal cap-like portion of the head of the dorsal horn, it relays pain, temperature and mechanical light touch information and consists mainly of column cells intersegmental column cells. These column cells synapse in cell at Rexed layers IV to VII, whose axons contribute to the ventral anterior and lateral spinal thalamic tracts. The homologous substantia gelatinosa in the medulla is the spinal trigeminal nucleus.

Nucleus proprius is located below the substantia gelatinosa in the head and neck of the dorsal horn. This cell group, sometimes called the chief sensory nucleus, is associated with mechanical and temperature sensations. It is a poorly defined cell column which extends through all segments of the spinal cord and its neurons contribute to ventral and lateral spinal thalamic tracts, as well as to spinal cerebellar tracts.

The axons originating in nucleus proprius project to the thalamus via the spinothalamic tract and to the cerebellum via the ventral spinocerebellar tract VSCT. Dorsal nucleus of Clarke is a cell column located in the mid-portion of the base form of the dorsal horn.

The axons from these cells pass uncrossed to the lateral funiculus and form the dorsal posterior spinocerebellar tract DSCT , which subserve unconscious proprioception from muscle spindles and Golgi tendon organs to the cerebellum, and some of them innervate spinal interneurons.

The dorsal nucleus of Clarke is found only in segments C8 to L3 of the spinal cord and is most prominent in lower thoracic and upper lumbar segments.

The homologous dorsal nucleus of Clarke in the medulla is the accessory cuneate nucleus, which is the origin of the cuneocerebellar tract CCT. Intermediolateral nucleus is located in the intermediate zone between the dorsal and the ventral horns in the spinal cord levels.

Extending from C8 to L3, it receives viscerosensory information and contains preganglionic sympathetic neurons, which form the lateral horn. A large proportion of its cells are root cells which send axons into the ventral spinal roots via the white rami to reach the sympathetic tract as preganglionic fibers. Similarly, cell columns in the intermediolateral nucleus located at the S2 to S4 levels contains preganglionic parasympathetic neurons Figure 3.

Lower motor neuron nuclei are located in the ventral horn of the spinal cord. The a motor neurons are the final common pathway of the motor system, and they innervate the visceral and skeletal muscles.

The distribution of cells and fibers within the gray matter of the spinal cord exhibits a pattern of lamination.

The cellular pattern of each lamina is composed of various sizes or shapes of neurons cytoarchitecture which led Rexed to propose a new classification based on 10 layers laminae. This classification is useful since it is related more accurately to function than the previous classification scheme which was based on major nuclear groups Figure 3. Laminae I to IV, in general, are concerned with exteroceptive sensation and comprise the dorsal horn, whereas laminae V and VI are concerned primarily with proprioceptive sensations.

Lamina VII is equivalent to the intermediate zone and acts as a relay between muscle spindle to midbrain and cerebellum, and laminae VIII-IX comprise the ventral horn and contain mainly motor neurons.

The axons of these neurons innervate mainly skeletal muscle. Lamina X surrounds the central canal and contains neuroglia. Rexed lamina I — Consists of a thin layer of cells that cap the tip of the dorsal horn with small dendrites and a complex array of nonmyelinated axons. Cells in lamina I respond mainly to noxious and thermal stimuli. Lamina I cell axons join the contralateral spinothalamic tract; this layer corresponds to nucleus posteromarginalis.

Rexed lamina II — Composed of tightly packed interneurons. This layer corresponds to the substantia gelatinosa and responds to noxious stimuli while others respond to non-noxious stimuli. The majority of neurons in Rexed lamina II axons receive information from sensory dorsal root ganglion cells as well as descending dorsolateral fasciculus DLF fibers.

High concentrations of substance P and opiate receptors have been identified in Rexed lamina II. The lamina is believed to be important for the modulation of sensory input, with the effect of determining which pattern of incoming information will produce sensations that will be interpreted by the brain as being painful.

Rexed lamina III — Composed of variable cell size, axons of these neurons bifurcate several times and form a dense plexus. Rexed lamina IV — The thickest of the first four laminae. In addition, dendrites of neurons in lamina IV radiate to lamina II, and respond to stimuli such as light touch. The ill-defined nucleus proprius is located in the head of this layer.

Some of the cells project to the thalamus via the contralateral and ipsilateral spinothalamic tract. Rexed lamina V — Composed neurons with their dendrites in lamina II. This lamina covers a broad zone extending across the neck of the dorsal horn and is divided into medial and lateral parts. Many of the Rexed lamina V cells project to the brain stem and the thalamus via the contralateral and ipsilateral spinothalamic tract.

Moreover, descending corticospinal and rubrospinal fibers synapse upon its cells. Rexed lamina VI — Is a broad layer which is best developed in the cervical and lumbar enlargements. Lamina VI divides also into medial and lateral parts. Group Ia afferent axons from muscle spindles terminate in the medial part at the C8 to L3 segmental levels and are the source of the ipsilateral spinocerebellar pathways.

Many of the small neurons are interneurons participating in spinal reflexes, while descending brainstem pathways project to the lateral zone of Rexed layer VI.

Rexed lamina VII — This lamina occupies a large heterogeneous region. This region is also known as the zona intermedia or intermediolateral nucleus. Dorsal column pathway. Anatomy of the pons. Tracts ascending and descending.

Ascending tracts. The spinal cord. Hema practical 05 hema staining. Hema practical 03 coagulation. Hema practical 02 hematology. Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd. Uzma Begum. Akanksha Mittal. Devi Priya. Sadaf Hassan , -- at Self-employed. Charity Nkonde. Share Tweet.

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This allows us to get in touch for more details if required. Please write a single word answer in lowercase this is an anti-spam measure. This field is for validation purposes and should be left unchanged. Introduction The central nervous system uses ascending and descending pathways to communicate with the external environment.

These are: Dorsal column and the medial lemniscus Spinothalamic tracts Spinocerebellar tracts You might also be interested in our Anatomy Flashcard Collection which contains over anatomy flashcards in addition to advanced features such as spaced repetition. Clinical relevance: assessing the ascending tracts Clinically, we assess two major sensory systems: the dorsal columns and the anterolateral system.

The dorsal columns are assesed by: Vibration: Hz tuning fork Joint propriocption: small-joint movement thumb, big toe Light touch: cotton wool The spinothalamic tracts are assessed by: Pain: pin-prick Temperature: cool and warm metal object. Clinical relevance: spinal cord syndromes A hemitransection, also known as Brown-Sequard syndrome , is the severing of one half of the spinal cord. Figure 3. Brown-Sequard table Notice that all the tracts affected are ipsilateral except for the spinothalamic tract , which is the only tract to decussate at or near the level of the spinal nerve root.

These deficits can be tailored to a lesion occurring at any spinal level. Figure 4. The tracts are responsible for carrying sensory and motor stimuli to and from the periphery respectively. Similarly, where are ascending and descending tracts located? Ascending tracts are found in all columns whereas descending tracts are found only in the lateral and the anterior columns. The spinal cord white matter and its three columns, and the topographical location of the main ascending spinal cord tracts.

In nervous system: The vertebrate system. Ascending tracts carry impulses along the spinal cord toward the brain, and descending tracts carry them from the brain or higher regions in the spinal cord to lower regions. The fasciculus gracilis is found throughout the spinal cord and begins at the caudal end of the spinal cord.

It comprises long ascending fibers from different spinal nerves which enter the spinal cord through the ipsilateral dorsal spinal root, including sacral, lumbar and lower six thoracic nerves.

Asked by: Veronique Elleboro asked in category: General Last Updated: 23rd April, What is the difference between the ascending and descending tracts of the spinal cord?

The only difference is the different locations where each order of neuron ends. Decussation is the cross-over of the tract from one side to the other. Therefore, there are instances where the left side of the body is controlled by the right brain hemisphere. What is the function of ascending tracts of the spinal cord? The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex.