Inferior End Of Spinal Cord
Chapter 3: Beefcake of the Spinal Cord
3.ane Introduction
| Figure 3.1 |
The spinal string is the most important structure between the body and the brain. The spinal string extends from the foramen magnum where information technology is continuous with the medulla to the level of the first or second lumbar vertebrae. Information technology is a vital link between the brain and the body, and from the torso to the brain. The spinal cord is 40 to 50 cm long and 1 cm to 1.5 cm in bore. Ii consecutive rows of nerve roots emerge on each of its sides. These nervus roots join distally to grade 31 pairs of spinal nerves. The spinal cord is a cylindrical construction of nervous tissue composed of white and grey matter, is uniformly organized and is divided into four regions: cervical (C), thoracic (T), lumbar (50) and sacral (Due south), (Figure 3.1), each of which is comprised of several segments. The spinal nerve contains motor and sensory nerve fibers to and from all parts of the body. Each spinal cord segment innervates a dermatome (run into beneath and Figure 3.v).
iii.2 General Features
- Similar cross-exclusive structures at all spinal cord levels (Figure 3.1).
- It carries sensory information (sensations) from the body and some from the head to the cardinal nervous system (CNS) via afferent fibers, and it performs the initial processing of this information.
- Motor neurons in the ventral horn project their axons into the periphery to innervate skeletal and smooth muscles that mediate voluntary and involuntary reflexes.
- It contains neurons whose descending axons mediate autonomic control for most of the visceral functions.
- Information technology is of great clinical importance considering it is a major site of traumatic injury and the locus for many disease processes.
Although the spinal string constitutes just almost 2% of the central nervous organisation (CNS), its functions are vital. Knowledge of spinal string functional beefcake makes it possible to diagnose the nature and location of cord damage and many string diseases.
3.three Segmental and Longitudinal Organisation
The spinal cord is divided into four different regions: the cervical, thoracic, lumbar and sacral regions (Figure 3.one). The dissimilar string regions tin be visually distinguished from one another. 2 enlargements of the spinal cord tin be visualized: The cervical enlargement, which extends between C3 to T1; and the lumbar enlargements which extends between L1 to S2 (Figure three.1).
The cord is segmentally organized. There are 31 segments, defined by 31 pairs of fretfulness exiting the cord. These nerves are divided into 8 cervical, 12 thoracic, five lumbar, 5 sacral, and ane coccygeal nerve (Effigy three.2). Dorsal and ventral roots enter and exit the vertebral column respectively through intervertebral foramen at the vertebral segments corresponding to the spinal segment.
| Effigy 3.2 |
The cord is sheathed in the same three meninges every bit is the brain: the pia, arachnoid and dura. The dura is the tough outer sheath, the arachnoid lies beneath it, and the pia closely adheres to the surface of the cord (Effigy 3.3). The spinal cord is attached to the dura by a series of lateral denticulate ligaments emanating from the pial folds.
| Figure iii.3 |
During the initial third month of embryonic development, the spinal cord extends the entire length of the vertebral culvert and both grow at about the same rate. As development continues, the body and the vertebral column go along to grow at a much greater rate than the spinal string proper. This results in deportation of the lower parts of the spinal cord with relation to the vertebrae column. The outcome of this uneven growth is that the adult spinal string extends to the level of the first or second lumbar vertebrae, and the nerves grow to exit through the aforementioned intervertebral foramina as they did during embryonic development. This growth of the nerve roots occurring within the vertebral canal, results in the lumbar, sacral, and coccygeal roots extending to their appropriate vertebral levels (Figure 3.2).
All spinal fretfulness, except the kickoff, exit below their corresponding vertebrae. In the cervical segments, at that place are seven cervical vertebrae and 8 cervical fretfulness (Figure 3.2). C1-C7 nerves exit in a higher place their vertebrae whereas the C8 nerve exits below the C7 vertebra. Information technology leaves between the C7 vertebra and the first thoracic vertebra. Therefore, each subsequent nerve leaves the cord beneath the respective vertebra. In the thoracic and upper lumbar regions, the difference between the vertebrae and cord level is 3 segments. Therefore, the root filaments of spinal cord segments have to travel longer distances to reach the respective intervertebral foramen from which the spinal nerves emerge. The lumbosacral roots are known as the cauda equina (Figure three.ii).
Each spinal nervus is composed of nervus fibers that are related to the region of the muscles and skin that develops from ane body somite (segment). A spinal segment is divers past dorsal roots inbound and ventral roots exiting the cord, (i.e., a spinal cord section that gives ascent to one spinal nervus is considered as a segment.) (Effigy iii.4).
| Effigy 3.4 |
A dermatome is an expanse of skin supplied by peripheral nerve fibers originating from a single dorsal root ganglion. If a nerve is cutting, one loses awareness from that dermatome. Because each segment of the cord innervates a different region of the body, dermatomes can be precisely mapped on the body surface, and loss of sensation in a dermatome can indicate the exact level of spinal string damage in clinical assessment of injury (Figure 3.v). It is important to consider that at that place is some overlap between neighboring dermatomes. Because sensory information from the torso is relayed to the CNS through the dorsal roots, the axons originating from dorsal root ganglion cells are classified equally principal sensory afferents, and the dorsal root's neurons are the first lodge (1°) sensory neuron. Most axons in the ventral roots ascend from motor neurons in the ventral horn of the spinal string and innervate skeletal muscle. Others arise from the lateral horn and synapse on autonomic ganglia that innervate visceral organs. The ventral root axons join with the peripheral processes of the dorsal root ganglion cells to form mixed afferent and efferent spinal nerves, which merge to class peripheral fretfulness. Knowledge of the segmental innervation of the cutaneous area and the muscles is essential to diagnose the site of an injury.
| Figure 3.v |
3.4 Internal Structure of the Spinal Cord
A transverse section of the developed spinal cord shows white matter in the periphery, gray thing inside, and a tiny central canal filled with CSF at its centre. Surrounding the culvert is a unmarried layer of cells, the ependymal layer. Surrounding the ependymal layer is the gray matter – a region containing cell bodies – shaped like the letter "H" or a "butterfly". The two "wings" of the butterfly are continued across the midline by the dorsal gray commissure and below the white commissure (Figure 3.vi). The shape and size of the gray matter varies according to spinal string level. At the lower levels, the ratio between greyness matter and white matter is greater than in college levels, mainly because lower levels contain less ascending and descending nerve fibers. (Figure 3.one and Figure three.half-dozen).
| Figure iii.vi |
The gray affair mainly contains the prison cell bodies of neurons and glia and is divided into iv chief columns: dorsal horn, intermediate cavalcade, lateral horn and ventral horn column. (Figure 3.6).
The dorsal horn is found at all spinal cord levels and is comprised of sensory nuclei that receive and process incoming somatosensory data. From there, ascending projections emerge to transmit the sensory information to the midbrain and diencephalon. The intermediate column and the lateral horn contain autonomic neurons innervating visceral and pelvic organs. The ventral horn comprises motor neurons that innervate skeletal muscle.
At all the levels of the spinal cord, nerve cells in the greyness substance are multipolar, varying much in their morphology. Many of them are Golgi type I and Golgi type 2 nerve cells. The axons of Golgi type I are long and pass out of the gray thing into the ventral spinal roots or the fiber tracts of the white matter. The axons and dendrites of the Golgi type II cells are largely confined to the neighboring neurons in the gray affair.
A more recent classification of neurons within the grey matter is based on function. These cells are located at all levels of the spinal string 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 grey horns and vary greatly in size. The most prominent features of the root cells are large multipolar elements exceeding 25 µm of their somata. The root cells contribute their axons to the ventral roots of the spinal nerves and are grouped into two major divisions: ane) somatic efferent root neurons, which innervate the skeletal musculature; and ii) the visceral efferent root neurons, also chosen preganglionic autonomic axons, which send their axons to diverse autonomic ganglia.
The column or tract cells and their processes are located mainly in the dorsal grey horn and are confined entirely inside the CNS. The axons of the column cells form longitudinal ascending tracts that ascend in the white columns and stop upon neurons located rostrally in the encephalon stalk, cerebellum or diencephalon. Some column cells ship their axons upwards and downwardly the string to terminate in gray affair close to their origin and are known every bit intersegmental association cavalcade cells. Other column cell axons end within the segment in which they originate and are called intrasegmental clan column cells. Still other column cells transport their axons across the midline to terminate in gray matter close to their origin and are called commissure clan column cells.
The propriospinal cells are spinal interneurons whose axons exercise non get out the spinal cord proper. Propriospinal cells business relationship for nearly 90% of spinal neurons. Some of these fibers besides are found around the margin of the grayness matter of the cord and are collectively called the fasciculus proprius or the propriospinal or the archispinothalamic tract.
three.5 Spinal String Nuclei and Laminae
Spinal neurons are organized into nuclei and laminae.
3.6 Nuclei
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.
| Figure 3.seven |
Marginal zone nucleus or posterior marginalis, is plant at all spinal cord levels as a thin layer of column/tract cells (column cells) that caps the tip of the dorsal horn. The axons of its neurons contribute to the lateral spinothalamic tract which relays pain and temperature information to the diencephalon (Figure iii.7).
Substantia gelatinosa is found at all levels of the spinal cord. Located in the dorsal cap-similar portion of the head of the dorsal horn, information technology relays pain, temperature and mechanical (lite touch) data and consists mainly of column cells (intersegmental column cells). These column cells synapse in cell at Rexed layers Four 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 of operations form of the dorsal horn. The axons from these cells laissez passer 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 constitute just in segments C8 to L3 of the spinal string and is virtually 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 betwixt 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 class the lateral horn. A big 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 3.7).
Lower motor neuron nuclei are located in the ventral horn of the spinal cord. They contain predominantly motor nuclei consisting of α, β and γ motor neurons and are found at all levels of the spinal cord--they are root cells. The a motor neurons are the last common pathway of the motor system, and they innervate the visceral and skeletal muscles.
3.vii Rexed Laminae
The distribution of cells and fibers within the gray matter of the spinal cord exhibits a blueprint of lamination. The cellular blueprint of each lamina is equanimous of various sizes or shapes of neurons (cytoarchitecture) which led Rexed to suggest a new classification based on ten layers (laminae). This classification is useful since it is related more accurately to office than the previous classification scheme which was based on major nuclear groups (Figure 3.7).
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 every bit 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 prison cell axons join the contralateral spinothalamic tract; this layer corresponds to nucleus posteromarginalis.
Rexed lamina II – Equanimous of tightly packed interneurons. This layer corresponds to the substantia gelatinosa and responds to noxious stimuli while others reply to non-noxious stimuli. The majority of neurons in Rexed lamina 2 axons receive information from sensory dorsal root ganglion cells likewise as descending dorsolateral fasciculus (DLF) fibers. They send axons to Rexed laminae III and IV (fasciculus proprius). High concentrations of substance P and opiate receptors have been identified in Rexed lamina Ii. The lamina is believed to exist important for the modulation of sensory input, with the effect of determining which pattern of incoming information volition produce sensations that will be interpreted by the brain as beingness painful.
Rexed lamina III – Equanimous of variable cell size, axons of these neurons bifurcate several times and form a dense plexus. Cells in this layer receive axodendritic synapses from Aβ fibers inbound dorsal root fibers. It contains dendrites of cells from laminae Four, V and VI. Nearly of the neurons in lamina 3 office as propriospinal/interneuron cells.
Rexed lamina IV – The thickest of the first four laminae. Cells in this layer receive Aß axons which carry predominantly non-baneful data. In addition, dendrites of neurons in lamina IV radiate to lamina II, and respond to stimuli such as calorie-free bear on. The ill-defined nucleus proprius is located in the head of this layer. Some of the cells projection to the thalamus via the contralateral and ipsilateral spinothalamic tract.
Rexed lamina 5 – Composed neurons with their dendrites in lamina Two. The neurons in this lamina receive monosynaptic information from Aß, Ad and C axons which also carry nociceptive data from visceral organs. This lamina covers a broad zone extending beyond the neck of the dorsal horn and is divided into medial and lateral parts. Many of the Rexed lamina Five 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 6 – Is a broad layer which is best developed in the cervical and lumbar enlargements. Lamina Half-dozen 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 big heterogeneous region. This region is also known every bit the zona intermedia (or intermediolateral nucleus). Its shape and boundaries vary along the length of the string. Lamina VII neurons receive data from Rexed lamina II to Vi as well equally visceral afferent fibers, and they serve as an intermediary relay in transmission of visceral motor neurons impulses. The dorsal nucleus of Clarke forms a prominent round oval cell cavalcade from C8 to L3. The big cells give rise to uncrossed nerve fibers of the dorsal spinocerebellar tract (DSCT). Cells in laminae Five to VII, which do not form a detached nucleus, give rising to uncrossed fibers that form the ventral spinocerebellar tract (VSCT). Cells in the lateral horn of the cord in segments T1 and L3 give rise to preganglionic sympathetic fibers to innervate postganglionic cells located in the sympathetic ganglia outside the cord. Lateral horn neurons at segments S2 to S4 requite rise to preganglionic neurons of the sacral parasympathetic fibers to innervate postganglionic cells located in peripheral ganglia.
Rexed lamina 8 – Includes an expanse at the base of the ventral horn, but its shape differs at various string levels. In the cord enlargements, the lamina occupies only the medial function of the ventral horn, where descending vestibulospinal and reticulospinal fibers terminate. The neurons of lamina 8 modulate motor activity, most probably via g motor neurons which innervate the intrafusal muscle fibers.
Rexed lamina Ix – Equanimous of several singled-out groups of big a motor neurons and small γ and β motor neurons embedded within this layer. Its size and shape differ at various string levels. In the cord enlargements the number of α motor neurons increase and they form numerous groups. The α motor neurons are large and multipolar cells and give ascension to ventral root fibers to supply extrafusal skeletal muscle fibers, while the modest γ motor neurons give rise to the intrafusal musculus fibers. The α motor neurons are somatotopically organized.
Rexed lamina 10 – Neurons in Rexed lamina X environs the cardinal culvert and occupy the commissural lateral expanse of the gray commissure, which also contains decussating axons.
In summary, laminae I-IV are concerned with exteroceptive sensations, whereas laminae Five and VI are concerned primarily with proprioceptive sensation and deed as a relay between the periphery to the midbrain and the cerebellum. Laminae VIII and IX form the concluding motor pathway to initiate and modulate motor activity via α, β and γ motor neurons, which innervate striated muscle. All visceral motor neurons are located in lamina Seven and innervate neurons in autonomic ganglia.
3.eight White Matter
Surrounding the gray matter is white thing containing myelinated and unmyelinated nervus fibers. These fibers comport information upward (ascending) or down (descending) the cord. The white matter is divided into the dorsal (or posterior) column (or funiculus), lateral cavalcade and ventral (or anterior) column (Figure 3.eight). The inductive white commissure resides in the centre of the spinal cord, and it contains crossing nervus fibers that vest to the spinothalamic tracts, spinocerebellar tracts, and anterior corticospinal tracts. Three general nerve fiber types can be distinguished in the spinal cord white matter: one) long ascending nerve fibers originally from the column cells, which make synaptic connections to neurons in various brainstem nuclei, cerebellum and dorsal thalamus, two) long descending nerve fibers originating from the cognitive cortex and diverse brainstem nuclei to synapse within the different Rexed layers in the spinal cord greyness matter, and 3) shorter nerve fibers interconnecting various spinal cord levels such equally the fibers responsible for the coordination of flexor reflexes. Ascending tracts are found in all columns whereas descending tracts are establish only in the lateral and the inductive columns.
| Figure 3.8 |
Four different terms are often used to depict bundles of axons such as those found in the white matter: funiculus, fasciculus, tract, and pathway. Funiculus is a morphological term to describe a big grouping of nervus fibers which are located in a given area (e.1000., posterior funiculus). Within a funiculus, groups of fibers from various origins, which share common features, are sometimes bundled in smaller bundles of axons called fasciculus, (e.g., fasciculus proprius [Figure 3.viii]). Fasciculus is primarily a morphological term whereas tracts and pathways are also terms applied to nerve fiber bundles which have a functional connotation. A tract is a grouping of nerve fibers which usually has the same origin, destination, and form and also has like functions. The tract proper noun is derived from their origin and their termination (i.east., corticospinal tract - a tract that originates in the cortex and terminates in the spinal string; lateral spinothalamic tract - a tract originated in the lateral spinal cord and ends in the thalamus). A pathway unremarkably refers to the entire neuronal excursion responsible for a specific part, and it includes all the nuclei and tracts which are associated with that office. For instance, the spinothalamic pathway includes the cell bodies of origin (in the dorsal root ganglia), their axons as they project through the dorsal roots, synapses in the spinal string, and projections of second and third order neurons across the white commissure, which ascend to the thalamus in the spinothalamic tracts.
3.9 Spinal Cord Tracts
The spinal cord white matter contains ascending and descending tracts.
Ascending tracts (Effigy 3.viii). The nerve fibers contain the ascending tract sally from the first order (1°) neuron located in the dorsal root ganglion (DRG). The ascending tracts transmit sensory information from the sensory receptors to higher levels of the CNS. The ascending gracile and cuneate fasciculi occupying the dorsal cavalcade, and sometimes are named the dorsal funiculus. These fibers bear information related to tactile, two bespeak discrimination of simultaneously applied pressure level, vibration, position, and movement sense and conscious proprioception. In the lateral column (funiculus), the neospinothalamic tract (or lateral spinothalamic tract) is located more anteriorly and laterally, and carries hurting, temperature and rough touch data from somatic and visceral structures. Nearby laterally, the dorsal and ventral spinocerebellar tracts carry unconscious proprioception information from muscles and joints of the lower extremity to the cerebellum. In the ventral column (funiculus) there are four prominent tracts: one) the paleospinothalamic tract (or anterior spinothalamic tract) is located which carry pain, temperature, and data associated with touch to the encephalon stem nuclei and to the diencephalon, 2) the spinoolivary tract carries information from Golgi tendon organs to the cerebellum, 3) the spinoreticular tract, and 4) the spinotectal tract. Intersegmental nerve fibers traveling for several segments (ii to 4) and are located every bit a thin layer around the gray matter is known equally fasciculus proprius, spinospinal or archispinothalamic tract. It carries hurting data to the brain stalk and diencephalon.
Descending tracts (Effigy iii.nine). The descending tracts originate from different cortical areas and from encephalon stem nuclei. The descending pathway conduct data associated with maintenance of motor activities such equally posture, residuum, muscle tone, and visceral and somatic reflex action. These include the lateral corticospinal tract and the rubrospinal tracts located in the lateral cavalcade (funiculus). These tracts bear data associated with voluntary movement. Other tracts such every bit the reticulospinal vestibulospinal and the anterior corticospinal tract mediate balance and postural movements (Figure iii.9). Lissauer'southward tract, which is wedged between the dorsal horn and the surface of the spinal cord carry the descending fibers of the dorsolateral funiculus (DFL), which regulate incoming pain awareness at the spinal level, and intersegmental fibers. Boosted details most ascending and descending tracts are described in the adjacent few capacity.
| Figure 3.9 |
iii.10 Dorsal Root
| Figure three.ten |
Data from the pare, skeletal musculus and joints is relayed to the spinal cord by sensory cells located in the dorsal root ganglia. The dorsal root fibers are the axons originated from the chief sensory dorsal root ganglion cells. Each ascending dorsal root axon, before reaching the spinal cord, bifurcates into ascending and descending branches entering several segments below and higher up their own segment. The ascending dorsal root fibers and the descending ventral root fibers from and to discrete body areas form a spinal nervus (Figure 3.10). In that location are 31 paired spinal fretfulness. The dorsal root fibers segregate into lateral and medial divisions. The lateral division contains about of the unmyelinated and small myelinated axons carrying pain and temperature information to be terminated in the Rexed laminae I, II, and IV of the greyness matter. The medial segmentation of dorsal root fibers consists mainly of myelinated axons conducting sensory fibers from pare, muscles and joints; information technology enters the dorsal/posterior column/funiculus and arise in the dorsal column to exist terminated in the ipsilateral nucleus gracilis or nucleus cuneatus at the medulla oblongata region, i.east., the axons of the beginning-society (i°) sensory neurons synapse in the medulla oblongata on the second order (2°) neurons (in nucleus gracilis or nucleus cuneatus). In entering the spinal cord, all fibers send collaterals to different Rexed lamina.
Axons entering the cord in the sacral region are found in the dorsal cavalcade almost the midline and comprise the fasciculus gracilis, whereas axons that enter at higher levels are added in lateral positions and contain the fasciculus cuneatus (Effigy iii.11). This orderly representation is termed "somatotopic representation".
| Figure three.eleven |
3.11 Ventral Root
Ventral root fibers are the axons of motor and visceral efferent fibers and emerge from poorly defined ventral lateral sulcus every bit ventral rootlets. The ventral rootlets from discrete spinal cord section unite and form the ventral root, which contain motor nervus axons from motor and visceral motor neurons. The α motor nervus axons innervate the extrafusal musculus fibers while the small γ motor neuron axons innervate the intrafusal muscle fibers located within the muscle spindles. The visceral neurons send preganglionic fibers to innervate the visceral organs. All these fibers join the dorsal root fibers distal to the dorsal root ganglion to form the spinal nerve (Figure 3.10).
iii.12 Spinal Nerve Roots
The spinal nerve roots are formed by the union of dorsal and ventral roots within the intervertebral foramen, resulting in a mixed nerve joined together and forming the spinal nervus (Figure 3.x). Spinal nerve rami include the dorsal master nerves (ramus), which innervates the skin and muscles of the back, and the ventral primary nerves (ramus), which innervates the ventral lateral muscles and pare of the torso, extremities and visceral organs. The ventral and dorsal roots besides provide the anchorage and fixation of the spinal cord to the vertebral cauda.
3.13 Claret Supply of the Spinal Cord
The arterial blood supply to the spinal string in the upper cervical regions is derived from two branches of the vertebral arteries, the anterior spinal artery and the posterior spinal arteries (Figure 3.12). At the level of medulla, the paired inductive spinal arteries join to form a single avenue that lies in the anterior median fissure of the spinal cord. The posterior spinal arteries are paired and course an anastomotic chain over the posterior aspect of the spinal cord. A plexus of pocket-sized arteries, the arterial vasocorona, on the surface of the cord constitutes an anastomotic connection between the anterior and posterior spinal arteries. This organisation provides uninterrupted claret supplies along the unabridged length of the spinal cord.
| Figure three.12 |
At spinal cord regions below upper cervical levels, the anterior and posterior spinal arteries narrow and form an anastomotic network with radicular arteries. The radicular arteries are branches of the cervical, body, intercostal & iliac arteries. The radicular arteries supply nigh of the lower levels of the spinal cord. In that location are approximately 6 to 8 pairs of radicular arteries supplying the inductive and posterior spinal string (Figure 3.12).
Test Your Cognition
- Question 1
- A
- B
- C
- D
- E
The spinal cord...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments
C. Contains the cell bodies of postganglionic sympathetic efferent neurons
D. Ends at the conus medullaris
E. Has no arachnoid membrane
The spinal string...
A. Occupies the lumbar cistern This answer is Wrong.
The spinal cord does non occupy the lumbar cistern.
B. Has twelve (12) cervical segments
C. Contains the cell bodies of postganglionic sympathetic efferent neurons
D. Ends at the conus medullaris
Due east. Has no arachnoid membrane
The spinal cord...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments This respond is INCORRECT.
The spinal string has seven (7) cervical segments.
C. Contains the cell bodies of postganglionic sympathetic efferent neurons
D. Ends at the conus medullaris
E. Has no arachnoid membrane
The spinal cord...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments
C. Contains the prison cell bodies of postganglionic sympathetic efferent neurons This reply is INCORRECT.
Postganglionic neurons are located in the periphery, not in the spinal string.
D. Ends at the conus medullaris
Due east. Has no arachnoid membrane
The spinal string...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments
C. Contains the cell bodies of postganglionic sympathetic efferent neurons
D. Ends at the conus medullaris This answer is Right!
E. Has no arachnoid membrane
The spinal cord...
A. Occupies the lumbar cistern
B. Has twelve (12) cervical segments
C. Contains the cell bodies of postganglionic sympathetic efferent neurons
D. Ends at the conus medullaris
E. Has no arachnoid membrane This respond is INCORRECT.
Arachnoid membrane covers the spinal cord.
- Question 2
- A
- B
- C
- D
- E
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar
Eastward. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal This answer is Incorrect.
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar
E. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic This respond is Correct!
From these tracts, only the lateral spinothalamic tract crosses at the entry level.
C. Ventral spinocerebellar
D. Inductive spinocerebellar
Eastward. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal cord level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar This answer is INCORRECT.
D. Anterior spinocerebellar
Due east. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal string level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar This answer is Wrong.
Eastward. Dorsal spinocerebellar
Which of the following tracts crosses at the spinal string level of entry?
A. Corticospinal
B. Ventral spinothalamic
C. Ventral spinocerebellar
D. Anterior spinocerebellar
E. Dorsal spinocerebellar This respond is INCORRECT.
- Question three
- A
- B
- C
- D
- East
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal artery
D. Basilar artery
Due east. Posterior communicating artery
The claret supply for the corticospinal tract is derived from the:
A. Vertebral arteries This reply is Incorrect.
B. Posterior spinal arteries
C. Anterior spinal artery
D. Basilar artery
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries This respond is INCORRECT.
C. Anterior spinal artery
D. Basilar artery
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal artery This reply is CORRECT!
The anterior spinal artery supplies the corticospinal tract and the other tracts in this region.
D. Basilar artery
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Anterior spinal avenue
D. Basilar artery This answer is INCORRECT.
E. Posterior communicating artery
The blood supply for the corticospinal tract is derived from the:
A. Vertebral arteries
B. Posterior spinal arteries
C. Inductive spinal artery
D. Basilar avenue
E. Posterior communicating avenue This answer is INCORRECT.
- Question 4
- A
- B
- C
- D
- E
In the laminar somatotopic system of the dorsal columns, the almost lateral fibers correspond:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region
Due east. Coccygeal region
In the laminar somatotopic organization of the dorsal columns, the nigh lateral fibers represent:
A. Sacral region This answer is Wrong.
B. Thoracic region
C. Lumbar region
D. Cervical region
E. Coccygeal region
In the laminar somatotopic organization of the dorsal columns, the most lateral fibers represent:
A. Sacral region
B. Thoracic region This answer is INCORRECT.
C. Lumbar region
D. Cervical region
E. Coccygeal region
In the laminar somatotopic organization of the dorsal columns, the most lateral fibers stand for:
A. Sacral region
B. Thoracic region
C. Lumbar region This respond is INCORRECT.
D. Cervical region
E. Coccygeal region
In the laminar somatotopic organization of the dorsal columns, the almost lateral fibers correspond:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region This reply is CORRECT!
The fibers inbound at the lumbar region are located in the lateral portion of the dorsal columns.
East. Coccygeal region
In the laminar somatotopic organization of the dorsal columns, the most lateral fibers correspond:
A. Sacral region
B. Thoracic region
C. Lumbar region
D. Cervical region
E. Coccygeal region This answer is INCORRECT.
- Question 5
- A
- B
- C
- D
- E
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia
E. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia This answer is Incorrect.
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia
E. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure This reply is Right!
Syringomyelia syndrome results from lesions in the inductive spinal white commissure that results in losing pain and temperature sensation at the level of the lesion.
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia
Eastward. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract This answer is Incorrect.
D. Ventral root ganglia
East. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia This answer is INCORRECT.
E. Fibers of the dorsal spinocerebellar tract
Syringomyelia syndrome occurs with selective spinal lesions in the:
A. Dorsal root ganglia
B. Fibers decussating in the spinal white commissure
C. Fibers of the anterior spinal thalamic tract
D. Ventral root ganglia
E. Fibers of the dorsal spinocerebellar tract This answer is Incorrect.
- Question 6
- A
- B
- C
- D
- E
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II This answer is Wrong.
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons This answer is Wrong.
C. Somatic efferent neurons
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons This answer is Right!
The axons of the spinal root neurons are the somatic efferent fibers.
D. Internuncial neurons
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons This answer is Incorrect.
E. Commissural neurons
Spinal root neurons are:
A. Neurons in the laminae II
B. Motor neurons
C. Somatic efferent neurons
D. Internuncial neurons
Due east. Commissural neurons This answer is INCORRECT.
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Inferior End Of Spinal Cord,
Source: https://nba.uth.tmc.edu/neuroscience/m/s2/chapter03.html
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