Term
| Is the spinal cord housed in the vertebral? |
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Definition
| It is housed in the vertebral canal, protected by bone, surrounded by meninges, bathed and suspended in cerebrospinal fluid (CSF) and anchored at its caudal end by the filum terminale, an extension of the pia mater. |
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Term
| The spinal cord is anchored by what? |
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Definition
| At its caudal end by the filum terminale, an extension of the pia mater. |
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Term
| How many pairs of spinal nerves are there? |
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Definition
There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
- Thus, the spinal cord in considered to have 31 segments.
- Each segment consists of ventral roots, dorsal roots, a dorsal root ganglion, and the spinal cord gray matter (ventral horn and dorsal horn) and white matter at that level
- Ventral horns generally contain the somas of ventral horn motor neurons that project there axons to muscle
- Dorsal root ganglions contain the somas of pseudounipolar sensory neurons whose peripheral axons carry information from peripheral skin and muscle receptors. Their central axons carry that sensory information into the CNS through the dorsal root entry zone and many synapse on interneurons within the dorsal horn. |
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Term
| Each spinal cord segment consists of what? |
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Definition
| Each segment consists of ventral roots, dorsal roots, a dorsal root ganglion, and the spinal cord gray matter (ventral horn and dorsal horn) and white matter at that level |
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Term
| Ventral horns general project their axons where? |
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Definition
| Ventral horns generally contain the somas of ventral horn motor neurons that project there axons to muscle |
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Term
| Dorsal root ganglion contain what and their axons carry what type of information? |
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Definition
| Dorsal root ganglions contain the somas of pseudounipolar sensory neurons whose peripheral axons carry information from peripheral skin and muscle receptors. Their central axons carry that sensory information into the CNS through the dorsal root entry zone and many synapse on interneurons within the dorsal horn. |
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Term
| Where does the adult spinal cord end? |
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Definition
| The adult SC ends at about the L1 vertebral level. |
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Term
| The spinal nerves below L1 are collectively termed... |
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Definition
| cauda equina (horses tail) |
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Term
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Definition
| Level below L1 in which CSF can be withdrawn in a lumbar puncture. |
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Term
| Viewing the entire length of the SC, it is possible to observe two enlargements called... |
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Definition
The cervical enlargement and the lumbosacral enlargement. Due to the presence of sensory and motor neurons supplying the extremities, the ventral horns and dorsal funiculi of SC segments at the level of the enlargements are quite large. Ventral horns contain large alpha motor neurons that innervate skeletal muscles.
- The cervical enlargement lies between segments C5 ,C6, C7, C8 and T1 and gives rise to spinal nerves forming the brachial plexus.
- The lumbosacral enlargement lies between segments L1 through L4 to form the lumbar plexus and L4 through S2 to form the sacral plexus. |
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Term
| The cervical enlargement and the lumbosacral enlargement lie between what? |
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Definition
- The cervical enlargement lies between segments C5 ,C6, C7, C8 and T1 and gives rise to spinal nerves forming the brachial plexus.
- The lumbosacral enlargement lies between segments L1 through L4 to form the lumbar plexus and L4 through S2 to form the sacral plexus. |
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Term
| Cross-sectional anatomy of the spinal cord reveals several features: |
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Definition
- the ventral median fissure,
- the dorsal median sulcus,
- dorsal intermediate sulcus (only present from T6 and up), and the
- dorsolateral sulcus. |
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Term
| The white matter regions of the SC are divided into... |
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Definition
Three funiculi or columns which contain motor and sensory pathways.
-Dorsal (posterior) funiculus (also called the dorsal column
-Lateral funiculus or lateral column of the SC white matter
-Ventral (Anterior) funiculus, or ventral column of SC |
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Term
| Dorsal (posterior) funiculus (also called the dorsal column) |
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Definition
| Location of fasciculus gracilis and fasciculus cuneatus. The dorsal funiculus is largest at the cervical levels because it contains ascending fibers of both the fasciculus gracilis and fasciculus cuneatus whereas the lumbar levels only contain the fasciculus gracilis. Progressively more sensory fibers accumulate at each level from the caudal to the rostral direction. (Think about the school bus analogy) |
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Term
| Lateral funiculus or lateral column of the SC white matter |
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Definition
| The location of lateral corticospinal tract, rubrospinal tract, and dorsal and ventral spinocerebellar tracts. Part of the lateral spinothalamic tract is in the lateral funiculus and part is in the ventral funiculus. |
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Term
| Ventral (Anterior) funiculus, or ventral column of SC |
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Definition
| The location of anterior corticospinal tract, reticulospinal tracts, lateral vestibulospinal tract, tectospinal tract, medial longitudinal fasciculus, and part of the lateral spinothalamic tract. |
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Term
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Definition
| The cervical segments are relatively large and ovoid in shape. The increased size is due to the large number of ascending and descending axons present at these levels (think of the school bus analogy) and the large number of motor neurons in ventral gray matter. |
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Term
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Definition
| The thoracic segments are smaller because they do not contain as many motor neurons (not as much musculature to innervate in the trunk regions) and contain less axons compared to the cervical levels . The thoracic segments contain a lateral horn (also called the intermediolateral cell column). This region marks the location of cell bodies of preganglionic sympathetic (type B motor neurons). The lateral horn is present in all thoracic segments. |
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Term
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Definition
| The lumbar segments have massive ventral and dorsal horns. The upper lumbar segments have a lateral horn (as do the thoracic segments). The lumbar segments also have a particularly well-developed nucleus dorsalis (also called Clarke's nucleus or column which actually extends from C8-L2). Clarke's column is especially prominent in the lumbar segments. It contains the cell bodies of neurons of the dorsal spinocerebellar tract. |
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Term
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Definition
| Cross sections through the sacral segments are relatively small with large amounts of gray matter. There are large ventral and dorsal horns, and little white matter as most of the descending motor pathways have already given off most of their terminations at higher segments. The ascending pathways are just beginning to collect axons at the more caudal segments (again think of the school bus analogy). Preganglionic parasympathetic fibers arise from Rexed's lamina VII of the sacral segments (see below), but, unlike the case for the sympathetic system, there is no lateral horn present at that level. |
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Term
| Gray Matter of the Spinal Cord is grossly broken down into 4 regions that contain multiple nuclei and and 10 layers (Rexed's laminae): |
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Definition
Dorsal horn: Laminae I - VI
Intermediate zone: Lamina VII
Ventral horn: Laminae VIII-IX
Central canal region: Lamina X |
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Term
| Dorsal Horn Laminae I, II, III, IV, V, VI |
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Definition
Axons enter the dorsal horn of the spinal gray matter via the dorsal root entry zone and travel trhrough Lissauer's tract. These axons are considered afferent fibers and carry sensory information from the periphery.
- The smallest fibers, C afferents (unmyelinated) and A-delta afferents (lightly myelinated) have terminal branches in a region of the dorsal horn called the substantia gelatinosa, located in Rexed's lamina II. These small fibers carry sensations of pain and temperature.
- Afferents terminating in Rexed's lamina III and IV respond to low intensity stimulation (e.g., light touch from hair receptors).
- Lamina V contains many interneurons.
- Lamina VI is especially prominent in the cervical and lumbosacral enlargements. Some branches of Group Ia and Ib muscle afferents synapse onto neurons in this region. |
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Term
| Substantia gelatinosa, located in Rexed's lamina II are what type of fibers and carry what type of sensation? |
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Definition
| Are small fibers carry sensations of pain and temperature |
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Term
| Afferents terminating in Rexed's lamina III and IV respond to... |
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Definition
| Low intensity stimulation (e.g., light touch from hair receptors). |
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Term
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Definition
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Term
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Definition
| Is especially prominent in the cervical and lumbosacral enlargements. Some branches of Group Ia and Ib muscle afferents synapse onto neurons in this region. |
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Term
| Intermediate zone: Lamina VII... |
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Definition
| It contains Clarke's column. It extends primarily from C8 to L2 and cell bodies located there give rise to the dorsal spinocerebellar tract. |
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Term
| Ventral Horn: Laminae VIII and IX... |
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Definition
Lamina VIII contains terminations of many fibers of descending motor pathways.
- Lamina IX is present in distinct clusters. This lamina is important because it is the location of cell bodies of large alpha motor neurons (and gamma motor neurons). In general, motor neurons to more distal musculature are located laterally, whereas the motor neurons innervating axial muscles are located medially in the lamina IX clusters in the ventral horn. |
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Term
| Central Canal Region: Lamina X... |
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Definition
| Located around the central canal and contains many interneurons that send axons across the midline. |
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Term
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Definition
1. As afferents enter the SC through Lissauer's tract, the small fine fibers take a lateral position, whereas the large afferents enter more medially in the tract. The medial group contains thick, heavily myelinated (A-beta, Group Ia, Ib, II) afferents. The lateral group contains the thin, unmyelinated and lightly myelinated (Group C [also called Group IV] and A-delta [also called Group III]) fibers.
2. The medial group contains central axons of encapsulated somatic receptors (e.g., muscle spindles, tendon organs, Pacinian corpuscles, Meissner's corpuscles). The lateral group contains central processes of free nerve endings (A-delta and C fibers) which relay crude touch, pain and temperature sensations.
3. Once afferents have entered the SC, some will ascend or descend and take part in intersegmental reflexes. Some medial (thick, myelinated, primarily A-beta) axons ascend in the dorsal columns (without synapsing) to the level of the medulla. The central, ascending projections of these afferents form the fasciculus gracilis and fasciculus cuneatus, which carry discriminative sensation (fine touch, pressure, vibratory sensation) from the lower extremities and upper extremities, respectively.
4. Some large medial afferents terminate in Clarke's column. Clarke's column receives afferents primarily from the lower extremity. Afferents from muscle spindles (Ia afferents) send off collaterals to Clark's column to synapse with neurons which then form the dorsal spinocerebellar tract. Other collaterals of Ia afferents terminate directly (monosynaptically) onto alpha motor neurons in lamina IX of the ventral horn. |
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