Spinal cord – Medulla spinalis
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Central nervous system
The spinal cord is enclosed in the vertebral canal and is covered with the meninges. Its structure is similar to the primitive neural tube with the central canal inside. In early stages of development, the spinal cord fills the vertebral canal completely and segment position corresponds to the respective vertebra. The vertebral column grows quicker than the spinal cord. Hence, the caudal part of the vertebral canal contains just nerve roots (cauda equina) and the caudal end of the spinal cord is situated at the level of L1–L2. The spinal cord consists of 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal). Topography
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• 1 Cranially: continuous with medulla oblongata • 1.1 Cranial borderline:
1.1
– foramen magnum – decussation of pyramids (decussatio pyramidum) – crossing of pyramidal tract – exit of the first cervical nerve (C1) between the occipital bone and atlas 2 Caudally: the level of L1–L2 2.1 Medullary cone (conus medullaris) 2.2 Spinal part of filum terminale (pars spinalis fili terminalis) – as a glial string follows the medullary cone, – in the sacral area, it merges with the spinal dura mater 2.3 Cauda equina consists of roots of lumbar, sacral and coccygeal nerves caudally to the medullar cone
2.1
Columns (columnae) are terms for 3D grey matter and horns (cornua) describe two dimensional distribution of grey matter at the level of one segment.
2.3 2.2
Anterior view
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Lateral view
Vertebromedullary topography The Chipault´s rule: describes the mutual shift of corresponding spinal cord segment and vertebra 1 Spinous processes of cranial C vertebrae – correspond to the same cord segments 2 Spinous processes of caudal C vertebrae – segment + 1 (e.g. C7 vertebra = 8th C segment) 3 Spinous processes of cranial T vertebrae – segment + 2 (e.g. T3 vertebra = 5th T segment) 4 Spinous processes of caudal T vertebrae – segment + 3 5 Vertebrae T10–T12 – lumbar segments L1–L4 6 Vertebrae T12–L1 (epiconus) – lumbar and sacral segments L5–S2 7 Vertebrae L1–L2 (conus) – sacral and single coccygeal segments S3–S5 and Co
• • • • • • •
1 2
C7
3 T5 T8
4
T10 T12
5
L1
6
L2
7
Layers and spaces of the vertebral canal Layers – from a vertebra towards the surface of the spinal cord
• 1 Vertebral periosteum (endorhachis) • 2 Spinal dura mater (dura mater spinalis) • 3 Spinal arachnoid mater (arachnoidea mater spinalis) • 4 Spinal pia mater (pia mater spinalis)
Vertebromedullary topography
Spaces
• 5 Epidural space (spatium epidurale)
– situated between the periosteum and spinal dura mater – consists of loose and adipose connective tissue and venous vertebral plexus (plexus venosi vertebrales interni) 6 Subdural space (spatium subdurale) – represent a virtual space between the spinal dura mater and arachnoid mater 7 Subarachnoid/leptomeningeal space (spatium subarachnoideum) – situated between the spinal arachnoid mater and pia mater – is filled with cerebrospinal fluid (liquor cerebrospinalis)
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4 7 3 6 5 2 1
• 398
Spinal cord ascent (ascensus medullae spinalis) is a term used for non-proportional growth of the vertebral column and spinal cord (see vertebromedullary rule and topography)
Segments are not visible macroscopically.
2.1
2.2
Spinal cord length is 40 to 50 cm and weight is almost 30 g.
Segmental stratification is used for describing spinal nerves and nervous plexus (e.g. the brachial plexus is composed of the segments C5 to C8 with connection from the C4 and T1 segment)
1.1
2
• • •
Myelos is a Greek term for the spinal cord.
Layers and spaces of the vertebral canal
Spinal cord is fixed within the vertebral canal by meninges, ligaments (derivation of spinal pia mater) – denticulate ligament (ligamentum denticulatum), at the level of individual segments by the exits of spinal nerves and caudally it is fixed by the spinal part of filum terminale. Scheme of a spinal nerve see page 337. Meninges see page 471. Vascular supply of the spinal cord see page 476. Vertebral column see page 568.
Clinical notes Syndrome of conus medullaris is an affection of the medullary cone where the segment S3 to S5 are localized. It is manifested by a decrease or loss of sensation in saddle-shape distribution (perianal, perigenital and inner femoral region), typical are disorders of the sphincters and loss of the anal reflex (leakage of urine and faeces), sexual disturbances (loss of erection). The motor system affection includes palsy of the pelvis floor muscles, imperceptible palsy of the short flexors of the foot and extensor muscles of the foot. Syndrome of epiconus is an affection of the epiconus of the spinal cord where the segments L5 to S2 are localized. It is manifested by a palsy and atrophy of the extensors of the foot, muscles of the leg (foot extension and flection are affected or impossible), sensation is impaired in the L5 to S2 dermatoms, also autonomic urinary bladder can occur.