General
- Conus medullaris: lowest part of the spinal cord is conical
- Filum terminale: a fibrous cord below conus
- Prolongation of pia mater
- Attached to posterior surface of the 1st piece of coccyx
- The location of where the following ends:
- Conus L2
- Thecal sac S2
Dimensions of the cord
- Length of the cord is about 45 cm.
- Flattened cylinder.
- The transverse diameter shows two enlargements at the cervical level and lumbar level
- Cervical enlargement
- Lumbar enlargement
Age wise changes in the cord
- Early foetal life (3rd month), the spinal cord is as long as the vertebral canal and each spinal nerve arises from the cord at the level of the corresponding intervertebral foramen.
- Gradually ascends to reach the level of the third lumbar vertebra at the time of birth and to the lower border of the first lumbar vertebra in the adult
Functions of spinal cord
- It acts as a pathway for motor information, which travels down the spinal cord.
- It serves as a passage for sensory information in the reverse direction.
- It is a centre for coordinating simple reflexes.
External features of spinal cord
- Blends indistinguishably into the medulla at a level arbitrarily set to be at the upper limit of the dorsal and ventral rootlets forming the first cervical nerve
- Easier to differentiate the transition on the ventral than on the dorsal surface because the ventral rootlets of the first cervical nerve are always present, whereas the dorsal rootlets are absent in many cases.
- The fact that the junction of the spinal cord and medulla is situated at the rostral margin of the first cervical root means that the medulla, and not the spinal cord, occupies the foramen magnum.
- The spinal cord immediately below the level of the foramen magnum is round, and it is divided by one fissure and several sulci.
- The anteromedian fissure and the posteromedian sulcus divide the spinal cord into symmetrical halves.
- Anteromedian fissure
- Deep: reaches a depth of several mm.
- Contains anterior spinal artery.
- Posteromedian sulcus
- Much shallower, and from it the posteromedian septum penetrates the spinal cord, almost reaching the central canal.
- Each half of the cord is further subdivided into posterior, lateral and anterior regions by anterolateral and posterolateral sulci.
- The posterior lateral sulcus is situated along the line where the dorsal roots enter the spinal cord.
- The posterior funiculus is situated between the posteromedian and posterior lateral sulci.
- At the upper cervical level, the surface of each posterior funiculus is divided by another shallow longitudinal furrow, the posterior intermediate sulcus, into the
- Fasciculus gracilis medially
- Fasciculus cuneatus laterally.
- The anterior funiculus includes the zone of emergence of the ventral roots.
- The region of the spinal cord between the posterior lateral sulcus and the anteromedian fissure is divided into anterior and lateral funiculi by the exiting ventral rootlets of the spinal nerves.
- The lateral funiculus lies between the ventral roots and the posterior lateral sulcus. In the upper cervical region, the rootlets that unite to form the spinal part of the accessory nerve emerge through the lateral funiculus.
Types of rexed lamina
Rexed Lamina | Description |
Lamina I | Substantia marginalis (marginal nucleus; receives/relays pain and temperature from Lissauer’s tract) |
Lamina II/III | Substantia gelatinosa (first-order neurons of spinothalamic tract synapse) |
Lamina III/IV/V | Nucleus proprius (first-order neurons of spinothalamic tract synapse) |
Lamina VI | Base of the dorsal horn |
Lamina VII | Intermediolateral nucleus (T1-L2; sympathetic output) and nucleus dorsalis (Clarke’s column; proprioception via spinocerebellar tract) |
Lamina VIII | Motor interneurons |
Lamina IX | Lateral and medial motor neurons; cervical phrenic and spinal accessory nuclei; sacral Onuf’s nucleus (S2 level; pudendal nerve origin; micturition, defecation) |
Lamina X | Substantia gelatinosa centralis |
Nociceptive afferents enter the dorsal horn and terminate both superficially (laminae I and II) and more deeply (in laminae V, VI, and VII), as well as around the central canal. Low-threshold tactile afferents, in contrast, spare the superficial laminae and send their terminals primarily to laminae III and IV (sometimes called the nucleus proprius).
Spinal cord tracts
- Motoneurons are somatotopiccally organized:
Ventral | Extensor muscles | E |
Dorsally | Flexor muscles | F |
Lateral | Distal limb muscles | D |
Medial | Proximal limb muscles | P |
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