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Wednesday, October 13, 2010

Anatomy of spinal cord

          It starts at the foramen magnum and ends at the L1-L2.
Spinal Cord is 2cm in diameter and 43 – 45cm long.
It has greater diameter  at cervical and lumbar region due to cervical and lumbar plexus respectively. There are 21 pairs of spinal nerves which are classified below.
8 pairs of cervical spinal nerves
12 pairs of thoracic spinal nerves
5 pairs of lumbar spinal nerves
5 pairs of sacral spinal nerves
1 pair of coccygeal spinal nerves

Sensory tracts of spinal cord
Anterior spinothalamic and Lateral spinothalamic tract
          These tracts conduct nerve impulses responsible for pain, warmth, cold, itching, tickling, deep pressure, and crude poorly localized sensation of touch.
Posterior column
          This tract perceives the following sensations.
Propioception: sensation of joint, muscle and tendon positions.
Discriminative touch: to localized exactly which part of the body is touched.
2-point discrimination: two parts fairly close to each other can be differentiated.
Light pressure
Motor tracts of spinal cord
Direct pathway (pyramidal)
Indirect (extra-pyramidal)
Direct tracts
  • Lateral corticospinal tract
          At the junction of medulla oblongata and spinal cord 90%of motor tracts cross over to the opposite side. They control skillfull and fine movements of distal part.
Anterior corticospinal tract
          This tract is formed by 10% motor tracts and they cross-over at their exiting level from spinal cord. They control movements other than skillful.
  • Cortico-bulbar tract
          They start in brain and also ends in the brain. They help in positioning, equilibrium, balance in response to visual stimulus. They also maintain muscle tone.

Indirect tracts
  • Vestibulo-spinal tract: Present in internal ear responsible for equilibrium.
  • Rubro-spinal tract: Present in the red nucleus of mid brain responsible for trunk muscles( movements).
  • Lateral-reticulo-spinal tract: Present in reticular formation of brain stem. It inhibits flexor reflexes and facilitates extensor reflexes.
  • Medial reticulo-spinal tract: Present in reticular formation of brain stem. It inhibits flexor reflexes and facilitates extensor reflexes.


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