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.
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.
Motor tracts of spinal cord
Direct pathway (pyramidal)
- Lateral corticospinal tract
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
- 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.