The Spinal Cord


 

The functions of the spinal cord:

  1. Acts as a relay for somatosensory information
    Stimuli -> Spinal Cord -> CNS or
    Stimuli -> Spinal Cord (in Reflexes)
  2. Carries both afferent and efferent neurons
  3. Contains interneurons and motor neurones that control the movement of the trunk and limbs.
    Motor neurones can be excited or inhibited by the Cerebral Cortex

Surface Anatomy:

The length in an adult varies between 42 to 45 cm.  It extends from Medulla Oblongata to the Upper Border of L2.
Two enlargements of the spinal cord can be seen at the beginning and at the end of it.

  1. Intumescentia Cervicalis [= The cervical (superior) enlargement] – C4 to Th1
  2. Intumescentia Lumbalis [= The lumbar (inferior) enlargement] – Th9 to Th12

These are produced by expansions of the gray matter – Provide and receive nerves from the upper and lower extremities.

Conus Medullaris (The Medullar Cone):

  • Around L1 – L2
  • Filum Terminale arises from here. This is an extension of the pia mater that continues down the vertebral canal and attaches the spinal cord to the fist segment of coccyx.
Illustration from Grey, Henry. 1918. Fig. 662

Longitudinal grooves divide the spinal cord into the right and left halves. The ventral groove is referred to as the ventral median fissure, and the dorsal groove is referred to as the dorsal median sulcus.

The ventral median fissure is a deeper groove containing connective tissue of the pia mater and is suplied by the anterior spinal artery.

Ventral roots of the spinal nerves are attached to a shallow groove in this region, called the ventrolateral sulcus (sulcus ventrolateralis).

The dorsal median sulcus, which is shallower, contains the dorsal septum from glial elements.

The dorsolateral sulcus (posterolateralis sulcus) is the name give to the positon of the attachments of the dorsal roots of the spinal nerves.

The dorsal intermediate sulcus (sulcus intermedius posterior) separates fasciculus gracilis from fasciculus cuneatus.

Illustration from Grey, Henry. 1918. Fig. 664

Both dorsal and ventral roots are attached in a line of rootlets (fila radicularia). Before the ventral and the dorsal roots join enlargements (ganglia) can be observed. These contain the primary pseudounipolar sensory neurones (see below).

Dorsal root ganglia at the level of the C1 and Coccygeal Vertebrae are absent in 50% of people.

There is a total of 31 pairs of spinal nerves devided as:

  • 8 Cervical – Between the occipital bone and C1

  • 12 Thoracic – Begin between Th1 and Th2

  • 5 Lumbar – Begin between L1 and L2

  • 5 Sacral – Begin at the most cranial sacral foramina

  • 1 Coccygeal – Emerges between S1 and S2

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