Spinal cord

The Spinal Cord: As mentioned before, the medulla oblongata becomes the spinal cord after passing through the foramen magnum. 

Conus Medullaris: The spinal cord then extends to the region of L1 & L2 vertebrae & thins down in this cone-shaped region.

Cauda Equina: A bundle of nerve roots that resemble a horse’s tail fill the rest of the vertebral column from L2 to S4 vertebrae, since the spinal cord stops at the L1 & L2 vertebrae. It innervates the pelvic organs & lower extremity. 

Grooves: the spinal cord has an anterior deep groove called anterior median fissure & a posterior shallow groove called the posterior median sulcus. 

Central Canal: A pathway traveling within the spinal cord, located in the midline & center of the spinal cord where CSF flows as well. Closed in adults, but open in children.

Spinal Gray Matter: The spinal gray matter is a butterfly-shaped core. Take note that the gray matter in the spinal cord is deep, unlike in the brain where it is located superficial. 

  • Horns

    • Anterior Horn: The anterior portion, known as the anterior (ventral) horn, is made up of cell bodies of the motor neurons of the spinal cord, also referred to as lower motor neurons. The axons of these nerves exit via the anterior (ventral) spinal nerve roots. 

    • Posterior Horn: The posterior (dorsal) horn receive axons from the dorsal root ganglia (singular: ganglion), which house the cell bodies of the sensory neurons & are housed just outside the cord. 

    • Lateral Horn: In the thoracic & lumbar regions only, a lateral horn is present & contains cell bodies of the sympathetic division (fight or flight) of the autonomic nervous system (motor nervous system that controls glands, cardiac muscle, & smooth muscle). 

    • Gray Commissure: Found in the midline; connects left & right portions of spinal gray matter.

Enlargements: These are thicker/wider sections in the spinal cord & there are 2 of them:

  • Cervical Enlargement:  Gives rise to the nerves of the upper limbs.

  • Lumbar Enlargement: Gives rise to the lumbar & pelvic nerves.

Spinal White Matter: The remaining spinal cord that surrounds the spinal gray matter is known as the spinal white matter. Take note that white matter in the brain is deep, unlike the white matter of the spinal cord which is located superficial.

  • This contains groups of axons carrying information up the cord via the ascending fibers or down the cord via the descending fibers. 

  • These fibers are grouped in columns called funiculi (singular: funiculus). Which are divided into 3 sections called anterior, posterior, & lateral funiculi. 

  • The funiculi are divided up into tracts, which contain axons that have the same functional role & are defined primarily by the structures they connect. 

Spinal Nerve Roots: Each spinal nerve arises from 2 points of root attachments to the spinal cord:

  • Anterior/Ventral Spinal Nerve Roots: Formed by 6-8 anterior/ventral spinal nerve rootlets, carries motor axons & efferent signals away from the spinal cord. The motor nerves' neurosoma/cell bodies are found within the spinal cord's gray matter.

  • Posterior/Dorsal Spinal Nerve Roots: Formed by 6-8 posterior/dorsal spinal nerve rootlets, carries sensory axons & afferent signals towards the spinal cord.

    • Posterior/Dorsal Root Ganglion: (plural: ganglia) It contains the neurosoma/cell body of the sensory nerves traveling to the spinal cord. It is easy to find since it has a bulbous/swollen appearance. Seeing this ganglion is a good landmark to use & confirm that you are at the posterior side of the spinal cord.

Spinal Nerves: Formed by the fusion of the anterior & posterior spinal nerve roots. It contains both sensory & motor axons. Therefore, it is a mixed nerve that takes efferent signals away from the spinal cord & to the body by the way of the anterior spinal nerve roots, executing a motor action. While, it carries sensory signals sensed by the body back to the spinal cord via the posterior spinal nerve roots & root ganglion.

Spinal Meninges: They (dura, arachnoid, & pia mater) are organized the same way as the cranium 

  • There are surrounding fibers called the denticulate ligaments (extensions of the pia mater that extends to the dura mater) which anchors the spinal cord & limit its side-to-side movements.

  • The spinal meninges are an extension of the cranial meninges. However, in the spinal cord the dura mater is not adherent to the vertebrae the way it is in the skull, so there is space between the dura & spinal column known as the epidural space. It is filled with loose connective tissue, adipose tissue, & blood vessels.

  • Again, the major difference is the epidural space which exists in the spinal column but not in the cranial cavity. The spinal cord also has subdural & subarachnoid spaces.

  • Filum Terminale: It is an extension of the pia mater that anchors the spinal cord to the coccyx vertebra.