General arrangement and surfaces
Anatomically, the spinal cord is located in the vertebral canal. This natural bony container securely protects the nervous tissue.
Upon detailed examination of this structure, anatomists distinguish precisely 4 surfaces:
- Anterior;
- Posterior;
- Two lateral.
This spatial division helps to accurately describe the emergence of nerve roots and the course of pathways later on.
Skeletotopic boundaries
For clinical practice, it is extremely important to understand where the spinal cord begins and where it ends. Its boundaries have clear landmarks in relation to bony structures (skeletotopy).
Upper boundary The spinal cord has no sharp anatomical boundary when transitioning into the brain — it smoothly continues into the medulla oblongata (medulla oblongata). However, skeletotopically, this boundary is defined very clearly: it corresponds to the level between the lower edge of the foramen magnum and the upper edge of the first cervical vertebra.
Lower boundary The lower boundary has age-related features due to the uneven growth of the spinal cord and spinal column during development:
- In an adult, the spinal cord ends high — at the level of the I–II lumbar vertebrae.
- In a newborn child, the spinal cord is relatively longer and reaches the level of the III lumbar vertebra.
Medullary cone and terminal filum
In its lower part, the spinal cord tapers. This tapering forms the so-called medullary cone (conus medullaris).
A slender cord called the terminal filum (filum terminale) extends from the apex of the medullary cone. It plays a key role by fixing the spinal cord in the vertebral canal, preventing it from shifting.
The terminal filum is heterogeneous and structurally divided into two parts:
- Internal terminal filum (filum terminale internum);
- External terminal filum (filum terminale externum) — this part is a derivative of the dura mater.
It is important to note that the terminal filum is not just an empty ligament. It is accompanied by blood vessels and may contain the roots of the coccygeal nerves.
Briefly: answers to topical questions
Which anatomical structures fix the spinal cord in the vertebral canal?
The spinal cord is fixed in the vertebral canal by the terminal filum. It is a continuation of the thinned lower part of the spinal cord.
- Terminal filum (filum terminale) — extends downwards from the apex of the medullary cone (conus medullaris), is accompanied by blood vessels, and may contain coccygeal nerve roots.
Two parts of this formation are distinguished:
- Internal terminal filum (filum terminale internum).
- External terminal filum (filum terminale externum) — is a derivative of the dura mater.
At the very bottom of the terminal filum, there are two coccygeal ganglia.
To which bone does the external terminal filum of the spinal cord attach?
The terminal filum of the spinal cord attaches to the second coccygeal vertebra. The provided materials do not contain a separate clarification of the attachment point exclusively for the external part of the filum; fixation is indicated for the structure as a whole.
- Terminal filum (filum terminale) — a thin structure into which the medullary cone (conus medullaris) caudally tapers.
It extends downward from the apex of the medullary cone, and at its very bottom, two coccygeal ganglia are located.
Class and exam questions
Where is the spinal cord located?
It is located in the vertebral canal.
How does the spinal cord transition into the brain?
It transitions into the medulla oblongata smoothly, without a sharp macroscopic boundary. Skeletotopically, this is the level between the foramen magnum and the upper edge of the first cervical vertebra.
What is the difference in the lower boundary of the spinal cord between an adult and a newborn?
In an adult, it ends at the level of the I–II lumbar vertebrae, whereas in a newborn, it is located lower — at the level of the III lumbar vertebra.
What is the terminal filum made of?
It is divided into internal and external parts. The external part is a derivative of the dura mater. Additionally, the filum is accompanied by vessels and may include the roots of the coccygeal nerves.
What else to study on this topic
- Medulla oblongata and its topographic connections
- Dura mater as the source of formation of the external terminal filum
- Blood vessels accompanying the terminal filum
- Roots of the coccygeal nerves and their course in the vertebral canal
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