1. Anatomy of the spinal cord
Prof. Mujahid Khan

2. Objectives Objectives of the lecture:
At the end of the lecture, the students should be able to:
• Describe the external features of the spinal cord regarding position, beginning, termination, segments and enlargements
• Define the terms “cauda equina” and “ filum terminale”
• Describe the sites of exit of spinal nerves from vertebral column
• Describe in brief the blood supply of the spinal cord
• List the important nuclei in the grey matter of the spinal cord and identify their location
• List the important tracts in the white matter of the spinal cord and identify their location and types of fibres

3. Spinal Cord Function:
Provides innervation of trunk and limbs via spinal nerves and peripheral branches
Receives primary afferent fibres from peripheral receptors and visceral structures
Sends motor axons to skeletal muscle
Houses preganglionic neurons of sympathetic and parasympathetic nervous system

4. External Anatomy of the Spinal Cord
From: 4
External Anatomy of the Spinal Cord
The spinal cord is a segmental structure, giving rise to 31 paired spinal nerves
Note the two enlargements
CERVICAL, related to the upper limb
LUMBAR, related to the lower limb

5. External Anatomy of the Spinal Cord
A series of rootlets emerge from the dorsal and ventral aspects of each segment of the cord and coalesce to form a dorsal and ventral root respectively
These roots pass through the subarachnoid space until they reach the appropriate intervertebral foramina
As they pass through the foramina the dorsal root is enlarged by the dorsal root ganglion
The roots fuse to form the mixed spinal nerve, which produces dorsal and ventral rami

6. External Anatomy of the Spinal Cord
The spinal cord is continuous with the medulla oblongata at a site just below the foramen magnum
it terminates in a tapered cone-shape called the conus medularis which in turn, continues as a thin connective tissue cord called the filum terminale which is anchored to the dorsum of the coccyx

7. External Anatomy of the Spinal Cord
Spinal cord ends at the L1 vertebral level (L2 at birth)
It is thus necessary to differentiate the spinal segment from the vertebral level
For example, the L2 spinal segment is the segment that provides the L2 spinal nerve and innervates the L2 dermatome, BUT, it is actually found in the vertebral canal associated with the T11 vertebra

8. Dermatomes Dermatome is a segment of skin supplied by one spinal nerve
Cutaneous areas supplied by adjacent spinal nerves overlap
No sensory loss after interruption of a single spinal nerve or dorsal root
Al examination

9. External Anatomy of the Spinal Cord: Meninges
The spinal meninges are continuous with the cranial meninges via the foramen magnum
include all 3 layers, the dura mater, arachnoid mater and pia mater
The spinal cord is suspended in the canal by a ribbon of tissue on the lateral aspects of the cord called the denticulate ligament
This ligament is formed of pia and arachnoid tissue and attaches to the dura at points along the length of the cord
Note that just as with the brain, the subarachnoid space is filled with CSF

10. External Anatomy of the Spinal Cord

11. Blood supply
Three longitudinal vessels run the length of the spinal cord
These are:
A single anterior spinal artery and
Paired posterior spinal arteries

13. The anterior spinal artery arises from the two vertebral arteries at the level of the medulla

14. The posterior spinal arteries arise from either the vertebral arteries or the posterior inferior cerebellar arteries

15. Anastomosis with radicular arteries derived from segmental vessels, including the ascending cervical, intercostal and lumbar arteries
Radicular arteries pass through the intervertebral foramina and divide into anterior and posterior branches, which run with the dorsal and ventral spinal nerve roots, respectively

16. The venous drainage of the cord follows a basically similar pattern to the arterial supply
Anterior
Posterior

17. Internal Features

18. Internal Anatomy of the Spinal Cord
The cord is made up of an outer layer of white matter and an inner, ‘H’ shaped core of grey matter
Dorsal median sulcus and septum
A small central canal extends the length of the spinal cord. Rostrally it opens into the 4th ventricle, Caudally it is a blind ending
Ventral median fissure

19. Internal Anatomy of the Spinal Cord
Cervical
The relative sizes and proportions of grey and white matter vary significantly in different regions
Grey matter is greatest at cervical and lumbar enlargements
White matter is greatest at cervical levels and is progressively less at more caudal levels
Thoracic
Lumbar
Sacral

20. Posteriorly by median septum
The spinal cord is incompletely divided into two equal parts:
Posteriorly by median septum
Anteriorly by median fissure WM GM

21. Two lateral horns are added in thoracic & upper lumbar segments
The arrangement of grey matter resembles the shape of the letter H, having two dorsal and two ventral horns/columns
Two lateral horns are added in thoracic & upper lumbar segments
The area of grey matter lying transversely across the midline is thin grey commissure, that surrounds the central canal and White Commissure:
Lies ventral to the gray commissure
The white matter consists of three funiculi: dorsal, lateral & ventral
Dorsal horn DF LF VF
Ventral horn
Grey commissure

22. Neuronal Architecture of Spinal Grey Matter
Cells are clustered into groups, which occur in long columns
In transverse section, these columns appear as layers, especially within the dorsal horn
These layers are called the laminae of Rexed
laminae of Rexed are numbered consecutively by Roman numerals, starting from the tip of the dorsal horn and moving ventrally into the ventral horn

23. Organization of Gray Matter
1. Dorsal horns: contain somatic sensory (SS) and visceral sensory (VS) cell bodies
2. Ventral horns: contain somatic motor cell bodies (SM)
3. Lateral horns: located ONLY in T1 to L2-3 and S2-4 segments, contain visceral motor cell bodies (VM)

24. Nerve Cell Groups in Dorsal Horn
4 main groups
Substantia gelatinosa
Nucleus proprius
Nucleus dorsalis (Clark’s column, nucleus thoracis)
Visceral afferent nucleus

25. Motor neurons are organized in 3 groups:
Medial: present in most segments, innervates muscles of neck and trunk (including intercostal and abdominal muscles)
Central: smallest, present in some cervical (phrenic C3-5, spinal accessory C1- 6) and lumbosacral (L2- S1) segments
Lateral: present in cervical and lumbosacral segments, innervates muscles of the limbs

26. Nerve Cell Groups in Lateral Horn
Small column composed of small neurons
Extends from T1 to L2-3 segments:
sympathetic fibers
Extends from S2-4 segments:
parasympathetic fibers

27. White Matter
Consists of mixture of nerve fibers, neuroglia and blood vessels. White color is due to high proportion of myelinated nerve fibers
The nerve fibers are arranged as bundles running vertically through the cord
A group of nerve fibers (axons) that share a common origin, termination and function form a tract or fasciculus
Tracts are often named according to their points of origin and destination, e.g. spinothalamic, corticospinal
Depending on their function, the spinal tracts are divided into ascending and descending tracts

28. Organization of White Matter
Divided into three funiculi (columns): posterior, lateral & anterior.
Anterior white commissure
Dorsolateral tract of Lissauer (at the tip of dorsal horn)

29. Most of the fibers divide into ascending and descending branches:
ascending sensory fibers terminate in the gracile and cuneate nuclei in the medulla
The descending fibers terminate in the dorsal horn

30. References
Clinical Neuroanatomy for Medical Students, Richard S. Snell-6th Edition.
Clinical Neuroanatomy and related neuroscience. M.J.T. FitzGerald, Jean Folan-Curran, Fourth Edition.
Crossman, AR and Neary D, Neuroanatomy: An Illustrated Colour Text.
Haines, DE, Neuroanatomy: An Atlas of Structures, Sections and Systems.