Spinal cord: Anatomy & Function

Spinal cordAnatomy and function of the spinal cord. Spinal nerves
~ 13 min

In this note, we are going to discuss the anatomy of the spinal cord. We will cover the structure of segments, roots, gray and white matter, and briefly consider the spinal nerves.

Spinal cord - cross section
Spinal cord - cross section

What is the spinal cord?

The spinal cord, along with the brain, is a part of the central nervous system. It is located in the vertebral canal from the foramen magnum approximately to the level of L1/L2 and has a segmental organization.

Spinal cord - anterior aspect
Spinal cord - anterior aspect

The vertebral canal is formed by vertebral foramina in the center of each vertebra.

Vertebral canal (canalis vertebralis) / Vertebral foramen (foramen vertebrale)
Vertebral canal (canalis vertebralis) / Vertebral foramen (foramen vertebrale)
Foramen magnum
Foramen magnum

Spinal cord segments

A segment is a part of the spinal cord from which one pair of spinal nerves emerges, meaning one nerve on the left and one on the right.

Spinal cord segment
Spinal cord segment
Spinal nerve
Spinal nerve

There are 31 spinal cord segments:

  • 8 cervical
Cervical segments
Cervical segments
  • 12 thoracic
Thoracic segments
Thoracic segments
  • 5 lumbar
Lumbar segments
Lumbar segments
  • 5 sacral
Sacral segments
Sacral segments
  • 1 coccygeal
Coccygeal segment
Coccygeal segment

Segments and spinal nerves are designated with the corresponding letter and an Arabic numeral.

Spinal cord roots

Each spinal nerve is attached to the spinal cord by anterior and posterior roots.

The posterior root contains processes of sensory (or afferent) neurons, carrying information to the CNS.

Posterior root
Posterior root
Afferent fibers
Afferent fibers

The bodies of these neurons form an enlargement on the posterior root, known as the spinal ganglion.

Spinal ganglion
Spinal ganglion

The anterior root contains processes of motor (or efferent) neurons, carrying information from the CNS.

Anterior root
Anterior root
Efferent fibers
Efferent fibers

Their bodies are located in the anterior horns of the spinal cord’s gray matter. We will discuss this in more detail a bit later.

Spinal nerves exit the spinal cord below the corresponding vertebrae. For example, nerve L5 exits below the L5 vertebra. The exception is related only to cervical nerves, which exit above the corresponding vertebrae, and the C8 nerve – above the first thoracic vertebra.

Intervertebral foramen
Intervertebral foramen
Projection of spinal nerve roots
Projection of spinal nerve roots

Enlargements of the Spinal Cord

At the points where spinal nerves, which innervate the limbs, emerge, the spinal cord forms enlargements.

The cervical enlargement, at the level of C5-T1, corresponds to the upper limbs.

Cervical enlargement
Cervical enlargement

The lumbosacral enlargement, at the level of L1-S3, corresponds to the lower limbs.

Lumbosacral enlargement
Lumbosacral enlargement

The roots of the lower spinal nerves are quite long. Due to their external similarity, the bundle of these roots is called the cauda equina (horse’s tail).

Cauda equina
Cauda equina

Because the spinal cord develops relatively slowly, it does not reach the full length of the vertebral column and ends at the level of the first or second lumbar vertebrae. The lower end of the spinal cord is called the conus medullaris.

Conus medullaris
Conus medullaris

It continues into the filum terminale, the upper part of which still contains some elements of nervous tissue, while the lower part does not and consists only of connective tissue elements.

Filum terminale
Filum terminale

External features

The external surface of the spinal cord has several depressions:

  • The anterior median fissure runs along the anterior surface.
Anterior median fissure
Anterior median fissure
Anterior median fissure
Anterior median fissure
  • The posterior median sulcus runs along the posterior surface.
Posterior median sulcus
Posterior median sulcus
Posterior median sulcus
Posterior median sulcus
  • The anterolateral sulcus is located where the anterior roots emerge from the spinal cord.
Anterolateral sulcus
Anterolateral sulcus
  • The posterolateral sulcus is located where the posterior roots enter the spinal cord.
Posterolateral sulcus
Posterolateral sulcus

Inside the organ, there is a central canal filled with cerebrospinal fluid.

Central canal
Central canal

Superiorly, it communicates with the ventricular system of the brain, and inferiorly, it forms a blind-ending terminal ventricle.

Gray matter

Like other parts of the CNS, the spinal cord is composed of gray and white matter.

The gray matter surrounds the central canal. It consists of neuronal cell bodies and has a «butterfly» or an «H» shape in cross-section.

Gray matter
Gray matter

The gray matter is differentiated into anterior horns and posterior horns. Additionally, from T1 to L2, there is also a lateral horn, which contains the neurons of the sympathetic nervous system.

Anterior horn
Anterior horn
Posterior horn
Posterior horn
Lateral horn
Lateral horn

The gray matter of the left and right sides is connected by the anterior gray commissure and the posterior gray commissure.

Posterior gray commissure
Posterior gray commissure
Anterior gray commissure
Anterior gray commissure

Cells with similar structure and functions are grouped into nuclei.

  • In the anterior horn, there are 5 nuclei, which serve as motor centers
  • In the posterior horn, there are also 5 nuclei, serving as sensory centers
  • In the intermediate zone between the horns, there are an additional 2 nuclei
Spinal cord nuclei (diagram)
Spinal cord nuclei (diagram)

The gray matter can also be divided into 10 layers (the so-called Rexed laminae). Essentially, these are the same as nuclei, just under a different name. Thus, certain elements of the gray matter correspond to specific laminae.

White matter

White matter
White matter

The gray matter is surrounded by white matter, which forms 3 columns (funiculi):

  • The anterior funiculus
Anterior funiculus
Anterior funiculus
  • The posterior funiculus
Posterior funiculus
Posterior funiculus
  • The lateral funiculus
Lateral funiculus
Lateral funiculus

These funiculi consist of neuronal processes that are grouped into large bundles, known as tracts. These tracts connect different segments of the spinal cord with each other, as well as with the brain.

There are three types of tracts:

  • Ascending tracts, which go towards the brain, are predominantly found in the posterior funiculus
  • Descending tracts, which travel from the brain, are predominantly found in the anterior funiculus
  • Propriospinal (associative) tracts, which go from one spinal segment to another

The lateral funiculus contains both ascending and descending tracts, approximately in equal amounts.

Spinal cord meninges

In the vertebral canal, the spinal cord is covered by three meninges:

The pia mater is the innermost layer.

Pia mater
Pia mater

On the sides, it forms extensions known as the denticulate ligaments,

Denticulate ligaments
Denticulate ligaments
Denticulate ligaments
Denticulate ligaments

which hold the spinal cord in the center of the vertebral canal.

The arachnoid mater is separated from the pia mater by the subarachnoid space, which is filled with cerebrospinal fluid.

Arachnoid mater
Arachnoid mater
Subarachnoid space
Subarachnoid space

The dura mater is separated from the bone by the epidural space,

Dura mater
Dura mater
Dura mater
Dura mater
Epidural space
Epidural space

which contains connective and adipose tissue, as well as venous plexuses. The dura mater smoothly continues into the outer covering of the nerves – the epineurium.

Epineurium
Epineurium

Arterial blood supply

Arterial blood supply to the spinal cord is provided by two systems:

These are the longitudinal vessels that ascend and descend along the surface of the spinal cord:

  • The anterior spinal artery
Anterior spinal artery
Anterior spinal artery
Anterior spinal artery
Anterior spinal artery
  • Two posterior spinal arteries
Posterior spinal artery
Posterior spinal artery
Posterior spinal artery
Posterior spinal artery

As well as branches from various arteries, depending on the section of the spinal cord. They enter the vertebral canal through the intervertebral foramina and are called segmental spinal arteries.

Segmental spinal artery
Segmental spinal artery

In each segment, a segmental artery divides into two branches: an anterior radicular and a posterior radicular artery.

Anterior radicular artery
Anterior radicular artery
Posterior radicular artery
Posterior radicular artery

Additionally, segmental medullary arteries branch off from the segmental spinal arteries. They are directly connected with the longitudinal vessels, acting as anastomoses between two systems.

Segmental spinal artery
Segmental spinal artery

These arteries are not present in every segment; there are about ten in total, the largest of which is called the artery of Adamkiewicz and is located on the left at the level of approximately 9-12 thoracic segments.

Venous Drainage

Venous drainage from the spinal cord is provided by several veins:

  • The anterior spinal vein
Anterior spinal vein
Anterior spinal vein
Anterior spinal vein
Anterior spinal vein
  • The posterior spinal vein
Posterior spinal vein
Posterior spinal vein
Posterior spinal vein
Posterior spinal vein

Two pairs of small veins at the entry points of the anterior and posterior roots

Anterolateral spinal veins
Anterolateral spinal veins
Anterolateral spinal veins
Anterolateral spinal veins

Blood from these veins drains into the vertebral venous plexus, located in the epidural space. From there, it is drained into the large systemic veins of the corresponding body areas.

Vertebral venous plexus - anterior
Vertebral venous plexus - anterior
Vertebral venous plexus - posterior
Vertebral venous plexus - posterior

Dermatomes and Myotomes

Each segment of the spinal cord corresponds to a strictly defined area of the body that receives innervation from that segment. If it is related to the skin area, it is called a dermatome; if it concerns a skeletal muscle or part of it, it is called a myotome. There is a dermatome map used in diagnosing various sensory disorders.

Golosary

Spinal cord: Anatomy & Function

spinal cord
medulla spinalis
vertebral canal
canalis vertebralis
spinal nerve
nervus spinalis
anterior root
radix anterior
posterior root
radix posterior
spinal ganglion
ganglion spinale
cervical enlargement
intumescentia cervicalis
lumbosacral enlargement
intumescentia lumbosacralis
cauda equina
cauda equina
conus medullaris
conus medullaris
filum terminale
filum terminale
anterior median fissure
fissura mediana anterior
posterior median sulcus
sulcus medianus posterior
anterolateral sulcus
sulcus anterolateralis
posterolateral sulcus
sulcus posterolateralis
central canal
canalis centralis
terminal ventricle
ventriculus terminalis
gray matter
substantia grisea
anterior horn
cornu anterius
lateral horn
cornu laterale
posterior horn
cornu posterius
white matter
substantia alba
anterior gray commissure
commissura grisea anterior
posterior gray commissure
commissura grisea posterior
anterior funiculus
funiculus anterior
lateral funiculus
funiculus lateralis
posterior funiculus
funiculus posterior
pia mater
pia mater
arachnoid mater
arachnoidea mater
dura mater
dura mater
subarachnoid space
spatium subarachnoidale
Main screen of the Easy Anatomy 3D app

Download Easy Anatomy 3D and try it for free

  • 3D Atlas
  • Interactive notes
  • Videos on Anatomy
  • Anatomy flashcards

Easy Anatomy

Learn anatomy effectively

3.2K

Функция доступна в приложении

Download the app