AnatomyNeuroanatomySpinal cord

AnatomyNeuroanatomySpinal cord

Spinal cord

Author: Jana Vasković, MD • Reviewer: Nicola McLaren, MSc
Last reviewed: November 03, 2023
Reading time: 12 minutes

Spinal cord (lateral-left view)

You know that situation when you forget that you’ve put your phone in your back pocket and then you hear a crack when you sit down? You probably freeze for a moment and think, “Oh I hope that was my spine”.

Well, even though a broken display may cost as much as a kidney on the black market, we guarantee you that nothing is worth as much as a complete and healthy spinal cord. The spinal cord’s function reflects its anatomy. It is essential for conducting impulses from the brain to the body and generating reflexes that make our daily functioning smooth. This page will focus on spinal cord anatomy and provide you with an insight into why this yellow cable-like structure is an essential conduit for normal functioning of the body.

Key facts about the spinal cord
Definition and function	A part of the central nervous system located in the spinal canal that conveys the information between the brain and the periphery.
Structure and segments	- Composed of an outer layer of white matter and centrally located gray matter. - Along its length, it consists of the cervical, thoracic, lumbar, sacral, and coccygeal segments.
Spinal nerves	31 pair of nerves that emerge from the segments of the spinal cord to innervate the body structures; 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair of spinal nerves.

Contents

Anatomy
Spinal cord tracts
Spinal nerves
Reflex arc
Sources
Related articles

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Anatomy

The spinal cord is part of the central nervous system (CNS). It is situated inside the vertebral canal of the vertebral column. During development, there’s a disproportion between spinal cord growth and vertebral column growth. The spinal cord finishes growing at the age of 4, while the vertebral column finishes growing at age 14-18. This is the reason why, in adults, the spinal cord occupies only the upper two thirds of the vertebral canal.

The spinal cord is a continuation of the brainstem. It extends from the foramen magnum at the base of the skull to the L1/L2 vertebra where it terminates as the conus medullaris (medullary cone). A thin thread called filum terminale extends from the tip of the conus medullaris all the way to the 1st coccygeal vertebra (Co1) and anchors the spinal cord in place.

You can easy remember the extent of the spinal cord with a mnemonic 'SCULL', which stands for ' Spinal Cord Until L2 (LL)'.

It's important to master the basics of the nervous system before delving into the details of specific structures like the spinal cord. Check if your knowledge is up to par with our nervous system anatomy practice quizzes.

Throughout its length, the spinal cord shows two well defined enlargements to accommodate for innervation of the upper and lower limbs: one at the cervical level (upper limbs), and one at the lumbosacral level (lower limbs).

Like the vertebral column, the spinal cord is divided into segments: cervical, thoracic, lumbar, sacral, and coccygeal. Each segment of the spinal cord provides several pairs of spinal nerves, which exit from vertebral canal through the intervertebral foramina. There are 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair of spinal nerves (a total of 31 pairs).

Learn more about the spinal cord with our learning material.

Cross section

The spinal cord is made of gray and white matter just like other parts of the CNS. It shows four surfaces: anterior, posterior, and two lateral. They feature fissures (anterior) and sulci (anterolateral, posterolateral, and posterior).

The gray matter is the butterfly-shaped central part of the spinal cord and is comprised of neuronal cell bodies. It shows anterior, lateral, and posterior horns. White matter surrounds the gray matter and is made of axons. It contains pathways that connect the brain with the rest of the body.

Keep learning about the white and grey matter of the spinal cord using our spinal cord diagram labeling exercises and quizzes!

Solidify your knowledge about the spinal cord structures with our interactive study materials.

Spinal meninges

The spinal cord and spinal nerve roots are wrapped within three layers called meninges. The outermost is the dura mater, underneath it is the arachnoid mater, and the deepest is the pia mater. Dura mater has two layers (periosteal and meningeal), between which is the epidural space. Between the arachnoid and pia mater is the subarachnoid space, it is filled with cerebrospinal fluid.
Interested to know everything about the spinal membranes? Sure, check out our study unit:

Blood supply

The spinal cord is supplied by branches of the vertebral and segmental arteries.

The vertebral artery gives rise to anterior and posterior spinal arteries. Segmental arteries, such as the deep cervical, ascending cervical, and posterior intercostal give rise to 31 pairs of radicular arterial branches which supply the roots of spinal nerves.

Similar named veins accompany the arteries. Anterior and posterior spinal veins drain into radicular veins, which then empty into the (internal and external) vertebral venous plexus. This network eventually empties into the vertebral (neck) and segmental (trunk) veins. Blood supply is always an inevitable part of any anatomy study unit.

Here you can find out everything about spinal cord blood supply:

Spinal cord tracts

Spinal cord neural pathways are found within the spinal cord white matter. On each side, the white matter is divided into three funiculi: anterior, lateral, and posterior.

Ascending tracts convey information from the periphery to the brain. On the other hand, the descending tracts carry information from the brain to the periphery. The spinal cord is more than just a conduit, as it also modifies and integrates the information that pass through it.

Key facts about spinal cord tracts
Anterior funiculus	Ascending tract: - Anterior spinothalamic tract Descending tracts: - Anterior corticospinal tract - Vestibulospinal tract - Tectospinal tract - Reticulospinal tract
Lateral funiculus	Ascending tracts: - Posterior spinocerebellar tract - Anterior spinocerebellar tract - Lateral spinothalamic tract - Spinotectal tract - Posterolateral tract of Lissauer - Spinoreticular tract - Spino-olivary tract Descending tracts: - Lateral corticospinal tract - Rubrospinal tract - Lateral reticulospinal tract - Descending autonomic tracts - Olivospinal tract
Posterior funiculus	Ascending tracts: - Gracile fasciculus of Gol - Cuneate fasciculus of Burdach

Master spinal cord anatomy and fortify your understanding of the nervous system by going through this study content.

Spinal nerves

Spinal nerves are grouped as cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and coccygeal (Co1), depending from which segment of the spinal cord they extend.

Segmentation of the spinal cord corresponds to the intrauterine period in which the spinal cord occupies the entire vertebral canal. For this reason in adulthood, where the vertebral column is longer than the cord, each spinal cord segment is located higher than its corresponding vertebra. These differences become more obvious distally towards the lumbar and sacral segments of the spinal cord–for example spinal cord segment L5 is at the level of the L1 vertebra.

Spinal nerves, however, exit the vertebral column at their correspondly numbered vertebrae. Cervical spinal nerves exit through the intervertebral foramina directly above their corresponding vertebrae, whilst thoracic, lumbar and sacral spinal nerves exit directly below.

In order for the more distal spinal nerves to exit they must first descend through the vertebral canal. Since the lumbar and sacral spinal nerves are the farthest from their intervertebral foramina, they are the longest. While descending towards their corresponding intervertebral foramina, lumbosacral spinal nerves form a bundle called the cauda equina (meaning horse’s tail).

Each spinal nerve has an anterior and posterior root. Anterior roots transmit motor information, and they originate from the anterior horns of the gray matter and exit the spinal cord through the anterolateral sulcus. The posterior roots transmit sensory information and have sensory ganglion attached to them. They originate from the posterior horns of gray matter and exit through the posterolateral sulcus of the spinal cord.

The anterior and posterior roots merge just before the intervertebral foramen, and form the trunk of the spinal nerve. The trunk is very short, and soon after exiting the vertebral column, it divides into four branches: anterior ramus, posterior ramus, communicating ramus, and meningeal ramus.

Check out this study unit about the spinal nerves to learn more:

Reflex arc

A huge part of spinal cord function is under the influence of the brain, as it functions to relay information to and from the periphery. But there are many reflexes that are generated in the spinal cord independently from the brain. Spinal reflexes are either monosynaptic or polysynaptic.

Monosynaptic reflexes play out with only two neurons participating in the reflex arc, one sensory and one motor. The first-order neuron (sensory) is in the spinal ganglion, while the second-order neuron (motor) is in the anterior horn of the spinal cord). The sensory neuron gathers impulses from the muscle and sends this information to the motor neuron which innervates the same muscle. The motor neuron then causes contraction of the innervated muscle. An example of a monosynaptic reflex is the stretch reflex.

Polysynaptic reflexes on the other hand have multiple neurons participating. Besides one sensory and one motor neuron, there are also one or more interneurons between them making this communication indirect. They are more complex than monosynaptic reflexes as they involve muscle groups instead of a single muscle. An example is the withdrawal reflex.

Master this interesting subject with these articles, and then take our customized quiz specially designed to test your knowledge about the anatomy, supply and function of the spinal cord!

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Blumenfeld, H. (2018). Neuroanatomy through clinical cases (2nd ed.). Sunderland, MA: Sinauer.
Haines, D. E. (2012). Neuroanatomy: an atlas of structures, sections, and systems (8th ed.). Philadelphia, PA: Wolters Kluwer/ Lippincott Williams & Wilkins Health.
Jacobson, S., & Marcus, E. M. (2008). Neuroanatomy for the neuroscientist. New York: Springer.
Kahle, W., Frotscher, M., & Spitzer, G. (2003). Nervous system and sensory organs. New York: Thieme.
Waxman, S. G. (2010). Clinical neuroanatomy (26th ed.). New York: McGraw-Hill Medical.

Illustrations:

Spinal cord (lateral left view) - Paul Kim
Spinal cord (diagram) - Rebecca Betts
Spinal cord cross section (diagram) - Paul Kim
Spinal meninges (diagram) - Rebecca Betts
Spinal cord blood supply (diagram) - Rebecca Betts
Spinal cord tracts (diagram) - Paul Kim
Spinal nerves (diagram) - Irina Münstermann

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