The spinal cord is a long, thin, tubular structure made up of
nervous tissue, which extends from the
medulla oblongata
The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...
in the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
to the
lumbar
In tetrapod anatomy, lumbar is an adjective that means ''of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum.''
The lumbar region is sometimes referred to as the lower spine, or as an area of the back i ...
region of the
vertebral column (backbone). The backbone encloses the
central canal of the spinal cord, which contains
cerebrospinal fluid. The
brain and spinal cord together make up the
central nervous system (CNS). In
humans, the spinal cord begins at the
occipital bone
The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobe ...
, passing through the
foramen magnum
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
and then enters the
spinal canal at the beginning of the
cervical vertebrae
In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
. The spinal cord extends down to between the first and second
lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around long in adult men and around long in adult women. The diameter of the spinal cord ranges from in the
cervical and lumbar regions to in the
thoracic area.
The spinal cord functions primarily in the transmission of
nerve signals from the
motor cortex to the body, and from the
afferent fibers of the
sensory neurons to the
sensory cortex The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as a term for the primary and secondary cortices of the different senses (two cortices each, on left and right hemisphere): the visual cortex on the occi ...
. It is also a center for coordinating many
reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
es and contains
reflex arcs that can independently control reflexes.
It is also the location of groups of
spinal interneurons that make up the
neural circuit
A neural circuit is a population of neurons interconnected by synapses to carry out a specific function when activated. Neural circuits interconnect to one another to form large scale brain networks.
Biological neural networks have inspired the ...
s known as
central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.
Structure

The spinal cord is the main pathway for information connecting the brain and
peripheral nervous system.
Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the
foramen magnum
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
, and continues through to the
conus medullaris near the second
lumbar vertebra before terminating in a fibrous extension known as the
filum terminale.
It is about long in males and about in females,
ovoid
An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or ...
-shaped, and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C5 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk. The lumbar enlargement, located between L1 and S3, handles sensory input and motor output coming from and going to the legs.
The spinal cord is continuous with the caudal portion of the medulla, running from the base of the
skull to the body of the first lumbar vertebra. It does not run the full length of the vertebral column in adults. It is made of 31 segments from which branch one pair of sensory nerve roots and one pair of motor nerve roots. The nerve roots then merge into bilaterally symmetrical pairs of
spinal nerve
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into th ...
s. The peripheral nervous system is made up of these spinal roots, nerves, and
ganglia
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...
.
The dorsal roots are afferent
fascicles, receiving sensory information from the skin, muscles, and visceral organs to be relayed to the brain. The roots terminate in
dorsal root ganglia, which are composed of the cell bodies of the corresponding neurons. Ventral roots consist of
efferent fibers that arise from motor neurons whose cell bodies are found in the ventral (or anterior) gray horns of the spinal cord.
The spinal cord (and brain) are protected by three layers of tissue or membranes called
meninges
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
, that surround the canal. The
dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the
vertebrae is a space called the
epidural space. The epidural space is filled with
adipose tissue, and it contains a network of
blood vessels. The
arachnoid mater
The arachnoid mater (or simply arachnoid) is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural c ...
, the middle protective layer, is named for its open, spiderweb-like appearance. The space between the arachnoid and the underlying
pia mater is called the
subarachnoid space
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
. The subarachnoid space contains
cerebrospinal fluid (CSF), which can be sampled with a
lumbar puncture
Lumbar puncture (LP), also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing. The main reason for a lumbar puncture is to ...
, or "spinal tap" procedure. The delicate pia mater, the innermost protective layer, is tightly associated with the surface of the spinal cord. The cord is stabilized within the dura mater by the connecting
denticulate ligaments
Denticulate ligaments (also known as dentate ligaments) are lateral projections of the spinal pia mater forming triangular-shaped ligaments that anchor the spinal cord along its length to the dura mater on each side. There are usually 21 denticula ...
, which extend from the enveloping pia mater laterally between the dorsal and ventral roots. The
dural sac
Dural is a suburb of Sydney, in the state of New South Wales, Australia 36 kilometres north-west of the Sydney central business district in the Local government in Australia, local government areas of Hornsby Shire and The Hills Shire. Dural is ...
ends at the vertebral level of the second
sacral vertebra.
In cross-section, the peripheral region of the cord contains neuronal
white matter tracts containing
sensory
Sensory may refer to:
Biology
* Sensory ecology, how organisms obtain information about their environment
* Sensory neuron, nerve cell responsible for transmitting information about external stimuli
* Sensory perception, the process of acquiri ...
and
motor axons. Internal to this peripheral region is the
grey matter, which contains the
nerve cell bodies arranged in the three
grey columns that give the region its butterfly-shape. This central region surrounds the
central canal, which is an extension of the
fourth ventricle and contains cerebrospinal fluid.
The spinal cord is elliptical in cross section, being compressed dorsolaterally. Two prominent grooves, or sulci, run along its length. The
posterior median sulcus is the groove in the dorsal side, and the
anterior median fissure is the groove in the ventral side.
Segments

The human spinal cord is divided into segments where pairs of spinal nerves (mixed; sensory and motor) form. Six to eight motor nerve rootlets branch out of right and left ventralateral sulci in a very orderly manner. Nerve rootlets combine to form nerve roots. Likewise, sensory nerve rootlets form off right and left dorsal lateral sulci and form sensory nerve roots. The ventral (motor) and dorsal (sensory) roots combine to form
spinal nerve
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into th ...
s (mixed; motor and sensory), one on each side of the spinal cord. Spinal nerves, with the exception of C1 and C2, form inside the
intervertebral foramen (IVF). These rootlets form the demarcation between the central and peripheral nervous systems.

Generally, the spinal cord segments do not correspond to bony vertebra levels. As the spinal cord terminates at the L1-L2 level, other segments of the spinal cord would be positioned superior to their corresponding bony vertebral body. For example, the T11 spinal segment is located higher than the T11 bony vertebra, and the sacral spinal cord segment is higher than the L1 vertebral body.
The
grey column, (as three regions of grey columns) in the center of the cord, is shaped like a butterfly and consists of cell bodies of
interneurons, motor neurons,
neuroglia
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...
cells and
unmyelinated axons. The
anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
and
posterior grey column present as projections of the grey matter and are also known as the horns of the spinal cord. Together, the grey columns and the
gray commissure form the "grey H."
The white matter is located outside of the grey matter and consists almost totally of
myelinated motor and sensory axons. "Columns" of white matter carry information either up or down the spinal cord.
The spinal cord proper terminates in a region called the
conus medullaris, while the
pia mater continues as an extension called the
filum terminale, which anchors the spinal cord to the
coccyx. The
cauda equina ("horse's tail") is a collection of nerves inferior to the conus medullaris that continue to travel through the vertebral column to the coccyx. The cauda equina forms because the spinal cord stops growing in length at about age four, even though the vertebral column continues to lengthen until adulthood. This results in sacral spinal nerves originating in the upper lumbar region. For that reason, the spinal cord occupies only two-thirds of the vertebral canal. The inferior part of the vertebral canal is filled with cerebrospinal fluid (CSF) and the space is called the lumbar cistern.
Within the Central Nervous System (CNS), nerve cell bodies are generally organized into functional clusters, called nuclei. Axons within the CNS are grouped into tracts.
There are 31 spinal cord nerve segments in a human spinal cord:
* 8 cervical segments forming 8 pairs of
cervical nerves (C1 spinal nerves exit the spinal column between the foramen magnum and the C1 vertebra; C2 nerves exit between the posterior arch of the C1 vertebra and the lamina of C2; C3–C8 spinal nerves pass through the IVF above their corresponding cervical vertebrae, with the exception of the C8 pair which exit between the C7 and T1 vertebrae)
* 12 thoracic segments forming 12 pairs of
thoracic nerves
* 5 lumbar segments forming 5 pairs of
lumbar nerves
* 5 sacral segments forming 5 pairs of
sacral nerves
* 1 coccygeal segment
In the fetus, vertebral segments correspond with spinal cord segments. However, because the
vertebral column grows longer than the spinal cord, spinal cord segments do not correspond to vertebral segments in the adult, particularly in the lower spinal cord. For example, lumbar and sacral spinal cord segments are found between vertebral levels T9 and L2, and the spinal cord ends around the L1/L2 vertebral level, forming a structure known as the conus medullaris.
Although the spinal cord cell bodies end around the L1/L2 vertebral level, the spinal nerves for each segment exit at the level of the corresponding vertebra. For the nerves of the lower spinal cord, this means that they exit the vertebral column much lower (more caudally) than their roots. As these nerves travel from their respective roots to their point of exit from the vertebral column, the nerves of the lower spinal segments form a bundle called the cauda equina.
There are two regions where the spinal cord enlarges:
*
Cervical enlargement
The cervical enlargement corresponds with the attachments of the large nerves which supply the upper limbs.
Located just above the brachial plexus, it extends from about the fifth cervical to the first thoracic vertebra, its maximum circumferen ...
– corresponds roughly to the
brachial plexus nerves, which innervate the
upper limb. It includes spinal cord segments from about C4 to T1. The vertebral levels of the enlargement are roughly the same (C4 to T1).
*
Lumbar enlargement
The lumbar enlargement (or lumbosacral enlargement) is a widened area of the spinal cord that gives attachment to the nerves which supply the lower limbs.
It commences about the level of T11 and ends at L2, and reaches its maximum circumference, o ...
– corresponds to the
lumbosacral plexus nerves, which innervate the
lower limb. It comprises the spinal cord segments from L2 to S3 and is found about the vertebral levels of T9 to T12.
Development

The spinal cord is made from part of the
neural tube during development. There are four stages of the spinal cord that arises from the neural tube: The neural plate, neural fold, neural tube, and the spinal cord. Neural differentiation occurs within the spinal cord portion of the tube. As the neural tube begins to develop, the
notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...
begins to secrete a factor known as
Sonic hedgehog
Sonic hedgehog protein (SHH) is encoded for by the ''SHH'' gene. The protein is named after the character ''Sonic the Hedgehog''.
This signaling molecule is key in regulating embryonic morphogenesis in all animals. SHH controls organogenesis and ...
(SHH). As a result, the
floor plate then also begins to secrete SHH, and this will induce the basal plate to develop
motor neurons. During the maturation of the neural tube, its lateral walls thicken and form a longitudinal groove called the
sulcus limitans. This extends the length of the spinal cord into dorsal and ventral portions as well. Meanwhile, the overlying
ectoderm
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...
secretes
bone morphogenetic protein
Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of piv ...
(BMP). This induces the
roof plate
A roof (plural, : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of ...
to begin to secrete BMP, which will induce the
alar plate to develop
sensory neurons. Opposing gradients of such morphogens as BMP and SHH form different domains of dividing cells along the dorsal ventral axis. Dorsal root ganglion neurons differentiate from neural crest progenitors. As the dorsal and ventral column cells proliferate, the lumen of the neural tube narrows to form the small central canal of the spinal cord. The alar plate and the basal plate are separated by the sulcus limitans.
Additionally, the floor plate also secretes
netrins. The netrins act as chemoattractants to
decussation of pain and temperature sensory neurons in the alar plate across the anterior white commissure, where they then ascend towards the
thalamus. Following the closure of the caudal neuropore and formation of the brain's ventricles that contain the choroid plexus tissue, the central canal of the caudal spinal cord is filled with cerebrospinal fluid.
Earlier findings by Viktor Hamburger and Rita Levi-Montalcini in the chick embryo have been confirmed by more recent studies which have demonstrated that the elimination of neuronal cells by
programmed cell death (PCD) is necessary for the correct assembly of the nervous system.
Overall, spontaneous embryonic activity has been shown to play a role in neuron and muscle development but is probably not involved in the initial formation of connections between spinal neurons.
Blood supply
The spinal cord is supplied with blood by three arteries that run along its length starting in the brain, and many arteries that approach it through the sides of the spinal column. The three longitudinal arteries are the
anterior spinal artery, and the right and left
posterior spinal arteries
The posterior spinal artery (dorsal spinal arteries) arises from the vertebral artery in 25% of humans or the posterior inferior cerebellar artery in 75% of humans, adjacent to the medulla oblongata. It supplies the grey and white posterior columns ...
.
These travel in the
subarachnoid
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
space and send branches into the spinal cord. They form
anastomoses (connections) via the anterior and posterior
segmental medullary arteries, which enter the spinal cord at various points along its length.
The actual blood flow caudally through these arteries, derived from the posterior cerebral circulation, is inadequate to maintain the spinal cord beyond the cervical segments.
The major contribution to the arterial blood supply of the spinal cord below the cervical region comes from the radially arranged posterior and anterior
radicular arteries, which run into the spinal cord alongside the dorsal and ventral nerve roots, but with one exception do not connect directly with any of the three longitudinal arteries.
These intercostal and lumbar radicular arteries arise from the aorta, provide major anastomoses and supplement the blood flow to the spinal cord. In humans the largest of the anterior radicular arteries is known as the
artery of Adamkiewicz, or anterior radicularis magna (ARM) artery, which usually arises between L1 and L2, but can arise anywhere from T9 to L5. Impaired blood flow through these critical radicular arteries, especially during surgical procedures that involve abrupt disruption of blood flow through the aorta for example during aortic aneurysm repair, can result in spinal cord infarction and paraplegia.
Function
Somatosensory organization

In the
dorsal column-medial lemniscus tract, a primary neuron's axon enters the spinal cord and then enters the dorsal column. Here the dorsal column connects to the axon of the nerve cell. If the primary axon enters below spinal level T6, the axon travels in the
gracile fasciculus
Gracility is slenderness, the condition of being gracile, which means slender. It derives from the Latin adjective ''gracilis'' (masculine or feminine), or ''gracile'' ( neuter), which in either form means slender, and when transferred for examp ...
, the medial part of the column. If the axon enters above level T6, then it travels in the
cuneate fasciculus
Cuneate means "wedge-shaped", and can apply to:
* Cuneate leaf, a leaf shape
* Cuneate nucleus, a part of the brainstem
* Cuneate fasciculus
Cuneate means "wedge-shaped", and can apply to:
* Cuneate leaf, a leaf shape
* Cuneate nucleus, a part o ...
, which is lateral to the fasciculus gracilis. Either way, the primary axon ascends to the lower
medulla, where it leaves its fasciculus and synapses with a secondary neuron in one of the
dorsal column nuclei: either the
nucleus gracilis
In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the bottom of the medulla oblongata. Both nu ...
or the
nucleus cuneatus
In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the bottom of the medulla oblongata. Both nu ...
, depending on the pathway it took. At this point, the secondary axon leaves its nucleus and passes anteriorly and medially. The collection of secondary axons that do this are known as
internal arcuate fibers. The internal arcuate fibers
decussate
Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. .
Similarly, the anatomical term chiasma is named aft ...
and continue ascending as the contralateral
medial lemniscus. Secondary axons from the medial lemniscus finally terminate in the
ventral posterolateral nucleus (VPLN) of the
thalamus, where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the
internal capsule and end in the
primary sensory cortex
In neuroanatomy, the postcentral gyrus is a prominent gyrus in the lateral parietal lobe of the human brain. It is the location of the primary somatosensory cortex, the main sensory receptive area for the sense of touch. Like other sensory areas, ...
.
The proprioception of the lower limbs differs from the upper limbs and upper trunk. There is a four-neuron pathway for lower limb proprioception. This pathway initially follows the dorsal spino-cerebellar pathway. It is arranged as follows: proprioceptive receptors of lower limb → peripheral process → dorsal root ganglion → central process →
Clarke's column → 2nd order neuron → spinocerebellar tract →cerebellum.
The anterolateral system works somewhat differently. Its primary neurons axons enter the spinal cord and then ascend one to two levels before synapsing in the
substantia gelatinosa. The tract that ascends before synapsing is known as
Lissauer's tract. After synapsing, secondary axons decussate and ascend in the anterior lateral portion of the spinal cord as the
spinothalamic tract. This tract ascends all the way to the VPLN, where it synapses on tertiary neurons. Tertiary neuronal axons then travel to the primary sensory cortex via the posterior limb of the internal capsule.
Some of the "pain fibers" in the ALS deviate from their pathway towards the VPLN. In one such deviation, axons travel towards the
reticular formation
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation ...
in the midbrain. The reticular formation then projects to a number of places including the
hippocampus (to create memories about the pain), the
centromedian nucleus (to cause diffuse, non-specific pain) and various parts of the cortex. Additionally, some ALS axons project to the
periaqueductal gray in the pons, and the axons forming the periaqueductal gray then project to the
nucleus raphes magnus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucle ...
, which projects back down to where the pain signal is coming from and inhibits it. This helps control the sensation of pain to some degree.
Motor organization
The
corticospinal tract serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei.
Cortical upper motor neurons originate from
Brodmann areas 1, 2, 3, 4, and 6 and then descend in the posterior limb of the
internal capsule, through the
crus cerebri, down through the pons, and to the
medullary pyramids
In neuroanatomy, the medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit ...
, where about 90% of the axons cross to the contralateral side at the decussation of the pyramids. They then descend as the lateral corticospinal tract. These axons synapse with lower motor neurons in the ventral
horns of all levels of the spinal cord. The remaining 10% of axons descend on the ipsilateral side as the ventral corticospinal tract. These axons also synapse with lower motor neurons in the ventral horns. Most of them will cross to the contralateral side of the cord (via the
anterior white commissure) right before synapsing.
The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons. These are the
rubrospinal tract, the
vestibulospinal tract, the
tectospinal tract and the
reticulospinal tract. The rubrospinal tract descends with the lateral corticospinal tract, and the remaining three descend with the anterior corticospinal tract.
The function of lower motor neurons can be divided into two different groups: the lateral corticospinal tract and the anterior cortical spinal tract. The lateral tract contains upper motor neuronal
axons
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, th ...
which synapse on dorsal lateral (DL) lower motor neurons. The DL neurons are involved in
distal
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
limb control. Therefore, these DL neurons are found specifically only in the cervical and lumbosacral enlargements within the spinal cord. There is no decussation in the lateral corticospinal tract after the decussation at the medullary pyramids.
The anterior corticospinal tract descends
ipsilaterally in the anterior column, where the axons emerge and either synapse on lower ventromedial (VM) motor neurons in the ventral horn ipsilaterally or descussate at the
anterior white commissure where they synapse on VM lower motor neurons
contralaterally . The tectospinal, vestibulospinal and reticulospinal descend ipsilaterally in the anterior column but do not synapse across the anterior white commissure. Rather, they only synapse on VM lower motor neurons ipsilaterally. The VM lower motor neurons control the large, postural muscles of the
axial skeleton. These lower motor neurons, unlike those of the DL, are located in the ventral horn all the way throughout the spinal cord.
Spinocerebellar tracts
Proprioceptive information in the body travels up the spinal cord via three tracks. Below L2, the proprioceptive information travels up the spinal cord in the
ventral spinocerebellar tract. Also known as the anterior spinocerebellar tract, sensory receptors take in the information and travel into the spinal cord. The cell bodies of these primary neurons are located in the
dorsal root ganglia. In the spinal cord, the axons synapse and the secondary neuronal axons decussates and then travel up to the
superior cerebellar peduncle
In the human brain, the superior cerebellar peduncle (brachium conjunctivum) is a paired structure of white matter that connects the cerebellum to the midbrain. It consists mainly of efferent fibers, the cerebellothalamic tract that runs from a cer ...
where they decussate again. From here, the information is brought to deep nuclei of the cerebellum including the
fastigial
The fastigial nucleus is located in the cerebellum. It is one of the four deep cerebellar nuclei (the others being the nucleus dentatus, nucleus emboliformis and nucleus globosus), and is grey matter embedded in the white matter of the cerebell ...
and
interposed nuclei.
From the levels of L2 to T1, proprioceptive information enters the spinal cord and ascends ipsilaterally, where it synapses in
Clarke's nucleus. The secondary neuronal axons continue to ascend ipsilaterally and then pass into the cerebellum via the
inferior cerebellar peduncle. This tract is known as the dorsal spinocerebellar tract.
From above T1, proprioceptive primary axons enter the spinal cord and ascend ipsilaterally until reaching the
accessory cuneate nucleus, where they synapse. The secondary axons pass into the cerebellum via the inferior cerebellar peduncle where again, these axons synapse on cerebellar deep nuclei. This tract is known as the
cuneocerebellar tract.
Motor information travels from the brain down the spinal cord via
descending spinal cord tracts. Descending tracts involve two neurons: the upper motor neuron (UMN) and lower motor neuron (LMN).
[Saladin. Anatomy and Physiology, 5th Ed.] A nerve signal travels down the upper motor neuron until it synapses with the lower motor neuron in the spinal cord. Then, the lower motor neuron conducts the nerve signal to the spinal root where efferent nerve fibers carry the motor signal toward the target muscle. The descending tracts are composed of white matter. There are several descending tracts serving different functions. The corticospinal tracts (lateral and anterior) are responsible for coordinated limb movements.
Clinical significance
A
congenital disorder is
diastematomyelia in which part of the spinal cord is split usually at the level of the upper lumbar vertebrae. Sometimes the split can be along the length of the spinal cord.
Injury
Spinal cord injuries can be caused by trauma to the spinal column (stretching, bruising, applying pressure, severing, laceration, etc.). The vertebral bones or
intervertebral disks can shatter, causing the spinal cord to be punctured by a sharp fragment of
bone. Usually, victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In milder cases, a victim might only suffer loss of
hand
A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...
or foot function. More severe injuries may result in
paraplegia
Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek ()
"half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neural ...
,
tetraplegia (also known as quadriplegia), or full body
paralysis
Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 50 ...
below the site of injury to the spinal cord.
Damage to upper motor neuron axons in the spinal cord results in a characteristic pattern of ipsilateral deficits. These include
hyperreflexia,
hypertonia and muscle weakness. Lower motor neuronal damage results in its own characteristic pattern of deficits. Rather than an entire side of deficits, there is a pattern relating to the
myotome affected by the damage. Additionally, lower motor neurons are characterized by muscle weakness,
hypotonia,
hyporeflexia and
muscle atrophy
Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness ...
.
Spinal shock and
neurogenic shock can occur from a spinal injury. Spinal shock is usually temporary, lasting only for 24–48 hours, and is a temporary absence of sensory and motor functions. Neurogenic shock lasts for weeks and can lead to a loss of muscle tone due to disuse of the muscles below the injured site.
The two areas of the spinal cord most commonly injured are the
cervical spine (C1–C7) and the
lumbar spine (L1–L5). (The notation C1, C7, L1, L5 refer to the location of a specific
vertebra in either the cervical, thoracic, or lumbar region of the spine.) Spinal cord injury can also be non-traumatic and caused by disease (
transverse myelitis,
polio,
spina bifida,
Friedreich's ataxia,
spinal cord tumor,
spinal stenosis etc.)
Globally, it is expected there are around 40 to 80 cases of spinal cord injury per million population, and approximately 90% of these cases result from traumatic events.
Real or suspected spinal cord injuries need immediate immobilisation including that of the head.
Scans will be needed to assess the injury. A steroid,
methylprednisolone, can be of help as can physical therapy and possibly
antioxidant
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
s. Treatments need to focus on limiting post-injury cell death, promoting cell regeneration, and replacing lost cells. Regeneration is facilitated by maintaining electric transmission in neural elements.
Stenosis
Spinal stenosis at the lumbar region are usually due to
disc herniation, hypertrophy of the
facet joint
The facet joints (or zygapophysial joints, zygapophyseal, apophyseal, or Z-joints) are a set of synovial, plane joints between the articular processes of two adjacent vertebrae. There are two facet joints in each spinal motion segment and e ...
and
ligamentum flavum
The ligamenta flava (singular, ''ligamentum flavum'', Latin for ''yellow ligament'') are a series of ligaments that connect the ventral parts of the laminae of adjacent vertebrae. They help to preserve upright posture, preventing hyperflexion, a ...
,
osteophyte, and
spondylolisthesis. Uncommon cause of lumbar spinal stenosis is due to spinal epidural
lipomatosis, a condition where there is excessive deposit of fat in the epidural space, causing compression of nerve root and spinal cord. The epidural fat can be seen as low density on CT scan and high intensity on T2-weighted
fast spin echo MRI images.
Tumours
Spinal tumour
Spinal tumors are neoplasms located in either the vertebral column or the spinal cord. There are three main types of spinal tumors classified based on their location: extradural and intradural (intradural-intramedullary and intradural-extramedullar ...
s can occur in the spinal cord and these can be either inside (intradural) or outside (extradural) the
dura mater.
Procedures
The spinal cord ends at the level of vertebrae L1–L2, while the
subarachnoid space
In anatomy, the meninges (, ''singular:'' meninx ( or ), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in th ...
—the compartment that contains
cerebrospinal fluid— extends down to the lower border of S2.
Lumbar puncture
Lumbar puncture (LP), also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing. The main reason for a lumbar puncture is to ...
s in adults are usually performed between L3–L5 (
cauda equina level) in order to avoid damage to the spinal cord.
In the fetus, the spinal cord extends the full length of the spine and regresses as the body grows.
Additional images
Image:Spinal Cord Sectional Anatomy.png, Spinal Cord Sectional Anatomy. Animation in the reference.
Image:Gray663.png, Diagrams of the spinal cord.
Image:Gray664.png, Cross-section through the spinal cord at the mid-thoracic level.
Image:Gray666.png, Cross-sections of the spinal cord at varying levels.
Image:Cervical vertebra english.png, Cervical vertebra
Image:Gray796.png, A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots.
Image:Sobo 1909 611.png, The spinal cord with dura
Dura may also refer to: Đura such as, for example, Đura Bajalović
Geography
* Dura language, a critically endangered language of Nepal
* Dura, Africa, an ancient city and former bishopric, now a Catholic titular see
* Dura-Europos, an ancient c ...
cut open, showing the exits of the spinal nerves.
Image:Sobo 1909 612.png, The spinal cord showing how the anterior and posterior roots join in the spinal nerves.
Image:Sobo 1909 613.png, The spinal cord showing how the anterior and posterior roots join in the spinal nerves.
Image:Sobo 1909 614.png, A longer view of the spinal cord.
Image:Sobo 1909 615.png, Projections of the spinal cord into the nerves (red motor, blue sensory).
Image:Sobo 1909 616.png, Projections of the spinal cord into the nerves (red motor, blue sensory).
Image:Rabbitspinalcord100x1.jpg, Cross-section of rabbit spinal cord.
File:Neurons-spinal-cord-rat.jpg, Cross section of adult rat spinal cord stained using Cajal method.
See also
*
Brown-Séquard syndrome
*
Hereditary spastic paraplegia (HSP, or familial spastic paraplegia – FSP, Strümpell–Lorrain syndrome)
*
Myelomere A myelomere is the segment of spinal cord to which a given pair of dorsal and ventral roots is attached.
Because the adult spinal cord does not extend down as far as the vertebral column does, the lower myelomeres are not opposite their correspondi ...
*
Neutral spine
*
Poliomyelitis
Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe sym ...
*
Post-polio syndrome
*
Redlich–Obersteiner's zone
The Redlich–Obersteiner's zone, also known as the root entry zone, is a boundary between the central nervous system (CNS) and the peripheral nervous system (PNS).[Subacute combined degeneration of spinal cord
Subacute combined degeneration of spinal cord, also known as myelosis funiculus, or funicular myelosis, also Lichtheim's disease, and Putnam-Dana syndrome, refers to degeneration of the posterior and lateral columns of the spinal cord as a result ...]
*
Tethered spinal cord syndrome
*
Upper-limb surgery in tetraplegia
Upper-limb surgery in tetraplegia includes a number of surgical interventions that can help improve the quality of life of a patient with tetraplegia.
Loss of upper-limb function in patients with following a spinal cord injury is a major barrier ...
References
External links
Spinal Cord Histology– A multitude of great images from the
University of Cincinnati
*
eMedicine: Spinal Cord, Topographical and Functional Anatomy* WebMD. May 17, 2005
Spina Bifida – Topic OverviewInformation about spina bifida in fetuses and throughout adulthood. WebMD children's health. Retrieved March 19, 2007.
Potential for spinal injury repair Retrieved February 6, 2008.
4000 sets of digital images, showing spatial expression patterns for various genes in adult and juvenile mouse spinal cordsfrom the
Allen Institute for Brain ScienceSpinal cord photomicrographs
{{DEFAULTSORT:Spinal Cord
Sensory systems
Motor system
Bones of the vertebral column
Skeletal system