SPINAL CORD: PARTS AND FUNCTIONS (WITH PICTURES) - GEOGRAFÍA - 2025

The spinal cord is a tubular bundle that contains a long, thin structure of nerve tissue and supporting cells. This region of the body covers a large part of the body, specifically it slides from the medulla oblongata of the brainstem (brain) to the lumbar region.

The main function of the spinal cord is to transmit nerve impulses to the 31 pairs of nerves in the medulla oblongata. In this way, it is the region in charge of communicating the brain with the body.

Communication between the body and the brain is carried out through two main transmission mechanisms: the afferent function that sends nerve impulses from the trunk, neck and extremities to the brain, and the efferent function that carries signals from the brain to different regions of the body..

The spinal cord is one of the structures of the body that has a greater study and analysis of both its anatomy and its main functions. It is established that it is one of the most important and compromised regions of the body.

Features of the spinal cord

Evolutionarily, the spinal cord is the first region of the nervous system to appear. It is a necessary structure to integrate bodily functions, communicate them with brain function and relate them to the outside world.

For this reason, not only primates but all vertebrate beings are characterized by having a spinal cord in their body.

In this sense, there are areas of the skin called dermatomes, which are constituted as organized segments. These segments contain their representation in the spinal cord.

Thus, depending on the excitatory or inhibitory processes present in the spinal cord, the different segments of the skin originate primary responses or spinal reflexes. These reflexes are characterized by always producing the same response to the same stimuli, without requiring more processors.

An example of this basic function of the spinal cord would be the transmission of pain caused by a puncture in the skin. The fact of receiving damage in a specific skin region automatically translates into a sensation of pain that is transmitted to the brain.

Thus, in general, the spinal cord constitutes a set of functional segments with connections both afferent (from the body to the brain) and efferent (from the brain to the body). Specifically, there are currently eight cervical, twelve thoracic, five lumbar, and six sacrococcygeal segments.

Cervical (8 pairs), thoracic (12 pairs) and lumbar (5 pairs) segments. Under the lumbar is the sacrococcygeus (5 pairs of sacral nerves and 1 coccygeal nerve).

The cervical segments primarily control the neck, diaphragm, and upper extremities. Instead, the dorsal segments control the thorax and abdomen, the lumbar segments the lower extremities, and the sacrococcygeal segments regulate the functioning of the pelvis and sphincters.

Spinal Cord Parts - Anatomy

Anatomically, the spinal cord has two main elements of study: its external anatomy and its internal anatomy.

External anatomy refers to the qualities of the superficial regions of the spinal cord, while internal anatomy refers to the structures and substances that the spinal cord houses inside.

In this sense, it should be noted that the spinal cord is a highly complex structure. It has multiple elements both inside and outside, as well as multiple properties that are scientifically relevant.

The study of the anatomical properties of the spinal cord has increased the knowledge about the characteristics of this delicate structure of the organism.

Likewise, it has also made it possible to identify the functioning of the spinal cord and detect possible injuries or conditions that can occur in this part of the body.

External anatomy

Vertebral column with spinal cord.

First of all, it should be noted that the spinal cord is the most extensive nervous tissue in the human body. In fact, the axons of the neurons it houses can reach up to a meter in length, being much larger than the neurons of the brain.

It weighs approximately thirty grams in total, and in its full development it can reach a length of between 40 and 45 centimeters. It appears to be somewhat higher in men (45 centimeters) than in women (43 centimeters). This fact is due to the fact that men's bodies tend to be somewhat higher than women's.

Spinal cord marked in blue

The spinal cord is located within the intravertebral bone called the spinal canal, which is located from the foramen magnum to the first or second lumbar vertebra.

In this way, the spinal cord of a newborn reaches the lumbar vertebra three and in embryos it is up to the base of the coccyx of the body. Based on these data, it becomes clear that it is one of the first regions of the body to form.

On the other hand, it has a cylindrical shape in the upper cervical and ventral segments. Instead, it assumes an ovoid shape with a transverse diameter greater than the obverse in the lower cervical and thoracic segments.

Keep in mind that the spinal cord is an asymmetric structure in most people. That is, it tends to be larger in the right hemibody of individuals.

Other important elements about the external anatomical properties of the spinal cord are: the faces and the membranes.

Faces

Externally, the spinal cord has two faces and two main edges. Specifically, it contains a front face, a back face, and two side edges.

The anterior aspect of the spinal cord contains, in its midline, an anterior medial sulcus, which laterally borders the anterior collateral sulci. These anterior collateral grooves are the apparent origins of the motor or efferent nerve roots of the spinal nerves.

The posterior surface also has a medial posterior sulcus, which extends through a septum until reaching the central gray matter. The posterior aspect of the spinal cord is bordered on the sides by the posterior collateral grooves, which correspond to the apparent origins of the sensory nerve roots of the spinal nerves.

On the other hand, the spinal cord presents two main thickenings (regions where its diameter increases). One of them is located in the cervical region while the other is located in the lumbar area.

Cervical thickening is called cervical intumscence and is located between the fourth cervical vertebra and the first vertebra of the trunk. The thickening is formed by the roots of the nerves that transmit sensitivity and motor action from the upper limbs.

Lumbar thickening is called lumbosacral intumscence and is located between the eleventh vertebra of the trunk and the first lumbar vertebra. In this case, the thickening is due to the nerve roots that transmit sensitivity and motor action to and from the lower extremities.

Finally, in the lower portion, the faces of the spinal cord thin out notably, ending later in the shape of a cone point in the coccyx region. This last region of the medulla is called the terminal cone.

In the lateral pates, the spinal cord has two toothed ligaments as a fixation element. On the other hand, in the lower part, the medulla continues with the terminal filum, which extends to the dural cul-de-sac at the level of the second vertebra of the sacrum.

Membranes

The spinal cord contains three membranes that surround its entire structure. These are: the pia mater, the arachnoid mater, and the dura mater.

Cross section of the spinal cord and its membranes

a) Piamother

The pia mater is an internal meninge that protects both the brain and the spinal cord. It is near the nerve structures and is responsible for covering the convolutions of the brain.

Likewise, the pia mater generates choroid formations, which are applied against the ependymal membrane of the ventricles.

A space filled with cerebrospinal fluid called the subarachnoid space is located above the pia mater. Above this space, there is the most homogeneous and distinguishable part of arachnoids, which forms a fine, transparent and lax network that does not enter the grooves of the spinal cord.

b) Arachnoids

The arachnoids are an intermediate meninx that also protects both the brain and the spinal cord. It is located just below the dura and its main function is to distribute cerebrospinal fluid, which circulates through the subarachnoid space.

This membrane is formed by an external and homogeneous lamina, as well as an internal areolar layer that contains large meshes and that constitutes the subarachnoid space.

The external lamina of the arachnoids adheres directly to the dura. The subarachnoid cavity is cylindrical and surrounds the spinal cord and its roots along the entire length of the vertebral canal (to the bottom of the dural sacrum).

c) Dura mater

Finally, the dura is the outermost membrane of the medulla. It constitutes a hollow cylinder that is formed mainly by a fibrous, thick, solid and not very extensible wall.

The outer surface of the dura is regularly rounded and responds to the bony walls and ligaments of the spinal canal. The posterior part of the outer surface of this membrane is in contact with the posterior longitudinal ligament. Instead, laterally, it continues around each spinal nerve.

The inner surface of the dura is smooth and polished, corresponding to the arachnoid. Its upper end continues without clear limits with the cranial dura mater. Its lower end constitutes the dural cul-de-sac, which stops between the second and third sacral vertebrae.

Internal anatomy

Gray matter (1,2,3). White matter (4-13)

Internally, the spinal cord is mainly made up of regions of white matter and regions of gray matter.

Transversely, the medulla contains a wide area of ​​gray matter throughout its length and in its different divisions. This region assumes an "H" or butterfly shape.

Around the region made up of gray matter, the spinal cord contains another region made up of white matter. Thus, the spinal cord characterized by having gray matter in the center and white matter in the peripheral regions.

White and gray matter

This organization is important as it forms an inverse structure to that of the brain. That is, the encephalic regions are characterized by having white matter in the central areas and gray matter in the peripheral regions, however, the spinal cord presents an opposite organization.

The internal and posterior processes of the spinal cord are relatively thin. These extensions are called posterior horns and practically reach the posterior sulcus.

For their part, the anterior extensions are wide and rounded. They are called anterior horns and reach the brain regions.

The three-dimensional arrangement of both the anterior and posterior horns makes it possible to form a series of columns that run through the spinal cord and that constitute the anterior and posterior gray columns.

At a functional level, the posterior horns are responsible for carrying out somato-sensitive activities. They are made up of sensory neurons that receive the impulses that reach the posterior roots.

In this sense, the main function of the posterior horns (those furthest from the skull) is to receive stimuli and transmit them to the brain regions.

The anterior horns, on the other hand, are functionally somato-motor. They are made up of motor neurons whose axons come out through the anterior roots.

On the other hand, a small lateral horn is located in the upper thoracic and lumbar segments. This emerges from the union of the anterior horn with the posterior horn and is characterized by containing sympathetic visceral neurons.

Finally, on the lateral part of the base of the posterior horn of the upper cervical segments is a region called the reticular formation. This formation is characterized by containing mixed white matter and gray matter.

1- Gray matter

The gray matter of the spinal cord is a region that is composed primarily of neuronal bodies and supporting cells. This region contains two anterior gray antlers and two posterior gray antlers, which are joined by a gray commissure.

The gray commissure of the spinal cord is in turn divided by a posterior region and an anterior region. This division of the commissure is made by a small central foramen called the ependymal or ependymal medullary duct.

In the thoracic and lumbar region of the spinal cord, lateral gray horns that have a wedge shape are detected. These horns are formed by the bodies of the neurons of the sympathetic autonomic system.

The consistency of the lateral gray horns is uniform, although the substance that surrounds the ependymal canal is somewhat more transparent and softer than the others. This specific region of the gray matter in the spinal cord is known as the central gelatinous substance.

2- White matter

The white matter of the spinal cord is characterized by surrounding the gray matter. That is, it forms a region that completely surrounds the gray matter that is inside.

The white matter of the spinal cord is made up of the axons of neurons (not the nuclei). These axons are the parts of the cell that carry information, which is why this region is classified as a transmission structure.

The white matter of the spinal cord is divided into three main regions: the anterior region, the lateral region, and the posterior region.

The entry site of the dorsal root is detected through a dorso-lateral sulcus, and the entry of the ventral root is determined by a ventro-lateral sulcus.

These two grooves allow the white matter to divide into a dorsal funiculus called a lateral funiculus and a ventral funiculus.

Cells and functions

At the microscopic level, the spinal cord is characterized by containing different types of cells. This region of the body has ependymal cells, elongated cells, and neurological cells.

These types of cells are organized differently in each region of the spinal cord. The microscopically most interesting areas are the gray matter and the white matter.

Gray matter cells

The gray matter of the spinal cord varies its function and the type of neurons it houses in each area. Thus, it has different properties in its dorsal horn, it is an intermediolateral horn, in its ventral horn and in the intermediate zone.

The dorsal horn of the gray matter receives axons from the dorsal ganglia through its posterior region. This transmission of axons from the dorsal ganglia is carried out by the homonymous roots and is characterized by containing mainly sensitive bundles.

In this sense, the dorsal horn of the gray matter comprises the nucleus of the clarke commune, the place where synapses are made between the fibers that transmit deep unconscious sensitivity.

On the other hand, the dorsal horn of the gray matter also contains the gelatinous substance of rolling, a region where fiber synapses take place that transmits thermo-analgesic sensitivity.

Finally, the nucleus of the dorsal horn is characterized by synapsing the fibers that transmit tactile sensitivity.

Only upper thoracic and lumbar segments of the spinal cord are found on the intermediolateral horn of the gray matter. This region is packed with preganglionic neurons.

Finally, the central horn is composed of axons of multipolar motor neurons, and the intermediate zone is characterized by housing a large number of interneurons.

White matter cells

The white matter of the spinal cord is made up mainly of a large number of nerve fibers, glia, and blood vessels.

In the posterior cord of the white matter are the axons of sensory neurons, whose nuclei are located in the dorsal ganglia. These neurons participate in two modes of conscious proprioception: kinesthesia and epicritic touch.

The posterior cord of the white matter is also characterized by being composed of two different bundles: the Goll bundle in the medial regions and the Burdach bundle in the lateral areas.

The lateral cord of the white matter instead contains both ascending and descending pathways. The ascending axons are responsible for conducting the stimulus of pain, temperature, and thick touch. Instead, the descending fibers are mainly motor neurons, which are responsible for the control of voluntary movements.

Finally, the anterior cord of the white matter also contains ascending and descending pathways. Ascending neurons transmit spinotectal (reflex movements), spinoolivar (skin sensation), and spinothalamic (gross touch and pressure) information. The descending pathways contain motor neurons that are responsible for movement control.

Spinal cord injuries

Incomplete injuries

The upper image shows the syndromes caused by incomplete spinal cord injuries.

Myelopathy

Spinal cord disease (myelopathy) is a disease characterized by causing a chronic alteration of the spinal cord.

This disease is often used to name conditions of the spinal cord that have not been caused by trauma.

The effects of myelopathy may depend on the degree of damage caused to the spinal cord, so a complete injury (if all the symptoms of the disease are present) or an incomplete injury (if only some are present) can result.

Spinal cord injury can generate several symptoms, the main ones are: paralysis or loss of sensation in the muscles of the trunk, neck and extremities, bladder, anal or seminal sphincter disorders and blockage of the sympathetic system, causing hypotension, bradycardia or abdominal distension.

Injuries by region

On the other hand, spinal cord injuries, whether due to myelopathy or trauma to regions of the spinal cord, vary markedly depending on the region affected. For this reason, it is often essential to detect the region of the injured spinal cord.

As has been seen, each spinal segment is responsible for carrying out a series of specific actions related to movement, perception, the functioning of the parasympathetic system and the control of different organs.

In this sense, it has now been detected that injuries to the fourth and seventh cervical vertebrae cause paralysis of the four extremities, and the involvement of the eleventh vertebra of the thorax causes paralysis of the lower extremities.

References

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