Spinal cord

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 SPINAL CORD

Spinal cordMarrow means crumb and indicates what is inside. Thus we have the spinal cord within the bones, more precisely within the spinal canal.
The spinal cord is a cylindrical mass of nervous tissue located within the spinal canal without completely occupying it. In the adult man it measures approximately 45 cm being a little smaller in the woman.
Cranially the medulla is limited with the bulb, approximately at the level of the foramen magnum of the occipital bone. The marrow caudal limit is of clinical importance and in adults it is usually at L2.
The medulla ends by tapering to form a cone, the medullar cone, which continues with a thin meningeal filament, the terminal filament.

Marrow Shape and Structure

The medulla is approximately cylindrical in shape, flattened in the anterior-posterior direction. Its caliber is not uniform because it has two dilations called cervical swelling and lumbar swelling.

 These medullary swelling correspond to the areas in which they are connected to the thick nerve roots that form the brachial and lumbosacral plexus, destined for the innervation of the upper and lower limbs. Spinal Cord Intumescencesrespectively.

The formation of these swelling is due to the greater number of neurons and, therefore, nerve fibers entering or leaving these areas.

Cervical swelling extends from segments C4 to T1 of the spinal cord and lumbar swelling (lumbosacral) extends from segments T11 to L1 of the spinal cord.

The surface of the spinal cord has the following longitudinal grooves, which run the length of the spinal cord: the posterior median sulcus, anterior median fissure, anterior lateral sulcus and posterior lateral sulcus.

In the cervical cord there is also the posterior intermediate sulcus that lies between the posterior median sulcus and the posterior lateral sulcus and which continues in a posterior intermediate septum within the posterior funicular.

In the anterior lateral and posterior lateral grooves, they connect respectively the ventral and dorsal roots of the spinal nerves.

SPINAL CORD SECTIONS IN ALL REGIONS
 
Spinal Cord Sections
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

In the medulla, the gray matter is located within the white and is in the shape of a butterfly or a & #8220; H & #8221; In it we distinguish on each side three columns that appear in the cuts as horns and which are the anterior, posterior and lateral columns. The lateral spine only appears in the thoracic medulla and part of the lumbar medulla. In the center of the gray matter is the central canal of the medulla.

The white matter is made up of fibers, most of them myelinic, which rise and fall in the medulla and which can be grouped on each side into three funicles or cords:

Anterior Funicular: situated between the anterior midline and anterior lateral sulcus.

Lateral Funicular: Situated between the anterior lateral and posterior lateral grooves.

Posterior Funicular: Located between the posterior lateral sulcus and the posterior median sulcus, the latter being linked to gray matter by the posterior median septum. In the cervical part of the medulla the posterior funiculus is divided by the posterior intermediate sulcus into the gracilis fasciculus and the cuneiform fascicle.

Spinal Nerve Connections:
In the anterior lateral and posterior lateral grooves they are connected with small nerve filaments called root filaments, which unite to form, respectively, the ventral and dorsal roots of the spinal nerves. The two roots join together to form the spinal nerves, occurring at a point distal to the spinal ganglion in the dorsal root.

NERVOUS ROOTS
 Nervous Root
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

There are 31 pairs of spinal nerves to which correspond 31 spinal segments thus distributed.:

  • 8 cervicals
  • 12 thoracic
  • 5 lumbar
  • 5 sacrals
  • 1 coccygeal

We found 8 pairs of cervical nerves and only 7 cervical vertebrae because the first pair of spinal nerves comes out between the occipital and C1.

Relationship of nerve roots to vertebrae
 Relationship of Roots to the Spine
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

 

Marrow Topography:

Equine TailAt a level below the second lumbar vertebra we find only the meninges and nerve roots of the last spinal nerves, which are arranged around the medullary cone and terminal filament, together constitute the so-called equine tail.

Because nerve roots maintain their relationships with their intervertebral foramina, there is a lengthening of the roots and a decrease in the angle they make to the medulla. These phenomena are most pronounced in the caudal part of the medulla, leading to the formation of the equine tail.

Also as a consequence of the difference in growth rates between the spine and the medulla, we have the distancing of the medullary segments of the corresponding vertebrae. Thus, in adults, the T11 and T12 vertebrae correspond to the lumbar segments. To know what level of the marrow each vertebra corresponds to, we have the following rule: Between levels C2 and T10, we add number two to the spinous process of the vertebra and whether it has the underlying medullary segment. The spinous processes of T11 and T12 correspond to the five lumbar segments, while the spinous process of L1 corresponds to the five sacral segments.

Spinal Cone Terminal filament
Spinal Cone Terminal filament

Marrow Wrap:

The medulla is surrounded by fibrous membranes called meninges, which are: Dura, Arachnoid and Pi.

THE Dura mater and the thickest one that surrounds the whole marrow, like a glove, the dural sac. Cranially, it continues into the cranial dura, caudally it ends in a sac fundus at the level of vertebra S2. Lateral extensions of the dura mater sheath the roots of the spinal nerves, constituting a connective tissue (epineurium) that surrounds the nerves.

SPINAL CORD WRAPS
 Arachnoid

THE Arachnoid between the dura and the pia mater. It comprises a leaflet juxtaposed to the dura and a tangle of arachnoid trabeculae, which attach this leaflet to the pia mater.
THE Sink It is the most delicate and innermost membrane. It closely adheres to the superficial tissue of the medulla and penetrates the anterior median fissure. When the medulla terminates in the medullary cone, the pia mater continues caudally, forming an off-white filament called the terminal filament.

This filament pierces the bottom of the dural sac and continues until the sacral hiatus. As it passes through the dural sac, the terminal filament receives several extensions of the dura mater and the assembly is called the dura mater filament. This, when inserted into the periosteum of the dorsal surface of the coccyx, constitutes the coccygeal ligament. The pia mater forms on each side of the medulla a longitudinal fold called the denticulate ligament, which is arranged in a frontal plane along the entire length of the medulla.

The medial margin of each ligament continues with the pia mater of the lateral aspect of the medulla along a continuous line that runs between the dorsal and ventral roots. The lateral margin has about 21 triangular processes that fit firmly into the arachnoid and dura mater at a point that changes with the emergence of the spinal nerves. The two denticulated ligaments are elements of spinal cord fixation and important reference points in surgeries of this organ.
Spinal Cord Wrap
Among the meninges there are spaces that are important for the medical clinic due to the pathologies that may be involved with these structures, such as: extradural hematoma, meningitis, etc. The epidural or extradural space lies between the dura and the periosteum of the vertebral canal.

It contains adipose tissue and a large number of veins that make up the internal vertebral venous plexus. The subdural space between the dura and arachnoid is a narrow slit containing a small amount of fluid. The subarachnoid space contains a fairly large amount of cerebrospinal fluid or cerebrospinal fluid. Some authors still consider another space called subpial, located between the pia mater and the nervous tissue.

Structures of
Nervous system
Nervous tissue

Brainstem

Cerebellum

Diencephalon

Telencephalon

Meninges and CSF

Brain Vascularization

Peripheral Nervous System

 

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