The axon of the lower motor neuron then leads the rest of the way to the muscle or other target organ. For adults, this is usually the first or second lumbar vertebrae. A ganglion is a cluster of neurosomas outside the central nervous system.

Performing the role of a bridge or mediating organ, its upper end lies at the level of occipital bone, while the lower end meets lumbar vertebrae.

Below is a 3D model of the spinal cord, which is fully interactive. MNT is the registered trade mark of Healthline Media. At various vertebral levels, the segmental spinal arteries also give off segmental medullary arteries.

However, here you will find that three segments of the region fuse together to form a single unit. According to the American Academy of Neurological Surgeons (AANS), almost half of all spinal cord injuries are complete. For their amelioration, your health care provider may advise you different treatment measures mainly depending on the type and severity of the disorder, but the most frequently recommended strategies include drug administration and surgical therapy. Because of its whitish color, the outer section of the spinal cord—which is formed by bundles of myelinated axons—is called white matter. Second-order neurons send  their fibers up the spinocerebellar tracts and end in the cerebellum. The meningeal branch reenters the vertebral canal and innervates the meninges, vertebrae, and spinal ligaments with sensory and motor fibers. The dura mater forms a loose-fitting sleeve called the dural sheath around the spinal cord. In two areas, the spinal cord is a little thicker than elsewhere. They are components of the sympathetic nervous system. From this point, nervous tissue, including axons of both motor and sensory neurons, extends downward to become spinal nerves at the remaining lumbar and sacral levels forming a structure called the cauda equina (horse’s tail). At the level of vertebra S2, it exits the lower end of the cistern and fuses with the dura mater, and the two form a coccygeal ligament that anchors the cord and meninges to vertebra Co1. Anesthetics are sometimes introduced to this space to block pain signals during childbirth or surgery; this procedure is called epidural anesthesia. Figure 12. Motor fibers of the intercostal nerves innervate the internal oblique, external oblique, and transverse abdominal muscles. at the cervical regions the thickness is about 1/2 inch while reaching the lumbar vertebrae the size is reduced to just 1/4 inches in diameter. Third-order fibers go from the thalamus to the cerebral cortex. An additional lateral horn is visible on each side of the gray matter from segments T2 through L1 of the cord. Several of these tracts undergo decussation as they pass up or down the brainstem and spinal cord—meaning that they cross over from the left side of the body to the right, or vice versa. The spinal cord is a cylindrical shaped bundle of nerve fibers that is connected to the brain at the brain stem. Although continuous with the brain, the spinal cord begins where nervous tissue leaves the cranial cavity at the level of the foramen magnum. A complete spinal cord injury causes a complete loss of sensation and motor function below the level of the injury. It usually stops in the top parts of the lumbar spine. It is therefore susceptible to injury. The major ascending tracts are as follows. The lateral vestibulospinal tract passes down the anterior column of the spinal cord and facilitates neurons that control extensor muscles of the limbs, thus inducing the limbs to stiffen and straighten. The spinal cord and brain are enclosed in three fibrous membranes called meninges (singular meninx). five sacral nerve pairs leave your backbone just beneath each bony segment and are named as S1, S2, S3, S4 and S5. A graduate in biological sciences and a PhD scholar (NCBA&E University, Lahore), M. Isaac combines his vast experience with a keen and critical eye to create practical and inherently engaging content on the human body. Figure 13. The spinal cord is made of gray and white matter just like other parts of the CNS. motor and sensory nerves, each running in opposite direction relative to the other. Extending right from the medulla oblongata and running through vertebral column in your body, it resembles a long, thin, tubular structure that is composed of nervous tissue and the accessory cells. It is a tough membrane about as thick as a rubber kitchen glove, composed of multiple layers of dense irregular connective tissue. The nerve then exits the vertebral canal through the intervertebral foramen. The brain and spinal cord are the major components of … The white matter of the spinal cord surrounds the gray matter. The lateral and medial reticulospinal tracts originate in the reticular formation of the brainstem. The spinal cord has a central core of gray matter that looks somewhat butterfly- or H-shaped in cross sections. The posterior horn receives sensory nerve fibers from the spinal nerves, which usually synapse with networks of interneurons in the horn.

From superficial to deep, they are the dura mater, arachnoid mater, and pia mater. Gray matter has a relatively dull color because it contains little myelin.
Cerebral spinal fluid analysis: What does it show? Described more fully in the human brain article. Spinal nerve damage is assessed by testing the dermatomes with pinpricks and noting areas in which the patient has no sensation. It may seem odd that it has a sacral region when the cord itself ends well above the sacrum. When a sample of cerebrospinal fluid is needed for clinical purposes, it is taken from the lumbar cistern by a procedure called lumbar puncture (or colloquially, spinal tap). In the lumbosacral region, there is a similar lumbar enlargement that issues nerves to the pelvic region and lower limbs. It continues beyond the medullary cone as a fibrous strand, the terminal filum, within the lumbar cistern. They also innervate the bones of the corresponding regions, and carry autonomic fibers to some viscera and blood vessels, thus adjusting blood flow to local needs. The second protective layer is the meninges, three membranes that lie between the bony encasement and the nervous tissue in both the brain and spinal cord. Thus, spinal nerves C1 through C7 emerge superior to the correspondingly numbered vertebrae (nerve C5 above vertebra C5, for example); nerve C8 emerges inferior to vertebra C7; and below this, all the remaining nerves emerge inferior to the correspondingly numbered vertebrae (nerve L3 inferior to vertebra L3, for example). The cuneate fasciculus joins the gracile fasciculus at the T6 level. They feature fissures (anterior) and sulci (anterolateral, posterolateral, and posterior). The tectospinal tract begins in a midbrain region called the tectum and crosses to the contralateral side of the midbrain. Based on their association with the different regions of vertebrae, these segments can be grouped into five broader categories which are briefly described as under: Being the anterior most segments of the spinal cord that run across seven cervical vertebrae, it is located along the neck region. The symptoms usually occur around the spinal cord but may also spread to arms and legs. These are seen only in spinal nerves T1 through L2. In the middle of the commissure is the central canal, which is collapsed in most areas of the adult spinal cord, but in some places (and in young children) remains open, lined with ependymal cells, and filled with cerebrospinal fluid. If a person were to take a “slice” of the spinal cord horizontally, they would see a circular area in the middle covered in protective layers (the meninges). One of the most important sensory roles of these nerves is proprioception, in which the brain receives information about body position and movements from nerve endings in the muscles, tendons, and joints. It is enveloped in an epineurium continuous with that of the nerve. Besides injuries, a number of diseases have been identified affecting the region, viz. The first cervical nerve emerges between the skull and atlas, and the others emerge through intervertebral foramina, including the anterior and posterior foramina of the sacrum and the sacral hiatus. Three layers of tissue protect the spinal cord: the dura mater, arachnoid mater, and pia mater.

The core consists mainly of two posterior (dorsal) horns, which extend toward the posterolateral surfaces of the cord, and two thicker anterior (ventral) horns, which extend toward the anterolateral surfaces. infections, inflammations, tumors, and degenerative disorders. Some viruses can invade the CNS by way of the spinal nerve roots (e.g varicella-zoster virus of shingles and herpes simplex virus of core sores or genital herpes). The diameter ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area. Somatosensory signals are for touch, heat, cold, stretch, pressure, pain, and other sensations. It plays a role in the control of  head position. It is one of the parts of spinal cord that is protected by five lumbar vertebrae, it gives rise to five pairs of nervous extensions each of which emerges below the associated vertebra. It consists of first-order nerve fibers that travel up the ipsilateral side of the spinal cord and terminate at the gracile nucleus in the medulla oblongata of the brainstem.

This tract gets smaller as it descends and gives off nerve fibers, and usually disappears by the midthoracic level. Although the spinal cord is not visibly segmented, the part supplied by each pair of nerves is called a segment. Except in the thoracic region, the anterior rami branch and merge repeatedly to form five webs called nerve plexuses: the small cervical plexus in the neck, the brachial plexus near the shoulder, the lumbar plexus of the lower back, the sacral plexus immediately inferior to this, and finally, the tiny coccygeal plexus adjacent to the lower sacrum and coccyx.
The spinal cord tapers to a point and ends near the intervertebral disc that separates the first (L1) and second lumbar (L2) vertebrae, adults, although it can end as high as thoracic vertebra T12 or as low as the disc between vertebrae lumbar vertebrae L2 and L3. Children’s spinal cords may stop slightly lower, at the second or third lumbar vertebrae.

Segmental spinal arteries arise predominantly from the vertebral and deep cervical arteries in the neck, the posterior intercostal arteries in the thorax, and the lumbar arteries in the abdomen. The spinal cord has a crucial role to play in various functions of our body — including the movement of our limbs and the transmission of sensory and motor nerve impulses to and from the brain. It descends through the brainstem to the upper spinal cord on that side, going only as far as the neck. Many of these fibers have their origin or destination in a region called the brainstem. These membranes separate the soft tissue of the central nervous system from the bones of the vertebrae and skull. Bear in mind that each tract is repeated on the right and left sides of the spinal cord.

This article covers the key anatomy of the spinal cord and its functions. The spinothalamic tract and some smaller tracts form the anterolateral system, which passes up the anterior and lateral columns of the spinal cord. Arising from the lumbar enlargement and medullary cone is a bundle of nerve roots that occupy the vertebral canal from L2 (lumbar vertbra L2) to S5 (sacral vertbra S5). Spinal cord (cross section) google_ad_client: "ca-pub-9759235379140764", Distal to the vertebrae, the branches of a spinal nerve are more complex. Myelin is much like the insulation around electrical wires. Figure 14.


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