Learning objectives
By the end of this section, you will be able to:
- Name the main areas of the adult brain.
- Describe the connections between the brain and the brain stem through the diencephalon and from these areas to the spinal cord.
- Recognize complex connections in the subcortical structures of the basal ganglia.
- Explain the distribution of gray and white matter in the spinal cord.
The description of the CNS focuses on the structures of the brain, but the spinal cord is another important organ in this system. While the brain develops as a result of the expansion of the neural tube into primary and then secondary vesicles, the spinal cord maintains the neural tube structure and specializes only in certain areas. As the newborn's spinal cord continues to develop, anatomical features become visible on its surface. The front center line is marked byfisura medial anterior, and the rear center line is marked bymedian posterior groove. The axons enter the posterior side throughdorsal (posterior) nerve root., meaningsurco posterolateralon Both Sides. The axons that leave the anterior side do so throughventral (frontal) nerve root. Note that often the terms dorsal (dorsal = "back") and ventral (ventral = "belly") are used interchangeably with the terms posterior and anterior, especially when referring to the nerves and structures of the spinal cord. You must learn to be comfortable in both cases.
In general, the posterior zones are in charge of sensory functions and the anterior zones are related to motor functions. This is due to the early development of the spinal cord, which divides intoplato baseiplaca alar. The basal plate is closest to the ventral midline of the neural tube, which will become the anterior surface of the spinal cord and give rise to motor neurons. The wing plate is located on the dorsal side of the neural tube and gives rise to neurons that receive sensory input from the periphery.
The length of the spinal cord is divided into areas corresponding to the areas of the spine. The name of the area of the spinal cord corresponds to the level at which the spinal nerves pass through the intervertebral openings. Directly adjacent to the brainstem is the cervical region, then the thoracic region, then the lumbar region, and finally the sacral region. The spinal cord does not take up the entire length of the spine, because after the first year or two, the spinal cord does not grow significantly, but the skeleton continues to grow. Nerves from the spinal cord pass through the intervertebral formins at the appropriate levels. As the spine grows, these nerves grow with it, forming a long bundle of nerves that resembles a horse's tail and is called thehorse's tail. The sacral spinal cord is located at the level of the upper bones of the lumbar vertebrae. Spinal nerves extend from different levels to the proper level of the spine.
gray horns
In cross section, the gray matter of the spinal cord looks like an ink blot, while the distribution of gray matter on one side is reproduced on the other; the shape resembles a bulbous capital letter "H". As it is shown inFigure 14.4.1Gray matter is divided into areas called horns. Herear cornerIt is responsible for sensory processing. Hefront cornersends motor signals to skeletal muscles. Heside corner, found only in the thoracic, upper lumbar, and sacral regions, is a central component of the sympathetic division of the autonomic nervous system.
Some of the largest neurons in the spinal cord are the multipolar motor neurons of the anterior horn. The fibers that cause skeletal muscle contraction are the axons of these neurons. The motor neuron that causes the big toe to twitch, for example, is located in the sacral spinal cord. The axon, which must extend to the belly of this muscle, can measure up to a meter in length. The nerve cell body supporting this long fiber must be quite large, possibly several hundred micrometers in diameter, making it one of the largest cells in the body.
white columns
Just as the gray matter is divided into horns, the white matter of the spinal cord is divided into columns.rising sectionsNervous system fibers in these columns carry sensory information to the brain whiledescending sectionsTransmit motor commands from the brain. Looking at the spinal cord longitudinally, the columns run along its length as continuous bands of white matter. Between the two posterior horns of the gray matter arerear columns. Between the two anterior horns and delimited by the axons of the motor neurons that leave the area of the gray matter are locatedfront columns. The white matter on either side of the spinal cord, between the dorsal horn and the axons of the anterior horn neurons, is locatedside columns. The posterior columns are formed by ascending axons. The anterior and lateral columns are made up of many different groups of axons, both ascending and descending; the latter carry motor commands from the brain to the spinal cord to control output to the periphery.
Third Party Website
Watch thisvideolearn about the gray matter of the spinal cord, which receives information from the dorsal (posterior) root fibers and sends it via the ventral (anterior) root fibers. As discussed in this video, these connections represent the interactions of the CNS with peripheral structures in terms of sensory and motor functions. The spinal cord in the cervical and lumbar regions increases in size as a result of an increased population of neurons. What are these extensions responsible for?
Glossary
- placa alar
- the developmental area of the spinal cord that gives rise to the dorsal horn of the gray matter
- columna frontal
- White matter between the anterior horns of the spinal cord, made up of many different groups of axons, both ascending and descending.
- front corner
- Gray matter of the spinal cord containing multipolar motor neurons, sometimes called the ventral horn.
- fisura medial anterior
- the deep midline of the anterior spinal cord, which marks the separation between the right and left sides of the cord
- rising wire
- Central nervous system fibers that carry sensory information from the spinal cord or its periphery to the brain.
- plato base
- the developmental area of the spinal cord where the lateral and anterior horns of the gray matter are formed
- horse's tail
- a bundle of spinal nerve roots that descends from the lower spinal cord below the first lumbar vertebra and lies in the vertebral cavity; looks like a ponytail
- descending chord
- Central nervous system fibers that carry motor commands from the brain to the spinal cord or periphery.
- dorsal (posterior) nerve root.
- axons entering the dorsal horn of the spinal cord
- columna lateral
- white matter of spinal cord between posterior horn on one side and anterior horn axons on same side; It consists of many different groups of axons, both ascending and descending, that carry motor commands to and from the brain.
- side corner
- area of gray matter of the spinal cord in the thoracic, upper lumbar, and sacral regions, which is the central element of the sympathetic nervous system of the autonomic nervous system
- rear columns
- the white matter of the spinal cord, which is located between the posterior horns of the gray matter, sometimes called the dorsal column; It is made up of ascending axons that carry sensory information to the brain.
- rear corner
- an area of gray matter in the spinal cord that receives sensory input, sometimes called the dorsal horn
- median posterior groove
- a midline feature of the posterior spinal cord that marks the separation between the right and left sides of the cord
- surco posterolateral
- A feature of the posterior spinal cord that marks the entrance of the posterior nerve roots and the separation of the posterior and lateral columns of white matter.
- ventral (frontal) nerve root
- axons emanating from the anterior or lateral horns of the spinal cord
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FAQs
What is the normal anatomy of the spinal cord? ›
Your spinal cord is the long, cylindrical structure that connects your brain and lower back. It contains tissues, fluids and nerve cells. A bony column of vertebrae surrounds and protects your spinal cord. Your spinal cord helps carry electrical nerve signals throughout your body.
At what level does the spinal cord end and why is it important? ›The vertebral column consists of seven cervical, twelve thoracic, and five lumbar segments. In adults, the cord terminates at the level of L1-L2. Thus the cord spans within 20 bony vertebrae. In a child, it terminates at the upper border of L3.
How complicated is the spinal cord? ›The spinal cord study is one of the most complex yet quite a fascinating part of the nervous system. Its complex connections, the development defects, the lesions, and clinical presentation are quite overwhelming and warrants a better understanding of its anatomical and physiological nature.
What are the levels of the spinal cord? ›There are seven cervical vertebrae (C1 through C7), which are in the neck. There are 12 thoracic vertebrae (T1 through T12), which are located in the upper back. There are five lumbar vertebrae (L1 through L5), which are found in the lower back. Below those are five sacral vertebrae, which are fused to form the sacrum.