The nervous system is made up of two parts:
the central nervous system, made up of the brain comprising the brain, brainstem, and cerebellum located in the cranial box, and the spinal cord located in the spinal canal. Its role is to receive, record, interpret the signals arriving from the periphery, and organize the response to be sent. * -the peripheral nervous system, made up of the cranial nerves and the spinal nerves which are attached to the central nervous system. Its role is to convey information from peripheral sensitivity or pain receptors to the central nervous system, and to transmit motor commands emitted by nerve centers.
1. The entire brain is located in the cranium. It is made up of:
The brain, situated entirely in the supratentorial space, and formed of two right and left hemispheres, incompletely separated from each other by the interhemispheric fissure marked by the scythe of the brain, and united one to the 'other to their central part
The brainstem, which emerges from the underside of the brain, and has three parts from top to bottom: the right and left cerebral peduncles, the annular protuberance, and the medulla oblongata. From the brainstem emerge all the cranial nerves except the optic nerve and the olfactory nerve located entirely above the tent of the cerebellum.
The cerebellum, located like the brainstem in the posterior fossa and therefore separated from the brain by the tent of the cerebellum. It is formed by two right and left hemispheres, united by the vermis. They are connected to the brainstem on the right as well as on the left by the upper, middle, and lower cerebellar peduncles.
2. The spinal cord extends the brainstem and medulla oblongata. It begins immediately below the foramen magnum. It is located entirely in the spinal canal, which it does not occupy to its full height, as the cord ends approximately at the level of the first lumbar vertebra (L1). From the marrow and from each intervertebral space emerge the spinal nerves consisting of an anterior motor root and a posterior sensory root.
Below L1 and up to the sacrum, the spinal canal is occupied by the roots of the spinal nerves originating from the lumbar cord; all of these roots form what is called by resemblance "the ponytail".
3. Gray matter and white matter
At whatever level, the central nervous system is made up of two different parts characterized by their color: the gray matter and the white matter. In the brain, we describe
a layer of gray matter covering all the hemispheres whose grooves it follows: this is the cerebral cortex or cerebral cortex.
a layer of white matter immediately below the gray bark.
a more complex central area where we can distinguish a part of white matter, which are the corners of the two hemispheres, and a part of gray matter clusters, the basal ganglia.
In the brainstem, gray matter predominates (reticulated substance) and occurs in clusters which are the original nuclei of the cranial nerves. In the cerebellum, gray matter occupies the cerebellar bark or cerebellar cortex, under which white matter and basal ganglia are found. At the level of the spinal cord, the gray matter forms the center, present throughout the height of the spinal cord, drawing an H or butterfly shape on a cross section.
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