NERVIOUS SYSTEM
The nervous
system can be separated into different parts due to its structure or function:
Structurally, it
can be divided into the central nervous system (CNS) andrich perifénervous
system(SNP)).
Functionally, it
can be divided intosomic andautonomous parts.
CNS is composed
of the brain and spinal cord; both develop from the neural tube in the embryo.
E l SNP is made up of all nerve structures external to the CNS that connect the
CNS to the body. The elements of this system develop from the growth of neural
crest cells outside the CNS. It consists of the spinal and cranial nerves, the
visceral nerves and plexus, and the enteric nervous system. The detailed
anatomy of a characteristic spinal nerve is described in Chapter 2, which also
lists the spinal nerves. Cranial nerves are described in chapter 8. For their
part, detailed descriptions of nerve plexus are included in chapters referring
to the specific regions in which these plexus are located.
Central nervous
system Brain parts are the brain, cerebellum and brain stem. The brain
hemispheres consist of an external portion or gray substance containing the
cellular bodies, an internal portion or white substance consisting of the axons
that form tracts or pathways, and the ventricles, which are spaces occupied by
cerebrospinal fluid (CSF).
The cerebellum
has two lateral lobes and a portion in the middle line. The components of the
brain stem are the midbrain, bulge and spinal bulb. A more detailed analysis of
the brain is included in Chapter 8. Spinal cord The spinal cord is the part of
the CNS that occupies the upper two-thirds of the spinal canal. It is
approximately cylindrical and circular or oval cross-sectional, with a central
duct.
Functional subdivisions of the CNS
Functionally, the
nervous system can be divided into a somatic and an autonomous part.
The somic
part(soma is theGreek término to designate the body) inerts the structures
(skin and the largestofthelastsqueltic)derived from the is primarily involved
with the reception and response to information from the external environment.
The auto nomaor
vegetative partinerts the body's org anicsystems and other visceral elements,
such as thesmooth musculo and theglándulas, in the peripheral regions of the
Body. It is primarily involved in the detection and response to information of
the internal environment.
Somatic part of the nervous system
The somatic part
of the nervous system consists of:
Nerves that carry
conscious sensitivity from peripheral regions to the CNS.
Nerves that
inertvoluntary muscles.
Somatic nerves
arise segmentally along the CNS in association with the somites, which are also
arranged segmentally along each side of the neural tube). Part of each somita
(dermomyotoma)gives rise to skeletal muscle and skin dermis. As the
dermomyotoma cells differ, they migrate to the posterior (dorsal) and anterior
(ventral) areas of the developing body:
•
Previouslymigrating cells originate the limband trunk muscles
(hipaxialmuscles)and associated dermis.
Thelulas that
migrate later give rise to theintrínsecosorders of thetrunk's dorsalsystem
(epaxialmuculos) and to the associated dermis.