Anatomy of the nervous system
A large portion of the body is under the nervous system's control through somatic (voluntary)
and autonomic (involuntary) processes. To comprehend how many of these functions are
feasible, the architecture of the nervous system must be detailed in great depth. According to
the physiological principle of localization of function, certain structures are solely in charge
of carrying out predetermined functions. Although it is a fundamental idea in all of anatomy
and physiology, the nervous system does a great job of illuminating it.
Gray or white matter, which are two different forms of fresh, unstained nerve tissue, can be
exceedingly difficult to perceive any detail within. But when certain areas and structures were
characterized, they were connected to particular functions. A thorough explanation of the
nervous system's architecture that delves deeply into the nature of the central and peripheral
structures is necessary to comprehend these structures and the roles they play.
The commencement of the neurological system's research should begin in the womb, where
each individual human existence begins. The nervous system's embryonic growth provides a
straightforward framework on which increasingly more intricate structures can be created.
With this foundation in place, a comprehensive analysis of the nervoussystem is possible.
The Embryologic Perspective
The brain is a complex organ composed of gray parts and white matter, which can be hard to
distinguish. Starting from an embryologic perspective allows you to understand more easily
how the parts relate to each other. The embryonic nervous system begins as a very simple
structure—essentially just a straight line, which then gets increasingly complex. Looking at
the development of the nervous system with a couple of early snapshots makes it easier to
understand the whole complex system.
In the adult brain, many structures that seem to be near one another are not linked, and the
connections that do exist may seem random. However, the system has an underlying order
that results from the way various components grow. The primary areas of the nervous system
can be identified by observing the trend of development.
The Neural Tube
To begin, a sperm cell and an egg cell fuse to become a fertilized egg. The fertilized egg cell,
or zygote, starts dividing to generate the cells that make up an entire organism. Sixteen days
after fertilization, the developing embryo’s cells belong to one of three germ layers that give
rise to the different tissues in the body. The endoderm, or inner tissue, is responsible for
generating the lining tissues of various spaces within the body, such as the mucosae of the
digestive and respiratory systems.
The mesoderm, or middle tissue, gives rise to most of the muscle and connective tissues.
Finally the ectoderm, or outer tissue, develops into the integumentary system (the skin) and
the nervous system. It is probably not difficult to see that the outer tissue of the embryo
becomes the outer covering of the body. But how is it responsible for the nervous system?
As the embryo develops, a portion of the ectoderm differentiates into a specialized region of
neuroectoderm, which is the precursor for the tissue of the nervous system. Molecular signals
induce cells in this region to differentiate into the neuroepithelium, forming a neural plate.
The cells then begin to change shape, causing the tissue to buckle and fold inward
A neural groove forms, visible as a line along the dorsal surface of the embryo. The ridge-
, like edge on eitherside of the neural groove is referred as the neural fold. As the neural folds
come together and converge, the underlying structure forms into a tube just beneath the
ectoderm called the neural tube. Cells from the neural folds then separate from the ectoderm
to form a cluster of cells referred to as the neural crest, which runs lateral to the neural tube.
The neural crest migrates away from the nascent, or embryonic, central nervous system (CNS)
that will form along the neural groove and develops into several parts of the peripheral
nervous system (PNS), including the enteric nervous tissue. Many tissues that are not part of
the nervous system also arise from the neural crest, such as craniofacial cartilage and bone,
and melanocytes
Primary Vesicles
As the anterior end of the neural tube starts to develop into the brain, it undergoes a couple of
enlargements; the result is the production of sac-like vesicles. Similar to a child’s balloon
animal, the long, straight neural tube begins to take on a new shape. Three vesicles form at the
first stage, which are called primary vesicles. These vesicles are given names that are based
on Greek words, the main root word being enkephalon, which means “brain” (en- = “inside”;
kephalon = “head”).
The prefix to each generally corresponds to its position along the length of the developing
nervous system.
The prosencephalon (pros- = “in front”) is the forward-most vesicle, and the term can be
loosely translated to mean forebrain. The mesencephalon (mes- = “middle”) is the next
vesicle, which can be called the midbrain. The third vesicle at this stage is the
rhombencephalon. The first part of this word is also the root of the word rhombus, which is
a geometrical figure with four sides of equal length (a square is a rhombus with 90° angles).
Whereas prosencephalon and mesencephalon translate into the English words forebrain and
midbrain, there is not a word for “four-sided-figure-brain.” However, the third vesicle can be
called the hindbrain. One way of thinking about how the brain is arranged is to use these
three regions—forebrain, midbrain, and hindbrain—which are based on the primary vesicle
stage of development.
Secondary Vesicles
The brain continues to develop, and the vesicles differentiate further .The three primary
vesicles become five secondary vesicles. The prosencephalon enlarges into two new vesicles
called the telencephalon and the diencephalon. The telecephalon will become the cerebrum.
The diencephalon gives rise to several adult structures; two that will be important are the
thalamus and the hypothalamus. In the embryonic diencephalon, a structure known as the eye
cup develops, which will eventually become the retina, the nervous tissue of the eye called the
retina. This is a rare example of nervous tissue developing as part of the CNS structures in the
embryo, but becoming a peripheral structure in the fully formed nervous system.
The mesencephalon does not differentiate into any finer divisions. The midbrain is an
established region of the brain at the primary vesicle stage of development and remains that
way. The rest of the brain develops around it and constitutes a large percentage of the mass of
the brain. Dividing the brain into forebrain, midbrain, and hindbrain is useful in considering
its developmental pattern, but the midbrain is a small proportion of the entire brain, relatively
speaking.
The rhombencephalon develops into the metencephalon and myelencephalon. The
A large portion of the body is under the nervous system's control through somatic (voluntary)
and autonomic (involuntary) processes. To comprehend how many of these functions are
feasible, the architecture of the nervous system must be detailed in great depth. According to
the physiological principle of localization of function, certain structures are solely in charge
of carrying out predetermined functions. Although it is a fundamental idea in all of anatomy
and physiology, the nervous system does a great job of illuminating it.
Gray or white matter, which are two different forms of fresh, unstained nerve tissue, can be
exceedingly difficult to perceive any detail within. But when certain areas and structures were
characterized, they were connected to particular functions. A thorough explanation of the
nervous system's architecture that delves deeply into the nature of the central and peripheral
structures is necessary to comprehend these structures and the roles they play.
The commencement of the neurological system's research should begin in the womb, where
each individual human existence begins. The nervous system's embryonic growth provides a
straightforward framework on which increasingly more intricate structures can be created.
With this foundation in place, a comprehensive analysis of the nervoussystem is possible.
The Embryologic Perspective
The brain is a complex organ composed of gray parts and white matter, which can be hard to
distinguish. Starting from an embryologic perspective allows you to understand more easily
how the parts relate to each other. The embryonic nervous system begins as a very simple
structure—essentially just a straight line, which then gets increasingly complex. Looking at
the development of the nervous system with a couple of early snapshots makes it easier to
understand the whole complex system.
In the adult brain, many structures that seem to be near one another are not linked, and the
connections that do exist may seem random. However, the system has an underlying order
that results from the way various components grow. The primary areas of the nervous system
can be identified by observing the trend of development.
The Neural Tube
To begin, a sperm cell and an egg cell fuse to become a fertilized egg. The fertilized egg cell,
or zygote, starts dividing to generate the cells that make up an entire organism. Sixteen days
after fertilization, the developing embryo’s cells belong to one of three germ layers that give
rise to the different tissues in the body. The endoderm, or inner tissue, is responsible for
generating the lining tissues of various spaces within the body, such as the mucosae of the
digestive and respiratory systems.
The mesoderm, or middle tissue, gives rise to most of the muscle and connective tissues.
Finally the ectoderm, or outer tissue, develops into the integumentary system (the skin) and
the nervous system. It is probably not difficult to see that the outer tissue of the embryo
becomes the outer covering of the body. But how is it responsible for the nervous system?
As the embryo develops, a portion of the ectoderm differentiates into a specialized region of
neuroectoderm, which is the precursor for the tissue of the nervous system. Molecular signals
induce cells in this region to differentiate into the neuroepithelium, forming a neural plate.
The cells then begin to change shape, causing the tissue to buckle and fold inward
A neural groove forms, visible as a line along the dorsal surface of the embryo. The ridge-
, like edge on eitherside of the neural groove is referred as the neural fold. As the neural folds
come together and converge, the underlying structure forms into a tube just beneath the
ectoderm called the neural tube. Cells from the neural folds then separate from the ectoderm
to form a cluster of cells referred to as the neural crest, which runs lateral to the neural tube.
The neural crest migrates away from the nascent, or embryonic, central nervous system (CNS)
that will form along the neural groove and develops into several parts of the peripheral
nervous system (PNS), including the enteric nervous tissue. Many tissues that are not part of
the nervous system also arise from the neural crest, such as craniofacial cartilage and bone,
and melanocytes
Primary Vesicles
As the anterior end of the neural tube starts to develop into the brain, it undergoes a couple of
enlargements; the result is the production of sac-like vesicles. Similar to a child’s balloon
animal, the long, straight neural tube begins to take on a new shape. Three vesicles form at the
first stage, which are called primary vesicles. These vesicles are given names that are based
on Greek words, the main root word being enkephalon, which means “brain” (en- = “inside”;
kephalon = “head”).
The prefix to each generally corresponds to its position along the length of the developing
nervous system.
The prosencephalon (pros- = “in front”) is the forward-most vesicle, and the term can be
loosely translated to mean forebrain. The mesencephalon (mes- = “middle”) is the next
vesicle, which can be called the midbrain. The third vesicle at this stage is the
rhombencephalon. The first part of this word is also the root of the word rhombus, which is
a geometrical figure with four sides of equal length (a square is a rhombus with 90° angles).
Whereas prosencephalon and mesencephalon translate into the English words forebrain and
midbrain, there is not a word for “four-sided-figure-brain.” However, the third vesicle can be
called the hindbrain. One way of thinking about how the brain is arranged is to use these
three regions—forebrain, midbrain, and hindbrain—which are based on the primary vesicle
stage of development.
Secondary Vesicles
The brain continues to develop, and the vesicles differentiate further .The three primary
vesicles become five secondary vesicles. The prosencephalon enlarges into two new vesicles
called the telencephalon and the diencephalon. The telecephalon will become the cerebrum.
The diencephalon gives rise to several adult structures; two that will be important are the
thalamus and the hypothalamus. In the embryonic diencephalon, a structure known as the eye
cup develops, which will eventually become the retina, the nervous tissue of the eye called the
retina. This is a rare example of nervous tissue developing as part of the CNS structures in the
embryo, but becoming a peripheral structure in the fully formed nervous system.
The mesencephalon does not differentiate into any finer divisions. The midbrain is an
established region of the brain at the primary vesicle stage of development and remains that
way. The rest of the brain develops around it and constitutes a large percentage of the mass of
the brain. Dividing the brain into forebrain, midbrain, and hindbrain is useful in considering
its developmental pattern, but the midbrain is a small proportion of the entire brain, relatively
speaking.
The rhombencephalon develops into the metencephalon and myelencephalon. The
