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The human nervous system, the system that conducts impulses from sensory receptors to the brain and spinal cord and to other parts of the body. Like other higher vertebrates, the human nervous system consists of two main parts: the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves that send impulses to and from the central nervous system). In humans, the brain is particularly large and well developed.
Parts Of The Human Nervous System And Their Functions
Almost all neurons or nerve cells are generated prenatally and in most cases are not later replaced by new neurons. Morphologically, the nervous system appears 18 days after fertilization, with the formation of the neural plate. Functionally, in the second prenatal month, the first sign of arousal occurs in the second prenatal month, when stimulation by touching the upper lip evokes the head withdrawal response. Many head, trunk and leg exercises can be developed in the third month.
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During development, the nervous system undergoes dramatic changes to achieve complex organization. On average, 2.5 million neurons per minute must be generated during prenatal life to produce the approximately 1 trillion neurons found in the mature brain. This includes the formation of neural circuits consisting of 100 trillion synapses. This is because each potential neuron is ultimately connected to a select set of other neurons or specific targets such as sensory endings. Moreover, synaptic connections with other neurons are formed on the cell membranes of the target neurons. It cannot be assumed that the totality of these phenomena is the only product of the genetic code, because there are not enough genes for such complexity. Instead, the differentiation and subsequent development of embryonic cells into mature neurons and glial cells is achieved by two types of influences: (1) specific sets of genes and (2) environmental stimuli from inside and outside the embryo. Genetic influences are crucial to the development of the nervous system in orderly and timed sequences. For example, cell differentiation relies on a series of signals that control transcription, a process by which deoxyribonucleic acid (DNA) molecules are formed into ribonucleic acid (RNA) molecules that express genetic messages that control cellular activity. The environmental influences of the embryo itself include cellular signals that include dynamic molecular factors (
Neuronal development). External environmental factors include nutrition, sensory experiences, social interaction, and learning. All this is important for the correct differentiation of individual neurons and the determination of the details of synaptic connections. Therefore, the nervous system needs constant stimulation throughout life to maintain its functional activity.
In the second week of prenatal life, the rapidly growing blastocyst (the bundle of cells from which the fertilized egg divides) migrates to the embryonic disc. The embryonic disc soon acquires three layers: ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer). In the mesoderm, the notochord, which serves as a temporary spine, grows into the axial body. Both the mesoderm and notochord release chemicals, and undifferentiated ectoderm cells thicken to form the dorsal midline of the body. The neural plate is made up of neural progenitor cells called neuroepithelial cells.
Morphological development). Neuroepithelial cells begin to divide, divide and form immature neurons and neuroglia; This in turn migrates from the neural tube to its final destination. Each nerve produces dendrites and axons; Axons extend and form branches, the ends of which form synaptic connections with selected sets of neurons or muscle fibers.
The Nervous System’s Role In Trauma
Remarkable events in this early development include the systematic migration of billions of neurons, the growth of their axons (many of which travel widely throughout the brain), and the formation of thousands of synapses between individual axons and their target neurons. The migration and growth of neurons are at least partly dependent on chemical and physical influences. The growing axon terminals (called growth cones) sense and respond to various molecular signals by directing axons and nerve branches to appropriate targets and avoiding those that try to converge to inappropriate targets. Once synaptic contact is established, the target cell releases a trophic factor (e.g., nerve growth factor) necessary for the survival of the neuron synapsing with it. Physical cues include contact cues or the migration of immature neurons along glial fibers.
In some developing nervous systems, synaptic connections are initially not precise or stable, and then orderly reorganization occurs, including the removal of many cells and synapses. The instability of some synaptic connections persists until a critical period is reached. Past environmental influences play an important role in correctly identifying neurons and modulating many synaptic connections. After the critical period, synaptic connections become stable and less susceptible to changes under the influence of the environment. This suggests that certain skills and senses may be affected during development (including postnatal life) and that for some mental skills, this adaptation continues into adulthood and late life. This article needs more citations to explain. Help improve this article by adding quotes from credible sources. An item without a source can be suspected and removed. Find Sources: “Local Nervous System” – News Newspapers Books Scientist JSTOR (May 2020) (Learn how and what to remove this news template)
The peripheral nervous system (PNS) is one of the two parts that make up the nervous system of primates, the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia that lie outside the brain and spinal cord.
The main function of the PNS is to connect the CNS to the limbs and organs, especially the brain and spinal cord, and act as a transmitter between the rest of the body.
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Unlike the CNS, the PNS is not protected by the spine and skull or by the blood-brain barrier, which makes it vulnerable to toxins.
The peripheral nervous system can be divided into the somatic nervous system and the autonomic nervous system. In the somatic nervous system, the cranial nerves are part of the PNS, with the exception of the optic nerve (cranial nerve II) along with the retina. The second cranial nerve is not a true peripheral nerve, but a decephalon tract.
The connection between the CNS and the organs allows the system to exist in two different functional states: sympathetic and parasympathetic.
The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system is under voluntary control and transmits signals from the brain to organs such as muscles. The somatic nervous system is part of the somatic nervous system and transmits signals such as taste and touch to the spinal cord and brain. The autonomic nervous system is a “self-regulating” system that affects the functioning of organs that are beyond voluntary control, such as the heart rate or digestive functions.
Human Nervous System Chart
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The somatic nervous system includes the sori nervous system and the somatossoric system and consists of sori nerves and somatic nerves and many nerves that perform both functions.
Cranial nerves in the head and neck carry somatosensory information. There are twelve cranial nerves that originate in the brainstem and mainly control the functions of the anatomical structures of the head, with the exception of some. One unique cranial nerve is the vagus nerve, which receives sensory information from organs in the chest and abdomen. Another unique cranial nerve is the accessory nerve responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which are exclusive to the scalp.
In the rest of the body, spinal nerves are responsible for somatosensory information. They arise from the spinal cord. Often, these individual nerves form a network of interconnected nerve roots (a “plexus”). These nerves control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. These nerve roots are named according to the adjacent spinal cords. In the cervical region, the roots of the spinal nerves emerge above the corresponding vertebrae (i.e., the nerve root from the cranial and 1st cervical vertebrae is called the C1 nerve). From the thoracic region to the coccyx region, the roots of the spinal nerves exit below the corresponding spinal cord. This should be noted
Structure And Function Of The Nervous System
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