File Name: nervous system parts and function .zip
In biology , the nervous system is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events.
The central nervous system CNS is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric animals —i. It consists of a large nerve running from the anterior to the posterior, with the anterior end is enlarged into the brain.
Not all animals with a central nervous system have a brain, although the large majority do. The rest of this article exclusively discusses the vertebrate central nervous system, which is radically distinct from all other animals. In vertebrates the brain and spinal cord are both enclosed in the meninges. Within the meninges the brain and spinal cord are bathed in cerebral spinal fluid which replaces the body fluid found outside the cells of all bilateral animals. In vertebrates the CNS is contained within the dorsal body cavity , with the brain is housed in the cranial cavity within the skull , and the spinal cord is housed in the spinal canal within the vertebrae.
In vertebrates the CNS also includes the retina  and the optic nerve cranial nerve II ,   as well as the olfactory nerves and olfactory epithelium. The olfactory epithelium is the only central nervous tissue outside the meninges in direct contact with the environment, which opens up a pathway for therapeutic agents which cannot otherwise cross the meninges barrier.
The CNS consists of the two major structures: the brain and spinal cord. The brain is encased in the skull, and protected by the cranium. Microscopically, there are differences between the neurons and tissue of the CNS and the peripheral nervous system PNS.
The white matter consists of axons and oligodendrocytes , while the gray matter consists of neurons and unmyelinated fibers. Both tissues include a number of glial cells although the white matter contains more , which are often referred to as supporting cells of the CNS. Different forms of glial cells have different functions, some acting almost as scaffolding for neuroblasts to climb during neurogenesis such as bergmann glia , while others such as microglia are a specialized form of macrophage , involved in the immune system of the brain as well as the clearance of various metabolites from the brain tissue.
Upon CNS injury astrocytes will proliferate, causing gliosis , a form of neuronal scar tissue, lacking in functional neurons.
The brain cerebrum as well as midbrain and hindbrain consists of a cortex , composed of neuron-bodies constituting gray matter, while internally there is more white matter that form tracts and commissures. Apart from cortical gray matter there is also subcortical gray matter making up a large number of different nuclei. From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves sometimes segmental nerves .
The nerves connect the spinal cord to skin, joints, muscles etc. All in all 31 spinal nerves project from the brain stem,  some forming plexa as they branch out, such as the brachial plexa , sacral plexa etc.
The spinal cord relays information up to the brain through spinal tracts through the "final common pathway"  to the thalamus and ultimately to the cortex. Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex. Apart from the spinal cord, there are also peripheral nerves of the PNS that synapse through intermediaries or ganglia directly on the CNS. These 12 nerves exist in the head and neck region and are called cranial nerves.
Cranial nerves bring information to the CNS to and from the face, as well as to certain muscles such as the trapezius muscle , which is innervated by accessory nerves  as well as certain cervical spinal nerves. Two pairs of cranial nerves; the olfactory nerves and the optic nerves  are often considered structures of the CNS. This is because they do not synapse first on peripheral ganglia, but directly on CNS neurons.
The olfactory epithelium is significant in that it consists of CNS tissue expressed in direct contact to the environment, allowing for administration of certain pharmaceuticals and drugs. At the anterior end of the spinal cord lies the brain. It is often the main structure referred to when speaking of the nervous system in general. The brain is the major functional unit of the CNS. While the spinal cord has certain processing ability such as that of spinal locomotion and can process reflexes , the brain is the major processing unit of the nervous system.
The brainstem consists of the medulla , the pons and the midbrain. The medulla can be referred to as an extension of the spinal cord, which both have similar organization and functional properties. Regulatory functions of the medulla nuclei include control of blood pressure and breathing.
Other nuclei are involved in balance , taste , hearing , and control of muscles of the face and neck. The next structure rostral to the medulla is the pons, which lies on the ventral anterior side of the brainstem. Nuclei in the pons include pontine nuclei which work with the cerebellum and transmit information between the cerebellum and the cerebral cortex.
The midbrain, or mesencephalon, is situated above and rostral to the pons. It includes nuclei linking distinct parts of the motor system, including the cerebellum, the basal ganglia and both cerebral hemispheres , among others. Additionally, parts of the visual and auditory systems are located in the midbrain, including control of automatic eye movements.
The brainstem at large provides entry and exit to the brain for a number of pathways for motor and autonomic control of the face and neck through cranial nerves,  Autonomic control of the organs is mediated by the tenth cranial nerve. Such functions may engage the heart , blood vessels , and pupils , among others. The brainstem also holds the reticular formation , a group of nuclei involved in both arousal and alertness.
The cerebellum lies behind the pons. The cerebellum is composed of several dividing fissures and lobes. Its function includes the control of posture and the coordination of movements of parts of the body, including the eyes and head, as well as the limbs. Further, it is involved in motion that has been learned and perfected through practice, and it will adapt to new learned movements.
These connections have been shown by the use of medical imaging techniques, such as functional MRI and Positron emission tomography. The body of the cerebellum holds more neurons than any other structure of the brain, including that of the larger cerebrum , but is also more extensively understood than other structures of the brain, as it includes fewer types of different neurons.
The two structures of the diencephalon worth noting are the thalamus and the hypothalamus. The thalamus acts as a linkage between incoming pathways from the peripheral nervous system as well as the optical nerve though it does not receive input from the olfactory nerve to the cerebral hemispheres.
Previously it was considered only a "relay station", but it is engaged in the sorting of information that will reach cerebral hemispheres neocortex. Apart from its function of sorting information from the periphery, the thalamus also connects the cerebellum and basal ganglia with the cerebrum. In common with the aforementioned reticular system the thalamus is involved in wakefullness and consciousness, such as though the SCN.
The hypothalamus engages in functions of a number of primitive emotions or feelings such as hunger , thirst and maternal bonding. This is regulated partly through control of secretion of hormones from the pituitary gland. Additionally the hypothalamus plays a role in motivation and many other behaviors of the individual.
The cerebrum of cerebral hemispheres make up the largest visual portion of the human brain. Various structures combine to form the cerebral hemispheres, among others: the cortex, basal ganglia, amygdala and hippocampus.
The hemispheres together control a large portion of the functions of the human brain such as emotion, memory, perception and motor functions. Apart from this the cerebral hemispheres stand for the cognitive capabilities of the brain.
Connecting each of the hemispheres is the corpus callosum as well as several additional commissures. Functionally, the cerebral cortex is involved in planning and carrying out of everyday tasks. The hippocampus is involved in storage of memories, the amygdala plays a role in perception and communication of emotion, while the basal ganglia play a major role in the coordination of voluntary movement. Both act to add myelin sheaths to the axons, which acts as a form of insulation allowing for better and faster proliferation of electrical signals along the nerves.
Axons in the CNS are often very short, barely a few millimeters, and do not need the same degree of isolation as peripheral nerves. Some peripheral nerves can be over 1 meter in length, such as the nerves to the big toe. To ensure signals move at sufficient speed, myelination is needed. The way in which the Schwann cells and oligodendrocytes myelinate nerves differ. A Schwann cell usually myelinates a single axon, completely surrounding it.
Sometimes, they may myelinate many axons, especially when in areas of short axons. They do this by sending out thin projections of their cell membrane , which envelop and enclose the axon. During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove the neural folds become elevated, and ultimately meet, transforming the groove into a closed tube called the neural tube.
At this stage, the walls of the neural tube contain proliferating neural stem cells in a region called the ventricular zone. The neural stem cells, principally radial glial cells , multiply and generate neurons through the process of neurogenesis , forming the rudiment of the CNS. The neural tube gives rise to both brain and spinal cord. The anterior or 'rostral' portion of the neural tube initially differentiates into three brain vesicles pockets : the prosencephalon at the front, the mesencephalon , and, between the mesencephalon and the spinal cord, the rhombencephalon.
By six weeks in the human embryo the prosencephalon then divides further into the telencephalon and diencephalon ; and the rhombencephalon divides into the metencephalon and myelencephalon. The spinal cord is derived from the posterior or 'caudal' portion of the neural tube.
As a vertebrate grows, these vesicles differentiate further still. The telencephalon differentiates into, among other things, the striatum , the hippocampus and the neocortex , and its cavity becomes the first and second ventricles. Diencephalon elaborations include the subthalamus , hypothalamus , thalamus and epithalamus , and its cavity forms the third ventricle. The tectum , pretectum , cerebral peduncle and other structures develop out of the mesencephalon, and its cavity grows into the mesencephalic duct cerebral aqueduct.
The metencephalon becomes, among other things, the pons and the cerebellum , the myelencephalon forms the medulla oblongata , and their cavities develop into the fourth ventricle. Diagram depicting the main subdivisions of the embryonic vertebrate brain, later forming forebrain , midbrain and hindbrain. Tectum , Cerebral peduncle , Pretectum , Mesencephalic duct. Pons , Cerebellum. Planarians , members of the phylum Platyhelminthes flatworms , have the simplest, clearly defined delineation of a nervous system into a CNS and a PNS.
In arthropods , the ventral nerve cord , the subesophageal ganglia and the supraesophageal ganglia are usually seen as making up the CNS. Arthropoda, unlike vertebrates, have inhibitory motor neurons due to their small size. The major trend that can be observed is towards a progressive telencephalisation: the telencephalon of reptiles is only an appendix to the large olfactory bulb , while in mammals it makes up most of the volume of the CNS.
In the human brain, the telencephalon covers most of the diencephalon and the mesencephalon. Indeed, the allometric study of brain size among different species shows a striking continuity from rats to whales, and allows us to complete the knowledge about the evolution of the CNS obtained through cranial endocasts.
Mammals — which appear in the fossil record after the first fishes, amphibians, and reptiles — are the only vertebrates to possess the evolutionarily recent, outermost part of the cerebral cortex known as the neocortex. There are many CNS diseases and conditions, including infections such as encephalitis and poliomyelitis , early-onset neurological disorders including ADHD and autism , late-onset neurodegenerative diseases such as Alzheimer's disease , Parkinson's disease , and essential tremor , autoimmune and inflammatory diseases such as multiple sclerosis and acute disseminated encephalomyelitis , genetic disorders such as Krabbe's disease and Huntington's disease , as well as amyotrophic lateral sclerosis and adrenoleukodystrophy.
Lastly, cancers of the central nervous system can cause severe illness and, when malignant , can have very high mortality rates.
Introduction to the Central Nervous System
Nervous system , organized group of cells specialized for the conduction of electrochemical stimuli from sensory receptors through a network to the site at which a response occurs. All living organisms are able to detect changes within themselves and in their environments. Changes in the external environment include those of light , temperature , sound , motion, and odour , while changes in the internal environment include those in the position of the head and limbs as well as in the internal organs. Once detected, these internal and external changes must be analyzed and acted upon in order to survive. As life on Earth evolved and the environment became more complex, the survival of organisms depended upon how well they could respond to changes in their surroundings.
The Central Nervous System
The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal cord form the control center known as the central nervous system CNS , where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system PNS monitor conditions inside and outside of the body and send this information to the CNS.
The central nervous system consists of the brain and spinal cord. This article gives a brief overview of the central nervous system CNS. We will look at the types of cells involved, different regions within the brain, spinal circuitry, and how the CNS can be affected by disease and injury. Here are some key points about the central nervous system. More detail and supporting information is in the main article.
The brain and the spinal cord are the central nervous system, and they represent the main organs of the nervous system. The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. The regulation of homeostasis is governed by a specialized region in the brain. The coordination of reflexes depends on the integration of sensory and motor pathways in the spinal cord.
The central nervous system CNS is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric animals —i.