Central nervous system
The central nervous system (CNS) is that portion of the vertebrate nervous system that is composed of the brain and spinal cord. Together with the peripheral nervous system (PNS), the other major portion of the nervous system, the CNS coordinates the body's interaction with the environment. The CNS is contained within the dorsal cavity, with the brain within the cranial subcavity (the skull), and the spinal cord in the spinal cavity (within the vertebral column).
Overview
The nervous system is that network of specialized cells, tissues, and organs that coordinates the body's interaction with the environment, such as sensing the environment, monitoring organs, and coordinating the activity of muscles. The nervous system of vertebrate animals is divided into the central nervous system and the peripheral nervous system (PNS). The CNS comprises the brain and spinal cord, whereas the PNS consists of the nerves and neurons that reside or extend outside the central nervous system, such as to serve the limbs and organs.
All parts of the nervous system are made of nervous tissue, which conducts electrical impulses. Prominent components in a nervous system include neurons and nerves. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS.
The nerves that pass through the spinal cord, and nerves from the PNS, provide sensory input to the brain, which processes the information and initiates responses. The spinal cord serves as the main route for the movement of sensory information to and form the brain (Chamberlin and Narins 2005). Information flows to the CNS from the PNS, which senses the internal and external environment, and the response of the brain flows to the various organs and tissues by means of the spinal cord nerve network (Chamberlin and Narins 2005).
The brain and spinal cord are covered by three layers of meninges, which are membranes of connective tissue. Between the layers is also an extracellular fluid called the cerebrospinal fluid. The meninges protect and nourish the neural tissue.
The brain is divided into the three major regions of the forebrain (prosencephalon), the midbrain (mesencephalon), and the hindbrain (rhombencephalon). The brain also has internal cavities (ventricles), which are filled with cerebrospinal fluid and connect with the spinal cavity.
The spinal cord is a long column of neural tissue, extending from the brain downward through a canal in the vertebra, which protect it.
The spinal cord and the brain have nerve cells called neurons, as well as glial cells that provide physical and metabolic support. Glial cells, also called neuroglia or simply glia, are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system. In the human brain, glia are estimated to outnumber neurons by about 10 to 1 (SFN 2000).
The axons of the neurons may or may not be coated with myelin. Myelin is a phospholipid layer that is an outgrowth of glial cells. In the human spinal cord, the axons coated with myelin are on the outside and the axons and dendrites are on the inside, while in the brain this is reversed (Chamberlin and Narins 2005). Myelin coated axons appear white, and thus these regions of the CNS are called "white matter" while "gray matter" is composed of unmyelinated neurons.
Since the strong theoretical influence of cybernetics in the fifties, the CNS is conceived as a system devoted to information processing, where an appropriate motor output is computed as a response to a sensory input. Yet, many threads of research suggest that motor activity exists well before the maturation of the sensory systems and then, that the senses only influence behavior without dictating it. This has brought the conception of the CNS as an autonomous system.
See main article on Brain Function
In the developing fetus, the CNS originates from the neural plate, a specialised region of the ectoderm, the most external of the three embryonic layers. During embryonic development, the neural plate folds and forms the neural tube. The internal cavity of the neural tube will give rise to the ventricular system. The regions of the neural tube will differentiate progressively into transversal systems. First, the whole neural tube will differentiate into its two major subdivisions: spinal cord (caudal) and brain (rostral/cephalic). Consecutively, the brain will differentiate into brainstem and prosencephalon. Later, the brainstem will subdivide into rhombencephalon and mesencephalon, and the prosencephalon into diencephalon and telencephalon.
See main article on Neural development
The CNS is covered by the meninges, the brain is protected by the skull and the spinal cord by the vertebrae. The rhombencephalon gives rise to the pons, the cerebellum and the medulla oblongata, its cavity becomes the fourth ventricle. The mesencephalon gives rise to the tectum, pretectum, cerebral peduncle and its cavity develops into the mesencephalic duct or cerebral aqueduct. The diencephalon give rise to the subthalamus, hypothalamus, thalamus and epithalamus, its cavity to the third ventricle. Finally, the telencephalon gives rise to the striatum (caudate nucleus and putamen), the hippocampus and the neocortex, its cavity becomes the lateral (first and second) ventricles.
See main article on Neuroanatomy
The basic pattern of the CNS is highly conserved throughout the different species of vertebrates and during evolution. The major trend that can be observed is towards a progressive telencephalisation: while in the reptilian brain that region is only an appendix to the large olfactory bulb, it represent most of the volume of the mammalian 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.
See main article on Brain Evolution (Other relevant articles: Brain, Evolution, Encephalization, Neocortex, Archicortex, Vertebrate)
Parts of the vertebrate CNS
| Spinal cord | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Brain | Brain stem | Rhombencephalon |
Pons, Cerebellum, Medulla oblongata |
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| Mesencephalon |
Tectum, Cerebral peduncle, Pretectum, Mesencephalic duct |
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| Prosencephalon | Diencephalon |
Epithalamus, Thalamus, Hypothalamus, Subthalamus, Pituitary gland, Pineal gland, Third ventricle |
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| Telencephalon |
Rhinencephalon, Amygdala, Hippocampus, Neocortex, Lateral ventricles |
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See also
- Glossary of anatomical terminology, definitions and abbreviations
- List of regions in the human brain
- Central nervous system infection
- Neuroradiology
ReferencesISBN links support NWE through referral fees
Society for Neuroscience. 2000. Astrocytes. Brain Briefings December 2000.
Chamberlin, Stacey L., and Brigham Narins. 2005. The Gale encyclopedia of neurological disorders. Detroit: Thomson Gale. ISBN 078769150X.
External links
- Sylvius: 400+ structure neuroanatomical visual glossary; used by over half of U.S. medical schools
- High-Resolution Cytoarchitectural Primate Brain Atlases
- Human Brains: A Learning Tool.
- Explaining the human nervous system.
- Nervous System - Back Pain - Anatomy (info on nerve pairs).
- Textbook in Medical Physiology And Pathophysiology, many links
- Brain and Cranial Nerves, Anatomy and Physiology Lecture, Northland Community College
- Latest Research on the Brain and Central Nervous System From ScienceDaily
Neurons (gray matter): soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine)
types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron (GSA, GVA, Type Ia sensory fiber), Efferent nerve/Motor nerve/Motor neuron (GSE, GVE, Alpha motor neuron, Gamma motoneurons, Upper motor neuron, Lower motor neuron), Interneuron (Renshaw)
Synapses: neuropil, boutons, synaptic vesicle, neuromuscular junction, electrical synapse
Sensory receptors: Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor, Hair cell, Taste bud
Glial cells: astrocyte, ependymal cells, microglia, radial glia
Myelination (white matter): Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
closely related Connective tissue: epineurium, perineurium, endoneurium, nerve fascicle, meninges
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