Nerve

2008-04-08T12:17:00.000-07:00

Nerve
From Wikipedia, the free encyclopedia

Nerves (yellow)

A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the non-axon glial cells that ensheath the axons in myelin.

Anatomy
Nerves are part of the Peripheral Nervous System . Afferent nerves convey sensory signals to the Central Nervous System, for example from skin or organs, while efferent nerves conduct stimulatory signals from the central nervous system to the muscles and glands. Afferent and efferent axons are often arranged together, forming mixed nerves. For example, the median nerve controls motor and sensory function in the hand.

Billions of long nerve cells, called neurons, make up the body's nervous system. Neurons receive and transmit chemical-electrical messages to and from the brain. Each neuron is long and thin. One end receives messages and the other transmits the message to the next neuron. The messages "jump" across a gap from one neuron cell to another.
Each peripheral nerve is covered externally by a dense sheath of connective tissue, the epineurium. Underlying this is a layer of flat cells forming a complete sleeve, the perineurium. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurial sheath. This forms an unbroken tube which extends from the surface of the spinal cord to the level at which the axon synapses with its muscle fibres or ends in sensory receptors. The endoneurial sheath consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Peripheral nerves are richly supplied with blood.

Most nerves connect to the Central Nervous System through the spinal cord. The twelve cranial nerves, however, connect directly to parts of the brain. Spinal nerves are given letter-number combinations according to the vertebra through which they connect to the spinal column. Cranial nerves are assigned numbers, usually expressed as Roman numerals from I to XII. In addition, most major nerves have descriptive names. Inside the central nervous system, distinguishable bundles of axons are termed tracts rather than nerves.

The signals that nerves carry, sometimes called nerve impulses, are also known as action potentials. These are rapidly (up to 120 m/s) traveling electrical waves, which typically begin in the cell body of a neuron and propagate down the axon to its tip or "terminus." The signals cross over from the terminus of the axon to the adjacent neurotransmitter receptor through a gap called the synapse. Motor neurons innervate or activate muscles groups.

Clinical importance
Damage to nerves can be caused by physical injury, swelling (e.g. carpal tunnel syndrome), autoimmune diseases (e.g. Guillain-Barre Syndrome), infection (neuritis), Diabetes, or failure of the blood vessels surrounding the nerve. A pinched nerve occurs when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis. Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain occurs because when a nerve is damaged, signalling is defective from all parts of the area from which the nerve receives input, not just the site of the damage. Neurologists usually diagnose disorders of the nerves by a physical examination, including the testing of reflexes, walking and other directed movements, muscle weakness, proprioception, and the sense of touch. This initial exam can be followed with tests such as nerve conduction study and electromyography (EMG).

See also
Nervous System
Dermatome (Anatomy)
Nerve injury

Additional images

Peripheral nerve, cross section

v • d • eNerves:
spinal nerves
Cervical (8)
C1, C2, C3, C4, C5, C6, C7, C8 anterior (Cervical plexus, Brachial plexus) - posterior (Posterior branches of cervical nerves, Suboccipital - C1, Greater occipital - C2, Third occipital - C3)
Thoracic (12)
T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12anterior (Intercostal, Intercostobrachial - T2, Thoraco-abdominal nerves - T7-T11, Subcostal - T12) - posterior (Posterior branches of thoracic nerves)
Lumbar (5)
L1, L2, L3, L4, L5anterior (Lumbar plexus, Lumbosacral trunk) - posterior (Posterior branches of the lumbar nerves, Superior cluneal L1-L3)
Sacral (5)
S1, S2, S3, S4, S5anterior (Sacral plexus) - posterior (Posterior branches of sacral nerves, Medial cluneal nerves)
Coccygeal (1)
anterior (Coccygeal plexus) - posterior (Posterior branch of coccygeal nerve)

v • d • eNerves of head and neck:
the cranial nerves
olfactory (AON->I)
olfactory bulb - olfactory tract
optic (LGN->II)
optic chiasm - optic tract
oculomotor (ON,EWN->III)
superior branch (parasympathetic root of ciliary ganglion/ciliary ganglion) - inferior branch
trochlear (TN->IV)
no significant branches
trigeminal (PSN,TSN,MN,TMN->V)
trigeminal ganglion • ophthalmic • maxillary • mandibular
abducens (AN->VI)
no significant branches
facial (FMN,SN,SSN->VII)
near origin
nervus intermedius • geniculate
inside facial canal
greater petrosal (pterygopalatine ganglion) - nerve to the stapedius - chorda tympani (lingual nerve, submandibular ganglion)
at stylomastoid foramen
posterior auricular - suprahyoid (digastric, stylohyoid) - parotid plexus (temporal, zygomatic, buccal, mandibular, cervical)
vestibulocochlear (VN,CN->VIII)
cochlear (striae medullares, lateral lemniscus) • vestibular (Scarpa's ganglion)
glossopharyngeal (NA,ISN,SN->IX)
before jugular fossa
ganglia (superior, inferior)
after jugular fossa
tympanic (tympanic plexus, lesser petrosal, otic ganglion) • stylopharyngeal branch • pharyngeal branches • tonsillar branches • lingual branches • carotid sinus
vagus (NA,DNVN,SN->X)
before jugular fossa
ganglia (superior, inferior)
after jugular fossa
meningeal branch - auricular branch
neck
pharyngeal branch (pharyngeal plexus) - superior laryngeal (external, internal) - recurrent laryngeal (inferior) - superior cervical cardiac
thorax
inferior cardiac - pulmonary - vagal trunks (anterior, posterior)
abdomen
celiac - renal - hepatic - anterior gastric - posterior gastric
accessory (NA,SAN->XI)
cranial - spinal
hypoglossal (HN->XII)
lingual branches

v • d • eNerves of head and neck: the cervical plexus (C1-C4)
superficial
C2-C3: Lesser occipital • Greater auricular • Transverse cervicalC3-C4: Supraclavicular
deep
C1-C3: Ansa cervicalis (superior root, inferior root)C3-C5: Phrenic

v • d • eNerves of upper limbs (primarily): the brachial plexus (C5-T1)
Supraclavicular
root (dorsal scapular, long thoracic) - upper trunk (suprascapular, to the subclavius)
Infraclavicular: lateral cord
lateral pectoral
musculocutaneous (lateral cutaneous of forearm)median/lateral root: anterior interosseous - palmar - recurrent - common palmar digital (proper palmar digital)
Infraclavicular: medial cord
medial pectoral
cutaneous: medial cutaneous of forearm • medial cutaneous of arm
ulnar: muscular - palmar - dorsal (dorsal digital nerves) - superficial (common palmar digital, proper palmar digital) - deep median/medial root: see above
Infraclavicular: posterior cord
subscapular (upper, lower) • thoracodorsal
axillary (superior lateral cutaneous of arm)radial: muscular - cutaneous (posterior of arm, inferior lateral of arm, posterior of forearm) - superficial (dorsal digital nerves) - deep (posterior interosseous)
Other
cutaneous innervation of the upper limbs

v • d • eNerves - autonomic nervous system (sympathetic nervous system/ganglion/trunks and parasympathetic nervous system/ganglion)
Head/cranial
Ciliary ganglion: roots (Sensory, Parasympathetic, Sympathetic) - Short ciliary
Pterygopalatine ganglion: deep petrosal - nerve of pterygoid canalbranches of distribution: greater palatine (inferior posterior nasal branches) - lesser palatine - nasopalatine (medial superior posterior nasal branches) - pharyngeal
Submandibular ganglion Otic ganglion
Neck/cervical
paravertebral ganglia: Cervical ganglia (Superior, Middle, Inferior) - Stellate ganglion prevertebral plexus: Cavernous plexus - Internal carotid
Chest/thorax
paravertebral ganglia: Thoracic ganglia
prevertebral plexus: Cardiac plexus - Esophageal plexus - Pulmonary plexus - Thoracic aortic plexus
splanchnic nerves: cardiopulmonary - thoracic cardiac nerves: Superior - Middle - Inferior
Abdomen/Lumbar
paravertebral ganglia: Lumbar ganglia
prevertebral ganglia: Celiac ganglia (Aorticorenal) - Superior mesenteric ganglion - Inferior mesenteric ganglion
prevertebral plexus: Celiac plexus - (Hepatic, Splenic, Pancreatic) - aorticorenal (Abdominal aortic plexus, Renal/Suprarenal) - Superior mesenteric (Gastric) - Inferior mesenteric (Spermatic, Ovarian) - Superior hypogastric (hypogastric nerve, Superior rectal) - Inferior hypogastric (Vesical, Prostatic/Cavernous nerves of penis, Uterovaginal, Middle rectal)
splanchnic nerves: Lumbar splanchnic nerves enteric nervous system: Meissner's plexus • Auerbach's plexus
Pelvis/sacral
paravertebral ganglia: Sacral ganglia - Ganglion impar splanchnic nerves: Pelvic splanchnic nerves - Sacral splanchnic nerves
All
Rami communicans (White, Gray) - Preganglionic fibers - Postganglionic fibers

v • d • eNerves of lower limbs and lower torso: the lumbosacral plexus (L1-Co)
lumbar plexus (L1-L4)
iliohypogastric: lateral cutaneous branch - anterior cutaneous branch
ilioinguinal: anterior scrotal ♂/labial ♀
genitofemoral: femoral branch/lumboinguinal - genital branch
lateral cutaneous of thigh: patellar
obturator: anterior (cutaneous) - posterior - accessory femoral: anterior cutaneous branches - saphenous (infrapatellar, medial crural cutaneous)
sacral plexus (L4-S4)
sciatic
common fibular: lateral sural cutaneous (sural communicating branch) - deep fibular (lateral terminal branch, medial terminal branch, dorsal digital) - superficial fibular (medial dorsal cutaneous, intermediate dorsal cutaneous, dorsal digital)
tibial: medial sural cutaneous - medial calcaneal - medial plantar (common plantar digital nerves, proper plantar digital) - lateral plantar (deep branch, superficial branch, common plantar digital, proper plantar digital)sural: lateral dorsal cutaneous - lateral calcaneal
other
muscular: superior gluteal/inferior gluteal - lateral rotator group (to quadratus femoris, to obturator internus, to the piriformis)cutaneous: posterior cutaneous of thigh (inferior cluneal, perineal branches) - perforating cutaneous
coccygeal plexus (S4-Co)
pudendal: inferior anal - perineal (deep, posterior scrotal ♂/labial ♀) - dorsal of the penis ♂/clitoris ♀anococcygeal
cutaneous innervation of the lower limbs

Retrieved from "http://en.wikipedia.org/wiki/Nerve"
Categories: Nervous system Neuroanatomy

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Nervous System

2008-04-07T14:39:00.000-07:00

Nervous system
From Wikipedia, the free encyclopedia

Neuroscience Portal
The nervous system is a highly specialized network whose principal components are nerves called neurons. Neurons are interconnected to each other in complex arrangements, and have the property of conducting, using electrochemical signals, a great variety of stimuli both within the nervous tissue as well as from and towards most of the other tissues. Thus, neurons coordinate multiple functions in organisms. Nervous systems are found in many multicellular animals but differ greatly in complexity between species.[1]

The Human Nervous System

Red is CNS and blue is PNS.

Nervous system in humans
The human nervous system can be observed both with gross anatomy, (which describes the parts that are large enough to be seen with the plain eye,) and microanatomy, (which describes the system at a cellular level.) At gross anatomy, the nervous system can be grouped in distinct organs, these being actually stations which the neural pathways cross through. Thus, with a didactical purpose, these organs, according to their ubication, can be divided in two parts: the central nervous system (CNS) and the peripheral nervous system (PNS).[2]

Central nervous system

The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. The CNS is contained within the dorsal cavity, with the brain within the cranial cavity, and the spinal cord in the spinal cavity. The CNS is covered by the meninges. The brain is also protected by the skull, and the spinal cord is also protected by the vertebrae. The nervous system can be connected into many systems that can function together. The two systems are central nervous system (CNS)and the peripheral nervous system (PNS).
Centralnervoussystem
Brain
Prosencephalon
Telencephalon
Rhinencephalon, Amygdala, Hippocampus, Neocortex, Lateral ventricles
Diencephalon
Epithalamus, Thalamus, Hypothalamus, Subthalamus, Pituitary gland, Pineal gland, Third ventricle
Brain stem
Mesencephalon
Tectum, Cerebral peduncle, Pretectum, Mesencephalic duct
Rhombencephalon
Metencephalon
Pons, Cerebellum,
Myelencephalon
Medulla oblongata
Spinal cord

Peripheral nervous system
Main article: Peripheral Nervous System
The PNS consists of all the other nervous structures that do not lie within it. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS.

Microanatomy
The nervous system is, on a small scale, primarily made up of neurons. However, glial cells also play a major role.

Neurons
Main article: Neuron
They are the core components of both the central nervous system & peripheral nervous system. Neurons are sensors that send electric messages to the Central Nervous System which send the electric messages back to the neurons telling them how to react, where the messages are finally sent back directly to the brain. These messages travel at a usual pace of 100 meters per second.

Glial cells
Main article: Glial cell
Glial cells 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.[3]
Glial cells provide support and protection for neurons. They are thus known as the "glue" of the nervous system. The four main functions of glial cells are to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy pathogens and remove dead neurons.

Physiological division
A less anatomical but much more functional division of the human nervous system is that classifying it according to the role that the different neural pathways play, regardless whether these cross through the CNS or the PNS:

The somatic nervous system is responsible for coordinating the body's movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control.
The autonomic nervous system is then split into the sympathetic division, parasympathetic division, and enteric division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.

In turn, these pathways can be divided according to the direction in which they conduct stimuli:

Afferent system by sensory neurons, which carry impulses from a receptor to the CNS
Efferent system by motor neurons, which carry impulses from the CNS to an effector
Relay system by relay neurons (also called interneurons), which transmit impulses between the sensory and motor neurones.

A useful mnemonic to remember the nature of Afferent vs Efferent is SAME DAVE: Sensory Afferent, Motor Efferent; Dorsal Afferent, Ventral Efferent

However, there are relay neurons in the CNS as well.

The junction between two neurones is called a synapse. There is a very narrow gap (about 20nm in width) between the neurons - the synaptic cleft, where an action potential is transmitted from one neuron to a neighboring one. They do this by relaying the message with the use of neurotransmitters which the next neuron then receives the electrical signal, known as a nerve impulse. The nerve impulse is determined by the neurotransmitter to then carry the message to its appropriate destination. These nerve impulses are a change in ion balance in the nerve cell, which the central nervous system can then interpret. The fact that the nervous system uses a mixture of electrical and chemical signals makes it incredibly fast, which is necessary to acknowledge the presence of danger. For example, a hand touching a hot stove. If the nervous system was only comprised of chemical signals, the body would not tell the arm to move fast enough to escape dangerous burns. So the speed of the nervous system is a necessity for life.

Physiological division

Somatic nervous system

Autonomic nervous system

Parasympathetic

Development
Main article: Neural development in humans
Some landmarks of embryonic neural development include the birth and differentiation of neurons from stem cell precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through the embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory.

Importance
Many people have lost basic motor skills and other skills because of spinal chord injuries. If this portion is damaged, the biggest nerve and the most important one gets damaged. This leads to paralysis or other permanent damages.

The nervous system is able to make basic motor skills and other skills possible. The basic 5 senses of texture, taste, sight, smell,and hearing are powered by the nervous system. If disabled, basic motor skills may be lost.

Development
Main article: Neural development
Neural development in most species have many similarities neural development in humans.

References
^ "Nervous System". Columbia Encyclopedia. Columbia University Press. Retrieved on 4/1/08.
^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall, 132-144. ISBN 0-13-981176-1.
^ sfn.org Society for Neuroscience, 2000

[edit] External links
Neuroscience for Kids
The Human Brain Project Homepage
Kimball's Biology Pages, CNS
Kimball's Biology Pages, PNS
[show]
v • d • e Systems and systems science
Systems categories
Conceptual systems · Physical systems · Social systems · Systems · Systems theory · Systems science · Systems scientists
Systems
Biological system · Complex system · Complex adaptive system · Conceptual system · Cultural system · Dynamical system · Economic system · Ecosystem · Formal system · Global Positioning System · Human anatomy · Information systems · Legal systems of the world · Living systems · Systems of measurement · Metric system · Multi-agent system · Nervous system · Nonlinearity · Operating system · Physical system · Political system · Sensory system · Social structure · Solar System · Systems art
Theoretical fields
Chaos theory · Complex systems · Control theory · Cybernetics · Scientific holism · Sociotechnical systems theory · Systems biology · System dynamics · Systems ecology · Systems engineering · Systems psychology · Systems science · Systems theory
Systems scientists
Russell L. Ackoff · William Ross Ashby · Gregory Bateson · Stafford Beer · Ludwig von Bertalanffy · Kenneth E. Boulding · Peter Checkland · C. West Churchman · Heinz von Foerster · Charles François · Jay Wright Forrester · Ralph W. Gerard · Debora Hammond · George Klir · Niklas Luhmann · Humberto Maturana · Donella Meadows · Mihajlo D. Mesarovic · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Francisco Varela · John N. Warfield · Norbert Wiener
[show]
v • d • e Human organ systems
Cardiovascular system • Digestive system • Endocrine system • Immune system • Integumentary system • Lymphatic system • Muscular system • Nervous system • Reproductive system • Respiratory system • Skeletal system • Urinary system
[show]
v • d • eNervous system
Central nervous system
Brain • Spinal cord
Autonomic nervous system
Sympathetic • Parasympathetic
Other
Peripheral nervous system • Somatic nervous system • Enteric nervous system • Sensory system
[show]
v • d • eNervous system, receptors: somatosensory system
Medial lemniscus
Touch/mechanoreceptors: Pacinian corpuscles • Meissner's corpuscles • Merkel's discs • Ruffini endings • Free nerve endings • Hair cells • Baroreceptor
Proprioception: Golgi organ • Muscle spindle (Intrafusal muscle fiber • Nuclear chain fiber • Nuclear bag fiber)
Spinothalamic tract
Pain: Nociception and Nociceptors
Temperature: Thermoreceptors
[show]
v • d • e Histology: nervous tissue
Neurons (gray matter)
soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine, apical dendrite, basal dendrite)types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron
GSA, GVA, SSA, SVA, fibers (Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain)
Efferent nerve/Motor nerve/Motor neuron
GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (α motorneuron, γ motorneuron)
Synapses
neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
Sensory receptors
Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells
astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)
Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues
epineurium, perineurium, endoneurium, nerve fascicle, meninges
[show]
v • d • eNervous system physiology: neurophysiology
Evoked potential
Bereitschaftspotential - P300 - Auditory evoked potential - Somatosensory evoked potentials - Somatosensory evoked potentials - Visual evoked potential - Excitatory postsynaptic potential
Reflex
Baroreflex - Acoustic reflex - H-reflex - Oculocardiac reflex - Pupillary reflex - Stretch reflex - Vestibulo-ocular reflex - Startle reaction
Other
Arousal (Wakefulness) - Axoplasmic transport - Intracranial pressure - Chronaxie - Lateralization of brain function - Membrane potential - Action potential - Nerve regeneration - Long-term potentiation - Sensation - Sleep - Neurotransmission
[show]
v • d • e Pathology of the nervous system, primarily CNS (G00-G47, 320-349)
Inflammatory diseasesof the CNS
Meningitis (Arachnoiditis) - Encephalitis - Myelitis - Encephalomyelitis (Acute disseminated) - Tropical spastic paraparesis
Systemic atrophiesprimarily affecting the CNS
Huntington's disease - Spinocerebellar ataxia (Friedreich's ataxia, Ataxia telangiectasia, Hereditary spastic paraplegia) -Dentatorubral-pallidoluysian atrophy - Spinal muscular atrophy: Werdnig-Hoffman disease - Kugelberg-Welander disease - Fazio Londe syndrome -MND (Amyotrophic lateral sclerosis (ALS), Progressive muscular atrophy (PMA), Progressive bulbar, Pseudobulbar, PLS)
Extrapyramidal andmovement disorders
Parkinson's disease - Neuroleptic malignant syndrome - Postencephalitic parkinsonism - Pantothenate kinase-associated neurodegeneration - Progressive supranuclear palsy - Striatonigral degeneration - Dystonia/Dyskinesia (Spasmodic torticollis, Meige's syndrome, Blepharospasm) - Essential tremor - Myoclonus - Lafora disease - Chorea (Choreoathetosis) - Restless legs syndrome - Stiff person syndrome
Other degenerative /demyelinating diseases
Alzheimer's disease - Pick's disease - Alpers' disease - Dementia with Lewy bodies - Leigh's disease - Multiple sclerosis - Devic's disease - Central pontine myelinolysis - Transverse myelitis
Seizure/epilepsy
Focal (Simple partial, Complex partial) - Generalised (Tonic-clonic, Absence, Atonic, Benign familial neonatal) - Lennox-Gastaut - West - Epilepsia partialis continua - Status epilepticus (Complex partial status epilepticus)
Headache
Migraine (Familial hemiplegic) - Cluster - Vascular - Tension
Vascular
Transient ischemic attack (Amaurosis fugax, Transient global amnesia) - Cerebrovascular disease (MCA, ACA, PCA, Foville's syndrome, Millard-Gubler syndrome, Lateral medullary syndrome, Weber's syndrome, Lacunar stroke)
Sleep disorders
Insomnia - Hypersomnia - Sleep apnea (Ondine's curse) - Narcolepsy - Cataplexy - Kleine-Levin syndrome - Circadian rhythm sleep disorder - Delayed sleep phase syndrome - Advanced sleep phase syndrome
Other
Hydrocephalus (Normal pressure) - Idiopathic intracranial hypertension - Encephalopathy - Brain herniation - Cerebral edema - Reye's syndrome - Syringomyelia - Syringobulbia - Spinal cord compression
[show]
v • d • e Prenatal development/Mammalian development of nervous system
General neural development/neurulation/neurula
Notochord - Neuroectoderm - Neural plate - Neural folds - Neural groove
Neural crest - Neural tube (Neuromere/Rhombomere, Cephalic flexure)Alar plate - Basal plate
Eye development
Optic vesicles - Optic stalk - Optic cup - Lens placode
Auditory development
Auditory vesicle - Auditory pit
[show]
v • d • e Surgery, Nervous system: neurosurgical procedures (ICD-9-CM V3 01-05)
Skull, brain, and cerebral meninges
Craniotomy - Decompressive craniectomy - Lobotomy - Hemispherectomy - Ventriculostomy - Anterior temporal lobectomy
Spinal cord and spinal canal
Spinal cord and roots (Cordotomy - Rhizotomy) - Intervertebral discs (Discectomy - Intervertebral disc annuloplasty - Intervertebral disc arthroplasty) - Vertebral bones (Laminotomy - Laminectomy - Laminoplasty - Corpectomy - Facetectomy - Foraminotomy - Vertebral fusion - Vertebral fixation) - Lumbar puncture
Cranial and peripheral nerves
Ganglionectomy - Nerve block
Sympathetic nerves or ganglia
Endoscopic thoracic sympathectomy
Other
Axotomy - Hypophysectomy - Vagotomy
Retrieved from "http://en.wikipedia.org/wiki/Nervous_system"
Categories: Nervous system
Hidden category: Articles needing additional references from November 2007

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Central Nervous System

2008-04-07T12:49:00.000-07:00

Central Nervous System
From Wikipedia, the free encyclopedia

A diagram showing the CNS:
1. Brain
2. Central nervous system (brain and spinal cord)
3. Spinal cord

The central nervous system (CNS) represents the largest part of the nervous system, including the brain and the spinal cord. Together with the Peripheral Nervous System , it has a fundamental role in the control of behavior. The CNS is contained within the dorsal cavity, with the brain within the cranial cavity, and the spinal cord in the spinal cavity. The CNS is covered by the meninges. The brain is also protected by the skull, and the spinal cord is also protected by the vertebrae. [1]

Function
Main article: Brain Function
Since the strong theoretical influence of cybernetics in the fifties, the central nervous system 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 behaviour without dictating it. This has brought the conception of the CNS as an autonomous system.

Development
Main article: Neural development
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: brain (rostral/cephalic) and spinal cord (caudal). Consecutively, the brain will differentiate into prosencephalon and brainstem. Later, the prosencephalon will subdivide into telencephalon and diencephalon, and the brainstem into mesencephalon and rhombencephalon.

Neuroanatomy
Main article: Neuroanatomy
The telencephalon gives rise to the striatum (caudate nucleus and putamen), the hippocampus and the neocortex, its cavity becomes the lateral ventricles (first and second ventricles). The diencephalon give rise to the subthalamus, hypothalamus, thalamus and epithalamus, its cavity to the third ventricle. The mesencephalon gives rise to the tectum, pretectum, cerebral peduncle and its cavity develops into the mesencephalic duct or cerebral aqueduct. Finally, the rhombencephalon gives rise to the pons, the cerebellum and the medulla oblongata, its cavity becomes the fourth ventricle.
Centralnervoussystem
I Brain
A Prosencephalon
1. Telencephalon
2. Rhinencephalon,
3. Amygdala,
4. Hippocampus,
5. Neocortex,
6. Lateral ventricles
B Diencephalon
1. Epithalamus,
2. Thalamus, Hypothalamus, Subthalamus, Pituitary gland, Pineal gland, Third ventricle
Brain stem
Mesencephalon
Tectum, Cerebral peduncle, Pretectum, Mesencephalic duct
Rhombencephalon
Metencephalon
Pons, Cerebellum,
Myelencephalon
Medulla oblongata
Spinal cord

Evolution
Main article: Brain
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 represents 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 also: Encephalization, Neocortex, Archicortex

Parts of the vertebrate CNS
Main article: List of regions in the human brain
In addition to the structures seen to the right in table above, a vast number of structures are present in the adult brain.

See also
Glossary of anatomical terminology, definitions and abbreviations
List of regions in the human brain
Central nervous system infection
Neuroradiology

References
^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall, 132-144. ISBN 0-13-981176-1.

External links
Sylvius: 400+ structure neuroanatomical visual glossary
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
[show]
v • d • e Nervous system
Central nervous system
Brain • Spinal cord
Autonomic nervous system
Sympathetic • Parasympathetic
Other
Peripheral nervous system • Somatic nervous system • Enteric nervous system • Sensory system
[show]
v • d • e Histology: nervous tissue
Neurons (gray matter)
soma, axon (axon hillock, axoplasm, axolemma, neurofibril/neurofilament), dendrite (Nissl body, dendritic spine, apical dendrite, basal dendrite)types (bipolar, pseudounipolar, multipolar, pyramidal, Purkinje, granule)
Afferent nerve/Sensory nerve/Sensory neuron
GSA, GVA, SSA, SVA, fibers (Ia, Ib or Golgi, II or Aβ, III or Aδ or fast pain, IV or C or slow pain)
Efferent nerve/Motor nerve/Motor neuron
GSE, GVE, SVE, Upper motor neuron, Lower motor neuron (α motorneuron, γ motorneuron)
Synapses
neuropil, synaptic vesicle, neuromuscular junction, electrical synapse - Interneuron (Renshaw)
Sensory receptors
Free nerve ending, Meissner's corpuscle, Merkel nerve ending, Muscle spindle, Pacinian corpuscle, Ruffini ending, Olfactory receptor neuron, Photoreceptor cell, Hair cell, Taste bud
Glial cells
astrocyte, oligodendrocyte, ependymal cells, microglia, radial glia
Myelination (white matter)
Schwann cell, oligodendrocyte, nodes of Ranvier, internode, Schmidt-Lanterman incisures, neurolemma
Related connective tissues
epineurium, perineurium, endoneurium, nerve fascicle, meninges
Retrieved from "http://en.wikipedia.org/wiki/Central_nervous_system"
Categories: Neurology Nervous system Central nervous system

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Peripheral Nervous System

2008-04-07T12:47:00.000-07:00

Peripheral Nervous System
From Wikipedia, the free encyclopedia

Peripheral nervous system can be divided into the somatic nervous system and the autonomic nervous system. (PNS) The PNS is not protected by bone, leaving it exposed to injury, unlike the central nervous system, which is made of the brain and spinal cord, to serve the limbs and organs. [1]

General classification
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The peripheral nervous system can be classified either by direction of neurons or by function.

By direction of neurons
There are three types of directions of the neurones:
Sensory system by sensory neurons,between the sensory and motor neurones. However, there are relay neurons in the CNS as well.

By function
By function, the peripheral nervous system is divided into the somatic nervous system , autonomic nervous system and the enteric nervous system. The somatic nervous system is responsible for coordinating the body movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control. The autonomic nervous system is then split into the sympathetic division, parasympathetic division, and enteric division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon.

Naming of specific nerves
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The Human Nervous System. Blue is PNS while red is CNS.Ten out of the twelve cranial nerves originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions. The nuclei of cranial nerves I and II lie in the forebrain and thalamus, respectively, and are thus not considered to be true cranial nerves. CN X (10) receives visceral sensory information from the thorax and abdomen, and CN XI (11) is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which is exclusively in the head.

Spinal nerves take their origins from the spinal cord. They 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. The naming convention for spinal nerves is to name it after the vertebra immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertebrae and 8 cervical spinal nerves.

Cervical spinal nerves (C1-C4)
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Further information: Cervical plexus
The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that subserve the neck and back of head.

Spinal nerve C1 is called the suboccipital nerve which provides motor innervation to muscles at the base of the skull. C2 and C3 form many of the nerves of the neck, providing both sensory and motor control. These include the greater occipital nerve which provides sensation to the back of the head, the lesser occipital nerve which provides sensation to the area behind the ears, the greater auricular nerve and the lesser auricular nerve. See occipital neuralgia. The phrenic nerve arises from nerve roots C3, C4 and C5. It innervates the diaphragm, enabling breathing. If the spinal cord is transected above C3, then spontaneous breathing is not possible. See myelopathy

Brachial plexus (C5-T1)
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Further information: Brachial plexus
The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1,combine to form the brachial plexus, or plexus brachialis, a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the arm and upper back. Although the brachial plexus may appear tangled, it is highly organized and predictable, with little variation between people. See brachial plexus injuries

Before forming three cords
The first nerve off the brachial plexus, or plexus brachialis, is the dorsal scapular nerve, arising from C5 nerve root, and innervating the rhomboids and the levator scapulae muscles. The long thoracic nerve arises from C5, C6 and C7 to innervate the serratus anterior. The brachial plexus first forms three trunks, the superior trunk, composed of the C5 and C6 nerve roots, the middle trunk, made of the C7 nerve root, and the inferior trunk, made of the C8 and T1 nerve roots. The suprascapular nerve is an early branch of the superior trunk. It innervates the suprascapular and infrascapular muscles, part of the rotator cuff. The trunks reshuffle as they traverse towards the arm into cords. There are three of them. The lateral cord is made up of fibers from the superior and middle trunk. The posterior cord is made up of fibers from all three trunks. The medial cord is composed of fibers solely from the medial trunk.

The Nervous System

The brain and nervous system form an intricate network of electrical signals that are responsible for coordinating muscles, the senses, speech, memories, thought and emotion.

Several diseases that directly affect the nervous system have a genetic component: some are due to a mutation in a single gene, others are proving to have a more complex mode of inheritance. As our understanding of the pathogenesis of neurodegenerative disorders deepens, common themes begin to emerge: Alzheimer brain plaques and the inclusion bodies found in Parkinson disease contain at least one common component, while Huntington disease, fragile X syndrome and spinocerebellar atrophy are all 'dynamic mutation' diseases in which there is an expansion of a DNA repeat sequence. Apoptosis is emerging as one of the molecular mechanisms invoked in several neurodegenerative diseases, as are other, specific, intracellular signaling events. The biosynthesis of myelin and the regulation of cholesterol traffic also figure in Charcot-Marie-Tooth and Neimann-Pick disease, respectively.

Medial cord
The medial cord gives rise to the following nerves:

The median pectoral nerve, C8 and T1, to the pectoralis muscle
The medial brachial cutaneous nerve, T1
The medial antebrachial cutaneous nerve, C8 and T1
The median nerve, partly. The other part comes from the lateral cord. C7, C8 and T1 nerve roots. The first branch of the median nerve is to the pronator teres muscle, then the flexor carpi radialis, the palmaris longus and the flexor digitorum superficialis. The median nerve provides sensation to the anterior palm, the anterior thumb, index finger and middle finger. It is the nerve compressed in carpal tunnel syndrome.

The ulnar nerve originates in nerve roots C7, C8 and T1. It provides sensation to the ring and pinky fingers. It innervates the flexor carpi ulnaris muscle, the flexor digitorum profundus muscle to the ring and pinky fingers, and the intrinsic muscles of the hand (the interosseous muscle, the lumbrical muscles and the flexor pollicus brevis muscle). This nerve traverses a groove on the elbow called the cubital tunnel, also known as the funny bone. Striking the nerve at this point produces an unpleasant sensation in the ring and little finger.

Neurotransmitters
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The main neurotransmitters of the peripheral nervous system are acetylcholine and noradrenaline. However, there are several other neurotransmitters as well, jointly labeled Non-noradrenergic, non-cholinergic (NANC) transmitters. Examples of such transmitters include non-peptides: ATP, GABA, dopamine, NO, and peptides: neuropeptide Y, VIP, GnRH, Substance P and CGRP. [2]

References
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^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall, 132-144. ISBN 0-13-981176-1.
^ Pharmacology, (Rang, Dale, Ritter & Moore, ISBN 0443071454, 5:th ed., Churchill Livingstone 2003). Page 132.
This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (November 2007)
[hide]v • d • eNervous system
Central nervous system Brain • Spinal cord
Autonomic nervous system Sympathetic • Parasympathetic
Other Peripheral nervous system • Somatic nervous system • Enteric nervous system • Sensory system

Retrieved from "http://en.wikipedia.org/wiki/Peripheral_nervous_system"
Categories: Peripheral nervous system Neuroanatomy
Hidden category: Articles needing additional references from November 2007

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