A report on Nerve

Nerves (yellow) in the arm
Cross-section of a nerve
Micrograph demonstrating perineural invasion of prostate cancer. H&E stain.

Enclosed, cable-like bundle of nerve fibers in the peripheral nervous system.

- Nerve
Nerves (yellow) in the arm

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An axon of a multipolar neuron

Axon

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Long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body.

Long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body.

An axon of a multipolar neuron
A typical myelinated axon
A dissected human brain, showing grey matter and white matter
Detail showing microtubules at axon hillock and initial segment.
TEM of a myelinated axon in cross-section.
Cross section of an axon: (1) Axon (2) Nucleus 
(3) Schwann cell (4) Myelin sheath (5) Neurilemma
(A) pyramidal cell, interneuron, and short durationwaveform (Axon), overlay of the three average waveforms;
(B) Average and standard error of peak-trough time for pyramidal cells interneurons, and putative axons;
(C) Scatter plot of signal to noise ratios for individual units againstpeak-trough time for axons, pyramidal cells (PYR) and interneurons (INT).
Axon of nine-day-old mouse with growth cone visible

A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousands of synaptic terminals.

Schematic diagram showing the central nervous system in yellow, peripheral in orange

Central nervous system

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Part of the nervous system consisting primarily of the brain and spinal cord.

Part of the nervous system consisting primarily of the brain and spinal cord.

Schematic diagram showing the central nervous system in yellow, peripheral in orange
Dissection of a human brain with labels showing the clear division between white and gray matter.
Diagram of the columns and of the course of the fibers in the spinal cord. Sensory synapses occur in the dorsal spinal cord (above in this image), and motor nerves leave through the ventral (as well as lateral) horns of the spinal cord as seen below in the image.
Different ways in which the CNS can be activated without engaging the cortex, and making us aware of the actions. The above example shows the process in which the pupil dilates during dim light, activating neurons in the spinal cord. The second example shows the constriction of the pupil as a result of the activation of the Eddinger-Westphal nucleus (a cerebral ganglion).
A map over the different structures of the nervous systems in the body, showing the CNS, PNS, autonomic nervous system, and enteric nervous system.
Schematic image showing the locations of a few tracts of the spinal cord.
Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex.
Diagram depicting the main subdivisions of the embryonic vertebrate brain, later forming forebrain, midbrain and hindbrain.
Development of the neural tube

From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves (sometimes segmental nerves ).

The human nervous system. Sky blue is PNS; yellow is CNS.

Peripheral nervous system

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One of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS).

One of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS).

The human nervous system. Sky blue is PNS; yellow is CNS.
3D Medical Animation still shot of Lumbosacral Plexus

The PNS consists of the nerves and ganglia outside the brain and spinal cord.

The PNS has satellite cells and Schwann cells.

Schwann cell

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Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS).

Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS).

The PNS has satellite cells and Schwann cells.
A Schwann cell in culture.

Schwann cells are involved in many important aspects of peripheral nerve biology—the conduction of nervous impulses along axons, nerve development and regeneration, trophic support for neurons, production of the nerve extracellular matrix, modulation of neuromuscular synaptic activity, and presentation of antigens to T-lymphocytes.

Anatomy of a multipolar neuron

Neuron

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Electrically excitable cell that communicates with other cells via specialized connections called synapses.

Electrically excitable cell that communicates with other cells via specialized connections called synapses.

Anatomy of a multipolar neuron
Schematic of an anatomically accurate single pyramidal neuron, the primary excitatory neuron of cerebral cortex, with a synaptic connection from an incoming axon onto a dendritic spine.
Diagram of the components of a neuron
Neuron cell body
Diagram of a typical myelinated vertebrate motor neuron
Golgi-stained neurons in human hippocampal tissue
Actin filaments in a mouse cortical neuron in culture
Image of pyramidal neurons in mouse cerebral cortex expressing green fluorescent protein. The red staining indicates GABAergic interneurons.
SMI32-stained pyramidal neurons in cerebral cortex
Different kinds of neurons:
1 Unipolar neuron
2 Bipolar neuron
3 Multipolar neuron
4 Pseudounipolar neuron
Synaptic vesicles containing neurotransmitters
A signal propagating down an axon to the cell body and dendrites of the next cell
Chemical synapse
An annotated diagram of the stages of an action potential propagating down an axon including the role of ion concentration and pump and channel proteins.
As long as the stimulus reaches the threshold, the full response would be given. Larger stimulus does not result in a larger response, vice versa.
Drawing by Camillo Golgi of a hippocampus stained using the silver nitrate method
Drawing of a Purkinje cell in the cerebellar cortex done by Santiago Ramón y Cajal, demonstrating the ability of Golgi's staining method to reveal fine detail
Drawing of neurons in the pigeon cerebellum, by Spanish neuroscientist Santiago Ramón y Cajal in 1899. (A) denotes Purkinje cells and (B) denotes granule cells, both of which are multipolar.
Guillain–Barré syndrome – demyelination

Axons may bundle into fascicles that make up the nerves in the peripheral nervous system (like strands of wire make up cables).

Structure of simplified neuron in the PNS

Myelin

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Structure of simplified neuron in the PNS
Transmission electron micrograph of a cross-section of a myelinated PNS axon, generated at the Electron Microscopy Facility at Trinity College, Hartford, Connecticut
Action potential propagation in myelinated neurons is faster than in unmyelinated neurons because of Saltatory conduction.

Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon.

The human nervous system

Nervous system

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Highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body.

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 human nervous system
Diagram showing the major divisions of the vertebrate nervous system.
Horizontal section of the head of an adult female human, showing skin, skull, and brain with gray matter (brown in this image) and underlying white matter
Nervous system of a bilaterian animal, in the form of a nerve cord with segmental enlargements, and a "brain" at the front
Area of the human body surface innervated by each spinal nerve
Earthworm nervous system. Top: side view of the front of the worm. Bottom: nervous system in isolation, viewed from above
Internal anatomy of a spider, showing the nervous system in blue
Major elements in synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron. When the wave reaches a synapse, it provokes release of a small amount of neurotransmitter molecules, which bind to chemical receptor molecules in the membrane of the target cell.
Illustration of pain pathway, from René Descartes's Treatise of Man
Simplified schema of basic nervous system function: signals are picked up by sensory receptors and sent to the spinal cord and brain, where processing occurs that results in signals sent back to the spinal cord and then out to motor neurons
Layers protecting the brain and spinal cord.

The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body.

Left View of the human brain from below, showing origins of cranial nerves. Right Juxtaposed skull base with foramina in which many nerves exit the skull.

Cranial nerves

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Left View of the human brain from below, showing origins of cranial nerves. Right Juxtaposed skull base with foramina in which many nerves exit the skull.
The oculomotor (III), troclear (IV) and abducens (VI) nerves supply the muscle of the eye. Damage will affect the movement of the eye in various ways, shown here.
The facial nerve (VII) supplies the muscles of facial expression. Damage to the nerve causes a lack of muscle tone on the affected side, as can be seen on the right side of the face here.
A damaged glossopharyngeal nerve (IX) may cause the uvula to deviate to the affected side.
The cranial nerves in the horse.
Ventral view of a sheep's brain. The exits of the various cranial nerves are marked with red.

Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs.

Nerve fascicle

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A nerve fascicle, is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system.

White matter tracts within a human brain, as visualized by MRI tractography

Nerve tract

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Bundle of nerve fibers connecting nuclei of the central nervous system.

Bundle of nerve fibers connecting nuclei of the central nervous system.

White matter tracts within a human brain, as visualized by MRI tractography
The cingulum shown in red in the cingulate gyrus.

In the peripheral nervous system this is known as a nerve, and has associated connective tissue.