Comparison between tract and nerve

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  Comparison between tract and nerve Nerve Nerve contain bundle of axons (nerve fibers) in the peripheral nervous system (PNS) that transmits signals between the central nervous system (CNS) and other parts of the body. It is the most important part of peripheral nervous system Location: Peripheral nervous system. Structure: Made of axons, connective tissue layers (endoneurium: axon is surrounded by it , perineurium: bundle of axons are surrounded by it, epineurium: whole nerve trunk is surrounded by it), and blood vessels. It gets myelination by Schwann cell   Function: Carries sensory signals to the CNS (afferent) from peripheral part of body or motor signals carry from from the CNS (efferent) to target organs like skeletal muscle, cardiac muscle, smooth muscle or glands Example: Sciatic nerve, median nerve, except optic nerve (though optic nerve is technically part of CNS in develop...
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Difference between white rami and gray rami communicans

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Difference between white rami and gray rami communicans


Gray and white rami communicans are related with sympathetic system.
Both gray and white rami communicans are attached with ventral ramus of thoracic and lumbar spinal nerves. Only gray rami communicans are attached with ventral ramus of cervical, sacral and coccygeal spinal nerves.
Through white rami communicans pre-ganglionic sympathetic fibre leave the spinal nerves and enter into sympathetic ganglia . pre- ganglionic fibres are myelinated so it looks white. Through gray rami communicans post-ganglionic sympathetic fibre again enter into the spinal nerve , leave the sympathetic ganglia. Post ganglionic sympathetic fibres are non- myelinated so it looks gray.
Gray and white rami communicans are the lateral branch of sympathetic ganglia which connect ventral ramus of corresponding spinal nerve. White rami communicans has distal connection with ventral ramus of spinal nerve. Gray rami communicans has proximal connection with ventral ramus of spinal nerve. In thoracic and lumbar region pre-ganglionic fibres reach to sympathetic ganglia by using white rami communicans and corresponding ventral ramus of spinal nerve . in cervical and sacral region there are no corresponding white rami communicans of ventral ramus of spinal nerves . pre- ganglionic fibres enter into the corresponding sympathetic ganglia , some are ascend to cervical sympathetic ganglia and some fibres are descend to the sacral sympathetic ganglia. So cervical and sacral region lacks white rami communicans .
 pre-ganglionic sympathetic neurons are present in the lateral horn of gray matter of spinal cord ... pre-ganglionic fibres leave the spinal cord through the ventral root  of spinal nerve, spinal nerve trunk,.... through white rami communicans they enter into the sympathetic ganglion   

Post ganglionic neurons are present within the sympathetic ganglia ---- post -ganglionic fibres leave the sympathetic ganglia through gray rami communicans --- again enter into the ventral ramus of spinal nerve and distributed along the ventral and dorsal ramus of spinal nerve --- they innervate smooth muscle cells of vessel, sweat gland , arrector pili muscle(smooth muscle )  of the skin
White rami communicans
Gray rami communicans
Convey pre-ganglionic fibres of sympathetic system
Convey post-ganglionic fibres of sympathetic system
Fibres are myelinated
Fibres are non-myelinated
It is situated away from the spinal cord
It is situated near the spinal cord
It is only present in the thoracic and lumbar spinal nerves
It is present in all spinal nerves
Through white rami communicans pre-ganglionic fibres enter into the sympathetic ganglia
Through gray  rami communicans post-ganglionic fibres leave the sympathetic ganglia

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