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 hemiazygos and accessory hemiazygos vein

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Difference between hemiazygos and accessory hemiazygos vein
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Topics
Hemiazygos vein
Accessory hemiazygos vein
Location
It is also known as inferior hemiazygos vein . it lies on the left side only and corresconds to the lower part of the azygos vein
It is also known as superior hemiazygos vein . it lies on the left side only and corresponds to the upper part of azygos vein
Tributaries
1.    Lower 3 (9-11th ) left posterior intercostals veins
2.    Left subcostal vein
3.    Left ascending lumbar vein
4.    Small esophageal and mediastinal veins
1.    5th to 8th left posterior intercostals vein
2.    Left bronchial veins (occationally )
Formation
It is formed on the left side similar to the azygos vein by the union of left ascending lumbar vein and left subcostal vein
It may arise from the posterior surface of the left renal vein
The accessory hemiazygos vein is formed by the confluence of the middle left posterior intercostal veins. 
Course
The hemiazygos vein enters the thorax either through the aortic hiatus or directly through the diaphragmatic crura. It then courses superiorly to the left of the midline in the posterior mediastinum, adjacent to the thoracic vertebrae until the level of T8 or T9 vertebral bodies, where it crosses the midline anteriorly to the vertebral column to drain into the azygos vein. 
It descends to the left of midline, adjacent to the thoracic vertebrae and crosses posteriorly to the aorta at the level of T7-8 to drain into the azygos vein. It normally anastomoses with the left superior intercostal vein.
Variant anatomy
·         hemiazygos continuation of the IVC: often occurs with duplicated IVCs
·         interazygos vein: occurs when forming a common trunk with the accessory hemiazygos vein anterior to the aorta
·         drains via a common trunk with the hemiazygos vein into the azygos vein
·         forms a common trunk with the hemiazygos vein that passes anterior to the aorta called the interazygos vein 2
·         drains directly into the left brachiocephalic vein (rare) 
Drainage area
·         It drains the left inferior hemithorax
·         It drains the left superior hemithorax. 

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