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Angiosperms have both tracheids and vessel elements. [1] A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of conductive cell, called vessel elements, to transport water through the xylem.
A vessel element or vessel member (also called a xylem vessel) [1] is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in most angiosperms (flowering plants) and in some gymnosperms such as cycads and Ephedra, but absent in conifers. Vessel elements are the main feature distinguishing the ...
The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels. [6] Xylem also contains two other type of cells: parenchyma and fibers. [7] Xylem can be found:
The arachnoid mater makes arachnoid villi, small protrusions through the dura mater into the venous sinuses of the brain, which allow CSF to exit the subarachnoid space and enter the blood stream. Unlike the dura mater, which receives a rich vascular supply from numerous arteries, the arachnoid mater is avascular (lacking blood vessels).
The medulla and pons also contain numerous small nuclei with a wide variety of sensory, motor, and regulatory functions. In the peripheral nervous system (PNS), a cluster of cell bodies of neurons (homologous to a CNS nucleus) is called a ganglion. The fascicles of nerve fibers in the PNS (homologous to CNS tracts) are called nerves.
Brain cells make up the functional tissue of the brain. The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges, blood vessels, and ducts. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells, also known as neuroglia. [1]
The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous sinuses (channels) found between the periosteal and meningeal layers of dura mater in the brain. [ 1 ] [ 2 ] They receive blood from the cerebral veins , and cerebrospinal fluid (CSF) from the subarachnoid space via arachnoid granulations .
Embryonic vertebrate subdivisions of the developing human brain hindbrain or rhombencephalon is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla , pons , and cerebellum .