Chapter 7- The Cells of the Nervous System

Types of glial cells in the central nervous system
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provide the insulating myelin sheaths of the axons of some neurons in the central nervous system

are small cells with relatively few processes. In the white matter of the brain, as shown here, they provide the myelin sheaths that insulate axons. A single oligodendrocyte can wrap its membranous processes around many axons. In the gray matter, perineural oligodendrocytes surround and support the cell bodies of neurons
myelinate the axon of neurons in the peripheral nervous system

furnish the myelin sheaths for axons in the peripheral nervous system. During development, several Schwann cells are positioned along the length of a single axon. Each cell forms a myelin sheath approximately 1 mm long between two nodes of Ranvier. The sheath is formed as the inner tongue of the Schwann cell turns around the axon several times, wrapping the axon in layers of membrane. In actuality, the layers of myelin are more compact than what is shown here.
irregular, roughly star-shaped cell bodies and large numbers of processes; they support neurons and modulate neuronal signaling in several ways

a major class of glial cells in the central nervous system, are characterized by their star-like shape and the broad end-feet on their processes. Because these end-feet put the astrocyte into contact with both capillaries and neurons, astrocytes are thought to have a nutritive function. Astrocytes also play an important role in maintaining the blood-brain barrier (described later in the chapter)

The cell body and nucleus of a spinal motor neuron are surrounded by a double layered membrane, the nuclear envelope, which is continuous with the endoplasmic reticulum. The space between the two membrane layers that constitutes the nuclear envelope is continuous with the lumen of the endoplasmic reticulum. Dendrites emerge from the basal aspect of the neuron, the axon from the apical aspect.
are the bones of the cytoskeleton.

Neurofilaments are related to intermediate filaments of other cell types, including the cytokeratins of epithelial cells (hair and nails), glial fibrillary acidic protein in astrocytes, and desmin in muscle. Unlike microtubules, neurofilaments are stable and almost totally polymerized in the cell.
MicrofilamentsLong, thin fibers that function in the movement and support of the cell are the thinnest of the three main types of fibers that make up the cytoskeleton (Figure 7-6C). Like thin filaments of muscle, microfilaments are made up of two strands of polymerized globular actin monomers, each bearing an ATP or adenosine diphosphate (ADP), wound into a double-stranded helix. Actin is a major constituent of all cells, perhaps the most abundant animal protein in natureExplain how membrane trafficking occurs in the neuron....1. Proteins and lipids of secretory organelles are synthesized in the endoplasmic reticulum and transported to the Golgi complex, where large dense-core vesicles (peptide-containing secretory granules) and synaptic vesicle precursors are assembled. 2. Large dense-core vesicles and transport vesicles carry synaptic vesicle proteins down the axon via axonal transport. 3. At the nerve terminals, the synaptic vesicles are assembled and loaded with nonpeptide neurotransmitters. Synaptic vesicles and large dense-core vesicles release their contents by exocytosis. 4. Following exocytosis, large dense-core vesicle membranes are returned to the cell body for reuse or degradation. Synaptic vesicle membranes undergo many cycles of local exocytosis and endocytosis in the presynaptic terminal.Explain protein synthesis in the endoplasmic reticulumFree and membrane-bound polysomes translate mRNA that encodes proteins with a variety of destinations. Messenger RNA, transcribed from genomic DNA in the neuron's nucleus, emerges into the cytoplasm through nuclear pores to form polyribosomes (see enlargement). The polypeptides that become secretory and membrane proteins are translocated across the membrane of the rough endoplasmic reticulum.