Myelin, is produced by oligodendrocytes in the central nervous system (CNS) and by Schwann cells in the peripheral nervous system (PNS)

Nervous, central (CNS) and peripheral nervous system (PNS)

Myelin, which insulates neuronal projections and permits rapid (saltatory) conduction, is produced by oligodendroglia (oligodendrocytes) in the central nervous system (CNS) and by Schwann cells in the peripheral nervous system (PNS). Microglia are brain macrophages. Astrocytes have a complicated role in physical and metabolic support of neurons.

Astrocytes induce and maintain the blood-brain-barrier, but they do not constitute the barrier function of the blood-brain barrier which is established by endothelial tight junctions (zonula occludens). Neurons conduct electrochemical impulses and move neurotransmitters to their synaptic termini by axoplasmic transport.

Transneuronal transmission is accomplished by calcium-regulated release of synaptic vesicles. Neurons also synapse with muscle cells. A typical contact between a myelinated neuron and skeletal muscle (neuromuscular junction) is shown below.

Neuromuscular junction.Axonal terminals (telodendria) rest in shallow depressions (primary clefts) on the surface of the striated muscle fiber. Secondary clefts increase the surface area for interaction with a neurotransmitter (acetylcholine). Muscle cell nuclei and mitochondria are abundant near the junction.
Neuromuscular junction.Axonal terminals (telodendria) rest in shallow depressions (primary clefts) on the surface of the striated muscle fiber. Secondary clefts increase the surface area for interaction with a neurotransmitter (acetylcholine). Muscle cell nuclei and mitochondria are abundant near the junction.

In the cerebral and cerebellar cortices, gray matter (cell bodies and immediately adjacent processes) is located peripherally and white matter centrally; this pattern is reversed in the spinal cord. Cerebellar cortex consists of molecular, Purkinje, and granular layers [mnemonic: miles per gallon (MPG)] with extensive arborization of the neuronal processes. The cerebral cortex consists of a homogenous layer I with multiple deeper layers of large pyramidal and other types of neurons. The number of layers varies, depending on the cortical region. Neuronal cell bodies (perikarya) are also localized in ganglia in the peripheral nervous system and autonomic nervous system (ANS).

0 komentar:

Post a Comment

Note: Only a member of this blog may post a comment.