2 Neuroscience2.4 Cells
2.4 Cells
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Written by Resident Doctor Committee · Published
Neurones and glia
Neurones are principal (projection) neurones or local interneurones, and the glial cells are astrocytes, oligodendrocytes, microglia and ependymal cells.
The cell cycle
Interphase (G1, S and G2) is the longest stage, in which the cell grows and copies its deoxyribonucleic acid (DNA) and organelles.
DNA is copied in S phase, and the cell divides only in M phase.
G2 lies between completed DNA synthesis and the start of mitosis, so an agent that blocks entry to mitosis holds cells in G2.
G0 is a resting state outside the cycle: mature neurones stay in it for essentially their whole life, whereas hepatocytes rest there only temporarily.
New neurones therefore come from progenitor populations, not from mature neurones dividing.
The centromere is the site on a chromosome where spindle microtubules attach through the kinetochore, whereas the centrosome is the microtubule-organising centre that nucleates and organises the spindle.
Organelles of the neurone
Organelle | Function | Contrast or detail |
|---|---|---|
Nissl substance | Rough endoplasmic reticulum with ribosomes in the soma and dendrites; translates messenger ribonucleic acid into protein | The Golgi apparatus modifies and packages protein already made |
Smooth endoplasmic reticulum | Makes membrane phospholipids and steroid hormones; stores calcium | Rough endoplasmic reticulum makes protein on its ribosomes |
Mitochondria | Make most neuronal adenosine triphosphate by oxidative phosphorylation | Carried to the presynaptic terminal, where energy demand is highest |
Endosome | Sorting compartment of the endocytic pathway | Returns internalised membrane and receptors to the surface and sends the rest to lysosomes |
Lysosome | Breaks down material passed on from endosomes |
Nissl substance occurs only in neurones, whereas melanin pigments some brainstem neurones but is also made by melanocytes.
In the acidic early endosome, low-density lipoprotein (LDL) separates from its receptor; the receptor is recycled and the LDL passes on to the lysosome.