The neuronal doctrine states that the neuron is the structural and functional unit of the nervous system. Neurons are individual cells, which are not continuous to other neurons. The neuron has three parts: the dendrites, the soma and the axon. Conduction takes place in the direction from dendrites to soma, to the end of the axon. Dendrites increases the surface area and receive inputs. The axon carries information over long distances. The initial segment is called the hillock, this is the origin of action potentials. Axons are covered by myelin to improve conduction. There are gaps between myelin sheath which allow salutatory conduction. The axon terminals are where neurotransmitter are released from the presynaptic neuron to the postsynaptic neuron.
Dendritic spines are protrusions from the stalk of a dendrite that synapses with a single axon. Spines have a bulbous head and thin neck. There are two types of transport. Firstly, retrograde transport. This is transport from axon terminals to the cell body, mediated by dyneins. This sort of transport takes place for transport of viruses, toxins and growth factors. Next, there is anterograde transport, this is from the soma to the axon terminals. It is mediated by kinesins. Anterograde transport can be fast and slow transport.
Motor neuron disease (ALS) is a disease resulting from inhibition of axonal transport. Inhibition leads to loss of function, loss of synapses and therefore voluntary muscles waste away.
Synaptosomes are plasma membrane enclosed structures derived from synapses. It is a controversial topic but it is believed that they contain proteins and machinery that promote protein synthesis, for example ribosomes and mRNA.
Neuronal activity regulates both translation and protein targeting. Dendritically translated genes include: calcium signally related proteins (for example alpha-CaMKII), cytokine proteins (for example MAP2), and receptors (for example NMDA receptors.) Synaptic stimulation may globally upregulate translation, recruit translation of specific mRNAs and suppress translation.
Microglia are described as scavengers, they find foreign materials, damaged cells and apotopic cells and activate phagocytes. Astrocytes are glial cells that mop up transmitter and correct the ionic environment.
Glial fibrillary acidic protein is a marker for glial cells. It is an intermediate filament protein found inside the glial cells. Exosomes are extracellular vesicles that are released from cells.
As previously mentioned, myelin surrounds the axons forming a supportive, insulating layer that allows salutatory conduction. This is the fast firing of action potentials at the nodes of Ranvier (gaps). Myelin speeds up conduction by 10 times and occupies 100th of the space. Large plasma membrane sheets are spirally wrapped (forming intraperiod lines) and then compacted (forming intracellular dense lines.) Initial tucking under of sheets is completed by adhesion molecules. The central nervous system and peripheral nervous system use slightly different proteins for adhesion. The CNS uses Proteolipid protein (PLP), which is a transmembrane protein that interacts with PLP on adjacent major dense lines. Myelin basic protein (MBP) is found in the extracellular space (intraperiod lines), it is highly charged. MBP is found in the peripheral nervous system too. Rather than PLP, the PNS has protein zero, which acts like PLP. Mutations in these proteins can cause disease. For example, multiple sclerosis. Myelin associated glycoprotein is another protein that has repeat structures of either immunoglobulin or fibronectin. MAG is necessary for initial tucking under of myelin sheath.