Cellular Organization of the Nervous System Flashcards
What are the two groups into which vertebrate neurons are classified?
Bipolar (only two processes directly arise from the soma) and multipolar (many dendrites and one axon directly arise from the soma).
What four types of membrane channels allow ions to flow across the membranes?
Leak channels, modality-gated channels, ligand-gated channels, and voltage-gated channels.
How is the membrane resting potential maintained?
Negatively charged molecules trapped inside the neuron, because they are too large to diffuse out; the sodium-potassium pump; passive diffusion of ions through leak channels.
What is the typical resting membrane potential of a neuron?
About -70mV.
About how much depolarization is required to generate an action potential?
About 15mV depolarization triggers an action potential.
What is the difference between the absolute refractory period and the relative refractory period?
The absolute refractory period is a period of time during which an action potential CANNOT be generated due to sodium channels being unable to open for a period of time.
The relative refractory period is a period of time (after the absolute refractory period) during which an action potential may be generated, but its generation requires a stronger stimulus than a normal action potential.
What is the purpose of the refractory period?
It promotes the forward propagation of the action potential while preventing any backwards effect up the axon.
What two features influence the speed of an action potential?
Diameter of the axon (increased diameter increases speed); myelination.
What is the purpose of myelination?
It prevents leakage of current across the membrane, allowing an action potential to propagate further down the axon without dissipating.
What are the three groups of macroglial cells?
Astrocytes, oligodendrocytes, and Schwann cells.
What is the purpose of astrocytes?
They can release glutamate; they can also take up extracellular potassium; they play a role in development; they can take up debris; they can connect capillaries to neurons and thus provide nutrients to the cell (they form tight junctions around the capillaries and help in creating the BBB).
What is the purpose of oligodendrocytes?
They create myelin for axons of the CNS. They supply myelin to several axons.
What is the purpose of Schwann cells?
They create myelin for axons of the PNS. One Schwann cell supplies myelin for only one axon, though it takes several Schwann cells to myelinate a single axon. They can also ingest and destroy bacteria and other cells when peripheral nerves are inflamed.
What is the purpose of microglial cells?
They act as the immune system of the CNS and clean the neural environment.
Multiple sclerosis is an autoimmune disease where antibodies tag myelin in CNS nerves. What occurs after the myelin is targeted?
Oligodendrocytes are destroyed, the microglia eat the myelin debris, and astrocytes proliferate, causing scarring.
