Since K+ diffuses out of neurons during the production of nerve impulses (described later), this function may be important in maintaining the proper ionic environment for neurons.
2. Astrocytes take up some neurotransmitters released from the axon terminals of neurons. For example, the neurotransmitter glutamate is taken into astrocytes and transformed into glutamine (fig. 7.10). The glutamine is then released back to the neurons, which can use it to reform the neurotransmitter glutamate.
3. The astrocyte end-feet surrounding blood capillaries take up glucose from the blood. The glucose is metabolized into lactic acid, or lactate (fig. 7.10). The lactate is then released and use as an energy source by neurons, which metabolize it aerobically into CO2 and H2O for the production of ATP.
4. Astrocytes appear to be needed for the formation of synapses in the CNS. Few synapses form in the absence of astrocytes, and those that do are defective. Normal synapses in the CNS are ensheathed by astrocytes (fig. 7.10).
5. Astrocytes induce the formation of the blood-brain barrier. The nature of the blood-brain barrier is described in the next section.
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