0
In support of neurons glial cells offer:
nourishment—Glial cells attach neurons to blood vessels and supply nutrients
and oxygen to neurons, maintain ionic balance and help control the chemical
composition of fluid surrounding neurons. The L-arginine for NO production is
mainly supplied mainly from glial cells. They produce cerebrospinal fluid!
insulation—Glia produce the fatty insulating myelin sheath around axons to
insulate one neuron from another, to form a matrix surrounding neurons and
hold them in place, this matrix serves to isolate synapses limiting the dispersion of
transmitter substances released.
Phagocyctosis—Glia act as scavengers, removing debris after injury or neuronal
death and to destroy and remove the carcasses of dead neurons. Phagocytosis
occurs when an astrocyte contacts a piece of neural debris with its processes (arm
of the astrocyte) and then pushes itself against the debris eventually engulfing and
digesting it.
Glycoysis—Aerobic glycolysis in the CNS involves interactions between
neurons and astrocytes. The entrance of glucose into the central nervous system
from the capillaries occurs primarily through astrocytes. Astrocytes are strategically
placed between capillaries and neurons and play an essential role in neuronal
energy metabolism and brain glycogen is localized in astrocytes in brain tissue.
Astrocytes provide nourishment to neurons by receiving glucose from capillaries,
Astrocytes first metabolize glucose to its metabolic intermediate lactate and secrete
lactate, releasing it into the extra cellular fluid surrounding the neurons. The
neurons receive the lactate from the extra cellular fluid and transport it to their
mitochondria to use as a primary substrate for oxidative metabolism to create
energy. In this process astrocytes store a small amount of glycogen, which stays on
reserve for times when the metabolic rate of neurons in the area is especially high.
Neuronal activity regulates the rate of aerobic glycolysis by a mechanism
involving glutamate release from neurons and glutamate uptake into astrocytes.
Glutamate is the primary neurotransmitter released by excitatory synapses in the
CNS. Glutamate is taken up by astrocytes by a Na+ cotransporter. Na+ influx into
astrocytes stimulates the astrocytic sodium pump which produces ADP. Increased
levels of astrocytic ADP will stimulate glycolysis and lactate transport into neurons.
Lactate uptake by neurons will stimulate neuronal oxidative ATP production.
Glucose can be incorporated into lipids, proteins, and glycogen, and it is also
the precursor of certain neurotransmitters such as g-aminobutyric acid (GABA),
glutamate, and acetylcholine.
schwann cells support the peripheral nervous system, while the central nervous
system is supported by glial cells. As the peripheral nerves form, the Schwann cells
migrate peripherally from the spinal ganglia, parallel to the axons, and encase them
with their cytoplasm. The myelin sheath is created by a synthesis and wrapping
of Schwann cell plasma membrane around the axon. During the breakdown of
damaged axons Schwann cells participate in myelin phagocytosis prior to the
recruitment of macrophages. They produce heat shock protein, only when they
have transformed into these myelin-“eating” cells from myelinating cells. I am