2.2 Holographic Study of Structural and Functional Characteristics …
87
electron microscope, the studies detected contacts between axons of two neurons and
even between their bodies. They also detected the dynamics of synaptic connections:
Some of them can disappear, others—appear. In this process, the functional load,
which neurons receive or do not receive, is very important.
If healthy experimental animals after their birth were kept in utter darkness, then
synaptic connections of those neurons of brain visual centers, which perceive and
process only the information about light (so-called monosensory neurons), were
not developing. In the result, the animals became blind though they had all other
visual organ elements: Pupil, nervous tunic of eyeball and moreover all nervous
conduction paths were saved. The fewer the animals were kept in darkness, the
easier it was to restore the function of monosensory neurons and to restore their
sight. Such experiments were carried out with the neurons of the auditory center, and
the results were similar.
The experiments prove that neurons of all brain centers—visual, auditory, motor
and others—for its healthy growth need information gain and adequate functional
gain. Only in this case, multilateral interneuronic connections are formed, which to
a considerable degree detect the reliability and plasticity of all mechanisms of the
central nervous system including adaptation mechanism, training mechanism and
memorization mechanism. Brain language is the language of electrical pulses, as
well as chemical pulses [208] and possibly optical pulses (see Sect. 2.2.7).
Now let us describe structural and functional characteristics of a nerve fiber. Nerve
fiber consists of axon and layers. Axon in comparison with nerve cell body has other
features. For example, impulses in it are transferred with the velocity up to 100 m/s,
while in brain gray substance, it is 1–2 m/s. Myelin sheath appears at a distance of
50–100 μm from the cell body and disappears in the nerve ending zone. Myelinated
nerve fibers have the diameter from 2 up to 20 μm. The relation of axon diameter
and the diameter of the whole fiber is used to be constant and equal to 0.51:1. Myelin
sheath because of its high refraction is used as a lens, that is why the axon parts under
it seems to be thicker in comparison with the parts in the area of Ranvie interceptions,
where the myelin sheath is absent (Fig. 2.9).
As a rule, axons are surrounded by thick fat (myelin) sheath, which is periodically
(in 1–2 mm) broken by Ranvie interceptions (1 μm). Myelin segments are used as
insulating joint. Nerve fiber on these parts is similar to passive communication. Only
the part of cellulated surface in Ranvie interceptions is electrically active. It is very
convenient to study unmyelinated squid axons, which sometimes have the diameter
of 1 mm. In such fibers, which are also called smooth grain, the whole surface is
electrically active.
Axon can be represented as a hollow tube filled with an electrolytic solution, which
was dipped into extracellular fluid. This tube wall—axon membrane—consists of
lipids and proteins. Membrane thickness is ~7 nm. Electric membrane rest resistance
is quite high, it is about 10
3
/cm
2 , and its capacity is about 1 mcF/cm
2 . Axon
membrane separates the internal filling solution from the external one having another
composition. So, inside, in axoplasm, in comparison with the environment (K—10
mmol/l, Na—460 mmol/l, Cl—540 mmol/l), the K ions concentration is quite high
(400 mmol/l), and Na and Cl ions concentration is quite low (50 mmol/l). Rest
87
electron microscope, the studies detected contacts between axons of two neurons and
even between their bodies. They also detected the dynamics of synaptic connections:
Some of them can disappear, others—appear. In this process, the functional load,
which neurons receive or do not receive, is very important.
If healthy experimental animals after their birth were kept in utter darkness, then
synaptic connections of those neurons of brain visual centers, which perceive and
process only the information about light (so-called monosensory neurons), were
not developing. In the result, the animals became blind though they had all other
visual organ elements: Pupil, nervous tunic of eyeball and moreover all nervous
conduction paths were saved. The fewer the animals were kept in darkness, the
easier it was to restore the function of monosensory neurons and to restore their
sight. Such experiments were carried out with the neurons of the auditory center, and
the results were similar.
The experiments prove that neurons of all brain centers—visual, auditory, motor
and others—for its healthy growth need information gain and adequate functional
gain. Only in this case, multilateral interneuronic connections are formed, which to
a considerable degree detect the reliability and plasticity of all mechanisms of the
central nervous system including adaptation mechanism, training mechanism and
memorization mechanism. Brain language is the language of electrical pulses, as
well as chemical pulses [208] and possibly optical pulses (see Sect. 2.2.7).
Now let us describe structural and functional characteristics of a nerve fiber. Nerve
fiber consists of axon and layers. Axon in comparison with nerve cell body has other
features. For example, impulses in it are transferred with the velocity up to 100 m/s,
while in brain gray substance, it is 1–2 m/s. Myelin sheath appears at a distance of
50–100 μm from the cell body and disappears in the nerve ending zone. Myelinated
nerve fibers have the diameter from 2 up to 20 μm. The relation of axon diameter
and the diameter of the whole fiber is used to be constant and equal to 0.51:1. Myelin
sheath because of its high refraction is used as a lens, that is why the axon parts under
it seems to be thicker in comparison with the parts in the area of Ranvie interceptions,
where the myelin sheath is absent (Fig. 2.9).
As a rule, axons are surrounded by thick fat (myelin) sheath, which is periodically
(in 1–2 mm) broken by Ranvie interceptions (1 μm). Myelin segments are used as
insulating joint. Nerve fiber on these parts is similar to passive communication. Only
the part of cellulated surface in Ranvie interceptions is electrically active. It is very
convenient to study unmyelinated squid axons, which sometimes have the diameter
of 1 mm. In such fibers, which are also called smooth grain, the whole surface is
electrically active.
Axon can be represented as a hollow tube filled with an electrolytic solution, which
was dipped into extracellular fluid. This tube wall—axon membrane—consists of
lipids and proteins. Membrane thickness is ~7 nm. Electric membrane rest resistance
is quite high, it is about 10
3
/cm
2 , and its capacity is about 1 mcF/cm
2 . Axon
membrane separates the internal filling solution from the external one having another
composition. So, inside, in axoplasm, in comparison with the environment (K—10
mmol/l, Na—460 mmol/l, Cl—540 mmol/l), the K ions concentration is quite high
(400 mmol/l), and Na and Cl ions concentration is quite low (50 mmol/l). Rest