According to the function the neurons may be afferent (sensory), intercalary and efferent.
Sensory/Afferent neurons: carry the sensory impulses from periphery to the central nervous
system.
A. Somatic sensory neurons – receptors monitor outside conditions.
B. Visceral sensory neurons – receptors monitor internal conditions.
Motor/Efferent neurons: carry the motor impulses from central nervous system to the
peripheral effector organs like muscles, glands, blood vessels, etc.
A. Somatic motor neurons – innervate skeletal muscle, conscious control or reflexes.
B. Visceral/Autonomic motor neurons – innervate effectors on smooth muscle, cardiac
muscle, glands, adipose tissue.
Interneurons /Associative: they bind different-typed neurons. Distribute sensory info and
coordinate motor activity between sensory and motor neurons in brain, spinal cord,
autonomic ganglia. Most are multipolar.
2. Physiological properties of nerve cells and the functions of the structural
elements of the neuron (soma, axon, dendrites).
Soma/Cell body: The body of neuron contains different intracellular organelles necessary to
provide the vital activity of the cell. Its membrane is covered by the synapses, that is, plays an
important role in the perception and integration of the signals.
Dendrites: The dendrites transmit signals in the direction to the body of the neuron.
They are powerfully branched, and their total surface surpasses significantly the surface of
the neuron’s body. This allows more synapses to locate on the dendrites. Dendrite and cell
body serve as neuron input zone.
Axon: The axon transmits nerve impulses in the direction from the body of the neuron. The
action potentials are transmitted along the axon to its end. So, transmitting signals to the
great distances, axon connects the neurons with each other and with the effector organs.
3. Morphological and biophysical characteristics of neurons that provide their
specific functions (perception, integration, communication).
NO ANSWER
4. Trigger characteristics of the neuron. Action potential of the nerve cell.
Axon hillock it is first portion of the axon plus the region of the cell body from
which the axon leaves; neuron’s trigger zone; the greatest excitability has the membrane of
the initial segment of axon – axon hillock (threshold of depolarization in 3 times lower than in
other sites).
, The action potentials are transmitted along the axon to its end.
Explanation: Membrane potential is the difference in charges between the outer and inner
surfaces of a membrane. The stimulus causes the recharge of a membrane. The excited site
of a membrane becomes charged negatively in comparison with unexcited one. The
mechanism of the recharge is the passive change of a membrane potential which is
connected with the energy of the stimulus. The result of the recharge is the difference of
potentials between the excited site of a membrane (-) and unexcited sites (+).It leads to the
appearance of the power line of a direct current (this is the flow of electrons). It leaves a
membrane in the next, unexcited site and depolarizes it due to the exit of electrons. The
result is the difference of potentials between this excited site of a membrane (-) and the next
unexcited sites (+).Local currents depolarize the adjacent regions. The result is the
propagation of excitement.
5. Reflex principle of functioning of nervous system (R. Descartes, G. Prokhazka,
I.M.Sechenov, I. Pavlov, P.K.Anokhin).
The idea of reflex activity principle of the nervous system was first introduced in the middle
of the XVII century by R. Descartes – the great French naturalist and philosopher. The reflex
theory was an important step in the development of the materialistic ideas about the
mechanism of organism's reactions. Because this theory showed that in the basis of the
responses of the organism was the principle of determinism, that is, the principle of the
cause and effect relationships.
The term “reflex” was suggested in the XVIII century by Czech Physiologist G. Prochaska.
I. M. Sechenov proved the reflex nature of the psychical activity.
I. P. Pavlov discovered the conditioned reflexes and showed that conditioned reflex can
connect any stimulation with any effector organ. He saw in the conditioned reflex the factor
of future.
P. K. Anokhin discovered the feedback in the reflex arc. He pointed out that thanks to the
feedback, the nerve center receives information about the result of the reflex and makes
corresponding corrections. After any repetition of the reflex the nerve center itself becomes
more experienced.
So, as distinct from the three-component (afferent, central, efferent parts) reflex arc of
Descartes that of Anokhin's is four components (afferent, central, efferent parts and the
feedback).
6. Structural basis of reflex activity. The reflex arc and its elements.
Reflex arc is the nerve pathway between the receptor and effector.
01. Receptor, 02. Afferent nerve fiber, 03. Nervous Center, 04. Efferent nerve fiber, 05.
Effector organ, 06. Feedback
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