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الكلية كلية طب الاسنان     القسم  العلوم الاساسية     المرحلة 2
أستاذ المادة حيدر حميد عباس الحيدري       09/09/2020 23:34:14
Nervous System Functions:
[1]. Coordinate the activities of other systems (along with the endocrine system) through .sense and respond to internal and external events, therefore, it maintains homeostasis of the body.
[2]. Store experiences (memory) and establish patterns of response based on prior experiences (learning). More than 99% of all sensory information are discarded by the brain as unimportant. A small fraction of the selected important sensory information is processed in the CNS and then either appropriate motor response occurs (through sensory-somatic or autonomic nervous systems) or to be stored by a process called memory.
The functional levels of CNS: The intercommunication between the external environment and the CNS is mediated by the sensory-somatic peripheral nervous system, while the intercommunication between the internal environment and the CNS is mediated by autonomic peripheral nervous system. The CNS can be divided into three functional levels:
1- Spinal cord level: Spinal cord acts (a) as a conduit for signals from the periphery of the body to the brain or in opposite direction from the brain back to the body. In addition to this function (b) many reflex control centers are located in the spinal cord, which are in turn controlled by higher levels of CNS.
2-The lower brain level (subcortical level): Most of the subconscious activities of the body are controlled in the lower areas of the brain, i.e. medulla, pons, epencephalon, hypothalamus, thalamus, cerebellum, basal ganglia. Such of these activities are control of arterial pressure, respiration, control of equilibrium, feeding reflexes, many emotional patterns such as anger, excitement, sexual activities, reaction to pain, reaction to pleasure.
3-The higher brain level (cortical level): Cerebral cortex converts the lower CNS function into very determinative precise operations. In addition, the cerebral cortex is a very large memory storehouse and it is essential for most of our thought processes in association with the lower CNS centers.


























The neuronal pools: Neuronal pool is a collection of intercommunicated neurons. Each pool has its own special characteristics of organization which cause it to process signals in its own special way. The examples of such pools are basal ganglia, specific nuclei in the thalamus, and cerebellum etc. The CNS is made up of hundreds or even thousands of separate neuronal pools. Each pool has many separate fiber tracts coming to it (afferent fibers) and other leaving it (efferent fibers). The input signals to the neuronal pool may excite, inhibit, or facilitate the neurons within the pool.
The neuronal pool may:
1.Amplify the input signal and transmit these amplified signals
to one or different directions (divergence).
2.It may summate the effects of multiple incoming signals that
converge on the same pool (convergence).
3.Sometimes an incoming signal to a neuronal pool causes an output excitatory signal going in one direction and at the same time an inhibitory signal going elsewhere.
4.Sometimes a signal entering a pool causes a prolonged output discharge, called after-discharge, even after the incoming signal is over. The mechanisms by which after - discharge occurs are the following:
[a]- Synaptic after-discharge: When excitatory synapses discharge on the surface of postsynaptic neuron a long-acting synaptic transmitter substances.
[b]- Parallel circuit for after-discharge: When the input signal spreads through a series of neurons in the neuronal pool and from many of these neurons impulses keep converging on an output neuron.
[c]- Reverberatory circuit for after-discharge: When excitatory signal stimulate a neuron in a neuronal pool, the excited neuron in the pool feeds back to re-excite itself. Examples of reverberatory system are those which occur during respiration in which the inspiratory neuronal pool in the medulla become excited for about 2 sec during each respiratory cycle. Also one theory of wakefulness is that continual reverberation occurs somewhere within the brain stem to keep a wakefulness area excited during the waking hours.
5. Some neuronal pools emit output signals continuously even without excitatory input signals. This occur probably due to the rhythmical property of the neurons within the pool or due to the reverberating circuits.


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .