Functional Brain Systems
- a functional brain system is a network of neurons that work together and span relatively large distances within the brain.
- the limbic system
- located on the medial aspect of each cerebral hemisphere and in the diencephalon
- cerebral structures encircle the midbrain and include parts of the rhinencephalon and part of the amygdala
- diencephalonic structures include the hypothalamus and the anterior thalamic nuclei
- the fornix (and other tracts) links the limbic regions together
- the limbic system is involved in emotions and feelings
- psychosomatic illnesses have their root in the limbic system
- cardiac arrest is the most extreme consequence of severe emotional upheaval
- thoughts and feelings are intimately linked due to the limbic system's interaction with the prefrontal lobes
- this explains why sometimes emotions override logic
- this also explains why logic sometimes suppresses emotion
- the hippocampus and the amygdala also play a role in long term memory storage
- lesions of the amygdala can result in emotion-related personality changes : docility, restlessness, pugnaciousness, oversexed behavior, etc.
- lesions of the cingulate gyrus destroys the will and the desire to act
the reticular formation- extends through the central core of the brain stem with radiations to the cerebral cortex
- composed of loosely clustered neurons in otherwise white matter
- the reticular neurons can be localized into three broad columns : the raphe nuclei (midline), the medial nuclear group (lateral to the raphe) and the lateral nuclear group (lateral to the medial and raphe)
- individual reticular neurons project to cells in the hypothalamus, thalamus, cerebellum, and spinal cord
- the widespread connections make the reticular formation ideal for arousing the brain as a whole
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the reticular activating system (RAS) sends a continuous stream of
impulses to the cerebral cortex, promoting consciousness, and seems
to also act as a filter for the flood of sensory inputs (ascending
sensory tracts synapse with RAS neurons, enhancing their arousing effects)
- the RAS and the cerebral cortex ignore roughly 99% of all sensory stimuli
- LSD removes these sensory dampeners, promoting sensory overload
- the RAS is inhibited by sleep centers and depressed also by alcohol, sleep-inducers and tranquilizers
- severe injury to the RAS can result in a coma
- the motor
arm of the reticular formation helps control skeletal muscles during coarse
limb movements and other reticular motor nuclei (vasomotor, cardiac and
respiratory centers of the medulla), regular visceral motor function
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