The human nervous system can be thought of as a series of steps or levels (Figure 12-11).
Each level is more complex than the level just below.
No level is completely overpowered by upper levels, but each level is controlled or guided by the next upper level as it functions.
Label 1 Reflexes
The simplest and lowest level of control is the reflex arc. The reflex arc operates essentially on the level of the sensory input.
Segmental reflexes produce a wider reaction to a stimulus than the reflex arc.
For this purpose, the nervous system is organized more complexly. Thus, information spreads to a wider area of CNS. We can observe a greater reaction to the stimulus.
Label 2 Brainstem center – Visceral Centers of the Medulla
Within the brainstem, there is a well integrated series of control centers.
Visceral Centers of the Medulla
There is a group of nuclei in the medulla of the hindbrainstem. Together, these nuclei control the visceral activities of the body, such as respiration, heart beat, etc.
Label 3 Brainstem center – Reticular Formation
Within the substance of the brainstem is a diffuse system called the reticular formation.
The reticular formation has a facilitory (excitatory) area and an inhibitory area.
Thus, this control area tends to activate or slow down activities of the body.
For example, it is responsible for producing sleep or wakefulness.
Label 4 Brainstem center - Hypothalamus
The hypothalamus is a higher control center for visceral activities of the body.
It is found associated with the thalamus.
Label 5 Brainstem center - Thalamus
The thalamus is a group of nuclei found together in the forebrainstem.
The thalamus is the major relay center of sensory inputs from the body.
Label 6 Cerebellum
The cerebellum has been greatly developed, with many functional subdivisions.
It is the primary center for the integration and control of patterned, sequential motions of the body.
The cerebellum is also the center of control of body posture and equilibrium.
Label 7 Cerebrum
In humans, the highest level of nervous control is localized in the cerebrum.
It is at this level that conscious sensation and volitional motor activity are localized.
Even so, we can clearly designate three levels of control within the cerebrum:
Visceral (Vegetative) Level
This level is concerned primarily with visceral activities of the body, as related to fight-or-flight, fear, and other emotions.
Patterned (Stereotyped) Motor Actions
Here, activities of the body are standardized and repetitive in nature.
An example of a stereotyped pattern of muscle activity would be the sequence of muscle actions involved in walking.
The volitional level is the highest and newest level of control.
Here, cognition (thinking) occurs, and unique, brand-new solutions can be created.
Summary screen - Changes With Development or Injury
Babinski's reflex involves dorsiflexion of the big toe when the sole of the foot is stimulated.
It can be normally observed in infants up to 18 months of age.
As the pyramidal motor pathways develops completely, this reflex disappears.
However, if the pyramidal motor system is injured, the Babinski reflex tends to return.
Thus, it is possible to evaluate the extent of development of an individual by identifying the highest level of control.
In the case of injury, the highest active level of control helps determine the site of the injury.