To understand sensory and perceptual disturbances, one must
first be aware of the difference between sensation and
perception. Sensation is the physical energy, and perception the
subjective experience(Crow, 1981). Sensation originates with a
particular stimulus, which is conveyed by the neurons to the
thalamus,where the neurons synapse, or connect, with other
neurons, they then connect with the parietal lobe of the brain.
Perception is the way in which each person individually
organizes and consciously interprets these sensations.
Disturbances can occur with either the process of sensing or that
of perception. Cognition is the way people think, learn, and make
judgments.
Common Functions Controlled by the Nervous System
The nervous system orchestrates or coordinates the vital
functions of the body. Three of the more important functions of
the nervous system are sensation, perception and cognition.
SENSATION
The million of the sensory receptors all over the external surface
of the body and in mucous membranes are highly sensitive to
changes in the environment. These receptors send messages tho
the CNS (Central Nervous System). Within the spinal cord these
sensory perceptions from the periphery may be immedietly
routed to appreciate locations. If, for example, the fingers should
touch a hot kettle, a reflex are within the spinal cord is activated
and they are immedietly drawn away. The position of the body in
space and the various body parts is constantly monidulla, pons,
mesencephalon, amygdala, and hypothalamus. The body
responds with coordinated movements that keep the persons
standing or make walking movements coordinated. Lower brain
centers are also responsible for the coordination of such activities
as swallowthing.
PERCEPTION
Perception is the development of an awareness of something
within the environment. Perception is a complex phenomenon
that begin with the stimulus from the sensory receptor, but
involves the processing of that stimulus within the brain.
According to Guyton (1992), the brain simply discards as
unimportant or irrelevant 99% of the sensory input it receives.
The brain selectively passes on sensory data as a part of its
integrative function. Strong sensory signals are most likely to be
communicated within the brain. The brain will also communicate
sensory signals that relate to meaningful stimuli. One of the
simplest examples of this is your heightened awareness of people
driving cars that are of the same make and model as the new car
you just purchased (Fig. 31-4).
Another part of perception is the ability of the brain to sort stimuli
into patterns that are meaningful. Because of this ability, you may
see a portion of a face and immedietly perceive what the whole
face would look like. This same ability may cause an individual to
perceive something different than what is there. When an
individual sees a movement out of the corner of the eye and
responds as if a person were there, that may be because the
brain filled in the details. The brain can also convert distorted or
nonmeaningful stimuli into a meaningful pattern. If a person puts
on prism glasses that invert all visual stimuli, after a period of
time the brain will convert these stimuli into patterns that allow
the person to perceive objects in their correct relationships.
COGNITION
Cognition, also called mentation, which is controlled by the cortex
of ther brain, refers to intellectual functioning. That is the ability
to think, recall events, calculate numbers, and the solve
problems. Cognition also involves more indepth thinking such as
the ability to formulate and move towards goals. Abstraction and
creativity are other important parts of mentation.
Awareness is the ability to respond to sensory input. Level of
awareness s the degree to which person is aware of the
surroundings. Parts of cognition is to be alert and aware of ones
surroundings and therefore able to respond. Normally people are
alert and aware of their surroundings.
Another aspect of cognition is orientation, which is the persons
awareness of the environment in relationship to specific aspects
of person, place, and time. Person refers to an understanding both
who of he or she is, and who others in the environment are.
Orientation to place is the ability to identify current location, such
as a hospital in a specific city. Orientation to time is the ability to
understand the day and date and might be further expanded to
an understanding of the time of day.
There may be a considerable discrepancy between awareness and
orientation. A person can be alert and interested in the
surroundings and responsive to interpersonal relationships and at
the same time be disoriented as to person, place or time. For
example, a patient may sit in the dayroom and play cards skillfully
and annatedly, all the while recounting numerous telephone alls
from the president requestin help with internaonal affairs. Such a
patient is considered to hav a normal level of awareness while
being obviously disoriented.
