The Cerebellum and Hypothalamus Help
Introduction to The Cerebellum and Hypothalamus
The thalamus and postcentral gyrus (primary or general sensory cortex) are not the only places in the human brain that receive sensory information. Two other very important sensory areas are the cerebellum ( sair -uh- BELL -um) or “little cerebrum” ( cerebell ) and the hypothalamus ( high -poh- THAL -uh-mus) or region “below” ( hypo -) the “thalamus.” (Review Figure 14.11.)
The cerebellum is involved in proprioception ( proh -pree-oh- SEP -shun). This long term literally means “the process of receiving” (- ception ) sensations from “one’s own” ( propri ) self. In more direct language, proprioception involves the receiving of sensory stimuli that indicate the relative position of the entire body and its parts within space. The sensory receptors for proprioception are often found within the skeletal muscles and joints. Thus, you can sense or feel that you are standing upright, or that you have raised your arm up off a table, without even having to look! By providing proprioception, the cerebellum helps the body maintain its vertical balance and reduces the amount of shaking during automatic reflex movements.
The Hypothalamus And Negative Feedback
The hypothalamus, like the thalamus, lies buried deep within the cerebrum. It contains a number of control centers for homeostasis. It includes, for instance, the temperature control center . Recall that oral body temperature usually varies up-and-down in a roughly S-shaped pattern, within its normal range. And remember how thermoregulation (homeostasis of body temperature) is maintained by processes occurring within the skin, such as sweating and vasodilation. The logical question we can ask is, “Okay, just what part of the body is it, that controls the mechanisms responsible for carrying out thermoregulation?” The answer is this: Certain neurons within the temperature control center of the hypothalamus establish and maintain the set-point for oral body temperature. A set-point is defined as the long-term average value of a body variable: that is, it is the point at which the variable seems to be set . Oral body temperature, for example, seems to be set at an average value of about 98.6 degrees F. [ Study suggestion: Visualize the thermostat in your own house or apartment. What is the usual “set-point” temperature where you keep the thermostat?]
Obviously, when certain factors raise the body temperature too far above this set-point (or too far below it), then some type of control system has to be engaged. Usually, the human body uses a negative feedback control system to correct or minimize the amount of change.
In general, a negative feedback control system is a collection of anatomical and physiological components that operate to produce an outcome or response which curves or feeds back upon the initial stimulus in a negative manner. By this it is meant that the final outcome of the system curves (feeds back) upon the initial stimulus to remove or correct it. (Consult Figure 14.12, A.)
Consider, for instance, a situation where the temperature in a room starts to rise above its set-point value on the thermostat (Figure 14.12, B). As the temperature begins to rise towards the upper limit of its normal range, a negative feedback temperature control system kicks in. The rise in temperature acts as a stimulus for the air conditioner in the unit. It begins to blow cold air into the room. Soon, the room temperature drops back down towards its set-point value on the thermostat. The intial stimulus (rise in room temperature above the set-point level) has therefore been corrected or removed. Hence, a negative feedback control system has been in operation.
Within the human body, of course, increased sweating and vasodilation of skin blood vessels would have a similar negative feedback effect upon any significant rise in oral body temperature beyond its set-point of about 98.6 degrees F. A group of neurons within the temperature control center of the hypothalamus direct this sweating and vasodilation process to occur.
In addition to the temperature control center, the hypothalamus has numerous other control centers. These include a hunger center , thirst center , pleasure center , and many other centers that help control some important body variable and thus maintain homeostasis.
Integration and Association Areas of the Brain
In addition to the major motor and sensory areas of the Central Nervous System (brain and spinal cord), there are a number of critical sensory integration or association areas . These areas make meaningful connections or associations between incoming stimuli, so that recognition and learning tend to occur. Take, for instance, the primary visual area at the back of the cerebrum, and the visual association area located just in front of it. The primary visual area receives visual impulses from the retina ( RET -ih-nah) in the rear wall of the eyeball. These visual impulses travel to the primary visual area over the optic ( AHP -tik) nerves . But these visual impulses don’t make any sense to us until they are sent forward to the visual association area. Here the separate bits of visual information are ordered and assembled into meaningful patterns and images that we can recognize, such as the familiar face of a good friend.