Human Body Responses: Sensory, Heat, Exercise, Cerebellum
Sensory Receptors
- Meissner: Detects light touch, such as gentle caresses.
- Merkel: Detects sustained pressure on the skin’s surface.
- Pacinian: Detects deep, wide-field vibrations. These are unmyelinated.
- Ruffini: Detects skin stretching and sustained pressure.
Physiological Response to Heat
Heating the skin leads to increased cutaneous blood flow. Venous return from the extremities to the heart occurs through superficial veins. If the thermal gradient is large enough, sweating occurs, leading to skin cooling by evaporation.
Adaptation to Heat
When a person not accustomed to or trained physically has a high cardiac output for the first time during intensive exercise in a hot environment, they will soon experience marked elevations of central and superficial temperature, and their heart rate will reach maximum values. This is often accompanied by dizziness and nausea. If these people are subjected to the same conditions for 8-10 days or less, the threshold temperature at which sweating starts decreases, as does the superficial central temperature. In addition, they will sweat more heavily, and cardiac output will be lost more rapidly. After 10 days, the elevations of the central temperature are similar to those achieved by exercise in the cold.
Physical Exercise
Central temperature rises to reach a new level that is proportional to metabolism and independent, within a wide range, of environmental temperature. Elevated temperature is due to muscle contraction. The most important route of heat loss is evaporation. People who sweat profusely are more capable of regulating their central temperature efficiently because sweat dissipates heat and represents a waste of reserve fluid. Under conditions of very high relative humidity, heat balance cannot be achieved, and the central temperature continues to rise, potentially leading to heat stroke.
Cerebellar Removal
Removal of the cerebellum can result in the following:
- Hypotonia
- Decomposition of movement
- Ataxia
- Dysmetria
- Adiadochokinesia
- Intention tremor
- Asynergy
- Asthenia
- Abnormal posture
- Abnormal spinal reflexes
Regions of the Cerebellum
- Vestibulocerebellum (Flocculonodular): Involved in balance and eye movement.
- Spinocerebellum (Medial Hemisphere): Involved in motor performance.
- Cerebrocerebellum (Lateral Hemisphere): Involved in motor planning (closed circuit).
Core Temperature and Body Surface Temperature
Core temperature is constituted by the head, chest cavity, and abdominal cavity. Central temperature is regulated and maintained constant within fairly narrow limits. Rectal and esophageal temperatures measure core temperature. Surface temperature is a measure of the skin, subcutaneous tissue, and muscle mass. Surface temperature varies with environmental conditions. Body temperature is the sum of the central temperature and superficial temperature, each multiplied by a constant.
Regulation of Body Temperature
Body temperature regulation is a system consisting of a series of receptors for temperature on the surface of the body (skin), spinal cord, and hypothalamus. An integrating center is located in the hypothalamus, whose mission is to receive and integrate information from a reference point encoded in the central nervous system itself (37ºC). This operation generates the appropriate thermoregulatory responses to adjust or maintain constant central temperature. The difference between the reference information should be known as the coefficient of variation. A major difference between afferent input and the reference point indicates a higher coefficient of variation.
Fever
Fever is an increase in body temperature caused by an increase in the benchmark temperature in the hypothalamus. It rises from 37 to 39ºC. When the new set point is reached, the system begins to function as before, creating a new balance between heat production and loss. In a neutral environment, intense vasoconstriction occurs, and the basal metabolic rate increases. In a warm environment, increased sweating may occur.
Heat-Related Illnesses
Heat Exhaustion
Symptoms include headache, nausea, vomiting, tinnitus, chills, and diarrhea. The patient may be unconscious with a rectal temperature of 40ºC.
Heat Syncope
Characterized by a transient loss of consciousness due to the diversion of large volumes of blood to dilated skin vessels. This decreases venous return and stroke volume, which decreases blood pressure, leading to cerebral ischemia and loss of consciousness.
Heat Stroke
This is a medical emergency. Rectal temperature is typically between 41-43ºC. The patient is unconscious with much-diminished reflexes. Delirium and seizures may occur. Central temperature must be lowered urgently to prevent irreversible brain injury.