Understanding Sensory Responses and Thermoregulation in Humans
RC Sensory
Meissner’s corpuscles detect surface touch or gentle caresses.
Merkel cells detect surface pressure.
Pacini’s corpuscles detect vibration, phasic deep, wide field, and are unmyelinated.
Ruffini endings detect skin stretch.
Physiological Response to Heat
Heat increases skin temperature, leading to increased cutaneous blood flow. Venous return from the extremities to the heart occurs via superficial veins. If the thermal gradient is large enough, sweating begins, leading to skin cooling through evaporation.
Adaptation to Heat
When a person unaccustomed to physical exertion exercises in a hot environment for the first time, they may experience marked elevations in central and superficial temperature, with heart rate reaching maximum values. This is often accompanied by dizziness and nausea. If these individuals are subjected to the same conditions for 8-10 days or less, the threshold temperature at which sweating begins decreases, and they experience lower cutaneous and central temperatures, in addition to sweating more heavily and losing fluids more rapidly. After 10 days, the elevations in central temperature become similar to those achieved during exercise in cooler conditions.
Physical Exercise
During exercise, central temperature rises to a new level proportional to metabolism and remains independent across a wide range of environmental temperatures. Elevated temperature during exercise is primarily due to muscle contraction. The most significant route of heat loss is through evaporation. Individuals who sweat profusely can regulate their central temperature more efficiently, as sweat dissipates heat and represents a loss of fluid reserves. Under conditions of very high air relative humidity, heat balance cannot be achieved, and central temperature continues to rise, potentially leading to thermal shock.
Removal of Cerebellar Function
Symptoms may include hypotonia, decomposition of movement, ataxia, dysmetria, adiadochokinesia, intention tremor, asynergy, asthenia, abnormal posture, and altered spinal reflexes.
Regions of the Cerebellum
Vestibulocerebellum (flocculonodular lobe) is involved in roll and eye movement.
Spinocerebellum (medial hemisphere) is responsible for motor performance.
Cerebrocerebellum (lateral hemisphere) is involved in motor planning and coordination.
Core Temperature and Body Surface
Central temperature is constituted by the head, chest cavity, and abdominal cavity. It is regulated and maintained within fairly narrow limits. Rectal and esophageal temperatures are used to measure central temperature.
Surface temperature is a measure of the skin, subcutaneous tissue, and muscle mass, and it varies with environmental conditions.
Body temperature is the sum of central temperature and superficial temperature multiplied by a constant.
Regulation of Temperature
This system consists of a series of receptors for temperature on the surface of the body (skin), muscle, hypothalamus, and a center located in the hypothalamus, which receives and integrates information from a reference point encoded in the central nervous system (37 ºC). This operation generates appropriate thermoregulatory responses to maintain constant central temperature. The difference between the reference information and actual input is known as the coefficient of variation. A significant difference between afferent input and the reference point results in a higher coefficient of variation.
Fever
Fever is characterized by an increase in temperature due to an elevated set point in the hypothalamus, rising from 37 to 39 ºC. When the temperature reaches this new set point, the system begins to function as before, creating a new balance between heat production and loss. In a neutral environment, vasoconstriction occurs, and basal metabolic rate increases. In warmer temperatures, increased sweating may occur.
Heat Exhaustion
Symptoms include headache, nausea, vomiting, tinnitus, chills, and diarrhea. The patient may be unconscious with a rectal temperature of 40 ºC.
Heat Syncope
This condition involves transient loss of consciousness due to the diversion of large volumes of blood to dilated skin vessels, decreasing venous return and cardiac output, which can lead to cerebral ischemia and loss of consciousness.
Heat Stroke
This is a medical emergency characterized by a rectal temperature of 41-43 ºC. The patient may be unconscious and exhibit diminished reflexes. Symptoms may include delirium and seizures. Urgent measures should be taken to lower central temperature to prevent irreversible brain injury.