19.12
Termosensación
La termosensación periférica es la percepción de la temperatura exterior. Un cambio de temperatura (en la superficie de la piel y otros tejidos) es de…
- [Narrador] La termosensación periférica,
la percepción de temperatura externa,
inicia con la piel.
Terminaciones nerviosas libres localizadas a diferentes
profundidades
contienen termoreceptores, canales iónicos encerrados
del potencial de receptor transitorio,
o la familia TRP.
Los receptores están dedicados a temperaturas específicas.
Por ejemplo, en grupo sensible al calor
el primer receptor para ser descubierto,
TRPV1, se activa a temperaturas
superiores a 42 grados Celsius.
Interesantemente, TRPV1 también tiene
un sitio de vinculación para la capsaicina,
el componente activo del ají.
Cunado una temperatura específica causa
que suficientes canales iónicos TRP se abran,
despolariza las terminaciones neriviosas
transduciendo temperatura en señales electrónicas.
Por ende, la temperatura está codificada
por la tasa de actividad.
Mientras la temperatura incrementa,
disparando incrementos en las fibras detectoras de calidez
y se disminuye en las de frío.
La calidez inocua y la información de frío
viajan separadamente a través de pequeñas fibras C
no mielinizadas
que conducen señales lentamente.
El fío también puede ser llevado por axones delta A
mielinizados dedicados rápidamente.
La información de temperatura dolorosa
es llevada por axones A delta y C,
los cuales no son separados en frío y calor.
Todos los termoaferentes entran
en los ganglios de la raíz dorsal de la columna.
Aquí, la información es decusada,
lo que significa que cambia de lado,
antes de ser enviada al hipotálamo.
De ahí, la información de temperatura inocua
es enviada a la corteza orbitofrontal.
Y la información de temperatura dolorosa
es procesada en la corteza cingulada anterior.
View the full transcript and gain access to JoVE Core videos
Q1: What are TRP receptors and where are they located in the skin?
TRP (Transient Receptor Potential) receptors are temperature-sensitive ion channels located on free nerve endings in the skin at varying depths. Cold-detecting receptors sit closer to the skin surface than warm-detecting ones. These gated ion channels transduce temperature changes into electrical signals that the nervous system interprets as thermal sensations, functioning as part of the sensory system and perception.
Q2: How do cold receptors like TRPM8 and TRPA1 differ in their temperature sensitivity?
TRPM8 receptors respond to innocuous cold between 10-26°C and are activated by menthol, explaining mint's cool sensation. TRPA1 receptors activate at noxious cold below 17°C, producing painful cold sensations. Both receptor types allow the nervous system to distinguish between comfortable coolness and dangerous freezing temperatures.
Q3: Why does capsaicin from chili peppers create a burning sensation?
Capsaicin binds to TRPV1 receptors, which normally activate at temperatures above 42°C. By binding to these heat-sensitive receptors, capsaicin triggers the same neural response as actual heat, creating a burning sensation without changing the food's temperature. This explains why spicy foods feel hot despite being room temperature.
Q4: How does temperature information travel from the skin to the brain?
Innocuous warm and cold signals travel separately via unmyelinated C-fibers and myelinated A-delta fibers, which conduct at different speeds. All temperature signals enter the dorsal root ganglion at the spine, where they decussate (switch sides) before reaching the hypothalamus. From there, innocuous signals reach the orbitofrontal cortex, while painful temperature information reaches the anterior cingulate cortex.
Q5: What is the temperature range where humans first consciously detect warmth and cold?
Humans first consciously detect coldness around 31°C and warmth around 34°C. This narrow range between 31-34°C is similar to normal skin surface temperature and may feel neutral. Pain from cold emerges below 12°C, while pain from heat begins above 45°C, creating distinct perceptual thresholds.
Q6: How do warm-detecting receptors like TRPV3 and TRPM2 respond to different temperatures?
Multiple warm receptors detect innocuous heat at overlapping but distinct ranges: TRPM2 activates at 23-38°C, TRPV4 at 27-34°C, and TRPV3 at 33-40°C. This receptor diversity allows fine discrimination of comfortable warmth. TRPV1 and TRPV2 detect painful heat above 42°C and 52°C respectively, protecting against tissue damage.
Q7: How does temperature depolarize nerve endings and create electrical signals?
When temperature activates TRP ion channels, they open and allow cations to flow into nerve endings, depolarizing the membrane. This depolarization converts thermal energy into electrical signals. Temperature is coded by the firing rate: as temperature increases, warm-detecting fibers fire faster while cold-detecting fibers fire slower, allowing the brain to interpret temperature intensity.