19.11
Somatosensación
El sistema somatosensorial transmite información sensorial desde la piel, las membranas mucosas, las extremidades y las articulaciones. La somatosensa…
[Narrador] Durante la somatosensación, el sentido del tacto,
las neuronas sensoriales en la piel
primero detectan la alteración mecánica por medio
de los receptores mecánicos
si el esímulo son vibraciones ligeras,
los corpúsculos de Meissner responden a ellas.
Con la presencia constante adicional,
los discos de Merkel reaccionan, ya que se adaptan
lentamente.
Las terminaciones de Ruffini, también de lenta adaptación,
responden a estímulos más profundos y sostenidos.
Si esto se vuelve repetitivo, se detecta
por los corpúsculos de Pacini.
Después de la detección, las sensaciones se transducen
a señales eléctricas, y viajan a través de la espina dorsal,
específicamente a los ganglios de la raíz dorsal,
donde se procesa en la misma área del cuerpo,
llamada dermatoma, formando una única raíz dorsal.
Continuando en el tronco encefálico,
la médula en particular, la información sensorial
decusa, es decir, cruza hacia el otro lado
antes de ser enviado al tálamo.
De aquí, el mensaje es finalmente enviado
a la corteza somatosensorial.
Esta región cortical contiene el mapa del cuerpo
llamado homúnculo.
Debido a la decusación, el lado izquierdo del cuerpo
es representado en el cortex derecho y viceversa.
Los dedos ocupan una gran área cortical
porque tienen una alta densidad de mecanorreceptores
con áreas receptivas pequeñas,
lo cual les otorga una mejor discriminación de estímulos.
En contraste, la espalda tiene menos receptores
y mayores áreas receptivas,
y de este modo una representación cortical menor.
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Q1: What are the four main types of mechanoreceptors in hairless skin?
The four main mechanoreceptors are Meissner corpuscles, Merkel disks, Ruffini endings, and Pacinian corpuscles. Meissner corpuscles and Pacinian corpuscles are rapidly adapting and detect dynamic stimuli like vibrations. Merkel disks and Ruffini endings are slow adapting and respond to sustained touch and pressure.
Q2: How does the somatosensory pathway transmit information from skin to brain?
Mechanoreceptors in skin detect stimuli and send signals through primary neurons to the dorsal root ganglion. Secondary neurons in the medulla decussate, crossing to the opposite side before reaching the thalamus. Tertiary neurons then carry the signal to the somatosensory cortex, where the body is mapped as a homunculus.
Q3: Why do fingers have larger cortical representation than the back?
Fingers have a high density of mechanoreceptors with small receptive fields, enabling better stimulus discrimination. This dense receptor distribution requires more cortical area for processing fine sensory details. In contrast, the back has fewer receptors and larger receptive fields, resulting in smaller cortical representation.
Q4: What is decussation and why does it occur in the somatosensory pathway?
Decussation is the crossing of sensory information from one side of the body to the opposite side of the brain. This occurs in the medulla when secondary neurons cross over before sending signals to the thalamus. As a result, the left side of the body is processed in the right cortex and vice versa.
Q5: What is a dermatome and how does it relate to the dorsal root ganglion?
A dermatome is a designated area of skin innervated by sensory neurons from a single dorsal root ganglion. Primary neurons with cell bodies in the dorsal root ganglia extend axons to specific dermatomes. Each dermatome represents a distinct region where sensory information is initially detected before traveling to the spinal cord.
Q6: How can the somatosensory cortex reorganize after injury or specialized use?
The somatosensory cortex undergoes cortical reorganization when body regions do not function as intended. Braille readers develop larger finger representations in the cortex due to intensive tactile training. In forearm amputees, the cortical region previously connected to the amputated arm can be remapped to adjacent regions, sometimes causing phantom limb sensations.
Q7: How do slow-adapting and rapidly-adapting mechanoreceptors differ in function?
Slow-adapting mechanoreceptors like Merkel disks and Ruffini endings continue responding to prolonged contact, detecting sustained touch and pressure. Rapidly-adapting mechanoreceptors like Meissner corpuscles and Pacinian corpuscles respond to dynamic stimuli such as vibrations and changing pressure. This functional difference allows the sensory system to detect both constant and changing tactile information.