Somatosensory System: Receptors, Pathways, and Sensory Modalities
Somatosensory System
Generalidades
The somatosensory system processes information from various sensory receptors, including:
- Mechanoreceptors (pressure, touch)
- Thermoreceptors (temperature)
- Electromagnetic receptors (light, heat, sound)
- Chemoreceptors (chemicals, taste, smell)
- Nociceptors (pain)
Receptors
Sensory receptors are specialized cells that convert physical or chemical stimuli into electrical signals (action potentials). They are classified based on their location and adaptation properties:
- Exteroceptors: Located on the skin and detect external stimuli like touch, temperature, pain, taste, smell, vision, and hearing.
- Interoceptors: Located in internal organs and blood vessels.
- Proprioceptors: Located in muscles, tendons, and joints and provide information about body position and movement.
Adaptation
Receptors can be classified as either rapidly adapting (e.g., Pacinian corpuscles) or slowly adapting (e.g., Ruffini endings) based on their response to sustained stimuli.
Sensory Modalities
The somatosensory system is responsible for various sensory modalities, including:
- Touch: Mediated by mechanoreceptors like Meissner’s corpuscles, Pacinian corpuscles, and Merkel’s discs.
- Temperature: Mediated by thermoreceptors that detect cold and heat.
- Pain: Mediated by nociceptors that respond to tissue damage or potential harm.
Pain
Pain is a complex sensory experience that can be acute or chronic. It is mediated by nociceptors and involves various neurotransmitters and pathways, including the spinothalamic tract and the endogenous opioid system.
Taste
Taste is the sense that allows us to perceive the chemical nature of substances. Taste receptors are located in taste buds on the tongue and are responsible for detecting five basic tastes: sweet, salty, sour, bitter, and umami.
Smell
Smell, or olfaction, is the sense that allows us to perceive odors. Olfactory receptors are located in the olfactory epithelium in the nasal cavity. The process of olfaction involves the binding of odor molecules to receptors, which triggers a signal transduction cascade that leads to the generation of action potentials.
Hearing
Hearing is the sense that allows us to perceive sound. The ear is responsible for capturing, processing, and transmitting sound waves to the brain. The auditory pathway involves the cochlea, the auditory nerve, and various brainstem nuclei and cortical areas.
Motility
Motility refers to the ability of organisms to move. There are different types of motility, including:
- Postural motility: Maintains body posture and muscle tone.
- Voluntary motor: Conscious and controlled movements.
- Reflexive motility: Involuntary movements in response to stimuli.
- Automatic motility: Involuntary movements that do not require conscious control.
Motor Control
The control of movement involves various brain regions and pathways, including the motor cortex, the basal ganglia, the cerebellum, and the spinal cord. The pyramidal and extrapyramidal systems work together to coordinate and execute movements.