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The Master of Rhythm in Biology: How Does CPG Drive Our Gait and Breathing?
In biology, central pattern generators (CPGs) are neural circuits capable of producing rhythmic transport autonomously, without the need for external rhythmic input. They drive behaviors such as our gait, breathing, swimming and even chewing, playing a central role in the movement of living organisms. The operation of CPG not only demonstrates biological adaptability, but also provides ways for our bodies to adapt in changing environments.
CPG is characterized by its ability to self-organize and its ability to flexibly adjust in response to external stimuli.
Characteristics of CPG neurons
CPG neurons possess a variety of intrinsic membrane properties, which enable them to perform different functions. Some neurons undergo bursts of action potentials in the absence of external stimulation, while others exhibit postinhibitory rebound after inhibition is removed. In addition, the firing frequency of CPG neurons under stable depolarization will also adapt, that is, the frequency will gradually decrease over time.
Rhythm generation
In CPG networks, there are two main types of rhythm generation mechanisms: clock-driven rhythm generation (pacemaker) and interactive inhibition (reciprocal inhibition). In a "clock-driven" network, some neurons act as core oscillators (pacemakers), driving other non-burst neurons to perform rhythmic patterns. In an "interactive inhibition" network, two groups of neurons inhibit each other, forming half-center oscillators. When these neurons are connected to each other, they can produce alternating activity patterns.
Even in isolation, these neurons can produce a rhythmic output that provides a physiological basis for their requests.
The impact of neuromodulation
Neuromodulation is critical to the function of CPG. Organisms must adapt their behavior to changes in the internal and external environment. The adjustment of CPG may change its functional combination and produce different output modes. When neuromodulatory input is lost, the generation of certain movement patterns may be completely lost. For example, the application of various neuromodulators can evoke different movement patterns, which further demonstrates the essential role of neuromodulation in adaptive movement.
The role of sensory feedback
Although CPG's theoretical preset rhythm and pattern are centrally generated, CPG can also be adjusted based on sensory feedback. This information may affect the overall adjustment of the pattern. For example, when walking, if there is a stone in one foot, even if the sensation is only present in a certain phase, it will still affect the entire gait pattern.
Changes in sensory input can target different pattern phases and may lead to the occurrence of reflex reversal phenomena.
Multiple functions of CPG
CPG plays an important role in multiple functions, especially in movement, breathing and other oscillatory functions. For example, as early as 1911, scientists discovered that the spinal cord can produce gait patterns without commands from the brain. This discovery subsequently gained widespread support in the swimming patterns of a variety of organisms, including vertebrates and certain invertebrates, such as sharks.
Conclusion
It can be seen from these studies that the operation of CPG not only reflects the internal structure of organisms and the precise operation of the nervous system, but also implies that neuromodulation and sensory feedback introduce the behavioral adaptability of organisms. With the advancement of science, understanding how CPG affects our movement and breathing is still a hot topic in current research, which makes us wonder: How will future research change our understanding and application of biological rhythms?
