Neuroscience of rhythm

The neuroscience of rhythm refers to the various forms of rhythm generated by the central nervous system (CNS). Nerve cells, also known as neurons in the human brain are capable of firing in specific patterns which cause oscillations. The brain possesses many different types of oscillators with different periods. Oscillators are simultaneously outputting frequencies from .02 Hz to 600 Hz. It is now well known that a computer is capable of running thousands of processes with just one high frequency clock. Humans have many different clocks as a result of evolution. Prior organisms had no need for a fast responding oscillator. This multi-clock system permits quick response to constantly changing sensory input while still maintaining the autonomic processes that sustain life. This method modulates and controls a great deal of bodily functions.

The autonomic nervous system is responsible for many of the regulatory processes that sustain human life. Autonomic regulation is involuntary, meaning we do not have to think about it for it to take place. A great deal of these are dependent upon a certain rhythm, such as sleep, heart rate, and breathing.

Circadian literally translates to "about a day" in Latin. This refers to the human 24-hour cycle of sleep and wakefulness. This cycle is driven by light. The human body must photoentrain or synchronize itself with light in order to make this happen. The rod cells are the photoreceptor cells in the retina capable of sensing light. However, they are not what sets the biological clock. The photosensitive retinal ganglion cells contain a pigment called melanopsin. This photopigment is depolarized in the presence of light, unlike the rods which are hyperpolarized. Melanopsin encodes the day-night cycle to the suprachiasmatic nucleus (SCN) via the retinohypothalamic tract. The SCN evokes a response from the spinal cord. Preganglionic neurons in the spinal cord modulate the superior cervical ganglia, which synapses on the pineal gland. The pineal gland synthesizes the neurohormone melatonin from tryptophan. Melatonin is secreted into the bloodstream where it affects neural activity by interacting with melatonin receptors on the SCN. The SCN is then able to influence the sleep wake cycle, acting as the "apex of a hierarchy" that governs physiological timing functions. "Rest and sleep are the best example of self-organized operations within neuronal circuits".

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