Related Experiment Video
Updated: Jul 11, 2026

10:41
Visualizing Protein Kinase A Activity In Head-fixed Behaving Mice Using In Vivo Two-photon Fluorescence Lifetime Imaging Microscopy
Published on: June 7, 2019
[Definition of unit internal (physiological) time]
Summary
Internal physiological time is defined by metabolism rate. Higher metabolism speeds up internal time, while lower metabolism slows it down, making time perception individual.
Area of Science:
- Metabolic studies
- Physiological time measurement
Context:
- Metabolism (q(t)) is the energy consumed per unit mass per unit time.
- Internal time (tau(t)) is defined as the physical time for unit mass to consume one unit of energy.
- tau(t) = 1/q(t).
Purpose:
- To define a unit of internal physiological time based on metabolism.
- To explore the relationship between metabolic rate and the perception of time.
Summary:
- Unit physiological time (tau(t)) is inversely proportional to specific metabolism (q(t)).
- The rate of metabolism dictates the subjective experience of time's passage.
- Higher metabolic rates lead to a perceived acceleration of physical time, while lower rates cause a perceived deceleration.
Impact:
- Internal time is shown to be variable and individual, dependent on metabolic rate.
- This challenges the notion of a universal, constant flow of time.
- The concept may offer new perspectives on aging and species-specific metabolic characteristics, like Rubner's constant.
Related Concept Videos
Measurement: Standard Units
Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement (a unit), and an indication of the uncertainty of the measurement. While the number and unit are explicitly represented when a quantity is written, the uncertainty is an aspect of the errors in the measurement results.
Basic Continuous Time Signals
Basic continuous-time signals include the unit step function, unit impulse function, and unit ramp function, collectively referred to as singularity functions. Singularity functions are characterized by discontinuities or discontinuous derivatives.
The unit step function, denoted u(t), is zero for negative time values and one for positive time values, exhibiting a discontinuity at t=0. This function often represents abrupt changes, such as the step voltage introduced when turning a car's...
The unit step function, denoted u(t), is zero for negative time values and one for positive time values, exhibiting a discontinuity at t=0. This function often represents abrupt changes, such as the step voltage introduced when turning a car's...
Rectangular and Triangular Pulse Function
The unit rectangular pulse function is mathematically represented by a rectangular function centered at the origin with a height of one unit. This function is defined by two parameters: T, which specifies the center location of the pulse along the time axis, and τ, which determines the pulse duration.
For example, consider a rectangular pulse with a 5V amplitude, a 3-second duration, and centered at t=2 seconds. This pulse can be expressed using the rectangular function, written as,
For example, consider a rectangular pulse with a 5V amplitude, a 3-second duration, and centered at t=2 seconds. This pulse can be expressed using the rectangular function, written as,
Noncompartmental Analysis: Mean Residence Time
According to statistical moment theory, mean residence time (MRT) is an important measure in pharmacokinetics. MRT can be defined as the expected mean of a probability density function distribution. It provides valuable insights into drug disposition in the body.
After the administration of a drug through intravenous bolus injection, the drug molecules are distributed throughout the body and remain there for varying periods. The MRT represents the average time these drug molecules stay in the...
After the administration of a drug through intravenous bolus injection, the drug molecules are distributed throughout the body and remain there for varying periods. The MRT represents the average time these drug molecules stay in the...
Internal Energy
The internal energy of a thermodynamic system is the sum of the kinetic and potential energies of all the molecules or entities in the system. The kinetic energy of an individual molecule includes contributions due to its rotation and vibration, as well as its translational energy. The potential energy is associated only with the interactions between one molecule and the other molecules of the system. Neither the system's location nor its motion is of any consequence as far as the internal...
Internal Energy
The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with initial internal energy, Uinitial, undergoes a change in energy (transfer of work or heat), and the final internal energy of the system is Ufinal. Change in internal energy equals the difference between Ufinal and Uinitial.

