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As the signal travels from photoreceptors to larger neurons, action potentials must be created for the signal to have enough strength to reach the CNS. [4] If the stimulus does not warrant a strong enough response, it is said to not reach absolute threshold, and the body does not react. However, if the stimulus is strong enough to create an ...
Jablonski diagram including vibrational levels for absorbance, non-radiative decay, and fluorescence. When a molecule absorbs a photon, the photon energy is converted and increases the molecule's internal energy level. Likewise, when an excited molecule releases energy, it can do so in the form of a photon.
All cells in animal body tissues are electrically polarized – in other words, they maintain a voltage difference across the cell's plasma membrane, known as the membrane potential. This electrical polarization results from a complex interplay between protein structures embedded in the membrane called ion pumps and ion channels.
For example, curare is a poison that stops acetylcholine from depolarizing the postsynaptic membrane, causing paralysis. Strychnine blocks the inhibitory effects of the neurotransmitter glycine , which causes the body to pick up and react to weaker and previously ignored stimuli, resulting in uncontrollable muscle spasms .
where y i is the output of the i th neuron, x j is the j th input neuron signal, w ij is the synaptic weight (or strength of connection) between the neurons i and j, and φ is the activation function. While this model has seen success in machine-learning applications, it is a poor model for real (biological) neurons, because it lacks time ...
The following diagram is provided as an overview of and topical guide to the human nervous system: Human nervous system. Human nervous system – the part of the human body that coordinates a person's voluntary and involuntary actions and transmits signals between different parts of the body.
Each gap junction (sometimes called a nexus) contains numerous gap junction channels that cross the plasma membranes of both cells. [11] With a lumen diameter of about 1.2 to 2.0 nm, [2] [12] the pore of a gap junction channel is wide enough to allow ions and even medium-size molecules like signaling molecules to flow from one cell to the next, [2] [13] thereby connecting the two cells' cytoplasm.
For example, a doctor may insert a catheter containing an electrode into the heart to record the heart muscle's electrical activity. Another example of clinical electrophysiology is clinical neurophysiology. In this medical specialty, doctors measure the electrical properties of the brain, spinal cord, and nerves.