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(irritability), the ability of living cells, from the simplest unicellular organisms to the nerve cells of man, to sense environmental changes and to respond to these changes (stimuli) with excitation. Excitability is linked to the existence in the cell membrane of special molecular structures possessing specific sensitivity to various stimuli, such as electric current and chemical, mechanical, and thermal agents. Since the main component of excitation in nerve and muscle cells (fibers) is action potential, the excitability of these cells is usually judged by the threshold current strength or threshold shift in potential, which is sufficient for action potential to arise. The threshold current strength is depen-dent upon the duration of the stimulus. The threshold shift in potential, however, does not change with variation in the duration of the stimulus. The generation of action potential is based on increased permeability of the cell membrane to sodium ions. Accordingly, any agent that prevents the sodium permeability of a membrane from increasing causes excitability to decrease. Local anesthetics used in medicine, such as Novocain, cocaine, and dicaine, as well as various narcotics, such as ether barbiturates, are based on this mechanism.

The term “excitability” is also frequently used in medical and biological literature to characterize the state of the nerve centers in the brain and spinal cord, for example, the respiratory and vasomotor centers. In such cases excitability is judged by the lowest intensity of a stimulus that is required to elicit a reflex response.


References in periodicals archive ?
Peripheral sensory stimulation changes motor cortex excitability.
The changes that EOLs and thymol made on rheobase and chronaxie (parameters more directly related to nerve excitability) show that they reduce neuronal excitability, which might indicate a possible potential for local anesthesia use.
To test the link between motor excitability and the neural basis for contagious yawning the Nottingham research team used transcranial magnetic stimulation (TMS).
15] also showed improvements in paretic grip-lift performance accompanied by an immediate facilitation of ipsilesional M1 excitability after iTBS to the ipsilesional motor area.
By boosting muscular excitability PEAK ATP provides a critical advantage to athletes who want to increase the intensity and/or frequency of their workouts and ultimately see better results from their efforts," said Larry Kolb, president of TSI USA Inc.
sup][24] Hyperthermia-induced seizures can significantly modify neuronal excitability in limbic circuits.
sup][1],[7] Many BD pathophysiology studies have consistently shown altered homeostasis of biologically active alkali and alkaline earth metals along with alterations in neuronal excitability and activity.
In cell models of ALS, Retigabine has shown the ability to reduce excitability and prolong survival in the lab.
Supernormal excitability and conduction in the His-Purkinje system of the dog.
Your GP could apply a nip and tuck for well-being, a snip to remove negativity and a bypass to lower the excitability factor, reduce stress and induce calm and produce a bland model citizen who will cause no trouble, commit no crime and who needs no vote because consensus has been built in.
In this work a physical model for the reduced excitability in neurons exposed to a constant magnetic field is presented.
It is well documented that any changes in H-reflex amplitude, latency and recovery time reflect the changes in spinal motor neuron excitability [8,11,12].