Boots – shoes – and leggings
Patent
1994-10-13
1997-07-15
Mai, Tan V.
Boots, shoes, and leggings
395 24, 326 36, G06G 700
Patent
active
056489269
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electronic instantiation of a biological neuron and, in particular, to an integrated circuit that emulates a biological neuron in real-time (or faster).
It is well known that biological neurons occurring in nervous systems of animals are cells delimited by an enclosing cell membrane that in its various regions is recognised as the cell body (or soma), a number of branching dendrites and an axon. The computational properties of the neurons are intimately linked to the controlled flow of ions across the cell membrane and the subsequent flow of ions within the cell. The dendrites collect information from axons of other neurons, via synapses (or contacts) between the dendrites and axons, and pass the information to the cell body. Each neuron is in contact with thousands of other neurons via the dendrite/axon interactions. The dendrites pass the collected information to the cell body.
In its resting or polarized state, the inside of a region of membrane fluctuates about a voltage of approximately -70 mV with respect to the outside of the membrane. The voltage fluctuation is due to the continual flux of various ions, in particular sodium and potassium ions, into and out of the cell via membrane conductances. These ionic conductances of the cell membrane are voltage- ion- and ligand-sensitive. These ionic conductances are responsive to the state of the local membrane and in turn affect the state of the local membrane. For example, some regions of membrane contain voltage-sensitive conductances that act to amplify the current flowing across the membrane. This current propagates from the local region to nearby regions of membrane affecting its polarization. The most extensively studied example of this phenomenon is the generation of an action potential.
If the stimuli fed by the dendrites to the cell body are such that the voltage difference between the inside and the outside of the membrane depolarizes past a threshold of approximately -50 mV, an avalanche effect occurs as more and more positively charged ions enter the membrane. This results in the voltage of the inside of the membrane shifting past zero to approximately +50 mV. As this occurs, an action potential (nerve impulse) is initiated, which lasts about 1 millisecond.
FIG. 1a shows an intrasomatic current injection into a neuron and FIG. 1b shows the resulting change in membrane potential of the neuron. As can be seen, if a subthreshold current stimulus of 0.20 nA (broken line) is entered, a simple charging response (broken line in FIG. 1b) of the membrane results. On the contrary, if a higher, suprathreshold stimulus of 0.26 nA is entered into the neuron, a discharge action potential spike occurs. In this regard, the peak of the spike approaches the equilibrium potential for sodium ENA.
As the action potential travels from one point on the membrane to the next, the previous point becomes repolarised--i.e. its resting voltage is restored. Repolarisation results from a change in the membrane permeability to certain ions, such as potassium, which move from inside the membrane to outside. In this way, the voltage inside of the membrane reverts back to its resting voltage of approximately -70 mV.
As the action potential propagates along the membrane, in particular down the axon, the signal is transmitted to any other neuron having a dendrite in contact with the axon through which the nerve impulse is passing. The contact is usually via a synapse, a structure at which the axon is closely opposed to the dendrite of its target cell.
In practice, the synapses release chemicals when activated which affect the postsynaptic membrane permeability to certain ions, thereby causing the membrane voltage to change. Each synapse contributes either to the hyperpolarisation or the depolarisation of the neuron membrane as a whole. However, if the depolarisation is large enough, and the threshold voltage is passed (as mentioned above), the avalanche effect occurs and an action potential is produced. Since this action potential is repeatedly
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Douglas Rodney James
Mahowald Michelle Anne
Mai Tan V.
Medical Research Council
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