I have to know how fast an electric synapse in the brain is. I know there are two types of transmissions between nuerons, electric and chemical, how fast are each?
Answer in any unit fine : Miles per hour preferred.
Nerve cell membranes have a capacitance of 1 microfarad per square centimeter, so the capacitance of a relatively small 30 square micron node of Ranvier is 3 x 10-13 farads (assuming small nodes tends to overestimate the computational power of the brain). The internodal region is about 1,000 microns in length, 500 times longer than the 2 micron node, but because of the myelin sheath its capacitance is about 250 times lower per square micron or only twice that of the node. The total capacitance of a single node and internodal gap is thus about 9 x 10-13 farads. The total energy in joules held by such a capacitor at 0.11 volts is 1/2 V2 x C, or 1/2 x 0.112 x 9 x 10-13, or 5 x 10-15 joules. This capacitor is discharged and then recharged whenever a nerve impulse passes, dissipating 5 x 10-15 joules. A 10 watt brain can therefore do at most 2 x 1015 such Ranvier ops per second. Both larger myelinated fibers and unmyelinated fibers dissipate more energy. Various other factors not considered here increase the total energy per nerve impulse , causing us to somewhat overestimate the number of Ranvier ops the brain can perform. It still provides a useful upper bound and is unlikely to be in error by more than an order of magnitude.
To translate Ranvier ops (1-millimeter jumps) into synapse operations we must know the average distance between synapses, which is not normally given in neuroscience texts. We can estimate it: a human can recognize an image in about 100 milliseconds, which can take at most 100 one-millisecond synapse delays. A single signal probably travels 100 millimeters in that time (from the eye to the back of the brain, and then some). If it passes 100 synapses in 100 millimeters then it passes one synapse every millimeter--which means one synapse operation is about one Ranvier operation.
The total computational power of the brain is limited by several factors, including the ability to propagate nerve impulses from one place in the brain to another. Propagating a nerve impulse a distance of 1 millimeter requires about 5 x 10-15 joules. Because the total energy dissipated by the brain is about 10 watts, this means nerve impulses can collectively travel at most 2 x 1015 millimeters per second. By estimating the distance between synapses we can in turn estimate how many synapse operations per second the brain can do. This estimate is only slightly smaller than one based on multiplying the estimated number of synapses by the average firing rate, and two orders of magnitude greater than one based on functional estimates of retinal computational power. It seems reasonable to conclude that the human brain has a raw computational power between 1013 and 1016 operations per second.
The Nervous System is the body's information gatherer, storage center and control system. Its overall function is to collect information about the external conditions in relation to the body's internal state, to analyze this information, and to initiate appropriate responses to satisfy certain needs (Maintain Homeostasis). The most powerful of these needs is survival. The nerves do not form one single system, but several which are interrelated. Some of these are physically separate, others are different in function only. The brain and spinal cord make up the Central Nervous System (CNS). The Peripheral Nervous System (PNS) is responsible for the body functions which are Not under conscious control - like the heartbeat or the digestive system. The smooth operation of the Peripheral Nervous System is achieved by dividing it into Sympathetic and Parasympathetic Systems. These are opposing actions and check on each other to provide a balance. The nervous system uses electrical impulses, which travel along the length of the cells (Neurons). The cell processes information from the sensory nerves and initiates an action within milliseconds. These impulses can travel at up to 250 miles per hour, while other Systems such as the Endocrine System may take many hours to respond with hormones.
Nerve cell membranes have a capacitance of 1 microfarad per square centimeter, so the capacitance of a relatively small 30 square micron node of Ranvier is 3 x 10-13 farads (assuming small nodes tends to overestimate the computational power of the brain). The internodal region is about 1,000 microns in length, 500 times longer than the 2 micron node, but because of the myelin sheath its capacitance is about 250 times lower per square micron or only twice that of the node. The total capacitance of a single node and internodal gap is thus about 9 x 10-13 farads. The total energy in joules held by such a capacitor at 0.11 volts is 1/2 V2 x C, or 1/2 x 0.112 x 9 x 10-13, or 5 x 10-15 joules. This capacitor is discharged and then recharged whenever a nerve impulse passes, dissipating 5 x 10-15 joules. A 10 watt brain can therefore do at most 2 x 1015 such Ranvier ops per second. Both larger myelinated fibers and unmyelinated fibers dissipate more energy. Various other factors not considered here increase the total energy per nerve impulse , causing us to somewhat overestimate the number of Ranvier ops the brain can perform. It still provides a useful upper bound and is unlikely to be in error by more than an order of magnitude.
To translate Ranvier ops (1-millimeter jumps) into synapse operations we must know the average distance between synapses, which is not normally given in neuroscience texts. We can estimate it: a human can recognize an image in about 100 milliseconds, which can take at most 100 one-millisecond synapse delays. A single signal probably travels 100 millimeters in that time (from the eye to the back of the brain, and then some). If it passes 100 synapses in 100 millimeters then it passes one synapse every millimeter--which means one synapse operation is about one Ranvier operation.
The total computational power of the brain is limited by several factors, including the ability to propagate nerve impulses from one place in the brain to another. Propagating a nerve impulse a distance of 1 millimeter requires about 5 x 10-15 joules. Because the total energy dissipated by the brain is about 10 watts, this means nerve impulses can collectively travel at most 2 x 1015 millimeters per second. By estimating the distance between synapses we can in turn estimate how many synapse operations per second the brain can do. This estimate is only slightly smaller than one based on multiplying the estimated number of synapses by the average firing rate, and two orders of magnitude greater than one based on functional estimates of retinal computational power. It seems reasonable to conclude that the human brain has a raw computational power between 1013 and 1016 operations per second.
The Nervous System is the body's information gatherer, storage center and control system. Its overall function is to collect information about the external conditions in relation to the body's internal state, to analyze this information, and to initiate appropriate responses to satisfy certain needs (Maintain Homeostasis). The most powerful of these needs is survival. The nerves do not form one single system, but several which are interrelated. Some of these are physically separate, others are different in function only. The brain and spinal cord make up the Central Nervous System (CNS). The Peripheral Nervous System (PNS) is responsible for the body functions which are Not under conscious control - like the heartbeat or the digestive system. The smooth operation of the Peripheral Nervous System is achieved by dividing it into Sympathetic and Parasympathetic Systems. These are opposing actions and check on each other to provide a balance. The nervous system uses electrical impulses, which travel along the length of the cells (Neurons). The cell processes information from the sensory nerves and initiates an action within milliseconds. These impulses can travel at up to 250 miles per hour, while other Systems such as the Endocrine System may take many hours to respond with hormones.
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