Origin of the EMG SignalTo create v

Origin of the EMG Signal
To create voluntary muscle movement, an action potential must travel from initiation in the brain
to the target muscle. It travels from the brain, into the spinal cord, and then to an efferent nerve
which synapses on the target muscle fiber. Each muscle fiber is innervated by a single neuron.
However, one neuron innervates several hundred muscle fibers. The number of muscle fibers
innervated by a single neuron is called the innervation ratio. A lower innervation ratio
corresponds to finer control of muscle forces.
The connection between a nerve and a muscle is called the neuromuscular junction. The action
potential propagates down the motorneuron and causes the release of acetylcholine (Ach), a
neurotransmitter, at the neuromuscular junction. As Ach is released, it travels across the
neuromuscular junction and causes Ach gated receptors on the muscle fiber to open. When these
gates open, sodium ions flow into the cell depolarizing it. This potential change activates
voltage dependent sodium channels resulting in an action potential that propagates throughout
the muscle fiber. The action currents create potentials in the extracellular space that are recorded
as EMG.
These action currents travel deep into the muscle fiber by means of the transverse tubule system.
These currents cause a potential change that triggers the release of calcium ions from the
sarcoplasmic reticulum inside the muscle fibers. Inside the muscle fiber are two filaments, actin
and myosin. Actin sites are normally closed, however, in the presence of calcium, these sites
open. When these sites are open the myosin head can insert in the actin site. Once inserted, the
myosin filament contracts to pull the actin site closer to itself, releases, and then repeats with the
next actin site. Therefore, the amount of calcium that is released acts to grade the strength and
duration of the muscle contraction. A fraction of a second later the calcium ions are taken back
into the muscle cells, causing release of the actin and myosin elements, leading to muscle
relaxation. This mechanism allows activation of a muscle fiber to occur 60 to 100 times a
second.
The process described above occurs for a single action potential. A single action potential
typically lasts 1-3 milliseconds, but the time of muscle contraction as a result of a single action
potential will last 10-100 milliseconds. The contraction of a muscle as a result of a single action
potential is called a twitch. If more action potentials come after the first one at a successive rate,
the muscle does not have time to relax and the twitches begin to add. If the twitches occur with a
high enough frequency, the force output of the muscle will plateau. This plateau is called a
tetanus response. There are two types of tetanus, fused and unfused. In unfused tetanus, the
frequency of action potentials is still fairly low, and so muscle twitches can still be seen. A fused
tetanus occurs when the rate of action potentials becomes much faster, so much that the effects
of the individual twitches can no longer be seen.
There are two methods the body uses to recruit muscle force. These methods are temporal and
spatial summation. For most muscle contractions, the firing rate of action potentials is usually
higher than 8 Hz, but not usually higher than 25 Hz during times of concentrated contraction.
This method of summing the action potentials to create muscle contraction is known as temporal

Kết quả (Việt) 1:

Origin of the EMG SignalTo create voluntary muscle movement, an action potential must travel from initiation in the brainto the target muscle. It travels from the brain, into the spinal cord, and then to an efferent nervewhich synapses on the target muscle fiber. Each muscle fiber is innervated by a single neuron.However, one neuron innervates several hundred muscle fibers. The number of muscle fibersinnervated by a single neuron is called the innervation ratio. A lower innervation ratiocorresponds to finer control of muscle forces.The connection between a nerve and a muscle is called the neuromuscular junction. The actionpotential propagates down the motorneuron and causes the release of acetylcholine (Ach), aneurotransmitter, at the neuromuscular junction. As Ach is released, it travels across theneuromuscular junction and causes Ach gated receptors on the muscle fiber to open. When thesegates open, sodium ions flow into the cell depolarizing it. This potential change activatesvoltage dependent sodium channels resulting in an action potential that propagates throughoutthe muscle fiber. The action currents create potentials in the extracellular space that are recordedas EMG.These action currents travel deep into the muscle fiber by means of the transverse tubule system.These currents cause a potential change that triggers the release of calcium ions from thesarcoplasmic reticulum inside the muscle fibers. Inside the muscle fiber are two filaments, actinand myosin. Actin sites are normally closed, however, in the presence of calcium, these sitesopen. When these sites are open the myosin head can insert in the actin site. Once inserted, themyosin filament contracts to pull the actin site closer to itself, releases, and then repeats with thenext actin site. Therefore, the amount of calcium that is released acts to grade the strength andduration of the muscle contraction. A fraction of a second later the calcium ions are taken backinto the muscle cells, causing release of the actin and myosin elements, leading to musclerelaxation. This mechanism allows activation of a muscle fiber to occur 60 to 100 times asecond.The process described above occurs for a single action potential. A single action potentialtypically lasts 1-3 milliseconds, but the time of muscle contraction as a result of a single actionpotential will last 10-100 milliseconds. The contraction of a muscle as a result of a single actionpotential is called a twitch. If more action potentials come after the first one at a successive rate,the muscle does not have time to relax and the twitches begin to add. If the twitches occur with ahigh enough frequency, the force output of the muscle will plateau. This plateau is called atetanus response. There are two types of tetanus, fused and unfused. In unfused tetanus, thefrequency of action potentials is still fairly low, and so muscle twitches can still be seen. A fuseduốn ván xảy ra khi vận hành động tiềm năng trở nên nhanh hơn nhiều, rất nhiều mà những ảnh hưởngtwitches cá nhân có thể không còn được thấy.Không có hai phương pháp cơ thể sử dụng để tuyển dụng lực lượng cơ bắp. Những phương pháp này là thời gian vàkhông gian tổng kết. Đối với hầu hết các cơn co thắt cơ bắp, với tỷ lệ bắn hành động tiềm năng là thườngcao hơn 8 Hz, nhưng không thường cao hơn 25 Hz thời của tập trung co.Phương pháp tổng hợp tiềm năng hành động để tạo ra co cơ bắp được gọi là thời gian