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r r r r generate, create data matrix none in software projects QR Code Overview Laboratory data sheets Include you r handwritten data sheets (or a copy), which should consist of a log of the procedures you used, any special circumstances, and the measurements you recorded manually.. Laboratory Exercise 18 The electromyogram (EMG). Purpose To investig ate the electrical potentials produced by skeletal muscles; to build a circuit that ampli es, recti es, and lters these signals; to relate the processed signal to the force of muscular contraction; and to determine the possibilities and limitations of using the EMG for control purposes.. Equipment r r r r r r r r r r r r r r r r IBM PC with data-acquisition and control adapter Set of weights with nger loop Three oating Ag(AgCl) skin electrodes Isolation ampli er circuit with two triax cables for connection to skin electrodes, AD625 instrumentation ampli er, Burr Brown 3656 isolation ampli er, powered by a wall-plug sealed power supply 12-V power supply Two 10- F, 25-V electrolytic capacitors (put between power and ground at circuit board) Six 0.1- F bypass capacitors (put between power and ground on all chips) Superstrip circuit board Digital oscilloscope Two coaxial cables Headphone Two 1N914 diodes Three LF356 op amps Three 1-k resistors Three 5.1-k resistors Three 10-k resistors.

Sensors and actuators r Two 100-k resistors r Two 20-k trimpots r Capacitors (one each): 1, 3.3, and 10 F Background 1. The motor unit and its action potential signal The motor u Software gs1 datamatrix barcode nit is the smallest unit of the skeletal muscle that can be controlled by the nervous system (Laboratory Figure 18.1). The motor neuron causes a single twitch of its associated muscle bers by sending an action potential down one of its axons (Laboratory Figure 18.

2). When that action potential reaches a motor end plate, a small amount of acetylcholine is released, which produces an action potential in the muscle cells. Individual muscle cells conduct action potentials similar to those conducted by axons.

In an actively contracting muscle, the many parallel bers (cells) making up the muscle will be conducting such action potentials at various repetition rates. With suitable electrodes, this barrage of electrical activity can be detected and recorded as the. Axons from other nerve cells Cell body Node of Ranvier Axon Motor end plate Myelin sheath Skeletal muscle fibers Laboratory Software data matrix barcodes Figure 18.1 Motor unit consisting of a nerve cell, axon, motor end plates, and skeletal muscle bers. The motor unit is the smallest element of the skeletal muscle that can be controlled by the nervous system.

. Laboratory Exercise 18: The electromyogram (EMG). Depolarization 0 Inside outside potential (mV) Repolarization 100 0 0.5 Time (ms) 1.0.

Laboratory Figure 18.2 Action potential as measured in an axon or muscle cell. electromyog ram (EMG). In some cases, needle electrodes are inserted through the skin directly into the muscle under study. If the needles are ne enough, little damage results.

For most practical purposes, however, the activity is detected by electrodes placed on the skin surface over the muscle. After pickup by the electrodes, the signal can be processed and used for control purposes. EMG activity has commonly been used in the control of orthotic prosthetic devices such as arti cial hands and arms but it need not be limited to control aids for the physically handicapped.

The EMG is the result of many motor units producing action potentials without close synchronization and its frequency content is in the 100 Hz to 10 kHz region. The ECG (observed in Laboratory Exercise 17 The human heart) is the result of large masses of cardiac muscle depolarizing synchronously for ef cient pumping action..

Summary of steps in skeletal muscle contraction and recovery The followi ng steps present a simpli ed sequence of events in skeletal muscle contraction: 1. Higher brain function decides which muscles to contract and how hard. 2.

A number of motor units (spatial summation) are pulsed at a chosen frequency (temporal summation) to produce the desired force. 3. To pulse a motor neuron, several axons from other nerve cells liberate acetylcholine at synaptic junctions on the cell body, which triggers an action potential that travels down the motor axon (1 100 m/s) to the motor end plate.

4. An action potential is due to the sudden inrush of Na+ ions, which are normally excluded from the interior. The increase in membrane potential (from 85 to +20 mV internal) momentarily opens up Na+ channels and so propagates the action potential along the length of the axon.

5. When the action potential reaches the motor end plate, acetylcholine is again liberated, which triggers an action potential along the length of the muscle ber itself. 6.

In the muscle ber, the action potential triggers the release of Ca++ ions, which cause actin and myosin laments to slide forcefully and produce mechanical contraction..
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