Victor Forge
The human body contains over 600 muscles, and each of these muscles plays a role in moving our body in space. Extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint, resulting in the straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed (bent) elbow. There are various techniques and instruments used to evaluate and record the electrical activity produced by skeletal muscles, such as electromyography (EMG) and muscle spindles. EMG is performed using an electromyograph to detect the electric potential generated by muscle cells, while muscle spindles are sensory receptors that inform the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching.
| Characteristics | Values |
|---|---|
| Muscle extensions detection technique | Electromyography (EMG) |
| EMG technique | Involves evaluating and recording the electrical activity produced by skeletal muscles |
| EMG instrument | Electromyograph |
| EMG record | Electromyogram |
| EMG procedure | Needle EMG and Surface EMG |
| Needle EMG procedure | Insertion of a monopolar or concentric needle electrode through the skin into the muscle tissue |
| Surface EMG procedure | Used in physiotherapy to monitor muscle activation |
| Muscle spindle function | Informs the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching |
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What You'll Learn
Muscle spindles
The muscle spindle is a critical component of the body's sensorimotor system. When a muscle is stretched, the change in length is transmitted to the spindles and their intrafusal fibres, which are subsequently stretched. This stimulation of the muscle spindle is known as the stretch or myotatic reflex. The stretch reflex causes the muscle to contract, preventing it from being stretched too far or too quickly.
The sensory endings of a primary (group Ia) afferent and a secondary (group II) afferent coil around the non-contractile central portions of the intrafusal fibres. The primary type Ia sensory fibres spiral around all intrafusal muscle fibres, ending near the middle of each fibre. The secondary type II sensory fibres end adjacent to the central regions of the static bag and chain fibres. These fibres send information to the central nervous system (CNS) via stretch-sensitive mechanically-gated ion channels of the axons. The CNS uses this information to compute the position and movement of our extremities in space, which is essential for motor control, maintaining posture, and a stable gait.
Gamma motor neurons, also known as fusimotor neurons, activate the intrafusal muscle fibres, changing their firing rate and stretch-sensitivity. Upon release of acetylcholine by the active gamma motor neuron, the end portions of the intrafusal muscle fibres contract, elongating the non-contractile central portions. This opens stretch-sensitive ion channels of the sensory endings, increasing the probability of action potential firing and further increasing the stretch-sensitivity of the muscle spindle.
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Sensory neuron activity
Muscle spindles, which are delicate sensory receptors present in almost every muscle, play a crucial role in detecting muscle extensions. They provide essential information to the central nervous system (CNS) about changes in muscle length and stretching speed, enabling the CNS to compute body position, movement, and maintain posture and gait.
Electromyography (EMG) is another technique used to evaluate and record electrical activity in skeletal muscles. An instrument called an electromyograph detects the electric potential generated by muscle cells during activation. This method can be used to detect abnormalities, activation levels, and analyse biomechanics. EMG can be performed using needle electrodes inserted into the muscle tissue or as a non-invasive surface EMG, which is commonly used in physiotherapy to monitor muscle activation.
Surface EMG has been studied for its potential to detect neuromuscular diseases and its applications in sports to reduce soft tissue injuries and improve performance. However, it is limited in distinguishing between neuropathic and myopathic conditions and diagnosing specific neuromuscular diseases.
In summary, sensory neuron activity from muscle spindles and electromyography techniques are valuable tools for understanding muscle extensions, detecting abnormalities, and improving human performance and health. These methods provide insights into the complex functioning of the human body and its movements.
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Electromyography (EMG)
EMG helps to detect neuromuscular abnormalities and is used to identify the presence, location, and extent of diseases that damage nerves and muscles. The test involves inserting small needles or electrodes into the muscle to measure its electrical activity during rest, slight contraction, and forceful contraction. The electrical activity is then displayed on an oscilloscope and can also be heard through an audio amplifier.
The EMG procedure typically follows a nerve conduction study (NCS), which measures the amount and speed of electrical impulse conduction through a nerve. This initial step helps determine nerve damage and destruction. During the EMG, the electrodes are retracted a few millimetres at a time, and the electrical activity is analysed at each location to obtain an accurate study of the entire muscle.
The history of EMG dates back to the 17th century when Francesco Redi discovered that the electric ray fish's muscle tissue generated electricity. Over the following centuries, various scientists contributed to the understanding of electricity's role in muscle contraction and the development of techniques to record electrical activity during muscle contractions. The term "electromyography" was introduced in 1890 by Marey, who also made the first recording of electrical activity.
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Prime movers and antagonists
The human body has over 600 muscles, and the muscular system involves understanding where each muscle attaches to bones and how they help move joints. The muscle that is primarily responsible for a movement is called the prime mover, or agonist. It provides the primary force driving the action. The triceps brachii, for example, is a prime mover of elbow extension, helping to straighten the elbow joint.
The antagonist muscle works in opposition to the prime mover. It provides some resistance and/or reverses a given movement. For example, the biceps brachii, brachialis, and brachioradialis flex the elbow, which is the opposite action to the triceps brachii. Prime movers and antagonists are often paired up on opposite sides of a joint, with their roles reversing as the movement changes direction.
Synergists are muscles that assist the prime mover in its role. The anconeus, for example, acts as a synergist in elbow extension. A fixator is a type of synergist that makes the insertion site more stable. Stabilizers, meanwhile, act to keep bones immobile when needed. For example, back muscles are stabilizers when they are keeping your posture sturdy.
The body's muscles are controlled by the central nervous system (CNS), which receives information from sensory receptors called muscle spindles. These receptors inform the CNS about changes in the length of individual muscles and the speed of stretching. This allows the CNS to compute the position and movement of our extremities in space, which is essential for motor control, posture, and gait.
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Stabilizers
In addition to their role in movement, stabilizers also play a crucial part in injury prevention and rehabilitation. For example, back extension exercises are often used in the rehabilitation of low back pain. By strengthening the stabilizers in the back, these exercises can help to prevent future injuries and improve posture.
Overall, stabilizers are an important type of muscle function that helps to keep bones immobile, maintain posture, and prevent injuries. By understanding the role of stabilizers, we can design effective exercise routines that improve performance, reduce the risk of injury, and promote balanced muscle development.
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Frequently asked questions
Electromyography is a technique used to evaluate and record the electrical activity produced by skeletal muscles. It is performed using an instrument called an electromyograph to produce a record called an electromyogram.
An electromyograph detects the electric potential generated by muscle cells when they are electrically or neurologically activated. The signals can be analysed to detect abnormalities, activation level, or recruitment order, or to analyse the biomechanics of human or animal movement.
Muscle spindles are delicate sensory receptors present in almost every muscle. They inform the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching. This information is used by the CNS to compute the position and movement of our extremities in space, which is essential for motor control, maintaining posture, and a stable gait.
