10.4 Nervous System Control of Muscle Tension
2 min read•june 18, 2024
Muscles contract in various ways, from shortening to lengthening under tension. These contractions depend on the overlap of thick and in sarcomeres. Understanding muscle contraction types helps explain how we move and generate force in everyday activities.
Muscle twitches have distinct phases, from the initial stimulus to relaxation. Tension control mechanisms like and allow for sustained contractions. Neuromuscular control, involving motor units and , orchestrates muscle movements in response to nerve signals.
Muscle Contraction Types and Characteristics
Types of muscle contractions
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- increases causing the muscle to shorten (biceps contracting to lift a weight)
- maintains constant muscle tension throughout the contraction and includes both concentric and eccentric contractions
- lengthens the muscle while under tension when the opposing force is greater than the force generated by the muscle (biceps lengthening while lowering a weight)
Length-tension relationship in muscles
- Maximum tension generation occurs with optimal overlap of thick and thin filaments at a length of approximately 2.0-2.2 μm
- Decreased tension occurs when the is either too short due to less overlap of thick and thin filaments or too long due to decreased overlap and fewer formed
- Passive tension generated by the elastic components of the muscle increases as the muscle is stretched beyond its resting length
Muscle Twitch and Tension Control
Phases of muscle twitches
- is the time between the arrival of and the start of muscle contraction when are released from the
- increases tension as the muscle shortens and cross-bridges form between and filaments
- decreases tension as the muscle returns to its resting length and calcium ions are actively pumped back into the sarcoplasmic reticulum
Mechanisms of muscle tension control
- Wave summation occurs when a second stimulus is applied before the muscle has fully relaxed from the first stimulus resulting in a higher peak tension than a single
- Tetanus is a sustained muscle contraction resulting from rapid, repeated stimulation and can be either:
- with slight relaxation between stimuli
- with no relaxation between stimuli resulting in a smooth, continuous contraction
- () progressively increases muscle tension with repeated stimulation at a constant frequency due to increased calcium ion availability and enhanced contractile mechanism efficiency
Neuromuscular Control
- Motor units consist of a and all the muscle fibers it innervates
- The is the site where a motor neuron communicates with a
- Acetylcholine is the neurotransmitter released at the neuromuscular junction to initiate muscle contraction
- The states that a muscle fiber either contracts fully or not at all in response to stimulation
Key Terms to Review (53)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a crucial role in the communication between neurons, the activation of muscle fibers, and the regulation of various physiological processes in the body. It is a key player in the functioning of the nervous system, muscle tissues, and the autonomic nervous system.
Acetylcholine (ACh): Acetylcholine is a neurotransmitter in the nervous system that plays a crucial role in stimulating muscle contractions and is involved in various brain functions including memory and learning. In the context of skeletal muscle, it is essential for transmitting nerve signals to muscle cells, leading to muscle movement.
Actin: Actin is a globular protein that forms long, thin filaments which are a major component of the cytoskeleton in all eukaryotic cells and is crucial in the contraction of skeletal muscles. It works together with myosin to convert chemical energy into mechanical energy, leading to muscle movement.
Actin: Actin is a globular protein that is a key structural component of the cytoskeleton in eukaryotic cells. It is involved in a wide range of cellular processes, including muscle contraction, cell motility, cell division, and the maintenance of cell shape and integrity.
Action Potential: An action potential is a rapid, transient electrical signal that travels along the cell membrane of excitable cells, such as neurons and muscle cells. It is the fundamental unit of communication in the nervous system, enabling the transmission of information between different parts of the body.
All-or-None Principle: The all-or-none principle is a fundamental concept in physiology that describes how certain biological processes, such as the generation of action potentials in neurons and the contraction of muscle fibers, occur in an all-or-nothing manner. This principle states that these processes either occur fully or not at all, with no intermediate or partial responses.
Calcium Ions: Calcium ions (Ca2+) are essential mineral ions that play crucial roles in various physiological processes, including muscle contraction, nerve impulse transmission, and cellular signaling. These positively charged ions are involved in a wide range of functions throughout the body, making them a key topic in the study of anatomy and physiology.
Complete Tetanus: Complete tetanus is a severe and life-threatening condition caused by the neurotoxin produced by the bacterium Clostridium tetani. It is characterized by sustained, painful muscle contractions and spasms throughout the body, leading to respiratory failure and death if left untreated.
Concentric contraction: Concentric contraction is the shortening of a muscle during contraction, as it generates force to overcome resistance. This type of muscle action occurs when the tension developed by the muscle is greater than the external load on the muscle.
Concentric Contraction: A concentric contraction is a type of muscle contraction where the muscle shortens as it generates force. This occurs when the muscle's tension overcomes the resistance it is working against, causing the muscle to contract and the joint to move.
Contraction phase: The contraction phase is the period during which muscle fibers actively shorten to generate force following stimulation by the nervous system. It is a crucial part of muscle movement, where tension in the muscle increases but the length decreases.
Cross-Bridges: Cross-bridges are temporary molecular structures that form between the myosin heads on the thick filaments and the actin binding sites on the thin filaments in skeletal muscle fibers. These cross-bridges are essential for the contraction and movement of muscles by generating the force required for muscle contraction.
Eccentric contraction: Eccentric contraction occurs when a muscle lengthens under tension, often to control the speed of movement or resist gravity. It is an integral part of movements such as lowering a weight or descending stairs, where the muscle actively elongates.
Eccentric Contraction: An eccentric contraction occurs when a muscle lengthens while generating force. This happens when the muscle is resisting an external load that is greater than the muscle's own tension, causing it to elongate rather than shorten during the contraction.
Graded muscle response: Graded muscle response is the ability of a muscle to exhibit varying levels of contraction strength in response to different levels of stimulation. This ensures muscles can produce precise movements or apply the necessary force for specific tasks.
Hypertonia: Hypertonia is a condition characterized by abnormally high muscle tone, resulting in stiffness and resistance to movement. It occurs when there's excessive activity in the muscles controlled by the nervous system.
Hypotonia: Hypotonia is a condition characterized by decreased muscle tone, making muscles feel more relaxed than normal even at rest. It affects the ability to maintain posture and can impact movement control, often resulting from issues in nervous system or muscle function.
Incomplete Tetanus: Incomplete tetanus, also known as partial tetanus, is a condition where the muscle contractions associated with tetanus are not fully developed or generalized. In this state, the muscle spasms are limited to the specific muscles or muscle groups initially affected by the tetanus-causing bacteria, rather than spreading throughout the body.
Isometric contraction: Isometric contraction occurs when a muscle exerts force without changing its length, effectively generating tension while the angles of joints and the muscle's overall length remain unchanged. This type of muscle action is crucial for maintaining posture and stabilizing joints.
Isotonic contraction: Isotonic contraction is a type of muscle action where the muscle changes length while the tension remains constant, commonly occurring during most everyday activities. This process facilitates movement of the body or objects by shortening (concentric contraction) or lengthening (eccentric contraction) of the muscle.
Isotonic Contraction: Isotonic contraction is a type of muscle contraction where the muscle shortens while maintaining a constant tension throughout the movement. This is in contrast to isometric contraction, where the muscle length remains constant during the contraction.
Isotonic contractions: Isotonic contractions occur when a muscle changes length, either shortening or lengthening, while the tension remains constant. This type of contraction is common during everyday activities such as walking or lifting objects.
Latent period: The latent period is the brief time lapse between the application of a stimulus to a muscle and the start of its contraction. It represents the period during which the muscle prepares for contraction but no visible change in tension occurs.
Latent Period: The latent period is the brief interval between the initiation of a muscle contraction and the actual shortening of the muscle fibers. This delay occurs after a stimulus is applied and involves various physiological processes, including excitation-contraction coupling, where electrical impulses lead to muscle fiber activation. Understanding the latent period is essential in recognizing how nervous system signals translate into muscle tension.
Length-tension relationship: The length-tension relationship refers to the optimal length at which muscle fibers can generate the greatest force during contraction. This concept illustrates how the overlap between actin and myosin filaments within the sarcomere influences muscle tension, with the maximum force occurring at an intermediate muscle length, where there is sufficient overlap of these proteins.
Lower motor neuron: A lower motor neuron is a type of nerve cell that directly connects to and innervates muscle fibers, enabling movements and reflexes by transmitting signals from the brain and spinal cord. It is crucial for the execution of voluntary and involuntary actions by translating neural commands into muscle activity.
Motor Neuron: A motor neuron is a type of nerve cell that transmits signals from the central nervous system to the muscles, triggering muscle contraction and movement. Motor neurons are a crucial component in the nervous system's control and regulation of muscle tension and physical activity.
Motor unit: A motor unit consists of a single motor neuron and all the muscle fibers it innervates. It is the smallest functional unit in the nervous system control of muscle tension, crucial for producing movement by contracting muscles.
Motor Unit: A motor unit is the basic functional unit of skeletal muscle control, consisting of a single motor neuron and all the muscle fibers it innervates. It is the smallest unit that can be activated by the nervous system to produce a contraction of muscle tissue.
Muscle Fiber: A muscle fiber is the basic contractile unit of skeletal muscle, composed of many myofibrils that allow the muscle to shorten and generate force. Muscle fibers are essential for the proper functioning of the muscle tissues described in the Overview of Muscle Tissues topic, as well as the nervous system's control of muscle tension.
Muscle tension: Muscle tension is the force generated by a muscle or group of muscles when they contract in response to signals from the nervous system. It varies depending on the number of muscle fibers contracting and their rate of contraction.
Muscle tone: Muscle tone is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It helps maintain posture and ensures that muscles are ready for action.
Muscle Twitch: A muscle twitch is a brief, involuntary contraction of a muscle or a small group of muscle fibers. It occurs due to the activation of motor units within the muscle, resulting in a localized movement or tremor.
Myogram: A myogram is a graphical recording of a muscle contraction, showing the force and duration of the contraction. It results from electrical activity within the muscle as it responds to stimulation.
Myosin: Myosin is a type of motor protein found in muscle cells that, through its interaction with actin, plays a crucial role in muscle contraction and movement. It converts chemical energy in the form of ATP to mechanical energy, thus enabling the muscles to contract.
Myosin: Myosin is a motor protein that is essential for muscle contraction and movement. It is a key component of the contractile apparatus within muscle fibers and interacts with the actin filaments to generate the force required for muscle movement and locomotion.
Neuromuscular Junction: The neuromuscular junction is the site where a motor neuron from the nervous system connects with and transmits signals to a muscle fiber, enabling muscle contraction. It is a critical interface that facilitates the communication between the nervous and muscular systems, allowing for the voluntary control of skeletal muscle movement.
Neuromuscular junction (NMJ): The neuromuscular junction is a specialized synapse between a motor neuron and a skeletal muscle fiber, facilitating the transmission of electrical signals that result in muscle contraction. It plays a pivotal role in converting neural commands into mechanical movement.
Recruitment: In the context of muscle tissue, recruitment refers to the process by which the nervous system activates more motor units to increase muscle tension. This occurs when a task requires more strength than what is initially provided by the currently active motor units.
Relaxation phase: The relaxation phase is a period during the muscle contraction cycle when a muscle returns to its initial resting state after tension. It involves the cessation of nerve signals and the outflow of calcium ions from the muscle fibers, allowing them to relax.
Sarcomere: A sarcomere is the basic contractile unit of muscle fiber in skeletal muscle, made up of long protein filaments including actin and myosin that slide past each other to produce a muscle contraction. It is bounded by Z lines to which the actin filaments are attached.
Sarcomere: The sarcomere is the fundamental contractile unit of skeletal, cardiac, and smooth muscle fibers. It is the basic structural and functional unit responsible for the contraction and relaxation of muscle tissue, and is a key component in the overall process of muscle motion and activity.
Sarcoplasmic reticulum: The sarcoplasmic reticulum is a specialized form of endoplasmic reticulum found in muscle cells that functions primarily to store and release calcium ions (Ca²+) during muscle contraction and relaxation. This organelle plays a critical role in regulating calcium levels, which are essential for muscle fiber contraction, allowing muscles to contract and relax in response to stimulation.
Staircase Phenomenon: The staircase phenomenon, also known as the 'treppe' effect, describes the gradual increase in muscle tension or contraction strength that occurs with repeated stimulation of a muscle at a fixed frequency. This phenomenon is significant as it reflects how the nervous system can control muscle tension more effectively through an increased frequency of action potentials, leading to a more forceful contraction over time.
Tetanus: Tetanus is a serious and potentially life-threatening condition caused by a bacterium that produces a powerful neurotoxin, leading to severe muscle spasms and rigidity. It is particularly relevant in the context of the nervous system's control of muscle tension and the function of cardiac muscle tissue.
The Action Potential: An action potential is a rapid, temporary change in the electrical membrane potential of a neuron or muscle cell, allowing it to transmit a signal. It involves an influx of sodium ions into the cell followed by an efflux of potassium ions, restoring the original electrical condition.
Thick filaments: Thick filaments are one of the main components of muscle fibers, primarily composed of the protein myosin. These filaments play a crucial role in muscle contraction by interacting with thin filaments during the sliding filament mechanism. Understanding thick filaments is essential for grasping how muscles generate force and respond to signals from the nervous system.
Thin filaments: Thin filaments are essential protein structures found in muscle cells, primarily composed of actin, along with troponin and tropomyosin. These filaments play a crucial role in muscle contraction by interacting with thick filaments, which consist of myosin. The interaction between thin and thick filaments is regulated by the nervous system through signals that control muscle tension.
Treppe: Treppe is a phenomenon observed in muscle tissue where consecutive stimulations result in progressively stronger contractions until a plateau is reached. This occurs when muscle fibers are stimulated frequently without allowing them to fully relax, leading to an increased efficiency in muscle contraction.
Treppe: Treppe, also known as the staircase effect, is a phenomenon observed in skeletal muscle contraction where the force or tension of the muscle increases with each successive contraction, even when the stimulation remains constant. This effect is closely related to the nervous system's control of muscle tension.
Twitch: A twitch is the rapid, brief contraction of a muscle fiber following a single stimulus. It represents the basic unit of muscle force production in response to neural input from the nervous system.
Types of Muscle Fibers: Types of muscle fibers refer to the different categories of fibers within skeletal muscles, each with unique characteristics and functions. These include slow-twitch (Type I) fibers, which are fatigue-resistant and suited for endurance activities, and fast-twitch fibers (Type II), which are less resistant to fatigue but capable of generating more power and speed.
Wave summation: Wave summation is the phenomenon where muscle fibers produce stronger contractions by being stimulated rapidly before they can fully relax from a previous stimulus. This results in an increased force of contraction due to the additive effect of individual muscle twitch contractions.