unit 3 Peripheral Neuromuscular Mechanisms

A motor neuron and all the muscle fibers it controls.

Activating more motor units to produce more force.

Motor units are activated in order of size (small to large).

The connection between a motor neuron and a muscle fiber.

The main neurotransmitter released at the NMJ for muscle activation.

The relationship between muscle length and force generation.

Sensory information about body position and movement.

Sensory receptor detecting muscle stretch and speed.

Sensory receptor detecting muscle tension.

Muscle's response to external forces, for stability and movement control.

Changes in motor unit recruitment and muscle fiber characteristics with training, improving motor performance.

Activation of specific motor units in a coordinated pattern to produce movement.

Motor control that accounts for external factors and adapts movements in response.

Impaired motor function and proprioception from nerve damage affecting movement coordination.

Sensory receptors providing continuous information about position and the surrounding environment to improve accuracy.

Pre-activated commands that coordinate muscle actions before movement initiation, for precise movement timing and coordination.

Muscle contraction type and speed determined by task demands (force, speed) and recruited muscle fibers.

Sensory signals adjusting motor commands to correct movements

Simultaneous activation of opposing muscles for maintaining stability and accurate movements.

A sensory receptor located in tendons that detects changes in muscle tension, helping to prevent excessive muscle force by triggering relaxation.

A reduction in the ability of the nervous system and muscles to generate or maintain force, affecting muscle function, strength, and endurance.

The ability of the nervous system, muscles, and connective tissue to adapt and change in response to repeated use and activation patterns.

Sensory information from receptors like muscle spindles and GTOs allows the nervous system to constantly adjust muscle activity for accurate and efficient movement.

A motor unit consists of a motor neuron and all the muscle fibers it innervates. These units are crucial for generating force and controlling both precise and forceful movements.

The NMJ is the point where a motor neuron's axon terminal connects to a muscle fiber. Acetylcholine (ACh), a neurotransmitter, is released at the NMJ, triggering a muscle action potential that leads to muscle contraction.

The Size Principle states that smaller motor units are recruited before larger ones, depending on the force needed. This allows for precise control of movements and gradual increase in force.

Muscle spindles are sensory receptors embedded within muscles that detect changes in muscle length and speed of stretch. This information is sent to the brain for control and coordination.

GTOs are sensory receptors located in tendons, which detect muscle tension. When force is too great, they reflexively inhibit muscle contraction to protect against injury.

Muscles have different fiber types (Type I, Type IIa, Type IIx) with varying speed, fatigue resistance, and force production.

The specialized synapse where a motor neuron communicates with a muscle fiber, releasing acetylcholine to trigger muscle contraction.

Sensory receptors in joints provide information about position, movement, pressure, and speed, crucial for coordination and balance.

Damage to nerves outside the brain and spinal cord disrupts communication between the CNS and muscles, leading to weakness, paralysis, or altered movement.

Muscle fiber types provide a range of capabilities, allowing for fine control, powerful movements, and endurance. This diversity enables the body to adapt to different movement demands.

Muscle spindles sense muscle stretch, activating the stretch reflex to maintain posture and tone. GTOs sense tension and inhibit contraction to prevent injury. They work together to regulate force and protect muscles.

Continuous sensory input from muscles, tendons, and joints informs the brain about body position and movement, allowing for adjustments in movement strategies.

The ability to modify movement patterns based on sensory feedback and experience, leading to improved performance over time.

The brain organizes movement control in a layered system, with higher levels planning actions and lower levels executing them.

The brain predicts and anticipates needed movements based on planning and past experience, adjusting motor commands before movement starts.

Sensory feedback provides information about ongoing movement, enabling the brain to adjust motor commands during movement.

The cerebellum coordinates and refines motor commands, ensuring smooth, precise movements and timing.

The basal ganglia initiates and terminates movements, regulates muscle force, and plays a role in learning new motor skills.

The simultaneous activation of multiple muscles around a joint to provide stability and ensure smooth movement transitions.

The brain's ability to adapt and modify its structure and function in response to experiences, including practicing new movements and motor skills.

A skill with a clear beginning and end, often performed quickly. Example: throwing a ball.

A skill composed of multiple discrete movements strung together. Example: Playing a musical piece.

A skill with no clear beginning or end, performed for an extended period of time. Example: Swimming.

The time it takes to respond to a single, predictable stimulus. Example: Pressing a button when a light turns on.

The time it takes to respond to multiple stimuli, each requiring a different response. Example: Choosing the correct button to press based on the color of a light.

The relationship between the length of a muscle and the amount of force it can produce. Optimal length provides the greatest force.

Force produced by the contraction of muscle fibers. Achieved when actin and myosin filaments overlap optimally.

Force generated by the elastic properties of muscle tissue, even when not actively contracting.

The length of a muscle at which it can generate the most active force.

The sum of active and passive force in a muscle.

The contractile element (CE) is the part of the muscle that produces force, primarily made up of proteins like actin and myosin.

Elastic elements (EE) store and release force through recoil. They consist of connective tissues (parallel) and tendons (series).

The nervous system controls the timing and amount of muscle contraction, impacting muscle stiffness, force absorption, and recoil.

Muscle shortens as it produces force, like lifting a weight.

Muscle lengthens while producing force, resisting external force, like lowering a weight slowly.

A movement pattern where a muscle is stretched (eccentric contraction) before being shortened (concentric contraction). It allows for greater force output compared to just a concentric contraction.

Exercises that involve rapid stretching and shortening of muscles, improving the stretch-shortening cycle.

While stretching can improve flexibility, it can negatively impact the stretch-shortening cycle by decreasing muscle stiffness, making it harder to generate powerful movements.

The SSC allows for greater force production compared to only performing a concentric contraction. This is due to the elastic element of the muscle being preloaded during the eccentric phase.

The junction between two neurons or a neuron and a muscle fiber, where information is transmitted.

The nervous system controls force output by (1) recruiting more motor units, (2) increasing firing frequency of motor neurons, and (3) altering muscle fiber type activation.

The coordination of muscle fibers within a single muscle to produce a smooth and efficient movement.

The coordination of different muscles working together to achieve a complex movement.

The regulation of a motor unit's firing rate to control the amount of force produced. Higher firing rate leads to more force.

The maximum force output of a muscle where individual twitch contractions are completely merged into a smooth, sustained contraction. This is achieved when action potentials fire at a very high rate.

The accumulation of tension in a muscle fiber when successive action potentials arrive before the previous contraction has fully relaxed, resulting in a stronger contraction.

A higher firing rate of action potentials in a motor unit results in stronger muscle contractions since the individual twitches summate to generate greater force. This relationship is known as rate coding.

The part of the muscle that actively generates force, mainly composed of proteins like actin and myosin.

The elastic component of muscle, storing and releasing energy, consisting of connective tissues and tendons.

While improving flexibility, stretching decreases muscle stiffness, which can negatively impact the stretch-shortening cycle, leading to less powerful movements.

A synapse is a specialized junction where communication occurs between two neurons or between a neuron and a muscle fiber.

Dendrites are branches of a neuron that receive information from other neurons.

Axons are long, slender projections of a neuron that transmit signals to other neurons or muscle fibers.

Different types of motor units exist, based on muscle fiber types (Type I, IIa, IIx), which vary in speed, power, and fatigue resistance.

A muscle twitch is the contractile response of a muscle to a single action potential.

The all-or-none principle states that a single motor unit either contracts completely or not at all.

The nervous system regulates force output by (1) recruiting more motor units, (2) increasing firing frequency of motor neurons, and (3) altering muscle fiber type activation.

Intramuscular coordination refers to the smooth and efficient coordination of muscle fibers within a single muscle.

A muscle can act as an agonist (mover), stabilizer (keeps joint stable), or neutralizer (prevents unwanted movement) depending on the task.

The muscle primarily responsible for a specific movement.

A muscle that keeps a joint steady during movement.

Motor units are activated in order of size, from smallest to largest, as more force is needed.

Small motor unit, slow-twitch fibers, resistant to fatigue. For sustained, low-force activities.

Medium-sized motor unit, fast-twitch fibers, moderately resistant to fatigue. For moderate, sustained efforts.

Large motor unit, fast-twitch fibers, fatigue quickly. For maximal force output.

Elastic elements in muscle, like connective tissues and tendons, store and release energy during contraction, contributing to greater force output.

Calcium ions (Ca++) are essential for muscle contraction. Higher Ca++ levels mean more cross-bridges form, generating more force.

Orderly recruitment allows for smooth, gradual force increases, preventing abrupt movements. It also ensures that fatigue-resistant fibers are activated first, maximizing endurance.

Larger motor units have larger cell bodies (somas) and require a stronger excitatory input from the nervous system to reach their threshold for activation.

Smaller motor units are innervated by smaller motor neurons and primarily contain fatigue-resistant type I fibers. They are recruited early and contribute to endurance tasks. Larger motor units contain more fatigable type II fibers and are recruited for high-intensity tasks.

Type I fibers are fatigue-resistant and are predominantly recruited for low-intensity, prolonged activities like walking or low-intensity running. These fibers are innervated by smaller motor neurons.

Type II fibers are larger and more powerful, but fatigue quickly. They are primarily recruited for high-intensity, short-duration activities like sprinting or jumping. These fibers are innervated by larger motor neurons.

The motor neuron pool encompasses all the motor neurons that innervate a specific muscle. These pools vary in size depending on the muscle's size and function.

As more motor units are recruited, the total muscle force increases. This is because more muscle fibers are activated, resulting in more contractile elements working together.

The nervous system can regulate muscle force output by recruiting more motor units, increasing the firing rate of motor neurons, or activating different types of muscle fibers.

High-intensity exercise utilizes more large motor units to produce high force output, while low-intensity exercise predominantly utilizes smaller motor units to maintain low force output over a longer duration.