Nervous System Overview Quiz
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Questions and Answers

What are the primary components of the peripheral nervous system?

  • Motor neurons and sensory neurons
  • Cranial nerves and spinal nerves (correct)
  • Central and peripheral nerves
  • Efferent and afferent pathways

    • Which of the following correctly defines afferent neurons?

  • Nerves that transmit sensory information to the body
  • Nerves that regulate movement and motor behavior
  • Nerves that originate in the spinal cord
  • Nerves that transmit sensory information to the central nervous system (correct)

    • What structure in a typical neuron is primarily responsible for signal transmission?

  • Axon (correct)
  • Nucleus
  • Dendrites
  • Myelin sheath

    • Which part of the central nervous system contains the cell bodies of upper motor neurons?

    <p>Brain and spinal cord</p> Signup and view all the answers

    What role do neurotransmitters play in the nervous system?

    <p>They facilitate communication between nerves at synapses.</p> Signup and view all the answers

    What defines a motor unit in the context of muscle contraction?

    <p>The alpha motor nerve and all the muscle fibers it innervates.</p> Signup and view all the answers

    What is the function of the myelin sheath?

    <p>To enhance the speed of action potential conduction along the axon.</p> Signup and view all the answers

    What variation can occur in the number of muscle fibers for a single motor unit?

    <p>It can vary depending on the muscle's function.</p> Signup and view all the answers

    What is the primary neurotransmitter synthesized at the neuromuscular junction?

    <p>Acetylcholine</p> Signup and view all the answers

    What is the typical resting membrane potential of nerve and muscle cells?

    <p>-60 to -90 millivolts</p> Signup and view all the answers

    What process occurs when the cell membrane becomes less negatively charged in response to a stimulus?

    <p>Depolarization</p> Signup and view all the answers

    What term describes the capacity of nerve and muscle cells to respond to a stimulus?

    <p>Irritability</p> Signup and view all the answers

    Which of the following contributes to the potential difference across a cell membrane?

    <p>Differences in ion concentrations</p> Signup and view all the answers

    What structural feature allows muscle fibers to tightly adhere to the neuromuscular junction?

    <p>Motor plate</p> Signup and view all the answers

    How does the electrochemical impulse move along a muscle cell's membrane after depolarization?

    <p>By an electrochemical mechanism</p> Signup and view all the answers

    What happens to the potential difference across a muscle cell's membrane during an action potential?

    <p>It changes and becomes positive</p> Signup and view all the answers

    What is the role of ATP in the process of muscle contraction?

    <p>ATP splits to provide energy for the flexion of the cross bridge.</p> Signup and view all the answers

    What initiates the coupling of the cross bridge to the actin site?

    <p>The presence of calcium ions.</p> Signup and view all the answers

    What happens to the position of the Z lines during muscle contraction?

    <p>They move closer together as actin is pulled along myosin.</p> Signup and view all the answers

    What occurs during the recharging phase of the cross bridge cycle?

    <p>ATP binds to the myosin head preparing it for the next contraction.</p> Signup and view all the answers

    How often does the process of coupling and uncoupling of the cross bridge occur during strong muscle contractions?

    <p>Multiple times per second.</p> Signup and view all the answers

    What is the function of the epimysium in muscle structure?

    <p>To separate individual muscles from each other</p> Signup and view all the answers

    Which term refers to the subdivision of a muscle into sections?

    <p>Fasciculus</p> Signup and view all the answers

    What are the primary protein components found in myofilaments?

    <p>Actin and myosin</p> Signup and view all the answers

    What defines a sarcomere in muscle fibers?

    <p>The functional unit of muscle contraction between two Z-lines</p> Signup and view all the answers

    What is the significance of the A band in skeletal muscle structure?

    <p>It contains myosin filaments and their overlap with actin</p> Signup and view all the answers

    What is the primary substance found in the sarcoplasm of muscle fibers?

    <p>Gelatin-like substance</p> Signup and view all the answers

    How do the light and dark striations in skeletal muscle appear?

    <p>Due to the arrangement of actin and myosin filaments</p> Signup and view all the answers

    What is the role of mitochondria in muscle fibers?

    <p>To produce energy through metabolic processes</p> Signup and view all the answers

    What happens to the I band during muscle contraction?

    <p>It decreases in size.</p> Signup and view all the answers

    Which band remains unchanged during the contraction of a muscle?

    <p>A band</p> Signup and view all the answers

    What is the role of actin during muscle contraction?

    <p>It provides the binding site for myosin.</p> Signup and view all the answers

    What characterizes the area known as the H band?

    <p>It contains only myosin filaments.</p> Signup and view all the answers

    During muscle activation, what do the myosin heads that form cross bridges do?

    <p>Project laterally and move actin.</p> Signup and view all the answers

    What occurs to the H band during muscle contraction?

    <p>It shrinks to a point of disappearance.</p> Signup and view all the answers

    How does the Sliding Filament Theory describe muscle contraction?

    <p>Actin and myosin filaments slide past each other.</p> Signup and view all the answers

    What happens to Z lines during contraction of the muscle?

    <p>They come closer together.</p> Signup and view all the answers

    What primarily determines muscle tone?

    <p>The level of reflex sensitivity and intrinsic muscle stiffness</p> Signup and view all the answers

    Which of the following describes the spinal reflex arc most accurately?

    <p>A simple neural pathway that links sensory input to motor output exclusively through the spinal cord</p> Signup and view all the answers

    The stretch reflex is primarily triggered by which event?

    <p>A sudden stretch of the muscle</p> Signup and view all the answers

    Which component is critical for the transmission of signals in the stretch reflex?

    <p>Afferent neurons from the stretch receptor</p> Signup and view all the answers

    What modifies the stereotypical responses provided by spinal reflexes?

    <p>Central nervous system's alertness and arousal</p> Signup and view all the answers

    What role do interneurons play within the spinal cord during reflex actions?

    <p>They connect sensory inputs to motor neuron outputs</p> Signup and view all the answers

    In which scenario does the stretch reflex specifically engage the biceps muscle?

    <p>When an unexpected load increase occurs suddenly</p> Signup and view all the answers

    What best characterizes the spinal region's function concerning movement regulation?

    <p>It plays a key role in automatic control of movement and reflex actions</p> Signup and view all the answers

    What is the primary mechanism behind reciprocal inhibition during stretching?

    <p>Activation of the opposing muscle while stretching the target muscle</p> Signup and view all the answers

    How do pattern generators contribute to movement?

    <p>They create complex activation patterns for movement through neural connections</p> Signup and view all the answers

    What principle describes the recruitment order of motor units during muscle contraction?

    <p>Size principle of recruitment</p> Signup and view all the answers

    What role do interneurons play in the spinal cord regarding movement?

    <p>They create adaptable networks that activate flexor and extensor muscles</p> Signup and view all the answers

    How does the recruitment principle affect overall muscle tension?

    <p>Increases overall tension by activating more motor units</p> Signup and view all the answers

    What effect does actively contracting the quadriceps have when stretching the hamstrings?

    <p>It allows the hamstrings to relax, facilitating a more effective stretch</p> Signup and view all the answers

    How do the flexible networks of interneurons adapt to changes in tasks and environments?

    <p>By modifying the neural connections based on sensory feedback and experiences</p> Signup and view all the answers

    Which type of muscle fibers are primarily involved in sustained activities due to their fatigue resistance?

    <p>Slow twitch type 1 fibers</p> Signup and view all the answers

    What happens to muscle force when both the number of active motor units and their firing rates increase?

    <p>Muscle force increases significantly</p> Signup and view all the answers

    Which motor units are typically recruited last during high force requirements?

    <p>Larger, fast-twitch units</p> Signup and view all the answers

    What role do proprioceptors play in muscle activation?

    <p>They detect changes in tension and position</p> Signup and view all the answers

    What is the effect of increasing the frequency of stimulation of individual motor units?

    <p>Increases the percentage of maximum tension developed</p> Signup and view all the answers

    What pattern best describes the activation of muscle fibers in a motor unit during contraction?

    <p>All muscle fibers in the unit contract simultaneously</p> Signup and view all the answers

    What role do proprioceptors play in the body?

    <p>They provide input on joint position and movement.</p> Signup and view all the answers

    What is the primary function of muscle spindles?

    <p>To detect changes in muscle length and stretch.</p> Signup and view all the answers

    How does muscle tone manifest in skeletal muscles?

    <p>As a constant state of readiness and tension.</p> Signup and view all the answers

    Which of the following correctly distinguishes kinesthesia from joint position sense?

    <p>Kinesthesia describes dynamic joint motion, whereas position sense describes static awareness.</p> Signup and view all the answers

    What happens to muscle spindle activity when the muscle is stretched?

    <p>Muscle spindles send more nerve impulses to stimulate alpha motor neurons.</p> Signup and view all the answers

    What is primarily characterized by the varying number of muscle spindles in different muscle groups?

    <p>Their sensitivity to change in movement.</p> Signup and view all the answers

    What determines the frequency of muscle spindle discharge?

    <p>The length of the muscle fiber relative to the muscle spindle.</p> Signup and view all the answers

    Which statement accurately reflects the neuromuscular response during voluntary movement?

    <p>Motor control centers adjust muscle activation based on integrated sensory signals.</p> Signup and view all the answers

    What occurs during an isometric contraction?

    <p>Muscle produces force with no change in joint angle</p> Signup and view all the answers

    Which characteristic defines eccentric contractions?

    <p>Muscle lengthens in response to an external force greater than its own force</p> Signup and view all the answers

    In what way do isotonic contractions differ from isometric contractions?

    <p>Isometric contractions maintain a constant muscle length</p> Signup and view all the answers

    What situation would most likely involve eccentric muscle contractions?

    <p>Decelerating while running to stop</p> Signup and view all the answers

    Which type of muscle contraction is characterized by a constant rate of movement?

    <p>Isokinetic contraction</p> Signup and view all the answers

    What is a primary characteristic of concentric contractions?

    <p>Muscle fibers shorten when overcoming resistance</p> Signup and view all the answers

    Which best describes the dynamic nature of isotonic contractions?

    <p>Muscle tension changes as the joint moves through its range</p> Signup and view all the answers

    How does an eccentric contraction contribute to activities like jumping?

    <p>It provides shock absorption during landing</p> Signup and view all the answers

    What is the primary function of the resistance mechanism in an isokinetic device?

    <p>To ensure maximum muscle output throughout the range of motion</p> Signup and view all the answers

    In electromyography (EMG), what is the role of multi-channel instruments?

    <p>To record electrical activity from multiple electrodes simultaneously</p> Signup and view all the answers

    How is an agonist characterized in terms of muscle action?

    <p>It is the primary muscle responsible for initiating and controlling movements</p> Signup and view all the answers

    What describes the function of an antagonist muscle during movement?

    <p>It provides passive support through elongation or shortening</p> Signup and view all the answers

    Which statement accurately describes the role of synergist muscles?

    <p>They assist the agonist by providing additional force or stability</p> Signup and view all the answers

    What is one of the key benefits of using surface electrodes in EMG recordings?

    <p>They allow for non-invasive monitoring of muscle activity</p> Signup and view all the answers

    What is the significance of recording muscle activation patterns during specific movements?

    <p>To determine the sequence of muscle engagement and their functional roles</p> Signup and view all the answers

    What role does the axis of rotation play in the function of an isokinetic device?

    <p>It aligns with the moving joint's axis for effective resistance</p> Signup and view all the answers

    What is the primary role of synergist muscles during movement?

    <p>To stabilize the movement and enhance the efficiency of the agonist.</p> Signup and view all the answers

    Which of the following statements regarding muscle contractions is correct?

    <p>Eccentric contractions are characterized by the muscle lengthening under tension.</p> Signup and view all the answers

    What factor does NOT influence muscle activity during different movements?

    <p>The type of clothing worn during exercise.</p> Signup and view all the answers

    In a situation where the proximal attachment moves towards a fixed distal attachment, what type of exercise is being performed?

    <p>Closed kinematic chain exercise.</p> Signup and view all the answers

    Which statement accurately describes muscle activation during the supine position?

    <p>The triceps control elbow flexion in an eccentric manner.</p> Signup and view all the answers

    What is the relationship between agonists and antagonists during muscle action?

    <p>They can alternate roles depending on the specific movement being executed.</p> Signup and view all the answers

    Which of the following factors can lead to inefficient and ineffective agonistic movement?

    <p>Lack of stabilizers that support the primary muscle action.</p> Signup and view all the answers

    Which contraction type occurs when the distal segment moves against gravity?

    <p>Concentric contraction.</p> Signup and view all the answers

    What describes the phenomenon when a muscle is unable to shorten enough to achieve full motion across all its joints?

    <p>Active muscle insufficiency</p> Signup and view all the answers

    What is the result of actin and myosin overlap reduction in a muscle that is shortened?

    <p>Decreased cross-bridge formation</p> Signup and view all the answers

    Which of the following occurs during passive muscle insufficiency?

    <p>There is insufficient length in the muscle to allow full mobility.</p> Signup and view all the answers

    What happens to the finger extensors when the wrist is fully flexed and the fist is closed?

    <p>They passively lengthen.</p> Signup and view all the answers

    What effect does a muscle being in a lengthened position compared to its optimum length have on actin filaments?

    <p>It reduces potential for cross-bridges.</p> Signup and view all the answers

    What happens to the tissue when the force applied exceeds the elastic range?

    <p>It becomes permanently elongated.</p> Signup and view all the answers

    At what point do microscopic ruptures begin to occur in the tissue structure?

    <p>During the necking range.</p> Signup and view all the answers

    What is the institutional maximum estimation of a muscle's ability to shorten?

    <p>70% of resting length.</p> Signup and view all the answers

    What occurs to the extensor muscles when attempting to make a tight fist with a fully flexed wrist?

    <p>They become actively shortened.</p> Signup and view all the answers

    What occurs if the tissue stress continues beyond the necking range?

    <p>Macroscopic damage to the tissue occurs.</p> Signup and view all the answers

    What is described by the term 'functional excursion' of a muscle?

    <p>The distance to which a muscle can shorten after elongation.</p> Signup and view all the answers

    What is the consequence of not having enough length in the finger extensors during a tight fist action?

    <p>Limited range in wrist and finger flexion.</p> Signup and view all the answers

    What is true about the tissue's state when it enters the failure range?

    <p>It exhibits less strength than before.</p> Signup and view all the answers

    What term describes the resistance to an external force that causes permanent deformation in tissues?

    <p>Viscosity</p> Signup and view all the answers

    Which of the following best describes the elastic range within the stress-strain curve?

    <p>Area where tissue can return to its original length after stress removal</p> Signup and view all the answers

    What is the significance of the toe region in the stress-strain curve?

    <p>Tissue has a wavy appearance and slack is being taken up</p> Signup and view all the answers

    How does extensibility differ from creep in tissue mechanics?

    <p>Extensibility refers to immediate elongation, while creep occurs under sustained low-level stress.</p> Signup and view all the answers

    Which of the following statements about viscoelasticity is accurate?

    <p>It permits tissues to change shape but return to the original form with light force.</p> Signup and view all the answers

    What is the purpose of applying heat to tissue before stretching?

    <p>To lower viscosity and enhance pliability of the tissue</p> Signup and view all the answers

    In the context of muscle mechanics, what does strain refer to?

    <p>The degree of deformation a tissue can tolerate before injury</p> Signup and view all the answers

    Which characteristic of human tissue does the stress-strain curve represent?

    <p>The reaction of human tissue to varying applied stresses</p> Signup and view all the answers

    What factor besides muscle force influences the torque produced at a joint?

    <p>The moment arm of the muscle</p> Signup and view all the answers

    How does the speed of contraction affect the force developed by a muscle?

    <p>Slower speeds allow for greater force development</p> Signup and view all the answers

    What primarily determines the amount of active tension produced during muscle contractions?

    <p>The number of activated motor units and their firing rate</p> Signup and view all the answers

    What is the relationship between the number of cross bridges formed and the speed of muscle contraction?

    <p>Fewer cross bridges are formed at higher speeds</p> Signup and view all the answers

    What effect does recruiting a greater number of motor units have on muscle contraction?

    <p>It allows for greater active tension production</p> Signup and view all the answers

    What happens to the force-generating capacity of a muscle as the contraction speed increases?

    <p>The force-generating capacity decreases</p> Signup and view all the answers

    What defines the concept of active tension within muscle fibers?

    <p>The force created by cross bridges between actin and myosin</p> Signup and view all the answers

    Why does a muscle exhibit a decreased ability to produce force with increasing contraction speed?

    <p>As a result of reduced cross bridge cycling time</p> Signup and view all the answers

    Which muscle architecture provides greater speed of motion?

    <p>Muscles in series</p> Signup and view all the answers

    What is the relationship between muscle size and strength?

    <p>Larger muscles typically exhibit greater strength.</p> Signup and view all the answers

    Which type of muscle fiber arrangement sacrifices speed for greater force production?

    <p>Pennate muscle fibers</p> Signup and view all the answers

    What effect occurs as the muscle is lengthened in terms of active tension?

    <p>Active tension decreases while passive tension increases</p> Signup and view all the answers

    What describes a key characteristic of fusiform muscles?

    <p>They allow for greater shortening distance with less force.</p> Signup and view all the answers

    What is the optimal sarcomere length at which active tension is developed?

    <p>Between 75% to 105% of resting length</p> Signup and view all the answers

    How do pennate muscles differ from fusiform muscles in terms of their design?

    <p>Pennate muscles attach at angles to a central tendon while fusiform muscles are parallel.</p> Signup and view all the answers

    How does the moment arm of a muscle affect its torque generation?

    <p>Torque varies depending on joint position and moment arm alignment</p> Signup and view all the answers

    Which factor does NOT directly impact muscle strength?

    <p>Dietary fat intake</p> Signup and view all the answers

    What characterizes the total length-tension relationship curve of a muscle?

    <p>It is a combination of both active and passive length-tension relationships</p> Signup and view all the answers

    What happens to muscle fibers when they are arranged in parallel?

    <p>They create greater forces.</p> Signup and view all the answers

    What happens to the force generated by muscle fibers as they get closer together?

    <p>Force generation decreases due to reduced actin-myosin interactions</p> Signup and view all the answers

    Which of the following statements about muscle hypertrophy is correct?

    <p>It can occur due to inactivity over time.</p> Signup and view all the answers

    What is indicated by the plateau in the active length-tension relationship curve?

    <p>Optimal sarcomere length with maximal actin-myosin cross bridge formation</p> Signup and view all the answers

    What happens to isometric tension as a muscle is lengthened beyond resting length?

    <p>It decreases progressively with lengthening</p> Signup and view all the answers

    Why do joints limit extreme shortening or lengthening of muscles?

    <p>To avoid potentially injurious ranges of motion</p> Signup and view all the answers

    What is the relationship between the size of motor neurons and their excitability?

    <p>Larger motor neurons are less excitable.</p> Signup and view all the answers

    Which muscle fiber type is primarily recruited for long-lasting activities?

    <p>Type one fibers</p> Signup and view all the answers

    How does grip strength compare between genders before puberty?

    <p>Grip strength is about the same in both genders.</p> Signup and view all the answers

    At what stage does male muscle mass significantly increase compared to female muscle mass?

    <p>After puberty</p> Signup and view all the answers

    What are the factors influencing exceptions in muscle strength between individuals?

    <p>Genetics and specific conditioning levels</p> Signup and view all the answers

    What is the primary muscle fiber type used for quick bursts of activity?

    <p>Type two fibers</p> Signup and view all the answers

    What trend is observed in grip strength from childhood to adulthood?

    <p>Grip strength peaks between the ages of 20 to 30.</p> Signup and view all the answers

    Which of the following statements is true regarding muscle strength per cross-sectional area?

    <p>Muscle strength per cross-sectional area is similar across genders.</p> Signup and view all the answers

    What primarily contributes to the increase in passive tension in a muscle?

    <p>The stretch of elastic components like fascia</p> Signup and view all the answers

    At what condition is the resting length of a muscle defined?

    <p>When there are maximum available cross bridges</p> Signup and view all the answers

    What happens to active tension as the muscle shortens beyond its resting length?

    <p>Active tension declines due to fewer cross bridges</p> Signup and view all the answers

    Which architectural design is commonly seen in the muscles of the body?

    <p>Multipennate</p> Signup and view all the answers

    How does passive tension behave after the muscle length exceeds its resting position?

    <p>It increases as the muscle is stretched further</p> Signup and view all the answers

    What defines the contribution of passive tension to overall muscle force during lengthening?

    <p>It adds to active tension during muscle lengthening</p> Signup and view all the answers

    What is the relationship between muscle stiffness and passive tension?

    <p>Increased passive tension contributes to increased muscle stiffness</p> Signup and view all the answers

    What occurs when the sarcomere reaches its shortest position?

    <p>There are no remaining cross bridges</p> Signup and view all the answers

    Study Notes

    Nervous System Overview

    • Comprised of two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
    • CNS includes the brain and spinal cord; PNS consists of nerves that leave the CNS, including cranial nerves.
    • Peripheral nerve fibers are organized into sensory, motor, and mixed nerves (containing both neuron types).

    Neuron Types and Functions

    • Afferent neurons: Transmit sensory information to the CNS.
    • Efferent neurons: Regulate movement and motor behavior, sending signals from the CNS to the body.
    • Upper motor neurons: Located in the CNS; their cell bodies and axons reside in the brain and spinal cord.
    • Neurons vary in shape and size, typically consisting of a cell body, dendrites (short processes), and a long axon that ends in axon terminals.

    Muscle Contraction Mechanism

    • The motor unit: Functional unit of muscle contraction, includes an alpha motor neuron and the muscle fibers it innervates.
    • Alpha motor neurons are primarily responsible for skeletal muscle innervation.
    • Each muscle contains multiple motor units, varying in fiber numbers and motor units.

    Action Potential and Muscle Impulse

    • The nervous system uses action potentials to control muscle fibers.
    • At the neuromuscular junction (a specialized synapse), nerve fibers connect tightly to muscle fibers without penetrating their membranes.
    • Acetylcholine is synthesized in mitochondria at this junction, triggering muscle contractions.

    Membrane Potentials

    • Living cells have a potential difference across their membranes due to ion distribution; intracellular fluids are typically negative, whereas extracellular fluids are positive.
    • Resting potential: The negative membrane potential, ranging from -60 to -90 millivolts when cells are inactive.
    • Irritability: The ability of nervous and muscular tissues to react to a stimulus.
    • Upon stimulation, cells undergo depolarization, making the membrane potential less negative and more positive, allowing the electrochemical impulse to propagate.

    Muscle Structure

    • Muscles are encased in epimysium, a thin connective tissue, ensuring separation between adjacent muscles.
    • Fasciculus refers to subdivisions within a muscle, composed of multiple muscle fibers.
    • Muscle fibers, or muscle cells, are the building blocks of muscles and contain several nuclei.
    • Myofibrils are rod-like structures within muscle fibers, spanning their entire length.

    Myofibril Composition

    • Each myofibril is enveloped by a sarcolemma and filled with sarcoplasm, a gelatin-like substance housing mitochondria and sarcoplasmic reticulum.
    • Mitochondria are responsible for metabolic processes within muscle cells.
    • Myofibrils comprise bundles of myofilaments, which consist of actin (thin filament) and myosin (thick filament).

    Sarcomere Structure

    • The sarcomere is the functional unit of a myofibril, defined by Z-lines at both ends.
    • Myosin filaments dominate the A band, which overlaps with actin, while the H band solely comprises myosin.
    • I bands consist only of actin filaments and are anchored to the Z lines.

    Muscle Contraction Mechanics

    • During muscle contraction, the A band remains constant in length, while the I band shortens and the H band can disappear as Z lines move closer together.
    • Actin filaments slide towards each other during contraction, facilitated by cross-bridge interactions.

    Cross-Bridge Mechanism

    • Myosin has protruding cross-bridges that connect to actin during muscle activation, allowing for muscle shortening.
    • The process of crossing bridges involves ATP, which energizes myosin to interact with actin.
    • Calcium ions released from the sarcoplasmic reticulum trigger the coupling of cross-bridges with actin binding sites.

    Sliding Filament Theory

    • This theory posits that muscle contraction is generated by actin and myosin filaments sliding past one another.
    • A strong contraction requires many repetitions of the cross-bridge cycle, activating numerous sites.
    • ATP splits to release energy, facilitating the flexion of myosin heads that pull actin filaments closer.

    Muscle Activation and Recovery

    • The cycle of coupling, flexing, uncoupling, and re-coupling occurs rapidly to sustain muscle contraction.
    • Z-lines approach one another, contributing to the overall shortening of the muscle during contraction.

    Motor Units and Recruitment Principles

    • A motor unit consists of a single motor neuron and the muscle fibers it innervates, varying from three muscle fibers in eye muscles to hundreds in limb muscles.
    • All muscle fibers within a motor unit contract or relax simultaneously due to the all-or-none principle.
    • The size principle indicates that smaller motor neurons are recruited first for tasks requiring less force, while larger, fast-twitch motor units are recruited for greater strength.
    • Recruitment principle states that activating more motor units simultaneously increases overall muscle tension.
    • Rate coding principle shows that increasing the frequency of motor neuron stimulation raises the muscle fibers' tension by summing twitch contractions.

    Sensory Signals and Proprioception

    • Proprioceptors provide sensory feedback regarding muscle tension and position, integrating with inputs from the eyes and vestibular system for balanced motor control.
    • Proprioception involves feedback from muscle spindles, tendons, and joints, conveying joint position and movement specifics such as direction and speed.
    • Kinesthesia refers to the awareness of dynamic joint motion, while static position awareness is simply referred to as position sense.

    Muscle Spindles and Muscle Tone

    • Muscle spindles act as stretch receptors located within skeletal muscles, alerting the nervous system to muscle length and stretch rate changes.
    • Small muscles (e.g., eye, hand, foot) contain numerous muscle spindles for heightened sensitivity to movement changes.
    • Muscle tone, defined as resting tension and stiffness, reflects the excitability of motor neuron pools and intrinsic muscle stiffness, heavily affected by muscle spindle sensitivity.

    Reflex Mechanisms in Motor Control

    • The spinal cord plays a crucial role in reflex actions, muscle synergy, and central pattern generators.
    • Stretch reflex involves a quick response to sudden muscle stretch via spinal impulses, leading to muscle contraction (e.g., knee-jerk reflex).
    • Reciprocal inhibition occurs when one muscle contracts while its opposing muscle relaxes, facilitating movements such as stretching (e.g., contracting quadriceps while stretching hamstrings).

    Central Pattern Generators

    • Central pattern generators enable complex and adaptable movement patterns like walking and stepping, involving interconnected spinal interneurons.
    • These adaptable networks facilitate coordinated activation of flexor and extensor muscles based on sensory feedback and task demands, allowing for workflow efficiency and responsiveness to environmental changes.

    Muscle Contraction Types

    • Isometric Contraction: Static contraction with no change in joint angle; muscle produces force without notable length change.
    • Muscle Strength Definition: Force generated about a joint during maximum isometric contraction.
    • Isotonic Contraction: Muscle tension remains constant while muscle shortens or lengthens; often misunderstood as any joint movement.
    • Concentric Contraction: Muscle shortens to overcome external resistance, moving body segments.
    • Eccentric Contraction: Muscle lengthens under tension; insertion points move away as the muscle returns to normal length, involved in deceleration and shock absorption.

    Isokinetic Contraction

    • Isokinetic Contraction: Rate of movement remains constant; utilizes specialized devices to control speed without allowing acceleration.
    • Device Mechanics: Aligns with rotational axis of joints; accommodates resistance to maintain maximum muscle output through motion.

    Electromyography (EMG)

    • Electromyography: Technique to record muscle output activity using surface or indwelling electrodes.
    • Multi-Channel Instruments: Allow simultaneous recording of multiple muscles' contraction and relaxation patterns.
    • EMG Application: Analyzes sequence of muscle activation and relaxation during various activities.

    Muscle Classification

    • Agonist: Principal muscle producing motion or maintaining posture; actively contracts during actions (concentric, eccentric, isometric).
    • Antagonist: Muscle that opposes the action of the agonist; typically inactive during activities but allows for desired movements through passive elongation.
    • Synergist: Muscle that assists agonistic actions; may provide identical or complementary actions to assist movement.

    Muscle Function and Considerations

    • Functional Relationships: Agonist, antagonist, and synergist relationships vary based on activity, body position, and resistance direction.
    • Identifying Muscle Actions: Requires understanding anatomical attachments; proximal attachments stabilize while distal ones move in concentric contractions.
    • Synergistic Actions: Critical for effective movement; without synergists, agonist actions can be inefficient.

    EMG in Different Positions

    • Gravity's Role: Movement of distal segments often assisted by gravity; muscles rarely act alone, usually in conjunction with others.
    • Example of EMG Activation: During elbow flexion against gravity, the biceps is activated; in a supine position, the triceps may perform eccentric control while bending the elbow.

    Muscle Characteristics and Mechanical Properties

    • Stress: A force applied to a tissue segment, categorized into compression, shear, torsion, bending, and twisting.
    • Strain: Deformation proportional to stress, indicating how much a tissue can stretch before injury.
    • Extensibility: The ability of tissue to stretch, elongate, or expand; relevant in rehabilitation through techniques like creep.
    • Creep: Elongation of tissue due to low-level stress over time, helpful for gentle stretching of tissues.
    • Viscosity: Resistance to flow or deformation; human tissues exhibit viscosity similar to fluids, impacting how they respond to heating or cooling.
    • Elasticity: Capability to return to original length after being stretched, illustrated by rubber bands.
    • Viscoelasticity: Resistance to change in shape, characterized by permanent deformation beyond elastic limits.

    Stress-Strain Curve

    • Stress-Strain Curve: Displays the relationship between stress (force) and strain (deformation) for different tissues, with distinct regions.
    • Toe Region: Initial phase where tissue slack is removed. Tissue appears crimped or wavy at rest.
    • Elastic Range: Tissue elongates linearly in response to stress, returning to normal length when force is released.
    • Plastic Region: Beyond elastic limits, tissue begins to experience microscopic damage leading to a permanent change in length.
    • Necking Range: Increased microscopic ruptures occur, weakening the tissue significantly.
    • Failure Range: Critical point where tissue suddenly ruptures, indicating the structural limits have been exceeded.

    Muscle Excursion and Function

    • Functional Excursion: The maximum distance a muscle can shorten after being elongated, heavily influenced by joint movement.
    • Two-Joint Muscles: Exhibit the greatest variation in excursion; clinical estimates suggest a maximum shortening of 70% from resting length.
    • Active Muscle Insufficiency: Occurs when a muscle cannot shorten sufficiently to enable full range of motion across all joints it crosses, as seen in finger flexors with a flexed wrist.
    • Passive Muscle Insufficiency: Happens when a two-joint muscle cannot stretch enough for full motion at all crossed joints, leading to limitations, such as finger extensors unable to accommodate a fully flexed wrist.

    Muscle Mechanics

    • Actin-Myosin Interaction: Shortening of a muscle reduces overlap between actin and myosin, affecting cross-bridge formation and overall contractile strength.
    • Optimal Length: The length at which muscles generate maximum force; if lengthened too far, cross-bridge formation declines, impacting muscle strength and function.

    Muscle Force Fundamentals

    • Muscle force generation relies on multiple factors including neurological, metabolic, endocrine, and psychological aspects.
    • Key anatomical factors influencing muscle strength include muscle size, fiber architecture, passive components, length-tension relationships, moment arm length, contraction speed, and age/gender.

    Muscle Fiber Arrangement

    • Parallel fibers: Side-by-side arrangement leads to greater force output.
    • Series fibers: End-to-end arrangement provides increased speed of motion.
    • A muscle's strength correlates with its cross-sectional area; larger cross-sectional muscles are stronger than smaller counterparts.

    Muscle Types

    • Fusiform/strap muscles: Long and parallel fascicles; allow for greater shortening distances but produce less force (e.g., sartorius muscle).
    • Pennate muscles: Fibers attach obliquely to a central tendon. Variants include:
      • Unipennate: One parallel fiber group.
      • Bipennate: Two fiber groups.
      • Multipennate: Multiple fiber groups with more than one tendon; these typically produce more force at the cost of speed.

    Passive and Active Tension

    • Passive components (fascia, endomysium, perimysium, epimysium) contribute to muscle stiffness and elastic properties.
    • Passive tension: Increases as a muscle stretches beyond resting length, akin to stretching a rubber band.
    • Active tension: Generated through actin-myosin cross-bridges during muscle contraction; diminishes as muscles shorten or lengthen beyond their resting length.

    Length-Tension Relationships

    • Optimal sarcomere length maximizes active tension, typically between 75%-105% of resting length.
    • As muscle length deviates from optimal, both active and passive tensions alter, with active tension declining at extremes.
    • Total muscle tension is a combination of active and passive components, showing a plateau at optimal muscle length.

    Moment Arm and Torque

    • The moment arm functions as a lever arm for rotation around joints, affecting torque generation.
    • Torque varies depending on the muscle's position during a joint's range of motion, influencing the moment arm length relative to joints.

    Muscle Contraction Speed

    • An inverse relationship exists between contraction speed and force; slower contractions yield higher force due to increased cross-bridge interactions.
    • Maximum isometric tension occurs at zero velocity, as cross-bridge formation maximizes in static conditions.

    Motor Unit Recruitment

    • Active tension depends on the number and firing rate of motor units, which are composed of a motor neuron and the associated muscle fibers.
    • Smaller motor units are recruited before larger ones, and type I (slow-twitch) fibers activate prior to type II (fast-twitch) fibers.

    Age and Gender Influences

    • Males generally exhibit greater strength than females, especially noticeable after puberty.
    • Muscle strength increases from infancy to adolescence, peaking between ages 20 to 30, followed by gradual decline.
    • After puberty, males can develop up to 50% more muscle mass than females, although muscle strength per cross-sectional area remains similar across genders.
    • Individual variations exist due to genetic factors and conditioning influenced by diet and exercise.

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    Related Documents

    Nervous System and Action Potential PDF
    Muscle Structure and Function PDF
    Motor Recruitment PDF
    2.5 Motor Activity PDF
    Muscle Characteristics PDF
    Muscle Force Lecture PDF

    Description

    Test your knowledge on the nervous system and action potentials. This quiz covers both the central and peripheral nervous systems, including their structures and functions. Ensure you understand key concepts like cranial nerves and nerve organization.

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