Movement Science Wk 1 - Structure and Function of Muscle

Questions and Answers

What specifically occurs at the neuromuscular junction?

Actin and myosin filaments slide past each other.

Motor neuron releases acetylcholine to communicate with muscle fibers. (correct)

Calcium is released into the muscle fiber.

ATP is synthesized to fuel muscle contraction.

Which type of muscle fibers would be most efficient for a marathon runner?

Type IIb Fibers (fast glycolytic)

Type IIa Fibers (fast oxidative)

Type III Fibers (hypothetical)

Type I Fibers (slow-twitch) (correct)

In the sliding filament theory, what role do myosin heads play?

Myosin heads release ATP to provide energy during contraction.

Myosin heads bind to calcium to initiate contraction.

Myosin heads pull actin filaments toward the sarcomere center. (correct)

Myosin heads transport calcium ions to troponin.

What is the primary function of the epimysium?

It surrounds the entire muscle. Signup and view all the answers

Which energy system is primarily utilized during a 100-meter sprint?

Phosphagen System Signup and view all the answers

What causes fatigue during prolonged muscular activity?

Accumulation of lactic acid and depletion of ATP. Signup and view all the answers

In excitation-contraction coupling, calcium ions primarily interact with which protein?

Troponin Signup and view all the answers

What is a characteristic feature of Type IIa muscle fibers?

Ability to utilize both aerobic and anaerobic metabolism. Signup and view all the answers

Which connective tissue surrounds individual muscle fibers?

Endomysium Signup and view all the answers

What triggers the release of calcium ions during muscle contraction?

Action potentials in the muscle fiber. Signup and view all the answers

Which component of the nervous system is responsible for sending sensory information to the central nervous system?

Afferent nerves Signup and view all the answers

What is the primary role of efferent nerves in the nervous system?

Facilitate movement and motor behavior Signup and view all the answers

What are upper motor neurons primarily associated with?

Cell bodies located in the brain and spinal cord Signup and view all the answers

Which part of a neuron is responsible for receiving signals from other neurons?

Dendrites Signup and view all the answers

What initiates an action potential in a neuron?

Change in membrane potential Signup and view all the answers

Which of the following best describes the structure of a motor unit?

One motor neuron and all the muscle fibers it innervates Signup and view all the answers

What is the purpose of an action potential in the context of movement?

To transmit signals for muscle contraction Signup and view all the answers

The central nervous system is primarily composed of which of the following?

Brain and spinal cord Signup and view all the answers

Which component of a neuron contains the nucleus?

Cell body Signup and view all the answers

How does the speed of a contraction affect the force that a muscle can develop?

Slower contractions lead to increased force development. Signup and view all the answers

Which statement best describes the principle of active tension in muscle force production?

Active tension is generated by cross bridges between actin and myosin. Signup and view all the answers

What effect does age have on muscle strength, according to current observations?

Grip strength in males and females is equal before puberty. Signup and view all the answers

What is the effect of motor neuron size on its excitability?

Larger motor neurons are less excitable. Signup and view all the answers

What phenomenon occurs when a two-joint muscle cannot for a full range of motion due to its position?

Active Muscle Insufficiency Signup and view all the answers

What role do the z-lines play within a sarcomere?

They mark the boundaries between adjacent sarcomeres. Signup and view all the answers

What happens to the I band during muscle contraction?

It decreases in width. Signup and view all the answers

Which statement best describes the role of actin in muscle contraction?

Actin serves as a thin filament that interacts with myosin during contraction. Signup and view all the answers

What is the primary function of the perimysium in muscle tissue?

It subdivides muscles into fasciculi. Signup and view all the answers

Which principle describes the recruitment of muscle fibers during increased tension?

Size principle. Signup and view all the answers

What structural change occurs in the H band during muscle contraction?

It no longer exists. Signup and view all the answers

How are the myosin and actin filaments arranged within a sarcomere?

They are positioned to create distinct light and dark bands. Signup and view all the answers

Which process occurs during the coupling phase of muscle contraction?

Myosin heads split ATP into ADP and energy. Signup and view all the answers

What is described as the maximum distance a muscle can shorten after being fully elongated?

Functional excursion Signup and view all the answers

What occurs when a two-joint muscle cannot stretch sufficiently for full range of motion in the opposing direction?

Passive muscle insufficiency Signup and view all the answers

Which muscle fiber type is designed to provide greater shortening distance at the expense of force?

Fusiform muscle fibers Signup and view all the answers

Within the length-tension relationship, what occurs to active tension as the muscle shortens?

It decreases Signup and view all the answers

What structural characteristic typically provides parallel muscle fibers with greater force compared to series muscle fibers?

Muscle width Signup and view all the answers

What is the relationship between muscle fibers' intensities and the arrangement of muscle fibers in a pennate formation?

More fibers yield greater force Signup and view all the answers

Which of the following muscle properties primarily contribute to muscle tension during lengthening?

Passive tension Signup and view all the answers

In the context of muscle function, what does the moment arm of a muscle primarily affect?

Joint torque Signup and view all the answers

What primarily determines muscle tone?

Level of excitability of motor neurons Signup and view all the answers

Which type of muscle fiber is characterized by high myoglobin content and is fatigue-resistant?

Type I fibers Signup and view all the answers

Which type of muscle fibers, when arranged in series, is associated with increased speed of motion?

Fusiform Signup and view all the answers

As a muscle lengthens beyond its resting position, what happens to the ability to produce active tension?

It decreases due to fewer cross bridges Signup and view all the answers

What is the correct order of motor unit recruitment?

Small slow-twitch motor units first, then large fast-twitch units Signup and view all the answers

What is the main function of muscle spindles?

To provide information about muscle length and stretch rate Signup and view all the answers

What characterizes Type IIb muscle fibers?

Low myoglobin, few mitochondria, and high glycolytic enzyme content Signup and view all the answers

How does reciprocal inhibition function during muscle activation?

Opposing muscles are activated while agonist muscles are inhibited Signup and view all the answers

What primarily influences the adaptation of muscle fiber types?

Changing demands of physical activities Signup and view all the answers

What does EMG stand for, and what is its purpose?

Electromyography for recording electrical activity of muscles Signup and view all the answers

In muscle activation, what defines an isotonic contraction?

Muscle tension remains constant as the muscle shortens or lengthens Signup and view all the answers

What primarily causes a twitch contraction of a muscle fiber?

Firing of a single motor unit Signup and view all the answers

Study Notes

Neural Control Of Muscle Movement

Motor Units: Composed of a motor neuron and the muscle fibers it innervates.
Neuromuscular Junction: Site where motor neuron communicates with muscle fiber, releasing acetylcholine (ACh).
Action Potential: Electrical signal that travels along the motor neuron to trigger muscle contraction.
Excitation-Contraction Coupling: Process linking action potential in muscle fiber to muscle contraction, involving calcium release from the sarcoplasmic reticulum.

Muscle Fiber Types

Type I Fibers (Slow-Twitch):
- High endurance, fatigue-resistant.
- Rich in myoglobin and mitochondria.
- Primarily used in aerobic activities (e.g., long-distance running).
Type II Fibers (Fast-Twitch):
- Subdivided into Type IIa (fast oxidative) and Type IIb (fast glycolytic).
- Type IIa: Moderate endurance, can use both aerobic and anaerobic metabolism.
- Type IIb: Low endurance, primarily anaerobic, used for short bursts of power (e.g., sprinting).

Muscle Contraction Mechanisms

Sliding Filament Theory:
- Actin and myosin filaments slide past each other, causing muscle shortening.
Cross-Bridge Cycle:
- Myosin heads bind to actin, pull, release, and reset for continued contraction.
Role of Calcium (Ca2+):
- Calcium ions bind to troponin, moving tropomyosin away from actin binding sites, allowing contraction.

Muscle Anatomy

Muscle Structure:
- Composed of bundles (fascicles) of muscle fibers.
- Each fiber contains myofibrils, which contain sarcomeres (functional units).
Connective Tissue:
- Endomysium: Surrounds individual muscle fibers.
- Perimysium: Surrounds fascicles.
- Epimysium: Surrounds the entire muscle.
Tendons: Connect muscle to bone, transmitting force generated during contraction.

Energy Production In Muscles

ATP (Adenosine Triphosphate): Primary energy currency for muscle contraction.
Energy Systems:
- Phosphagen System: Provides immediate energy via creatine phosphate for short bursts.
- Anaerobic Glycolysis: Breaks down glucose without oxygen for fast but limited energy.
- Aerobic Respiration: Utilizes oxygen for long-lasting energy, producing ATP from carbohydrates and fats.
Fatigue: Result of depletion of energy reserves (ATP, glycogen) and accumulation of metabolic byproducts like lactic acid.

Neural Control Of Muscle Movement

Motor units consist of a motor neuron and the muscle fibers it innervates, crucial for muscle activation.
The neuromuscular junction is where motor neurons release acetylcholine (ACh) to communicate with muscle fibers.
An action potential is an electrical signal that travels along the motor neuron, essential for initiating muscle contraction.
Excitation-contraction coupling involves the release of calcium ions from the sarcoplasmic reticulum, linking the action potential to muscle contraction.

Muscle Fiber Types

Type I fibers, known as slow-twitch fibers, are characterized by high endurance and resistance to fatigue.
- They contain a high concentration of myoglobin and mitochondria, making them suitable for aerobic activities like long-distance running.
Type II fibers, or fast-twitch fibers, are divided into:
- Type IIa (fast oxidative) fibers provide moderate endurance and can utilize both aerobic and anaerobic metabolism.
- Type IIb (fast glycolytic) fibers are suited for low endurance activities and primarily rely on anaerobic metabolism for quick, explosive movements such as sprinting.

Muscle Contraction Mechanisms

The sliding filament theory explains that actin and myosin filaments slide past each other, resulting in muscle shortening during contraction.
The cross-bridge cycle describes the process where myosin heads bind to actin, perform a power stroke, release, and reset, allowing continued contraction.
Calcium ions play a crucial role by binding to troponin, which shifts tropomyosin away from actin binding sites, enabling contraction to occur.

Muscle Anatomy

Muscles are structured in bundles known as fascicles, each containing individual muscle fibers.
- Muscle fibers consist of myofibrils, which include functional units called sarcomeres.
Connective tissue envelops the muscle components:
- Endomysium surrounds each muscle fiber.
- Perimysium encases bundles of fibers (fascicles).
- Epimysium covers the entire muscle, providing structural support.
Tendons are fibrous connective tissues that connect muscles to bones, transmitting the force generated during muscle contraction.

Energy Production In Muscles

ATP (Adenosine Triphosphate) serves as the primary energy currency required for muscle contractions.
Muscle energy systems include:
- The phosphagen system, which supplies immediate energy through creatine phosphate for short, explosive efforts.
- Anaerobic glycolysis, which breaks down glucose without oxygen to yield fast but limited energy.
- Aerobic respiration, which generates sustained energy by utilizing oxygen to produce ATP from carbohydrates and fats.
Muscle fatigue occurs due to the depletion of energy reserves (ATP, glycogen) and the accumulation of metabolic byproducts such as lactic acid.

Nervous System Components

Central Nervous System (CNS) encompasses the brain and spinal cord, acting as the control center for processing information and coordinating responses.
Peripheral Nervous System (PNS) connects the CNS to the rest of the body, including limbs and organs.
Afferent Nerves transmit sensory information from peripheral receptors to the CNS, allowing the body to perceive environmental stimuli.
Efferent Nerves convey signals from the CNS to muscles and glands, regulating movement and motor behavior.

Motor Unit

A motor unit consists of a single motor neuron and all the muscle fibers it innervates, working together to produce muscle contractions.
The size of a motor unit influences the precision of movement; smaller units allow for fine motor control, while larger units produce more force.

Neuron Structure

Neurons are the fundamental units of the nervous system, comprised of a cell body containing the nucleus, dendrites for receiving signals, and an axon for transmitting impulses.
Axon terminals release neurotransmitters to communicate with other neurons or muscle fibers.

Action Potential

An action potential is a rapid electrical signal that travels along the axon of a neuron, resulting from the movement of ions across the neuron's membrane.
Its purpose in movement is to initiate and propagate signals that lead to muscle contraction, contributing to physical activity and reflexes.

Upper Motor Neurons

Initial efferent signals originate from upper motor neurons located within the CNS, with their connections and cell bodies situated in the brain and spinal cord.
These neurons play a crucial role in controlling voluntary movements by sending commands to spinal motor neurons.

Muscle Structure and Function

Muscle fibers, also known as muscle cells, are the basic building blocks of muscles.
Epimysium is a thin connective tissue that surrounds each muscle, separating it from adjacent muscles.
The perimysium subdivides the muscle into sections called fasciculi, each composed of numerous muscle fibers.
Myofibrils within muscle fibers span the length of each fiber and are surrounded by the sarcolemma and sarcoplasm.
Each myofibril contains myofilaments made of actin (thin filament) and myosin (thick filament).
A sarcomere, the basic functional unit of a myofibril, is defined by z-lines and includes actin and myosin.

Sarcomere Structure

Sarcomeres create light and dark striations seen in skeletal muscle, with A bands being darker and H bands containing only myosin.
The I band contains only actin and decreases during muscle contraction.
Muscle contraction involves actin filaments sliding past myosin to shorten the muscle.

Muscle Contraction and Relaxation

During contraction, the I band decreases, and H band disappears, as actin slides toward the center.
The sliding filament theory explains how actin and myosin interact to produce muscle contraction.
Myosin heads form cross-bridges with actin, releasing energy from ATP for muscle movement.

Motor Recruitment and Sensory Signals

Smallest motor units are activated first, increasing muscle tension through the recruitment principle.
Firing rate coding principle states that increasing the frequency of stimulation results in maximum tension.
All muscle fibers in a motor unit contract simultaneously due to the All-or-None principle.
Proprioceptors provide feedback on muscle tension and position, aiding movement control.

Muscle Fiber Types

Type I (slow-twitch) fibers are aerobic, fatigue-resistant, and high in myoglobin, suited for endurance.
Type II (fast-twitch) fibers are larger, quicker to fatigue, and ideal for short bursts of strength.
Type IIa fibers show characteristics of both Type I and II, while Type IIb fibers have high glycolytic enzyme content.

Muscle Activity Types

Isometric: Muscle generates force without changing joint angle.
Isotonic: Muscle tension remains constant while changing length, with concentric shortening and eccentric lengthening.
Isokinetic: Muscle contracts at a constant rate of movement.

Muscle Functional Activity

Agonist muscles produce movement, while antagonists oppose the motion, with synergists assisting the agonist.
Muscle relationships can change based on body position and activity demands.

Muscle Characteristics

Stress refers to the force applied, and strain describes deformation under stress.
Extensibility is the ability to stretch, while elasticity refers to returning to original length after stretching.
Creep occurs when low-level loads cause elongation over time.

Active and Passive Muscle Insufficiency

Active insufficiency occurs when a muscle cannot shorten enough to produce full motion across multiple joints.
Passive insufficiency happens when a two-joint muscle cannot stretch sufficiently for full range motion in the opposite direction.

Muscle Force Factors

Influenced by muscle size, architecture, passive components, moment arm, and speed of contraction.
Parallel muscle fibers provide greater force, while series fibers enhance speed.
Pennate fibers, arranged at angles, produce greater force at the cost of speed.

Length-Tension Relationship

Maximum force develops when muscles are at resting length due to optimal cross-bridge formation.
Active tension decreases when muscles are stretched beyond resting length.

Moment Arm and Torque Production

The moment arm affects the torque a muscle can generate around a joint.
Muscle ability to produce torque is determined by its force and moment arm at specific joint angles.

Speed of Contraction

Speed inversely correlates with force; slower contraction allows for greater force development.
Maximum isometric force occurs with no movement, while faster speeds reduce effective force due to fewer cross-bridges.

Active Tension Production

Active tension results from cross-bridge formations between actin and myosin.
The quantity of active tension is influenced by motor unit recruitment and firing rates.### Muscle Fiber Recruitment and Function
Muscle fibers vary in recruitment; slower type I fibers are engaged before faster type II fibers.
Type I fibers support endurance and posture; type II fibers are activated for quick, powerful movements.
Motor unit recruitment follows a size principle, progressing from smaller to larger muscle cells.

Age and Gender Influence on Muscle Strength

Muscle strength develops from birth until adolescence, peaking around ages 20-30 before declining gradually.
Grip strength is comparable between genders until puberty, after which males typically show superior grip strength.
Significant strength differences emerge during middle age, attributed to increased muscle mass in males post-puberty; men can have up to 50% more muscle mass than women.
Despite gender differences in muscle mass, muscle strength per cross-sectional area remains similar across genders.
Proportion of fast-twitch muscle fibers is comparable in both genders.

Variability in Muscle Development

Variability in biological maturation rates can lead to differences in muscle development.
Individual genetics and conditioning greatly influence muscle strength, reinforced through diet and exercise.

Muscle Characteristics

Extensibility: The ability of muscle tissue to stretch or expand.
Creep: Lengthening of tissue due to sustained low-level loads over time.
Viscosity: Internal resistance to flow, resulting in friction.
Elasticity: Capacity to stretch and return to original shape after deformation.
Strain: Muscle's ability to endure stress before injury occurs.

Muscle Insufficiency

Active Muscle Insufficiency: Two-joint muscles cannot fully shorten to allow complete motion across all joints simultaneously (e.g., squeezing with a neutral wrist vs. a flexed wrist).
Passive Muscle Insufficiency: Two-joint muscles may not stretch adequately to allow full range of motion in the opposing direction (e.g., hip flexion limiting knee extension due to hamstring tightness).

Muscle Reflexes and Inhibition

Autogenic Inhibition: Golgi Tendon Organs (GTOs) sense excessive force and inhibit the contracting muscle while facilitating the opposing muscle to prevent injury.
Stretch Reflex: Detects changes in muscle length and the rate of those changes to help maintain muscle stability.
Reciprocal Inhibition: Activation of an agonist muscle leads to relaxation of the antagonist muscle, aiding coordinated motion.

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Description

This quiz covers the neural mechanisms involved in muscle movement, focusing on motor units, neuromuscular junctions, and the processes that lead to muscle contraction. Additionally, it explores different muscle fiber types and their functions, providing insights into how they are utilized in various physical activities.