Clinical Kinesiology Chapter 6 Quiz

Chapter 6: Muscular System

• This chapter is from a book titled "Clinical Kinesiology and Anatomy, Seventh Edition," by Lynn S. Lippert.
• The book is published by F.A. Davis Company.

Characteristics of Muscle

• Normal resting length: the length of a muscle not changed by active contraction or external force.
• Four properties of muscle:
  • Irritability
  • Contractility
  • Extensibility
  • Elasticity

Irritability

• Ability to respond to a stimulus (nerve impulse or external stretch), resulting in a muscle contraction.

Contractility

• Ability to contract, generating force when stimulated.
• Types of contractions:
  • Concentric: muscle shortens
  • Eccentric: muscle lengthens
  • Isometric: no change in muscle length

Extensibility

• Ability of a muscle to lengthen when a force is applied.

Elasticity

• Ability to return to normal resting length after a force is removed.

Anatomy of a Muscle

• A muscle is made up of muscle fibers bundled into fascicles.
• Each muscle fiber is composed of smaller bundles called myofibrils.
• Myofibrils are divided into sarcomeres, the units where length changes occur.
• Sarcomeres contain two types of filaments: thin actin filaments and thicker myosin filaments.
• Two actin filaments are present on each side of a myosin filament.
• Actin filaments do not extend into the middle of a sarcomere.
• Myosin heads project from myosin filaments and bind with actin filaments temporarily when the muscle contracts.

Sliding Filament Theory

• Binding of myosin heads to actin is called cross-bridges.
• When myosin heads bind with actin, the actin filaments slide closer or further from the other actin filament,
  • Shortening contraction: actin filaments move toward the center of the sarcomere.
  • Lengthening contraction: actin filaments move away from the center of the sarcomere.
  • Isometric contraction: minimal sliding occurs.
• The number of cross-bridges formed determines the force generated.
• At resting length, the maximum number of cross-bridges can be formed.
• When muscle length is greater or less than resting length, the number of cross-bridges decreases, reducing force.

Fiber Types

• Type I: Slow-twitch or slow oxidative fibers
  • Smaller diameter
  • Slower to respond to stimulus
  • Sustain longer contractions
  • Rich blood supply, red color
  • Use oxygen as an energy source
  • Good for endurance and low-force activities, like postural muscles.
• Type II: Fast-twitch or fast glycolytic fibers
  • Larger diameter
  • Respond quickly to stimulus
  • Relax quickly after stimulation, avoiding fatigue
  • Less blood supply, pale (white) color
  • Use existing glycogen stores as an energy source
  • Prone to fatigue, suitable for short bursts of high-force activities.

Motor Units

• Muscle fibers, innervated by the same motor neuron.

• Fibers are distributed among several fascicles.

• Number of muscle fibers per motor unit varies.

  • Fewer fibers in motor units: precision movements
  • More fibers in motor units: powerful movements

• Gradation of the number of motor units recruited is based on the force required.

• Musculotendinous junction: where muscle meets the tendon.

• Tenoperiosteal junction: where tendon meets bone.

• Origin: proximal attachment of the muscle.

• Insertion: distal attachment of the muscle.

Muscle Fiber Arrangement

• Amount of force a muscle can generate is proportional to its cross-sectional area.
• Cross-sectional area is related to muscle fiber orientation.
  • Parallel muscle fibers: fibers extend the entire length of the muscle.
  • Oblique muscle fibers: more cross-sectional area possible, shorter; attached obliquely to tendon.
• Angle of insertion: the angle at which the muscle attaches to a bone or structure, changes throughout ROM (Range of Motion).
• Line of pull: line drawn from origin to insertion, accounts for muscle's direction of pull and the twist.
• Angle of pennation: the angle at which oblique fibers attach to muscle tendons; contributes to force.

Muscle Shapes

• Parallel muscles:
  • Strap
  • Fusiform
  • Triangular
• Oblique muscles:
  • Unipennate
  • Bipennate
  • Multipennate

Muscle Names

• Muscle names are based on different characteristics like location, shape, action, number of heads/divisions, attachments, fiber orientation, and size.

Roles of Muscles

• Agonist: muscle primarily responsible for the desired motion.
• Antagonist: muscle that performs the opposite motion of the agonist.
• Synergist: two or more muscles contracting together to produce a motion neither could perform individually.
• Co-contraction: simultaneous contraction of agonist and antagonist muscles.

Types of Muscle Contraction

• Isometric: force is produced without changing muscle length.
• Concentric: muscle attachments move toward each other, shortening the muscle, often overcoming gravity.
• Eccentric: muscle attachments move away from each other, lengthening the muscle, often slowing down movement, or deceleration.

Active and Passive Insufficiency

• Multi-joint muscles experience active and passive insufficiency.

• Active insufficiency: unable to shorten simultaneously through their full ROM at all the joints they span. -Example: biceps brachii shortening in both elbow and shoulder flexion.

• Passive insufficiency: unable to lengthen simultaneously through their full ROM at all the joints they span. -Example: hamstrings lengthening in both hip and knee extension.

• Tenodesis: a passive form of using insufficiency in certain cases.

  • Example: closing a fist using wrist extension and flexion.

Adaptive Lengthening and Shortening

• Muscle length can change over time if maintained in a shortened or lengthened position.
• This is related to the addition and/or loss of sarcomere structure in the muscle.

Common Pathologies of Muscle and Tendon

• Strain: overstretching of a muscle.
• Rupture: complete tearing of a tendon.
• Trigger points: hyperirritable, painful points in a muscle.
• Tendonitis: inflammation of a tendon.

Test your knowledge on the muscular system as covered in Chapter 6 of 'Clinical Kinesiology and Anatomy, Seventh Edition' by Lynn S. Lippert. Explore concepts such as muscle properties, types of contractions, and the anatomy of muscles. This quiz will challenge your understanding of crucial topics in kinesiology.