Learning unit 1 - muscle system_05c93127fd995efa72d907f1a842678a

Primary Responsibilities:
- Responsible for movement of the body and all its joints.
- Muscle contraction produces the force that causes joint movement.
Additional Functions:
- Provide protection.
- Provide dynamic stability of joints.
- Contribute to posture and support.
- Produce a major portion of total body heat.

Muscles can be categorized as Superficial and Deep.
Examples of Major Skeletal Muscles:
- Superficial: Platysma, Deltoid, Frontalis, Orbicularis oculi, Zygomaticus major, Biceps brachii, etc.
- Deep: Triceps brachii, Latissimus dorsi, Gracilis, Gastrocnemius, etc.

215 pairs of skeletal muscles usually work in cooperation to perform opposite actions at the joints they cross.
Aggregate Muscle Action: Muscles work in groups rather than independently to achieve a given joint motion.

Muscle Shape and Arrangement Implications:
- Affects muscle's ability to exert force.
- Influences range of movement effectively exerted onto the bones.
Cross-Section Diameter:
- Affects muscle's ability to exert force; greater cross-section diameter leads to greater force.
Muscle Length:
- Longer muscles can shorten through a greater range.
- More effective in moving joints through large ranges of motion.

Major Types: Parallel and Pennate.
- Parallel Muscles:
  - Arranged parallel to the length of the muscle.
  - Produce greater range of movement than similar-sized pennate muscles.
Parallel Fibers Categorization:
- Flat: E.g., Rectus abdominus, external oblique.
- Fusiform: E.g., Brachialis, biceps brachii.
- Strap: E.g., Sartorius.
- Radiate: E.g., Pectoralis major, trapezius.
- Sphincter or Circular: E.g., Orbicularis oris.
Pennate Fibers:
- Have shorter fibers, arranged obliquely to their tendons.
- Types of Pennate Muscles:
  - Unipennate: E.g., Biceps femoris, extensor digitorum longus.
  - Bipennate: E.g., Rectus femoris.
  - Multipennate: E.g., Deltoid.
- Bipennate and unipennate produce the strongest contractions.

Four Properties:
1. Irritability or Excitability: Sensitivity to stimuli (chemical, electrical, mechanical).
2. Contractility: Ability to contract and develop tension against resistance when stimulated.
3. Extensibility: Ability to be stretched beyond resting length.
4. Elasticity: Ability to return to original length after stretching.

Intrinsic: Refers to muscles within or belonging solely to the body part on which they act (e.g., small muscles in the hand).
Extrinsic: Pertains to muscles arising outside the body part on which they act (e.g., forearm muscles that insert on fingers).
Action: Specific movement of a joint resulting from muscle contraction (e.g., flexion at elbow).
- Actions usually involve groups of muscles working together.
Innervation: Segment of nervous system providing stimulus to muscle fibers in a specific muscle.
Amplitude: Range of muscle fiber length between maximal and minimal lengthening.
Gaster (Belly or Body): Central, fleshy portion of the muscle that increases in diameter when contracted.
Tendon: Fibrous connective tissue linking muscles to bones.
- A muscle may have multiple tendons (e.g., triceps brachii).
Aponeurosis: Tendinous expansion resembling a flattened tendon.
Fascia: Sheet or band of fibrous connective tissue encompassing and separating body parts.
Origin: Proximal attachment of a muscle, often the least movable part.
Insertion: Distal attachment of a muscle, generally the most movable part.

Passive Movement: Occurs without muscle contraction, solely due to external forces.
Contraction: Defined as when tension is developed in a muscle.
- Key Types: Isometric, Isotonic (Concentric and Eccentric).

Joint angles remain constant while muscle tension develops.
Important for maintaining static positions and preventing movement from external forces.

Involves active tension for joint movement.
Two types:
- Concentric Contraction: Muscle shortens while developing active tension, overcoming resistance (e.g., biceps curling).
- Eccentric Contraction: Muscle lengthens while developing active tension, controlling descent of resistance (e.g., lowering weight).

Agonist Muscles: Cause joint motion through concentric contraction; known as prime movers.
Antagonist Muscles: Opposite action to agonists; help by relaxing to allow movement.
Stabilizer Muscles: Surround joints to stabilize the area while other limbs exert force.
Synergist Muscles: Assist agonists, helping refine movements and prevent undesired motions.
- Helping Synergists: Have opposing actions to assist in movements.
- True Synergists: Prevent undesired actions without affecting the agonist's motion.
Neutralizer Muscles: Counteract actions of other muscles to prevent unwanted movements.
Force Couple Muscles: Multiple forces pulling in different directions on an object, causing rotation.

Multiple Actions: Agonist muscles perform multiple actions during contraction, depending on several factors (motor units, joint position, etc.).
Antagonistic Actions: Performance of opposite actions