Muscle Organization and Function

Muscle Organization and Function

  • Muscle organization affects power, range, and speed of muscle movement

  • Fascicles

    • Muscle cells (fibers) are organized in bundles called fascicles.

  • Classification of Skeletal Muscles

    • By the way fascicles are organized:

    • Parallel

    • Convergent

    • Pennate

    • Circular

    • By relationships of fascicles to tendons.

Parallel Muscles

  • Definition: Fascicles are parallel to the long axis of a straplike muscle.

  • Example: Biceps brachii.

  • Functional Note: The power of parallel muscles depends on the total number of myofibrils. The tension developed is directly related to the cross-section of the muscle:

    • 1 in² (6.45 cm²) of cross-section can develop 50 lb (23 kg) of tension.

Convergent Muscles

  • Definition: A broad area of muscle converges on a single attachment site, which can be a tendon, aponeurosis, or raphe.

  • Muscle Functionality: Fascicles converge toward a single tendon insertion, allowing muscle fibers to pull in different directions depending on stimulation.

  • Example: Pectoralis muscles.

Pennate Muscles

  • Definition: Fascicles form an angle with the tendon.

  • Key Characteristics:

    • Short fascicles attach obliquely to a central tendon running the length of the muscle.

    • Do not move as far as parallel muscles but contain more myofibrils and therefore develop more tension.

  • Types of Pennate Muscles:

    • Unipennate: Fibers on one side of the tendon (e.g., extensor digitorum).

    • Bipennate: Fibers on both sides of the tendon (e.g., rectus femoris).

    • Multipennate: Tendon branches within the muscle (e.g., deltoid).

Circular Muscles

  • Also called: Sphincters.

  • Definition: Fascicles arranged in concentric rings.

  • Functionality: These muscles open and close to guard entrances of the body.

  • Example: Orbicularis oris muscle of the mouth.

Origin and Insertions

  • Origin: The bone(s) that does less movement, typically superior to the insertion.

  • Insertion: The element(s) that moves when the muscle contracts.

Muscle Attachments to Other Tissues

  • Actions: Movements produced by muscle contraction, including various body movements such as flexion, extension, and adduction.

    • These actions are described in terms of bone, joint, or region.

  • Muscle Interactions: Muscles often work in groups to maximize efficiency. Smaller muscles typically reach maximum tension before larger, primary muscles.

  • Definitions of Muscle Roles:

    • Agonist (Prime Mover): Produces a particular movement.

    • Antagonist: Opposes the movement of a particular agonist.

    • Synergist: A smaller muscle that assists a larger agonist.

    • Fixator: Helps start motion or stabilize the origin of the agonist.

  • Note: Agonists and antagonists typically work in pairs. When one contracts, the other stretches (e.g., flexors–extensors, abductors–adductors).

Naming Skeletal Muscles

  • Descriptive names for skeletal muscles can be based on:

    • Location in the body.

    • Origin and insertion.

    • Fascicle organization.

    • Relative position.

    • Structural characteristics.

    • Action.

Location in the Body

  • Descriptive names identify body regions.

  • Example: Temporalis muscle.

Origin and Insertion

  • The first part of a muscle's name indicates the origin, while the second part indicates the insertion.

  • Example: Genioglossus muscle.

Fascicle Organization

  • Describes the orientation of fascicles within the muscle.

  • Examples:

    • Rectus (straight)

    • Transversus (across)

    • Oblique (angled)

Position

  • Terms:

    • Externus (superficialis): Visible at the body surface.

    • Internus (profundus): Deep muscles.

    • Extrinsic: Muscles outside an organ that provide stability.

    • Intrinsic: Muscles inside an organ.

Structural Characteristics

  • Number of tendons:

    • bi (2), tri (3).

  • Shape Terms:

    • Trapezius, deltoid, rhomboid.

  • Size Terms: Many terms refer to muscle size.

Action

  • Movement Terms:

    • Flexor

    • Extensor

    • Retractor.

  • Occupational Terms:

    • Example: Risor (laughter).

Terms Indicating Specific Regions of the Body

  • Definitions:

    • Abdominis: abdomen

    • Anconeus: elbow

    • Auricularis: auricle of ear

    • Brachialis: brachium

    • Capitis: head

    • Carpi: wrist

    • Cervicis: neck

    • Cleido-/-clavius: related to the clavicle

Additional Terms Indicating Specific Regions of the Body

  • Definitions:

    • Coccygeus: coccyx

    • Costalis: ribs

    • Cutaneous: skin

    • Femoris: femur

    • Genio-: chin

    • Glosso-/-glossal: tongue

    • Hallucis: great toe

    • Ilio-: ilium

    • Inguinal: groin

Additional Terms Indicating Specific Regions of the Body

  • Definitions:

    • Lumborum: lumbar region

    • Nasalis: nose

    • Nuchal: back of neck

    • Oculo-: eye

    • Oris: mouth

    • Palpebrae: eyelid

    • Pollicis: thumb

    • Popliteus: behind the knee

    • Psoas: loin

Additional Terms Indicating Specific Regions of the Body

  • Definitions:

    • Radialis: radius

    • Scapularis: scapula

    • Temporalis: temples

    • Thoracis: thoracic region

    • Tibialis: tibia

    • Ulnaris: ulna

    • Uro-: urinary

Terms Indicating Position

  • Definitions:

    • Anterior: front

    • Externus: superficial

    • Extrinsic: outside

    • Inferioris: below

    • Internus: deep, internal

    • Intrinsic: inside

    • Lateralis: lateral

    • Medialis/medius: medial, middle

Terms Indicating Position, Direction, or Fascicle Organization

  • Definitions:

    • Oblique: angled

    • Posterior: back

    • Profundus: deep

    • Rectus: straight, parallel

    • Superficialis: superficial

    • Superioris: above

    • Transversus: across

Terms Indicating Structural Characteristics of the Muscle

  • Nature of Origin Terms:

    • Biceps (two heads)

    • Triceps (three heads)

    • Quadriceps (four heads)

Terms Indicating Structural Characteristics of the Muscle

  • Shape Terms:

    • Deltoid (triangle)

    • Orbicularis (circle)

    • Pectinate (comblike)

    • Piriformis (pear-shaped)

    • Platy- (flat)

    • Pyramidal (pyramid)

Additional Terms Indicating Structural Characteristics of the Muscle

  • Shape Terms:

    • Rhomboid

    • Serratus (serrated)

    • Splenius (bandage)

    • Teres (long and round)

    • Trapezius (trapezoid)

Additional Terms Indicating Structural Characteristics of the Muscle

  • Other Striking Features:

    • Alba (white)

    • Brevis (short)

    • Gracilis (slender)

    • Lata (wide)

    • Latissimus (widest)

    • Longissimus (longest)

    • Longus (long)

Additional Terms Indicating Structural Characteristics of the Muscle

  • Other Striking Features:

    • Magnus (large)

    • Major (larger)

    • Maximus (largest)

    • Minimus (smallest)

    • Minor (smaller)

    • Vastus (great)

Terms Indicating Actions

  • General Actions:

    • Abductor

    • Adductor

    • Depressor

    • Extensor

    • Flexor

    • Levator

    • Pronator

    • Rotator

    • Supinator

    • Tensor

Terms Indicating Specific Actions

  • Specific Examples:

    • Buccinator (trumpeter)

    • Risorius (laughter)

    • Sartorius (like a tailor)