Introduction to Muscles of the Body

  • Discuss the configuration, pattern, and orientation of muscles in the body.
  • Muscles present in various shapes and sizes which contribute to their functions.

Muscle Fibers and Fascicles

  • Definition of fascicles as the linear lines you see running through the muscle.
    • Important to note: term "striation" not used—focus on linear patterns instead.
  • Understanding fascicular orientation helps determine muscle movement.
    • The contraction movement of a muscle affects the movement of the corresponding skeletal system.

Types of Muscle Fiber Configurations

Fusiform Muscles

  • Definition: These muscles have spindle-shaped fascicles with a tapered end.
    • Example Muscles: Biceps and Triceps.
    • Movement: Allows hinge-like motion corresponding to linear fascicle arrangement.

Circular Muscles

  • Definition: Muscles that are arranged in concentric circles.
    • Movement Pattern: Fibers contract to close an opening, resembling twisting configuration.
    • Example Locations:
    • Lips
    • Eyes
    • Anus
    • Vaginal region (labia)
    • Gastrointestinal system (stomach and intestine)
    • Bladder
    • Blood vessels (to control blood flow)
  • Example of Circular Smooth Muscle:
    • Action during pupillary reflex when exposed to bright light.

Converging Muscles

  • Definition: Muscles where fascicles converge towards a single insertion point.
    • Example Muscles: Pectoralis Major.

Parallel Muscles

  • Definition: Muscle fibers are aligned in the same orientation resembling a strap.
    • Example Muscles: Sartorius, Rectus Abdominis.
    • Parallel muscles provide a large range of motion but less power.

Pennate Muscles

  • Definition: Fascicle arrangement resembles a feather.
    • Types: Unipenate, Bipennate, and Multipennate.
    • Example of Unipenate: Fibularis Longus.
    • Example of Bipennate: Rectus Femoris.
    • Example of Multipennate: Deltoid muscle.

Muscle Characteristics and Functional Implications

  • Muscles designed for power vs. range of motion:
    • Parallel muscles offer greater range of motion.
    • Pennate muscles are stronger due to their angle of force application.
  • Example of Sartorius Muscle: Provides flexibility for movement across joints (hip and knee).
  • Example of Tensor Fascia Latae (TFL): Provides limited movement due to its weak contraction capacity despite being a strap muscle.

Naming Muscles in the Body

  • Total muscles in the human body: Approximately 487.
  • Focus on 97 primary muscles in this discussion.
  • Compartmentalizing muscles helps in memorization: based on location, action, or shape.

Location-based Naming

  • Example Muscles:
    • Biceps Brachii (arm)
    • Biceps Femoris (leg)
    • Intercostal muscles (muscles between ribs).

Shape-based Naming

  • Example Muscles:
    • Deltoid (triangular shape)
    • Trapezius (trapezoid shape)
  • Quadriceps referring to 'four bellies' (quad).

Size-based Naming

  • Terms: Maximus (large), Minimus (small), Longus (long), Brevis (short), Superficialis (more superficial), Profundus (deeper).

Direction of Fascicles

  • Rectus (vertical orientation) example: Rectus Abdominis.
  • Transverse: Muscle fibers run horizontally; example: Transverse Abdominis.
  • Oblique: Internal and External obliques have fibers oriented diagonally.

Attachment Point Naming

  • Example: Brachioradialis, which originates in the brachium and inserts in the radius.

Action-Based Naming

  • Example Muscles:
    • Pronator Teres (pronates forearm)
    • Supinator Teres (supinates forearm).
    • Various flexors based on the digits they target (e.g., Flexor pollicis for the thumb).

Muscle Origins and Insertions

  • Definition of "Origin": The fixed point of attachment that serves as an anchor.
  • Definition of "Insertion": The moving end of a muscle where it connects to the bone.
    • Most injuries occur at the insertion point during active contraction.

Examples of Injury Related to Origin and Insertion

  • Extensor Fibularis: Injury prone near the ankle rather than the knee.
  • Biceps Brachii: Common injuries near the antecubital fossa during contraction.

Primary Movers and Synergists

  • Definition of Primary Mover: The muscle primarily responsible for a specific movement.
    • Example: Trapezius has multiple functions across different sections—elevation, retraction, and depression of the shoulder.
  • Definition of Synergist: A muscle that aids the primary mover.
    • Example: Rhomboids act as synergists with the mid-fibers of the trapezius in retracting the scapula.

Functional Overview of Trapezius

  • Upper Trapezius: Responsible for shoulder elevation.
  • Mid Trapezius: Responsible for retraction of the scapula.
  • Lower Trapezius: Responsible for depressing the shoulder.