Muscles (medical term)

Muscles: Types and Characteristics

Types of Muscles

  • Three types of muscles:

    • Striated Muscle:

    • Under voluntary control.

    • Responsible for movement of all bones as well as the face and eyes.

    • Smooth Muscle:

    • Control is involuntary.

    • Moves internal organs including:

      • Digestive tract

      • Blood vessels

      • Ducts of glands

    • Cardiac Muscle:

    • Not consciously controlled.

    • Found exclusively in the heart.

Muscle Structure

Characteristics of Muscle Types

  • Striated Muscle:

    • Exhibits striations.

    • Contains multiple nuclei.

    • Includes contracting fibrils and connective tissue.

  • Smooth Muscle:

    • Lacks striations.

    • Contains a single nucleus.

    • Grows in sheets or layers.

  • Cardiac Muscle:

    • Exhibits striations similar to striated muscle.

    • Contains one or two nuclei.

Skeletal Muscles

Major Skeletal Muscles and Their Actions

  • Orbicularis Oculi:

    • Function: Closes eyelids, wrinkles forehead.

  • Sternocleidomastoid:

    • Function: Turns head.

  • Pectoralis Major:

    • Function: Adducts, flexes, and rotates shoulder inward.

  • Occipitofrontalis:

    • Function: Raises eyelids and draws scalp backward.

  • Temporalis:

    • Function: Closes jaw.

  • Masseter:

    • Function: Closes jaw for chewing.

  • Trapezius:

    • Function: Elevates shoulder.

  • Deltoid:

    • Function: Abducts shoulder.

  • Gluteus Maximus:

    • Function: Extends, abducts, and rotates thigh externally.

  • Biceps Femoris:

    • Function: Rotates leg externally and flexes knee.

  • Biceps Brachii:

    • Function: Flexes forearm and supinates (upward) forearm.

  • Triceps Brachii:

    • Function: Extends forearm and adducts arm.

  • Gastrocnemius:

    • Function: Bends knee and lifts heel off ground.

  • Achilles Tendon:

    • Critical for attachment and function of calf muscles.

Actions of Muscles

Types of Muscle Actions

  • Flexion: Decrease in the angle between two body parts.

  • Extension: Increase in the angle between two body parts.

  • Abduction: Movement away from the midline of the body.

  • Adduction: Movement towards the midline of the body.

  • Rotation: Turning around a central point.

  • Dorsiflexion: Bending the foot upwards.

  • Plantar Flexion: Bending the foot downwards.

  • Supination: Rotating the forearm so that the palm faces upward.

  • Pronation: Rotating the forearm so that the palm faces downward.

Vocabulary - Muscles

Key Terms Defined

  • Fascia: A band or sheet of connective tissue.

  • Insertion of a Muscle: The point of attachment that moves when the muscle contracts.

  • Origin of a Muscle: The point of attachment that remains stationary during contraction.

  • Plantar Flexion: Extension of the foot downward.

  • Pronation: Rotational movement which turns the palm downwards.

  • Rotation: A circular movement around a fixed point.

  • Skeletal Muscle: Muscle connected to the skeletal system, under voluntary control.

  • Smooth Muscle: Involuntary muscle found in internal organs.

  • Striated Muscle: Muscle tissue marked by transverse stripes; includes skeletal and cardiac muscles.

  • Supination: Rotational movement that turns the palm upwards.

  • Visceral Muscle: Smooth muscle found in the walls of hollow organs.

Terminology — Combining Forms

Muscle-Related Combining Forms

  • fasci/o: fascia

  • fibr/o: fibrous

  • leiomy/o: smooth muscle

  • my/o: muscle

  • myocardi/o: heart muscle

  • plant/o: sole of the foot

  • rhabdomy/o: skeletal muscle connected to bones

  • sarco: muscles and flesh

Suffixes in Muscle Terminology

Common Suffixes Defined

  • -asthenia: Lack of strength.

  • -trophy: Development or nourishment.

Prefixes in Muscle Terminology

Common Prefixes Defined

  • ab-: Away from.

  • ad-: Toward.

  • dorsi-: Back.

  • poly-: Many, much.

Pathology — Muscles

Muscle Diseases

  • Muscular dystrophy:

    • A group of inherited diseases resulting in progressive muscle weakness and degeneration without involvement of the nervous system.

  • Polymyositis:

    • A chronic inflammatory myopathy that may be an autoimmune disorder.

Clinical Procedures Related to Muscles

Procedures

  • Arthrocentesis: Procedure to remove fluid from a joint.

  • Arthrography: Imaging study of joints.

  • Arthroplasty: Surgical reconstruction or replacement of a joint.

  • Arthroscopy: Minimally invasive surgical procedure on a joint.

  • Bone density test: Assesses bone strength and risk of fractures.

  • Bone scan: Imaging test that helps diagnose bone diseases.

  • Computed tomography (CT): Advanced imaging technique that produces cross-sectional images.

  • Diskography: Imaging test to study intervertebral discs.

  • Electromyography (EMG): Tests electrical activity of muscles.

  • Magnetic resonance imaging (MRI): Advanced imaging technique for soft tissues.

  • Muscle biopsy: Procedure to remove a section of muscle for laboratory examination.