muscular system

Chapter 7 - The Muscular System

Introduction

  • Overview of the muscular system and its role in movement and stability.

  • Skeletal muscle as an organ comprising skeletal muscle tissue and connective tissues.

Parts of a Skeletal Muscle

  • Origin: The attachment to a stationary or fixed bone.

  • Insertion: The point of attachment to the bone that moves when the muscle contracts.

  • Body: The main part (belly) of the muscle that contracts.

Muscle Tissue Overview

  • Muscle tissue allows movement of the body and its parts.

  • Muscle fibers shorten to produce movement, which is driven by chemical energy from food converted into mechanical energy.

Types of Muscle Tissue

Skeletal Muscle

  • Also known as striated or voluntary muscle.

  • Comprises approximately 40% of body weight.

  • Microscopically shows crosswise stripes (striations) and can be consciously controlled.

Cardiac Muscle

  • Composes the bulk of heart tissue.

  • Characterized by intercalated disks and branched fibers.

  • Functions involuntarily and ensures efficient heart contractions.

Smooth Muscle

  • Also known as visceral muscle; it appears smooth under a microscope.

  • Located in the walls of hollow visceral structures such as the digestive tract and blood vessels.

  • Involuntary muscle; contractions are not consciously controlled.

Composition of Skeletal Muscle

  • Mainly composed of muscle fibers and connective tissues.

  • Muscles are connected to bones by tendons, which are strong cords of fibrous connective tissue.

  • Bursae are small synovial-lined sacs aiding in the reduction of friction.

Microscopic Structure of Muscle

  • Muscle fibers grouped into bundles, containing myofilaments:

    • Myosin (thick myofilaments)

    • Actin (thin myofilaments)

  • Sarcomeres are the basic functional units of contraction, separated by Z lines.

  • The sliding filament model explains how muscle contraction occurs with these myofilaments sliding past each other.

  • Contraction requires calcium ions and ATP.

Muscle Movement and Types

  • Muscles produce movement by contracting, pulling closer to the origin, resulting in joint movement.

  • Prime mover: Muscle mainly responsible for a given movement.

  • Synergist: Assists the prime mover.

  • Antagonist: Opposes the action of the prime mover.

Posture and Muscle Tone

  • Tonic contractions (only a few fibers shorten) help maintain posture and muscle tone.

  • Good posture prevents strain on the musculoskeletal system;

    • Poor posture can lead to fatigue and deformities.

Heat Production

  • Muscle contractions generate most body heat, maintaining normal body temperature.

  • Fever indicates higher body temperature, while hypothermia indicates lower than normal.

Muscle Fatigue and Recovery

  • Muscle fatigue results from repeated stimulation without rest, depleting ATP and oxygen.

  • Accumulation of lactic acid from anaerobic respiration contributes to fatigue.

  • Oxygen debt refers to the metabolic effort to return energy and oxygen reserves to pre-exercise levels after exertion.

Nervous System and Muscle Function

  • Nerve stimulation is necessary for muscle contraction; motor neurons transmit impulses to muscles.

  • A motor unit comprises a motor neuron and the muscle fibers it innervates.

Stimulus and Muscle Fiber Response

  • A threshold stimulus is needed to initiate muscle contraction.

  • Muscle fibers respond via an all-or-none principle: fibers contract fully or not at all.

  • Different motor units allow graded contractions.

Types of Muscle Contractions

  • Twitch Contractions: Single contraction not significant in normal activity.

  • Tetanic Contractions: Sustained muscle contractions from rapid stimuli.

  • Isotonic Contractions:

    • Concentric: Muscle shortens, moving insertion towards the origin.

    • Eccentric: Muscle lengthens under tension.

  • Isometric Contractions: Muscle tension increases without movement.

Impact of Exercise

  • Regular exercise enhances muscle tone, posture, heart and lung efficiency.

  • Inactivity leads to muscle atrophy, while exercise leads to hypertrophy (muscle enlargement).

Muscle Groups

Head and Neck

  • Facial Muscles: Orbicularis oculi, orbicularis oris, zygomaticus.

  • Muscles of Mastication: Masseter, temporalis.

  • Neck Muscles: Sternocleidomastoid, trapezius.

Upper Extremities

  • Pectoralis Major: Flexes arm.

  • Latissimus Dorsi: Extends arm.

  • Deltoid: Abducts arm.

  • Biceps Brachii: Flexes forearm.

  • Triceps Brachii: Extends forearm.

Trunk Muscles

  • Abdominal Muscles: Rectus abdominis, external oblique, internal oblique, transversus abdominis.

  • Respiratory Muscles: Intercostal muscles, diaphragm.

Lower Extremities

  • Iliopsoas: Flexes thigh.

  • Gluteus Maximus: Extends thigh.

  • Adductor Muscles: Adduct thighs.

  • Hamstring Group: Flexes lower leg (includes semimembranosus, semitendinosus, biceps femoris).

  • Quadriceps Femoris: Extends lower leg.

  • Tibialis Anterior: Dorsiflexes foot.

  • Gastrocnemius: Plantar flexes foot.

Movements of the Body

  • Flexion: Decreases angle between bones.

  • Extension: Increases angle between bones.

  • Abduction: Moves part away from body midline.

  • Adduction: Moves part toward body midline.

  • Rotation: Movement around a longitudinal axis.

Additional Movements

  • Supination/Pronation: Forearm rotation.

  • Dorsiflexion/Plantar Flexion: Foot movements.

  • Inversion/Eversion: Ankle movements.