MUSCULAR SYSTEM

• Functions of muscles:

  • Support the body
  • Allow for movement by making bones and other body parts move
  • Maintain constant body temperature
  • Assist in movement of substances in the body
  • Protect internal organs and stabilize joints
• Types of muscle tissues:

  1. Skeletal muscle tissue:

  • Moves bones of the skeleton
  • Striated
  • Works mainly in a voluntary manner

  2. Cardiac muscle tissue:

  • Forms most of the heart wall
  • Contracts to circulate blood
  • Striated
  • Action is involuntary
  • Exhibits autorhythmicity
• Cardiac muscle tissue features:

  • Intercalated discs: irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers
  • Desmosomes: component of intercalated discs which hold the fibers together
  • Can undergo hypertrophy in response to an increased workload
• Types of muscle tissues:

  3. Smooth muscle tissue:

  • Found in blood vessels, internal organs like the digestive system, respiratory system, and eyes
  • Nonstriated
  • Action is involuntary
• Types of smooth muscle tissue:

  • Visceral (single-unit) smooth muscle tissue: in tubular arrangements in small arteries, veins, and hollow organs
  • Multiunit smooth muscle tissue: found in arrector pili muscles, muscles of the iris, and ciliary body
• Movements of skeletal muscle:

  • Origin: end that does not move
  • Insertion: end that moves when muscle contracts
• Coordination among muscles:

  • Prime mover or agonist: contracts to cause an action
  • Antagonist: stretches and yields against movement of agonists
  • Synergists: aid the movement of the prime mover
• Naming muscles based on:

  • Direction
  • Size
  • Shape
  • Action
  • Number of origins
  • Location
• Facial muscles:

  • Orbicularis oculi muscle closes the eye, while the levator palpebrae superioris muscle opens it
  • Buccinator muscle forms the major muscular portion of the cheek
  • Extrinsic eye muscles move the eyeballs
  • Muscles of mastication move the mandible, including masseter, temporalis, and medial pterygoid
• Neck muscles:

  • Platysma: covers the anterolateral neck
  • Sternocleidomastoid: flexes the neck
  • Scalenes: move the first two ribs for breathing
• Tongue muscles:

  • Genioglossus: pulls the tongue downward and forward
  • Styloglossus: pulls the tongue upward and backward
  • Hyoglossus: pulls the tongue downward and flattens it
  • Palatoglossus: raises the back portion of the tongue
• Muscles for breathing:

  • Diaphragm powers breathing
  • Diaphragm + anterolateral abdominal muscles increase intra-abdominal pressure
  • Diaphragm has 3 major openings: esophageal, aortic, and caval
• Trunk muscles:

  • Anterior muscles include pectoralis major, intercostal muscles, and muscles of the abdominal girdle
  • Posterior muscles include trapezius, latissimus dorsi, erector spinae, quadratus lumborum, and deltoid
• Upper limb muscles:

  • Biceps brachii: prime mover for flexion of the forearm
  • Brachialis: lifts the ulna
  • Brachioradialis: weak muscle that inserts into the distal forearm
  • Triceps brachii: muscle fleshing out the posterior humerus
• Lower limb muscles:

  • Gluteus maximus: powerful hip extensor
• Lower Limb Muscles: Movement at Hip Joint

  • Gluteus maximus: powerful hip extensor bringing the thigh in line with the pelvis
  • Gluteus medius: hip abductor important in steadying the pelvis during walking
  • Iliopsoas: composed of iliacus and psoas major, prime mover of hip flexion
  • Adductor muscles: form muscle mass at the medial side of each thigh
• Lower Limb Muscles: Movement at Knee Joint

  • Hamstring group: biceps femoris, semimembranosus, and semitendinosus
  • Sartorius: flexes, abducts, and externally rotates the thigh, and flexes and internally rotates the leg
  • Quadriceps group: rectus femoris and three vastus muscles
• Lower Limb Muscles: Movement at Ankle and Foot

  • Tibialis anterior: superficial muscle on the anterior leg, prime mover of toe extension and dorsiflexor of the foot
  • Extensor digitorum longus: prime mover of toe extension and dorsiflexor of the foot
  • Fibularis muscles: longus, brevis, and tertius found on the lateral part of the leg
  • Gastrocnemius: two-bellied muscle forming the curved half of the posterior leg
  • Soleus: deep to the gastrocnemius
• Anatomical Structures of Skeletal Muscle

  • Fascia: broad band of irregular connective tissue lining the body wall and limbs
  • Epimysium: outermost layer of dense, irregular connective tissue
  • Perimysium: layer of dense, irregular connective tissue, composed of fascicles
  • Endomysium: penetrates the interior of each fascicle
• Anatomical Structures of Skeletal Muscle: Microscopic Anatomy

  • Sarcolemma: plasma membrane of a muscle cell
  • Transverse (T) tubules: tiny invaginations of the sarcolemma filled with interstitial fluid
  • Sarcoplasm: cytoplasm of a muscle fiber containing myoglobin
  • Myofibrils: contractile organelles of skeletal muscle
  • Sarcoplasmic reticulum: fluid-filled system of membranous sacs
• Sliding Filament Theory

  • Skeletal muscle shortens during contraction as thick and thin filaments slide past each other
  • Muscle contraction occurs because myosin heads attach to and "walk" along the thin filaments at both ends of a sarcomere
• Effects of Aging in Muscles

  1. Muscles not used are replaced by connective tissue then by fat
  2. Degeneration of mitochondria due to exposure to oxygen and free radicals
  3. Changes in the nervous and endocrine systems affect muscle structure and function
  4. Muscles become weaker with age but exercise can stimulate muscle build-up