Anatomy and Physiology of Skeletal Muscles

Nerve Supply – Motor Neurons stimulates muscle contraction

Blood Supply – Capillaries supply oxygen and nutrients

Connective Tissue Components :

Superficial fascia – Store water and fat, insulator, protection, pathway for nerves and blood vessels

Deep Fascia (Dense irregular connective tissue)- Holds the muscle fibers together and separates them into 3 groups – Endomysium which surrounds the individual muscle cell, Perimysium which surrounds several muscle cells and the Epimysium which surrounds the entire muscle.

Tendon Sheath – Covers tendons (ends of muscles) and secretes synovial fluid for lubrication.

Parts of the Muscle Cell

  1.   Sarcolemma – Cell membrane of a muscle cell encases cytoplasm and oranelles.
  2. Sarcoplasm – Cytoplasm of the muscle cell and surrounds the organelles.
  3. Sarcoplamic Reticulum – contains sarcomeres. Stores and releases calcium needed for muscle contraction.  Has Transverse Tubules to connect the cell membrane to the inside of the cell.  The T tubule helps spread the action potential or the nerve impulse into and out of the cell.
  4. Muscle cells have many nuclei and many mitochondria
  5. Myofibrils – composed of myofilaments.  Each muscle fiber contains myofibrils and each myofibril has thousands of myofilaments.     Actin, myosin, tropomysosin, troponin.  Actin and Myosin are attracted to each other.

Sarcomeres – are composed of myosin and actin filaments

Neuromuscular Junction – motor neurons connect with the nerve axon at the motor end plate. The end of the nerve axons are synaptic end bulbs which contain synaptic vesicles that store neurotransmitters – acetylcholine. The synaptic cleft is the space between the motor neuron and motor end plate.

Motor Unit – single motor neuron and the muscle it innervates.

Naming Skeletal Muscles

Individual muscles and muscle groups have been named using many different categories:

  1. By fiber and direction – External Obliques: at an oblique angle.  Rectus Femoris: Straight muscle
  2. By Location – Biceps Brachii: on the bracial or upper arm.  Biceps Femoris: on the femur (leg)
  3. By size. Glutues Maximus: Large.  Gluteus Minimus: Small
  4. By number of heads of the muscle.  Biceps Brachii has two heads.  Triceps Brachii has three heads.
  5. By the shape of the muscle.  Teres Major – teres is round or cylindrical.  Trapezius meaning ‘flat table’ in Greek.  Deltoid meaning a triangular shape.
  6. By the action.  Adductor longus – adducts. Levator Scapula – elevates scapula

Fiber arrangement and Function.

The shape of the muscle fibers and the size also help determine the function of a muscle.  Long fibers tend to produce a large range of motion but little force while short fibers produce short range of motion and greater force. The fiber arrangements and the number of fibers also contribute to the function of muscles.

Categories of fiber arrangements:

  1. Fusiform – Long fibers, long movements that are not forceful
  2. Pennate – Uni, Bi, Multi are feather shaped, short muscles and lie at an angle to the muscle and attach to one or more tendons that run the whole length of the muscle.
  3. Flat – flat, narrow attachment to a broad attachment like the trapezius or lattissimus dorsi
  4. Biceps – Two heads fuse into a single muscle belly as in the Biceps femoris
  5. Multi-bellied. one origin and one insertion but multiple bellies and intermediate tendons between the bellies as in the Rectus Abdominus
  6. Convergent -multiple fibers and points of origin converge into one point of insertion forming a triangle, like the Deltoid and pectoralis major.
  7. Parallel – long and oriented parallel with the muscle
  8. Circular – concentric rings around external body openings like sphincters

Names of Muscles by function

Mover – agonist – concentric contractions moving through  specified plane.  Prime mover

Antagonist – move opposite of the mover or agonist, usually located on the opposite side of the body/joint.  relaxes when the agonist contracts allowing movement.

Synergist – helper, neutralizer or stablizer.  aka guiding muscles

Fixator or stabilizer – isometrically contracts to support or stabilize the mover while it moves.

Neutralizer – stops the agonist from moving, work through isometric contractions

Support muscle -acts at other places than where the movement is occurring to hold something in position.