Muscles Anatomy

• Functions of muscles:

  1.     Producing movement​

  2.     Maintaining posture​

  3.     Stabilising joints​

  4.     Generating heat
•  

  Properties of muscles:

  ·       Able to contract (get shorter)​

  ·       Extensible (able to be stretched)​

  ·       Elastic ( able to return to their original length after being stretched)
• Skeletal Muscle:

  ·       muscles which are attached to the skeleton through tendons.​

  ·       make up 40% of human body mass

   

  Functions:

  ·       are voluntary and are mainly responsible for locomotion ( ability to move from place to place)​

  ·       Contractions of skeletal muscle brings movement at joints​

  ·       Gives the body form & contours​

  ·       Maintain posture
• Connective Tissue in Muscle:

   

  ·       Skeletal muscle are soft and fragile​

  ·       The multiple layers of connective tissue coverings in the muscle support and protect the delicate muscle cells and allow them to withstand the force of contraction needed for movement.​

  ·       The connective tissue also supplies a pathway for blood vessels and nerves

  ·       Amount of CT increases with age= decreasing muscular strength
• Cell membrane

  Structure:

  ·       Sarcolemma

  ·       Thin plasma membrane around the cell

  Function:

  ·       Normal cell membrane functioning

  ·       Involved in synaptic transmission of action potential propagation and exciting-contraction coupling
• Cytoplasm (Sarcoplasm)

  Structure:

  ·       Cytoplasm within the sarcolemma

  Function:

  ·       Storage and release of calcium ions
• Myofibrils

  muscle fibre itself contains cylindrical organelles known as myofibrils.​

   

  o   They lie parallel to each other and run the length of the fibre​

  Surrounding the myofibril there is a network of tubules and channels called the sarcoplasmic reticulum in which calcium is stored
•  

  Myofilaments (within myofibril)

  -       Actual units involved in contraction

  Structure:

  -       have symmetrical, alternating patterns of thick and thin elements​

  -       The arrangement of thick and thin filaments gives a banded or striated appearance to the muscle​

  -       These striations allow myofibrils to be divided into functional repeating segments called sarcomeres​
• Thick Myofilaments:

   

  ·       composed mainly of the protein myosin​

  ·       have a rod-like tail ending with two globular heads
• Thin Myofilaments:

  ·       composed mainly of the protein actin

  ·       contain active sites where myosin binds to during contraction

  Also contains two protein filaments:

  tropomyosin

  o   Main function: To prevent the muscles from contracting at the wrong time

  troponin

  o   Main function: to promotes muscle contraction
• Agonist: the muscle that causes the desired effect.​

  Antagonist: the muscle that has the opposite effect.
• Elbow movement:

  Scapular and humerus are stationary bones

  Radius and ulna are the bones that need to move

   
• Bicep- Origin:Scapula/humerus

  Insertion: Radius
• Triceps- Origin :Scapular/Humerus

  Insertion : Ulna
• Elbow Movement-Flexion

  Bicep is contracted- Agonist

  Tricep is relaxed- Antagonist
• Muscle Tone

  -       maintaining partial contraction of skeletal muscle to tighten a muscle but not produce movement

  -       Achieved by many different fibres taking turns to contract

  -       Muscle tone holds many of our body parts in position. ​

  -       Eg the head droops when we fall asleep due to loss of muscle tone

  -       Posture depends on muscle tone holding the body in a certain position​
• Sarcomere:

  arrangement of thick and thin filaments produces the striated appearance that allows myofibrils to be divided into units called sarcomeres​

  Movement of these two filaments relative to one another causes the lengthening and shortening of the sarcomere (and hence, relaxing and contracting of muscle)
• Thick filament: Made of hundreds of intertwined proteins known as Myosin​
• Thin filament: Mostly composed of intertwined strands of a protein known as Actin
• Z-disc: composed of large proteins and serve as an anchoring site for contractile proteins.

  Lines are pulled closer together during muscle contraction
•  

  M-line: The center of a sarcomere and contains proteins that function as anchoring sites for the Myosin molecules. ​

  The M-line also provides elasticity to the muscles due to the presence of elastic fibers.​
• A-band: Covers the length of the thick filament (Myosin) in a sarcomere. The amount of actin found in the A-band depends on how much the sarcomere is contracted. The size of the A-band remain constant during a muscle contraction.​
• I-band: The zone of a sarcomere that is not covered by Myosin molecules. The amount of actin molecules found in the I-band varies, depending on how much the sarcomere is contracted.