Anatomy of Skeletal Muscles

What are Prime movers - Agonists

• The muscle that contracts and produces the primary movement

  • Biceps brachii is the prime mover, contracting to flex the elbow

What are antagonists

• The muscle that opposes the prime mover's action, helping to control or slow down the movement.

  • Triceps brachii is the antagonist, lengthening and relaxing to allow the elbow to flex

What are Synergists

• Muscles that assist the prime mover in performing a joint action, either by adding force or by stabilizing the joint.

  • Brachialis and brachioradialis are synergists that help to flex the elbow

What are Stabilizers - Fixators

• Muscles that stabilize the origin of the prime mover, allowing the prime mover to contract more effectively.

  • Muscles of the shoulder and scapula act as fixators, stabilizing the shoulder joint to allow the biceps to contract effectively

Gross Anatomy

• Each skeletal muscle is a discrete organ made up of hundreds to thousands of muscle fibres (muscle cells)

• Muscle fibres are bundled into groups called fascicles

• Fascicles are then 

   grouped together to 

   form the whole 

   muscle

• Also, within each muscle are substantial amounts of connective tissue, blood vessels, and nerve fibres

What are Connetive Tissue layers

• Each muscle is held together by several different layers of connective tissue 

• Connective tissue is used to protect and support the soft and fragile muscle fibres, reinforce the muscle as a whole, and provide elasticity to the muscle tissue

• Blood vessels and nerve fibres enter and exit through the connective tissue layers

What is the Epimysium

Epimysium = surrounds all of fascicles = entire muscle

What is the Perimysium

Perimysium = surrounds fascicles (muscle fibres bundled together)

What is the ENdomysium

Endomysium = connective tissue that surrounds individual muscle fibre

More abt connective tissue

• Connective tissue gets coarser the further out it goes from the muscle fibre

• All these connective tissue sheaths are continuous with each other as well as with the tendons that join the muscles to bones

• When muscles fibres contract, they pull on these sheaths, which then transmit the force to the bone to be moved

Muscle attatchment to bone

• Attaches directly or indirectly

• Direct - epimysium adheres to and fuses with periosteum (outer membrane that covers bone)

• 
  Indirect - epimysium extends past muscle as a tendon and then attaches to periosteum of bone (most common type)

Direct vs. Indirect
(muscle attachment to bone)

One Muscle fiber(cell)

• Contains myofibrils (contractile units)

• Surrounded by plasma membrane called  sarcolemma (just below endomysium) and contains sarcoplasm (muscle cells cytoplasm) 

What are Myofibrils

• Thread-like (or rod-like) structures that run along entire length of muscle fibre 

• Contractile elements of skeletal muscle cells

• Contain even smaller contractile units called sarcomeres 

Think of one myofibril as a train – then picture hundreds to thousands of these myofibrils/trains running side by side in one muscle fibre

What are Sarcomeres

• Compartments along the myofibrils that contain filaments (actin & myosin)

• Allow for muscle contraction

Picture sarcomeres as the cars in the train

What are Filaments

• Delicate fibres that are found within each sarcomere 

• These are what slide past each other to contract (shorten) the muscle

• actin – thin filament

• myosin = thick filament, has heads and tails