The origin of a muscle is the place where the muscle is anchored to a fixed point on the skeleton by a tendon.
The insertion of a muscle is where the tendon is attached to a bone that is to be moved, eg the biceps has two origins - the top of the scapula and the glenoid cavity. These are fixed. The insertion is into the radius. The radius is moved by the biceps when we do a biceps curl.
Antagonistic muscles - skeletal muscles that work in pairs eg biceps / triceps.
Agonist - muscle that causes a particular movement. Also known as the prime mover.
Antagonist - muscle that causes the opposite movement to the agonist (eg in above example, triceps) For the hamstring curl, the agonist is the hamstring, the antagonist is the quadriceps.
Synergist - Helps the agonist by adding extra force or removing unwanted movement.
Fixator - Holds the origin of the agonist stable, eg muscles in neck that hold the head up.The role of muscles is not fixed, ie they can be agonists in one movement, synergists in a second and fixators in a third.
Muscle fibres differ in composition and function.
The main types of muscle fibre are:
Myoglobin - A protein in muscle similar to haemoglobin in blood that stores oxygen until it is needed by the mitochondria.
Notes on above:
Myofibrils - many thousands contained in muscle fibres.
Sliding filament theory of contraction
The sarcomere shortens but thick and thin myofilaments stay the same length, sliding over one another. Thin myofilaments slide inwards towards the H zone, causing it to disappear.
The thin myofilaments are called Actin and the thick myofilaments are called Myosin. Calcium is necessary to enable the Myosin to bind to the Actin to enable the muscle to contract. When the muscle is relaxed, the Myosin cannot bind to the Actin because the binding sites on the Actin head are blocked by trypomyosin. When calcium binds to troponin, it pulls the trypomyosin from the Actin heads, allowing the binding and the muscle contraction.
Different fibres may be activated at different times, enabling partial contractions to be sustained for long durations.
flaccid - muscles with less than normal tone (caused by illness, injury or lack of use).
Effects of exercise on muscles