Biceps Brachii

Examples of Biceps Brachii in the following topics:

• How Skeletal Muscles Produce Movements

  • Typical muscle pairings include the biceps brachii and triceps brachii, which act to flex or extend the forearm.
  • During flexing of the forearm the biceps brachii is the agonist muscle, pulling the forearm up towards the shoulder.
  • During flexing of the forearm, the brachioradialis and brachialis act as synergist muscles, aiding the biceps brachii in pulling the forearm up towards the shoulder.
  • The biceps brachii is the agonist, or primer mover, responsible for flexing the forearm.
  • The brachioradialis and brachialis are synergist muscles, and the rotator cuff (not shown) fixes the shoulder joint allowing the biceps brachii to exert greater force.

• Muscles of the Humerus that Act on the Forearm

  • Biceps Brachii - The biceps brachii is a two-headed muscle.
  • Coracobrachialis - The coracobrachialis lies within the two heads of the biceps brachii.
  • Brachialis - The brachialis muscle lies within the distal region of the biceps brachii.
  • Produced by the brachialis, biceps brachii, and brachioradialis of the forearm.
  • The biceps brachii is located in the anterior compartment of the upper arm and flexes and supinates the forearm at the elbow.

• Scapula

  • Immediately below the glenoid cavity is the infranglenoid tuberosity which is the origin for the long head of the triceps brachii.
  • Immediately above the glenoid cavity is the supraglenoid tubercle and associated hook like coracoid process, from which the long and short heads of the biceps brachii originate respectively.

• Humerus (The Upper Arm)

  • Between the two tubercles lies a deep grove termed the intertubercular sulcus through which the tendon of the long head of the biceps brachii runs.
  • As well as the deltoid the corocobrachialis, brachialis and brachioradialis attach to the anterior surface with the triceps brachii attaching to the posterior.

• Ulna and Radius (The Forearm)

  • The olecranon is a projection of bone which extends proximally from the ulna, the triceps brachii muscle attaches to it superioly.
  • Immediately below the head lies the radial tuberosity to which the biceps brachii attaches.

• How Skeletal Muscles Are Named

  • The biceps brachii is an example of a  fusiform parallel muscle, and is responsible for flexing the forearm.

• Muscles that Cause Movement at the Knee Joint

  • Biceps Femoris – A similar muscle to the biceps brachii in the upper arm and also double-headed.
  • Two synergistic muscles are associated with the biceps femoris, the semitendinosus and the semimembranosus.
  • Produced by the biceps femoris, semitendinosus, and semimembranosus muscles.
  • The knee joint allows for slight rotation when flexed, which is produced by the biceps femoris, semitendinosus, semimembranosus, gracilis, and sartorius.
  • The biceps femoris and synergistic semitendinosus and the semimembranosus muscles are responsible for flexing of the lower leg at the knee.

• Lever Systems

  • First-class levers are relatively uncommon in the body, but one example is the triceps brachii muscle of the upper arm which acts to extend the forearm.
  • Thinking of the relative distance between the points of attachment, the triceps brachii can be said to act at a mechanical disadvantage.
  • An example of a third-class lever in the body is the biceps brachii, which flexes the forearm towards the shoulder.

• Muscles that Cause Movement at the Hip Joint

  • Biceps Femoris – A similar muscle to the biceps brachii in the upper arm, also double-headed.
  • Two synergistic muscles are associated with the biceps femoris, the semitendinosus, and the semimembranosus.
  • Produced by the lateral rotator group of muscles and the biceps femoris, sartorius, and gluteus medius and minimus.

• Muscles of the Shoulder

  • Produced by the biceps brachii (both heads), pectoralis major, anterior deltoid, and corocobrachialis.
  • Muscles of the rotator cuff and presented with the triceps brachii.