Muscle Actions & Groups

Agonist

Muscle or muscle group that produces a desired movement; aka prime mover

Antagonist

Muscle or muscle group that directly opposes the action of the agonist

Synergist

Skeletal muscle that contracts at the same time as the agonist and assists it in carrying out its action

Fixator

Stabilize joints so that other actions can take place

Origin

The more stable of the attachment sites of a muscle. When a muscle contracts, it’s origin attachment sites do not move much. This provides stability so that the insertion can move bones or other structures.

Insertion

The more moveable of the attachment sites of the muscle. When a muscle contracts, it exerts traction on its insertion site

Muscles work together 

When a muscle is stimulated by a nerve impulse - acetylcholine is released at the neuromuscular junction, and a muscle contracts.

Muscle groups working together are considered

• Agonists

• Antagonists

• Synergists

• Fixators

Extrinsic muscles and those of the head and neck 

These muscles act to move the thoracic limb, support the trunk, or move the head and mouth 

Intrinsic muscles of the foreleg

These muscles work to flex or extend either the shoulder joint, the elbow, or the carpus. A small number work to provide rotational motion.

Muscles of the Pelvic Limb and Abdomen

Pelvic limb muscles work to extend or flex the joints of the pelvic limb; they can also abduct and adduct the limb; abdominal muscles stabilize and help move the spinal column (along with the epaxials).

Muscles of the head and neck control

facial expressions, enable chewing, move sensory structures such as eyes and ears.

Muscles of the head and neck support the

head and allow the neck to flex, extend, and move laterally.

Temporalis

closes mouth when chewing

Masseter

Elevates the mandible to close mouth when chewing

Brachiocephalicus

Pulls limb forward, extends shoulder

Trapezius

Elevates/abducts the limb

Latissimus dorsi

Draws limb caudally, flexes shoulder

Abdominal muscles support and protect the

abdominal cavity, the also help flex (arch) the back.

Abdominal muscles also assist in

urination, defecation, and parturition.

Muscles along the spinal column (hypaxial and epaxial) are

 designed to support the axial skeleton.

Epaxials

Muscles located dorsally along the spinal column. They are innervated by dorsal branches of spinal nerves and function to extend the vertebral column.

In the lumbar region (injections)

epaxial muscles are fused

The latissimus dorsi

wraps over the epaxial muscles, as does the deep thoracolumbar fascia.

Intercostal (between the ribs) muscles

increase and decrease the size of the thoracic cavity.

Inspiratory m.

muscles that increase the size of the thoracic cavity. External intercostals

Expiratory m.

muscles that decrease the size of the thoracic cavity. Internal intercostals

Diaphragm also contributes to

inspiration

Abdominal muscles act as

synergists for respiration

Epaxials

lateral processes of lumbar vertebrae

Fused muscles

most often we inject between L2-L5