Skeletal muscles each have an origin and an insertion. The end of the muscle that attaches to the bone being pulled is called the muscle’s insertion and the end of the muscle attached to a fixed, or stabilized, bone is called the origin. The muscle primarily responsible for a movement is called the prime mover, and muscles that assist in this action are called synergists. A synergist that makes the insertion site more stable is called a fixator. Meanwhile, a muscle with the opposite action of the prime mover is called an antagonist. Several factors contribute to the force generated by a skeletal muscle. One is the arrangement of the fascicles in the skeletal muscle. Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. Each arrangement has its own range of motion and ability to do work.
abduct
move away from midline in the sagittal plane
agonist
(also, prime mover) muscle whose contraction is responsible for producing a particular motion
antagonist
muscle that opposes the action of an agonist
belly
bulky central body of a muscle
bipennate
pennate muscle that has fascicles that are located on both sides of the tendon
circular
(also, sphincter) fascicles that are concentrically arranged around an opening
convergent
fascicles that extend over a broad area and converge on a common attachment site
fascicle
muscle fibers bundled by perimysium into a unit
fixator
synergist that assists an agonist by preventing or reducing movement at another joint, thereby stabilizing the origin of the agonist
flexion
movement that decreases the angle of a joint
fusiform
muscle that has fascicles that are spindle-shaped to create large bellies
insertion
end of a skeletal muscle that is attached to the structure (usually a bone) that is moved when the muscle contracts
multipennate
pennate muscle that has a tendon branching within it
origin
end of a skeletal muscle that is attached to another structure (usually a bone) in a fixed position
parallel
fascicles that extend in the same direction as the long axis of the muscle
pennate
fascicles that are arranged differently based on their angles to the tendon
prime mover
(also, agonist) principle muscle involved in an action
synergist
muscle whose contraction helps a prime mover in an action
unipennate
pennate muscle that has fascicles located on one side of the tendon
1. Which of the following is unique to the muscles of facial expression?
A) They all originate from the scalp musculature.
B) They insert onto the cartilage found around the face.
C) They only insert onto the facial bones.
D) They insert into the skin.
D
2. Which of the following helps an agonist work?
A) a synergist
B) a fixator
C) an insertion
D) an antagonist
A
3. Which of the following statements is correct about what happens during flexion?
A) The angle between bones is increased.
B) The angle between bones is decreased.
C) The bone moves away from the body.
D) The bone moves toward the center of the body.
B
4. Which is moved the least during muscle contraction?
A) the origin
B) the insertion
C) the ligaments
D) the joints
A
5. Which muscle has a convergent pattern of fascicles?
A) biceps brachii
B) gluteus maximus
C) pectoralis major
D) rectus femoris
C
6. A muscle that has a pattern of fascicles running along the long axis of the muscle has which of the following fascicle arrangements?
A) circular
B) pennate
C) parallel
D) rectus
C
7. Which arrangement best describes a bipennate muscle?
A) The muscle fibers feed in on an angle to a long tendon from both sides.
B) The muscle fibers feed in on an angle to a long tendon from all directions.
C) The muscle fibers feed in on an angle to a long tendon from one side.
D) The muscle fibers on one side of a tendon feed into it at a certain angle and muscle fibers on the other side of the tendon feed into it at the opposite angle.
A
1. What effect does fascicle arrangement have on a muscle’s action?
Fascicle arrangements determine what type of movement a muscle can make. For instance, circular muscles act as sphincters, closing orifices.
2. Movements of the body occur at joints. Describe how muscles are arranged around the joints of the body.
Muscles work in pairs to facilitate movement of the bones around the joints. Agonists are the prime movers while antagonists oppose or resist the movements of the agonists. Synergists assist the agonists, and fixators stabilize a muscle’s origin.
3. Explain how a synergist assists an agonist by being a fixator.
Agonists are the prime movers while antagonists oppose or resist the movements of the agonists. Synergists assist the agonists, and fixators stabilize a muscle’s origin.