Muscular System Study Guide: Muscle Actions, Naming, Fascicle Arrangements, Levers, Origins & Insertions

Q1. For each action below, identify which of the two labeled muscles you would expect to be the agonist and which you would expect to be the antagonist. Then, state roughly where on the body you would expect to find a synergist for each of these movements.

Background

Topic: Muscle Actions (Agonist, Antagonist, Synergist, Fixator)

This question tests your understanding of how muscles work together to produce movement. The agonist (prime mover) is the main muscle responsible for a movement, the antagonist opposes the action, and the synergist assists the agonist.

Key Terms:

• Agonist: The muscle primarily responsible for a movement.

• Antagonist: The muscle that opposes the action of the agonist.

• Synergist: A muscle that assists the agonist in performing the movement.

Step-by-Step Guidance

1. For each movement, identify which muscle is performing the main action (agonist) and which muscle is opposing it (antagonist).

2. Think about the location of the synergist: it is usually found near the joint or muscle group involved in the movement, helping to stabilize or add force.

3. For "Lifting your arm to the side," consider which muscle is responsible for abduction of the arm and which muscle would oppose this action.

4. For "Smiling," identify the muscle that elevates the corners of the mouth and the muscle that would oppose this action.

5. For each movement, consider where a synergist would be located (e.g., near the shoulder for arm movements, near the mouth for facial movements).

Try solving on your own before revealing the answer!

Final Answer:

Lifting your arm to the side:

• Agonist: Deltoid

• Antagonist: Teres major

• Synergist Location: Near the shoulder (e.g., supraspinatus)

Smiling:

• Agonist: Zygomaticus major

• Antagonist: Mentalis

• Synergist Location: Near the mouth (e.g., risorius)

Agonists initiate movement, antagonists oppose it, and synergists assist or stabilize the action.

Q2. True or False: A fixator works to stabilize the insertion of the antagonist. If false, choose the answer that best corrects the statement.

Background

Topic: Muscle Actions (Fixator)

This question tests your understanding of the role of a fixator muscle, which stabilizes a joint or bone during movement.

Key Terms:

• Fixator: A muscle that stabilizes the origin of the agonist, allowing the prime mover to act more efficiently.

• Origin: The attachment site of a muscle that remains relatively stationary during movement.

• Insertion: The attachment site that moves during muscle contraction.

Step-by-Step Guidance

1. Read the statement carefully and identify what a fixator does.

2. Recall that a fixator stabilizes a specific part of the muscle during movement.

3. Determine whether the fixator stabilizes the origin or insertion, and whether it is for the agonist or antagonist.

4. Review the answer choices to see which one correctly describes the fixator's function.

Try solving on your own before revealing the answer!

Final Answer:

b) False, the fixator stabilizes the origin of the agonist.

Fixators stabilize the origin of the prime mover (agonist), not the insertion or the antagonist.

Q3. The genioglossus is the primary muscle involved in sticking out your tongue. The styloglossus is responsible for pulling the tongue back in. What is the role of the styloglossus in sticking out your tongue?

Background

Topic: Muscle Actions (Agonist, Antagonist, Synergist, Fixator)

This question tests your ability to identify the role of a muscle based on its action relative to another muscle.

Key Terms:

• Agonist: Muscle responsible for the main action.

• Antagonist: Muscle that opposes the action of the agonist.

• Synergist: Muscle that assists the agonist.

• Fixator: Muscle that stabilizes the origin of the agonist.

Step-by-Step Guidance

1. Identify the action: sticking out the tongue (protrusion).

2. Determine which muscle is responsible for this action (genioglossus).

3. Identify the muscle that performs the opposite action (styloglossus pulls the tongue back in).

4. Recall the definitions of agonist and antagonist to decide the role of the styloglossus.

Try solving on your own before revealing the answer!

Final Answer:

c) Antagonist.

The styloglossus opposes the action of the genioglossus, making it the antagonist for sticking out the tongue.

Q4. The soleus, gastrocnemius, and tibialis anterior are all major muscles of the lower leg. The gastrocnemius and soleus are both located in the posterior region of the calf, while the tibialis anterior is located in the anterior region of the lower leg. Based only on this information, which statement is most likely true?

Background

Topic: Muscle Actions (Agonist, Antagonist, Synergist, Fixator)

This question tests your ability to infer muscle relationships based on their anatomical location.

Key Terms:

• Agonist: Main muscle responsible for movement.

• Antagonist: Muscle that opposes the action.

• Synergist: Muscle that assists the agonist.

• Fixator: Muscle that stabilizes the origin of the agonist.

Step-by-Step Guidance

1. Recall that muscles on opposite sides of a joint often act as antagonists.

2. Identify which muscles are located together (gastrocnemius and soleus) and which are on the opposite side (tibialis anterior).

3. Consider the likely actions of these muscles: posterior muscles typically plantar flex the foot, anterior muscles dorsiflex.

4. Use this information to determine which muscles are likely antagonists and which might be synergists.

Try solving on your own before revealing the answer!

Final Answer:

d) The gastrocnemius and the tibialis anterior are antagonists.

Posterior calf muscles (gastrocnemius, soleus) plantar flex the foot, while the anterior tibialis anterior dorsiflexes, making them antagonists.

Q5. Based on the name, how does the fibularis brevis compare to the fibularis longus?

Background

Topic: Muscle Naming Conventions

This question tests your understanding of how muscle names reflect their characteristics, such as length.

Key Terms:

• Brevis: Short

• Longus: Long

Step-by-Step Guidance

1. Analyze the terms "brevis" and "longus" in the muscle names.

2. Recall that "brevis" means short and "longus" means long.

3. Compare the expected length of the two muscles based on their names.

Try solving on your own before revealing the answer!

Final Answer:

a) The fibularis brevis muscle is relatively short while the fibularis longus is relatively long.

"Brevis" and "longus" are Latin terms used to describe muscle length.

Q6. Based on the name, how would you expect the orbicularis oris muscle to be shaped?

Background

Topic: Muscle Naming Conventions

This question tests your ability to deduce muscle shape from its name.

Key Terms:

• Orbicularis: Circular

• Oris: Related to the mouth

Step-by-Step Guidance

1. Break down the name "orbicularis oris" into its components.

2. Recall that "orbicularis" refers to a circular shape.

3. Consider the location (mouth) and typical shape of muscles in this region.

Try solving on your own before revealing the answer!

Final Answer:

c) Circular.

The orbicularis oris muscle forms a ring around the mouth, giving it a circular shape.

Q7. Which of the following muscle names does NOT provide information about the muscle’s actions?

Background

Topic: Muscle Naming Conventions

This question tests your ability to identify which muscle names describe their function and which do not.

Key Terms:

• Flexor, Abductor, Extensor: Indicate action

• Transverse: Indicates direction, not action

Step-by-Step Guidance

1. Review each muscle name and identify if it describes an action (e.g., flexion, abduction, extension).

2. Look for names that describe structure or orientation rather than function.

3. Compare "Transverse abdominis" to the others to see if it describes an action.

Try solving on your own before revealing the answer!

Final Answer:

c) Transverse abdominis.

"Transverse" describes the direction of muscle fibers, not the action performed by the muscle.

Q8. Which fascicle arrangement is most well suited to a muscle that needs to generate a lot of force over a small distance?

Background

Topic: Fascicle Arrangements

This question tests your understanding of how muscle fiber arrangement affects force and range of movement.

Key Terms:

• Pennate: Short fibers attach at an angle to a tendon, maximizing force.

• Multipennate: Multiple rows of pennate fibers, even greater force.

Step-by-Step Guidance

1. Recall that pennate arrangements allow for more fibers in a given area, increasing force.

2. Compare unipennate, bipennate, and multipennate arrangements for force generation.

3. Consider which arrangement is best for generating force over a small distance.

Try solving on your own before revealing the answer!

Final Answer:

b) Multipennate.

Multipennate muscles have the highest number of fibers, maximizing force generation over a small distance.

Q9. In what type of lever is the force applied between the fulcrum and the load?

Background

Topic: Lever Systems in Muscles

This question tests your understanding of lever classes and their arrangement in the body.

Key Terms:

• Fulcrum: Pivot point (joint)

• Effort: Force applied by muscle

• Load: Weight or resistance

• Third-class lever: Effort is between fulcrum and load

Step-by-Step Guidance

1. Recall the three classes of levers and their arrangements.

2. Identify which class has the effort applied between the fulcrum and the load.

3. Think about common examples in the human body (e.g., biceps curl).

Try solving on your own before revealing the answer!

Final Answer:

b) Third-class.

In a third-class lever, the effort is applied between the fulcrum and the load, as seen in most limb movements.

Q10. True or False: During a muscle contraction, the origin moves towards the insertion. If false, choose the answer that best corrects the statement.

Background

Topic: Muscle Origin and Insertion

This question tests your understanding of how muscles contract and which attachment site moves.

Key Terms:

• Origin: Stationary attachment site

• Insertion: Movable attachment site

Step-by-Step Guidance

1. Recall the definitions of origin and insertion.

2. Think about which part moves during contraction.

3. Review the answer choices to find the correct statement.

Try solving on your own before revealing the answer!

Final Answer:

b) False, the insertion moves towards the origin during contraction.

During muscle contraction, the insertion (movable end) moves toward the origin (stationary end).

Q11. The flexor carpi ulnaris is a muscle that adducts and flexes the hand at the wrist. The muscle attaches to both the humerus and the base of the 5th metacarpal. Based on the movement that this muscle performs, which attachment is the origin?

Background

Topic: Muscle Origin and Insertion

This question tests your ability to identify the origin based on the direction of movement.

Key Terms:

• Origin: Stationary attachment site

• Insertion: Movable attachment site

Step-by-Step Guidance

1. Recall that the origin is usually proximal and stationary, while the insertion is distal and moves.

2. Consider the movement: flexion and adduction of the hand at the wrist.

3. Determine which attachment site is closer to the trunk and which is farther away.

Try solving on your own before revealing the answer!

Final Answer:

a) Humerus.

The humerus is the origin because it is the stationary, proximal attachment site.

Q12. The diagram below shows some of the muscles used for chewing. Using your knowledge of the bones, identify the insertion of the masseter.

Background

Topic: Muscle Origin and Insertion

This question tests your ability to identify the insertion site of a muscle based on anatomical diagrams and bone names.

Key Terms:

• Masseter: Main muscle for jaw elevation

• Insertion: Movable attachment site

• Mandible: Lower jaw bone

Step-by-Step Guidance

1. Identify the masseter muscle in the diagram.

2. Recall that the masseter elevates the mandible (jaw).

3. Determine which bone moves during chewing (mandible).

4. Use your knowledge of anatomy to match the insertion site to the correct bone.

Try solving on your own before revealing the answer!

Final Answer:

c) Mandible.

The masseter inserts on the mandible, which moves during chewing.