Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

10. Muscles

Levers

Anatomy & Physiology

10. Muscles

Levers

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Problem 4

Textbook Question

The action of the biceps brachii muscle on the hinge joint of the elbow is an example of which kind of lever system?
a. First class
b. Second class
c. Third class
d. Fourth class

Verified step by step guidance

Understand the three types of lever systems in the human body: First-class levers have the fulcrum between the effort and the load, second-class levers have the load between the effort and the fulcrum, and third-class levers have the effort between the load and the fulcrum.

Identify the components of the lever system in the action of the biceps brachii muscle at the elbow joint: The fulcrum is the hinge joint of the elbow, the load is the weight being lifted (e.g., the forearm or an object in the hand), and the effort is the contraction of the biceps brachii muscle.

Determine the position of the effort relative to the fulcrum and the load: In this case, the effort (biceps brachii contraction) is applied between the fulcrum (elbow joint) and the load (forearm or object being lifted).

Compare this arrangement to the definitions of the lever systems: Since the effort is between the fulcrum and the load, this matches the characteristics of a third-class lever system.

Conclude that the action of the biceps brachii muscle on the hinge joint of the elbow is an example of a third-class lever system.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lever Systems

A lever system consists of a rigid bar (the lever) that pivots around a fixed point called the fulcrum. In biomechanics, levers are classified into three types based on the relative positions of the effort, load, and fulcrum. Understanding these classifications helps in analyzing how muscles and joints work together to produce movement.

Types of Levers

There are three classes of levers: first class, second class, and third class. In a first-class lever, the fulcrum is between the effort and the load (e.g., a seesaw). In a second-class lever, the load is between the fulcrum and the effort (e.g., a wheelbarrow). In a third-class lever, the effort is applied between the fulcrum and the load (e.g., the biceps brachii at the elbow).

Biceps Brachii and Elbow Joint

The biceps brachii muscle acts on the elbow joint, which is a hinge joint allowing flexion and extension. When the biceps contracts, it applies force to the forearm, lifting the load (e.g., weight in the hand). This action exemplifies a third-class lever system, where the effort (muscle contraction) is applied between the fulcrum (elbow joint) and the load (weight in hand).

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