Textbook Question
If 'adductor' is part of the name of a muscle, what does that tell you about the muscle?
a. It is a wide muscle.
b. It is a long muscle.
c. It raises a body part.
d. It pulls a body part toward the midline.
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Ch. 9 The Muscular System
Amerman2nd EditionHuman Anatomy & PhysiologyISBN: 9780136873822
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Table of contents
- Ch. 1 Introduction to Anatomy and Physiology26
- Ch. 2 The Chemistry of Life38
- Ch. 3 The Cell55
- Ch. 4 Histology47
- Ch. 5 The Integumentary System30
- Ch. 6 Bones and Bone Tissue36
- Ch. 7 The Skeletal System40
- Ch. 8 Articulations19
- Ch. 9 The Muscular System36
- Ch. 10 Muscle Tissue and Physiology29
- Ch. 11 Introduction to the Nervous System and Nervous Tissue28
- Ch. 12 The Central Nervous System42
- Ch. 13 The Peripheral Nervous System41
- Ch. 14 The Autonomic Nervous System and Homeostasis31
- Ch. 15 The Special Senses39
- Ch. 16 The Endocrine System42
- Ch. 17 The Cardiovascular System I: The Heart30
- Ch. 18 The Cardiovascular System II: The Blood Vessels43
- Ch. 19 Blood32
- Ch. 20 The Lymphatic System and Immunity45
- Ch. 21 The Respiratory System27
- Ch. 22 The Digestive System27
- Ch. 23 Metabolism and Nutrition7
- Ch. 24 The Urinary System39
- Ch. 25 Fluid, Electrolyte, and Acid-Base Homeostasis39
- Ch. 26 The Reproductive System10
- Ch. 27 Development and Heredity5
Chapter 9, Problem L2.4
Why do the three parts of the trapezius muscle have three different actions?
Verified step by step guidance1
Understand the anatomy of the trapezius muscle: The trapezius is a large, triangular muscle located in the upper back. It is divided into three distinct regions: the upper (descending), middle (transverse), and lower (ascending) fibers. Each region has different attachment points and orientations, which influence their actions.
Examine the attachment points: The upper fibers originate from the occipital bone and cervical vertebrae, the middle fibers originate from the thoracic vertebrae, and the lower fibers originate from the lower thoracic vertebrae. All fibers insert on the clavicle, acromion, and spine of the scapula. These attachment points determine the direction of pull when the muscle contracts.
Analyze the orientation of muscle fibers: The upper fibers are angled downward and laterally, the middle fibers run horizontally, and the lower fibers are angled upward and medially. The orientation of these fibers dictates the direction of force they exert on the scapula during contraction.
Relate fiber orientation to specific actions: The upper fibers elevate the scapula and assist in upward rotation, the middle fibers retract the scapula, and the lower fibers depress the scapula and assist in upward rotation. These actions are a result of the specific angles and directions of pull created by the fibers.
Consider the role of neural control: The trapezius muscle is innervated by the accessory nerve (cranial nerve XI) and receives input from the cervical spinal nerves. Neural signals coordinate the contraction of different parts of the muscle to produce distinct actions based on the body's needs, such as lifting the arm or stabilizing the shoulder.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Anatomy of the Trapezius Muscle
The trapezius muscle is a large, triangular muscle located in the upper back and neck, divided into three distinct parts: upper, middle, and lower. Each part has a unique origin, insertion, and fiber orientation, which contribute to its specific functions. Understanding the anatomy is crucial for comprehending how these parts can perform different actions.
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Muscle Naming
Muscle Fiber Orientation
The orientation of muscle fibers affects how a muscle contracts and the direction of force it generates. The upper fibers of the trapezius are oriented to elevate the scapula, while the middle fibers are aligned for retraction, and the lower fibers assist in depression. This variation in fiber direction is key to the different actions performed by each part of the muscle.
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Functional Roles of the Trapezius
The trapezius muscle plays a vital role in shoulder and neck movement, with each part contributing to specific actions. The upper part elevates the shoulders, the middle part retracts them, and the lower part helps in depressing the shoulders. Understanding these functional roles is essential for analyzing how the trapezius muscle facilitates complex movements in daily activities and sports.
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Related Practice
Textbook Question
Why do you think that the muscles of the erector spinae and transversospinal muscle groups remain in a state of continual contraction when we are upright?
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Textbook Question
Explain why strengthening the levator ani muscle may help improve bladder and bowel continence (voluntary control over urination and defecation).
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Textbook Question
Predict the location and function of the flexor digitorum profundus muscle based only on its name.
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Textbook Question
The rectus femoris muscle originates from the anterior superior iliac spine and inserts into the tibial tuberosity. Predict its main actions with only this information.
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Textbook Question
Explain how the diaphragm muscle is able to increase the size of the thoracic cavity even though it doesn't insert into a bone.
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