Chest and Shoulder Muscles of The Human Body
Embarking on a journey to explore the intricacies of the chest and shoulder muscles, this article aims to provide a comprehensive understanding of these vital components of the human body. We will meticulously dissect each muscle in these regions, examining their origins and insertions to understand how they function. We will investigate the isolated functions of these muscles, uncovering the specific roles they play in movements ranging from subtle to robust.
Moving beyond individual actions, our focus will shift to their integrated functions, revealing how these muscles work together to facilitate complex and coordinated upper body movements. We will also examine the aspect of innervation, highlighting the sophisticated neural connections that control and fine-tune the actions of these muscles. This comprehensive overview is tailored for a wide audience, including medical professionals, fitness enthusiasts, and anyone who is curious about the dynamic interplay of muscles that enable the upper body’s strength, mobility, and precision.
Defining Terms
Origin – The fixed attachment point of a muscle. This is typically the end of the muscle that attaches to the more stationary bone in a pair of bones being moved by that muscle. The origin is generally proximal, meaning closer to the center of the body, or on the more stable part of the skeletal structure.
Insertion – The insertion point of a muscle is where it attaches to the bone and is the part that moves during muscle contraction. This part of the muscle is usually located far from the center of the body, and moves towards the muscle’s origin when it contracts. Understanding the insertion point is important in determining a muscle’s function in movement and leverage, as it influences the direction and force of the movement produced by the muscle contraction.
Isolated Function – The term “isolated function” refers to the specific action a muscle performs when it contracts independently, without the influence of other muscles. Understanding this concept is crucial for comprehending the primary role of each muscle in movement, as it highlights the muscle’s unique ability to produce a particular movement at a joint. The study of isolated functions is often used to understand muscle imbalances, rehabilitation needs, and design targeted exercises for strengthening or stretching a specific muscle.
Integrated Function – The coordinated action of muscles is crucial during complex movements and requires them to work in concert with other muscles and body systems. Isolated function, which focuses on a muscle acting alone, is not enough to fully understand bodily movements. Integrated function, on the other hand, emphasizes how muscles function together in groups, providing a more holistic view of bodily movements. This concept is essential to comprehend how muscles contribute to overall body mechanics, stability, and efficiency during everyday activities and sports.
Innervation – the supply of nerves to a muscle, which enables the muscle to receive and respond to neural signals. This connection is crucial for muscle activation and control, as it allows the nervous system to regulate muscle contractions, both voluntary and involuntary. Innervation is a key aspect in understanding how muscles function, their responsiveness to stimuli, and their role in movement and sensation.
Concentric – refers to a type of muscle contraction in which the muscle fibers shorten as they contract. This occurs when a muscle generates enough force to overcome resistance, resulting in the movement of body parts towards each other. A common example of a concentric contraction is the upward movement during a bicep curl, where the bicep muscle shortens to lift the weight. Concentric contractions are integral to many types of physical activities and exercises, playing a key role in building muscle strength and movement.
Eccentric – refers to a type of muscle contraction where the muscle lengthens while under tension. This occurs when a muscle gradually controls or resists the movement caused by an external force, like gravity. Eccentric contractions are often associated with controlled lowering or decelerating actions, such as lowering a weight during a bicep curl or descending stairs. They play a crucial role in activities requiring controlled movements and are significant in muscle strengthening and injury prevention.
Isometric – refers to a type of muscle contraction where the muscle generates force without changing its length. During isometric exercises, the muscle neither shortens (as in concentric contractions) nor lengthens (as in eccentric contractions), but tension is still produced. Common examples include holding a plank position or maintaining a squat. Isometric contractions are essential for stabilizing joints and maintaining posture, and they are often used in rehabilitation and strength training programs.
Serratus Anterior
Origin
Ribs 4-12
Insertion
Medial border of the scapula
Isolated Function
Concentric action – Scapular protraction
Integrated Function
Eccentric action – Scapular retraction
Isometric action – Stabilizes the scapula
Innervation
Long thoracic nerve (C5-C7)
Rhomboids
Origin
Spinous processes of C7-T5
Insertion
Medial border of the scapula
Isolated Function
Concentric action – Produces scapular retraction and downward rotation
Integrated Function
Eccentric action – Scapular protraction and upward rotation
Isometric action – Stabilizes the scapula
Innervation
Dorsal scapular nerve (C4-C5)
Lower Trapezius
Origin
Spinous processes of T6-T12
Insertion
Spine of the scapula
Isolated Function
Concentric action – Scapular depression
Integrated Function
Eccentric action – Scapular elevation
Isometric action – Stabilizes the scapula
Innervation
Cranial nerve Xl and ventral rami C2-C4
Middle Trapezius
Origin
Spinous processes of T1-T5
Insertion
Acromion process of the scapula and superior aspect of the spine of the scapula
Isolated Function
Concentric action – Scapular retraction
Integrated Function
Eccentric action – Scapular protraction and elevation
Isometric action – Stabilizes scapula
Innervation
Cranial nerve Xl and ventral rami C2-C4
Upper Trapezius
Origin
External occipital protuberance of the skull and spinous process of C7
Insertion
Lateral third of the clavicle and acromion process of the scapula
Isolated Function
Concentric action – Cervical extension, lateral flexion and rotation and scapular elevation
Integrated Function
Eccentric action – Cervical flexion, lateral flexion, rotation and scapular depression
Isometric action – Stabilizes the cervical spine and scapula and stabilizes the medial border of the scapula creating a stable base for the prime movers during scapular abduction and upward rotation
Innervation
Cranial nerve Xl and ventral rami C2-C4
Pectoralis Major
Origin
Anterior surface of the clavicle, anterior surface of the sternum and cartilage of ribs 1-7
Insertion
Greater tubercle of the humerus
Isolated Function
Concentric action – Shoulder flexion (clavicular fibers), horizontal adduction and internal rotation
Integrated Function
Eccentric action – Shoulder extension, horizontal abduction and external rotation
Isometric – Stabilizes the shoulder girdle
Innervation
Medial and lateral pectoral neves (C5-C7)
Pectoralis Minor
Origin
Ribs 3-5
Insertion
Coracoid process of the scapula
Isolated Function
Concentric action – Protracts the scapula
Integrated Function
Eccentric action – Scapular retraction
Isometric action – Stabilizes the shoulder girdle
Innervation
Medial pectoral nerve (C6-T1)
Anterior Deltoid
Origin
Lateral third of the clavicle
Insertion
Deltoid tuberosity of the humerus
Isolated Function
Concentric action – Shoulder flexion and internal rotation
Integrated Function
Eccentric action – Shoulder extension and external rotation
Isometric action – Stabilizes the shoulder girdle
Innervation
Axillary nerve (C5-C6)
Medial Deltoid
Origin
Acromion process of the scapula
Insertion
Deltoid tuberosity of the humerus
Isolated Function
Concentric action – Shoulder abduction
Integrated Function
Eccentric action – Shoulder adduction
Isometric action – Stabilizes the shoulder girdle
Innervation
Axillary nerve (C5-C6)
Posterior Deltoid
Origin
Spine of the scapula
Insertion
Deltoid tuberosity of the humerus
Isolated Function
Concentric action – Shoulder extension and external rotation
Integrated Function
Eccentric action – Shoulder flexion and internal rotation
Isometric action – Stabilizes the shoulder girdle
Innervation
Axillary nerve (C5-C6)
Teres Major
Origin
Inferior angle of the scapula
Insertion
Lesser tubercle of the humerus
Isolated Function
Concentric action – Shoulder internal rotation, adduction and extension
Integrated Function
Eccentric action – Shoulder external rotation, abduction and flexion
Isometric action – Stabilizes the shoulder girdle
Innervation
Lower subscapular nerve
Teres Minor
Origin
Lateral border of the scapula
Insertion
Greater tubercle of the humerus
Isolated Function
Concentric action – Shoulder external rotation
Integrated Function
Eccentric action – Shoulder internal rotation
Isometric action – Stabilizes the shoulder girdle
Innervation
Axillary nerve (C5-C6)
Infraspinatus
Origin
Infraspinous fossa of the scapula
Insertion
Middle facet of the greater tubercle of the humerus
Isolated Function
Concentric action – Shoulder external rotation
Integrated Function
Eccentric action – Shoulder internal action
Isometric action – Stabilizes the shoulder girdle
Innervation
Suprascapular nerve (C5-C6)
Subscapularis
Origin
Subscapular fossa of the scapula
Insertion
Lesser tubercle of the humerus
Isolated Function
Concentric action – Shoulder internal rotation
Integrated Function
Eccentric action – Shoulder external rotation
Isometric action – Stabilizes the shoulder girdle
Innervation
Upper and lower subscapular nerves (C5-C6)
Supraspinatus
Origin
Supraspinous fossa of the scapula
Insertion
Superior facet of the greater tubercle of the humerus
Isolated Function
Concentric action – Abduction of the arm
Integrated Function
Eccentric action – Adduction of the arm
Isometric action – Stabilizes the shoulder girdle
Innervation
Suprascapular nerve (C5-C6)
Conclusion
In conclusion, our detailed exploration of the chest and shoulder muscles has offered a deep dive into the crucial roles these muscles play in the human body’s structure and function. We have navigated through each muscle, uncovering the intricacies of their origins, insertions, and the specific movements they facilitate both independently and in collaboration. The study of their innervation has further illuminated the complex neural control behind these movements, emphasizing the muscles’ significance in both everyday activities and specialized movements.
This journey into the anatomy of the chest and shoulder muscles is invaluable not just for medical and fitness professionals, but also for anyone seeking to understand and appreciate the sophisticated mechanics of the human body. As we conclude, it’s evident that these muscles, in their strength and versatility, are essential for a vast range of motions, contributing significantly to our overall physical capabilities and well-being.