Chapter 11- Appendicular muscles PDF

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Chapter 11- Appendicular muscles...

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Chapter 11: Appendicular Muscles The appendicular muscles function to move your upper and lower limbs, including the pectoral and pelvic girdles. Although some of these muscles have attachments to the axial skeleton, they are considered appendicular muscles as they move the appendicular skeleton. The appendicular muscles can be categorized in multiple different ways. We will organize and discuss them in compartments and regions, including the pectoral girdle, shoulder, arm, forearm, and hand of the upper limb and the pelvic girdle, gluteal region, thigh, leg, and foot of the lower limb. 11.3 Upper Limb The muscles of the upper limb will encompass superficial (extrinsic) back muscles and muscles of the shoulder, arm, forearm, and hand. All of these muscles will move an aspect of the upper limb Extrinsic Back Muscles Recall that the intrinsic back muscles, located in the deep back, attach only to the axial skeleton and primarily move the vertebral column and head. In contrast, the extrinsic back muscles are more superficial, and although some may originate from the axial skeleton, they will either attach to the pectoral girdle (the scapula and clavicle) or the arm (humerus). Thus, these muscles function to stabilize the scapula and aid in movements of the arm. The scapula has specific anatomical movements associated with it. These include elevation (upward movement) and depression (downward movement) and protraction (abduction), as seen with hunched shoulders, and retraction (adduction), as seen in proper posture. The scapula can also perform superior (upward) rotation and inferior (downward) rotation, in which the glenoid cavity of the scapula is angled upward or downward, respectively. Superior and inferior rotation occurs primarily during abduction and adduction of the arm at the shoulder. When the arm is abducted, the glenoid cavity moves superiorly, while when the arm is adducted, the glenoid cavity moves inferiorly.

The extrinsic back muscles are located superficially on the posterior body wall. Some of these muscles connect the axial skeleton to the pectoral girdle, including the levator scapulae, rhomboid major and minor, and trapezius. Others, the latissimus dorsi muscle, connects the axial skeleton to the humerus.

The trapezius muscle is a large, triangular shaped muscle that spans most of the back. When looking at both the right and left trapezius muscles, they form a diamond shape on the back. The trapezius attaches proximally to the superior nuchal line, the external occipital protuberance of the skull and the spinous processes of the cervical and thoracic vertebrae. There are multiple distal attachments for the trapezius muscle: the lateral portion of the clavicle and the acromion process and spine of the scpaula. The trapezius muscle can be divided into three major sections based on fiber direction. The superior (upper, descending) portion of the muscle elevates the scapula, the middle (transverse) portion retracts the scapula, and the inferior (lower, ascending) portion depresses scapula. Both the superior and inferior portions also aid in superior rotation of the scapula during abduction of the arm at the shoulder joint. The trapezius muscle is innervated by the (spinal) accessory nerve (CN XI). The latissimus dorsi muscle is another triangular-shaped muscle located inferior and deep to the trapezius muscle. The latissimus dorsi muscle has a proximal attachment to the spinous processes of the inferior thoracic vertebra, the thoracolumbar fascia (a thick connective tissue), and the iliac crests. The distal attachment is at the inferior margin of the intertubercular groove of the humerus, near the distal attachment for the pectoralis major muscle. As the latissimus dorsi muscle travels from the posterior body wall to attach anteriorly to the intertubercular groove of the humerus, it will function to extend the arm at the shoulder joint. It also will adduct and medially rotate the arm at the shoulder joint. it is innervated by the thoracodorsal nerve. The levator scapulae muscle is a narrow muscle located deep to the trapezius muscle. It attaches proximally to the transverse processes of cervical vertebrae and attaches distally to the superior angle and superior medial border of the scapula. The levator scapulae muscle functions

to elevate and inferiorly rotate the scapula. It is innervated by anterior primary rami from the third and fourth cervical levels (C3 and C4) and the dorsal scapular nerve. The rhomboid major and minor muscles are for their rhomboid shape. They are located deep to the trapezius with the much narrower rhomboid minor muscle located superior to the rhomboid major muscle, although they often are seen as one muscle. The rhomboid muscles attach proximally to the spinous processes of the thoracic vertebrae and attach distally to the medial border of the scapula. The rhomboid muscles elevate and retract the scapula. Both rhomboid major and minor are innervated by the dorsal scapular nerve.

Shoulder Muscles The shoulder muscles attach proximally to the pectoral girdle and distally to the humerus. This includes the pectoralis minor, serratus anterior, subclavius, deltoid, teres major muscles. The pectoralis major muscle is often included in this group of muscles; however, it attaches proximally to the axial skeleton and distally to the humerus.

The pectoralis major muscle is a fan-shaped muscle on the anterior chest. The pectorlais major muscle has multiple portions, or "heads." The clavicular head attaches proximally to the medial end of the clavicle, and the sternocostal head attaches proximally to the costal cartilages and sternum. Both heads have a common distal attachment to the intertubercular groove of the humerus. Both heads acting together with flex, adduct, and medially rotate the arm at the glenohumeral joint. The clavicular head flexes the arm from an extended position, while the sternocostal head extends the arm from a flexed position. The pectoralis major muscle is innervated by the medial and lateral pectoral nerves. The pectoralis minor is a small muscle, located deep to pectoralis major. It attaches proximally to the axial skeleton along the ribs then distally to the coracoid process of the scapula. Contraction of this muscle causes depression and protraction of the scapula. It is innervated by the medial pectoral nerve. The serratus anterior muscle is a large muscle that spans most of the rib cage. It is named for its serrated (saw-like) appearance. This muscle attaches to the anterior ribs and then spans the rib cage to attach to the medial (vertebral) border of the scapula. Note that this muscle is located on both the anterior and posterior body wall, but is best seen on from an anterior view. The serratus anterior muscle protracts and superior rotates the scapula. Due to its attachment to the medial border of the scapula, it also serves to stabilize the scapula against the posterior body wall. It is innervated by the long thoracic nerve. The serratus anterior muscle is innervated by the long thoracic nerve. This nerve runs along the lateral aspect of this muscle. Damage to the long thoracic nerve will result in a weakened or paralyzed serratus anterior muscle, resulting in a clinical sign known as a winged scapula. Recall that the serratus anterior muscle attaches to the medial border of the scapula. It functions to hold the scapula in its normal anatomical position against the rib cage. Thus, paralysis of this muscle will cause the medial border of the scapula to protrude, as the serratus anterior muscle will no longer be able to hold the scapula in place. The subclavius muscle is a small muscle that spans from the first rib to the clavicle. It functions to depress the clavicle and stabilize the shoulder. It is innervated by the nerve to subclavius. The deltoid muscle is a triangular shaped muscle, named for the Greek letter Delta (Δ). The deltoid muscle has three portions, or regions, similar to the trapezius muscle. The anterior (clavicular) portion attaches proximally along the clavicle. The lateral (acromial) portion attaches proximally to the acromion process. And the posterior (scapular, spinal) portion attaches proximally to the spine of the scapula. All three portions have a common distal attachment to the deltoid tuberosity of the humerus. Due to the differences in muscle fiber direction, each portion will have specific actions. The anterior portion will flex the arm at the shoulder joint. The lateral portion will abduct the arm at the shoulder joint. And the posterior portion will extend the arm at the shoulder joint. The primary movement associated with the deltoid muscle is abduction of the arm at the shoulder joint after initiation (the supraspinatus muscle, discussed later in this chapter, initiates the first 15 degrees of abduction). The axillary nerve, arising from the brachial plexus and located in the axilla, is commonly injured. An injury to the axillary nerve most often occurs due to a dislocation of the humerus, a fracture at the surgical neck of the humerus, or from compression of the axilla, such as seen in an improper use of crutches. As the axillary nerve innervates the deltoid and teres minor muscles, an injury to this nerve would cause weakness or paralysis of these muscles. This would lead to numbness in the shoulder and an inability to abduct the arm past the first 15 degrees.

The teres major muscle attaches proximally to the inferior angle of the scapula and crosses anteriorly to attach distally to the medial lip of the intertubercular groove. Due to its similar trajectory to the latissimus dorsi muscle, it will have the same actions: extension, adduction, and medial rotation of the arm at the shoulder joint. It is innervated by the lower subscapular nerve.

Rotator Cuff Muscles The rotator cuff muscles are a group of four muscles that cross tightly around the glenohumeral joint. These muscles will all function to move the arm and stabilize the glenohumeral (shoulder) joint. The muscles of the rotator cuff can be remembered using the acronym “SITS,” as they include the supraspinatus, infraspinatus, teres minor, and subscapularis muscles. The supraspinatus muscle originates on the posterior scapula in the supraspinous fossa and inserts on the greater tubercle of the humerus. The supraspinatus muscle acts to abduct the arm at the shoulder joint for the first 15 degrees of movement. The infraspinatus muscle originates in the infraspinous fossa of the scapula and inserts on the greater tubercle of the humerus. The teres minor muscle originates on the posterior inferior surface of the lateral border of the scapula and inserts on the greater tubercle. Both the infraspinatus and teres minor muscles act to laterally rotate the arm at the shoulder joint. Note the orientation of the muscle fibers of these three muscles in the 3D model below. The supraspinatus crosses superior to the shoulder joint, thus, acts to abduct the arm at the shoulder, while the infraspinatus and teres minor muscles cross posterior to the joint and thus laterally rotate the arm at the shoulder. Finally, the subscapularis muscle originates on the subscapular fossa on the anterior scapula and inserts on the lesser tubercle of the humerus. The subscapularis muscle acts to medially rotate the arm at the shoulder joint.

A rotator cuff injury can be caused by a variety of movements and can happen to anyone. You don’t have to be an athlete to experience rotator cuff injury or inflammation. An older physiology instructor with the habit of swinging her heavy backpack onto one shoulder to travel across campus slowly developed a painful shoulder. What seemed to be a minor problem eventually ballooned into a severely limited range of motion and pain that woke her up at night. The diagnosis? Rotator cuff tendinitis—an inflammation of the tendons surrounding the shoulder joint. Rest, heat, and anti-inflammatory medicine followed by careful self-administered physical therapy to bring back the normal range and prevent “frozen shoulder” restored normal function to the teacher’s shoulder joint. She now carries her backpack properly, on both shoulders, and is more mindful when she hoists it up!

An injury to the rotator cuff can range from mild inflammation of tendons and bursae to a complete tear of a tendon. In a rotator cuff injury, the most common muscle involved (injured) is the supraspinatus muscle. This muscle is sandwiched between the joint capsule of the glenohumeral joint and the acromion process of the scapula. Due to the muscle’s close association to these structures, repetitive motions of the shoulder, especially abduction, can lead to inflammation of the tendon of the supraspinatus muscle. In severe cases, the tendon of the supraspinatus muscle can tear, leading to a rotator cuff tear. Axillary Folds The region of the axilla is bounded anteriorly and posteriorly by the inferior borders or margins of muscles. These boundaries are referred to as the anterior and posterior axillary folds. The anterior axillary fold is composed of the pectoralis major muscle, while the posterior axillary fold is composed of the latissimus dorsi and teres major muscles.

Compartments The muscles found in the upper and lower limbs (arm, forearm, thigh, and leg) are divided into compartments by thick fascia (connective tissue) that surround the muscles and also extend between muscles to attach to bone as intermuscular septa. This allows for muscles in the same compartment to have the same blood supply and innervation, as well as similar actions. For example, in the upper limb, the anterior compartments will be flexors (of the arm, forearm, and/or hand), while the posterior compartment will be extensors (of the arm, forearm, and/or hand). Muscles of the Arm The muscles that are found either entirely or mostly in the arm will be discussed in this section. This includes muscles that cross the shoulder (glenohumeral) and/or elbow joints. In the arm, there is a thick fascia, known as brachial fasica, which extends as intermuscular septa to divide the arm into compartments. Therefore, we will discuss the arm muscles as either belonging to the anterior or posterior compartment.

Anterior Compartment of the Arm The anterior compartment of the arm contains the coracobrachialis, biceps brachii, and brachialis muscles. These three muscles will all be innervated by the musculocutaneous nerve. They will also all have similar actions: flexion of the arm and/or forearm. The coracobrachialis muscle is a small muscle that attaches proximally to the coracoid process of the scapula and distally to the superior medial shaft of the humerus. This muscle will flex and adduct the arm at the shoulder joint. The musculocutaneous nerve pierces the coracobrachialis muscle as it travels from the brachial plexus to the anterior compartment of the arm. As indicated by its name, the biceps brachii muscle has two "heads" (bi=two) that share a common distal attachment. The long head of the biceps brachii attaches proximally to the supraglenoid tubercle of the scapula and then crosses the shoulder joint to travel in the intertubercular groove. The short head of the biceps brachii attaches proximally to the coracoid process of the scapula and then runs medially to join the long head. Together, these muscle heads attach distally to the radial tuberosity of the radius. As both the long and short heads cross both the shoulder and elbow joints, they will act upon (move) both joints. The biceps brachii muscle will flex forearm at the elbow joint and weakly flex the arm at the shoulder joint. Examine the biceps brachii muscle in interactive model above and note the length of the muscle and the

number of attachments. Generally, as the length of the tendon and the more joints crossed increases, the muscle will be more unstable and have a weaker action. Although the biceps brachii flexes the forearm at the elbow and flexes the arm at the shoulder, the the biceps brachii's primary and most important function is supination. Due to its distal attachment at the radial tuberosity of the radius, contraction of the muscle will pull the radius laterally when the forearm is flexed. Test this on yourself by flexing your forearm and then pronating and supinating your forearm (like in the image below). Place your hand on your biceps and note when you can feel the muscle contracting (it should occur during supination). The brachialis muscle is located on the anterior humerus, deep to the biceps brachii muscle. It attaches proximally to the anterior surface of the humerus and distally to the coronoid process and ulnar tuberosity of the ulna. The brachialis muscle is the primary muscle that flexes the forearm at the elbow joint.

Posterior Compartment of the Arm The posterior compartment of the arm contains the triceps brachii muscle. This muscle is innervated by the radial nerve. As indicated by its name, the triceps brachii muscle has three "heads" (tri=three) that share a common distal attachment to the olecranon process of the ulna. The medial head of the triceps brachii attaches proximally to the medial shaft of the humerus, while the lateral head of the triceps brachii attaches proximally to the lateral shaft of the humerus. The long head of the triceps brachii attaches proximally to the infraglenoid tubercle of the scapula and is therefore the only head that crosses the shoulder joint. Thus, all three heads heads will extend the forearm at the elbow joint, while the long head will also extend the arm at the shoulder joint.

Muscles of the Forearm The muscles that are found either entirely or mostly in the forearm will be discussed in this section. This includes muscles that cross the joints of the elbow, wrist, and/or fingers and therefore will act upon the these joints. Recall that the digits of the hand are numbered from lateral to medial (I = thumb, II = pointer, index finger, III = middle finger, IV = ring finger, V = pinky, little finger). Also recall that muscles of the forearm are divided into compartments. These are primarily divided by the radius, ulna, and their interosseous membrane, as well as by a thick connective

tissue and intermuscular septa of the antebrachial fascia. Therefore, we will discuss the forearm muscles as either belonging to the anterior or posterior compartment

Anterior Compartment of the Forearm The anterior compartment of the forearm contains the multiple muscles that are innervated either by the median nerve or the ulnar nerve. Many of these muscles have a common proximal attachment to the medial epicondyle of the humerus, known as the common flexor tendon ("flexor wad"). They will also all have similar actions: pronation and/or flexion of the forearm, wrist, and/or fingers. Superficial Layer From medial to lateral: The pronator teres muscle has two heads. The humeral head has a proximal attachment to the medial epicondyle and supracondylar ridge of the humerus, while the ulnar head attaches proximally to the coronoid process of the ulna. Both heads have a common distal attachment to the lateral surface of the mid-shaft of the radius. As indicated by its name, the main action of the pronator teres muscle is pronation, although it does also weakly flex the forearm at the elbow joint. The flexor carpi radialis (FCR) muscle attaches proximally to the medial epicondyle of the humerus and attaches distally the bases of the second and third metacarpals. The flexor carpi radialis muscle flexes the forearm at the elbow joint and also flexes and abducts the wrist joint (radial deviation). The palmaris longus muscle is a very small muscle with a long tendon. The muscle attaches proximally to the medial epicondyle and distally the tendon blends into the palmar aponeurosis. This muscle flexes the wrist, albeit weakly. Palmaris longus is not present in every individual due to evolutionary forces. As we developed more muscles in our hand, specifically those that contribute to the mobility of our thumbs, we lost the need for this muscle. You can test to see if you have this muscle by touching the pads of your thumb and pinky fingers and the flexing the

wrist. If a narrow bulge is pres...