3.3

Components of the Synovial Joint

• Muscle
• Articular cartilage covers the bone surfaces within the joint.
• Convex joint member (ball).
• Joint capsule encloses the joint.
• Concave joint member (socket).
• Joint space is the area between the bones.
• Joint cavity.
• The synovial membrane lines the joint capsule and consists of the intima and subintima layers.
• Synovial cavity contains synovial fluid for lubrication.
• Hyaline articular cartilage covers the bone surfaces within the joint.
• Fibrous membrane is a component of the joint capsule.

Movements of Synovial Joints

• Extension is straightening a joint, while flexion is bending the joint.
• Abduction is moving a limb away from the midline, and adduction is moving it toward the midline.
• Medial (internal) rotation involves rotating a limb towards the midline.
• Lateral (external) rotation involves rotating a limb away from the midline.
• Circumduction is a circular movement at a joint.
• Dorsiflexion and plantarflexion occur at the ankle joint.
• Inversion and eversion occur at the subtalar and transverse tarsal joints.
• Opposition and Reposition.

Muscle Terminology

• Agonist (prime mover) muscles produce the most force during a particular joint action.
• Synergist muscles aid the prime mover by producing more power and stabilizing the joint.
• Antagonist muscles oppose the prime mover to limit speed or range of motion.
• Fixator muscles stabilize the bone that is the attachment for the prime mover's origin.

Muscle Classification

• Parallel muscles have a uniform width.
• Fusiform muscles are thick in the middle and tapered at the ends.
• Pennate muscles are feather-shaped with oblique insertion on a tendon.
• Pennate muscles provide higher force production and smaller excursions compared to nonpennate muscles.
• Convergent (triangular) muscles are broad with narrower ends.
• Circular muscles (sphincters) are arranged in a circular fashion.

Posterior Axioappendicular Muscles

• Muscles that connect the axial skeleton to the appendicular skeleton.
• These include the trapezius, latissimus dorsi, levator scapulae, and rhomboids.
• The trapezius is innervated by cranial nerve (CN) XI and elevates the shoulder (shrug), depresses the shoulder, and retracts the scapula medially.
• The latissimus dorsi is innervated by the thoracodorsal nerve and extends and adducts the humerus, pulling the body toward the arms in climbing or swimming.
• The rhomboids and levator scapulae are innervated by the dorsal scapular nerve (from C5 root).
• The rhomboids retract the scapula, and levator scapulae elevates the scapula, and medially rotate the inferior angle of the scapula.

Anterior Axioappendicular Muscles

• Include the subclavius, pectoralis major & pectoralis minor, and serratus anterior muscles.
• The pectoralis major is innervated by the lateral and medial pectoral nerves.
• The pectoralis major adducts the humerus, protracts the scapula, and medially rotates the humerus at the shoulder.
• The pectoralis minor is innervated by the medial pectoral nerve.
• The pectoralis Minor protracts and depresses the scapula and medially rotates the humerus at the shoulder.
• The subclavius is innervated by the subclavian nerve and holds the clavicle in the sternoclavicular joint.
• The serratus anterior is innervated by the long thoracic nerve and protracts the scapula (superior part), laterally rotates the scapula (inferior part), and elevates the ribs when the shoulder is fixed.

Scapulohumeral Muscles

• The deltoid is innervated by the axillary nerve
• The deltoid flexes, adducts, and internally rotates the humerus (anterior part); extends, adducts, and externally rotates the humerus (posterior part); and abducts the humerus (lateral part).
• The teres major is innervated by the subscapular nerve and adducts the humerus.

Rotator Cuff Muscles

• Includes the supraspinatus, infraspinatus, teres minor, and subscapularis; the teres major is NOT a part of the rotator cuff.
• The action of the rotator cuff is to hold the humeral head in place.
• The supraspinatus is innervated by the suprascapular nerve and abducts the humerus.
• The infraspinatus and teres minor are laterally rotate the humerus and are both innervated by the axillary nerve.
• The subscapularis medially rotates the humerus and is innervated by the subscapular nerve

Nerves and Innervation of the Axioappendicular & Scapulohumeral Muscles

• Roots:
• Long thoracic nerve innervates the serratus anterior.
• Dorsal scapular nerve innervates the levator scapulae and rhomboids.
• Superior trunk:
• Suprascapular nerve innervates the supraspinatus and infraspinatus.
• Subclavian nerve innervates the subclavius.
• Cord:
• Lateral pectoral nerve innervates the pectoralis major.
• Medial pectoral nerve innervates the pectoralis major/minor.
• Thoracodorsal nerve innervates the latissimus dorsi.
• Subscapular nerve innervates the subscapularis and teres major.
• Axillary nerve innervates the deltoid, and teres minor

Arm Compartments and Muscles

• The anterior compartment contains the musculocutaneous nerve and brachial artery.
• The posterior compartment contains the radial nerve and profunda brachii artery.
• Anterior Compartment Muscles:
• Coracobrachialis: Adducts humerus and flexes arm.
• Biceps Brachii: Supinates forearm, flexes supine forearm and helps hold humeral head in glenoid fossa.
• Brachialis: Flexes forearm in all positions.
• Posterior Compartment Muscles:
• Triceps Brachii: Extends forearm, resists dislocation of the shoulder, and extends & adducts humerus (long head).
• Anconeus

Forearm Osteology and Elbow Joint

• Bones of the forearm include the radius and ulna.
• The elbow joint is where the radius and ulna articulate with the humerus.
• Structures include: olecranon, head of radius, and trochlear notch.
• Anterior Elbow Joint: features the capitulum, trochlea, head of radius, and coronoid process.
• Posterior Elbow Joint: shows the olecranon, olecranon fossa, edge of trochlea, and head of radius.
• Ligaments of the Elbow: including the radial collateral ligament, ulnar collateral ligament, and annular ligament of the radius
• Arteries in and around the elbow joint: brachial artery, profunda brachii artery, radial collateral artery, radial recurrent artery, radial artery, common interosseous artery, superior/inferior ulnar collateral arteries, anterior/posterior ulnar recurrent arteries, and ulnar artery.
• Arterial Anastomoses: at the elbow joint.

Fascia of the Upper Limb

• Deltoid Fascia: Connective tissue covering the deltoid muscle.
• Clavipetoral Fascia: Surrounds the subclavius and pectoralis minor muscles.
• Brachial Fascia: The connective tissue sheath that surrounds the arm muscles.
• Axillary Fascia: Located at the base of the armpit, between the pectoralis major and latissimus dorsi muscles.