Joint Classification

Joint Classification

• Joints, also known as articulations, are where two or more bones meet.
• They provide mobility and hold the skeleton together.
• Fibrous joints are connected by collagen fibers of connective tissue, offering limited or no movement.
  • Sutures are found only in the skull, with extremely small collagen fibers and minimal movement.
  • Syndesmoses feature slightly longer collagen fibers, with examples including interosseous membranes (between radius/ulna and tibia/fibula), permitting slight movement.
  • Gomphoses are a type of syndesmosis, specifically tooth sockets.
• Cartilaginous joints connect bones with cartilage.
  • Synchondroses, united by hyaline cartilage (e.g. first rib to the manubrium), provide limited movement.
  • Symphyses are joined by fibrocartilage (e.g. interpubic disk), with limited movement.
• Synovial joints are the most common type, characterized by articular cartilage, a joint cavity, and a capsule. They allow for free movement.
  • Plane joints facilitate gliding motion between two flat surfaces (e.g. tarsal/carpal bones, vertebrae).
  • Hinge joints have one bone wrapping around another (e.g., humerus and ulna), allowing for biaxial movement.
  • Pivot joints permit rotation (e.g., pronation/supination of the forearm).
  • Condyloid joints feature a rounded surface fitting into a shallow cup (e.g., radius/ulna and proximal wrist bones), allowing biaxial movement.
  • Saddle joints have biaxial movement, allowing for a curved motion (e.g., carpal-metacarpal joint of the thumb).
  • Ball-and-socket joints allow movement in all directions (triaxial) (e.g., hip, shoulder joints).

Double-Jointed Individuals

• Double-jointed individuals don't have extra joints.
• Increased flexibility stems from more flexible articular/capsule ligaments.
• Reduced stability means a higher risk of injury.

Common Joint Injuries

• Cartilage tears are common overuse injuries (e.g., knee menisci).
  • Pieces of cartilage can interfere with joint function and are often surgically removed via arthroscopy.
• Sprains occur when ligaments reinforcing joints are torn or stretched.
  • Healing is slower due to poor vascularization.

Inflammatory/Degenerative Conditions

• Tendonitis is tendon inflammation from overuse, treated with rest, ice, and anti-inflammatory drugs.
• Arthritis encompasses over 100 conditions affecting joint comfort and function, involving joint inflammation.

Muscular System Overview

• Muscle tissue changes chemical energy to mechanical energy.
• Muscle fibers (muscle cells) are elongated.
• Cardiac muscle cells are specific to the heart.

Muscle Functions

• Movement
• Posture maintenance
• Heat generation (shivering)
• Joint stabilization
• Organ protection
• Substance regulation (constriction/dilation)
• Vasodilation/vasoconstriction

Skeletal Muscle

• Consciously controlled
• Rich blood supply
• Each fiber has a nerve ending (needs stimulation to contract).
• Multinucleated cells

Smooth Muscle

• Filaments arranged diagonally; non-striated.
• A single neuron often reaches many muscle fibers (allowing for coordinated contractions).
• Some have no nerve supply, relying on local chemicals and hormones.

Cardiac Muscle

• Thin and thick filaments, similar to skeletal muscle.
• Contractions are controlled locally by electrical/chemical signals (pacemaker).
• Interconnected, contracting as a unit.

Muscle Mechanics

• Origin: More fixed attachment point; Insertion: Attachment moving part.
• Muscles pull, not push.
  • One muscle elicits a motion, another reverses it.
  • Agonist: (prime mover) produces movement.
  • Antagonist: Opposes specific movement; relaxes while agonist acts.
  • Synergist: Assists the agonist.
  • Fixator: Stabilizes a joint/bone.
  • Reciprocal inhibition: Antagonist relaxes while agonist acts.
  • Concentric contraction: Agonist shortens.
  • Eccentric contraction: Agonist lengthens.

Muscle Names

• Based on location, shape, direction of fibers, size, number of origins, location of attachments, and action.

Joint Movement Types

• Elevation/Depression: Lifting/lowering (e.g., shoulder shrug).
• Protraction/Retraction: Forward/backward movement (e.g., jaw thrusting).
• Eversion/Inversion: Foot turning outward/inward.
• Supination/Pronation: Palm facing upward/downward.
• Circumduction: Limb rotation (e.g., arm circles).
• Abduction/Adduction: Movement away/towards midline.
• Dorsal/Plantar flexion: Foot movement up/down.
• Flexion/Extension: Angle opening/closing.

Back, Neck, and Shoulder Muscles

• Trapezius: Elevates, retracts, rotates scapula upward or downward.
• Rhomboids (minor & major): Retract and elevate, rotate scapula downward.
• Levator scapulae: Elevates and rotates scapula downward.
• Latissimus dorsi: Extends, adducts, and medially rotates the arm.
• Serratus anterior: Abducts and protracts scapula, and upward rotation.
• Pectoralis minor: Weakly protracts and rotates scapula downward.
• Pectoralis major: Flexes, extends (flexed arm), adducts, and medially rotates arm.
• Sternocleidomastoid: Flexes, laterally rotates, and flexes neck (bilaterally and unilaterally).
• Erector spinae: Extends and laterally flexes back (group of muscles).

Shoulder Muscles

• Deltoid: Flexes, extends, laterally/medially rotates, and abducts the arm.
• Rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis): Stabilize shoulder joint.
  • Supraspinatus: Abduction.
  • Infraspinatus: Lateral rotation.
  • Teres minor: Lateral rotation, extension.
  • Subscapularis: Medial rotation.
• Teres major: Medial rotation, extension, and adduction of arm (not a rotator cuff).

Arm Muscles

• Biceps brachii: Flexes elbow, supinates forearm, and flexes shoulder.
• Brachialis: Flexes elbow.
• Brachioradialis: Flexes elbow.
• Triceps brachii: Extends elbow, and extends arm (long head only).
• Anconeus: Synergist to triceps brachii; extends elbow.

Anterior Forearm Muscles

• Superficial group: Medial epicondyle origin, elbow flexion, wrist flexion.
  • Pronator teres: Pronates forearm.
  • Flexor carpi radialis: Wrist flexion.
  • Palmaris longus: Wrist flexion.
  • Flexor carpi ulnaris: Wrist flexion.
• Intermediate group: Flexion of wrist, fingers, elbow FDS.
• Deep group: Wrist flexion, finger flexion, and forearm pronation
  • Flexor digitorum profundus (FDF): Flexes fingers.
  • Flexor pollicis longus (FPL): Flexes thumb.
  • Pronator quadratus (PQ): Pronates forearm.

Posterior Forearm Muscles

• Superficial group: Lateral epicondyle origin, wrist and finger extension.
• Deep group: More varied actions; often relating to finger and/or thumb extension.

Thorax and Abdomen Muscles

• Diaphragm: Increases thoracic dimensions for inspiration.
• Intercostals:
  • External intercostals: Elevate ribs (inspiration).
  • Internal intercostals: Depress ribs (expiration).
• Abdominal muscles:
  • External oblique: Trunk flexion, lateral rotation, and compression.
  • Internal oblique: Same actions as external oblique.
  • Transverse abdominis: Compresses abdomen.
  • Rectus abdominis: Trunk flexion and compression.

Thigh Muscles

• Iliopsoas (psoas major & iliacus): Flexes and laterally rotates thigh.
• Tensor fasciae latae (TFL): Abducts and flexes thigh.
• Gluteus maximus: Extends and laterally rotates thigh.
• Gluteus medius & minimus: Abduct and medially rotate thigh.
• Sartorius: Flexes, laterally rotates, and abducts thigh; flexes knee.
• Quadriceps femoris: Extends knee;
  • Rectus femoris: Also flexes hip.
  • Vastus lateralis, medialis, intermedius: Extend knee.
• Adductor muscles: Adduct, abduct flex and extend thighs
  • Gracilis, pectineus, adductor brevis, longus, magnus
• Hamstrings (biceps femoris, semitendinosus, semimembranosus): Extend hip, flex knee.

Leg Muscles

• Popliteus: Flexes knee and medially rotates tibia (unlocks extended knee).
• Gastrocnemius: Plantar flexes ankle and flexes knee.
• Plantaris: Plantar flexes ankle and flexes knee (deep to gastrocnemius).
• Soleus: Plantar flexes ankle.
• Tibialis posterior: Plantar flexes and inverts foot.
• Flexor digitorum longus: Plantar flexes ankle, flexes toes.
• Flexor hallucis longus: Plantar flexes ankle, flexes big toe
• Tibialis anterior: Dorsiflexes ankle, inverts foot.
• Extensor digitorum longus: Dorsiflexes ankle, extends toes.
• Extensor hallucis longus: Dorsiflexes ankle, extends big toe.
• Peroneus (fibularis) longus, brevis, tertius: Evert foot , plantar flex ankle.