Exam 3 Study Guide: Skeletal System, Joints, and Muscular System

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Axial versus Appendicular Skeleton

Overview of the Human Skeleton

The human skeleton is divided into two main regions: the axial skeleton and the appendicular skeleton. Understanding their differences is fundamental to anatomy.

Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage (ribs and sternum). It supports and protects the organs of the head, neck, and trunk.
Appendicular Skeleton: Includes the bones of the limbs and the girdles (pectoral and pelvic) that attach them to the axial skeleton. It facilitates movement and manipulation of the environment.
Example: The femur is part of the appendicular skeleton, while the vertebrae are part of the axial skeleton.

Vertebral Column Anatomy and Landmarks

Structure and Function of the Vertebral Column

The vertebral column provides structural support, protects the spinal cord, and allows flexible movement.

Regions: Cervical (7), thoracic (12), lumbar (5), sacral (5 fused), coccygeal (4 fused).
Landmarks: Vertebral body, spinous process, transverse process, vertebral foramen, intervertebral discs.
Example: The atlas (C1) and axis (C2) are specialized cervical vertebrae allowing head rotation.

Skull Bones and Infant Skull Features

Skull Anatomy and Development

The skull protects the brain and forms the structure of the face. Infant skulls have unique features to accommodate growth.

Major Bones: Frontal, parietal, temporal, occipital, sphenoid, ethmoid, maxilla, mandible.
Infant Features: Fontanelles (soft spots) allow for brain growth and passage through the birth canal.
Example: The anterior fontanelle is the largest and closes by 18-24 months.

Upper and Lower Limb Bones

Major Bones of the Limbs

The limbs are composed of long, short, and irregular bones that enable movement and support.

Upper Limb: Humerus, radius, ulna, carpals, metacarpals, phalanges.
Lower Limb: Femur, tibia, fibula, patella, tarsals, metatarsals, phalanges.
Example: The humerus articulates with the scapula at the shoulder joint.

Joint Classifications and Movement Types

Types of Joints and Their Movements

Joints are classified by their structure and the type of movement they allow.

Structural Classification: Fibrous, cartilaginous, synovial.
Functional Classification: Synarthrosis (immovable), amphiarthrosis (slightly movable), diarthrosis (freely movable).
Movement Types: Flexion, extension, abduction, adduction, rotation, circumduction.
Example: The knee is a synovial hinge joint allowing flexion and extension.

Synovial Joint Structure and Function

Anatomy of Synovial Joints

Synovial joints are the most movable type of joint, characterized by a fluid-filled cavity.

Components: Articular cartilage, joint (synovial) cavity, synovial membrane, fibrous capsule, ligaments.
Function: Allow a wide range of movements and absorb shock.
Example: The shoulder (glenohumeral) joint is a ball-and-socket synovial joint.

Lever Systems in Human Movement

Biomechanics of Levers

Muscles and bones interact as lever systems to produce movement.

Types of Levers: First-class, second-class, third-class (most common in the body).
Components: Fulcrum, effort, load.
Example: The elbow joint acts as a third-class lever during biceps flexion.
Formula:

Major Skeletal Muscle Actions

Types of Muscle Movements

Skeletal muscles produce specific actions at joints.

Actions: Flexion, extension, abduction, adduction, rotation, pronation, supination.
Example: The quadriceps femoris extends the knee.

Muscle Origins, Insertions, and Agonists

Muscle Attachments and Roles

Muscles attach to bones at specific sites and play distinct roles in movement.

Origin: The fixed attachment point.
Insertion: The movable attachment point.
Agonist: The primary muscle responsible for movement.
Example: The biceps brachii originates at the scapula and inserts on the radius; it is the agonist for elbow flexion.

Rotator Cuff Muscles and Functions

Shoulder Stability and Movement

The rotator cuff is a group of muscles and tendons stabilizing the shoulder joint.

Muscles: Supraspinatus, infraspinatus, teres minor, subscapularis.
Functions: Stabilize the glenohumeral joint, allow rotation and abduction of the arm.
Example: The supraspinatus initiates abduction of the arm.

Skeletal Muscle Tissue Organization

Structure of Skeletal Muscle

Skeletal muscle tissue is organized into hierarchical structures for efficient contraction.

Levels: Muscle (organ), fascicle, muscle fiber (cell), myofibril, sarcomere.
Connective Tissue: Epimysium, perimysium, endomysium.
Example: The sarcomere is the functional unit of contraction.

Sliding Filament Theory of Contraction

Mechanism of Muscle Contraction

The sliding filament theory explains how muscles contract at the molecular level.

Key Proteins: Actin (thin filament), myosin (thick filament).
Process: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.
Formula:
Example: During contraction, the H zone and I band decrease in width.

Neuromuscular Junction Physiology

Communication Between Nerve and Muscle

The neuromuscular junction is where motor neurons stimulate muscle fibers.

Components: Motor neuron, synaptic cleft, muscle fiber, acetylcholine (ACh).
Process: ACh is released, binds to receptors, triggers action potential in muscle.
Example: Botulinum toxin blocks ACh release, causing paralysis.

Muscle Contraction and Force Generation

Factors Affecting Muscle Force

Muscle force depends on several physiological factors.

Factors: Number of fibers recruited, frequency of stimulation, muscle length, cross-sectional area.
Formula:
Example: Summation and tetanus increase force output.

Muscle Adaptations to Activity and Inactivity

Effects of Exercise and Disuse

Muscle tissue adapts to changes in activity level.

Activity: Increases muscle size (hypertrophy), strength, endurance.
Inactivity: Leads to muscle atrophy, decreased strength.
Example: Resistance training causes hypertrophy; immobilization causes atrophy.