Chapter 5 – The Skeletal System

Subdivisions of the Skeleton

The human skeleton is divided into two main subdivisions: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage. It forms the central axis of the body.

• Appendicular Skeleton: Includes the limbs and girdles (pectoral and pelvic), which are attached to the axial skeleton.

Functions of the Skeletal System

The skeletal system performs several vital functions necessary for human life.

• Support: Provides structural framework for the body.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Movement: Acts as levers for muscles to produce movement.

• Mineral Storage: Stores minerals such as calcium and phosphorus.

• Blood Cell Production: Houses bone marrow, which produces blood cells (hematopoiesis).

Classifications of Bones

Bones are classified based on their shapes:

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin and often curved (e.g., skull, ribs).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

Anatomical Areas of the Long Bone

Long bones have distinct anatomical regions:

• Diaphysis: Shaft of the bone, composed of compact bone.

• Epiphyses: Ends of the bone, mostly spongy bone covered by compact bone.

• Metaphysis: Region between diaphysis and epiphysis, includes the growth plate.

• Medullary Cavity: Central cavity containing bone marrow.

• Periosteum: Outer fibrous covering of the bone.

Microscopic Structure of Compact Bone

Compact bone is organized into structural units called osteons (Haversian systems).

• Osteon: Cylindrical structure containing a central canal surrounded by concentric lamellae.

• Central (Haversian) Canal: Contains blood vessels and nerves.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae for nutrient exchange.

Bone Formation and Remodeling

Bone formation occurs via two processes:

• Endochondral Ossification: Bone develops by replacing hyaline cartilage (most bones).

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue (e.g., flat bones of the skull).

• Bone Remodeling: Continuous process of bone resorption and formation, regulated by osteoclasts and osteoblasts.

Structural Categories of Joints

Joints are classified by their structure and the amount of movement they allow:

• Fibrous Joints: Bones joined by dense connective tissue; immovable (e.g., sutures in the skull).

• Cartilaginous Joints: Bones joined by cartilage; slightly movable (e.g., intervertebral discs).

• Synovial Joints: Bones separated by a joint cavity filled with synovial fluid; freely movable.

Types of Synovial Joints and Movements

There are six types of synovial joints, each allowing specific movements:

• Plane (Gliding) Joint: Allows sliding movements (e.g., intercarpal joints).

• Hinge Joint: Allows flexion and extension (e.g., elbow, knee).

• Pivot Joint: Allows rotation (e.g., proximal radioulnar joint).

• Condyloid (Ellipsoid) Joint: Allows movement in two planes (e.g., wrist).

• Saddle Joint: Allows movement in two planes (e.g., thumb).

• Ball-and-Socket Joint: Allows movement in all axes (e.g., shoulder, hip).

Osteoporosis

Osteoporosis is a condition characterized by decreased bone mass and increased risk of fractures.

• Modifiable Risk Factors: Diet low in calcium/vitamin D, sedentary lifestyle, smoking, excessive alcohol.

• Non-Modifiable Risk Factors: Age, gender (female), genetics, menopause.

Chapter 6 – The Muscular System

Types of Muscle Tissue

There are three types of muscle tissue, each with distinct characteristics:

• Skeletal Muscle: Voluntary, striated, attached to bones for movement.

• Cardiac Muscle: Involuntary, striated, found only in the heart.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs.

Muscle Coverings

Muscles are surrounded by connective tissue layers:

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds bundles of muscle fibers (fascicles).

• Epimysium: Surrounds the entire muscle.

Functions of the Muscular System

• Movement: Facilitates body movement.

• Posture: Maintains body position.

• Stabilization: Stabilizes joints.

• Heat Production: Generates heat during contraction.

Microscopic Structure of Skeletal Muscle

Skeletal muscle fibers are long, cylindrical cells containing multiple nuclei and organized myofibrils.

• Myofibrils: Composed of repeating units called sarcomeres.

• Sarcomere: Functional unit of muscle contraction, contains actin and myosin filaments.

• Sarcoplasmic Reticulum: Stores calcium ions necessary for contraction.

• T-tubules: Invaginations of the sarcolemma that transmit action potentials.

Initiation of Action Potential in Muscle Cell

An action potential is initiated when a motor neuron releases acetylcholine at the neuromuscular junction, depolarizing the muscle cell membrane.

• Depolarization: Sodium ions enter the muscle cell, generating an action potential.

• Propagation: Action potential travels along the sarcolemma and T-tubules.

Events of Muscle Cell Contraction (Sliding Filament Theory)

Muscle contraction occurs via the sliding filament theory:

• Calcium ions bind to troponin, exposing binding sites on actin.

• Myosin heads attach to actin, forming cross-bridges.

• Myosin heads pivot, pulling actin filaments toward the center of the sarcomere.

• ATP binds to myosin, causing it to release actin and reset for another cycle.

Equation:

Isometric vs. Isotonic Contractions

• Isometric Contraction: Muscle tension increases, but length remains the same (e.g., holding a weight steady).

• Isotonic Contraction: Muscle changes length while tension remains constant (e.g., lifting a weight).

Five Golden Rules of Skeletal Muscle Activity

• All muscles cross at least one joint.

• The bulk of the muscle lies proximal to the joint crossed.

• All muscles have at least two attachments: origin and insertion.

• Muscles can only pull; they never push.

• During contraction, the insertion moves toward the origin.

Types of Body Movements

• Flexion: Decreases the angle between bones.

• Extension: Increases the angle between bones.

• Abduction: Moves limb away from midline.

• Adduction: Moves limb toward midline.

• Rotation: Moves bone around its longitudinal axis.

• Circumduction: Circular movement of a limb.

Criteria for Naming Skeletal Muscles

• Direction of muscle fibers (e.g., rectus, transverse)

• Relative size (e.g., maximus, minimus)

• Location (e.g., temporalis)

• Number of origins (e.g., biceps, triceps)

• Location of origin and insertion (e.g., sternocleidomastoid)

• Shape (e.g., deltoid)

• Action (e.g., flexor, extensor)

Arrangements of Muscle Fascicles

• Parallel: Fascicles run parallel to the long axis (e.g., sartorius).

• Pennate: Fascicles attach obliquely to a central tendon (e.g., rectus femoris).

• Convergent: Fascicles converge toward a single tendon (e.g., pectoralis major).

• Circular: Fascicles arranged in concentric rings (e.g., orbicularis oris).

Chapter 7 – The Nervous System

General Functions of the Nervous System

The nervous system is responsible for communication, control, and integration of body functions.

• Sensory Input: Detects changes inside and outside the body.

• Integration: Processes and interprets sensory input.

• Motor Output: Initiates responses by activating muscles or glands.

Structural and Functional Classifications of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; integration and command center.

• Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines between CNS and body.

• Functional Divisions:

  • Somatic Nervous System: Voluntary control of skeletal muscles.

  • Autonomic Nervous System: Involuntary control of smooth muscle, cardiac muscle, and glands.

Structures and Functions of Neurons and Neuroglia

Neurons are the functional cells of the nervous system, specialized for transmitting electrical signals.

• Cell Body (Soma): Contains nucleus and organelles.

• Dendrites: Receive signals from other neurons.

• Axon: Transmits signals away from the cell body.

Neuroglia (glial cells) support and protect neurons. Six types include:

• Astrocytes: Support and regulate the environment around neurons (CNS).

• Microglia: Act as immune cells in the CNS.

• Ependymal Cells: Line ventricles and produce cerebrospinal fluid (CNS).

• Oligodendrocytes: Form myelin sheaths in the CNS.

• Satellite Cells: Support neurons in the PNS.

• Schwann Cells: Form myelin sheaths in the PNS.

General Structure of a Neuron

• Cell Body: Contains the nucleus.

• Dendrites: Short, branched extensions for receiving signals.

• Axon: Long extension for transmitting signals.

• Axon Terminals: Endings that release neurotransmitters.

Myelin and Myelination

Myelin is a fatty substance that insulates axons, increasing the speed of nerve impulse transmission.

• Function: Enables rapid conduction of action potentials via saltatory conduction.

• Cells Responsible: Oligodendrocytes (CNS) and Schwann Cells (PNS).

Additional info: Academic context and examples have been added to expand upon the original bullet points and ensure completeness for exam preparation.