Bones and Muscles

Total Bones in Human Body

206 bones

Main Functions of Bones

Structural support, protection, growth centre for cells, reservoirs for minerals, and movement

Axial Skeleton Definition

Comprised of the vertebral column (spine), spinal column, and skull; forms the core of the body

Axial Skeleton Function

Protects vital structures (heart, lungs, spinal cord, brain); serves as the origin point for most muscles

Appendicular Skeleton Definition

Includes moveable limbs and supporting structures (girdles) like the shoulders and pelvis

Appendicular Skeleton Function

Plays a key role in supporting body movement

5 Types of Bones

Long bones, flat bones, sesamoid bones, irregular bones, and short bones

Long Bones

Found in arms and legs

Flat Bones

Flat and thin bones that protect vital organs (e.g., scapula)

Sesamoid Bones

Small, flat bones wrapped in tendons that glide over body surfaces (e.g., patella)

Irregular Bones

Odd-looking bones with unique shapes

Short Bones

Commonly found in the wrists

Bone Density Maintenance

Exercise is key; bone density naturally declines with age, making consistent exercise necessary

Epiphyseal Plates

Growth plates shown as dark lines on X-rays; presence of growth plates indicates active bone growth

4 Forces on Bones

Tension (pulling/stretching), Torsion (twisting), Compression (pushing together), Shear (perpendicular or tangential force)

Simple Change vs Compound Change

Simple: bone does not break through skin; Compound: bone breaks through skin and is exposed to air (serious)

Simple Fracture Pattern

No separation of bone into parts; detectable line or crack ("hairline/greenstick")

Compound Fracture Pattern

Bone broken into pieces and breaks through the skin ("transverse"); caused by major force/blow

Comminuted Fracture Pattern

Shattered bone; causes accompanying muscle and ligament damage

Stress Fracture Pattern

Tiny crack in bone caused when an over-stressed muscle transfers impact directly to the bone

Fracture Symptoms

Sharp pain and tenderness upon palpation, swelling and discoloration, grinding sound on movement, inability to use the limb

Bone Healing

Bone heals through remodeling and may become even stronger than usual

Pivot Joint

One bone rotates around a single axis (uniaxial rotation); Example: Neck

Gliding Joint

Bone surfaces are nearly flat (uniaxial gliding); Example: Acromioclavicular joint

Hinge Joint

Convex and concave articulating surfaces (uniaxial flexion and extension); Example: Elbow

Saddle Joint

Bones fit together like a rider sitting on a horse (biaxial: flexion-extension, abduction-adduction); Example: Thumb

Condyloid Joint

Ovular convex shape and reciprocal concave surface (biaxial: flexion-extension, abduction-adduction); Example: Knuckles

Ball and Socket Joint

Rounded bone fits into a cup receptacle (multi-axial 3-axis rotation); Example: Hip

Tendons

Composed of collagen; attaches muscle to bone; vascular

Ligaments

Tough bands of white fibrous tissue; attaches bone to bone; avascular

Basics of Muscle

Over 600 muscles in the human body making up over 40% of body weight; responsible for movement, breathing, eating, and heartbeat

Skeletal Muscle

Attached to tendons; most prevalent type; voluntary and striated

Cardiac Muscle

Found only in the heart; involuntary and striated

Smooth Muscle

Surrounds internal organs and hair follicles; involuntary; organized in dense sheets

Muscle Fibre Irritability

Ability of a muscle to respond to stimuli

Muscle Fibre Conductivity

Ability of a muscle to transmit nerve impulses

Muscle Fibre Contractibility

Ability of a muscle to shorten in length

Muscle Fibre Elasticity

Ability of a muscle to stretch and return to its original position

Muscle Fibre Extensibility

Ability of a muscle to extend in length

Sarcolemma

Plasma membrane that encloses the myofibrils

Sarcoplasmic Reticulum

Network responsible for the release and absorption of calcium

Transverse Tubule System

Interconnecting rings connecting the outside of the fibre with filaments inside

Terminal Cisternae

Releases and removes calcium into the sarcoplasm

Transverse Tubule (T-Tubule)

Stores calcium

Myofibril

Thread-like structure containing actin and myosin

Sarcomere

Structural unit of striated muscle containing actin and myosin

Actin

Thin protein filament within the sarcomere

Myosin

Thick protein filament within the sarcomere

Muscle Origin

Where the muscle attaches closer to the centre of the body; attached to more stationary parts

Muscle Insertion

Where the muscle attaches further away from the centre of the body; attached to more mobile structures

How Muscles are Named

Action/Function, Direction of Fibres, Location, Number of Divisions/Heads, Shape, Points of Attachment

Antagonistic Pair: Elbow Flexion

Agonist: Biceps Brachii | Antagonist: Triceps Brachii

Antagonistic Pair: Shoulder Abduction

Agonist: Deltoid | Antagonist: Latissimus Dorsi

Antagonistic Pair: Medial Shoulder Rotation

Agonist: Pectoralis Major | Antagonist: Infraspinatus

Antagonistic Pair: Knee Extension

Agonist: Quadriceps | Antagonist: Hamstrings

Antagonistic Pair: Wrist Flexion

Agonist: Flexor Carpi Radialis | Antagonist: Extensor Carpi Radialis

Antagonistic Pair: Dorsi Flexion

Agonist: Tibialis Anterior | Antagonist: Gastrocnemius

Antagonistic Pair: Trunk Flexion

Agonist: Rectus Abdominis | Antagonist: Erector Spinae Group

Antagonistic Pair: Hip Flexion

Agonist: Iliopsoas | Antagonist: Gluteus Maximus

Fast Twitch Muscle Fibres

White appearance, fast contraction speed, anaerobic, fatigues quickly, large fibre diameter

Slow Twitch Muscle Fibres

Red appearance, slow contraction speed, aerobic, fatigue resistant, small fibre diameter

Concentric Contraction

Muscle shortens in length while generating force

Eccentric Contraction

Muscle lengthens while generating force

Isometric Contraction

Muscle length remains static while generating force

Muscle Cramp

Involuntary and forcibly contracted muscle that does not relax; caused commonly by dehydration or medications; relieved by stretching

Delayed Onset Muscle Soreness (DOMS)

Muscle soreness following intense exercise, caused by inflamed sarcolemma and microtears in muscle fibres