Human Body Systems: Muscles, Skeleton, Anatomy, Circulation

Posted on Apr 25, 2025 in Human Biology

Human Body Systems Fundamentals

Muscular System Basics

Muscle Types

  • Skeletal: Striated, voluntary, multinucleated.
  • Smooth: Non-striated, involuntary, single-nucleated.
  • Cardiac: Striated, involuntary, single/binucleated.

Muscle Properties

  • Contractility: Shortens with stimulation.
  • Extensibility: Stretches without damage.
  • Elasticity: Returns to original shape.

Muscle Fiber Types

  • Slow-Twitch (Type I): Endurance, aerobic.
  • Fast-Twitch (Type II): Quick, anaerobic (Type IIa, Type IIb).

Muscle Contraction Mechanism

Contraction: ATP and calcium enable actin-myosin filaments to slide, shortening muscle fibers.

Muscle Contraction Process

Muscles contract when the brain sends an electrical signal (action potential) through motor neurons to muscle fibers. At the neuromuscular junction, acetylcholine is released, triggering the action potential within the muscle. This potential travels along T-tubules to the sarcoplasmic reticulum, releasing calcium ions (Ca²⁺) which bind to troponin. This binding shifts tropomyosin, exposing actin binding sites.

With Ca²⁺ and ATP present, myosin heads attach to actin, pull it toward the M-line, and release, causing contraction. This cycle continues, shortening the sarcomere and contracting the muscle. A calcium deficiency could impair muscle contraction strength and neuron function.

Anatomy Fundamentals

What is Anatomy?

Anatomy: The study of body structure.

Types of Anatomy

  • Regional Anatomy: Study of the body in segments.
  • Clinical Anatomy: Applied in medicine.
  • Systemic Anatomy: Study of the body organized by systems.

Anatomical Terms

Anatomical Position

Standing with palms forward.

Anatomical Planes
  • Median Plane: Divides body into left and right halves.
  • Sagittal Plane: Parallel to the median plane.
  • Frontal/Coronal Plane: Divides body into front and back sections.
  • Transverse Plane: Divides body into upper and lower sections.
Anatomical Directions
  • Superior: Above
  • Inferior: Below
  • Medial: Toward the midline
  • Lateral: Away from the midline
  • Distal: Farther from the point of origin
  • Proximal: Closer to the point of origin
Movement Terms
  • Flexion/Extension: Decreasing/increasing the angle of a joint.
  • Abduction/Adduction: Moving away from/toward the midline.
  • Rotation/Circumduction: Rotational movements around an axis.
  • Dorsiflexion/Plantarflexion: Bending the foot upward/downward.
  • Eversion/Inversion: Moving the sole of the foot outward/inward.

Skeletal System Structure

Skeletal Divisions

  • Axial Skeleton: Skull, neck, and trunk.
  • Appendicular Skeleton: Limbs and girdles.

Bone Types

  • Long Bones: Tubular (e.g., femur).
  • Short Bones: Cuboidal (e.g., wrist bones).
  • Flat Bones: Protective (e.g., skull bones).
  • Irregular Bones: Various shapes (e.g., vertebrae).
  • Sesamoid Bones: Found in tendons (e.g., patella).

Vertebral Column Sections

  • Cervical (7 vertebrae): Neck region, supports head.
  • Thoracic (12 vertebrae): Mid-back, rib cage attachment.
  • Lumbar (5 vertebrae): Lower back, weight-bearing.
  • Sacrum (5 fused vertebrae): Pelvic stability.
  • Coccyx (4 fused vertebrae): Tailbone, muscle attachment.

Cartilage Types

  • Hyaline Cartilage: Found at the ends of long bones.
  • Fibrocartilage: Shock-absorbing (e.g., intervertebral discs).
  • Elastic Cartilage: Flexible (e.g., ear).

Joints

Joint Types
  • Fibrous Joints: Immovable (e.g., skull sutures).
  • Cartilaginous Joints: Slightly movable (e.g., vertebrae).
  • Synovial Joints: Freely movable with synovial fluid (e.g., hip, knee).
Synovial Joint Types
  • Ball and Socket: Multidirectional movement (e.g., hip, shoulder).
  • Hinge: Movement in one plane (e.g., elbow, knee).
  • Pivot: Rotation only (e.g., neck – atlas/axis).
  • Condyloid: Two-plane movement (e.g., wrist).
  • Saddle: Reciprocal concave-convex surfaces (e.g., thumb).
  • Gliding: Flat surfaces slide over each other (e.g., wrist bones, ankle bones).

Exercise Effects on Skeletal System

  • Bone Strength: Reinforced under stress.
  • Cartilage: Thickens for cushioning.
  • Tendons: Strengthened to handle muscle force.
  • Range of Movement: Increased with flexibility training.

Circulatory System Summary

  • Cardiovascular System: Comprises the heart, blood, and blood vessels.
  • Heart Structure: Four chambers (atria and ventricles), pumps deoxygenated and oxygenated blood.
  • Cardiac Cycle: Involves atrial and ventricular diastole and systole, averaging 72 beats per minute.
  • Blood Composition: Plasma, erythrocytes, leukocytes, and thrombocytes.
  • Blood Vessels: Arteries, arterioles, capillaries, venules, and veins facilitate blood flow.
  • Blood Pressure: Systolic and diastolic readings indicate heart function.
  • Exercise Impact: Increases cardiac output, stroke volume, and oxygen delivery to muscles.