Unit 2_ Human Skeleton

Human Skeleton Overview

Humorous Insight: Jokes about skeletons being easily rattled and calm because nothing gets under their skin.

Objectives of Human Osteology

  • Examining what the human body does well versus poorly, inviting self-reflection regarding personal capabilities (e.g., identifying personal strengths in mobility versus weakness in flexibility).

Human Osteology and Skeletal Biology

  • Human Osteology: Broad study of human bones, examining various aspects of bone structure and function.

  • Skeletal Biology: Focused on growth, development, remodeling, age changes, sexual dimorphism (differences in skeletal structure between sexes, such as wider pelvis in females), and population variation (variation in bone structure among different ethnicities).

Skeletal System Composition

  • Composed of bone and cartilage, providing structure and flexibility.

  • Adults typically have 206 bones; number may vary due to accessory bones (extra bones, such as an additional rib) or fused bones (e.g., sacral vertebrae fused into the sacrum).

Functions of the Skeletal System

  • Provides a rigid framework for support and protection of vital organs (e.g., the ribcage protects the heart and lungs; the skull protects the brain).

  • Offers a mechanical basis for movement through skeletal muscle contractions (e.g., the femur allows leg movement when muscles contract).

  • Physiological Functions: Forms blood cells in bone marrow (e.g., red blood cells produced in the femur) and stores nutrients like calcium (crucial for muscle function) and phosphorus (important for energy production).

Bone Types

  • Long Bones: Present in limbs (e.g., femur, humerus - the longest bone in the body).

  • Short Bones: Found in wrists (carpals, such as the scaphoid) and ankles (tarsals, such as the talus).

  • Flat Bones: Comprise the braincase (e.g., parietal bone, which forms part of the skull's roof).

  • Irregular Bones: Include facial bones (e.g., maxilla - upper jaw; vertebrae - irregular shape for flexibility and support).

  • Sesamoid Bones: Example is the patella (kneecap), which protects the knee joint.

Bone Formation and Maintenance

  • Osteoblasts: Bone-forming cells that synthesize bone material (e.g., active during growth spurts in children).

  • Produces osteoid (pre-bone tissue) leading to calcification via hydroxyapatite crystal deposition, essential for bone strength.

  • Osteocytes: Osteoblasts embedded in bony matrix, responsible for maintaining bone health (e.g., detecting stress on bones and signaling for remodeling).

  • Osteoclasts: Responsible for bone resorption, essential for bone remodeling (e.g., during weight loss or inactivity, where old bones are broken down to maintain balance).

Structure of Long Bones

  • External Parts: Diaphysis (shaft), epiphysis (ends), metaphysis (growth plate), and articular surface (joint surface).

  • Covered with periosteum (outer) full of nerves and blood vessels) and lined with endosteum (inner).

  • Internal Composition: Features cortical (compact, dense bone), subchondral (provides support for cartilage), trabecular (cancellous/spongy bone), and medullary cavity (contains bone marrow where blood cells are made).

Bone Remodeling

  • Bones are dynamic, living tissue that changes over time.

  • Wolff’s Law: Bones adapt in size/shape to forces applied; promotes bone formation via activity (e.g., lifting weights increases bone density) and reduces weak areas (osteoclast activity reduces bone over time where stress is minimal).

  • Osteoporosis: Condition leading to increased fragility and risk of fractures, often seen in older adults (such as hip fractures in elderly patients).

  • Osteopetrosis: Rare disorder of excessive, abnormal density in bones, can lead to increased fragility (e.g., patients may experience fractures more easily despite high bone density).

Anatomical Position

  • Defined as standing upright, facing forward, arms at sides with palms anterior, and feet parallel (this standard reference allows for precise communication in anatomy).

Directional Terms

  • Superior: Nearer to head (e.g., the head is superior to the abdomen).

  • Inferior: Nearer to feet (e.g., the feet are inferior to the knees).

  • Anterior: Front-facing (e.g., the chest is anterior to the back).

  • Posterior: Back-facing (e.g., the spine is posterior to the heart).

  • Medial: Closer to the median plane (e.g., the nose is medial to the eyes).

  • Lateral: Farther from the median plane (e.g., the ears are lateral to the head).

  • Proximal: Closer to trunk (e.g., the elbow is proximal to the wrist).

  • Distal: Farther from trunk (e.g., the fingers are distal to the wrist).

Major Bones Categorization

  • Axial Skeleton: Composed of cranium (e.g., frontal bone, which forms the forehead), vertebral column (spine for protection of the spinal cord), and thorax (ribs and sternum).

  • Appendicular Skeleton: Includes upper/lower limbs (e.g., arms: humerus; legs: femur), pectoral girdle (scapula and clavicle), and pelvic girdle (ilium, ischium, pubis).

Axial Skeleton Structure

  • Head: (includes cranium with various bones for protection).

  • Neck: (composed of cervical vertebrae - 7, supporting the head).

  • Trunk: (made up of thoracic vertebrae, lumbar vertebrae, and rib structures).

Osteological Terms and Common Names of Bones

  • Cranium: Skull (protects the brain).

  • Maxilla: Upper jaw (holds upper teeth).

  • Mandible: Lower jaw (only movable part of the skull).

  • Orbits: Eye sockets (houses the eyeballs and related structures).

  • Enumerates bones in the skull such as frontal, parietal (roof of the skull), zygomatic (cheekbone), etc.

Neurocranium vs. Splanchnocranium

  • Neurocranium: Back part housing the brain (e.g., occipital bone).

  • Splanchnocranium: Anterior face region (includes nasal and maxillary bones).

Bones of the Cranium

  • Includes parietal, occipital, temporal bones, maxilla, mandible, etc.; each serving protective and supportive functions.

Sutures of the Cranium

  • Frontal bone, sinus pathways, coronal (between frontal and parietal bones), squamosal (between parietal and temporal), lambdoid (between parietal and occipital), etc.

Eye Orbits

  • Composed of seven different bones including sphenoid, zygomatic (cheekbone), maxilla (upper jaw), frontal (forehead), and others.

Hyoid Bone

  • Unique in not articulating with another bone; supports attachment of various muscles and ligaments, important for speech and swallowing.

Dental Anatomy

  • Presence of four types of teeth: incisors (cutting), canines (tearing), premolars (grinding), and molars (crushing).

  • Deciduous vs. Adult Tooth Notation: Adult humans have 32 teeth while children have 20 (deciduous teeth).

Vertebral Column

  • Comprising 33 vertebrae divided into: cervical (7), thoracic (12), lumbar (5), sacral (5 fused), and coccygeal (4 fused) regions - allows for flexibility and movement.

Thorax Structure

  • Composed of sternum, rib pairs (12 pairs protecting the thoracic cavity), and associated vertebrae with intervertebral discs, providing stability and support.

Appendicular Skeleton Overview

  • Upper/lower limb bones with common names defined (e.g., Humerus in the upper arm, Femur in the thigh).

Pectoral and Pelvic Girdles

  • Pectoral Girdle: Involves the scapula (shoulder blade) and clavicle (collar bone), providing support to the upper limb.

  • Pelvis: Comprises os coxa (hip bone) divided into ilium, ischium, and pubis, supporting the weight of the upper body during standing and sitting.

Bipedal Adaptations

  • Defining characteristics distinguishing humans from quadrupeds include modified pelvis shape, longer lower limbs compared to arms, and alignment of the big toe, adapting for upright walking.

Comparison Between Humans and Apes

  • Discusses skeletal differences in locomotion: humans have an S-shaped spine for bipedalism while apes possess a C-shaped spine for quadrupedal movement; also differences in limb length ratios and hip joint structure.

Origins of Bipedalism

  • Evidence suggesting upright walking in hominins dates back 6-7 million years (e.g., fossils such as Ardipithecus ramidus).

  • Key fossil findings supporting modern-like gait traced back to Australopithecus afarensis (e.g., Lucy fossil provides evidence of bipedal movement).

Mismatch Hypothesis

  • Links health issues in modern humans (e.g., obesity, heart disease) to rapid cultural evolution outpacing biological adaptation, promoting chronic diseases due to sedentary lifestyles differing from those of our ancestors.

Persistence Running Hypothesis

  • Suggests adaptations for endurance running (e.g., longer legs and energy-efficient gait) influenced hunting practices in early humans.

Obstetrical Dilemma

  • Highlights trade-offs in pelvic structure regarding bipedal locomotion and delivery of large-brained infants (e.g., difficulties in childbirth due to a narrow pelvic canal).

Study Resources

  • References apps and websites for further learning about human osteology and skeletal anatomy, such as Visible Body and the American Association of Anatomists website.