‘Human Skeletal System’ is an important topic in general science. Often 2-3 questions are asked about this topic in most of the competitive exams like SSC, Banking, Rail and State government exams, etc. Dear Aspirants, at the end of this topic ‘Human Skeletal System‘ there is a link through which you can download the full PDF of the topic.
Introduction to the Human Skeletal System
What is the Human Skeletal system?
☞ The skeletal system is a network of bones and Cartilages.
☞ The skeletal system played a crucial role in the movement shown by the body.
☞ The human skeletal System is composed of around 270 bones at birth.
☞ In adulthood, some of the bones get fused together, and the total number of bones decreases to around 206 bones.
☞ These 270 bones (at birth) or 206 bones (Adult) worked together and build a framework, which protects soft organs in our body.
Composition of Skeletal System
☞ The human skeletal system consists of bones and cartilage.
☞ Bone and cartilage are specialized connective tissues.
☞ The Bone has a very hard matrix due to calcium salts.
☞ And the Cartilage has a slightly pliable matrix due to chondroitin salts.
☞ In human beings, the skeletal system is made up of 206 bones and a few cartilages.
Composition of Human Bones
☞ Bone consists of a 30% flexible matrix and 70% bound minerals.
☞ This Bone matrix is composed of 90 to 95% elastic collagen fibers.
☞ Collagen fibers are also known as ossein.
☞ An inorganic salt, Calcium phosphate hardens this bone matrix.
☞ So, Collagen and Calcium phosphate are the two principal components of bone.
☞ 99 percent of our body’s calcium is held in our bones and teeth.
☞ Bones have an internal structure similar to honeycomb.
Important Fact about Human Bones
• The longest bone in the Human Body – Femur (in the thigh)
• The smallest bone in the human body – Stapes (in the middle ear)
• The adult human skeleton is made up of – 206 bones
• The human infant is made up of – 270 bones
• Two principal components of bone – Collagen and Calcium phosphate
• The study of bones is called – Osteology
Types of Human Bones
☞ The human body consists of five types of bones. They are _
• 1 – Long Bones
• 2 – Short bones
• 3 – Flat bones
• 4 – Sesamoid bones
• 5 – Irregular bones.
◘ Long bones
• A long bone is a bone that has a shaft (diaphysis) and 2 expanded ends (epiphyses).
• It has a thick outside layer of compact bone and a bone marrow-filled inner medullary cavity.
• These bones tend to support body weight and help in movement.
• Example – Femur, Ulna.
• Femur is the longest bone in the human body.
◘ Short bones
• Short bones are as wide as they are long.
• Their primary function is to provide support and stability.
• Example – Carpals, Tarsals.
◘ Flat bones
• Flat bones are thin and curved.
• Flat bones have three layers.
• Two outer layers of compact bone,
• and an inner layer of spongy bone.
• Its principal function is to provide protection for the muscular attachment of our body.
• Example – Cranium (skull), the ilium (pelvis), sternum, and the rib cage.
◘ Sesamoid bones
• A sesamoid bone is a bone embedded within a tendon or a muscle.
• The name sesamoid is derived from the Arabic word sesamum (“sesame seed”), indicating the small size of most sesamoids.
• Example – Patella or kneecap
◘ Irregular bones
• As their name implies, these are completely irregular in shape.
• They are often protecting organs or tissues.
• Example – Hip bone, the base of the skull.
Types of Skeletal Systems
☞ Skeletal System is divided into two types_ They are
1. Exoskeleton
2. Endoskeleton
◘ Exoskeleton
• An exoskeleton (Exo means outer) is the external skeleton that is present on the body’s surface.
• Exoskeleton supports and protects the animal’s body.
• Exoskeleton which has a larger size are known as “shells”.
• Examples – the exoskeleton of grasshoppers, cockroaches, crabs, lobsters, and shells of snails, and clams.
• Tortoises and turtles, have both an endoskeleton and an exoskeleton.
Endoskeleton
• The skeleton found inside the body is called the endoskeleton.
• It originates from the mesoderm.
• The vertebrate endoskeleton is made up of bones and cartilages.
Difference between Endoskeleton and Exoskeleton
| Endoskeleton | Exoskeleton |
|---|---|
| Present inside the body | The present outer surface of the body |
| Endoskeleton is made up of bones and cartilage. | The exoskeleton is made up of scales, chitinous cuticles, and calcified shells. |
| It is found in vertebrates. | It is mainly found in arthropods (Spiders, millipedes, centipedes, crabs, insects, etc) |
| It is a living structure. | It is a non-living structure.. |
| It develops from the endoderm. | It develops from the ectoderm |
| Animals with endoskeleton do not undergo molting. | Animals with an exoskeleton are molted periodically during growth. |
Functions of Skeleton
◘ Protective Function
☞ The skeletal system protects the internal organs from injury by covering or surrounding them.
☞ For example – Ribs protect our lungs and heart, and Cranial bones, and the Spinal cord is protected by the vertebral column (spine). And the cranial bones (skull) protect our brain.
◘ Supportive Function
☞ The bones and cartilages of the skeletal system provide support to the soft body organs.
◘ Helps in Movement
☞ Semi-rigid connective tissue found on the skeleton support movement.
◘ Mineral reservation
☞ The tissue present in bones acts as a reservoir of important minerals, like calcium, and phosphorus.
☞ These minerals are stored in bone tissue.
☞ To maintain the level of these minerals, the stored minerals in the bone are released back into the bloodstream.
☞ Calcium ions, are essential for muscle contractions and are involved in the transmission of nerve impulses.
◘ Haematopoiesis
☞ The red bone marrow present in bone produced Red blood cells, white blood cells, and platelets. The production of red blood cells is known as hematopoiesis. [ hemato- = “blood”, -poiesis = “to make”]
◘ Other function
☞ The skeletal system also gives the body its shape and size, provides balance features to the body, and helps in breathing and hearing. (for example, the ear bones transmit the sound vibrations from the tympanic membranes to the internal ear)
Counting 206 Human bones (Table format)
☞ The adult human skeleton consists of 206 bones.
☞ These 206 bones are grouped into, the axial skeleton and appendicular skeleton.
☞ Parts of Appendicular skeleton
• Bones of the limbs
• Shoulders
• Pelvic girdle.
☞ Parts of Axial skeleton
• Bones of the skull
• Vertebral column
• Thoracic cage
Appendicular Skeleton
| Part of Body | Part of Endoskeleton | Region | Number of Bones | Number |
|---|---|---|---|---|
| Thorax Hip Forelimbs | Pectoral girdle Pelvic girdle | Shoulder | Scapula-Clavicle | 2 * 2 |
| Pelvis | Osinnominatum | 2 | ||
| Upper Arm | Humerus | 2 | ||
| Fore arm | Radius-Ulna | 4 | ||
| Wrist | Carpals | 16 | ||
| Palm | Metacarplas | 10 | ||
| Fingers | Phalanges | 28 * 2 | ||
| Thigh | Femur | 2 | ||
| Shank | Tibio-Fibula | 4 | ||
| Knee | Patella | 2 | ||
| Ankle | Tarsals | 14 | ||
| Sole | Metatarsals | 10 | ||
| Total | 126 | |||
Axial Skeleton
| Part of Body | Part of Endoskeleton | Region | Names of Bones | Number |
|---|---|---|---|---|
| Head | Skull | Cranium | Occipital | 1 |
| Parietal | 2 | |||
| Frontal | 1 | |||
| Temporal | 2 | |||
| Sphenoid | 1 | |||
| Ethmoid | 1 | |||
| Facial region | Nasal | 2 | ||
| Vomer | 1 | |||
| Turbinal | 2 | |||
| Lacrymal | 2 | |||
| Zygomatic | 2 | |||
| Palatine | 2 | |||
| Maxila | 2 | |||
| Mandible | 1 | |||
| Ear Ossicles | Malleus | 2 | ||
| Incus | 2 | |||
| Stapes | 2 | |||
| Back bone | Vertebral column | Hyoid | Hyoid body | 1 |
| Neck | Cervical vertebrae | 7 | ||
| Thorax | Thoracic vertebrae | 12 | ||
| Waist | Lumber vertebrae | 5 | ||
| Sacrum | Sacral vertebra Sacrum | 1 | ||
| Tail | Caudal vertebrae / Coccyx | 1 | ||
| Thorax | Sternum Ribs | — | Sternum | 1 |
| — | Ribs | 24 | ||
| Total | 80 | |||
| Total Bone = Appendicular Skeleton + Axial Skeleton = 126 + 80 = 206 |
|---|
Diagram of Axial and Appendicular skeletal system of Human
Counting 206 Human bones (Simplified format)
Appendicular Skeleton
• The appendicular skeleton, comprising the arms and legs, including the shoulder and pelvic girdles, contains 126 bones.
■ Bones in Arms
◘ Human Arms consist of 64 bones (32 in each arm)
◘ Bones in Upper Arm [ 3 × 2 = 6 bones , 3 on each side]
☞ Humerus – 2
♦ Under Pectoral girdle (shoulder)
☞ Scapula – 2
☞ Clavicles – 2
◘ Bones in Lower Arm( 2× 2 = 4 bones, 2 on each side)
☞ Ulna – 2
☞ Radius – 2
◘ Bones in Hand (27 × 2 = 54 bones, 27 in each hand)
♦ Under Carpals
☞ Scaphoid bone – 2.
☞ Lunate bone – 2.
☞ Triquetral bone – 2
☞ Pisiform bone – 2
☞ Trapezium – 2
☞ Trapezoid bone – 2
☞ Capitate bone – 2
☞ Hamate bone – 2
☞ Metacarpals ( 5 × 2 =10 bones, 5 on each side)
♦ Under Phalanges of the hand
☞ Proximal phalanges ( 5 × 2 =10 bones, 5 on each side)
☞ Intermediate phalanges (4 × 2 = 8 bones, 4 on each side)
☞ Distal phalanges (5 × 2 = 10 bones , 5 on each side)
✪ Total = 6 (upper arm) + 4 (lower arm) + 54 (both hands) = 64
■ Bones in Pelvis (pelvic girdle)
☞ Pelvis region contain Two coxal bone.
☞ These 2 coxal bone is made up of 3 region (fused together), They are: ilium, ischium, and pubis.
■ Bones in Leg
◘ There are a total of 30 × 2 = 60 bones , 30 in each leg.
☞ Femur – 1× 2 = 2 bones
☞ Patella or kneecap – 1× 2 = 2 bones
☞ Tibia – 1× 2 = 2 bones
☞ Fibula – 1× 2 = 2 bones.
♦ Bones in Foot (26 × 2 = 52 bones, 26 per foot)
♦ Human foot consists of Tarsals , Metatarsals and phalanges
➧ Bones in Tarsals (7 × 2 = 14 bones, 7 in each Tarsals )
☞ Calcaneus or heel bone – 1 × 2 bones
☞ Talus – 1 × 2 = 2 bones
☞ Navicular bone – 1 × 2=2 bones
☞ Medial cuneiform bone – 1 × 2=2 bones
☞ Intermediate cuneiform bone – 1 × 2 =2 bones
☞ Lateral cuneiform bone – 1 × 2=2 bones
☞ Cuboid bone – 1 × 2 = 2 bones
➧ Bones in Metatarsals – 10 bones
➧ Bones in Phalanges of the foot (14 × 2= 28 bones, 14 in each Phalanges )
☞ Proximal phalanges – 5 × 2 = 10 bones
☞ Intermediate phalanges – 4 × 2 = 8 bones
☞ Distal phalanges – 5 × 2 = 10 bones
Axial Skeleton
The axial skeleton, comprising the spine, chest and head, contains 80 bones.
■ Bones in Spine
◘ A fully grown adult have 26 bones in the spine.☞ Cervical vertebrae – 7 bones
☞ Thoracic vertebrae – 12 bones
☞ Lumbar vertebrae – 5 bones
☞ Sacrum – 1 bones (Adult)
☞ Coccygeal vertebrae – 1 bone
■ Bones in Chest (Thorax)
◘ There are 25 bones in the chest.
☞ Sternum – 1
☞ Ribs – 24, in 12 pairs
■ Hyoid Bone – 1
■ Bones in Skull
◘ Human skull made up of 22 bones
◘ Human Head contains 28 bones, including the bones of the middle ear.
| 28 bones in Head ➥ 22 + 6 = 28 | ||
|---|---|---|
| 22 bones in Skull ➥ 14 + 8 = 22 | 6 bones in Ear | |
| 8 Cranial Bones | 14 Facial Bones | 3 × 2 = 6 Bones |
| • Occipital bone • Parietal bones – 2 • Frontal bone • Temporal bones – 2 • Sphenoid bone • Ethmoid bone | • Nasal bones – 2 • Maxillae – 2 • Lacrimal bone – 2 • Zygomatic bone – 2 • Palatine bone – 2 • Inferior nasal concha – 2 • Vomer – 1 • Mandible – 1 | • Malleus – 2 • Incus – 2 • Stapes – 2 |
Disorders of Human Skeletal Systems
| Disease | Description |
|---|---|
| Osteoporosis | It is an age-related disorder in which bones lose mineral density, weaken, and break more easily than normal bones. |
| Osteoarthritis | Osteoarthritis occurs due to breakdown of joint cartilage and bone. The most common symptoms are joint pain and stiffness include joint swelling. |
| Paget’s disease | Paget’s disease is a chronic bone disorder that causes affected bones to become large and misshapen. |
| Bursitis | Bursitis is the painful swelling of a small, fluid-filled sac called a bursa due to physical injury.The most common locations for bursitis are in the shoulder, elbow and hip |
| Rickets | Rickets is a skeletal disorder in which the development of bone disrupted. Rickets caused by the lack of vitamin D. It is a common disease in children. It causes bone pain, poor growth and soft, weak bones that can lead to bone deformities |
| Osteomalacia | Osteomalacia is the most common nutritional deficiency among adults. Osteomalacia is a disorder of “bone softening” occurs due to prolonged deficiency of vitamin D. |
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