The skeletal system consists of 206 bones and other tissues that provide structure, protect organs, allow movement, and produce blood cells. It includes two divisions - the axial skeleton which includes the skull, vertebral column, and thoracic cage, and the appendicular skeleton which includes the shoulder and pelvic girdles and upper and lower limbs. Bones are classified based on their shape as long, short, flat, or irregular. Joints connect bones and are classified as fibrous, cartilaginous, or synovial joints which allow different types of movement. Skeletal muscles contract through the sliding filament mechanism in response to neuronal signals at the neuromuscular junction.

1. SKELETAL SYSTEM
By
Mr. Vinayak R. Bodhankar
M. Pharm. (QA)

2. Contents
 Introduction
 Structure of bone
 Functions of skeleton
 Classification
a) Axial
b) Appendicular
 The joints
 Classification of joints
 Disorders of joints
 Skeletal muscle
 Physiology of muscle contraction
 Neuromuscular junction

3. Introduction
 Bone tissues makes up about 18% of the total human body weight.
 The skeletal system supports and protects the body while giving it shape and form.
 Consist of 206 bones.
Composed of:
-Bones
-Cartilage
-Joints
-Ligaments
Osteology

4. Structure of bone
 Hardest connective tissue.
 Consist of 2 kind of tissue
1. Compact bone: Hard
2. Cancellous bone: Spongy
 Microscopic structure of bone
1. Haversian canal
2. Lamellae
3. Lacunae
4. Canaliculi

5. Functions of skeletal
1. Support
2. Boundaries
3. Protection
4. Movement
5. Blood cell production
6. Storehouse

6. Divisions of the Skeletal System
1. Axial skeleton
Skull, Vertebral column, thoracic cage.
2. Appendicular skeleton
Shoulder girdle, pelvic girdle
Upper and lower limbs

7. CLASSIFICATION OF BONE BASED ON SHAPE
• Long Bones
– Greater length than width and are slightly curved for strength
– Femur, tibia, fibula, humerus, ulna, radius, phalanges
• Short bones
– Cube-shaped and are nearly equal in length and width
– Carpal, tarsal
• Flat bones
– Thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue
– Cranial, sternum, ribs, scapulae
• Irregular bones
– Complex shapes and cannot be grouped into any of the previous categories
– Vertebrae, hip bones, some facial bones, calcaneus
• Sesamoid bones
– Protect tendons from excessive wear and tear
– Patellae, foot, hand

8. The Joints
Site at which two or more bones comes together.
Classification:
1. Fibrous joint / Fixed joint
2. Cartilagenous joint
3. Synovial joint
i) Ball and socket joint
ii) Hinge joint
iii) Double hinge joint
iv) Gliding joint
v) Pivot joint

9. Synovial joint

10. Hinge joint
c. gliding
d. Pivot
Pivot joint

11. Movements of different kinds of joint
 Ball & Socket joints – flexion and extension, abduction, adduction, circumduction,
external & internal rotation
 Hine joint - flexion and extension only
 Double hinge joint - flexion and extension, abduction, adduction, circumduction
 Gliding joint – slight movement increasing range of movement in all direction.
 Pivot joint – Rotation where they are pivoted

12. Disorders of Joints
Arthritis – Inflammation of joints.
It is of two types:
1. Acute arthritis
- Acute synovitis
- Traumatic synovitis
2. Chronic arthritis
- Tuberculous arthritis
- Rheumatoid arthritis
- Osteoarthritis
- Gout
- Dislocation
- Osteoporosis

13. Structure of skeletal

14. The Axial skeleton
The axial skeleton consists of :
1. Skull
Cranium: Base and vault
Face: 13 bones form the skeleton of face.
2. Vertebral column
3. Thoracic cage.

15. Bones of skull
Skull
A. Cranium
Frontal - 1
Parietal - 2
Occipital - 1
Temporal - 2
Sphenoid - 1
Ethmoid - 1
B. Face
Zygomatic – 2
Maxilla - 1
Nasal – 2
Lacrimal – 2
Vomer – 1
Palatine – 2
Conchae – 2
Mandible - 1

16. Vertebral column
 Consist of 24 separate movable bones called as Vertebrae.
 Divided into 3 groups:
a. Cervical – 7
b. Thoracic – 12
c. Lumbar – 5
 Fused bone
Sacrum – 5
Coccyx - 4

17. 1. Cervical vertebrae
They have 2 special features:
A. Transverse process
B. Spinous process
Atlas
First cervical vertebra consist of ring of bone.
Ring is divided into 2 parts.
Anterior – odontoid process.
Posterior – spinal cord.
Axis – Second cervical vertebra

18. 2. Lumbar vertebrae
Bodies – largest
Foramina - smallest
3. Thoracic vertebrae

19. Thoracic cage
12 pairs of ribs.
12 thoracic vertebrae
1 sternum
Parts of sternum
1. Mandibrum
2. Body
3. Xiphoid process

20. Appendicular skeleton
Shoulder girdle with upper limbs.
Bones
Clavicle – 2
Scapula – 2
On each side
Humerus – 1
Radius – 1
Ulna -1
Carpal – 8
Metacarpal – 5
Phalanges - 14

22. Pelvic girdle with lower limbs
Innominate bones – 2
Sacrum – 1
Bones of lower extremity:
Femur – 1
Tibia – 1
Fibula – 1
Patella – 1
Tarsal bone – 7
Metatarsal – 5
Phalanges - 14

23. Difference between male & female pelvic girdle
Female Male
Bones Lighter & Smaller Heavier & longer
Cavity Shallow and round Deep & funnel shaped
Sacrum More concave Less concave
Pubic arch Bones are movable Bones are immovable

24. Skeletal muscle
Epimycium: Whole muscle
Perimycium: Bundles of fibre
Endomycium: Single fibre

25. Physiology of muscle contraction
SLIDING FILAMENT MECHANISM
 The length of skeletal muscle shortens during contraction because the thick and thin filaments slide over one another. The process is
known as the sliding filament mechanism.
 The thick filament contains 300 myosin molecules.
 It contain two parts: 1. Myosin tail 2. Myosin heads
 Myosin tail forms the shaft of the thick filament and heads projects towards the thin filament.
 Thin filament contain actin, troponin and tropomyosin.
 At the onset of contraction, the sarcoplasmic reticulum release calcium ions into cytosol
 There they bind to troponin and cause troponin-tropomyosin complexes to move away from binding site on actin.
 Once the binding sites are free, the repeating sequence of events of the contraction cycle occurs that causes the filaments to slide on
each other.

26. Neuromuscular Junction
 Connection between large myelinated nerve fibre
and skeletal muscle fibre.
 Sarcolemma: membrane through which nerve fibre
passes.
 Branches of nerve fibre: Hypolemmal axons.
 Axons: Sole feet
 Sole feet contain vesicles that contains ACH

27. Physiology of Neuromuscular Junction