Detailed Notes -2- Chapter-17-Locomotion And Movement

17.3 SKELETAL SYSTEM

1. Composition and Function:

   • The skeletal system comprises bones and cartilages, providing a framework for the body and facilitating movement.
   • Bones and cartilages are specialized connective tissues with hard matrices (calcium salts in bones and chondroitin salts in cartilages).
   • The system consists of 206 bones and a few cartilages in humans.

2. Divisions of the Skeletal System:

   • The skeletal system is divided into two principal divisions: the axial and appendicular skeleton.
   • Axial skeleton includes 80 bones along the main axis of the body, comprising the skull, vertebral column, sternum, and ribs.
   • Appendicular skeleton consists of bones of the limbs and their girdles, supporting and facilitating movement of the upper and lower limbs.

3. Axial Skeleton:

   • The skull comprises cranial and facial bones, totaling 22 bones. Cranial bones protect the brain, while facial bones form the front part of the skull.
   • The vertebral column consists of 26 vertebrae, protecting the spinal cord and supporting the head, along with cervical, thoracic, lumbar, sacral, and coccygeal regions.
   • Sternum is a flat bone in the ventral midline of the thorax, while ribs are thin, flat bones connected dorsally to the vertebral column and ventrally to the sternum, forming the rib cage.

4. Appendicular Skeleton:

   • Consists of bones of the limbs and their girdles.
   • Forelimb bones include humerus, radius, ulna, carpals, metacarpals, and phalanges.
   • Hindlimb bones include femur, tibia, fibula, tarsals, metatarsals, and phalanges, with the patella covering the knee ventrally.
   • Pectoral and pelvic girdles articulate the upper and lower limbs, respectively, with the axial skeleton.
   • Pectoral girdle consists of clavicle and scapula, while pelvic girdle consists of coxal bones (ilium, ischium, and pubis) fused at the acetabulum.

17.4 JOINTS

1. Function and Importance:

   • Joints are crucial for all types of movements involving the bony parts of the body, including locomotory movements.
   • They serve as points of contact between bones or between bones and cartilages.
   • Muscular force is applied through joints, where they act as fulcrums for movement.

2. Classification of Joints:

   • Joints are classified into three major structural forms: fibrous, cartilaginous, and synovial.

3. Fibrous Joints:

   • Fibrous joints do not allow any movement.
   • They are exemplified by the flat skull bones, which fuse end-to-end with dense fibrous connective tissues (sutural ligaments) to form the cranium.

4. Cartilaginous Joints:

   • In cartilaginous joints, bones are joined together by cartilages.
   • An example is the joint between adjacent vertebrae in the vertebral column, which permits limited movements.

5. Synovial Joints:

   • Synovial joints are characterized by the presence of a fluid-filled synovial cavity between the articulating surfaces of two bones.
   • This arrangement allows considerable movement and flexibility.
   • Synovial joints play a vital role in locomotion and various other movements.
   • Examples of synovial joints include:
     • Ball and socket joint (e.g., shoulder joint between humerus and pectoral girdle)
     • Hinge joint (e.g., knee joint)
     • Pivot joint (e.g., joint between atlas and axis)
     • Gliding joint (e.g., between the carpals)
     • Saddle joint (e.g., between carpal and metacarpal of thumb).

17.5 DISORDERS OF MUSCULAR AND SKELETAL SYSTEM  

1. Myasthenia Gravis:

   • Autoimmune disorder affecting the neuromuscular junction.
   • Results in fatigue, weakness, and paralysis of skeletal muscles due to impaired communication between nerves and muscles.

2. Muscular Dystrophy:

   • Progressive degeneration of skeletal muscles, often due to genetic factors.
   • Results in muscle weakness and loss of muscle mass over time.

3. Tetany:

   • Rapid spasms or wild contractions in muscles.
   • Caused by low levels of calcium in body fluids, leading to hyperexcitability of nerves.

4. Arthritis:

   • Inflammation of joints, which can be caused by various factors including autoimmune reactions, infection, or wear and tear.
   • Symptoms include joint pain, stiffness, and swelling.

5. Osteoporosis:

   • Age-related disorder characterized by decreased bone mass and increased susceptibility to fractures.
   • Commonly associated with decreased estrogen levels, particularly in postmenopausal women.

6. Gout:

   • Inflammation of joints caused by the accumulation of uric acid crystals.
   • Typically affects the big toe but can also occur in other joints.
   • Often associated with dietary factors and metabolic disorders.