Locomotion and Movement

Movement is a fundamental characteristic of living beings, observed in animals and plants. For instance, unicellular organisms like Amoeba demonstrate a basic form of movement through the streaming of protoplasm. Additionally, many organisms exhibit movement via cilia, flagella, and tentacles. Movement often arises from seeking food, shelter, mates, optimal breeding sites, favorable weather conditions, or evading predators.

1.0Types of Movements

Cells of the human body exhibit mainly three types of movements. 

1. Ciliary—It occurs in most of our internal organs, which are lined by ciliated epithelium. For instance, the synchronized movements of cilia in the trachea aid in expelling dust particles and various foreign substances that are inhaled with atmospheric air.
2. Amoeboid—It occurs in most internal organs, lined by ciliated epithelium. For example, the synchronized movements of cilia in the trachea help remove dust particles and foreign substances inhaled by the air. Additionally, ciliary movement assists in ova transport through the female reproductive tract.
3. Muscular—This locomotion requires a perfectly coordinated activity of muscular, skeletal, and neural systems. Human beings, along with most multicellular organisms, effectively utilize the contractile properties of muscles for locomotion and various other movements. The movement of our limbs, jaws, tongue, and other body parts depends on muscular activity.

2.0Importance of Muscles in Locomotion

Skeletal Muscles

Skeletal muscles are intricately connected to the skeletal framework of the body. When examined under a microscope, these muscles display a striped pattern, meaning "striated muscles." Because they respond to voluntary signals from the nervous system, they are also referred to as voluntary muscles. Skeletal muscles play a crucial role in facilitating movement and maintaining body posture.

Structure of Contractile Proteins: 

• Each actin (thin) filament consists of two helical strands of filamentous (F) actin. Each F actin strand is a polymer composed of globular (G) actin monomers. Additionally, two tropomyosin filaments run parallel to the F actin strands along their entire length. At regular intervals, the complex protein troponin is found on the tropomyosin. In a resting state, a subunit of troponin covers the active binding sites for myosin on the actin filaments.

Mechanism of Muscle Contraction

• The sliding filament theory best explains the mechanism of muscle contraction. According to this theory, muscle fibers contract when thin filaments slide over thick filaments.

Visceral Muscles

Visceral muscles are found lining the inner walls of hollow organs in the body, like the digestive and reproductive systems. These muscles lack striations and appear smooth, meaning "smooth muscles" or non-striated muscles. Unlike skeletal muscles, their contractions are involuntary and not controlled consciously by the nervous system. They fulfill essential functions such as propelling food through the digestive tract and aiding in the transportation of gametes within the reproductive system.

Cardiac Muscles

Cardiac muscles comprise the heart's muscle tissue. These muscles consist of numerous cells that form a branching pattern unique to cardiac muscle tissue. Due to their organized structure, they appear striated. The muscle fibers are long, cylindrical, and branched, contributing to the heart's pumping. Unlike skeletal muscles, cardiac muscles are involuntary, meaning the nervous system does not directly control their contractions. This specialized muscle type is exclusive to the heart; hence, it is called cardiac muscle and is characterized by its striated structure.

3.0Skeletal System in Locomotion and Movement

The skeletal system is composed of a framework of bones and some cartilage. This system plays a crucial role in enabling body movement. In humans, the skeletal system comprises 206 bones and a few cartilages, and it is divided into two main sections: the axial skeleton and the appendicular skeleton.

Axial Skeleton

The axial skeleton comprises 80 bones distributed along the body's main axis. It includes the skull, vertebral column, sternum, and ribs.

1. Skull: The skull consists of 22 bones, including 22 cranial and facial bones. There are 8 cranial bones: 1 frontal, 2 parietal, 2 temporal, 1 occipital, 1 ethmoid, and 1 sphenoid.

2. Vertebral Column

The vertebral column consists of 26 sequentially arranged vertebrae positioned along the dorsal side of the body. It extends from the skull base and forms the trunk's primary framework. Each vertebra contains a central hollow structure known as the neural canal, which serves as a pathway for the spinal cord.  

3. Sternum and Ribs: The sternum is a flat bone located centrally on the front of the thorax. The thoracic cage includes 12 pairs of ribs, each a thin, flat bone. These ribs are dorsally connected to the vertebral column and ventrally attached to the sternum. Each rib has two articulation surfaces at its dorsal ends, giving it a bicephalic appearance. 

Appendicular Skeleton

1. Fore Limbs Bones: The bones of the hand (forelimb) include the humerus, radius, and ulna; 8 carpals (wrist bones); 5 metacarpals (palm bones); and 14 phalanges (digits). 

2. Hind Limbs Bones: The leg (hind limb) bones consist of the femur (thigh bone, the longest bone), tibia, and fibula; 7 tarsals (ankle bones); 5 metatarsals; and 14 phalanges (digits).

3. Pectoral and Pelvic Girdle

The bones of the pectoral and pelvic girdles facilitate the connection of the upper and lower limbs to the axial skeleton, respectively. Each girdle is composed of two halves. Each half of the pectoral girdle includes a clavicle and a scapula. The scapula is a large, triangular, flat bone on the back of the thorax between the second and seventh ribs. The scapula's dorsal, flat, triangular body features a slightly elevated ridge known as the spine, which extends into a flat, expanded process called the acromion. 

4.0Joints

Joints are crucial in facilitating all movements involving the body's bones, including locomotion. They serve as contact points between bones or between bones and cartilage. Muscles generate force to create movement through these joints, which function like fulcrums. The degree of movement at these joints varies based on several factors. Structurally, joints are classified into three major types: fibrous, cartilaginous, and synovial.

1. Fibrous Joints: Fibrous joints are immobile joints where bones are tightly connected by dense fibrous connective tissue, as seen in the flat bones of the skull. These bones fuse end-to-end through sutures, forming the cranium.

2. Cartilaginous Joints: In cartilaginous joints (synchondroses), bones are connected by cartilage. Ine joints between adjacent vertebrae follow this pattern in the vertebral column, allowing for restricted movement. Another example is the pubic symphysis, where the two halves of the pelvic girdle meet anteriorly and are connected by fibrous cartilage.

3. Synovial Joints: Synovial joints, or diarthroses, have a fluid-filled synovial cavity between the articulating bone surfaces, allowing for significant movement. This structural design enables various forms of locomotion and a wide range of other movements.

5.0Disorders of Skeletal System

1. Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction, leading to muscle fatigue, weakness, and paralysis of skeletal muscles.

2. Muscular dystrophy: A genetic disorder characterized by progressive degeneration of skeletal muscles.

3. Tetany: Rapid and uncontrollable muscle spasms (wild contractions) due to low calcium levels in body fluids.
4. Arthritis: Inflammation of the joints, which can cause pain, swelling, and stiffness.

5. Osteoporosis: Often associated with aging, osteoporosis is characterized by reduced bone density and an increased risk of fractures, frequently linked to declining estrogen levels.

6. Gout: Inflammation of the joints caused by the accumulation of uric acid crystals, leading to sudden and severe pain.