17. LOCOMOTION AND MOVEMENT

Cells of the human body exhibit three main types of movements, namely, amoeboid, ciliary and muscular.

The human body exhibits three primary movement types: amoeboid, ciliary, and muscular. Amoeboid movement is found in specialized cells like macrophages, which use pseudopodia (extensions of the cell) to move. This is facilitated by the streaming of the cell's protoplasm. Ciliary movement involves tiny hair-like structures called cilia that sweep substances along the surfaces of organs, like moving dust particles out of the lungs. Lastly, muscular movement refers to the action of muscle tissues enabling various body movements and is crucial for locomotion.

Think of amoeboid movement as a blob of jelly moving around a plate—its shape changes and it extends parts of itself to move. Ciliary movement is like a group of synchronized swimmers, waving their arms (cilia) to push water away, while muscular movement is akin to the way a train moves along tracks, where muscles are the engines that create movement.

Muscles have been classified using different criteria, namely location, appearance and nature of regulation of their activities. Based on their location, three types of muscles are identified: (i) Skeletal (ii) Visceral and (iii) Cardiac.

Muscles can be classified based on location into three main types: skeletal, visceral, and cardiac. Skeletal muscles are connected to bones and enable voluntary movements; they appear striated under a microscope. Visceral muscles, found in internal organs, are smooth and operate involuntarily without conscious control. Cardiac muscles are found only in the heart, are striated like skeletal muscles but involuntary like visceral muscles, coordinating heartbeats.

Imagine your arm lifting a book—that's your skeletal muscle at work. Now think of your stomach churning food; that's the visceral muscle silently doing its task. Finally, your heart beating in a rhythmic manner showcases cardiac muscle working tirelessly without you thinking about it. All three types work together to keep us functioning.

Each organised skeletal muscle in our body is made of a number of muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia. Each muscle bundle contains a number of muscle fibres.

Skeletal muscles are composed of bundles called fascicles, which are made of smaller units called muscle fibres. Each muscle fibre is covered by a protective layer known as sarcolemma and contains myofibrils that are organized in a straited pattern responsible for muscle contraction. The arrangement of these fibres in parallel helps muscles achieve significant strength and allows for coordination in movement.

You can think of muscle bundles as a rope made of many strands twisted together. Just like a rope is stronger when strands are combined, muscles can exert more force when fibres are arranged in bundles. When you lift something heavy, it's these bundles that work together to pull and lift it.

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.

The sliding filament theory explains how muscles contract. When a muscle receives a signal from the nervous system, calcium ions are released, allowing myosin heads to bind to actin filaments. The myosin heads pull the actins toward the center, causing the muscle to shorten and contract. This process requires energy from ATP and continues until the signal stops and calcium is pumped back into storage.

Imagine pulling a curtain closed. The curtain is like the actin filament, and your hand represents the myosin head. Each time you pull (contract), the curtain slides over the rod (thick filament), making it retract towards the center until it’s completely closed.

Skeletal system consists of a framework of bones and a few cartilages. This system has a significant role in movement shown by the body.

The skeletal system is primarily made up of bones and cartilage. It provides support, protects internal organs, and enables movement by acting as a lever system for muscles. In humans, the skeletal system consists of 206 bones and several cartilages and is divided into two main parts: the axial skeleton and the appendicular skeleton, responsible for supporting the head, neck, and trunk versus limb movement, respectively.

Think of your skeletal system as the frame of a house. Just as a house needs a strong frame to support its structure and keep it standing upright, your body relies on bones and cartilage to maintain its form, support its weight, and allow for movement as different parts interact with each other.

Joints are essential for all types of movements involving the bony parts of the body. Joints have been classified into three major structural forms, namely, fibrous, cartilaginous and synovial.

Joints connect bones and allow for movement. There are three main types: fibrous joints, which are immovable (like skull sutures); cartilaginous joints, which allow limited movement (like between vertebrae); and synovial joints, which permit a wide range of motion (like the knee and shoulder joints). The latter are crucial for locomotion and everyday activities.

Imagine a door hinge; it's like a synovial joint because it opens and closes. A glued door would be similar to a fibrous joint—completely immovable. A slightly stiff door could represent a cartilaginous joint—able to move a little but not freely. This analogy helps illustrate how the types of joints each serve specific roles in enabling or restricting movement.

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