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NCERT Notes for Class 11 Biology Chapter 17: Locomotion and Movement

NCERT and CBSE Notes for Class 11 Biology Chapter 17: Locomotion and Movement: The given article is a detailed introduction to the class 11 chapter “Locomotion and Movement”. The article discusses all the important topics and their related sub-topics which include muscles, types of muscles, muscle contraction, skeletal system, and a brief illustration of different types of bones present in the human body. 

Notes on Locomotion and Movement of NCERT Class 11 The article also looks into the structure of contractile protein and its functioning. A bunch of frequently asked questions are also included in this article for better understanding.



Locomotion and Movement

Movement is a fundamental characteristic of living organisms, exhibited by both animals and plants. It takes place in various forms, ranging from simple protoplasm in Amoeba to the movement of cilia, flagella, and tentacles in many organisms. Human beings have the ability to move their limbs, jaws, eyelids, tongue, and other organs with voluntary muscles. In these, some movements involve changing position or location and are known as locomotion. Locomotion includes walking, running, climbing, flying, and swimming.

The structures involved in locomotion may also play a vital role in other types of movement. For instance, in Paramecium, cilia assist in both food movement and locomotion. Hydra uses its tentacles for capturing prey and locomotion. Limbs are used by humans for changes in body posture and locomotion. These observations indicate that movements and locomotion are interconnected. So, it can be stated that “While all locomotions are movements, not all movements are locomotions”.



The methods of locomotion adapted by animals vary based on their habitats and specific needs. Generally, locomotion serves purposes such as searching for food, shelter, suitable breeding grounds, favorable climatic conditions, or escaping from predators.

Also Read: Locomotion and Movement

Types of Movement

Cells of the human body exhibit three major types of movements that are amoeboid, ciliary, and muscular.

Muscles

Muscle is a specialized tissue derived from the mesoderm. Muscles contribute approximately 40-50% of the body weight of a human adult. While looking into the properties of muscles it can be observed that they are excitable, contractile, extensible, and elastic.

Muscles are classified based on different criteria, including location, appearance, and nature of regulation of their activities. There are mainly three types of muscles that are identified based on their location; skeletal muscles, visceral muscles, and cardiac muscles.

Structure and Mechanism of Contraction

Skeletal muscles are composed of muscle bundles or fascicles held together by fascia. Each muscle bundle contains muscle fibers surrounded by the sarcolemma and sarcoplasm. The sarcoplasmic reticulum stores calcium ions, and myofibrils, composed of myofilaments, give the myofiber a striated appearance. Actin is predominantly found in the I-band, while myosin is primarily located in the A-band. Actin and myosin filaments are parallel to each other and arranged along the myofibril’s longitudinal axis. The Z-line divides the I-band, and the M-line holds the thick filaments together in the A-band. Sarcomeres, located between Z-lines, are the functional units responsible for muscle contraction. In a resting state, thin filaments overlap partially with thick filaments, leaving the H-zone unoverlapped.

Structure of Contractile Proteins

The structure of an actin (thin) filament is composed of two helically wound “F” (filamentous) actins. Each “F” actin is a polymer formed by monomeric “G” (globular) actins. Alongside the “F” actins, two filaments of the protein tropomyosin run parallel to them. Tropomyosin is a complex protein that is evenly distributed along the length of the actin filaments. In the resting state, a subunit of troponin covers or masks the active binding sites on the actin filaments, preventing myosin from binding to them.

On the other hand, the myosin (thick) filament is also a polymerized protein. It is composed of multiple monomeric proteins called meromyosins. A thick filament consists of two main components: heavy meromyosin (HMM) and light meromyosin (LMM).

The HMM component of the myosin filament includes the globular head, which possesses an active ATPase enzyme. It also has binding sites for ATP, as well as active sites for actin. The globular heads with short arms project outward from the surface of the polymerized myosin filament at regular intervals and angles, forming cross-arms.

In short, the actin filament is made up of polymerized “F” actins, accompanied by tropomyosin and troponin, while the myosin filament consists of polymerized meromyosins, with the globular heads containing ATPase and actin-binding sites.

Mechanism of Muscle Contraction

The sliding filament theory provides an explanation for muscle contraction, stating that thin filaments slide over thick filaments. Muscle contraction is initiated by a signal from the central nervous system (CNS) transmitted through a motor neuron. The motor neuron and the muscle fibers connect to form a motor unit. At the neuromuscular junction, the point of contact between the motor neuron and the muscle fiber’s sarcolemma, acetylcholine is released as a neurotransmitter, generating an action potential in the sarcolemma.

The action potential spreads through the muscle fiber, causing the release of calcium ions into the sarcoplasm. These calcium ions bind to a subunit of actins on actin filaments, uncovering active sites for myosin. Utilizing ATP hydrolysis, the myosin head binds to the exposed active sites on actin, forming a cross-bridge. The cross-bridge formation results in the pulling of attached actin filaments toward the center of the A-band. As a consequence, the Z-lines attached to these actins are also drawn inward, shortening the sarcomere and leading to muscle contraction.

During muscle contraction, the I-bands decrease in length, while the A-bands maintain their length. The myosin releases ADP and P1, returning to its relaxed state. A new ATP molecule binds, breaking the cross-bridge. ATP is hydrolyzed by the myosin head, initiating the cycle of cross-bridge formation and breakage, causing further sliding of the filaments. This process continues until calcium ions are pumped back to the sarcoplasmic reticulum, resulting in the masking of actin filaments and the return of Z-lines to their original position, leading to muscle relaxation.

The reaction time of muscle fibers can vary across different muscles. Repeated muscle activation can result in the accumulation of lactic acid due to the anaerobic breakdown of glycogen, leading to fatigue. Myoglobin, a red-colored oxygen-storing pigment, is found in muscles and is particularly high in red fibers. Red fibers appear reddish and contain numerous mitochondria for ATP production. On the other hand, white fibers have lower myoglobin content, a pale or whitish appearance, and fewer mitochondria, but a high amount of sarcoplasmic reticulum. White fibers rely on anaerobic processes for energy production.

Skeletal System

The skeletal system is composed of bones and cartilage, which provide a framework for the body and facilitate movement. Bone is a specialized connective tissue with a hard matrix containing calcium salts, while cartilage has a slightly pliable matrix due to chondroitin salts. In humans, the skeletal system consists of 206 bones and a few cartilages. It is divided into two main divisions: the axial skeleton and the appendicular skeleton.

Axial Skeleton

The axial skeleton includes 80 bones distributed along the main axis of the body. It comprises the skull, vertebral column, sternum, and ribs. The skull is composed of cranial and facial bones, totaling 22 bones. The cranial bones (8 in number) form the protective outer covering for the brain. The facial region consists of 14 skeletal bones at the front part of the skull. The hyoid bone, a U-shaped bone located at the base of the buccal cavity, is also part of the skull. Each middle ear contains three tiny bones called ear ossicles: malleus, incus, and stapes.

Vertebral column

The, positioned along the dorsal side of the body, consists of a series of 26 vertebrae. It spans from the base of the skull, forming the primary framework of the trunk. Each vertebra contains a central hollow region known as the neural canal, which provides a passage for the spinal cord. The first vertebra called the atlas, connects with the occipital condyles. Starting from the skull, the vertebral column is further classified into distinct regions: cervical (7), thoracic (12), lumbar (5), sacral (1-fused), and coccygeal (1-fused). Its essential functions include safeguarding the spinal cord, providing support for the head, and serving as an anchor for the attachment of the ribs and muscles of the back.

Sternum

The sternum, also known as the breastbone, is a flat bone located on the ventral midline of the thorax. It serves as an attachment point for the ribs and plays a role in protecting the underlying organs. There are 12 pairs of ribs in the human body. Each rib is a thin, flat bone that is connected dorsally to the vertebral column and ventrally to the sternum. It has two articulation surfaces on its dorsal end, giving it the name “bicephalic.”

The first seven pairs of ribs are known as true ribs. They are attached dorsally to the thoracic vertebrae and ventrally connected to the sternum through hyaline cartilage. The 8th, 9th, and 10th pairs of ribs are called vertebronchondral or false ribs which do not directly articulate with the sternum but instead join the seventh rib with the help of hyaline cartilage. The last two pairs of ribs (11th and 12th) are not connected ventrally and are called floating ribs. The thoracic vertebrae, ribs, and sternum together form the rib cage, which provides protection to the organs in the thoracic cavity.

Appendicular Skeleton

The appendicular skeleton comprises the bones of the limbs and their associated girdles. Each limb consists of a total of 30 bones. In the hand, which is part of the forelimb, we find the humerus, radius, ulna, eight carpals (wrist bones), five metacarpals (palm bones), and fourteen phalanges (digits). On the other hand, the leg, belonging to the hind limb, consists of the femur (the body’s longest bone), tibia, fibula, seven tarsals (ankle bones), five metatarsals, and fourteen phalanges. Additionally, the knee cap, known as the patella, is a cup-shaped bone that provides protection to the front of the knee joint.

Pectoral and Pelvic Girdle

The pectoral and pelvic girdles play crucial roles in connecting the upper and lower limbs, respectively, to the axial skeleton. Each girdle consists of two halves, with the pectoral girdle consisting of a clavicle (collarbone) and a scapula (shoulder blade). The scapula, a large triangular flat bone situated between the second and seventh ribs on the back of the thorax, features a spine and an acromion process that connects to the clavicle. The glenoid cavity, located below the acromion, forms the shoulder joint by articulating with the head of the humerus. The clavicle, commonly known as the collarbone, is a slender bone.

On the other hand, the pelvic girdle comprises two coxal bones that result from the fusion of the ilium, ischium, and pubis bones. The point where these bones merge creates the acetabulum, which connects to the thigh bone (femur). The two halves of the pelvic girdle meet at the front to form the pubic symphysis, which contains fibrous cartilage.

Both the pectoral and pelvic girdles, along with their associated bones, provide stability, support, and mobility to the upper and lower limbs. They enable the limbs to articulate with the axial skeleton and participate in various movements and activities.

Bones in the Skeletal System

The skeletal system consists of numerous bones that provide support, protection, and structure to the body. Here are the names of the major bones in the human skeletal system:

Joints

Joints play a crucial role in facilitating movement in the body. Joints serve as connections where bones come together, forming either direct articulations between bones or cartilage. Joints act as fulcrums where the force generated by muscles is used to carry out movements. There are three major structural forms of joints

Disorders of the Muscular and Skeletal System

Following are the disorders of the Muscular and Skeletal System:

FAQs on Locomotion and Movement

Q1. What is the primary function of the skeletal system?

Answer:

The primary function of the skeletal system is to provide structural support, protect internal organs, facilitate movement, produce blood cells, and store minerals.

Q2. How do tendons contribute to the movement?

Answer:

Tendons are tough, fibrous connective tissues that connect muscles to bones. They transmit the force generated by muscles to the bones, allowing movement to occur. Tendons also help stabilize joints and provide mechanical support to the musculoskeletal system.

Q3. What is the role of ligaments in the skeletal system?

Answer:

Ligaments are tough, fibrous connective tissues that connect bones to other bones and provide stability to joints. They help prevent excessive movement and maintain proper alignment of bones during joint motion.

Q4. What is the difference between ligaments and tendons?

Answer:

Ligaments are connective tissues that join bones together in a joint, providing stability and limiting excessive movement. Tendons, on the other hand, connect muscles to bones, enabling the transmission of muscle forces to produce movement and control joint actions.


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