Locomotion and Movement – Class 11 Biology | Free NEET Notes
Introduction By Learn Sufficient Notes💖
- Movement is a major feature of living organisms. Both animals and plants show different kinds of movements. In unicellular organisms like Amoeba, the streaming of protoplasm is a basic type of movement. Many organisms show movement through cilia, flagella, or tentacles.
- Humans can move body parts such as limbs, jaws, eyelids, and tongue. Some movements help in changing the position or location of the body. These are called locomotion and are done voluntarily. Examples include walking, running, climbing, flying, and swimming.
- The same body structures may be used for both movement and locomotion. For instance, in Paramoecium, cilia help in both moving food inside the body and in locomotion. In Hydra, tentacles are used to catch prey and also to move. In humans, limbs help in changing posture and also in locomotion.
- These examples show that movement and locomotion are closely related. It can be said that all locomotions are movements, but not all movements are locomotion.
- The type of locomotion depends on the habitat and the situation. Usually, animals move to find food, shelter, mates, breeding areas, better climate, or to escape from predators.
2. Various Kinds of Movements in the Human Body
- Cells in the human body show three main types of movements: amoeboid, ciliary, and muscular.
- Some specialized cells like macrophages and leucocytes in our blood perform amoeboid movement. This happens with the help of pseudopodia, which are formed by the streaming of protoplasm, similar to what we see in Amoeba. Structures inside the cell called cytoskeletal elements, such as microfilaments, also help in this type of movement.
- Ciliary movement happens in many internal tubular organs that are lined with ciliated epithelium. In the trachea, coordinated movement of cilia helps remove dust particles and foreign substances that are inhaled with the air. In females, the movement of the ovum through the reproductive tract is also supported by ciliary action.
- Muscular movement is used when we move our limbs, jaws, tongue, and other parts. This movement is possible due to the contractile property of muscles. In humans and most multicellular organisms, muscles are essential for both locomotion and other body movements.
- Locomotion depends on the well-coordinated work of the muscular system, skeletal system, and nervous system.
- In this chapter, you will study the types of muscles, their structure, how they contract, and the important features of the skeletal system.
3. Introduction to Muscles in the Human Body
- Flagellar movement helps in the swimming of sperm cells, maintaining water flow in the canal system of sponges, and in the locomotion of Protists like Euglena.
- Flagellar movement helps in the swimming of sperm cells, maintaining water flow in the canal system of sponges, and in the locomotion of Protists like Euglena.
- Muscles are classified based on their location, appearance, and how their activity is regulated. Based on location, there are three main types of muscles:
- Skeletal muscles
- Visceral muscles
- Cardiac muscles
Skeletal Muscles–
- Skeletal muscles are found close to the bones. Under a microscope, they show a striped appearance, so they are called striated muscles. These muscles work under voluntary control, meaning they are regulated by the nervous system, so they are also known as voluntary muscles. Their main function is to support body movement and posture changes.
Visceral Muscles-
- Visceral muscles are found in the walls of internal organs like the alimentary canal and reproductive tract. These muscles do not show striations and have a smooth appearance, so they are called smooth muscles or non-striated muscles. Their actions are involuntary, meaning they are not controlled by the nervous system. These muscles help move food in the digestive system and gametes in the reproductive system.
Cardiac Muscles-
- Cardiac muscles are found only in the heart. These muscle cells are arranged in a branching pattern to form the cardiac tissue. Under the microscope, they appear striated, like skeletal muscles. However, their actions are involuntary, meaning they are not directly controlled by the nervous system.
Structure of Muscle Fibre–
- A muscle fibre is covered by a plasma membrane called the sarcolemma. Inside, it contains a material called sarcoplasm. A muscle fibre is a syncytium, which means it has many nuclei in a single cell.
- The sarcoplasmic reticulum, which is the endoplasmic reticulum of the muscle, stores calcium ions. Inside the sarcoplasm, there are many long thread-like structures called myofibrils or myofilaments, arranged in parallel.
- Each myofibril has alternating dark and light bands. These bands are formed by two proteins: Actin and Myosin.
- The light bands are made of actin and are called I-bands (Isotropic bands).
- The dark bands are made of myosin and are called A-bands (Anisotropic bands).
Structure of Skeletal Muscle–
- Each skeletal muscle in our body is made up of many muscle bundles or fascicles. These fascicles are held together by a collagen-rich connective tissue layer called the fascia.
- Each muscle bundle contains several muscle fibres. A muscle fibre is covered by a plasma membrane called the sarcolemma, and its inner fluid is called sarcoplasm. Since one muscle fibre has many nuclei, it is known as a syncytium.
- The sarcoplasmic reticulum is a special form of endoplasmic reticulum found in muscle fibres, and it stores calcium ions, which are essential for muscle contraction.
- Inside the sarcoplasm, there are many long, thread-like structures called myofibrils or myofilaments. These are arranged in parallel and give the muscle its striped (striated) appearance. This appearance is due to the arrangement of two main proteins: actin and myosin.
- The light bands contain actin and are called I-bands or isotropic bands.
- The dark bands contain myosin and are called A-bands or anisotropic bands.
Arrangement of Actin and Myosin–
- The proteins actin and myosin are shaped like rods and are aligned parallel to each other and to the length of the myofibrils.
- Actin filaments are thin, while
- Myosin filaments are thicker.
- Because of this, they are often referred to as thin and thick filaments.
- In the center of each I-band, there is a Z-line, which is an elastic fibre. The actin (thin) filaments are attached to this Z-line. In the A-band, the myosin (thick) filaments are held together at the center by another line called the M-line.
- The A-bands and I-bands alternate throughout the length of each myofibril.
Sarcomere and H-zone-
- The region between two Z-lines is called a sarcomere. This is the functional unit of muscle contraction.
- When the muscle is at rest, the thin filaments slightly overlap the thick filaments on both sides. However, the central part of the thick filaments, where there is no overlapping, is known as the H-zone.
3. 1 Understanding the Framework of Contractile Proteins
Each actin filament (also called a thin filament) is made up of two ‘F’ actin chains twisted around each other in a helical structure. Each ‘F’ (filamentous) actin is a long chain of many small units called ‘G’ (globular) actins.
Along with the actin chains, two strands of another protein called tropomyosin run parallel to the F-actins throughout their length. Attached at regular intervals on the tropomyosin is a complex protein called troponin.
In the resting state, a subunit of troponin covers the active binding sites for myosin on the actin filament, thus preventing contraction.
Each myosin filament (also known as a thick filament) is made by combining many small proteins called meromyosins.
Each meromyosin has two main parts:
- A globular head with a short arm, known together as the heavy meromyosin (HMM)
- A long tail, called the light meromyosin (LMM)
The HMM parts (head and short arm) stick out from the myosin filament surface at regular angles and intervals. These projections are called cross arms.
The globular head of myosin works as an ATPase enzyme. It contains binding sites for ATP (for energy) and active sites for actin (for attachment during contraction).
3.2 How Muscles Contract – The Working Process
- The sliding filament theory explains the muscle contraction process. According to this theory, muscles contract when thin filaments (actin) slide over thick filaments (myosin).
Initiation of Contraction
Muscle contraction begins with a signal from the central nervous system (CNS). This signal travels through a motor neuron. A motor unit consists of a motor neuron and all the muscle fibres it controls.
The point where a motor neuron connects to the muscle fibre membrane (sarcolemma) is called the neuromuscular junction or motor end plate.
When a nerve signal reaches this junction, it releases a neurotransmitter called acetylcholine. This chemical creates an action potential in the sarcolemma, which spreads across the muscle fibre and causes the release of calcium ions (Ca²⁺) into the sarcoplasm.
Cross Bridge Formation and Filament Sliding
The rise in calcium levels allows calcium to bind to troponin on the actin filament, which removes the masking from the active sites on actin. Now, myosin heads, using energy from ATP hydrolysis, bind to these active sites on actin to form cross-bridges.
This action pulls the actin filaments toward the center of the A-band, which also pulls the Z-lines inward. This shortens the sarcomere, resulting in muscle contraction.
During this process, the I-bands become shorter, but the A-bands remain the same length.
The myosin head, after completing the pull, releases ADP and Pi and returns to its relaxed state. A new ATP molecule then binds to myosin, causing the cross-bridge to break.
ATP is again broken down, and the cross-bridge cycle repeats, resulting in continuous sliding of filaments.
Relaxation of Muscle
The contraction continues until calcium ions are pumped back into the sarcoplasmic reticulum (cisternae). This causes the active sites on actin to get masked again, and the Z-lines return to their original positions, leading to muscle relaxation.
Muscle Fatigue and Fibre Types
Different muscles have different reaction times. If a muscle is used repeatedly, it may develop fatigue due to lactic acid accumulation. This happens when glycogen breaks down anaerobically.
Muscles contain a red pigment called myoglobin, which stores oxygen. Muscles rich in myoglobin appear reddish and are called Red fibres. These have many mitochondria, and they perform aerobic respiration for ATP production. Hence, they are also known as aerobic muscles.
Some muscles have less myoglobin and appear whitish. These are known as White fibres. They have fewer mitochondria but more sarcoplasmic reticulum, and they depend on anaerobic respiration for energy.
4. Overview of the Human Skeletal Structure
The skeletal system forms the structural framework of the human body. It consists of bones and a few cartilages. This system plays a vital role in body movement.
Without jaw bones, we couldn’t chew, and without limb bones, walking would be impossible.
Types of Connective Tissues
- Bone is a specialised connective tissue with a hard matrix made of calcium salts.
- Cartilage is another connective tissue but has a slightly flexible matrix due to chondroitin salts.
Number and Divisions
In humans, the skeleton includes 206 bones and a few cartilages. The system is divided into two main parts:
- Axial Skeleton
- Appendicular Skeleton
Axial Skeleton
The axial skeleton has 80 bones and runs along the central axis of the body. It includes:
- Skull
- Vertebral column
- Sternum
- Ribs
Skull Structure
The skull contains 22 bones:
- 8 cranial bones form a hard, protective shell around the brain, known as the cranium.
- 14 facial bones form the front portion of the skull.
A special U-shaped bone called the hyoid is located at the base of the buccal cavity (mouth area).
Each middle ear has three small bones:
- Malleus
- Incus
- Stapes
Together, these are called the ear ossicles.
The skull connects to the top of the vertebral column through two occipital condyles, making it a dicondylic skull.
Vertebral Column
The vertebral column has 26 vertebrae arranged in a line along the back. It begins at the base of the skull and forms the main structure of the trunk.
Each vertebra has a hollow central part called the neural canal, through which the spinal cord passes.
- The first vertebra, called the atlas, connects with the occipital condyles of the skull.
The vertebral column is divided into five regions:
- Cervical – 7 vertebrae
- Thoracic – 12 vertebrae
- Lumbar – 5 vertebrae
- Sacral – 1 fused unit
- Coccygeal – 1 fused unit
All mammals, including humans, typically have 7 cervical vertebrae.
Functions of Vertebral Column
- Protects the spinal cord
- Supports the head
- Connects to ribs and muscles of the back
Sternum
The sternum is a flat bone located on the front side (ventral midline) of the chest (thorax).
There are 12 pairs of ribs in the human body. Each rib is a thin, flat bone that connects at the back (dorsally) to the vertebral column and at the front (ventrally) to the sternum. Each rib has two joint surfaces at the back, which is why they are called bicephalic. The first seven pairs are called true ribs because they connect directly to both the thoracic vertebrae at the back and to the sternum in front through hyaline cartilage. The 8th, 9th, and 10th pairs are called false ribs or vertebrochondral ribs. They do not connect directly to the sternum but instead join the seventh rib with the help of hyaline cartilage. The last two pairs, the 11th and 12th, are known as floating ribs because they are not attached to the sternum at all. Together, the thoracic vertebrae, ribs, and sternum form the rib cage, which protects vital organs like the lungs and heart.
The appendicular skeleton includes the bones of the limbs along with their girdles. Each limb has 30 bones. In the forelimb (hand), the bones are: humerus, radius, and ulna; followed by the carpals (which are the eight wrist bones), metacarpals (the five palm bones), and phalanges (the 14 finger bones). In the hind limb (leg), the main bones are: the femur (thigh bone and the longest bone in the body), tibia, and fibula. The ankle contains seven tarsal bones, the foot has five metatarsals, and the toes contain 14 phalanges. A cup-shaped bone called the patella, or knee cap, covers the knee joint from the front.
The girdles connect the limbs to the axial skeleton. The pectoral girdle connects the arms, while the pelvic girdle connects the legs. Each pectoral girdle has two halves, and each half is made of a clavicle and a scapula. The scapula is a large, flat, triangular bone located in the upper back between the second and seventh ribs. On its back, the scapula has a raised ridge called the spine, which ends in a flat extension called the acromion. The clavicle (commonly known as the collar bone) connects with the acromion. Below the acromion is a depression known as the glenoid cavity, where the head of the humerus fits, forming the shoulder joint. Each clavicle is a long, slender bone with two curves.
The pelvic girdle consists of two coxal bones. Each coxal bone is formed by the fusion of three bones — the ilium, ischium, and pubis. Where these three bones meet, they form a deep socket called the acetabulum, which holds the head of the femur (thigh bone) to create the hip joint. The two halves of the pelvic girdle are joined at the front at a point called the pubic symphysis, which contains a pad of fibrous cartilage that allows for slight movement and flexibility.
5. Connections Between Bones: Types of Joint
- Joints are important for all types of body movements, including locomotion.
- A joint is a point where two bones or a bone and cartilage meet. Joints work like a fulcrum to help transfer the force produced by muscles into movement.
- The ability of a joint to move depends on several factors. Based on structure, joints are divided into three main types: fibrous, cartilaginous, and synovial joints.
- Fibrous joints do not allow any movement. These are found in the flat bones of the skull, which are tightly joined together by dense fibrous connective tissues called sutures to form the cranium.
- In cartilaginous joints, bones are joined by cartilage. An example is the joints between the vertebrae in the spinal column, which allow limited movement.
- Synovial joints have a fluid-filled synovial cavity between the bones. This structure allows for free movement and supports locomotion and various other movements.
Examples of synovial joints include:
- Ball and socket joint – e.g., between the humerus and pectoral girdle
- Hinge joint – e.g., the knee joint
- Pivot joint – e.g., between the atlas and axis bones
- Gliding joint – e.g., between the carpal bones of the wrist
- Saddle joint – e.g., between the carpal and metacarpal of the thumb
6. Diseases Affecting Muscles and Bones
The muscular and skeletal systems, though robust, are prone to several disorders, some of which can severely affect mobility and overall health. Myasthenia gravis is a serious autoimmune disorder where the body’s immune system mistakenly attacks its own neuromuscular junctions. This leads to muscle fatigue, weakening, and even paralysis of skeletal muscles, making everyday tasks difficult. Muscular dystrophy refers to a group of genetic disorders where skeletal muscles gradually weaken and degenerate over time. It is typically inherited and can severely affect physical strength and posture. Tetany is another condition marked by sudden and rapid muscle spasms or wild, uncontrollable contractions. This often occurs due to low calcium (Ca++) levels in the body fluids, which disrupt normal muscle function. Arthritis is a common disorder involving the inflammation of joints, leading to pain, stiffness, and reduced movement. It can occur at any age and in various forms, like osteoarthritis or rheumatoid arthritis. Osteoporosis is an age-related bone disease, primarily seen in older adults, particularly post-menopausal women. It is characterized by reduced bone density and mass, increasing the risk of fractures. A major cause of osteoporosis is decreased estrogen levels in the body. Lastly, gout is a painful joint disorder that arises due to the accumulation of uric acid crystals in the joints. This leads to joint inflammation, swelling, and intense pain, usually starting with the big toe. Together, these disorders highlight the importance of maintaining healthy bones and muscles through proper nutrition, physical activity, and medical care.
7. Chapter Recap
- Movement is a basic characteristic of all living organisms. Various types of movement can be observed in animals, such as protoplasmic streaming, ciliary motion, and the movement of limbs, fins, or wings. When a voluntary movement leads to a change in position or place, it is known as locomotion. Animals generally move to find food, shelter, mating partners, favorable environments, or to protect themselves from danger. In humans, movement occurs in three main forms: amoeboid, ciliary, and muscular. Among these, muscular movement is central to locomotion and requires the coordinated action of muscle fibers. There are three types of muscles in the human body: skeletal muscles, which are striated, voluntary, and attached to bones; visceral muscles, which are smooth, involuntary, and found in the internal organs; and cardiac muscles, which are striated, branched, involuntary, and found only in the heart. Muscles exhibit properties like excitability, contractility, extensibility, and elasticity.
- Each muscle fiber is made up of many myofibrils, which in turn are composed of repeating units called sarcomeres. These are the functional units of muscle contraction. A sarcomere contains thick myosin filaments forming the central A band, and thin actin filaments forming the I bands on either side, connected by Z lines. In the resting state, the active sites on actin are blocked by a protein called troponin. When a motor neuron sends a signal to the muscle, it creates an action potential that triggers the release of calcium ions (Ca⁺⁺) from the sarcoplasmic reticulum. These calcium ions expose the active sites on actin, allowing myosin heads to bind and form cross bridges. Using energy from ATP, the myosin heads pull the actin filaments, causing them to slide over myosin, which results in muscle contraction. The process reverses when calcium is reabsorbed, the active sites are blocked again, cross bridges break, and the muscle relaxes.
- Repeated stimulation of muscles without adequate rest causes fatigue due to lactic acid buildup. Muscles are also classified based on the presence of myoglobin: Red muscle fibers contain more myoglobin and mitochondria, supporting sustained aerobic activity, while White muscle fibers have less myoglobin and rely more on anaerobic respiration for quick, short-term movements. The skeletal system, composed of bones and cartilages, provides support and shape to the body and enables movement. It is divided into two parts: the axial skeleton, which includes the skull, vertebral column, ribs, and sternum; and the appendicular skeleton, which includes limb bones and girdles. Joints connect bones or bones to cartilage and are of three main types: fibrous joints (immovable), cartilaginous joints (partially movable), and synovial joints (freely movable). Synovial joints are essential for body movement and include types like ball-and-socket, hinge, pivot, gliding, and saddle joints.
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