Please see Locomotion and Movement Class 11 Biology Revision Notes provided below. These revision notes have been prepared as per the latest syllabus and books for Class 11 Biology issues by CBSE, NCERT, and KVS. Students should revise these notes for Chapter 20 Locomotion and Movement daily and also prior to examinations for understanding all topics and to get better marks in exams. We have provided Class 11 Biology Notes for all chapters on our website.
Chapter 20 Locomotion and Movement Class 11 Biology Revision Notes
Locomotion is the voluntary movements resulting in a in location. All locomotion are movements but all movements are not locomotion. Both are interlinked. E.g.
♦ In Paramoecium, cilia help in the movement of food through cytopharynx and in locomotion
♦ Hydra use tentacles to capture prey and for locomotion.
♦ Limbs help to change body postures and for locomotion.
Types of movement in human being
1. Amoeboid movement: By pseudopodia formed by streaming of protoplasm as in Amoeba. Cytoskeletal elements like microfilaments also help for this. E.g. change Macrophages & leucocytes.
2. Ciliary movement: By cilia. E.g. ciliary movements in trachea (to remove dust particles and foreign substances), and oviducts (for the passage of ova).
3. Muscular movement: By muscles. E.g. movement of limbs.
Flagellar movement helps in the swimming of spermatozoa, maintenance of water current in the canal system of sponges and in locomotion of Protozoans like Euglena.
HUMAN MUSCULAR SYSTEM
♦ It includes muscles which are mesodermal in origin.
♦ Muscles constitute 40-50% of the body weight.
♦ Muscles have excitability, contractility, extensibility & elasticity.
♦ Based on location, muscles are 3 types:
STRUCTURE OF STRIATED MUSCLE
♦ Skeletal muscle is made of muscle bundles (fascicles) held together by collagenous connective tissue layer (fascia).
♦ Each fascicle contains many muscle fibres (muscle cells).
♦ Muscle fibres are lined by plasma membrane (sarcolemma) enclosing the sarcoplasm.
♦ Each muscle fibre contains myofilaments (myofibrils).
♦ Each myofibril has alternate dark (Anisotropic or Aband) and light striations (Isotropic or I- band). This is due to the presence of 2 fibrous contractile proteins – thin Actin filament and thick Myosin filament.
♦ I-bands contain actin. A- bands contain actin and myosin. They are arranged parallel to each other.
♦ A- band bears a lighter middle region (H band) formed of only myosin. A thin dark line (M- line) runs through the centre of H-zone.
♦ I- band is bisected by a dense dark band called Z- line. Region between two Z- lines is called sarcomere. They are the functional units of muscle contraction.
Structure of contractile proteins
♦ An actin filament is made of 2 filamentous (F) actins which form double helix.
♦ F- actin is a polymer of monomeric Globular (G) actins.
♦ Actin contains 2 other proteins (tropomyosin & troponin).
♦ Two filaments of tropomyosin run along the grooves of the F-actin double helix.
♦ Troponin has 3 subunits. It is seen at regular intervals on tropomyo sin. In the resting state, a subunit of troponin masks the binding sites for myosin on the actin filaments.
♦ Each myosin filament is a polymer of many monomeric proteins called Meromyosins.
♦ A meromyosin has 2 parts:
a. Heavy meromyosin or HMM or cross arm (globular head + short arm): It projects outwards.
b. Light meromyosin or LMM (tail).
♦ The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.
MECHANISM OF MUSCLE CONTRACTION
According to sliding filament theory, contraction of a muscle fibre occurs by the sliding of thin filaments over thick filaments.
The steps are given below:
♦ An impulse from the CNS reaches the neuromuscular junction (Motor- end plate) via motor neuron.
♦ Synaptic vesicles release a neurotransmitter Acetylcholine. It generates an action potential in the sarcolemma that spreads through the muscle fibre. It causes the release of Ca2+ ions from sarcoplasmic cisternae into sarcoplasm.
♦ Ca binds with a subunit of troponin on actin filaments and unmask the active sites for myosin.
♦ Using energy from ATP hydrolysis, myosin head binds to active sites on the actin to form cross bridge. This pulls actin filaments on both sides towards the centre of A- band. Actin filaments partially overlap so that H- zone disappears.
♦ The Z- line attached to actins is also pulled inwards. It causes a shortening (contraction) of sarcomere.
♦ I-bands get shortened, whereas A- bands retain the length.
♦ Myosin releases ADP and Pi and goes back to its relaxed state. A new ATP binds and the cross- bridge is broken.
♦ The ATP is again hydrolyzed by the myosin head and the above processes are repeated causing further sliding.
♦ When Ca2+ ions are pumped back to sarcoplasmic cisternae, actin filaments are again masked. As a result, Z- lines return to their original position. It results in relaxation.
♦ The reaction time of the fibres varies in different muscles.
♦ Repeated activation of muscles leads to the accumulation of the lactic acid causing muscle fatigue. This is due to anaerobic breakdown of glycogen in muscles.
Red muscle fibres and white muscle fibres
HUMAN SKELETAL SYSTEM
It consists of a framework of bones (206) & few cartilages. Human skeletal system has 2 parts: axial & appendicular.
1. Axial skeletal system (80 bones)
Includes bones of head, vertebral column, sternum & ribs.
a. Bones of Head (29 bones)
It includes skull, Hyoid and Ear ossicles.
Skull (22): Include cranial bones and facial bones.
Cranial bones (8): Include Frontal (1), Parietals (2), Temporals (2), Occipital (1), Sphenoid (1) & Ethmoid (1).
Facial bones (14): Include Nasals (2), Maxillae (2), Zygomatics (2), Lacrimals (2), Palatines (2), Inferior nasals (2), Mandible (1) and Vomer (1)Skull articulates with First vertebra (atlas) with the help of 2 occipital condyles (dicondylic skull).
Hyoid bone (1): U- shaped bone seen below buccal cavity.
Ear ossicles (3 x 2 = 6): Malleus (2), Incus (2) & stapes (2).
b. Vertebral column
♦ Formed of 26 vertebrae. Includes Cervical vertebrae (7), Thoracic vertebrae (12), Lumbar vertebrae (5) ,Sacral vertebrae (1- fused) and Coccygeal vertebrae (1- fused).
♦ Vertebra has a central hollow portion (neural canal) through which the spinal cord passes.
♦ Number of cervical vertebrae are 7 in almost all mammals.
♦ The vertebral column protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back.
c. Sternum or Breast bone (1)
♦ Flat bone on the ventral midline of thorax.
d. Ribs (12 pairs)
True ribs (first 7 pairs): They are attached to thoracic vertebrae and ventrally connected to sternum with the help of Hyaline cartilage.
Vertebrochondral (false) ribs (8th, 9th & 10th pairs): They do not articulate directly with the sternum but join the 7th rib with the help of Hyaline cartilage.
Floating ribs (11th & 12th pairs): They are not connected ventrally (no connection with sternum or other ribs).
♦ Each rib has 2 articulation surfaces on its dorsal end and is hence called bicephalic.
2. Appendicular skeletal system (126 bones)
a. Bones of fore- limbs (30 x 2 = 60)
Include Humerus (1), Radius (1), Ulna (1), Carpals (wrist bones-8), Metacarpals (palm bones- 5) & Phalanges (digits- 14)
b. Bones of hind- limbs (30 x 2 = 60)
Include Femur (thigh bone-1), Patella (knee cap-1), Tibia (1) & fibula (1), Tarsals (ankle bones- 7), Metatarsals (5) & Phalanges (digits- 14).
c. Pectoral girdles (2×2=4)
♦ Include clavicle (2) & scapula (2).
♦ Scapula is a large triangular flat bone situated in the dorsal part of the thorax between the second and 7th ribs.
♦ Scapula (shoulder blade) has a slightly elevated ridge (spine) which projects as a flat, expanded process (acromion). The clavicle (collarbone) articulates with this.
♦ Below the acromion is glenoid cavity which articulates with the head of humerus to form the shoulder joint.
d. Pelvic girdles (2)
♦ Formed of 2 coxal bones. Each coxal bone is formed by the fusion of 3 bones- Ilium, Ischium & pubis.
♦ At the point of fusion of Ilium, Ischium and Pubis is a cavity (Acetabulum) to which the thigh bone articulates.
♦ The 2 halves of the pelvic girdle meet ventrally to form pubic symphisis containing fibrous cartilage.
Joints are points of contact between bones, or between bones and cartilages. 3 types:
1. Fibrous (immovable) joints: E.g. sutures b/w skull bones.
2. Cartilaginous joints (Slightly movable joints): Bones are joined together with the help of cartilages. E.g. Joints between the adjacent vertebrae.
3. Synovial (movable) joints: They have a fluid filled synovial cavity between articulating surfaces of 2 bones.
Types of synovial joint
DISORDERS OF MUSCULAR & SKELETAL SYSTEMS
1. Myasthenia gravis: An auto immune disorder that affects neuromuscular junction. It leads to fatigue, weakening and paralysis of skeletal muscles.
2. Muscular dystrophy: Progressive degeneration of skeletal muscles. Mostly due to genetic disorder.
3. Tetany: Rapid muscle spasm due to low Ca2+ in body fluid.
4. Arthritis: Inflammation of joints.
5. Osteoporosis: Age- related disorder characterized by decreased bone mass and increased chances of fractures. Decreased level of estrogen is a common cause.
6. Gout: Inflammation of joints due to accumulation of uric acid crystals.