Locomotion and Movement

Locomotion and Types of Movement

Movement in Living Beings

• Movement is a key feature of living beings.
• Animals and plants show a wide range of movements.
• Examples:
  • Amoeba: Streaming of protoplasm.
  • Many organisms: Movement of cilia, flagella, and tentacles.
  • Humans: Movement of limbs, jaws, eyelids, tongue, etc.

Locomotion

• Locomotion: Voluntary movements resulting in a change of place or location.
• Examples: Walking, running, climbing, flying, swimming.
• Locomotory structures can also help in other types of movements.
  • Paramoecium: Cilia help in both locomotion and movement of food.
  • Hydra: Tentacles help in capturing prey and locomotion.
  • Humans: Limbs help in changing body postures and locomotion.

Link Between Movement and Locomotion

• All locomotions are movements, but not all movements are locomotions.

Reasons for Locomotion

• Search for food, shelter, mate, breeding grounds.
• Finding favorable climatic conditions.
• Escaping from enemies/predators.

Types of Movement

Amoeboid Movement

• Seen in specialized cells like macrophages and leucocytes in blood.
• Involves pseudopodia formed by the streaming of protoplasm.
• Cytoskeletal elements like microfilaments are involved.

Ciliary Movement

• Occurs in internal tubular organs lined by ciliated epithelium.
• Helps in removing dust particles and foreign substances in the trachea.
• Facilitates passage of ova through the female reproductive tract.

Muscular Movement

• Involves the movement of limbs, jaws, tongue, etc.
• Muscles have a contractile property used for locomotion and other movements.
• Requires coordinated activity of muscular, skeletal, and neural systems.

In this chapter, you will learn about:

• Types of muscles.
• Structure and mechanism of muscle contraction.
• Important aspects of the skeletal system.

Muscles

Introduction to Muscles

• Muscles are specialized tissues of mesodermal origin.
• Contribute 40-50% of the body weight in humans.
• Properties: Excitability, contractility, extensibility, and elasticity.

Types of Muscles

1. Skeletal Muscles
   • Location: Associated with the skeleton.
   • Appearance: Striated (striped).
   • Control: Voluntary.
   • Function: Movement and body posture.
2. Visceral Muscles
   • Location: Inner walls of hollow organs (e.g., alimentary canal, reproductive tract).
   • Appearance: Smooth (non-striated).
   • Control: Involuntary.
   • Function: Movement of food and gametes.
3. Cardiac Muscles
   • Location: Heart.
   • Appearance: Striated.
   • Control: Involuntary.
   • Function: Pumping blood.

Structure of Skeletal Muscle

• Muscle Bundles (Fascicles): Grouped together by connective tissue (fascia).
• Muscle Fibers: Each bundle contains muscle fibers lined by sarcolemma (plasma membrane) and sarcoplasm.
• Sarcoplasmic Reticulum: Stores calcium ions.
• Myofilaments/Myofibrils: Filaments arranged parallel in the sarcoplasm.

Myofibril Structure

• Dark Bands (A-bands): Contain myosin (thick filaments).
• Light Bands (I-bands): Contain actin (thin filaments).
• Z Line: Elastic fiber bisecting the I-band.
• M Line: Thin membrane holding thick filaments in the A-band.
• Sarcomere: Functional unit of contraction, between two Z lines.
• H Zone: Central part of thick filament not overlapped by thin filaments in a resting state.

Structure of Contractile Proteins

Actin (Thin) Filaments

• Made of two helical strands of ‘F’ (filamentous) actins.
• Each ‘F’ actin is a polymer of ‘G’ (globular) actins.
• Tropomyosin: Two filaments run alongside ‘F’ actins.
• Troponin: A complex protein found at intervals on tropomyosin.
  • Masks active binding sites for myosin on actin in resting state.

Myosin (Thick) Filaments

• Composed of polymerized proteins called Meromyosins.
• Each Meromyosin has two parts:
  1. Heavy Meromyosin (HMM): Globular head with a short arm.
  2. Light Meromyosin (LMM): Tail.
• Cross Arms: HMM components project outwards from the myosin filament.
• The globular head has:
  • ATPase activity.
  • Binding sites for ATP and actin.

Mechanism of Muscle Contraction

Sliding Filament Theory

• Muscle contraction occurs by sliding thin filaments over thick filaments.

Initiation of Contraction

• CNS sends a signal via a motor neuron.
• Motor unit: Motor neuron + muscle fibers it connects to.
• Neuromuscular junction (motor-end plate): Junction between motor neuron and muscle fiber.
• Neurotransmitter (Acetylcholine) is released, generating an action potential.
• Action potential spreads, releasing Ca++ into the sarcoplasm.
• Ca++ binds to troponin on actin, exposing active sites for myosin.

Contraction Process

• Myosin head, using ATP energy, forms a cross-bridge with actin.
• Actin filaments are pulled towards the center of ‘A’ band, shortening the sarcomere (contraction).
• ‘I’ bands reduce in length; ‘A’ bands retain length.
• Myosin releases ADP and P1, returning to a relaxed state.
• New ATP binds, breaking the cross-bridge.
• Cycle of cross-bridge formation and breakage repeats, causing sliding.
• Contraction continues until Ca++ is pumped back, causing relaxation.

Muscle Fatigue

• Repeated activation leads to lactic acid buildup from anaerobic glycogen breakdown, causing fatigue.

Types of Muscle Fibers

• Red fibers: High myoglobin, many mitochondria, appear reddish, aerobic muscles.
• White fibers: Low myoglobin, few mitochondria, high sarcoplasmic reticulum, depend on anaerobic energy, appear pale/whitish.

Skeletal System

Overview

• The skeletal system is made of bones and cartilages.
• It plays a key role in body movement.
• Bones have a hard matrix due to calcium salts.
• Cartilages have a pliable matrix due to chondroitin salts.
• Human skeletal system: 206 bones and a few cartilages.
• Divided into two main parts: axial skeleton and appendicular skeleton.

A. Axial Skeleton

• Composed of 80 bones along the body’s main axis.
• Includes the skull, vertebral column, sternum, and ribs.

Skull

• Made of 22 bones: 8 cranial and 14 facial.
• Cranial bones form the cranium, protecting the brain.
• Facial bones form the front part of the skull.
• Hyoid bone is U-shaped and at the base of the buccal cavity.
• Each ear has 3 tiny bones: Malleus, Incus, Stapes (Ear Ossicles).
• Skull connects to the vertebral column via occipital condyles (dicondylic skull).

Vertebral Column

• Composed of 26 vertebrae, dorsally placed.
• Extends from the skull base and supports the trunk.
• Vertebrae regions: cervical (7), thoracic (12), lumbar (5), sacral (1-fused), coccygeal (1-fused).
• Cervical vertebrae: 7 in almost all mammals.
• Protects the spinal cord, supports the head, and attaches to ribs and back muscles.
• First vertebra is called atlas, articulates with occipital condyles.

Sternum and Ribs

• Sternum: flat bone on ventral midline of thorax.
• 12 pairs of ribs: thin flat bones connected to the vertebral column and sternum.
• True ribs: First 7 pairs, attached to thoracic vertebrae and sternum via hyaline cartilage.
• False ribs: 8th, 9th, 10th pairs, join the seventh rib with hyaline cartilage, not directly connected to the sternum.
• Floating ribs: 11th and 12th pairs, not connected ventrally.
• Thoracic vertebrae, ribs, and sternum form the rib cage.

B. Appendicular Skeleton

• Made up of bones of limbs and their girdles.
• Each limb has 30 bones.

Bones of the Fore Limb (Hand)

• Humerus: Upper arm bone.
• Radius and Ulna: Forearm bones.
• Carpals: 8 wrist bones.
• Metacarpals: 5 palm bones.
• Phalanges: 14 finger bones.

Bones of the Hind Limb (Leg)

• Femur: Thigh bone, the longest bone.
• Tibia and Fibula: Leg bones.
• Tarsals: 7 ankle bones.
• Metatarsals: 5 foot bones.
• Phalanges: 14 toe bones.
• Patella: Knee cap.

Girdles

Pectoral Girdle

• Connects upper limbs to the axial skeleton.
• Each half has a clavicle and a scapula.
• Scapula: Large, triangular, flat bone on the back between ribs 2 and 7.
  • Spine: Slightly elevated ridge on the scapula.
  • Acromion: Flat, expanded process of the spine.
  • Glenoid Cavity: Depression below the acromion; connects with the humerus to form the shoulder joint.
• Clavicle: Long, slender bone with two curves; also known as the collar bone.

Pelvic Girdle

• Connects lower limbs to the axial skeleton.
• Made of two coxal bones.
  • Each coxal bone is formed by the fusion of three bones: ilium, ischium, and pubis.
  • Acetabulum: Cavity where the thigh bone articulates.
• The two halves of the pelvic girdle join at the pubic symphysis (fibrous cartilage).

Joints

Importance of Joints

• Essential for all body movements.
• Joints are points of contact between bones or between bones and cartilages.
• Muscles generate force to move through joints, which act as fulcrums.

Types of Joints

1. Fibrous Joints
   • No movement.
   • Example: Skull bones joined by sutures.
2. Cartilaginous Joints
   • Limited movement.
   • Example: Joints between vertebrae.
3. Synovial Joints
   • Allow considerable movement.
   • Fluid-filled synovial cavity between bones.
   • Examples:
     • Ball and Socket Joint: Between humerus and pectoral girdle.
     • Hinge Joint: Knee joint.
     • Pivot Joint: Between atlas and axis.
     • Gliding Joint: Between carpals.
     • Saddle Joint: Between carpal and metacarpal of thumb.

Disorders of Muscular and Skeletal System

• Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction; causes fatigue and muscle weakness.
• Muscular Dystrophy: Genetic disorder leading to progressive muscle degeneration.
• Tetany: Rapid muscle spasms due to low calcium levels.
• Arthritis: Joint inflammation.
• Osteoporosis: Age-related; decreased bone mass and increased fracture risk, often due to low estrogen levels.
• Gout: Joint inflammation caused by uric acid crystal accumulation.

Chapter Summary:

• Movement is essential for all living beings.
• Types of movement in animals include:
  • Protoplasmic streaming
  • Ciliary movements
  • Movements of fins, limbs, and wings
• Voluntary movement causing change in place is called locomotion.
• Animals move for food, shelter, mates, breeding grounds, better climate, or protection.
• Human body cells show amoeboid, ciliary, and muscular movements.
• Locomotion and other movements need coordinated muscular activities.

Types of Muscles in Our Body:

• Skeletal Muscles:
  • Attached to skeletal elements
  • Striated
  • Voluntary
• Visceral Muscles:
  • In inner walls of visceral organs
  • Nonstriated
  • Involuntary
• Cardiac Muscles:
  • Heart muscles
  • Striated, branched
  • Involuntary

Properties of Muscles:

• Excitability
• Contractility
• Extensibility
• Elasticity

Muscle Fibre:

• Anatomical unit of muscle
• Contains many parallel myofibrils
• Myofibrils have serial units called sarcomeres (functional units)
• Sarcomere structure:
  • Central ‘A’ band (thick myosin filaments)
  • Two half ‘I’ bands (thin actin filaments) on either side
  • Marked by ‘Z’ lines

Proteins in Muscles:

• Actin and myosin are contractile proteins
• Myosin head has ATPase, ATP binding sites, and active sites for actin

Muscle Contraction Mechanism:

• Motor neuron signal generates action potential in muscle fibre
• Ca++ released from sarcoplasmic reticulum
• Ca++ activates actin to bind with myosin head forming cross bridges
• Cross bridges pull actin filaments over myosin causing contraction
• Ca++ returns to sarcoplasmic reticulum, inactivating actin
• Cross bridges break, muscles relax

Muscle Fatigue:

• Caused by repeated stimulation

Muscle Types Based on Myoglobin:

• Red Fibres: High myoglobin
• White Fibres: Low myoglobin

Skeletal System:

• Made of bones and cartilages
• Divided into axial and appendicular skeletons
  • Axial Skeleton: Skull, vertebral column, ribs, sternum
  • Appendicular Skeleton: Limb bones, girdles

Types of Joints:

• Fibrous Joints: No movement
• Cartilaginous Joints: Limited movement
• Synovial Joints: Allow considerable movement, important for locomotion