Chapter 5: Locomotion and Movement

Introduction

Overview of Movement

• Movement is a basic feature of living beings.
• Animals and plants show various movements; unicellular organisms like Amoeba move by protoplasmic streaming.
• Movement types include cilia, flagella, and tentacles; humans move limbs, jaws, eyelids, tongue, etc.
• Locomotion is voluntary movement causing change in place: walking, running, climbing, flying, swimming.
• All locomotion is movement, but not all movement is locomotion.
• Examples: Paramecium uses cilia for food movement and locomotion; Hydra uses tentacles for prey capture and locomotion; humans use limbs for posture and locomotion.
• Locomotion helps in searching food, shelter, mates, breeding grounds, favorable climate, or escaping predators.

Memory Aids

• Locomotion = movement with change in place.
• Amoeba moves by streaming; Paramecium and Hydra use cilia/tentacles.
• Humans move limbs for posture and locomotion.

Quick Checkpoints

• What distinguishes locomotion from general movement?
• How do unicellular organisms move?
• Examples of locomotion in different organisms?
• Purpose of locomotion in animals?

Types of Movement

Cellular Movement Types

• Amoeboid/Pseudopodial movement: Movement by pseudopodia via cytoplasmic streaming; seen in Amoeba, macrophages, leucocytes; involves microfilaments.
• Ciliary movement: Movement by cilia in internal organs; clears microbes/dust in respiratory tract; transports ova in fallopian tubes and sperm in vasa efferentia.
• Muscular movement: Movement of limbs, jaws, tongue by alternate muscle contraction and relaxation.
• Flagellar movement: Movement by tail and middle piece propulsion; seen in human sperm, sponges' water current, and protozoans like Euglena.

Locomotion requires coordinated muscular, skeletal, and neural activity.

Memory Aids

• Amoeboid = pseudopodia + cytoplasmic streaming.
• Cilia clear and transport in body tubes.
• Muscles contract-relax for movement.
• Flagella propel sperm and protozoans.

Quick Checkpoints

• What causes amoeboid movement?
• Where is ciliary movement found in humans?
• How do muscles produce movement?
• Examples of flagellar movement?
• What systems coordinate locomotion?

Muscle

Overview

• Specialised tissue of mesodermal origin.
• Contributes 40-50% of adult human body weight.
• Properties: excitability, contractility, extensibility, elasticity.
• Three types based on location: Skeletal, Smooth, Cardiac.

Memory Aids

• Muscle = Mesoderm origin + Movement + Multiple types.
• Excitability and contractility are key muscle traits.

Quick Checkpoints

• What is the origin of muscle tissue?
• Name the three types of muscles.
• List special properties of muscles.

Skeletal Muscles

Characteristics

• Associated with skeleton; also called striped or striated muscles.
• Located in limbs, body wall, tongue, pharynx, upper oesophagus.
• Voluntary control by nervous system.
• Functions: locomotion, posture changes.

Memory Aids

• Skeletal = Striated + Voluntary + Attached to bones.

Quick Checkpoints

• Where are skeletal muscles found?
• Are skeletal muscles voluntary or involuntary?
• What actions do skeletal muscles perform?

Cardiac Muscles

Characteristics

• Found in heart walls and large veins entering heart (pulmonary veins, superior vena cava).
• Cylindrical, striated, branched, uninucleate fibers.
• Involuntary control.
• Intercalated discs transmit contraction waves between fibers.

Memory Aids

• Cardiac = Heart muscle + Involuntary + Intercalated discs.

Quick Checkpoints

• Where are cardiac muscles located?
• Describe the structure of cardiac muscle fibers.
• What is the function of intercalated discs?

Smooth Muscles

Characteristics

• Also called visceral, unstriped, or non-striated muscles; spindle-shaped.
• Located in walls of hollow visceral organs: posterior oesophagus, stomach, intestine, lungs, urinary and genital tracts, bladder, blood vessels, iris, dermis.
• Not attached to skeleton.
• Involuntary control by autonomic nervous system.
• Functions: transport of food in digestive tract, movement of gametes in genital tract.

Memory Aids

• Smooth = Spindle shape + Visceral organs + Involuntary.

Quick Checkpoints

• What shape are smooth muscle fibers?
• Where are smooth muscles found?
• Are smooth muscles voluntary or involuntary?

Structure of Skeletal System

Organization

• Muscle made of bundles called fascicles, held by connective tissue called fascia.
• Fascicles contain muscle fibers; fibers are long, cylindrical cells surrounded by sarcolemma.
• Muscle fiber cytoplasm = sarcoplasm, contains many nuclei (syncytium), mitochondria (sarcosomes), and sarcoplasmic reticulum storing calcium ions.
• Muscle fibers contain parallel filaments called myofilaments or myofibrils with alternating dark and light bands.

Striation and Bands

• Striations due to actin (thin) and myosin (thick) protein arrangement.
• Light band = 'I'-band (isotropic) with actin; dark band = 'A'-band (anisotropic) with myosin.
• Thin and thick filaments arranged rod-like, parallel to myofibril axis.
• Center of 'I' band has elastic 'Z' line (Z disc) where thin filaments attach.
• Thick filaments held at center of 'A' band by 'M' line.
• Segment between two Z lines = sarcomere, functional contractile unit.
• Resting sarcomere has overlapping thin filaments on thick filaments edges; central thick filament region without overlap = 'H' zone.

Memory Aids

• Striations = Actin (I-band) + Myosin (A-band).
• Sarcomere = Z line to Z line segment.
• H zone = Thick filament center without thin filament overlap.

Quick Checkpoints

• What causes muscle striations?
• Define sarcomere.
• What is the 'H' zone?

Structure of Contractile Proteins

Protein Components

• Four contractile proteins: myosin, actin, troponin, tropomyosin.
• Thin myofilament proteins:
  • Actin: Double-stranded F-actin helix made of G-actin monomers.
  • Tropomyosin: Double-stranded a-helical rod on F-actin; blocks active sites in resting state.
  • Troponin: Complex protein on tropomyosin; masks myosin binding sites on actin in resting state.
• Thick myofilament mainly myosin:
  • Myosin has two heavy and four light polypeptide chains forming two globular heads and a long tail.
  • Heads form crossbridges; split by trypsin into heavy meromyosin (HMM) and light meromyosin (LMM).
  • HMM heads have ATP and actin binding sites.

Memory Aids

• Thin filament = Actin + Tropomyosin + Troponin.
• Thick filament = Myosin with heads for ATP and actin binding.

Quick Checkpoints

• What proteins form thin myofilaments?
• Describe the structure of myosin.
• What is the role of troponin?

Mechanism of Muscle Contraction

Sliding Filament Theory

• Contraction by sliding of thin filaments over thick filaments.
• Proposed by A. F. Huxley & Ralph Niedergerke, and H.E. Huxley & Jean Hanson (1954).
• Initiated by CNS signal via motor neuron; motor unit = motor neuron + connected muscle fibers.
• Neuromuscular junction (motor end plate) releases acetylcholine, generating action potential in sarcolemma.
• Action potential causes Ca²⁺ release into sarcoplasm.
• Ca²⁺ binds troponin, exposing myosin binding sites on actin.
• Myosin heads bind actin using ATP energy, forming cross bridges.
• Myosin heads pivot, pulling actin towards sarcomere center, shortening sarcomere (contraction).
• 'I' bands shorten; 'A' bands remain constant length.
• ADP and phosphate released; ATP binds myosin head, breaking cross bridge.
• ATP hydrolyzed; cycle repeats until Ca²⁺ pumped back, masking actin sites (relaxation).
• Repeated contraction causes lactic acid buildup, leading to fatigue.

Memory Aids

• Sliding filament = Thin filaments slide over thick filaments.
• Ca²⁺ triggers exposure of myosin binding sites.
• ATP powers cross bridge cycling.

Quick Checkpoints

• What triggers muscle contraction at molecular level?
• Describe the role of ATP in contraction.
• What happens to sarcomere bands during contraction?

Additional Muscle Concepts

Key Points

• All-or-none law: muscle fiber contracts fully or not at all.
• Oxygen debt: anaerobic respiration during vigorous exercise produces lactic acid causing fatigue; extra oxygen needed to oxidize lactic acid.
• Rigor mortis: post-death muscle stiffening due to lack of ATP preventing actin-myosin separation.
• Antagonistic muscles: muscles acting in opposition, e.g., biceps (flexor) and triceps (extensor).

Memory Aids

• All-or-none: full contraction or none.
• Oxygen debt = lactic acid buildup + fatigue.
• Rigor mortis = no ATP, muscles stiffen after death.
• Antagonistic muscles = opposite actions.

Quick Checkpoints

• What is the all-or-none law?
• Explain oxygen debt in muscles.
• What causes rigor mortis?
• Define antagonistic muscles with example.

Joints

Structure and Function

• Joints connect bones or bones to cartilage, enabling movement.
• Ligaments connect bones; tendons connect bones to muscles.
• Muscle force acts on joints, which serve as fulcrums for movement.
• Joint mobility varies by structure and type.
• Three main types: fibrous, cartilaginous, synovial.

Types of Joints

• Fibrous joints: No movement; bones joined by dense fibrous tissue. Example: skull sutures, teeth to maxilla/mandible.
• Cartilaginous joints: Bones joined by cartilage; allow limited movement. Example: vertebral joints, pubic symphysis.
• Synovial joints: Have fluid-filled synovial cavity; allow free movement. Examples:
  • Ball and socket (humerus and pectoral girdle)
  • Hinge (knee joint)
  • Pivot (atlas and axis)
  • Gliding (carpals)
  • Saddle (carpal and metacarpal of thumb)

Memory Aids

• Fibrous = Fixed (no movement)
• Cartilaginous = Cartilage connects, allows some movement
• Synovial = Synovial fluid allows free movement
• Examples: Ball & Socket = Shoulder; Hinge = Knee; Pivot = Neck; Gliding = Wrist; Saddle = Thumb

Quick Checkpoints

• What connects bones and muscles?
• Which joint type allows no movement?
• Where is synovial fluid found?
• Name a joint that permits limited movement.
• Identify examples of synovial joints.

Disorders of Muscular and Skeletal System

Overview

• Includes diseases affecting bones and muscles.
• Common disorders involve mineral loss, genetic mutations, autoimmune issues, and metabolic defects.

Memory Aids

• Disorders = Bone + Muscle problems.
• Focus on mineral loss, gene mutation, immunity, metabolism.

Quick Checkpoints

• What causes mineral loss in bones?
• How do gene mutations affect muscles?
• What is the role of immunity in muscle disorders?

Osteoporosis

Key Points

• Age-related bone disease with loss of minerals and fibers from bone matrix.
• Major causes: hormone imbalances (calcitonin, parathormone, estrogen) and deficiencies of calcium and vitamin D.

Memory Aids

• Osteo = bone, porosis = porous (weak bones).
• Think: Hormone + mineral deficiency = weak bones.

Quick Checkpoints

• Which hormones regulate bone minerals?
• How does vitamin D deficiency affect bones?

Muscular Dystrophy

Key Points

• Caused by mutated gene on X-chromosome.
• Mutation leads to absence of dystrophin protein in skeletal muscles.
• Dystrophin deficiency prevents calcium release from muscle cells, blocking muscle contraction.

Memory Aids

• Muscular Dystrophy = X-linked gene mutation.
• Dystrophin missing = no muscle contraction.

Quick Checkpoints

• What is the role of dystrophin?
• Why does muscle contraction fail?

Myasthenia Gravis

Key Points

• Autoimmune disorder affecting neuromuscular junction.
• Leads to fatigue, weakening, and paralysis of skeletal muscles.

Memory Aids

• Myasthenia = muscle weakness.
• Autoimmune attack blocks nerve-muscle communication.

Quick Checkpoints

• What part of muscle function is affected?
• How does immunity cause muscle weakness?

Osteomalacia or Rickets

Key Points

• Occurs in childhood (rickets) or adults (osteomalacia).
• Bones have insufficient calcium and phosphorus.

Memory Aids

• Rickets = childhood bone softening.
• Low calcium/phosphorus = weak bones.

Quick Checkpoints

• What minerals are deficient?
• How does deficiency affect bone strength?

Arthritis

Key Points

• Inflammation of joints.
• Types: rheumatoid arthritis, osteoarthritis, infectious arthritis.

Memory Aids

• Arthritis = joint inflammation.
• Remember types by cause: autoimmune, wear & tear, infection.

Quick Checkpoints

• What causes joint inflammation?
• How do types differ?

Gout

Key Points

• Defect in purine metabolism.
• Excess uric acid and salts accumulate in joints.

Memory Aids

• Gout = uric acid buildup.
• Think purine metabolism defect → joint pain.

Quick Checkpoints

• What metabolic defect causes gout?
• Where does uric acid accumulate?

Tetany

Key Points

• Rapid muscle spasms due to low calcium (Ca⁺⁺) in body fluids.

Memory Aids

• Tetany = muscle spasms from low Ca⁺⁺.

Quick Checkpoints

• What ion deficiency causes tetany?
• How does low calcium affect muscles?

Human Skeletal System

Key Points

• Divided into skull, spinal column, rib cage, arms, pelvis, and legs.
• Skull: cranium and facial bones protect brain and shape face.
• Spinal column: cervical, thoracic, lumbar vertebrae support body and protect spinal cord.
• Rib cage: ribs, sternum, clavicle, scapula protect chest organs.
• Arms: humerus, radius, ulna bones.
• Pelvic girdle: ilium, pubis, ischium connect spine to legs.
• Legs: femur, patella, tibia, fibula bones.
• Hand bones: carpals, metacarpals, phalanges.
• Foot bones: tarsals, metatarsals, phalanges.

Memory Aids

• Skeleton parts: Head, Spine, Chest, Limbs, Pelvis.
• Hand and foot bones have carpals/tarsals, metacarpals/metatarsals, phalanges.

Quick Checkpoints

• What are the main parts of the skeleton?
• Which bones protect the brain?
• How are hand and foot bones classified?