Locomotion and Movement

Locomotion and Types of Movement

Movement in Living Beings

• Movement is one of the basic characteristics of living organisms.
• Both animals and plants exhibit different types of movements.
• Examples:
  • Amoeba: movement occurs by streaming of protoplasm.
  • Many organisms: show movement of cilia, flagella and tentacles.
  • Humans: exhibit movements of limbs, jaws, eyelids, tongue and other body parts.

Locomotion

• Locomotion: Voluntary movements resulting in a change of place or location of the organism.
• Examples: Walking, running, climbing, flying, swimming.
• Locomotory structures can also help in other types of movements.
  • Paramoecium: Cilia help in locomotion as well as movement of food through the cytopharynx.
  • Hydra: uses its tentacles for capturing prey and also for locomotion.
  • Humans: limbs are used for locomotion and for changes in body posture.

Link Between Movement and Locomotion

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

Need for Locomotion

• Locomotion helps organisms in:
  • Searching for food and shelter
  • Finding mates and suitable breeding grounds
  • Escaping from enemies and predators
  • Reaching favourable climatic conditions

Types of Movement

Amoeboid (Pseudopodial) Movement

• This type of movement occurs due to the formation of pseudopodia by cytoplasmic streaming.
• It is seen in Amoeba and also in specialised human cells such as macrophages and leucocytes.
• Cytoskeletal elements like microfilaments are involved.
• At the molecular level, actin, myosin and ATP participate in this movement.

Ciliary Movement

• Ciliary movement occurs in internal tubular organs lined by ciliated epithelium.
• In humans, it helps in removing dust particles and microbes from the upper respiratory tract.
• It also facilitates transport of ova in the fallopian tubes and movement of sperm in the vasa efferentia.

Flagellar Movement

• This type of movement is seen in human sperm, where the flagellum produces propulsion due to movement of the tail and middle piece.

Muscular Movement

• Muscular movement involves the movement of limbs, jaws, tongue and other body parts.
• It occurs due to alternate contraction and relaxation of muscles.
• Locomotion in higher animals requires coordinated activity of the muscular, skeletal and neural systems.

Muscles

Introduction

• Muscles are specialised tissues of mesodermal origin.
• In adult humans, muscles contribute about 40–50% of total body weight.
• Muscles possess four important properties:
  1. Excitability
  2. Contractility
  3. Extensibility
  4. Elasticity

Types of Muscles

1. Skeletal Muscles
   • Location: Closely associated with the skeletal system.
   • Appearance: Striated (striped).
   • Control: Under voluntary control of the nervous system
   • Example: Found in limbs, body wall, tongue, pharynx and the beginning of the oesophagus.
   • Function: Locomotion, maintenance of posture and body movements.
2. Smooth (Visceral) Muscles
   • Appearance: Non-striated and spindle-shaped.
   • Location: Inner walls of hollow visceral organs (e.g., alimentary canal, urinary bladder, blood vessels, uterus and respiratory tract).
   • Control: Not connected to the skeleton and are involuntary in nature.
   • Function: Movement of food in the digestive tract and transport of gametes.
3. Cardiac Muscles
   • Location: Walls of the heart and in parts of large veins where they enter the heart.
   • Appearance: Striated.
   • Control: Involuntary.
   • Features: Muscle fibres are branched and interconnected by specialised intercalated discs, which help in rapid transmission of contraction impulses.
   • Function: maintain rhythmic contraction of the heart.

Structure of Skeletal Muscle

• Muscle Bundles (Fascicles): Each skeletal muscle consists of many muscle bundles called fascicles.
• Fascicles are held together by a collagenous connective tissue sheath called fascia.
• Muscle Fibers: Each fascicle contains numerous muscle fibres.

Muscle Fibre

• A muscle fibre is long, cylindrical and multinucleate.
• It is bounded by a plasma membrane called sarcolemma and contains cytoplasm known as sarcoplasm.
• The sarcoplasm contains many mitochondria called sarcosomes and a specialised smooth endoplasmic reticulum called sarcoplasmic reticulum, which stores calcium ions essential for muscle contraction.

Myofibrils and Myofilaments

• Each muscle fibre contains hundreds to thousands of parallelly arranged myofibrils.
• Myofibrils are composed of two types of protein filaments:
  1. Thin filaments – actin
  2. Thick filaments – myosin

These filaments are arranged in a highly organised manner, producing alternating dark and light bands.

Banding Pattern of Myofibril

• A-band (anisotropic band): Dark band containing thick myosin filaments
• I-band (isotropic band): Light band containing thin actin filaments
• Z-line (Z-disc): Elastic fibre that bisects the I-band; thin filaments are attached here
• M-line: Thin fibrous membrane present at the centre of A-band holding thick filaments together

Sarcomere

• The portion of a myofibril between two successive Z-lines is called a sarcomere.
• It is the structural, functional and contractile unit of a muscle fibre.
• Each sarcomere contains a precise arrangement of thick and thin filaments.

H-zone

• In the resting state, the central region of the A-band where thin filaments do not overlap the thick filaments is called the H-zone.

Structure of Contractile Proteins

• Contractile proteins are responsible for muscle contraction.
• Skeletal muscle fibres mainly contain four proteins: actin, myosin, troponin and tropomyosin.

Actin (Thin) Filaments

Actin filaments form the thin myofilaments of muscle fibres.

• Each actin filament consists of two helical strands of filamentous actin (F-actin).
• Each F-actin is a polymer of many globular actin (G-actin) molecules.
• Each G-actin molecule has an active binding site for myosin.

Tropomyosin

• Tropomyosin consists of two long filamentous proteins arranged helically along the F-actin.
• In the resting state, tropomyosin lies over the active binding sites of actin, preventing interaction between actin and myosin.

Troponin

• Troponin is a complex protein present at regular intervals on the tropomyosin filament.
• In the resting state, one subunit of troponin masks the myosin-binding sites on actin.
• Binding of calcium ions to troponin causes a conformational change, exposing active sites on actin.

Myosin (Thick) Filaments

Myosin filaments form the thick myofilaments.

• Each myosin filament is made up of polymerised proteins called meromyosins.
• Each meromyosin has two parts:
  1. Heavy Meromyosin (HMM):
     • Forms the globular head and short arm
     • Projects outward as cross arms
     • Contains ATP-binding site
     • Contains actin-binding site
     • Shows ATPase activity
  2. Light Meromyosin (LMM):
     • Forms the long tail
     • Helps in filament assembly

The globular heads of HMM function as cross bridges during muscle contraction.

Mechanism of Muscle Contraction

Sliding Filament Theory

• Muscle contraction is best explained by the sliding filament theory.
• According to this theory, contraction occurs due to sliding of thin actin filaments over thick myosin filaments without any change in the length of the filaments.

• This theory was proposed independently in 1954 by:
  • A. F. Huxley and R. Niedergerke
  • H. E. Huxley and Jean Hanson

Initiation of Muscle Contraction

• A signal is sent by the central nervous system through a motor neuron.
• A motor neuron along with the muscle fibres it innervates forms a motor unit.
• The junction between the motor neuron and muscle fibre is called the neuromuscular junction or motor end plate.
• Arrival of the nerve impulse releases the neurotransmitter acetylcholine.
• Acetylcholine generates an action potential in the sarcolemma.
• The action potential spreads through the muscle fibre and causes the release of Ca²⁺ ions from the sarcoplasmic reticulum into the sarcoplasm.

Role of Calcium Ions

• Increase in Ca²⁺ concentration leads to binding of calcium with troponin.
• This removes the masking effect of tropomyosin on actin.
• Active binding sites on actin become exposed for myosin interaction.

Steps of Muscle Contraction

1. Cross-bridge formation
   • Energised myosin head (with ADP and Pi) binds to exposed actin site forming a cross bridge.
2. Power stroke
   • Release of ADP and Pi causes the myosin head to bend.
   • Actin filament is pulled towards the centre of the A-band.
   • Z-lines move closer, shortening the sarcomere.
3. Detachment of cross-bridge
   • A new ATP molecule binds to the myosin head.
   • Cross bridge breaks.
4. Reactivation of myosin head
   • ATP is hydrolysed by myosin ATPase.
   • Myosin head returns to its energised state.

This cycle repeats as long as ATP and Ca²⁺ are available.

Changes During Contraction

• Length of A-band remains constant.
• Length of I-band decreases.
• H-zone becomes reduced or disappears.
• Sarcomere shortens, resulting in muscle contraction.

Relaxation of Muscle

• Ca²⁺ ions are actively pumped back into the sarcoplasmic reticulum.
• Troponin returns to its original position.
• Tropomyosin again masks actin-binding sites.
• Cross-bridge cycling stops and muscle relaxes.

Muscle Fatigue

• Repeated and prolonged muscle activity leads to anaerobic breakdown of glycogen.
• Lactic acid accumulates in muscle fibres.
• This causes muscle fatigue and reduced efficiency.

Oxygen Debt

• During vigorous activity, muscles require more oxygen than supplied.
• Extra oxygen needed to oxidise accumulated lactic acid is called oxygen debt.

Types of Skeletal Muscle Fibres

1. Red fibers:
   • High myoglobin content, appear red.
   • Rich in mitochondria.
   • Perform aerobic respiration.
   • Produce less lactic acid.
   • Slow contraction but resistant to fatigue.
   • Example: Postural muscles (extensor muscles of back).
2. White fibers:
   • Low myoglobin content, appear pale or whitish.
   • Fewer mitochondria.
   • Abundant sarcoplasmic reticulum.
   • Depend on anaerobic respiration.
   • Fast contraction but fatigue quickly.
   • Example: Eye muscles.

Additional Important Concepts

• All-or-None Law
  • A muscle fibre contracts maximally once stimulated beyond threshold.
  • Partial contraction of a single muscle fibre does not occur.
• Rigor Mortis
  • Stiffening of muscles after death due to non-availability of ATP.
  • Actin and myosin remain bound.
  • Persists until protein degradation begins.
• Antagonistic Muscles
  • Muscles working in opposite directions are called antagonistic muscles.
  • Example:
    – Biceps: Flexor (bends the arm)
    – Triceps: Extensor (straightens the arm)

Skeletal System

Overview

• The skeletal system consists of a framework of bones and a few cartilages.
• It provides shape to the body, supports soft tissues, protects vital organs, and plays a major role in movement and locomotion.

• Bone and cartilage are specialised connective tissues.
  • Bone has a very hard matrix due to the presence of calcium salts.
  • Cartilage has a slightly pliable matrix due to chondroitin salts.

• In humans, the skeletal system consists of 206 bones and a few cartilages.

Types of Skeleton

Two main forms of skeleton are recognised:

1. Exoskeleton
   • Derived from epidermis
   • Ectodermal and non-living
   • Examples: hair, nails, claws, hoofs, horns, feathers
2. Endoskeleton
   • Present inside the body
   • Mesodermal and living
   • Formed of bones and cartilages in vertebrates

• Human skeleton is an endoskeleton and is divided into two main parts:
  1. Axial skeleton
  2. Appendicular skeleton

A. Axial Skeleton

• The axial skeleton lies along the longitudinal axis of the body.
• It supports and protects organs of the head, neck, and trunk.

• It consists of 80 bones and includes:
  • Skull
  • Vertebral column
  • Sternum
  • Ribs

Skull

• The human skull is composed of 22 bones arranged into two sets:

1. Cranial Bones
   • 8 bones
   • Form the cranium
   • Protect the brain
2. Facial Bones
   • 14 bones
   • Form the front part of the skull

Additional Bones Associated with Skull

• Hyoid Bone
  • Single, U-shaped bone
  • Present at the base of the buccal cavity
  • Does not articulate with any other bone
• Ear Ossicles
  • Three tiny bones present in each middle ear
  • Malleus
  • Incus
  • Stapes
  • Help in sound transmission

The skull articulates with the vertebral column by two occipital condyles.
This is called a dicondylic skull.

Vertebral Column

• The vertebral column, also called backbone or spine, is dorsally placed and extends from the base of the skull.
• Composed of 26 vertebrae
• Forms the main framework of the trunk
• Each vertebra has a central hollow neural canal through which the spinal cord passes

Regions of Vertebral Column

1. Cervical – 7 vertebrae
2. Thoracic – 12 vertebrae
3. Lumbar – 5 vertebrae
4. Sacral – 1 (fused)
5. Coccygeal – 1 (fused)

Important Points

• Number of cervical vertebrae is 7 in almost all mammals.
• First cervical vertebra is called atlas; it articulates with occipital condyles and supports the head.
• Second cervical vertebra is called axis and has an odontoid process.
• Vertebral column protects the spinal cord and provides attachment to ribs and back muscles.
• Coccyx is a vestigial tail.

Sternum and Ribs

• Sternum
  • Flat bone
  • Located on the ventral midline of the thorax
• Ribs
  • 12 pairs of thin, flat bones
  • Connected dorsally to thoracic vertebrae
  • Each rib is bicephalic (two articulation surfaces)

Types of Ribs

1. True Ribs
   • First 7 pairs
   • Attached dorsally to thoracic vertebrae
   • Ventrally connected to sternum by hyaline cartilage
2. False Ribs (Vertebrochondral ribs)
   • 8th, 9th, and 10th pairs
   • Do not directly attach to sternum
   • Join the 7th rib through hyaline cartilage
3. Floating Ribs
   • 11th and 12th pairs
   • Not connected ventrally

• Thoracic vertebrae, ribs, and sternum together form the rib cage.
• The rib cage protects heart, lungs, and kidneys and provides attachment for respiratory muscles.

B. Appendicular Skeleton

• The appendicular skeleton consists of bones of the limbs along with 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 (longest, largest, strongest bone).
• Tibia and Fibula: Leg bones.
• Tarsals: 7 ankle bones.
• Metatarsals: 5 foot bones.
• Phalanges: 14 toe bones.
• Patella: Knee cap (cup-shaped bone covering knee ventrally).

Hind limb bones are involved in weight bearing, support, and propulsion.

Girdles

Girdles help in articulation of limbs with the axial skeleton.

1. Pectoral Girdle

• Connects upper limbs to the axial skeleton.
• Each half consists of:
  1. Clavicle
  2. Scapula

• Scapula
  • Large, triangular, flat bone
  • Located on dorsal side of thorax between 2nd and 7th ribs
  • Has a ridge called spine
  • Spine ends in a flattened process called acromion
  • Below acromion is glenoid cavity which articulates with head of humerus to form shoulder joint
• Clavicle
  • Long, slender bone with two curvatures
  • Commonly called collar bone

2. Pelvic Girdle

• Connects lower limbs to the axial skeleton.
• Consists of two coxal (hip) bones
• Each coxal bone is formed by fusion of three bones:
  1. Ilium
  2. Ischium
  3. Pubis

• Acetabulum
  • Cavity at the point of fusion
  • Articulates with head of femur

The two halves of pelvic girdle meet ventrally at the pubic symphysis, containing fibrous cartilage.

Joints

• Joints are essential for all types of movements involving the bony parts of the body.
• They are the points of contact between two bones or between bones and cartilages.

• Ligaments join bones to bones, while tendons connect muscles to bones.
• Muscles generate force for movement, which is transmitted through joints.
• In this arrangement, joints act as fulcrums.

• The degree of movement at joints varies depending on their structure.

Types of Joints

1. Fibrous Joints

• Do not allow any movement
• Bones are joined by dense fibrous connective tissue
• Examples:
  • Skull bones joined by sutures to form the cranium
  • Joints between teeth and maxilla or mandible
• Function:
  • Provide strength and protection, especially for the brain

2. Cartilaginous Joints

• Bones are joined by cartilage
• Allow limited movement
• Examples:
  • Joints between adjacent vertebrae in the vertebral column
  • Pubic symphysis of the pelvic girdle
• Function:
  • Provide flexibility while maintaining strength

3. Synovial Joints

• Characterised by the presence of a fluid-filled synovial cavity between articulating bones
• Allow considerable movement
• Most common joints involved in locomotion

Major Types of Synovial Joints and Examples

1. Ball and Socket Joint
   • Example: Between humerus and pectoral girdle (shoulder joint)
   • Allows movement in all directions
2. Hinge Joint
   • Example: Knee joint
   • Allows movement in one plane
3. Pivot Joint
   • Example: Between atlas and axis
   • Allows rotational movement of head
4. Gliding Joint
   • Example: Between carpal bones of wrist
   • Allows sliding movements
5. Saddle Joint
   • Example: Between carpal and metacarpal of thumb
   • Allows flexibility and opposition of thumb

Disorders of Muscular and Skeletal System

1. Osteoporosis

• Age-related disorder
• Bone loses minerals and fibres from its matrix
• Results in fragile bones and increased fracture risk
• Causes:
  • Hormonal imbalance (estrogen, calcitonin, parathormone)
  • Deficiency of calcium and vitamin D

2. Muscular Dystrophy

• Genetic disorder caused by mutation of a gene on the X-chromosome
• Leads to absence or deficiency of dystrophin protein in skeletal muscles
• Effects:
  • Muscle fibres degenerate progressively
  • Weak or absent muscle contraction
  • Progressive muscle wasting

3. Myasthenia Gravis

• Autoimmune disorder
• Affects neuromuscular junction
• Effects:
  • Fatigue and weakness of skeletal muscles
  • May lead to paralysis in severe cases

4. Tetany

• Characterised by rapid muscle spasms or sustained contractions
• Cause:
  • Low calcium (Ca++) levels in body fluids

5. Arthritis

• Inflammation of joints
• Types include:
  • Rheumatoid arthritis
  • Osteoarthritis
  • Infectious arthritis
• Effects:
  • Pain, stiffness, swelling, and reduced joint movement

6. Gout

• Caused by defect in purine metabolism
• Excess uric acid and its salts accumulate in joints
• Effect:
  • Severe joint inflammation and pain

7. Osteomalacia / Rickets

• Occurs due to deficiency of calcium and phosphorus
• In children, the condition is called rickets
• Effect:
  • Soft and weak bones
  • Bone deformities in growing children

Chapter Summary:

• Movement is a fundamental characteristic of all living beings.
• Animals exhibit different types of movements such as protoplasmic streaming, ciliary movement, and movement of fins, limbs, and wings.
• Voluntary movement that results in a change of position or place is called locomotion.
• Locomotion helps animals in searching for food, shelter, mates, breeding grounds, favourable climatic conditions, and escaping from predators.

• Human body cells show three main types of movements: amoeboid movement, ciliary movement, and muscular movement.
• Amoeboid movement occurs in specialised cells like leucocytes.
• Ciliary movement occurs in organs lined with ciliated epithelium.
• Muscular movement is responsible for locomotion and most body movements and requires coordinated action of muscles, bones, and the nervous system.

• Human body cells show three main types of movements: amoeboid movement, ciliary movement, and muscular movement.
• Amoeboid movement occurs in specialised cells like leucocytes.
• Ciliary movement occurs in organs lined with ciliated epithelium.
• Muscular movement is responsible for locomotion and most body movements and requires coordinated action of muscles, bones, and the nervous system.

• Muscles are specialised tissues responsible for movement and locomotion.
• Based on structure, location, and control, muscles in the human body are of three types.
• Skeletal muscles are attached to skeletal elements, are striated in appearance, and are under voluntary control.
• Visceral muscles are found in the inner walls of hollow visceral organs, are non-striated, and function involuntarily.
• Cardiac muscles are present in the heart, are striated and branched, and work involuntarily.

• All muscles possess four basic properties: excitability (ability to respond to stimuli), contractility (ability to shorten), extensibility (ability to stretch), and elasticity (ability to return to original length).

• A muscle fibre is the anatomical and functional unit of a muscle.
• Each muscle fibre contains numerous parallel myofibrils.
• Myofibrils are made up of repeating structural and functional units called sarcomeres.
• A sarcomere consists of a central A band containing thick myosin filaments and two half I bands containing thin actin filaments on either side.
• The boundaries of a sarcomere are marked by Z lines.

• Actin and myosin are the main contractile proteins of muscle fibres.
• The myosin head possesses ATPase activity and has binding sites for ATP and actin, which are essential for muscle contraction.

• Muscle contraction is initiated when a motor neuron transmits a signal to the muscle fibre, generating an action potential.
• This leads to the release of calcium ions from the sarcoplasmic reticulum.
• Calcium ions activate actin, allowing myosin heads to form cross-bridges with actin filaments.
• The sliding of actin over myosin shortens the sarcomere, resulting in muscle contraction.
• When calcium ions are pumped back into the sarcoplasmic reticulum, actin becomes inactive, cross-bridges break, and the muscle relaxes.

• Repeated muscle activity can lead to muscle fatigue due to continuous stimulation.
• Based on myoglobin content, skeletal muscle fibres are of two types: red fibres, which contain high myoglobin and are adapted for sustained activity, and white fibres, which contain low myoglobin and are adapted for rapid, short-term activity.

• The skeletal system provides structural support and facilitates movement.
• It is made up of bones and cartilages and is divided into two major parts.
• The axial skeleton includes the skull, vertebral column, ribs, and sternum.
• The appendicular skeleton consists of the bones of the limbs and their girdles.

• Movement at the skeletal level is made possible by joints.
• Joints are of three main types: fibrous joints, which allow no movement; cartilaginous joints, which permit limited movement; and synovial joints, which allow free movement and play a major role in locomotion.