Locomotion and Movement

All living organisms show a characteristic phenomenon of either moving their whole body from one place to another place (locomotion or locomotory movement), or only a part of the body while the whole body remains fixed to a place (movement or non-locomotory movement).
Various acts of the body like walking, running, crawling, jumping, flying, swimming etc. are known as locomotory movements. The locomotion helps the organism to shift its entire body from one place to another. Generally, the animals show locomotory movements in search of food, mate and shelter. It also helps the animals to run from the adverse environmental conditions, and to move away from the predators.
Movements of limbs, appendages, head and trunk serve to change the posture of the body and maintain equilibrium against the gravity. For example, taking in of food involves the movements of tongue, jaws, snout, limbs in man; movements of external ear and eyeballs help to perceive the informations from the outside environments; movements of alimentary canal help to pass the food down; movements of heart circulate the blood in the body; lungs are ventilated by the movements of thoracic muscles and diaphragm etc.
Besides such locomotion and movements of the body, multicellular organisms can also move their individual cells like the movements seen in unicellular organisms. Some of the white blood cells and macrophages, which are phagocytic in nature, move through the tissues by amoeboid movements to reach the p aces of infection.
Ciliary movements occur in the upper respiratory tract, fallopian tubes and vasa efferentia tubes of testes. A mammalian sperm moves into the female reproductive tract by the flagellar movements. In sponges, flagellar movements of some cells occur to maintain the water current in them.
Most of the multicellular animals have muscle fibres for locomotion, limb movements as well as movements of internal organs. In all higher animals (vertebrates) there are mainly two systems that bring about movement and locomotion of the body. These two systems are skeletal system and muscular system that work in coordination with each other.
The force generated by muscle contraction is utilized to move bones of the skeleton like levers. This results in movements of limbs and appendages. So, the muscles working with the skeletal system are called skeletal muscles. Epithelio-muscular cells in the outer layer of the body wall and the nutritive muscular cells in the inner layer. Contractions and relaxations of these cells, respectively, shorten and elongate their processes.

MOVEMENTS IN SOME INVERTEBRATES

There are also many invertebrates like jellyfish, earthworm and leech, which are devoid of skeletons but possess muscles for their movements.
Movements in Hydra:
Hydra lacks well-developed muscular system. They have two types of contractile cells on its body wall, viz. movements seen in Hydra are looping, somersaulting, climbing, shortening and elongation etc.
Movements in Annelids:
Earthworms and leeches have muscle fibres of the body wall that help these animals to crawl on land. These muscle fibres are of two types – longitudinal muscle fibres; and circular muscle fibres. In earthworms, the locomotion of the body is brought about by alternate contraction of circular and longitudinal muscles, causing waves of thinning and thickening to pass backwards.
It involves partly pushing of the anterior end and partly of the posterior end. The coelomic fluid gives turgidity as it acts as hydraulic skeleton making the body wall tough.
Movements in Starfish:
Starfishes have got water vascular system that help them in their locomotion. Each arm of the starfish has two rows of tube feet underneath. Water enters these tube feet by the muscular contractions and this moves the animal over the surface of the substratum in water. Starfishes are bottom dwellers found in sea waters only.

MOVEMENTS IN HIGHER VERTEBRATES

In higher animals, movements and locomotion depend on the association of skeletal muscles with the skeletal system. The skeletal system consists of a specialized rigid connective tissue called bones. This skeletal system consists of many parts, each made of one or more bones.

HUMAN MUSCULAR SYSTEM

Based on location, muscles are 3 types

Skeletal muscles or striated muscles

Closely associated with skeleton.
They are striped appearance under the microscope and called Striated muscles.
They are under voluntary control of nervous system, hence called voluntary muscles.
These involved in locomotion and change of body postures.
Unbranched and multinucleated.

Visceral muscles or smooth muscles

These are in inner wall of hollow visceral organ.
Spindle shaped and uni-nucleated.
They do not exhibit any striation and are smooth in appearance.
They are called smooth muscles or non-striated muscles.
Their activities are not under voluntary control of nervous system hence called as involuntary muscles.
They assist in transport of food through digestive tract and gametes through the genital tract.

Cardiac muscles

The muscles of heart, involuntary in nature.
Cardiac muscle cells assemble in a branching pattern to form a cardiac muscle.
These are uni-nucleated with characteristic intercalated disc.

Properties of Muscle

Excitability
Contractility
Extensibility
Elasticity

Each organized skeletal muscle in our body is made of several muscle bundles called fascicles held together by common fibrous covering called fascia.
Each fascicle consists of several muscle fibres (cell) covered by a common fibrous perimysium.
Each muscle fibre is lined by the plasma membrane called sarcolemma, enclosing cytoplasm called sarcoplasm.
The sarcoplasm contains endoplasmic reticulum, called sarcoplasmic reticulum is the store house of calcium ion
Muscle fibre is a syncitium as the sarcoplasm contain many nuclei.

Muscle fibres contain many parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.

There are two types of myofibrils are present in the sarcoplasm –

Thin filament – Actin
Thick filament – Myosin.

The arrangement of thick and thin filament gives the characteristic striated appearance.
The light bands contain only actin filaments and are called I-band or isotropic band.
The dark band called ‘A’ or anisotropic band contains both actin and myosin.
In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it.
The thin filaments or actin are firmly attached with the ‘Z’ line.
The thick filaments or myosin in the ‘A’ band are also held together in the middle by a thin fibrous membrane called ‘M’ line.
The portion between two successive ‘Z’ lines is considered as the functional unit of the muscle called sarcomere.
Each ‘A’ band contains two overlap zone of thick and thin filament called ‘O’ band.
The central part of thick filament, not overlapped by thin filament is called ‘H’ band.
‘A’ band = 2(O) + H.
Thin filament or Actin:
Each actin filament is made of two ‘F’ actins helically wound to each other.
Each ‘F’ actin is made of polymer of monomeric ‘G’ (Globular) actin.
Each ‘F’ actin associated with another protein, tropomyosin also run throughout its length.
Another complex protein, Troponin is distributed at regular intervals on the tropomyosin.

Each troponin has three components –

Troponin-C binds with calcium.
Troponin-M, binds with the tropomyosin.
Troponin T, masks the active site on the ‘G’ actin (thin filament)

In the resting state a sub-unit of Troponin (Tn-T), masks the active binding sites on the thin filaments for myosin.

MECHANISM OF MUSCLE CONTRACTION

Mechanism of muscle contraction is explained by sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments.
Muscle contraction is initiated by a signal sent by the central nervous system via a motor neuron.
A motor neuron along with the muscle fibres connected to it constitutes a motor unit.
The junction between a motor neuron and the sarcolemma of the muscle fibre is called neuromuscular junction motor-end plate.
Neurotransmitter releases here which generates an action potential in sarcolemma.
These causes release of Ca++ into sarcoplasm.
These Ca++ binds with troponin, thereby remove masking of active site.
Myosin head binds to exposed active site on actin to form a cross bridge, utilizing energy from ATP hydrolysis.
This pulls the actin filament towards the centre of ‘A’ band.

• ‘Z’ lines also pulled inward thereby causing a shortening of sarcomere i.e. contraction.

• ‘I’ band get reduced, whereas the ‘A’ band retain the length.

During relaxation, the cross bridge between the actin and myosin break.
Ca++pumped back to sarcoplasmic cisternae.
Actin filament slide out of ‘A’ band and length of ‘I’ band increases. This returns the muscle to its original state.
Repeated muscle contraction causes accumulation of lactic acid, produced from anaerobic breakdown of glycogen leads to muscle fatigue.
Muscle contains red coloured oxygen storing pigment called myoglobin. Muscle with myoglobin called red muscle fibres, they are also containing large number of mitochondria which can utilize large amount of oxygen stored in them for ATP production also called aerobic muscle.
Some muscles possess very less quantity of myoglobin and less mitochondrion hence called white fibres. Amount of sarcoplasmic reticulum is high in these muscles. They depend on anaerobic process for energy.

FUNCTIONS OF SKELETAL SYSTEM

It provides a kind of framework for the body.
It provides shape and posture to the body.
It provides protection to some of the inner delicate organs like brain, spinal cord and lungs.
It gives rigid surface for the attachment of muscles with the help of tendons.
It helps in locomotion.
The bone marrow serves as the centre to produce red blood cells and white blood cells.
The movements of ribs and sternum help in breathing.
In the ear, the sound vibrations are conveyed from the tympanum to the internal ear by a set of three bones as in man.
It helps the body to be an integrated unit.
It serves to store various ions like calcium and phosphate, which are then released into the body at the time of need. These minerals perform various functions of the body.

Human skeleton consists of 206 bones in adult.

Axial skeleton – 80 bones
Appendicular skeleton – 126 bones

Axial skeleton

Skull – 29 bones.

Cranium – 8 bones form the brain box.
Facial – 14 bones form the front part of the face.
Hyoid – a single U-shaped bone at the base of the buccal cavity.
Ear ossicles – 6 bones- 3 on either side (Malleus, Incus and stapes)

The skull region articulates with the superior region of the vertebral column with the help of two occipital condyles hence called dicondylic skull.

Skull (29 bones)
Vertebral column

Vertebral column 26 bones

Cervical – 7 vertebrae.
Thoracic – 12 vertebrae.
Lumber – 5 vertebrae.
Sacral – 1 vertebra. (fused five bone)
Caudal – 1 vertebra (fused four bones)

Sternum (Breast bone)

1 bone in the middle line of the thorax.

Ribs – 12 pairs – (24 bones)

1-7 are true ribs (connected to the sternum directly)
8th, 9th, 10th pairs are called false ribs they attached to the 7th ribs.
11th and 12th not connected ventrally hence called floating ribs.

Ribs attaché dorsally to the vertebra and ventrally with the sternum by hyaline cartilage. Thoracic Ribs (12 pairs)

Bones of fore-limbs

Hind limb – 60 (30 in each)

Femur (thigh bone- the longest and heaviest bone) – 1 number.
Tibia and fibula – 2 bones.
Tarsals (ankle bone) – 7 bones.
Metatarsals – 5 in numbers.
Phalanges (digits) – 14 in numbers.
Patella (knee cap) – 1 bone.

Pectoral girdles: consists of 2 bones each = 4 bones.

Helps in articulation of fore limb with the axial skeleton.

Each pectoral girdle made of two halves.
Each half made of two bone the clavicle and scapula.
Scapula is a large triangular flat bone situated in the dorsal part of the thorax between the second and the seventh ribs.
Scapula is characterized by spine with acromion process.
Below acromion, is glenoid cavity to which head of humerus fits.
Clavicle is commonly called collar bone.

Pelvic girdle: 2 bones.

Pelvic girdle consists of two coxal bones.
Each coxal bone is formed of fusion of three bone

Ilium

Ischium

Pubis.

At the point of fusion of the three bones is a cavity
called acetabulum to which the femur articulates.
Two halves of the pelvic girdle meet ventrally to form the pubic symphysis containing fibrous cartilage.

JOINTS

Joints are the points of contact between bones, or between bones and cartilages. Force generated by the muscles is used to carry out movement through joints, where joint acts as a fulcrum.

Joints are classified into three types:

Fibrous joint
Cartilaginous joint
Synovial joint

Fibrous joints:

Do not allow any movements.
Found in flat bones which fuse end-to-end with the help of dense fibrous connective tissues in the form of sutures.
These types of joints are found in the bones of cranium

Cartilaginous joints:

The bones involved are joined together with the help of cartilages.
Permits very little movements.
Joint between the vertebral column are the example of such joints.

Synovial joints:

Characterized by the presence of a fluid filled synovial cavity between the articulating surfaces of the two bones.
Allow free movement between two bones.
The fluid inside it called synovial fluid covered by synovial membrane.

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 carpals and metacarpals of thumb

DISORDERS OF MUSCULAR AND SKELETAL SYSTEMS

Tetany

Tetany: rapid spasms (wild contractions) in muscle due to low Ca++ in body fluid.

Myasthenia gravis:

It is an auto-immune disorder.
Affects the neuromuscular junction leads to fatigue.
Caused weakening and paralysis of skeletal muscle

Muscular dystrophy

Muscular dystrophy: Progressive degeneration of skeletal muscle mostly due to genetic disorder.

Arthritis

inflammation of joints

Gout

inflammation of joints due to accumulation of uric acid crystals

Osteoporosis

age related disorder characterized by decreased bone mass and increased chances of fractures. Decrease levels of estrogen are a common cause.