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Support and Locomotion
Chapter 2
= Shape of Animals Under Influence of Movement=
Movement greatly affects the shape of animals; during movement, an animal faces a new environment with the change of place. During the course, it faces a great amount of external resistance. Also, the animal must be kept informed about the changes taking place around him. To overcome these problems a motile animal adapts in the following way:
On the other hand "Scosile" animals face similar environment around them, therefore they are "Radially Symmetrical" and are generally devoid of head and sence organs. Examples are Sea Cucumber and Sea Anemone.
= Conditions for Locomotion =
Three conditions are necessary for the locomotion are:
The animal must be propelled in the direction needed.
The body of animal must be supported during act of locomotion against the medium over which it applies force.
During locomotion, the body of animal becomes temporarily unstable and looses equilibrium but stability is restored soon by some mean.
= Musculo – Skeletal System =
Skeleton
"A rigid structure by which an animal converts force into work i.e. movement is called Skeleton."
It may be made up of bones, cartilage or hard plates. Muscles are attached with the skeleton for movement. Sometimes skeleton also serves to protect delicate internal organs.
Types of Skeleton
Skeletons are of three types:
This skeleton lies outside the body of animal. This skeleton is generally made up of hard plates called Shell. The shells are made up of different inorganic salts like Calcium Carbonate, Silika and Chitin etc. The advantage of Exoskeleton is that it not only helps in locomotion but also serves as a shelter. Disadvantage is that it restricts free movement as well as animals have to shed them time to time as they increase in size. Muscles are attached with the exoskeleton which serve to move them. Arthropods bear jointed Exoskeleton.
This skeleton lies inside the body surrounded by the muscles. It is generally made up of Cartilage and bones, which are derived from Mesoderm in vertebrates. Endoskeleton is composed of long shafts and plates of Cartilage and bones with which muscles are attached.
In vertebrates Endoskeleton is further classified into two portions:
(i) Axial Skeleton
Concerned with equilibrium and consist of vertebral column, ribs and skull.
(ii) Appendicular Skeleton
Concerned with locomotion and movement and consist of bones of upper or fore limbs or hind limbs, Pelvic and Pectoral girdles. Different bones of Endoskeleton are attached with each other at Joints. These joints may be fixed or moveable.
Advantage of Endoskeleton is that which provides support more effectively and also provides protection to the internal organs.
This type of skeleton is found in lower Invertebrates like Annelids and some Mollusks like Sea Anemone. In this skeleton instead of a rigid skeleton, pressurized fluid is used as skeleton. The animal being a tubular structure contains pressurized fluid surrounded by muscles. The fluid under pressure keeps the shape of the body constant. Contraction and relaxation of muscles changes the pressure and enables the animal to move.
= Joint =
Definition
"The place where two or more bones meet is called a Joint."
Types of Joints
There are two types of joints namely:
Examples of such joints are joints of Skull bones.
2. Moveable Joints
These joints are generally related to appendicular skeleton with which muscles are attached to produce various movements.
Moveable joints are of two varieties namely:
(i) Ball and Socket Joint
In which one of the bones forms a ball like head whereas the opposite bone forms a Socket in which ball is fitted. In this joint movement is much more extensive. Examples are hip joint and shoulder joint.
(ii) Hinge Joint
In this variety of joint one of the bone is provided generally with an over grown end which fits in a cavity over the opposite bone. Thus these joints show movement in one plane only. Examples are knee joint and Elbow joint.
Structure
Moveable joint is enclosed in a whitish tough, fibrous capsule internally lined with synovial membrane which secretes a viscous fluid called Synovial Fluid. It serves as a lubricant. Each of the bone is covered with a smooth Hyaline Cartilage, which serves to decrease the friction during movement.
= Muscles =
Definition
"A muscle is a tissue capable of contraction and relaxation."
Types of Muscles
In vertebrates, muscles are of three types:
These muscles are also called Skeletal Muscles as these muscles are concerned with movement and locomotion. These muscles are connected with bones by means of Tendons.
Structure
The skeletal muscle is composed of a large number of Muscle fibres, each fibre measures about 1 to 40mm in length. They are held together by connective tissue. The mass of a single fibre is called sareoplasm surrounded by sheath called sarcolemma. Sareoplasm contains a number of nuclei.
Each muscle fibre contains protein filaments called Myo fibrils. They are of two types i.e. thin proteins fibrils or Actin and thick protein fibrils called Myosin. Arrangement of these Myo fibrils produces transverse light (or A) Bands and Dark (or I) Bands respectively.
In each light band in its centre, there is a dark Z line. The relatively clear region in the dark band is called H-Band. The whole length between two Z lines is called Sarcomere.
The complex arrangement of different bands thus produces three regions i.e. region of thing filaments only, region of thick filaments only and area or region of overlapping, cross bridges project outward from the thick or Myosin filaments connecting it with Actin filaments.
Mechanism of Contraction
Skeleted muscle contracts i.e. becomes short in length due to sliding of actin filaments over myosin filaments. Thus filling the gaps of H-Band. Due to the sliding of filaments the I (or light) band and H-Band become shroter and the A (or dark) band becomes longer. The distance between Z to Z lines becomes smaller. After siding of filaments, cross bridges are attached to Actin filaments and contract due to which muscle as a whole becomes shorter and contracted. Whole process of cross bridging is energy dependent, energy is supplied by the splitting of ATP into ADP. When the ATP is totally consumed, further energy is supplied by the Ceratine Phosphate formed by the breakdown of Glycogen. On further, demand of energy, Glycogen breaks anaerobically leading to the formation of Lactic Acid. This lactic acid accumulates in muscles and causes muscle fatigue.
These muscles are called Involuntary because they function under the control of Autonomic Nervous system. These muscles are Spindle Shape i.e. pointed on both ends. Each muscle fibre contains fine Myo-fibrils but the arrangement is different from the skeletal Muscles. Generally they show no dark and light bands under microscope. They are found in viscera like alimentary canal, urinary bladder and blood vessels often in two layers i.e. longitudinal and Circular muscles.
These are special type of muscle found only in Heart. Microscopically these muscle are striated but they are under control of Autonomic Nervous System. A special feature of these muscle is that, the muscle fibres are interconnected. Therefore on stimulation heart contracto in one piece. The stimulus for contraction is generated by Sino-Auricular Node which discharges periodically by which the heart contracts Rhythmically. This inter connected arrangement is called Syncitium.
Classification of Different Groups of Muscles
Skeletal muscles are numerous and perform different types of movements but they can be grouped into seven namely:
= Locomotion in Protozoan =
In protozoans, locomotion is performed by a part of the cell called Locomotary Organelle. Different types of Protozoan movements are named according to the locomotary organelle involved. These are as follow:
Amoeba moves by means of Pseudopodia. These are fingers like projections of cytoplasm which are pushed outward in various directions when movement is desired. Whole of the cytoplasm flows in that Pseudopodia which comes in contact with mud or surface and all the other Pseudopodia are withdrawn. The process is repeated again and again for constant motion. This type of movement is also found in WBC of human blood.
In flagellates like Euglena and Trepanosome, locomotary organ is Flagellum. Each flagellum is a long thread like extension of cytoplasm showing Lashing Movement. It provides whipping movement against water, which drives the protozoan forward. Flagellum also serves as a sensory organ as well as food capturing organ. Example can be seen in Euglena.
In ciliated protozoans, the locomotary organs are fine, hair like, and short Cilia. These cilia are produced by the cell membrane, they bend and straighten alternately in groups and propel water backward enabling the organism to move forward. Example may be seen in Paramecium.
= Locomotion in Multicelluar Organisms=
In multicellular organisms locomotion is achieved by contraction and relaxation of muscles. These muscles lie in opposite groups. The animal pushes the medium i.e. water, ground or air backward with the help of locomotary organs. Different types of movements found in different animals are as follows:
Movement in Coelenterates
Coelenterates are devoid of skeletal muscles but their epidermis contains Myo-Epithelial Cells containing contractile Myo fibrils in the base. Contraction of these fibrils causes reduction in the length of that particular part. Examples are as follows:
1. Movement in Hydra
Hydra moves in several ways i.e. crawling, looping and somersaulting. In crawling, the cells of basal disc produce Pseudopodia by which it glides on the substratum.
In looping and somersaulting hydra bends towards one side and attaches with the mud or substratum with the help of Tantacles. Now it moves its basal disc to the direction required or releases it from the ground. In somersaulting, it again bends forward and attaches the basal disc to the ground and releases the tantacles from the ground.
2. Movement in Jelly Fish
Jellyfishes are umbrella like animals and they move by Jet Propulsion. This movement resembles opening and closing of an umbrella under water. When umbrella like jelly fish contacts its body, water in the hollow body is forced out through the mouth giving it thrust to move.
3. Movement in Helminths (Planaria)
Helminths or flatworms have got hydrostatic skeleton covered with three types of muscles, which are longitudinal, circular and Transverse. Simultaneous contraction of these muscles in one area forces the fluid to the opposite direction, which stretches the body. The part extends in the particular direction and enables the animal to move.
4. Movement in Echinoderms (Star Fish)
In star fish, the locomotary organs are Tube Feet attached with a hydraulic system of locomotion. Each tube foot is attached with a sac containing a fluid, which communicates with longitudinal canals of water circulatory system. Direction of the tube feet is directed by the muscles. When muscles attached with the sac or ampula contract, the fluid is forced or pumped into the feet which are guided by the muscles, thus enabling the animal to lift due to forceful downward ejection of water. When reaches the substratum back, the suckers provided at the bottom of the feet hold the substrate.
5. Locomotion in Molluscs or Snail
Snail or Molluscs has got a muscular foot. A wave of contraction runs on the under side of foot Anterio-Posteriorly or from front to the rear, which pushes the snail forward. Movement is further helped by the secretion of Slim, poured on the ground from a gland below mouth.
6. Locomotion in Earthworms
Earthworm moves by means of Hydrostatic Skeleton further helped by two sets of muscles namely Longitudinal and Circular muscles. The outer circular muscle when contract, there is an increase in the length of animal and decrease in its breadth. Increase in length is due to pressure on the fluid of body cavity.
When longitudinal muscles contract, the length of animal becomes short but there is increase in the breadth. Hydrostatic Skeleton is further helped by the Setae present on the ventral surface.
Locomotion takes place in Earthworm in a stepwise manner. First the Satae of posterior part of body anchor in the soil firmly. Circular muscles of anterior part contract, forming the fluid to anterior end forward. The new position of anterior end is secured by the Satae of this region, which anchor in the soil. Now the Satae of posterior part are retracted and longitudinal muscles of anterior part began to contract, pulling posterior part forward in a new position.
The whole process is repeated for many time during active movement of earthworm. The contraction of circular muscles and longitudinal muscle is always reciprocal during locomotion.
Types of Locomotion
Locomotion may be classified into different types according to the action of body or modification of animal’s locomotary organ. Different types of locomotion are as follows:
It is the locomotion of limbles animals in which whole body touches the ground. For example snake.
It is a slow movement of insects with many locomotary appandages (Polydactyly). For example Cockroach.
Movement of aquatic animals in which water is forced outward through a narrow opening giving the animal necessary thrust to move, is called Jet propulsion. For example Jellyfishes and Squids.
Movement of aquatic animals having fins is called swimming. For example Fish.
It is movement of certain terrestrial animals in which they use pair of their hind limbs. These animals push the ground backward and below forcefully with their hind limbs, gaining required thrust to move in a particular direction. For example Frog and Kangaroo.
This type of movement is common in Quadripods in which they push the ground with the help of their legs or two pairs of limbs. This mode of locomotion is further grouped into three classes according to the part of foot they use during walking:
(i) Plantigrade
In this, animal puts whole flat or sole of the foot on ground. This is adapted by the animals having vertical and slow gait. For example Bear and Man.
(ii) Digitigrade
In such mode of running, animal only puts the digits of the foot on the ground, this is adapted by quadripods with preying habits like dogs and cats.
(iii) Unguligrade
The animals only touch the ground with only one or two digits of their feet. These digits are hoofed and the rest of the foot is raised due to lengthening of the bones of effective and faster running. For example Horse, Deer, Cow and Goat.
7. Flying
In this type, animals use their forelimbs for locomotion. These forelimbs are provided with fold or skin or features with which animal push air behind and moves forward. However certain insects have got one or two pairs of papery wings by which they fly. For examples Bat, Sparrow, eagle, house fly and mosquitoes.
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