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 places 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 utilised 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.
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 places 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 utilised 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.
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 a well-developed muscular system. They have two types of contractile cells on its body wall, viz. epitheliomuscular 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. Various types of 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 a pushing of the anterior end and partly of the posterior end. The coelomic fluid gives turgidity as it acts as a hydraulic skeleton making the body wall tough. The worm moves at the rate of about 25 cm per minute.
Movements in Starfish:
Starfishes have got a water vascular system that help them in their locomotion. Each arm of the starfish has two rows of tube feet underneath. Water enters into 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 specialised rigid connective tissue called bones. This skeletal system consists of many parts, each made of one or more bones.
According to the shape and size, bones may be long (thigh bone and the upper arm bone); flat (breast bone and the shoulder girdle bone); or irregular (bones of he vertebral column). In all, the skeletal system consists of 206 bones in man. Some major parts of human skeleton consist of the following numbers of bone – skull or cranium (8), face (14), each forelimb (30), each hindlimb (30), vertebrae (24), sacrum (1), coccyx (1), sternum (1), ribs (24), pelvis (3), each shoulder girdle (2).
Functions of skeletal system:
1. It provides a kind of framework for the body.
2. It provides shape and posture to the body.
3. It provides protection to some of the inner delicate organs like brain, spinal cord and lungs.
4. It gives rigid surface for the attachment of muscles with the help of tendons.
5. It helps in locomotion.
6. The bone marrow serves as the centre for the production of red blood cells and white blood cells.
7. The movements of ribs and sternum help in breathing.
8. In the ear, the sound vibrations are conveyed from the tympanum to the internal ear by a set of three bones as in man.
9. It helps the body to be an integrated unit.
10. 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.
Joints:
The junctions where two or more bones articulate with each other are known as joints. These joints allow the movement of bones in different ways. According to the mobility they are of the following types:
1. Fixed or immovable or fibrous joints: At these joints the bones are held firmly together and movements are not allowed in between them. At these joints a dense and tough inextensible white fibrous tissue is present. For example, sutures that join the various bones of the skull.
2. Slightly movable or cartilaginous joints: At these joints a dense disc of white fibrocartilage is present that joins the opposite surfaces of the articulating bones. It allows only a little movement like bending and rotation. These joints are seen in between the vertebrae.
3. Freely movable or synovial joints: In this type of joint there is a fluid filled synovial cavity in between the movably articulated bones. The fluid is called as synovial fluid. A synovial membrane covers this fluid filled synovial cavity forming the capsule. The articulating bones are provided with cartilage caps. Ligaments are also present to hold the bones. It is of the following types:
(i) Ball and socket joint. In this, one of the bones forms a globular head while the other forms a cup – like socket into which head fits in. It allows a free movement in all directions e.g., shoulder girdle and hip girdle joints. Such joints may stretch (extend), fold (flex) and rotate the limb of the body. This may allow the movement of the limb towards the body or away from the body.
(ii) Hinge joint. Here the two bones are fitted like the hinge of a door so as to allow to and fro movements in one direction only. These joints are provided with strong ligaments. It is seen in elbow joint, knee joint and joints between phalanges of fingers and toes.
(iii) Pivot joint. In this type of joint, one bone is fixed while the other moves freely over it. The movement is, therefore, confined to a rotation around a longitudinal axis through the centre of the pivot e.g., movement of the skull over the odontoid processes of the first neck vertebra.
(iv) Gliding joint. It is a biaxial joint, the articulating bones of which can glide one above the other. It is seen in wrist bones that can glide over forearm bones, in zygapophysis by which vertebrae can glide one above the other e.g., some of the bones in the palm or in the sole of foot.
(v) Ellipsoid joints. They permit movements of articulating bones around two axes. Such joints are formed between the toe bones and some bones in the sole of foot.
Movements are produced at joints by contractions of skeletal muscles inserted into the articulating bones. Flexible connective tissue bonds called ligaments stabilise the joints by holding the articulating bones together.
Movements of Skeletal Muscles:
The skeletal muscles are made of striated muscle fibres and are under voluntary control. According to the type of movements, skeletal muscles can be classified as under:
1. Flexor. A muscle that bends one part upon another (e.g., leg upon thigh)
2. Extensor. The muscles responsible for straightening out a part of the body are termed extensor muscles (e.g., muscles concerned with the extension of foot).
3. Adductor. The muscle that is concerned with the movement of a part of the body towards the midline of the body is called the adductor muscle.
4. Abductor. The muscle which moves a part of the body away from the midline of the body is termed as abductor muscle.
5. Pronator. A muscle that brings about the rotation of body parts. For example, the rotation of fore arm to turn the palm downward or backward.
6. Supinator. It helps to rotate the fore arm and thus make the palm face upward or forward.
7.
Antagonistic muscles:
When the two muscles contract to bring out opposite movements at the same place, then they are called as antagonistic muscles. For example, biceps muscles present in the arm is a flexor for the elbow joint; and the triceps is its antagonistic muscle and acts as an extensor for that joints. During flexion movements the biceps contracts and triceps relaxes; while during extension movements biceps relaxes and triceps contracts.
Threshold stimulus:
The skeletal muscle has got large number of muscle fibres. Each of these muscle fibres if supplied with a motor nerve fibre. When the muscle contracts or shortens in length, it is due to the shortening of the individual muscle fibres. A muscle always contracts in response to a given stimulus and then it relaxes back to its original position. The stimulus to the nerve supplying the muscle can be thermal, electrical, mechanical or chemical in nature. There should always be some minimum strength of stimulus that will make the muscle respond or contract. This is known as threshold value of the stimulus. If the given stimulus is less than this threshold limit, the muscle fibres will not respond at all. Further, on stimulation, each muscle fibre contracts to its full. If the strength of stimulus is below the threshold value, then the muscle fibres will not respond.
If we increase the strength of stimulus beyond the threshold value, the muscle fibres will contract but the level of contraction is same as that for the threshold value. That means if the strength of stimulus is increased, the level of muscle contraction for the individual muscle fibre will be the same. This shows that either the muscle will contract to a given stimulus or it will not contract at all. This is known as all-or-none law. However, this force of contraction may depend upon other factors like changes in temperature, pH, or slight stretching of the fibre. But under all such changed conditions, increasing the strength of stimulus cannot increase the force of contraction. This all-or –none law is also followed by smooth muscles, cardiac muscles and the nerve fibres.
Muscle twitch and Tetanus:
When an electrical stimulus is given to a nerve supplying a muscle, the muscle fibres contract. This contraction of a single muscle fibre is known as muscle twitch. In this the muscle fibre contracts after an initial latent period, and then it relaxes back.
When a muscle is given series of stimuli continuously then it shows tetani. In this the second stimulus is given even before the muscle has relaxed from first, and the third stimulus is given even before the muscle has relaxed from the second and so on. Such a response of the muscle is known as tetanus.
Mechanism of muscle contraction:
A voluntary muscle fibre consists of numerous myofibrils which have their units as sarcomeres. Each myofibril is covered by the cisternae and tubules of sarcoplasmic reticulum at the I band; and at the junction of A and I band by a T-tubule that communicates with the exterior of cell. A sarcomere consists of a half-light band and a half dark band i.e., the distance between two Z-membranes. It also has primary and secondary filaments. The primary filaments are made up of a protein called myosin while secondary filaments are of actin.
As the stimulus is given to the muscle, the secondary filaments slide over to the primary filaments thus shortening the length of the light band or I-band. It is important to note that the length of dark band or A-band does not change. The actual site where sliding of the filaments occur is known as cross bridges. Thus in response to a stimulus, the overall length of the sarcomere and the myofibril decreases. A muscle never expands to a stimulus but always contracts in its length.
Chemical changes in muscle contraction:
ATP is the immediate source of energy for muscle contraction. Hence hydrolysis process occurs in the contracting muscle to convert ATP to ADP with the release of inorganic phosphate and energy by myosin ATPase:
ATPase
ATP+H2O -----------------> ADP + Pi
This energy released is used up in muscular contraction. For restoration of ATP, body muscles have also got another compound called creatine phosphate (CP). This is also an energy rich compound. It helps in the conversion of ADP to ATP again immediately. This happens at the end of muscular contraction.
ADP + CP ----------------> ATP + Creatine
Creatine formed during muscular contraction is again reconverted to creatine phosphate by the utilisation of ATP generated by carbohydrate oxidation:
ATP + C -----------------> CP + ADP
During muscle contraction, carbohydrates are metabolized through glycolysis in the muscle to produce ATP. This results in the formation of lactic acid from carbohydrates. During recovery after contraction, lactic acid is oxidized to carbon dioxide and water aerobically, giving more energy.
Fatigue:
Under heavy strain of muscular work one feels fatigue. The muscular fatigue may be defined as inability of muscular contraction after the prolonged stimulation. The fatigue occurs due to depletion of glycogen, oxygen and ATP and accumulation of lactic acid. Under deficiency of oxygen, the lactic acid is not reconverted into glycogen and is not oxidised to form water and CO2, then this lactic acid gets accumulated. When we allow resting for some time, the fatigue is removed and the muscle can contract again.
Distinguish between Red muscle fibres and White muscle fibres:
Birds and mammals consist of two types of skeletal or striated muscle fibres viz. red muscle fibres or slow fibres and white muscle fibres or fast fibres. A comparison of these two types of muscle fibres is given below:
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 a well-developed muscular system. They have two types of contractile cells on its body wall, viz. epitheliomuscular 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. Various types of 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 a pushing of the anterior end and partly of the posterior end. The coelomic fluid gives turgidity as it acts as a hydraulic skeleton making the body wall tough. The worm moves at the rate of about 25 cm per minute.
Movements in Starfish:
Starfishes have got a water vascular system that help them in their locomotion. Each arm of the starfish has two rows of tube feet underneath. Water enters into 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 specialised rigid connective tissue called bones. This skeletal system consists of many parts, each made of one or more bones.
According to the shape and size, bones may be long (thigh bone and the upper arm bone); flat (breast bone and the shoulder girdle bone); or irregular (bones of he vertebral column). In all, the skeletal system consists of 206 bones in man. Some major parts of human skeleton consist of the following numbers of bone – skull or cranium (8), face (14), each forelimb (30), each hindlimb (30), vertebrae (24), sacrum (1), coccyx (1), sternum (1), ribs (24), pelvis (3), each shoulder girdle (2).
Functions of skeletal system:
1. It provides a kind of framework for the body.
2. It provides shape and posture to the body.
3. It provides protection to some of the inner delicate organs like brain, spinal cord and lungs.
4. It gives rigid surface for the attachment of muscles with the help of tendons.
5. It helps in locomotion.
6. The bone marrow serves as the centre for the production of red blood cells and white blood cells.
7. The movements of ribs and sternum help in breathing.
8. In the ear, the sound vibrations are conveyed from the tympanum to the internal ear by a set of three bones as in man.
9. It helps the body to be an integrated unit.
10. 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.
Joints:
The junctions where two or more bones articulate with each other are known as joints. These joints allow the movement of bones in different ways. According to the mobility they are of the following types:
1. Fixed or immovable or fibrous joints: At these joints the bones are held firmly together and movements are not allowed in between them. At these joints a dense and tough inextensible white fibrous tissue is present. For example, sutures that join the various bones of the skull.
2. Slightly movable or cartilaginous joints: At these joints a dense disc of white fibrocartilage is present that joins the opposite surfaces of the articulating bones. It allows only a little movement like bending and rotation. These joints are seen in between the vertebrae.
3. Freely movable or synovial joints: In this type of joint there is a fluid filled synovial cavity in between the movably articulated bones. The fluid is called as synovial fluid. A synovial membrane covers this fluid filled synovial cavity forming the capsule. The articulating bones are provided with cartilage caps. Ligaments are also present to hold the bones. It is of the following types:
(i) Ball and socket joint. In this, one of the bones forms a globular head while the other forms a cup – like socket into which head fits in. It allows a free movement in all directions e.g., shoulder girdle and hip girdle joints. Such joints may stretch (extend), fold (flex) and rotate the limb of the body. This may allow the movement of the limb towards the body or away from the body.
(ii) Hinge joint. Here the two bones are fitted like the hinge of a door so as to allow to and fro movements in one direction only. These joints are provided with strong ligaments. It is seen in elbow joint, knee joint and joints between phalanges of fingers and toes.
(iii) Pivot joint. In this type of joint, one bone is fixed while the other moves freely over it. The movement is, therefore, confined to a rotation around a longitudinal axis through the centre of the pivot e.g., movement of the skull over the odontoid processes of the first neck vertebra.
(iv) Gliding joint. It is a biaxial joint, the articulating bones of which can glide one above the other. It is seen in wrist bones that can glide over forearm bones, in zygapophysis by which vertebrae can glide one above the other e.g., some of the bones in the palm or in the sole of foot.
(v) Ellipsoid joints. They permit movements of articulating bones around two axes. Such joints are formed between the toe bones and some bones in the sole of foot.
Movements are produced at joints by contractions of skeletal muscles inserted into the articulating bones. Flexible connective tissue bonds called ligaments stabilise the joints by holding the articulating bones together.
Movements of Skeletal Muscles:
The skeletal muscles are made of striated muscle fibres and are under voluntary control. According to the type of movements, skeletal muscles can be classified as under:
1. Flexor. A muscle that bends one part upon another (e.g., leg upon thigh)
2. Extensor. The muscles responsible for straightening out a part of the body are termed extensor muscles (e.g., muscles concerned with the extension of foot).
3. Adductor. The muscle that is concerned with the movement of a part of the body towards the midline of the body is called the adductor muscle.
4. Abductor. The muscle which moves a part of the body away from the midline of the body is termed as abductor muscle.
5. Pronator. A muscle that brings about the rotation of body parts. For example, the rotation of fore arm to turn the palm downward or backward.
6. Supinator. It helps to rotate the fore arm and thus make the palm face upward or forward.
7.
Antagonistic muscles:
When the two muscles contract to bring out opposite movements at the same place, then they are called as antagonistic muscles. For example, biceps muscles present in the arm is a flexor for the elbow joint; and the triceps is its antagonistic muscle and acts as an extensor for that joints. During flexion movements the biceps contracts and triceps relaxes; while during extension movements biceps relaxes and triceps contracts.
Threshold stimulus:
The skeletal muscle has got large number of muscle fibres. Each of these muscle fibres if supplied with a motor nerve fibre. When the muscle contracts or shortens in length, it is due to the shortening of the individual muscle fibres. A muscle always contracts in response to a given stimulus and then it relaxes back to its original position. The stimulus to the nerve supplying the muscle can be thermal, electrical, mechanical or chemical in nature. There should always be some minimum strength of stimulus that will make the muscle respond or contract. This is known as threshold value of the stimulus. If the given stimulus is less than this threshold limit, the muscle fibres will not respond at all. Further, on stimulation, each muscle fibre contracts to its full. If the strength of stimulus is below the threshold value, then the muscle fibres will not respond.
If we increase the strength of stimulus beyond the threshold value, the muscle fibres will contract but the level of contraction is same as that for the threshold value. That means if the strength of stimulus is increased, the level of muscle contraction for the individual muscle fibre will be the same. This shows that either the muscle will contract to a given stimulus or it will not contract at all. This is known as all-or-none law. However, this force of contraction may depend upon other factors like changes in temperature, pH, or slight stretching of the fibre. But under all such changed conditions, increasing the strength of stimulus cannot increase the force of contraction. This all-or –none law is also followed by smooth muscles, cardiac muscles and the nerve fibres.
Muscle twitch and Tetanus:
When an electrical stimulus is given to a nerve supplying a muscle, the muscle fibres contract. This contraction of a single muscle fibre is known as muscle twitch. In this the muscle fibre contracts after an initial latent period, and then it relaxes back.
When a muscle is given series of stimuli continuously then it shows tetani. In this the second stimulus is given even before the muscle has relaxed from first, and the third stimulus is given even before the muscle has relaxed from the second and so on. Such a response of the muscle is known as tetanus.
Mechanism of muscle contraction:
A voluntary muscle fibre consists of numerous myofibrils which have their units as sarcomeres. Each myofibril is covered by the cisternae and tubules of sarcoplasmic reticulum at the I band; and at the junction of A and I band by a T-tubule that communicates with the exterior of cell. A sarcomere consists of a half-light band and a half dark band i.e., the distance between two Z-membranes. It also has primary and secondary filaments. The primary filaments are made up of a protein called myosin while secondary filaments are of actin.
As the stimulus is given to the muscle, the secondary filaments slide over to the primary filaments thus shortening the length of the light band or I-band. It is important to note that the length of dark band or A-band does not change. The actual site where sliding of the filaments occur is known as cross bridges. Thus in response to a stimulus, the overall length of the sarcomere and the myofibril decreases. A muscle never expands to a stimulus but always contracts in its length.
Chemical changes in muscle contraction:
ATP is the immediate source of energy for muscle contraction. Hence hydrolysis process occurs in the contracting muscle to convert ATP to ADP with the release of inorganic phosphate and energy by myosin ATPase:
ATPase
ATP+H2O -----------------> ADP + Pi
This energy released is used up in muscular contraction. For restoration of ATP, body muscles have also got another compound called creatine phosphate (CP). This is also an energy rich compound. It helps in the conversion of ADP to ATP again immediately. This happens at the end of muscular contraction.
ADP + CP ----------------> ATP + Creatine
Creatine formed during muscular contraction is again reconverted to creatine phosphate by the utilisation of ATP generated by carbohydrate oxidation:
ATP + C -----------------> CP + ADP
During muscle contraction, carbohydrates are metabolized through glycolysis in the muscle to produce ATP. This results in the formation of lactic acid from carbohydrates. During recovery after contraction, lactic acid is oxidized to carbon dioxide and water aerobically, giving more energy.
Fatigue:
Under heavy strain of muscular work one feels fatigue. The muscular fatigue may be defined as inability of muscular contraction after the prolonged stimulation. The fatigue occurs due to depletion of glycogen, oxygen and ATP and accumulation of lactic acid. Under deficiency of oxygen, the lactic acid is not reconverted into glycogen and is not oxidised to form water and CO2, then this lactic acid gets accumulated. When we allow resting for some time, the fatigue is removed and the muscle can contract again.
Distinguish between Red muscle fibres and White muscle fibres:
Birds and mammals consist of two types of skeletal or striated muscle fibres viz. red muscle fibres or slow fibres and white muscle fibres or fast fibres. A comparison of these two types of muscle fibres is given below:
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