Locomotion
All living organisms exhibit movement. These movements take place with the help of some internal force. In human beings, there are two kinds of movements, such as - (I) Internal movements, (II) Locomotion.
I) Internal movements :
These include movements which may be voluntary or involuntary. Three types of muscles bring about these movements. e.g.,
a. Peristaltic movements in the alimentary canal, Constriction and dialation of blood vessels etc. They are controlled by smooth muscles.
b. Contraction and relaxation of the heart, is controlled by cardiac muscles.
c. Movements of limbs, head, trunk, eyeballs etc. are controlled by striated muscles.
Significance of movements :
1. The body movements help to maintain equilibrium against gravity.
2. It helps in food intake, speech etc.
3. Movements of the diaphragm and rib cage help in the breathing process.
4. Rhythmic movement of the heart helps in the circulation of blood.
II) Locomotion :
Locomotion is the characteristic feature of animals, which distinguishes the animals from plants. It is willful or voluntary act of displacement. The change in locus of whole body of living organism from one place to another place is called locomotion.
There are four basic types of locomotions found throughout the animals kingdom, such as:
1. Amoeboid movement - performed by pseudopodia e.g., Leucocytes.
2. Ciliary movements - performed by cilia e.g. ciliated epithelium.
3. Whorling movement - performed by flagella e.g., sperms
4. Muscular movements - performed by muscles e.g., limb movements.
Locomotion includes act of walking, running, creeping, swimming, hopping, flying, leaping and jumping.
In higher animals locomotion is performed by skeletal muscles. Human locomotion is the combined action of bones, joints and skeletal muscles. During locomotion, bones serve as lever, joints as fulcrum and the skeletal muscles generate force.
Significance of Locomotion :
It helps in escaping from predators. It also helps to move about in search of food, water and shelter. During reproduction i.e. courtship and mating, movements and locomotion are involved. Locomotion improves chances of survival and continuation of race.
Joints :
A place where two or more bones get articulated with one another is called a joint. Joints help to connect different parts of skeleton and form a basic framework of body.
Study of structure an functions of various joints is called arthrology. At joints the bones are connected to each other by to each other by ligaments. Ligaments are tough, elastic fibrous connective tissue bands or threads which connect bone to bone at joint. Ligaments keep the bones in proper position and avoid dislocation of bones during the movement.
Significance of joints is to help in locomotion. Joints also help in desirable voluntary movements of body parts. Joints bring flexibility in rigid skeleton. Some joints are protective and act as shock absorbers.
Classification of Joints :
On the basis of structure and degree of mobility, the joints are classified into three groups -
I. Synarthrosis/Fibrous joints/Fixed joints-
1. Sutures of skull,
2. Syndesmoses,
3. Gomphosis/Peg and socket joint.
II. Amphiarthrosis/Cartilagenous joints/Slightly moveable joints
1. Synchondrosis
2. Symphysis
3. Intervertebral joints
III. Diarthrosis/Synovial joints/Freely movable joints
1. Ball and socket joint
2. Hinge joint
3. Gliding joint
4. Condyloid joint
5. Saddle joint
6. Pivot joint
I. Synarthrosis (Fibrous joints):
The bones are united at the joints by thin or dense layer of white fibrous connective tissue. The white fibres are made up of a protein collagen. These joints are fixed i.e. can not permit any movement of articulating bones. Shorts and thick fibres do not allow movement of articulating bones. The line of fusion at joint is called suture. Fixed joints are primarily meant for growth and may permit moulding during childbirth. Usually these joints are the places of growth.
a) Sutures of skull (Serrate sutures):
These joints are found in flat and curved roofing bones of the skull. These joints are also called serrate joints because articulating surfaces of the bones show serrated margins. The bones are repeatedly interlocked, therefore joints become more fixed and protective in function.
The prominent sutures between cranial bones of skull are :
i) Coronal Suture - Present between Frontal bone and Parietal bones.
ii) Sagittal Suture - Present between two parietal bones.
iii) Lambdoidal Suture - Present between parietals and occipital bone.
iv) Lateral Suture - Present between temporal and parietal bones.
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| Sutures of skull |
In young or newborn, the roofing bones of skull leave about six gaps called fontanelles. Fontanelles permit flexibility for parturition and brain growth. At about 2 years of age the gaps are closed by ossification.
b) Syndesmoses - Fibrous connective tissue that connects two bones. e.g. tibia and fibula.
c) Gomphosis - Characteristic of thecodont teeth. The roots of the teeth are fixed in sockets (alveoli) of jaw bones. The fibrous connections in this case are many short periodontal ligaments.
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| Gomphosis joint |
II. Amphiarthrosis (Cartilagenous joints):
These are also called amphiarthroses because they are neither fixed nor freely movable. It is intermediate stage of joints when related to development and movement. They allow some movement in response to compression, tension or twisting. The line of fusion between articulating bones is called synchondrosis or symphysis. (Symphysis e.g. Intervertebral disc, Pubic Symphysis)
a) Synchondroses :
The connecting material is a hyaline cartilage. It is very soft and elastic with minimum strength e.g. Epiphyseal plate.
This epiphyseal plate is present between epiphyseal plate is present between epiphysis and diaphysis of the long bones. It is a temporary joint present in children and it gets ossified in adult. This joint provides the site and means growth of the long bones in children. It also contributes to the flexibility in the endoskeleton of children.
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| 1.Syndesmoses or 2. Synchondrosis |
b) Symphysis :
The connecting material is fibrocartilage. Fibrocartilage is an opaque, comparatively strong but flexible structure, due to the presence of numerous white fibres of collagen.
It is present between two pubic bones of the pelvic girdle. The pubic bones are connected by a disc of fibrocartilage. It allows slight movements as compression, bending, twisting etc. It makes the joint more flexible. In female, it helps to increase the size of the birth canal for easy parturition. In males, it is comparatively less flexible.
c) Intervertebral joints :
The joints are present between the centra of adjacent vertebrate of backbone. The connecting disc are fibro-cartilagenous. These joints help in shock absorption and protect the spinal cord from mechanical injury. These joints make the vertebral column slightly flexible.
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| a. Symphysis or b. Intervertebral joint |
III. Diarthroses (Synovial joints)
These are called perfect joints due to the presence of all well developed structures needed for free movement. These are most evolved and therefore, freely movable type of joints.
Typical synovial joint :
It consists of synovial cavity, synovial fluid, synovial membrane, capsule, ligaments and articulating surfaces covered by hyaline cartilage.
a) Synovial Membrane : It lines the cavity and forms a synovial capsule. The synovial membrane secretes synovial fluid. It encloses fluid filled synovial cavity and protects internal parts of joint.
b) Synovial fluid : It is a clear, yellowish, slimy and viscous fluid similar to lymph. The viscosity of fluid is due to hyaluronic acid secreted by the cells of the synovial membrane. It contains nutrients and mucus. The fluid lubricates the joint and nourishes hyaline cartilage.
The fluid also contains phagocytes, which remove micro organisms and cellular debris. deficiency of this fluid causes arthrosclerosis.
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| Typical synovial joint |
c) Hyaline cartilage : It covers the end of articulating surfaces of bone and avoids directs contact of friction between bones.
d) Ligaments : The joints are provided with capsular ligaments and numerous accessory ligaments. Accessory ligaments may be intra or extra capsular. Ligaments avoid dislocation of bones and makes the joints stronger.
On the basis of structure, functions, movements and shape of articulating bones the joints are named as -
1. Ball and socket joint :
The spherical head of one bone fits into a sup-shaped socket of other bone. These joints are prone for easy dislocation or separation o sudden strain. These joints allow multi-axial movements. The shoulder joint allows rotatory or circular movements (360°) and hip joint allows straight movements. Shoulder joints, Hip joint etc. are examples of ball and socket joint.
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| Ball and Socket joint |
2. Hinge joint :
Spoon shaped surface of one-bones fits into the concave cavity of other bone. There are strong collateral ligaments. These joints resist dislocation. These joints allow uniaxial (180) movements and resemble with the movements of door and window. In elbow joint the ulna works as hinges so only forward movement is possible. In knee joint the patella or knee cap works as hinge so only backward movements is possible.
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| Hinge joint |
Examples : Elbow joints, Knee joints.
3. Gliding joints :
The articular bones are permitted for gliding or sliding movements. These joints allow non-axial movements, which are neither back-forth nor side to side but irregular. The articulating surface is convex so friction is avoided. Intercarpal joints, Intertarsal joints, etc. are examples of gliding joint.
4. Condyloid joint :
These are also called ellipsoid joints. Oval shaped condyle of one bone fits into elliptical cavity of other bone. These joints allow biaxial movements i.e. forward - backward and side to side but not rotation. Radius carpal, Metacarpo - phalangeal joints are examples of condyloid joint.
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| Condyloid joint |
5. Saddle joint :
The characteristic of this joint is that the articulating surfaces of bones are saddle shaped i.e. each surface has both concave and convex area. Each surface is convex in one plane, concave in the perpendicular plane. It resembles with condyloid joint but it allows greater freedom of movement for the joint. This joint allows biaxial movement. Edges of first metacarpal and carpal (trapezium) of thumb is peripherally articulated so saddle joint makes free movement.
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| Saddle joint |
Carpo metacarpal joint thumb is example of saddle joint.
It is the most flexible joint in the body. Saddle joint has evolutionary significance in human evolution. It increases grasping power of fingers and helps in skillful work like writing, drawing, painting, etc.
6. Pivot joint :
Articular surfaces comprise a central bony pivot (dense) surrounded by an osteo-ligamentous ring. One bone remains fixed while other bone rotates freely around the pivot shaped process of fixed bone. It allows uniaxial movements i.e. rotation. Example of this joint is Atlanto - axial joint. Atlas moves along with skull around the pivot like odontoid process of axis. This joint allows rotation movement of the skull.
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| Pivot joint |