Support And Movement In Man

In higher animals, including man, the skeleton provides support, protection and helps in movement.

Support and movement in man is carried out with the help of skeleton and muscles. Skeleton is a hard framework of human body consisting of 206 bones of various shapes and sizes; long and short; flat or irregular. Skin and muscles form the external covering of the skeleton. Skeleton of man is divided into two major divisions:

1. Axial skeleton consists of the skull, the backbone (vertebral column), and the ribs. The backbone supports the ribs which are also attached to the breastbone, or sternum.
2. Appendicular skeleton consists of shoulder girdle (pectoral girdles), hips (pelvic girdles) and the bones of arms (humerus, radius & ulna), legs (femur, tibia & fibula), hands and feet.

The vertebral column forms the central supporting structure of the skeleton consisting of 33 individual bones called vertebrae (singular-vertebra).

Vertebral column supports the skull. Twelve pairs of ribs are attached to the upper part of the vertebral column and the limbs (arms & legs) are attached to it by means of girdles. The pelvic girdle is joined rigidly to its lower end. Pectoral girdle consists of a pair of collar bones and shoulder blades, which are not rigidly fixed to the vertebral column but held in place by muscles (fig. 14. 18).

Functions of skeleton in support and movement support

The skeleton holds the body off the ground and keeps its shape and helps in movement.

Movement

Many bones of the skeleton act as levers. When muscles pull on these bones, they produce movements such as the raising of the ribs during breathing (chapter 11) or the chewing action of the jaws and flexing of the arms. For a skeletal muscle to produce movement, both its ends need to have a firm attachment. The skeleton provides suitable points of attachment for the ends of muscles.

Muscles play role in the support of skeleton

The skeletal muscles which are firmly attached to the bones play an important role in the support of skeleton for example:

1. The muscle that lie at the back hold the backbone and the head in place.
2. The diaphragm, a muscular sheet that divides the body cavity into two parts, is attached to the lowest rib bones. Te muscles of the diaphragm and those connecting the ribs to one another, collectively forming part of the rib cage and are responsible for breathing.
3. The limbs are connected to the girdles by muscles, which are responsible for their movement.
4. The upper arms and thighs have muscles that are able to close and open the elbow and knee.
5. The fore arms and shanks have muscles that are responsible for the movement of the hands and feet.
6. Numerous muscles control the manipulation of the fingers and toes.

Action of flexors and extensors as a pair of opposing muscles.

Muscles are attached to the bones at two points. One end of a set of muscles is usually attached to an immovable and rigid bone while that of the other is attached to a movable bone. The first point of attachment is known as the origin of the muscle and the second as its insertion. Muscles may have more than one origin. Muscles may be attached directly to the bone or indirectly by means of tough, whitish cords of fibrous material called tendons.

Muscles can only contract and relax but not expand. When a muscle contracts, it becomes shorter and thicker and hence exerts a pulling force on the bone to which it is attached at the point of insertion. When a muscle relaxes, it lengthens and becomes thinner, muscles work by contraction only. To move a bone to and fro, there are two sets of muscles. When one set contracts, it moves the bone in one direction, and when the other set contracts, it moves the bone in the opposite direction i. e. these two sets of muscles are antagonistic to each other. When one member of antagonistic pair of muscles contracts, the other relaxes. Such movement is known as antagonistic movement or antagonism.

1. Bending of the arm at elbow joint is called flexion and the muscle that causes this movement is called flexor.
2. Straightening of the arm at elbow joint is called extension, and the muscle that causes this movement is called extensor.
3. One member of the pair of antagonistic muscles at elbow joint (fig. 14. 18) is: the bicep muscle that lies in front of the humerus, its upper end has two tendons (hence the name biceps) which have their origin on the shoulder blade of pectoral girdle. The lower end of the bicep has a single tendon attached to the radius.
4. The tricep muscle that lies behind the humerus. It has its origin on the shoulder blade and humerus as three tendons, hence the name triceps. Its lower end continues as a single tendon inserted on the ulna.

The contraction of the biceps causes the forearm to be pulled upward this flexion of the forearm at the elbow is effected only when the triceps muscle relaxes at the same time as the biceps contracts. Similarly, contraction of the triceps and relaxation of the biceps bring about extension or straightening of the forearm at the elbow joint.

Principle of leverage and an elbow joint

A lever is a rigid rod pivoted at a fixed point, the fulcrum. It is able to move about this point under the action of opposing forces. Bones, especially, the long bones, are like rigid rods capable of moving against another bone at a joint (the fulcrum) under the pull of muscle.

1. A first order lever has the fulcrum situated between the load and the effort.
2. In second order levers, the load lies between the fulcrum and the effort.
3. In the case of third kind of lever, effort is between the load and the fulcrum. The principle of leverage with reference to the elbow joint (fulcrum) of the arm shows that:
4. The flexion or bending of the arm may be considered as third order lever in which effort is between fulcrum and load (fig. 14. 19).
5. While its extension or straightening represents the first order lever. In this type of lever, fulcrum lies between load and effort (fig. 14.20).

The mechanical advantage or disadvantage of the bones working as levers depends on the position of the fulcrum, the nearer the fulcrum is to the load, the easier it will be to lift the load, i. e. the greater the advantage will be.

There will be a great disadvantage if the fulcrum is very near the effort. Bones usually act across joints in such a way that bones are worked as levers with a low mechanical advantage. The muscle can contract only a short distance, but because they are attached near to the joint, the movement at the end of the limb is greatly magnified. The biceps muscles of the arm may contract only about 10 cm, but the hand will move about 60 cm. from figure 14. 19 it can be seen that a small contraction of the biceps muscle (the effort) can produce a large movement of the fore arm (the load) around the elbow joint (the fulcrum).

Functions of tendons and ligaments in relation to movement

functions of tendons -Many of the muscles that extend your toes are actually in your lower leg. The tendons from these muscles travel over the front of your ankle, across the upper surface of the foot bones, and attach to the bones of our toes. Straps of ligaments over the ankle hold these tendons in place and allow them to bend at a right angle and elevate foot and toe.

Fig 14.21 tendons and ligaments

You have already studied above that the ends of the muscles are drawn out into tendons. These are straps of connective tissues which attach each end of the muscle to the skeleton. One end of the muscle is attached to a non-moving bone of the skeleton, through tendon. The other end is attached to the movable bone close to the joint.

The relevant bones of the joints are held together by ligaments. These are strong flexible bands of connective tissues. The ligaments prevent dislocation during normal movement. They also hold tendons in place and control their direction.

 Joints; location and their movements

When two bones meet, a joint is formed. They are movable or immovable.

1. The joints between the bones of the skull are fixed. They do not show any movement. In the case of the vertebrae. Only a very limited movement can occur.
2. The ball-and-socket joints of the shoulder and the hip allow movements in three directions; forwards, backwards and sideways.
3. The hinge joints of the elbow and knee allow movement in only one plane (fig. 14.23). the surfaces at the heads of the bones which move over each other are covered with a tough, slippery and smooth cartilage. This together with a liquid formed in the joint allows friction. Free movement.

Practical works: to examine parts of human skeleton.

Examine human skeleton and answer the following questions

1. Categorize numbered bones of:

(Write numbers only)

1.             Axial skeleton. Write down

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2. Appendicular skeleton.

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2. How many ribs are attached to the vertebral column? ——————————————————–
3. Name the bone, by means of which fore arm is attached to the vertebral column.——————–
4. Encircle hinge, ball and socket joint on the given diagram of human skeleton (fig. 14.18).

Defects of skeleton system – (a) Changes in bones

Bones become thinner, weaker and less flexible with aging. This is partly because required calcium level starts decreasing at the age of 34 years. This happens to every-body to some extent. In some people it is particularly serious. In such cases it results in a condition known as osteoporosis or softening of bones.

Although whole of the skeleton is affected by osteoporosis yet hips. Wrists and vertebrae tend to be affected worst of all. Even a minor fall can result in broken bone.

Fig. 14.22 (i) ball and socket joint (ii) hinge joint

Fig. 14.23 scanned electron micrograph of brittle and spongy fractured femur from a patient with osteoporosis. The dark areas show the affected portions of the bone.

Apart from the fractures, weaker bones in the spine may result in the:

Compression in the bones and intervertebral discs. Loss of height.

Collapse of vertebrae causing bending of spine.

Note: Osteoporosis or softening of bones is most common in elderly women affecting about I in 4 over the age of 60. A balanced diet rich in calcium and regular exercise helps to keep bones strong.

(b) Changes in joints

The load bearing joints such as knees and hips particularly show changes. Like fingers joints, they become stiff and painful.

1. Osteoarthritis is a complex joint disorder (fig 14.24). As ageing progresses, the smooth tough cartilage which covers the ends of bones at joints becomes weaker and less extensive. It gradually breaks down. In extreme cases, the ends of the bones may become exposed. They start to grate against each other. This results in swelling and deformation of joints.

Note:  A less frequent type of joint degeneration known as rheumatoid arthritis is common in older people than in young people. It is an auto-immune disease in which body’s immune system attacks its own tissues. Affected joints become hot and swollen during attacks.

2. In some cases membrane of the joints become thick. The joints swell and become stiff causing pain.
3. Some times excessive use of protein may result in the deposition of uric acid at joints causing swelling and pain.

© Dislocation of joints

This is the displacement of one more bones at a joint, caused by injury and sometimes by muscular action.

A severe sickening pain, abnormal appearance of joint along with swelling shows the dislocation of joints.

Fig. 14.24 a severe case of osteoarthritis in the left knee of a man showing the swelling and deformation of joints.

Support And Movement In Man – Key Points

• Support in man; woody and non-woody parts of plant is due to skeleton; various mechanical tissues and presence of water in their parenchymatous cells besides cylindrical distribution of conducting tissues respectively.
• Movement is response shown by a part of living organism towards or away from the stimulus while locomotion refers to the movement of whole organism from one place to another under the influence of stimulus.
• Supporting tissues of woody dicotyledonous stem is due to the secondary growth or thickening. This gives rice wood and bark from the activity of vascular cambium and cork cambium respectively.
• Movement of plant body as a whole is known as tactic movement. The movement of parts of plant towards or away from the stimulus is known as positive and negative tropism. The stimulus in this case is only from one direction.
• Tropism may be of three types; Geotropism, phototropism and Hydrotropism, the response is due to stimuli, force of gravity, light and water respectively.
• Nastic movements in parts of the plants are affected by a stimulus from all directions e. g. folding and unfolding of buds or leaves.
• Geotropism and phototropism are caused by a growth regulating substance or hormone called auxin.
• Investigations proved that auxins produced by the root and shoot apices caused the growth responses below these apices.
• Locomotion in Euglena is by a single whip like flagellum while that of Volvox by simultaneous action of flagella of all the cells of colony.
• Locomotion of movement in Amoeba is brought about by the flow of cytoplasm in finger like processes, pseudopodium. Paramecium moves with the help of cilia.
• Skeleton in man is of two types: axial and appendicular. It supports the body and helps to produce movements with the help of muscles.
• Muscles play an important role in the support of skeleton and responsible for the movements of parts of parts of the body.
• Action of biceps (flexor) and triceps (extensor) brings about bending and straightening of the limb and is known as antagonistic movement of the forearm.
• Tendons attach each end of the muscle to the skeleton while the relevant bones of the joints are held together by ligaments.
• Elbow joint acts like a lever with the low mechanical advantage.
• Ball and socket joints of shoulder and hip allow movement in three directions, forward, backwards and sideways. The hinge joints of elbow and knee allow movement in only one plane.
• Defects of skeletal system may be due to changes in bones and joints in old age causing diseases osteoporosis and osteoarthritis respectively.
• Dislocation of joint is the displacement of one or more bones at a joint.