Biology SME copy 1

Key unit competence: Explain the modes of locomotion in protists, insects, fish, amphibians, birds and mammals and the                                                      structure of muscles in relation to movement.

Introductory activity 6

Observe the following living organisms movements and respond to the following questions.

1. Among the above which ones are moving? Suggest reasons why animals carry out locomotion. 

 2. Discuss all adaptations that enable those organisms to move from one place to another

6.1 Need for locomotion and non-muscular movements 

Activity 6.1

Answer the following questions: 

1. Why do different animals and humans move?

2. Describe the locomotion of Amoeba and Paramecium.

6.1.1 Need for locomotion

 Movement or displacement is the change of position from one place to another. It is done either by a body part or the whole organism (locomotion). Locomotion, also called taxis, is the movement of the whole organism from one place to another. Animals need a locomotion for a variety of reasons such as:

i. to find food, water and shelter.

ii. to find a mate

iii. to find a suitable microhabitat

iv. to escape dangerous fire or predator 

v. to avoid competition with other animals of the same or different species

vi. to avoid overcrowding 

vii. to avoid unfavourable condition.

Locomotion requires the support systems (skeletons/ skeletal systems) to which muscles are attached in most animals.

6.1.2 Non-muscular movements 

Non-muscular movements are movements which do not involve muscles. Nonmuscular locomotion or movement is identified in animals that belong into Kingdom Protoctista. In this kingdom, there is: 

i. amoeboid locomotion e.g in moeba

ii. ciliary / ciliated locomotion in paramecium

iii.flagellar locomotion in euglena

a. Amoeboid movement

Amoeboid movement is the movement demonstrated by Amoeba and some other cells that are capable of changing their shape (e.g. phagocytes). 

In this locomotion:

 i. The plasmagel is converted to plasmasol, which slides towards the front of the cell, forming a pseudopodium and propelling the cell forward.

 ii. On reaching the tip of the pseudopodium, this plasmasol is reconverted into plasmagel; at the same time the plasmagel at the rear of the cell is converted into plasmasol and streams forward, thus maintaining continuous movement. This cytoplasmic streaming requires Ca2+ ions and ATP.

 iii.Amoeboid locomotion is brought about by reversible changes in the actin filaments of the cell’s cytoskeleton. Cross-linking of these filaments by other proteins creates a three-dimensional network with gel-like properties in the plasmagel region. 

 iv. Disassembly of this network causes reversion to the sol state of plasmasol.

b. Ciliated locomotion 

 Cilia (singular: cilium) are numerous shorter hair -like appendages extending from the surface of a living cell. Some living organisms, such as Paramecium, move by beating cilia.

Flagella (singular: flagellum) are long, thread-like appendages on the surface of some living cells that are capable of either undulating or rotational movement. Cilia and flagella have similar structure except that cilia are short and many. Both cilia and flagella consist of fine tubes composed of an extension of plasma membrane. Euglenas do not have cell walls, but they have an intricate cell membrane called a pellicle. The pellicle is folded into ribbon-like ridges, each ridge supported by microtubules.

The pellicle is tough and flexible, letting euglenas crawl through mud when there is not enough water for them to swim. During cilia or flagellum locomotion, 176176 tubules slide past each other in a movement similar to that of actin and myosin filaments in skeletal muscles. Hence, Ca²+ ions and ATP are also required in the ciliary locomotion. Considering the place where organisms move, there is aquatic locomotion (swimming), terrestrial locomotion (walking, running and hopping) and aerial locomotion(flight).

Application activity 6.1

1. Classify locomotions based on:

a. Types of moving organisms

b. Place where animal move

2. Draw a diagram showing how Amoeba proteus move from one place to another.

3. You are provided with Amoeba, Paramecium, Euglena and Trypanosoma in the table below.

i. Identify those organisms based on their structures.

ii. Relate the structures of those organisms to their locomotion.

6.2 Movement and support of fish in water, mammals and annelids. 

Activity 6.2

1. Observe the freshly collected fish or the figure, to label fins and lateral line.

2. Dissect a fresh fish or observe the above given diagram. Redraw and show the swim bladder and the arrangement of muscles

3. If you have a live fish, put it in water and observe its locomotion.

4. From what you have observed, draw and label the external and internal features that contribute to fish locomotion. 

5. In your free time, use your library books and internet to find how mammals and annelids move.

6.2.1 Movement and support of fish in water 

 Fish like other aquatic animals are adapted to such habitat in terms of locomotion due to its structural adaptive features particularly skeleton which gives shape as well as muscles arrangement and swim-bladder.

Adaptive features of fish for locomotion in water 

The streamlined body shape of the fish reduces friction between water and fish. The body of fish is mostly covered by scales which overlap one another and point backwards and lie close to the body. The scales are covered by mucus which reduces the drag.

Tail or caudal fin has a large surface area, which increases the amount of water that is displaced as it provides much of the push during swimming. Paired 178178 pectoral and pelvic fins bring about downward and upward movement. With pectoral fins, the control of direction of a fish in water is possible whereas the pelvic fins bring about the balance, preventing diving and rolling. There are also unpaired dorsal and anal fins for stabilizing the fish and thus preventing it from rolling or yawing. Fish is also adapted to locomotion in water by its strong tail muscles and highly flexible vertebrate column which enables the tail to move from side to side against water. In addition, inflexible head and neck maintain forward thrush.

Internally, a fish is adapted to swimming by swim bladder and muscles. Air or gas filled sac called swim-bladder, outgrowth of the pharynx, helps a fish to change its buoyancy as it alters the gas pressure in the bladder. So that, it floats at any depth in water without using its muscles. Swim-bladder also helps fishes to maintain a density that is equal to that of the surrounding water. Muscles or myotomes / myomeres (segments or sheets of muscles separated from its neighbor by a sheet of connective tissue) enable fishes to move in water owing the shapes of muscles that are located on either side of vertebral column.

Myotomes contribute to the mechanism of swimming by its arrangements. They may be parallel, V-shape, or W-shape arranged in bundles or blocks that are separated by myosepta. Although there are such arrangements, the myoseptal organization and orientation of fibres is complex. In bony fish, myomeres are V-shaped with new myomeres added posteriorly. With those myotomes, a fish swim by passing a wave of contracting muscle from anterior to posterior. Muscles near the head of the fish contract first and contraction proceeds posteriorly down the length of the fish to the caudal fin. Thus, a fish moves forward from the contraction and relaxation (antagonistic) of myotome on either side of the body.

Undulatory swimming of the fish is also powered by the segmental body musculature of the myotomes. Myotome and myosepta orient more perpendicularly to midline to push aside. Therefore, the fish can bend laterally. With contraction muscle fibres shorten by half their length while maintaining volume. Without myosepta, but simply a series of interconnected muscle fibres, then the wave would be much dampened.

6.2.2 Movement and support of mammals 

 Mammals are vertebrate animals constituting the class Mammalia, and characterized by the presence of mammary glands which in females (and sometimes males) produce milk for feeding (nursing) their young. They include, for example, dogs and humans. Most terrestrial animals can move by walking or running. All animals living on land move due to the musculoskeletal system. The rigid nature of bone also gives a structure for muscles to pull, by their contraction, to create a movement as they act as levers. The synovial joints also allow certain movements. The support and movement differ from specimen to another. Thus, animals can walk and run on land for moving from one place to another. This is possible by their endoskeleton and its muscles. By its muscles, flexor (a muscle whose contraction bends a limb or other part of the body) and extensor (a muscle whose contraction extends or straightens a limb or other part of the body or any or a muscle that increases the angle between members of a limb, as by straightening the elbow or knee or bending the wrist or spine backward); contractions of those muscles cause the limbs act as levers for them which result to the foot being pressed downwards and backwards against the ground. For example, flexor and extensor work as illustrated below:

Humans are bipedal as they walk on two legs. When standing upright, the weight is balanced over the two legs. When a stride is taken by the right leg, the heel is raised first by the contraction of the calf muscles. As this occurs, the weight of the body is brought over the left foot which is still in contact with the ground and acting as the prop for the rest of the body.

When the right leg extends the heel is the first part of the foot to touch the ground. The weight off the body is gradually transferred from the left side to a position over the right heel and then the body continues to move forward, over the right toes, backward pressure against the ground generally being exerted through the right big toe. Like human does, a bird also can walk on ground through the movement of contractions of its leg muscles particularly flexor and extensor.

Phases of walking 

One way to think about the phases of walking is to think of what happens to each foot when we walk. In this situation, there are two phases: Stance phase and Swing phase (Figure 6.10).

 1. Stance phase is the time when the foot is on the ground. During walking, it comprises about 60% of the walking cycle and for part of the stance phase, both feet will be on the ground for a period of time. During running the stance phase is less, and there is a period in the gait cycle when both feet are off the ground (float phase).

 2. Swing Phase occurs when one foot is on the ground and one in the air. The foot that is in the air is said to be in the “Swing” phase of gait.

Stages of stance phase

 A more convenient and precise way to think about the stance phase (foot on the ground) of walking is to consider the five sub-stages that a single foot undergoes (Figure 6.10). They are as follows: Heel strike, Early flatfoot, Late flatfoot, Heel rise, and Toe off. 

a. Heel strike 

The heel strike phase starts the moment when the heel first touches the ground and lasts until the whole foot is on the ground (early flatfoot stage).

b. Early flatfoot 

The beginning of the “early flatfoot” stage is defined as the moment that the whole foot is on the ground. The end of the “early flatfoot” stage occurs when the body’s center of gravity passes over top of the foot. The body’s center of gravity is located approximately in the pelvic area in front of the lower spine, when we stand and walk. The main purpose of the “early flatfoot” stage is to allow the foot to serve as a shock absorber, helping to cushion the force of the body weight landing on the foot. 

c. Late flatfoot 

Once the body’s center of gravity has passed in front of the neutral position, a person is said to be in the late flatfoot stage. The “late flatfoot” stage of gait ends when the heel lifts off the ground. During the “late flatfoot” phase of gait, the foot needs to go from being a flexible shock absorber to be a rigid lever that can serve to propel the body forward.

d. Heel rise 

As the name suggests, the heel rise phase begins when the heel begins to leave the ground. During this phase, the foot functions as a rigid lever to move the body forward. During this phase of walking, the forces that go through the foot are quite significant: often 2-3x a person’s body weight. This is because the foot creates a lever arm (centered on the ankle), which serves to magnify body weight forces. Given these high forces and considering that the average human takes 3000-5000 steps per day (an active person commonly takes 10,000 steps/day), it is not surprising that the foot can easily develop chronic repetitive stress-related problems, such as metatarsalgia, bunions, posterior tibial tendon dysfunction, peroneal tendonitis, and sesamoiditis. 

e. Toe off 

The toe off stage of gait begins as the toes leaves the ground. This represents the start of the swing phase. 

f. Running

 The defining difference between walking and running is that when running, there is a period of time both feet are off the ground (the “float” phase). Also, because running is associated with greater speeds, the forces that go through the foot when it lands can be substantially greater than during walking.

6.2.3. Support and locomotion in annelids

Annelids such as earthworms move by crawling.

Earthworms are organisms having hydrostatic skeleton with soft-bodied animals due to fluid secreted within the body and surrounded by the muscles of the body wall. They are capable to move by aid of their muscles. These muscles are not attached to any structures and thus can pull against each other. The combined effect of muscle contraction and fluid pressure serves to maintain the shape and form of the animal. Generally, there are two muscle layers, longitudinal in which muscle fibres are arranged parallel to the long axis from one end of a segment to another and circular with muscle fibres arranged in concentric circles to the circumference of the worm.

When those muscles act antagonistically against each other, locomotion is achieved. The fluid which acts as presssurisable hydrostatic skeleton contained in body cavity or coelom presses against the muscles which in turn are able to contract against the fluid. Earthworm movement is also helped by bristles like setae or called chaetae (hair like structures on ventral surfaces) which anchor the worms to the substrate. Contraction of the circular muscles makes the worm thinner, but because liquid is essentially incompressible (and so maintains a constant volume) and the increase in pressure forces the liquid outwards,stretching the worm, so the worm becomes longer and thinner. Contraction of the longitudinal fibres shortens the worm, former the coelomic liquid out to the sides and making the worm fatter. If the body is segmented, then such pressure is localized, and only certain segments will move or change shape.

1. Categorize the main muscles that contribute to the locomotion in mammals?

2. Draw an earthworm’s muscles that contribute to its locomotion.

3. Observe the following figure illustrating different instabilities of a fish in water and answer the following questions.

a. Identify each type of instability.

b. Interpret those instabilities.

6.3 Movement through air by birds and insects

Activity 6.3

You are provided with the bird (A) flying in the atmosphere and flying insect (B).

1. Search, using internet and books, Identify the adaptations that enable those organisms to fly.

2. Compare the flight of birds and flight of insects.

6.3.1 Movement through air by birds 

Bird can fly either by flapping their wings or gliding by spreading its wings. Like in animals moving on land, locomotion by flying in birds is brought about by the action of flexor and extensor muscles as well some other structures given diagram below like pectoralis major, pectoralis minor and keel of sternum.

Based on the diagram below , wings move down by the contraction of pectoralis major and then move up under the contraction of pectoralis minor.

Adaptations for flight in birds 

 i. Modification of the forelimbs to form wings to provide a large surface area for movement in air. 

ii. Presence of large pectoral muscles, the pectoralis major and minor, which moves wings.

 iii. A light skeleton made up of hollow and mainly small bones which can be easily moved in the air.

 iv. A rigid skeleton made up of fused bones with a deep keel like extension of the sternum which provides a large surface area for the attachment of flight muscles.

 v. An efficient breathing system with air sacs attached to the lungs necessary to provide oxygen for respiration and to remove the resulting carbon dioxide.

vi. A high metabolic rate for providing the high amount of energy required. 

vii. An efficient circulatory system necessary for transporting both the nutrients and respiratory gases at speed related with the body needs. 

viii. A high red blood cell count for efficient oxygen transport. 

ix. A keen eyesight to enable them to judge distances correctly especially on landing. 

x. A streamlined shape to reduce air resistance and allow smooth movement in the air. 

xi. Ability to fold the legs away during flight so as not to cause any unnecessary friction with the air

6.3.2 Movement through air by insects

The pterygotes are insects that either have wings or evolved from winged ancestors. The wings are born, like the legs on the thorax. The insect body can be divided into head, thorax and abdomen. The thorax consists of three segments, the prothoracic segment nearest the head, the middle mesothoracic segment and the hindmost metathoracic segment. The last two segments, the mesothoracic and metathoracic, each usually bear one pair of wings. These wings are extensions of the cuticular plates of the thorax (the dorsal plate or tergite and the side-plates pleurites or pleura). The structure of insect flight muscles is shown by the following figure.

Each thoracic segment is encased in four groups of cuticular plates: the notum (tergum) on the back, the sternum on the front and the pleura (singular pleuron) on the sides. 

 These four regions of the cutcicle are made up of cuticular plates, called respectably the tergites, sternites and pleurites, and softer artioculating membranes that connect the regions together. The flight muscles attach to certain of these plates or sclerites. 

There are two sets of flight muscles: direct and indirect muscles.

The direct muscles attach to the wing base, or more specifically to sclerites (cuticular plates of the exoskeleton) in the pleura (the groups of cuticular plates making up the sides of the insect) that then attach to the wing base. The base of the wing attaches to the notum and pleuron. The notum (or tergum) is the plate that forms the insect’s back and the pleuron its side.

Direct muscles attach to sclerites in the pleura at both ends. There are two paired sets of these muscles: the basalar muscles and the subalar muscles.

Power for the wing’s upstroke is generated by contraction of dorsal-ventral muscles (also called tergosternal muscles). These are called “indirect flight muscles” because they have no direct contact with the wings. They stretch from the notum to the sternum. When they contract, they pull the notum downward relative to the fulcrum point and force the wing tips up.

During flight, upstroke and downstroke muscles must contract in alternating sequence. There are two different mechanisms for controlling this muscle action, synchronous (neurogenic) and asynchronous (myogenic):

i. Insects with synchronous control have neurogenic flight muscles, meaning that each contraction is triggered by a separate nerve impulse. 

ii. Insects with asynchronous control depend almost entirely on indirect flight muscles for upstroke (dorsal-ventrals) and downstroke (dorsal-longitudinals). These muscles have developed myogenic properties, that is, they contract spontaneously if stretched beyond a certain threshold. When the nervous system sends a start signal, the dorsal-longitudinal and dorsal-ventral muscles begin contracting autonomously, each in response to stretching by the other. Contractions continue until the muscles receive a “stop” signal from the nervous system.

Brief, during the downstroke, the tergo-sternal muscles relax as the dorsal longitudinals contract, depressing the wing and generating lift as the wings move forwards and downwards. Basalar muscles contract, as the subalar relax, tilting the leading edge of the wing downwards (to prevent stalling).During the upstroke, the dorsal longitudinal muscles relax as the tergo-sternals contract, lowering the notum and raising the wings during the recovering stroke as the wings move backwards and upwards. subalar muscle contract as basalar muscles relax, raising the leading edge of the wing.

Application activity 6.3

1. A winged insect was taken from your environment and its wings were removed. Summarize the effect of this action to the flight of that insect.

2. Relate the downstroke to the flight of insect and birds

6.4 Comparison of jumping movements of grasshoppers and toads 

 Activity 6.4

Use a collecting net to catch a grasshopper and toad from school compound. Put them down on cemented ground for observing them very carefully when they make a jump and then answer to the following: 

1. Identify and describe anatomic structures that enable grasshoppers to jump. 

2. Illustrate how legs’ muscles behave when they are resting and or jumping.

a. Hopping locomotion of grasshopper

 Insects have a skeleton which is on the outside of the body called an exoskeleton. They can walk on the land, but they are mostly adapted to hopping owing to their muscles which are inside the hard shell as well as skeleton system. The muscles which make them capable to move are flexors and extensors which are antagonists, attached to internal surface of exoskeleton and the rear or back legs of a grasshopper which are long and muscular, adapted to hopping. Additionally, there are two main muscles:

i. the extensor tibiae muscle which contracts to extends the leg

ii. the flexor tibiae muscle which contracts to flex the leg. 

Those muscles pull on tendons which are attached to the tibia on either side of the joint pivot.

As illustrated above, flexor muscles bend a joint whereas extensor ones straighten it. The flexor muscle contracts contracts and the lower leg is pulled towards the body. Thus, the hind leg is folded in a Z shape and ready for jumping. Being in resting or sitting position, the extensor muscle contracts which allow the legs jerk or move very quickly backwards propelling the grasshopper.

i. The hind legs are folded in the shape of Z in the position at rest (flexor muscles contract).

ii. Extensor muscles contract. The legs of the grasshopper jerk backwards.

iii. The grasshopper propels forward and upward into the air.

b. Jumping of amphibians

On land, frogs and toads move by hopping. When a frog is at rest, the hind legs are folded up in the shape of a letter Z. When it hops, the legs are quickly straightened out, lifting the animal of the ground. The forelimbs are used as shock absorbers on landing and they also prop up (give support) the front end of the body when the animal is at rest.

Following are the stages of jumping in a frog

i. Long hind legs are folded in the shape of Z when the frog prepares to jump.

ii. Hind legs become straight when the frog jumps.

iii. Forelimbs stretched to outside when the frog prepares to land.

Application activity 6.4

1. Develop a table comparing the hopping of grasshopper and that of the from a toad

2. Observe the following grasshopper and answer the following questions.

Label the structures A and B.

3. Draw a leg of grasshopper and the one of toad when are jumping.

6.5 Types of muscles 

Activity 6.5

Aim: Dissection of a frog / toad heart and observation of myogenic contraction.

Materials required

Dissection pan with 4 needles, 20 ml of physiological liquid (Ringer’s solution), plastic eyedroppers,

suture needle with thread attached, razor blade, magnifying hand lens, pins, chloroform, cotton wool, frog or toad, bell jar, forceps, glass beaker, gloves, and water.

Procedure :

Dissecting frog heart and observe myogenic contraction.

- Collect a living frog or toad from the nearest swamp

- Prepare 20ml of Ringer’s liquid in a glass beaker

- Put the cotton wool imbibed of 10 ml of chloroform in the bell jar

- Put your frog in the bell jar for 5 minutes, then remove it

- Lay your frog dorsally and fix its four limbs with pins on the dissection dish

- Carry out the longitudinal section from the abdomen to the chest using surgical blade (razor blade) or scissor.

- Locate the pumping heart between the two lungs

- Use the suture needle with thread attached to tie blood vessels connected to heart

- Using the forceps and the surgical blade, remove gently the beating heart and put it in the beaker containing the Ringer’s liquid

- Write down your observation in the next 5 minutes.

- Wash your hand after experiment.

4. Use models or computer aided simulations to observe the relationship between muscles, joints and musculo-skeletal attachments of the antagonistic muscles of fish, birds, frogs and rabbits.

There are 3 types of muscle: skeletal, smooth, and cardiac.

a. Skeletal Muscle 

Skeletal muscle, as its name implies, is the muscle attached to the skeleton. It is also called striated muscle. The contraction of skeletal muscle is under voluntary control. These muscles are mainly responsible for movement of the body. Other purposes are posture maintenance, support of the joints, and heat production. While its contraction is fast and strong, skeletal muscle tires easily.

Antagonistic skeletal muscles Antagonistic muscles are pairs of muscles. The action of one member is opposite to that of the other member. Muscles can contract but they do not have the ability to lengthen (stretch) themselves. They are arranged in pairs such that after one muscle or muscle group contracts, a skeleton transfer the movement to stretch another muscle or muscle group. The pairs of muscles that stretch each other are said to be antagonistic.

 The biceps and triceps muscles of the arm are an example of an antagonistic pair. Contraction of the biceps moves the arm toward the body and stretches the triceps. Contraction of the triceps extends the arm and stretches the biceps. In this example the bicep is said to be the flexor while the triceps is the extensor. Extensors are not as strong as flexors.

b. Smooth muscle 

Smooth muscle is found in the walls of all the hollow organs of the body (except the heart). Its contraction reduces the size of these structures. Thus it regulates the flow of blood in the arteries, moves your breakfast along through your gastrointestinal tract, expels urine from your urinary bladder, sends babies out into the world from the uterus, and regulates the flow of air through the lungs. The contraction of smooth muscle is not under voluntary control. It is called involuntary muscle. It contracts slowly and is slow to tire.

c. Cardiac muscle Your heart is made of cardiac muscle. 

This type of muscle only exists in your heart. Unlike other types of muscle, cardiac muscle never gets tired. It works 193 automatically and constantly without ever pausing to rest. Cardiac muscle contracts to squeeze blood out of your heart and relaxes to fill your heart with blood.

Application activity 6.5

1. Observe the following muscles and answer the following questions

Identify the muscles X and Z.

 2. A nerve impulse moves from the central nervous system via the motor neuron and causes the muscle contraction. Link this contraction to the properties of this muscle.

6.6 Ultrastructure and functioning of striated muscle 

Activity 6.6: Research Activity

1. Use the books from the school library and search information from about the ultrastructure and functioning of striated muscle. 

2. Observe other biceps muscles and write your observations (shortening and thickening of the antagonistic muscles).

3. Research, using internet and library books, the structure of the motor end plate. 

4. Use of computer aided simulations to demonstrate the structure and functioning of the sarcomere during muscle contraction with reference to sliding filament theory. 

5. Use computer aided simulations to demonstrate the laws of muscle contraction (all or nothing, temporal summation and muscle fibre recruitment). 

6.6.1 Ultrastructure of striated muscle

The striated appearance of skeletal muscle fibres arises due to the organization of two contractile proteins or myofilaments (actin filaments and myosin ). 

The functional unit of contraction in a skeletal muscle fibre is the sarcomere, which runs from Z line to Z line. A sarcomere is broken down into a number of sections:

- Z line – Where the actin filaments are anchored.

- M line – Where the myosin filaments are anchored.

- I band – Contains only actin filaments.

- A band – The length of a myosin filament, may contain overlapping actin filaments.

- H zone – Contains only myosin filaments.

A useful acronym is MHAZI – the M line is inside the H zone which is inside the A band, whilst the Z line is inside the I band.

Based on their fibrous and dense tissues, their main function of striated muscles is movement through continuous contraction and relaxation. These muscles also help in; maintaining posture, stabilizing skeletal joints and producing body heat.

6.6.2 Functioning of striated muscle in contraction and relaxation

The excitability or the power of responding to an adequate stimulus is an innate property of the muscle. When a brief stimulus is given, the muscle contracts and this is followed by a wave of relaxation. This phenomenon is called a muscle twitch.

The Figure 11.21 shows a typical muscle curve of a skeletal muscle in response to single stimulation. The muscle curve can be recorded with the help of a kymograph. The curve indicates three phases: the latent phase, the contraction phase and the relaxation phase. The period between the stimulus and beginning of contraction is called the latent phase which lasts for about 0.01second. During this period chemical changes take place as a result of the stimulus. Latent period is required for traversing the excitation along the nerve and the neuromuscular junctions. The duration of the latent period varies with the species and depends on the type of muscle, temperature and condition of the muscle.

The contraction phase during which the muscle actually contracts lasts for about 0.04 second incase of frog muscle. Shortening of the muscle takes place due to chemical events which will be described in some details later. The third phase or the relaxation phase lasts for about 0.05 sec. The total time taken by a single muscle contraction is about 0.1 sec which varies with the temperature.

At low temperature contractions are prolonged, whereas with rising temperature the duration of contractions becomes shorter

a. Muscle twitch, summation, and tetanus

 A single action potential to the muscle fiber of a motor unit produces a muscle twitch, a rapid and succession of two or more action potentials is termed summation. At high stimulation frequencies, the overlapping twitches sum to one strong, steady contraction called tetanus. 

If the impulses are applied to a muscle in rapid succession through several motor units, one twitch will not have completely ended before the next begins. Since the muscle is already in a partially contracted state when the second twitch begins, the degree of muscle shortening in the second contraction will be slightly greater than the shortening that occurs with a single twitch. There are two types of twitch which are slow-twitch muscles and fast-twitch fibers.

- Slow-twitch are slower-contracting fibers but they are very efficient at using oxygen to create energy without lactic acid build-up. These fibers are used for high-endurance events like marathons. 

- Fast-twitch fibers are white fibers, that contract very quickly making them very strong and explosive but they also tire out very easily. The additional shortening due to the rapid succession of two or more action potentials is termed summation. At high stimulation frequencies, the overlapping twitches sum to one strong, steady contraction called tetanus.

This figure compares the tension developed in a muscle fiber in response to a single action potential in a motor neuron, a pair of action potentials, and a series of action potentials. The dashed lines show the tension that would have developed if only the first action potential had occurred. Motor unit recruitment refers to the activation of additional motor units to accomplish an increase in contractile strength in a muscle. A motor unit consists of one motor neuron and all of the muscle fibers it stimulates.

b. Tetanic contractions 

During normal activity such as locomotion, muscular contractions are not merely twitches lasting for a second or a fraction of it. They are sustained for a longer period during continued activity and exhibit compound or tetanic contractions. 

 This can be experimentally demonstrated by applying a number of stimuli to a muscle-nerve preparation in rapid succession with little interval between successive stimuli, the resulting contractions tend to fuse to give a maximum contraction. This sustained contraction is called complete tetanus which, however, varies with the kind of muscle and its condition. 

 If repetitive stimuli are applied to muscle with long periods of interval, the individual contractions can be seen because of little relaxation. This condition is known as incomplete tetanus.

More interesting information is available about the tetanus. When a muscle is in tetany, a musical note is produced by it which can be heard with the help of a stethoscope. The pitch of the note is indicative of the vibrations that are produced at a rate corresponding to the rate of application of stimuli. Most of the voluntary contractions are of tetanus types which are produced by a series of nerve impulses arriving in the muscle from the central nervous system

6.6.3. Neuromuscular junction 

This is a special kind of synapse where a motor nerve and muscle tissue meet. The membrane of the muscle fiber, the sarcolemma is very folded in this region and forms a structure known as an end plate. Electron microscopy shows us that the structure of the neuromuscular junction is remarkably similar to that of any other synapses. 

 The end of the motor nerve is full of mitochondria and synaptic vesicles which contain acetylcholine/neurotransmitter substances.

 It appears that when an impulse arrives at the end of the motor neuron, it increases permeability of the pre-synaptic membrane to calcium ions in the synaptic cleft. The electrical impulse gets changed into a chemical message and gets stored into the synaptic vesicles. The calcium ions then push the vesicles to fuse with the presynaptic membrane thus discharging their neurotransmitter substances by exocytosis. The neurotransmitter then diffuses through the synaptic cleft and get attached onto receptor sites on the sarcolemma. This causes the sodium gated channels to open thus causing a generator potential to be setup in the sarcolemma. If it reaches the threshold, an impulse is fired into the muscle fiber.

6.6.4. Laws of muscle contraction 

 The all-or-none law is the principle that the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential, the nerve or muscle fibre will give a complete response; otherwise, there is no response. It was first established by the American physiologist Henry Pickering Bowditch in 1871 for the contraction of heart muscle. 

A muscle contraction occurs when a muscle fiber generates tension through the movement of actin and myosin. The sarcomere is the functional unit of muscle contraction; it reaches from one Z-line to the next. In a relaxed muscle, the actin (thin filament) and myosin (thick filament) overlap. 

In a muscle contraction, the filaments slide past each other, shortening the sarcomere. This model of contraction is called the sliding filament mechanism. Sliding filament theory states that “ the actin filaments slide past myosin filaments because myosin filaments have cross-bridges that pull actin filaments inward, toward their Z line”

Table 6.1: Main components used in muscle contraction

Each muscle fiber contains cellular proteins and hundreds or thousands of myofibrils. Each myofibril is a long, cylindrical organelle that is made up of two types of protein filaments: actin and myosin. The actin filament is thin and threadlike; the thin actin filaments are anchored to structures called Z lines. The region from one Z line to the next makes up one sarcomere and the myosin filament is thicker. Myosin has a head region that uses energy from ATP to walk along the actin thin filament.

The overlapping arrangement of actin and myosin filaments gives skeletal muscle its striated appearance. When each end of the myosin thick filament moves along the actin filament, the two actin filaments at opposite sides of the sarcomere are drawn closer together and the sarcomere shortens. When a muscle fiber contracts, all sarcomeres contract at the same time, which pulls on the fiber ends.

When each end of the myosin thick filament moves along the actin filament, the two actin filaments at opposite sides of the sarcomere are drawn closer together and the sarcomere shortens. In the contacted sarcomere, the A bands do not change in length, but the I bands shorten and the H zone disappears. This behaviour can be explained by the sliding filament model of muscle contraction.

Stages of voluntary muscle contraction under control of the nervous system: 

1. A nerve impulse (action potential or wave of depolarization) travelling along the motor neuron reaches the motor end plate. 

2. Acetylcholine (Ach) is released into the synaptic cleft at the end plate, diffusing to the sarcolemma, and combines with the receptor sites (receptor proteins) of the muscle fiber. 

3. When the threshold value of the generator potential is reached, an action potential is created in the muscle fiber. (Ach in the cleft region is then hydrolyzed and then the products i.e. acetic acid and choline are reabsorbed into the motor end plate). 

4. The action potential is conducted to all microfibrils of the muscle fiber by the system of the transverse tubules (T tubules), and spread to the sarcoplasmic reticulum throughout the muscle fiber.

 5. Calcium ions (Ca2+) are released from the sarcoplasmic reticulum and bind to the blocking molecules of the actin filament, exposing the binding sites (ATP is involved in this movement).

6. The ‘heads’ of the cross-bridging myosin molecules attach to the newly exposed binding sites on the actin filaments. Release of energy by ATP hydrolysis accompanies cross-bridge formation. 

7. As a result, the shape of the myosin bridge changes. The ‘bending’ or ‘rowing’ action results. This is the power stroke. The fin filaments (actin molecules) are moved towards the center of the sarcomeres, producing muscle cell contraction. 

8. Fresh ATP attaches to the myosin head, releasing it from the binding site, and causing the cross-bridge myosin to straighten (it becomes ‘cocked’ for repeated movement). 

9. Myosin heads become attached further along the actin chain and repeats the movement sequence (referred to as a ‘ratchet mechanism’). 

10. When nervous stimulation of the sarcomere ceases, calcium ions are rapidly pumped back into the sarcoplasmic reticulum, and the calcium ions concentration falls below the threshold for contraction activity. The binding sites on the actin filaments are blocked again.

How motor unit summation develops muscle tension 

A skeletal muscle is an organ composed of multiple muscle cells or fibers, just like any organ is made up of a whole bunch of cells. These fibers are arranged in motor units, each of which is composed of a single motor neuron and all the muscle fibers that that motor neuron innervates. Each motor unit contracts in an all-or-none fashion. In other words, if the motor neuron is excited, it will stimulate all of the muscle fibers to contract - that is, all of the muscle fibers within that particular motor unit.

Application activity 6.6

1. You are provided with the following neuromuscular junction.

a. Identify the structures A, B and C.

b. Summarize the functions of B and C.

2. Draw a well labeled diagram of sliding filament model of muscular contraction

6.7 Types of joints

ACTIVITY 6.7

Discuss the following types of joints. Present your findings.

A joint is the junction between two or more bones. There are three major types of joints:

6.6.1 Immovable or fused joints or sutures 

These joints include the skull, sacrum, pelvis, and coccyx. As the name suggests, these joints are points where joints fuse or grow together. The place where they grow together is called the suture. These joints provide strength, support, and protection.

6.6.2 Slightly moveable joints 

These joints are located between the vertebrae of the upper spine. There is cartilage within the joints. They help pad and protect the bones. The bones are held together by ligaments. The ligaments are tightly bound and limit the movement of the bones. This protects the spinal cord.

6.6.3 Freely moveable or synovial joints 

At these joints the ends of the bones are covered with cartilage and there is a cavity that separates the bones. The bones are held in place by ligaments which stop the bones from moving too much. In addition to the ligaments the two bones are joined together by sleeve-like capsule. The capsule encloses the synovial cavity. The outer layer of the capsule is composed of ligaments. The inner layer of the capsule is the synovial membrane. The synovial membrane secretes the lubricating synovial fluid.

Lubrication is essential to prevent frictional wear and tear. The cartilage at the contact ends of the bones also reduces friction. The cartilage pads also act as shock absorbers against mechanical damage.

There are four classes of synovial joints

 i. Gliding: The bones of these joints move across each other, back-andforth and side-to-side. Examples are between the carpals of the wrist and tarsals of the ankle. 

ii. Pivot: These joints allow a turning movement. Examples are between the first and second vertebras when turning the head, between the ulna and the radius of the lower arm when turning the palm of the hand up or down.

 iii. Hinge: These joints allow movement in one plane during flexion and extension. They act, as the name implies, like the hinge of a door. Examples are bending the elbow or knee. 

 iv. Ball and Socket: This type of joint permits movement in three planes, i.e., in all directions. Examples are the shoulder and hip joints.

Table 6.2: Summary of the types of joints

Application activity 6.7

1. Associate the terms of column A and B

Skills lab 6

Aim: To get money and biological skills from bred fish.

Materials : pond, male fish, small capital, fish dissecting kit.

Procedure

As a student teacher, you have got a lot of information about fish locomotion. 

Do the following activities for getting more skills and money:

1. In one of fields of your family or school, make a fish pond.

2. Use a tube or make a canal on land using a hoe to orient water in that pond.

3. Request or buy living fishes from other person’s pond and place them in your pond.

4. Place different fish nutrients in your pond.your pond.

5. After those fish reproduction, take some of them and do the following practicals for becoming more skilled:

a. Place one of those fishes in a container such as a bucket, observe carefully the fish structure and locomotion and write a comprehensive account about them.

b. Dissect one of those fishes to identify all internal fish organs such as swimbladder contributing to their locomotion .

c. Sell some of those fishes to get money.

Portfolio Report

 i. Write your skills lab project implementation report focusing on how this skill lab has helped you to generate money and new biological skills, submit it to your teacher.

 ii. Bring a product ( bred fish) and present it to the whole class.

End unit assessment 6

1. What is the basic reason for the fact that animals show locomotion 

whereas plants do not?

2. Briefly explain the role of each of the following in a mammalian locomotion:

a. Bones

b. Joints

c. muscles

3. What is meant by endoskeleton?

4. Outline the main functions of the endoskeleton.

5. Explain the various types synovial of joints.

6. In relation to antagonistic muscles, explain how it is possible to lift and lower an object with your hands.

7. Outline the functions of fused joints and give an example.

8. What are the functions of muscle tissue?

9. What is the meaning of MHAZI in skeletal muscle fibres?

10. Explain what happened in refractory period in the sliding filament theory of muscle contraction.

11. Explain what happened when motor impulse reaches the end plate, the vesicles release acetylcholine into the synaptic cleft of the end plate.

12. Draw a well labeled diagram of human skeleton.

13. Describe ways of locomotion in Amoeba, Paramecium, Euglena and in Trypanosoma

14. Produce a cartoon showing different adaptive features of fish for aquatic locomotion.