Control and Coordination

1.0Introduction

All living organisms including plants and animals respond and react to environmental factors or stimuli. There is a necessity to develop some system for control and coordination of various body organs. To carry out a simple function such as picking up an object from the ground there has to be coordination of the eyes, hands, legs and the vertebral column. The eyes have to focus on the object, the hands have to pick it up and grasp it, the legs have to bend

"The nervous system, in coordination with the endocrine system communicates, integrates and coordinates the various organs and organ systems in the body." and so does the back bone (vertebral column). All these actions have to be coordinated in such a manner that they follow a particular sequence and the action is completed. A similar mechanism is also needed for internal functions of the body. The individuals also have to adjust to the changing conditions around them and vary their responses. At the same time, the internal conditions of the body should be maintained constant. There are two modes of control and coordination, chemical and nervous. Plant do not have a nervous system. They possess only chemical control and coordination. Animals have both chemical and nervous control and coordination. The two constitute neuroendocrine system.

Coordination in Animals

Animals have the ability of locomotion. This ability probably developed as they have to search for food. Since they move from one place to another, the animals have to continuously encounter changes in their environment. In order to maintain a steady state within the body, all animals should be able to perceive these changes and adapt to them.

With increasing complexity in their structure, the number and types of cells in the animal body increased. Thus, it became necessary to have some coordination mechanism. Two systems have been developed for better control and coordination of the various activities of the organisms. These systems are the Nervous System and the Endocrine System.

Nervous System

The nervous system in vertebrates is highly evolved. It is the control system for all our actions, thinking and behaviour. It is concerned with receiving stimuli from the external or internal environment of the body, interpreting these stimuli and producing the appropriate response to these stimuli. To achieve this, highly specialized cells are required which can receive the message and conduct them to the chief centres of nervous system where they are to be interpreted and then returned to the relevant part of the body. Neurons or nerve cells are the structural and functional unit of nervous system.

Each neuron has following two parts: (i) Cyton or cell body : Contains a central nucleus and cytoplasm with characteristic deeply stained particles called Nissl's granules [i.e. clumps of ribosomes]. (ii) Cell processes : These are of two types (a) Dendrites: These may be one to many, generally short and branched cytoplasmic processes. Dendrites are afferent processes because they receive impulse from receptor or other neuron and bring it to cyton. (b) Axon: It is a single generally long efferent process which conducts impulse away from cyton to other neuron. The longest cell in the body is neuron because axons can be more than one metre long. Axon has uniform thickness, but it has terminal thin branches called telodendria. Terminal end buttons or synaptic knobs occur at the end of telodendria.

At the end of axon of sensory neuron, the electrical impulse releases tiny amount of a chemical substance in the synapse. This chemical substance crosses the gap and starts similar electrical impulse on the dendrite of next neuron. This process continues till the electrical impulse reach the relay neurons in brain and spinal cord. These relay neurons connect in a similar way from the brain and spinal cord to the effector muscles and glands via motor neuron.

Why synapse acts as a one-way valve?

• Explanation: Synapses act like one-way valves. This is because the chemical substance is present at only one side of the gap i.e. neurotransmitters are released by axon endings only and received by dendrites of other neurons. In this way synapses ensure that nerve impulse travels only in one direction.

Neuromuscular Junction

A neuromuscular junction is a place in the body where the axons of motor nerves meet the muscle, thus transmitting message from the brain or spinal cord which causes the muscle to contract and relax.

How does a muscle cell move?

• Explanation: Muscle cells move by changing their shape so that they shorten. Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses. When this happens, new arrangements of these proteins give the muscle cells a shorter form.

2.0Reflex Action

A reflex action is a quick involuntary action in response to an external or internal stimulus, generally without involvement of the brain. E.g. A tap on the knee results in a spontaneous withdrawal i.e. a knee-jerk. Similarly, when we touch a hot object, we spontaneously withdraw our hand.

Reflex action are of two types: (1) Unconditioned reflex - which are inborn and inherited. e.g. sneezing and coughing (2) Conditioned reflex - which are learned reflexes. e.g. cycling and salivation on smelling one's favourite food.

Significance of Reflex Action

Act as an alarm which indicate about some unnatural incidents that are going to happen. Quick and sudden reflex protect us from dangers and injuries.

3.0Reflex Arc

A reflex arc is the shortest route that can be taken by an impulse from receptor to an effector.

The basic components of reflex arc are a receptor, a sensory neuron, a centre, a motor neuron and an effector. Components of reflex arc are -

(1) Receptor: The dendrite of sensory neuron receives stimulus and initiates a nerve impulse.

(2) Sensory neuron: The nerve impulse passes from the dendrites to the axon terminal branches of the sensory neuron in the spinal cord.

(3) Centre: It is the region in the spinal cord or brain where the incoming sensory impulse generates an outgoing motor impulse. Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.

(4) Motor neuron: It transmits the impulse generated by the sensory neuron in the centre to the effector organ of the body that will respond, such as a muscle or gland.

(5) Effector: It is the organ of the body that responds to motor nerve impulse.

What is the role of the brain in reflex action? The reflexes which involve only the spinal cord are called spinal reflexes. The spinal reflexes are produced in the spinal cord, but the message of reflex action taken also goes on to reach the brain where the thinking process occurs. Some reflex arcs involve the brain, rather than the spinal cord only. They are called cerebral reflexes. Closing of eyes when exposed to flash of light and salivation at the sight of tempting food are the examples of cerebral reflexes.

What reflexes are shown by our eyes to the changes in light intensity?

• Explanation: As the person enters a dark room from a brightly lit one, the pupil dilates to allow more light to enter the eye. On the contrary, when the person is exposed to light on leaving a dark room, the pupil constricts and the eyelids close partially to allow less light to enter into the eye. Note:- The difference between a reflex action and walking.

Reflex action:

• Reflex action is the immediate and involuntary action.
• It is regulated by the spinal cord.
• It occurs in a fraction of seconds.

Walking:

• Walking is a voluntary action which is under our control.
• It is controlled by brain.
• It takes longer time.

Animal perform three type of actions. These are reflex action, involuntary action (without will) and voluntary actions (with will).

The Vertebrate Nervous System Consists of Two Parts :

(1) Central Nervous System(2) Peripheral Nervous System

4.0Central Nervous System

The central nervous system consists of two parts - (i) upper large brain situated in the head (ii) the lower long and narrow spinal cord situated in the neck and trunk. It is continuation of brain downwards.

Brain

It is the part of the central nervous system that is present in the

Fore Brain

It is made up of cerebrum, hypothalamus and many other parts.

(a) Cerebrum It is the largest and main thinking part of the brain and is made up of two hemispheres called the cerebral hemispheres. The cerebrum has sensory areas, association areas and motor areas. Sensory areas receive the messages. There are different areas for hearing, smell, sight and so on in cerebrum. There are separate areas of association where this sensory information is interpreted by putting it together with information from the other receptors as well as with information that is already stored in the brain. The motor areas are responsible of the action of the voluntary muscles. The Cerebrum is also responsible for intelligence, memory, consciousness and will power.

(b) Hypothalamus Hypothalamus is an important region of the brain. It receives the taste and smell impulses, coordinates message from the autonomous nervous system, controls the heart rate, blood pressure, body temperature. It also forms an axis with the pituitary which is the main link between the nervous and the endocrine systems. It also has centres that control emotions, hunger, thirst, fatigue, sleep, body temperature and sweating. It secretes neurohormones which regulate the secretion of anterior lobe of pituitary.

Mid Brain

It is a small portion of the brain that serves as a relay centre for sensory information from the eyes and ears to the cerebrum. It also controls the reflex movements of the ears and eyes muscles. It provides a passage for the different neurons going in and coming out of the cerebrum.

Hind Brain

It consists of cerebellum, pons varolii and medulla oblongata.

(a) Cerebellum The cerebellum is second largest part of brain. It has very convoluted surface in order to provide the additional space for many more neurons. It is responsible for maintaining the balance while walking, swimming, riding, etc. It is also responsible for precision and the fine control of the voluntary movements. For example, we can do actions like eating while talking or listening. The action of eating, while talking is done automatically. This is controlled by the cerebellum. Alcohol effects the cerebellum.

(b) Pons Pons literally means bridge. It is hidden as it is well protected because of its importance. It has the breathing centre. It consists of fibre tracts that interconnect different regions of the brain.

(c) Medulla oblongata Medulla oblongata is the posterior most part of the brain which lies below the cerebellum. It controls activities such as sneezing, coughing, swallowing, salivation and vomiting. It contains centre which control respiration and cardiovascular reflexes and gastric secretion. It also controls rate of heart beat and expansion and contraction of blood vessels to regulate blood pressure.

Spinal cord

It is a collection of nervous tissue running along the back bone. It is protected by the vertebral column.

The functions of the spinal cord are: Coordinating spinal reflexes. It conducts sensory and motor impulse to and from the brain via

How is the nervous tissue protected from any damage?

• Explanation: External injuries are overcome by the central nervous system through protective shields. The spinal cord is encased in the vertebral column, and it is also surrounded by a fluid known as cerebrospinal fluid. The same fluid is also present in the cranium around the brain. In addition, the brain and spinal cord are guarded by layers of tissue described as meninges, namely duramater, arachnoid and piamater from outside to inside.

5.0Peripheral Nervous System

All the nerves arising from brain and spinal cord are included in peripheral nervous system. It is divided into a somatic neural system and autonomic neural system. Somatic nervous system consists of two sets of nerves:

(i) Cranial nerves Nerves arising from the brain are called cranial nerves. Nerves may be sensory, motor or mixed. 12 pairs of cranial nerves are found in humans.

(ii) Spinal Nerves Nerves arising from spinal cord are called spinal nerves. Each spinal nerve is of mixed type. In humans 31 pairs of spinal nerves are found.

We have learned in a previous class the pituitary gland is called master gland because it produces hormones that control other glands. Many glands like thyroid gland secrete their hormones when they receive orders from the pituitary gland through its hormones.

6.0Endocrine System

A group of endocrine glands which produce various hormones form the endocrine system. In addition to the nervous system, the endocrine system also helps in coordinating the activities of our body.

Endocrine glands - The duct less glands which pour their secretions directly into the blood are called endocrine glands. Hormones - they are non-nutrient chemicals which act as inter cellular messengers and are produced in trace amount. They are secretions of the endocrine glands and one of the important substances that control the body's chemistry. Also known as "Chemical messengers." The term hormone was introduced by Bayliss and Starling.

Physical and chemical properties of hormones

(i) These are secreted by endocrine glands. (ii) Hormones are secreted only when required. (iii) Their secretion is regulated by feedback mechanisms. (iv) These are generally released in the blood stream. (v) The molecules of most of the hormones are small. (vi) The secretion of hormones is always in very small quantity. (vii) Hormones are destroyed after use i.e. hormones cannot be stored in the body. Thyroxine is an exception.

Transfer of information in multicellular organisms

Electrical impulses are an excellent means for transfer of information rapidly. But there are some limitations to the use of electrical impulses. They will reach only those cells that are connected by nervous tissue. Once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanisms before it can generate and transmit a new impulse. So that multicellular organisms use another means of communication between cells namely, chemical communication. This will be slower and it can be done steadily and persistently because it can potentially reach all cells of the body. In chemical communication, stimulated cells release a chemical compound (hormone) which diffuse all around the original cells. If other cells around have the means to detect this compound using special molecules on their surfaces, then they would be able to recognize information and even transmit it.

Difference between Nervous and Hormonal Coordination

Chemical coordination in animals

In animals, chemical coordination is achieved through the agency of hormones which function as chemical messengers or informational molecules. Hormones are secreted in very small amounts by specialized tissues in the body called endocrine glands. These glands are ductless and pour their secretions directly into blood. Blood transports them to the target tissues/ organs.Hormones coordinate the activities of living organisms and also their growth. For example, the pancreas secretes two hormones-insulin and glucagon.

7.0Endocrine Glands

The various endocrine glands in humans are hypothalamus, pituitary gland, thyroid gland, parathyroid glands, pancreas, adrenal glands, ovary (in female) and testis (in males).

Pituitary gland is known as 'Master gland' of the body. It is because of the fact that the pituitary gland controls the functioning of most of the endocrine glands.

Hypothalamus plays an important role in the release of many hormones. For example, when the level of growth hormone is low, the hypothalamus releases growth hormone releasing factor which stimulates the pituitary gland to release growth hormone.

The gonads i.e. testes and ovary are both endocrine and non-endocrine in function. Their non endocrine function is to produce male and female reproductive cells i.e. sperm and ova respectively.

How does our body respond to emergency situation like fight?

• Explanation: In case of flight reaction to an emergency situation, adrenal glands release adrenaline into blood. (i) The heart begins to beat faster resulting in supply of more oxygen to the muscles. (ii) The blood to the digestive system and skin is reduced due to the contraction of smooth muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. (iii) The breathing rate increases because of the contraction of the diaphragm and the rib muscles. (iv) All these responses together enable the body to be ready to deal with the situation.

8.0Feedback Mechanism

Feedback mechanism is a regulatory mechanism in which presence of certain levels of substance promotes or inhibits its further formation. Hormone regulation is mostly done by feedback mechanism. A good example of negative feedback is the hormone insulin. Insulin is a hormone produced this makes the glucose level normal. With a fall in blood glucose level insulin secretion decreases. This checks the further fall in blood glucose level. So, negative feedback works to keep the blood glucose level normal.

Note: Iodine is important for the thyroid gland to make thyroxine hormone. Thyroxine regulates carbohydrates, proteins and fat metabolism in the body so as to provide the best balance for growth. If iodine is deficient in the diet, thyroxine cannot be produced and the thyroid gland at the neck swells, a condition called goitre. Use of iodized table-salt can provide the required amount of iodine in the diet.

9.0Coordination In Plants

Plants have neither a nervous system nor muscles. But they give response to stimuli. The higher plants are fixed to the substratum by means of roots. They cannot move from one place to another. They, therefore, show movement of their parts only. The plants coordinate their behaviour against environmental changes by using hormones. These hormones affect the growth of a plant, which may result in movement of shoot and root of plant.

Explain why the responses shown by plants are slow in comparison to animals.

• Explanation Plants do not have nervous systems like the animals have which is responsible for the quick response to stimuli. Instead, they use only hormones for producing reaction to external stimuli, which are responsible for the slow response to stimuli.

Movement in Plants

Plants show two different types of movement. The plants may either respond to various stimuli very slowly by growing e.g. when a seed germinates the root goes down and the stem comes up into the air or they can show rapid movements like leaves of sensitive plant move very quickly in response to touch by folding and drooping without growing.

Classification of plant movements

These are of two types -

Tropic Movement

Tropic movement is the directional movement of the part of a plant caused by its growth. The growth of a plant part in response to the stimulus can be towards the stimulus (positive tropism) or away from the stimulus (negative tropism).

Types of tropic movements

(1) Phototropism (2) Geotropism (3) Chemotropism (4) Hydrotropism (5) Thigmotropism

(1) Phototropism: The movement of a part of the plant in response to light is called phototropism. If the plant part moves towards light is called positive phototropism and if the plant part moves away from light, then it is called negative phototropism.

(2) Geotropism: The movement of a part of the plant in response to gravity is called geotropism. Roots of a plant move downwards in the direction of gravity it is called positive geotropism and stem of a plant moves upwards against the direction of gravity it is called negative geotropism.

(3) Chemotropism: The movement of a part of plant in response to a chemical stimulus is called chemotropism. e.g. Growth of pollen tube towards the ovule during the process of fertilization in a flower.

(4) Hydrotropism: The movement of a part of plant in response to water is called hydrotropism. Roots of seedling show positive hydrotropism.

(5) Thigmotropism: The movement of a part of plant in response to contact or support is called thigmotropism.e.g. Pea plants climb up other plants or fences by mean of tendrils. Tendrils are sensitive to touch. When tendrils come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of tendril away from the object. This causes the tendril to circle around the object and thus cling to it. Tendril is a thread, like structure which can be formed from modified shoots or leaves. It is used by climbing plants for support and attachment generally by twining around whatever it touches.

10.0ACTIVE BIOLOGY

Aim: To demonstrate the response of plant to the direction of light.

Method: (i) Take a plant in a conical flask with water. (ii) Take a cardboard box which is open from one side. (iii) Keep the flask in the box in such a manner that the open side of box faces light coming from the window and then observe it. (iv) Now turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days. Again, observe carefully to find the difference in the movement.

Observation (i) In the first case, the shoots bend towards light and the roots bend away from light. (ii) In the second case when the flask was turned it was found that the shoots grow again by bending towards light and roots grow by bending away from light.

Conclusion The shoots show positive phototropism while the roots show negative phototropism.

Plant A is kept in light which is coming from right direction and plant B is kept in light which is coming from left direction. What will happen if we inter change the positions of these two plants?

• Explanation: Plant B moves towards the right direction and plant A moves towards the left direction after interchanging the position because shoot gives positive response towards the light.

11.0ACTIVE BIOLOGY

Aim: To demonstrate that roots show hydrotropism.

Method: Place germinating seeds in moist saw dust contained in a sieve.

Observation: (i) The radicles pass down and come out of the sieve pores骨 under the influence of gravity (ii) After some growth, radicles move back and enter the saw dust again.

Conclusion: (i) This shows that roots show both hydrotropic response and geotropic response. (ii) The hydrotropic response of root is stronger than geotropic response

Nastic movement

Movement which is neither towards nor away from the stimuli is called nastic movement. It is growth independent movement.

Seismonastic/ Thigmonastic movements Such movements occur in response to touch (shock). These movements are very quick and are best seen in 'touch-me-not' plant (Mimosa pudica), also called ‘Chhui-mui' or ‘Lajwanti’ or 'sensitive plant'. If we touch the leaves of the chhui-mui plant with our finger, the stimulus is transmitted to its base and then to other parts through the xylem sap, probably in the form of a chemical. Due to which all its leaves immediately fold up and drop. After some time, the leaves regain their original status. Here, no growth is involved. Instead, plant cells change shape by changing the amount of water in them (turgor changes), resulting in folding up and drooping of leaves.

12.0Chemical Coordination in Plants

It takes place by the plant hormones or phytohormones. They help to coordinate growth, development and response to the environment. They are synthesized in minute quantities in one part of the plant body and simply diffuse to another part, where they influence specific physiological processes.

Growth promoters

(1) Auxins: Auxin was the first plant hormone discovered by Went. It promotes cell elongation, apical dominance and helps in root initiation in cutting or in callus differentiation. In vascular plants, specially in taller ones if apical bud is removed it causes fast growth of lateral buds. The influence of apical bud in suppressing the growth of lateral buds is termed as apical dominance.

Role of auxin in phototropism When growing plants detect light, a hormone called auxin, synthesized at shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot.

This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

A plant is grown in the open ground with the sunlight coming from above, then the stem of plant grows straight up. Why?

• Explanation: When the sunlight comes from above then the auxin hormone presents in the tip of stem spreads uniformly down the stem. Due to the equal presence of auxin both the sides of stem grow equally and thus it grows straight up.

(2) Gibberellins (G.A.): It is found in various plant parts such as root, stem, leaves, fruits and immature seeds. It stimulates stem elongation or helps in growth of the stem. It helps in breaking dormancy in seeds and buds. It promotes growth in fruits and increases size and number of fruits.

(3) Cytokinins (CK) Cytokinins promote cell division, and they are present in greater concentration in areas of rapid cell division such as in fruits and seeds. It promotes opening of stomata. Cytokinins suppress apical dominance (promotes lateral branches in the presence of apical bud). Help in secondary growth (growth in thickness). It helps in breaking the dormancy of seeds and buds.

Growth inhibitors

(1) Abscisic acid (ABA) It is called stress hormone which inhibits the growth. It promotes the closing of stomata under water stress condition thus effects wilting of leaves. It causes dormancy of seeds and promotes falling of leaves.

(2) Ethylene It is a gaseous hormone which promotes fruit growth and ripening. It prevents elongation of stem and roots in longitudinal direction. It promotes yellowing and senescence of leaves. Note: The effect of daylength (photoperiod) on the developmental process of a plant (like germination of seeds and flowering) is called photoperiodism. Photoperiod is longer in summer season which is required for flowering in wheat plants while shorter in autumn season which is required for flowering in tobacco plant.

13.0Biology Diagrams made Easy

14.0Chapter At a Glance

15.0SOME BASIC TERMS

• Neuron : Highly specialized cells which can detect, receive and transmit different kinds of stimuli.
• Stimuli : A stimulus causes an action or response, in an organism. It can be external (temperature, light, etc.) or internal (hunger, thirst, pain, etc.).
• Receptor : The sensory receptors enable us to be aware of the environment around us. It responds to the stimuli.
• Electrical impulse : It is also known as the nerve impulse. It is the passing of electrical current from one end of the neuron to the other end, which actually carries the information.
• Synapse : It is the junction place where two neurons communicate.
• Synaptic cleft : The space between two neurons at a synapse, where the nerve impulse is transmitted through certain chemical structures.
• Reflex action : It is body's immediate, involuntary response to an external stimulus to protect itself from the immediate harm. The brain is not involved directly as there is no thinking involved.
• Reflex arc : The pathway taken by the reflex action is referred to as reflex arc. It normally involves the receptors, sensory neuron, relay neuron and motor neuron, finally reaching the effector organs.
• Sensory neuron : These are a type of neuron that carries the nerve impulse from the sense organs to the CNS.
• Motor neuron : Neurons that take away nerve impulse from the CNS to the effector organs like muscle or glands.
• Relay neuron : Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.
• Feedback mechanism : Mechanism by which the release and functioning of hormones are regulated.