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Control and Coordination

Chapter: Control and Coordination

Introduction:

A living being does not live in isolation. It has to constantly interact with its external environment and has to respond properly for its survival. For example; when a hungry lion spots a deer, the lion has to quickly make a move so that it can have its food. On the other hand, the deer needs to quickly make a move to run for its life. The responses which a living being makes in relation to external stimuli are controlled and coordinated by a system; especially in complex animals.  In case of plants, movements are the result of growth. A seed germinates and grows, and we can see that the seedling moves over the course of a few days, it pushes soil aside and comes out. But if its growth were to be stopped, these movements would not happen.Also it becomes clear that all these movements, in response to the environment, are cautiously controlled. Each kind of a change in the environment evokes an appropriate movement in response. When we want to talk to our friends in class, we whisper, rather than shouting loudly. Clearly, the movement to be made depends on the event that is triggering it. Therefore, such controlled movement must be connected to the recognition of various events in the environment, followed by only the correct movement in response. In other words, living organisms must use systems providing control and coordination. Specialized tissues are used to provide these control and coordination activities.

Animal Nervous System:

  1. The neural system of all the animals is composed of highly specialized cells called neurons which can detect, receive and transmit different kind of stimuli.
  2. The neural organization is very simple in lower invertebrates. For example in hydra it is composed of a network of neurons.
  3. The neural system is better organized in insects, where a brain is present along with a number of ganglia and neural tissues. The vertebrates are said to contain more developed neural system.

Human Neural System:

The human neural system is divided into two parts:

  1. The Central Neural System (CNS).
  2. The Peripheral Neural System (PNS).

✓ The central nervous system is composed of brain and spinal cord; it is the site of information processing and control.
✓ The peripheral nervous system comprises of all the nerves of the body associated with CNS.

Have u ever wondered how can we respond by touching a hot object or how can we detect taste or smell ?

All information from our environment is detected by the specialised tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on. The receptors which help in detection of taste and smell are the gustatory receptors and olfactory receptors respectively.

Let us look at the structure of a nerve cell or a neuron before knowing how the information acquired by neuron is converted into a chemical signal.

Structure of Neuron:

The nervous tissue is made up of an organized network of nerve cells or neurons

 

Structure of a neuron

 

 

✓ A neuron is a microscopic structure composed of three major parts namely, cell body, dendrites and axon.
✓ The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules
✓ Short fibres which branch repeatedly and project outside the cell body are called dendrites.
✓ The axon is a long fibre, the distal end of which is branched

Generation and conduction of nerve impulses:

  1. The information from the external environment is acquired by the end of the dendritic tip of a nerve cell.  This will result in a chemical reaction that produces an electrical impulse.
  2. This impulse travels from dendrite to the cell body and then along the axon to its end.
  3. At the end of the axon, the electrical impulse sets off the release of some chemicals
  4. These chemicals cross the gap, or synapse, which is a junction between neuron and a neuron and start a similar electrical impulse in a dendrite of the next neuron.
  5. A similar synapse finally allows delivery of such impulses from neurons to other cells, such as muscles cells or gland.

What happens in Reflex Actions ?

Sudden action in response to something in the environment is called reflex action.  A common example is pulling back of hand from the flame. The reflex action is the entire process of response to a peripheral nervous stimulation happens reluctantly, i.e., without conscious effort or thought and also requires the participation of a part of the central nervous system. The reflex pathway comprises of at least one afferent neuron (receptor) and one efferent neuron (exciter) properly prearranged in a series. The afferent neuron receives signal from sensory organ and transmits the impulse via a dorsal nerve root into the CNS (at the level of spinal cord). The efferent neuron carries signals from CNS to the effector.  A reflex arc is formed by the stimulus and response.

Human brain:

The brain is the central information processing organ of our body and acts as the ‘command and control system’.  It controls the voluntary movements, balance of the body, functioning of vital involuntary organs (e.g. lungs, heart, kidney), thermoregulation, hunger, thirst, circadian rhythms of our bodies, activities of several endocrine glands and human behaviour. it is also site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts. The brain has three major parts or regions, namely the fore-brain, mid-brain and hind-brain.

Fore-brain:  

  1. It is main thinking part of the brain. There are certain regions in the fore brain which receive sensory impulses from various receptors.
  2. Separate areas of the fore-brain are specialized for hearing, smell, sight and so on.
  3. There are separate areas of association where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in the brain.
  4. The sensation of feeling full is because of a center associated with hunger, which is in a separate part of the fore-brain.

Mid brain:

 All the involuntary actions in the body such as blood pressure, vomiting, salivation are controlled by mid brain.

Hind brain:

Along with mid brain, hind brain also controls involuntary actions. Activities like walking in a straight line, riding a bicycle, picking up a pencil - These are possible due to a part of the hind-brain called the cerebellum. It is responsible for precision of voluntary actions and maintaining the posture and balance of the body.

How are these Tissues protected ?

Brain is a delicate organ performing many important functions in the body and hence it has to be protected. It is protected by bony structure called the skull. Inside the skull, the brain sits inside a fluid filled balloon like structure which provides shock absorption. The spinal cord is protected by vertebral column or the backbone.

How does the Nervous Tissue cause Action?

When a nerve impulse reaches the muscle, the muscle fiber must move. 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.

Coordination in Plants

Unlike animals, plants do not have a nervous system for control and coordination of movements. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air. When we touch the leaves of a sensitive plant they respond quickly to touch. But there is no growth involved in this movement. On the other hand, the directional movement of a seedling is caused by growth. If it is prevented from growing, it will not show any movement. So plants show two different types of movement – one dependent on growth and the other independent.

Immediate Response to Stimulus

When we touch a sensitive plant, the leaves of such plants respond immediately. This movement is because the plants also use electrical-chemical means to convey this information from cell to cell, plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shapes.

Movement Due to Growth

  1. Generally plants react to stimuli gradually by growing in a particular direction. It appears as if the plant is moving as this growth is directional.
  2. Light and gravity are some of the environmental triggers which change the directions that plant parts grow in. These directional movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it.
  3. Plants show tropism in reaction to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growth of shoots and roots in response to the pull of earth or gravity is called geotropism.
  4. Hydrotropism is the movement of plant induced by water. Let us take an example: growth movement of root toward water is positive hydrotropism and the growth of stem away from water is called negative hydrotropism.
  5. Chemotropism is the growth of pollen tubes towards ovules.

Coordination in plants

Different plant hormones help to coordinate growth, development and responses to the environment. They are synthesized at places away from where they act and simply diffuse to the area of action.

Auxins It is synthesized at the shoot tip, helps the cells to grow longer. 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.

Gibberlins:  They promote stem growth.

Cytokines: Cytokinins promote cell division, and it is natural that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds.

Hormones in Animals:

  1. Hormones are the regulatory substances produced by endocrine glands and transported into tissue fluids such as blood in order to stimulate specific cells or tissues into action.
  2. A hormone called adrenaline is secreted by adrenaline glands and is released directly into blood and then carried to different parts of the body.
  3. Adrenaline targets the heart as a result the heart beats faster resulting in more supply of oxygen to muscles.
  4. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles.
  5. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.