Chapter 7 Control and Coordination

Reflex action:- reflex action is a involuntary mechanism, spontaneous, automatic, rapid and mechanical response to the external stimuli on specific receptor without the will of an organism. eg. beating of heart, blinking of eyes, upward and downward movement of diaphragm during respiration.

Walking:- walking is a voluntary mechanism, slower than involuntary mechanism, occurs with the will of an organism. It requires brain involvement which sends the electrical signals to various body parts for the movement.

Synapse is a point of connection where two neurons gets connected or communicated, where one neuron sends information to another target nerve cell. Synapses are electrical or chemical. Electrical is where flow or exchange if ions occurs and in chemical synapse, they communicate using chemical messengers called hormones, or neurotransmitters.

Sensory nerves carry nerve impulses to the axon terminal which releases chemical messengers called neurotransmitters, then they goes through the synapse to reach the dendrite part of another neuron. And, finally these neurotransmitters goes to muscles, glands etc. to carry forward their actions.

Hind- brain parts cerebellum (back of the brain), maintains the posture and equillibrium of body. hind- brain consists of pons, cerebellum and medulla- which controls most of the involuntary actions (saliva secretion, vomiting, blood pressure, pupil contraction and relaxation etc.)

When we lighted an incense stick, then its fragnance diffuses and reaches our nose. which is detected by olfactory receptors. Then, through the sensory neurons these receptors goes in the special part of the brain, i.e, fore- brain :- detect the smell (where it is already stored as a memory), and converts in the form of electrical signals.

Reflex action is a rapid or quick response to stimulus (involuntary mechanism) because of lower number of synapses. so, the organism don't have enough time to think. The path of an impulse to travel only in one direction (reflex arc) as afferent to efferent neurons and this information also reaches the brain, where the brain records this event and stores it as a memory.

These are organic compounds which is synthesized by cells and tissues of plants called plant hormones/ phytohormones. They actively promote, or inhibit some factors and developmental processes of plants. five major groups of plants hormones are present:-

1. Auxin:- it stimulates cell elongation in stems by the protein expansin, which has low pH, 4.5. The amount of xylem and phloem ratio are regulated by auxin. 

2. Gibbererllin:- It promotes the internodal elongation of plants. It also helps in seed germination by activating vegetative growth of embryo in plants.

3.Cytokinin:- It involves the cell division in which formation, maintainance and growth of root apical meristem and shoot apical meristem by cytokinin's both positive regulators in shoot apical meristem and negative regulators in root apical merisrtem. Also helps in chloroplast maturation.

4. Abscisic acid:- It is also known as stress hormone which acts in the stress condition of a plant (eg. closing of stomata in extremely drought conditon). It also promotes the root and shoot growth with seed dormancy and germination, also includes wilting of leaves.

5. Ethylene:- It is a gaseous hormone, present in almost every plant because it is responsible for may factors like flowering, fruit ripening, rooting and also for senescence (depends on its concentration).

The movement of leaves of the sensitive plants shows the bending or drooping of leaves when they being touched by someone and they doesn't show any growth pattern in them.

On the other hand, the movement of shoot towards light shows the process of phototropism which is unidirectional & shows the growth pattern.

Auxin is a plant hormone produced in stem tips that helps in cell elongation or expansion. Auxin also helps in the process of phototropism by binding, which helps the plant to grow towards light direction.

Also shows more physiological effects like cell differentiation (shows relative amount of xylem and phloem), inhibits root elongation etc.

Auxin promotes the cell elongation and inhibits the growth of lateral buds (shows apical dominance) cause it is produced in the stems tips.

Tendrils are sensitive to touch. When tendrils found any support, auxin stimulates on the faster rate of the cell on the opposite side and tendril then forms a circle around their support.

Hydrotropism is a part of tropism process that shows in plants. The growth and movement of plant roots towards or away from moisture is hydrotropism.

Chemical coordination takes place in animals by the chemical messengers called hormones, which are secreted by the endocrine glands or occurs by the nervous system.

Hypothalamus is the important part in intergrating the nervous and endocrine system.

When endocrine glands secrete hormones, neurosecretory cells are present in the brain which secrets the neurotransmitters. And these chemical messengers get converted into electrical signals and goes into muscles or glands for the movement or for the growth and development of an animal.

Iodized salt contains potassium iodate, dextrose etc. which is neccessory for our body for secretion of thyroxine hormone by thyroid gland. Deficiency of iodized salt cause goitre. which results into the swelling of neck.

Adrenaline is a hormone also called epinephrine, produced by adrenal gland. It increases the heart rate, increase blood pressure, redistribute the blood to muscles. The breathing rate increases during the diaphragm contraction and the muscles contraction, also if blood pressure increases it allows more glucose level to get into the bloodstream when adrenaline hormone is secreted into the blood.

Insulin is a hormone produced in pancreas and that helps to control high glucose level. It converts the food which we are taking into the form of energy in the bloodstream.

Diabetes occurs when too much sugar is taken in food or found in blood (high blood glucose level). If any patient is suffering from diabetes, doctors give that patient a insulin injection and it cannot be taken as a pill because it is made up of protein or secreted in pancreas that if taken through mouth, then it is denatured by the digestive process.

 (d) Cytokinin

Cytokinin is a plant growth hormone also called phytohormones that promotes cell division (in shoot apical meristem or root apical meristem), morphogenesis (shoot & root initiation), chloroplast maturation and apical dominance (where main stem of the plant is dominant over side stem).

(b) Synapse

Synapse is a point of connections of two neurons. When a chemical reactions occurs in our body, it creates an electrical impulses from dendrite to the axon end. Then, it releases some chemicals and these chemicals goes in synapse and generate similar electrical impulses in dendrite of next neuron to  muscle cells or glands.

 (d) All of the above

Fore- brain is responsible for thinking, Medulla is responsible for the involuntary actions like breathing, heart rate, heart beat etc. And the voluntary actions like maintaining and balancing our body, comes under the part of hind- brain.

Receptors are transducers which exhibits sensitivity in various body parts. When our body receives any external or internal stimuli, it converts stimuli into nerve impulses (action potential) and send these impulses to other neurons, muscle fibres or glands.

If the receptors get damaged they will not detect the stimulus, as well our brain also will not detect the signals which will be harmful for our body (Eg. When we touch an cold or hot object or to getting burnt etc.)

Nervous system controls and coordinates the activities, bevahiour of animals, also maintains the homeostasis (internal body temperature) & is composed of two principal cells:-

• Neurons (nerve cells)

• Neuroglia or glial cells                                                                                                                                                                                                                                          

• Neurons:- These are the basic structural & functional unit of nervous system. They are specialized to respond to stimulus (any change in envirionment ,i.e, strong enough to initiate an nerve impulses) can be physical or chemical, conduct nerve impulses and release chemicals called neurotransmitters.

Nerve impulses travels at the speed ranges from 0.5 to 130 meters per second along plasma membrane of a neuron.

• Neroglia cells or glial cells (glia-glue) :- These cells nourishes, protects and support the neurons.

Phototropism is the process of growth of an organism in response to light reaction or stimulus. It is mostly seen in plants, but can also observed on other organisms. There are two types of phototropism:-

1. Positive phototropism:- Growth of plant towards the direction of light is positive phototropism.

2. Negative phototropism:- When growth of a plant is away from light is negative phototropism.

Several signalling molecules helps the plants to determine the light stimulus, activates genes & change the hormones for the growth of plant (i.e, auxine). This hormone helps the plants to have elongated cells on the farthest side from the light stimulus.

In spinal cord injury, the receptor signal and the nerve signal will get disrupted that is conducted by the brain. And both these signals meets at one point ,i.e, spinal cord where the signals get disrupted.

Plants do not have nervous or muscular system for movement or responsiveness like animals have. Plants only shows the growth (by growth hormones like phytohormones) with the attached substratum by giving them appropriate soil moisture, favourable environmental or physiological conditions. Various plant hormones are present for the plant growth like auxin, gibberellin, cytokinin, ethylene or abscisic acid.

Auxin is responsible for the growth of the stem, gibberellins are those growth hormones which enhances the long growth of stem according to the plant in the presence of meristematic cells, cytokinin acts on the cell division part of the plant, ethylene is a gas present in atmosphere and mainly responsible for fruit growth or ripening with root initiation ,And abscisic acid is responsible for seed development, stomatal closing, bud dormancy etc.

Control and coordination is important for the survival of living organisms. Control comes under endocrine system by sending chemical messengers called hormones and nervous system composed of neurons which controls our body by sending electrical signals called nerve impulses.

Coordination is working together of various parts of body of multicellular living organisms in a sequence to inhance the functions of each other. Control and coordination is important in organisms so that they can do voluntary, involuntary actions in their biological rhythm cycle (24 hour cycle or sleep-awake cycle).

Involuntary actions are very quick which is performed by animal without its will or without thinking of the actions but controlled by parts of brain, eg. Heart beating, hand pulling when we touch an hot object.

On the other hand, reflex actions are automatic, result of sudden impulse without any stimulus and it is not controlled by brain .famous eg. -  knee jerk (slow strike below the knee cap while sitting with freely hanging legs that kicks the legs forward), yawning, blinking of eyes, sneezing etc.

Nervous system:- It is consist of neurons, bundles of nerve fibres, neuroglia cells and have neurosecretory cells. Human nervous system is consist of two main parts:- CNS (central nervous system)- lies along the main axis of the body, consists of upper large brain in head or narrow spinal cord in neck or trunk. 

PNS (peripheral nervous system)- It is associated with the CNS defined by afferent nerve fibre that transmit impulses from receptors present in organs to CNS)  and efferent nerve fibre which transmit regulatory impulses from CNS to peripheral organs.

It is divided into two parts:

1. Somatic nervous system relays voluntary impulses from CNS to skeletal muscles.

2. Autonomic nervous system relays impulses from CNS to involuntary parts of the body.

On the other hand, hormonal mechanism is slower than nervous mechanism. Hormones are the chemical messengers which brings control, secreted by endocrine glands and released into the blood stream from axon ending. Various hormonal secretion is done by hypothalamus and are under control of secretion of neurosecretory cells.

sensitive plants- they are sensitive to touch, mostly their leaves like a plant chui mui (shows quick fold inward or droop when we touch their leaves). And they do not have special proteins for the movement they show only growth pattern.

Movement in our legs:- this is a voluntary action which depends on our willingness. They have special protein and muscles to contract by which they are able to walk or run. The nerve impulses sends to the brain and the brain sends signals the various body parts for the voluntary or as well as involuntary actions.