Control And Coordination

Transmission of nerve impulses between two neurons takes place through the synapse. Axon bulb releases specialized chemicals called as neurotransmitters like acetylcholine which help in chemical transfer of information through synapses into the dendrites of another neuron which receives the information and passes on further in a similar manner. These chemical messengers passes through synapses and start an electric impulse

Cerebellum in the Hind Brain maintains posture and equilibrium of the body. Hind brain is divided into Pons, Cerebellum and Medulla.

The temporal lobes of the brain are concerned with smell, hearing and taste. When an incense stick burns, it produces fumes of pleasant smells. The forebrain has regions that receive impulses from various receptor organs. So when the smell of aggarbatti reaches our olfactory receptors (in nose), the receptors send electrical or chemical impulses via neurons to the forebrain. The forebrain thus detects the smell of an aggarbatti.

Brain has no role in case of reflex action as it is an extremely quick action which does not involve any thinking by the brain.In case of reflex action the stimulus is received by the spinal cord and the only role that brain plays is to register the information that the reflex action has taken place

• Plant hormones (also called phytohormones) are small, signal molecules which are responsible for regulating plant cell processes.
• There are five major hormones which are
  • auxin
  • cytokinin
  • gibberellin
  • abscisic acid
  • ethylene.
• Each hormone differs in its effects.
• Auxins, gibberellins, and cytokinins act as growth stimulators.
• Abscisic acid and ethylene act as growth inhibitors.

The movement of leaves of sensitive plant are nastic movements that are independent of any stimulus, be it light.

Movement of a shoot towards light is due to phototropism which is a plant’s growth response to light source. The movement of shoot towards light is positive and the shoots are said to be positively phototropic. If the plant part grows away from light, it is known as negatively phototropic.

Auxins and Gibberellin are plant hormones that promote growth.

• Gibberellin controls stem elongation and also germination.

• Auxins bring about elongation of cells in shoot and thus are a growth regulator.

• Auxin is one of the major plant growth hormones.
• In tendrils, auxin is present in the tips.
• When a tendril comes in contact with a support, auxin stimulates faster cell growth on the opposite side.
• This makes the tendril curve and bend towards the support.
• This curving tendril can then encircle the support and sling around it.

Hydrotropism is the growth of roots in response to the unilateral stimulus of water. Roots are positively hydrotropic because they bend towards the source of water.

Experiment to demonstrate hydrotropism-

Germinate few seeds in moist dust in the ground. After some time you will observe that radicles start coming out of the ground but they start bending and again enter the moist saw dust. This happens because roots are positively hydrotropic. They bend towards the source of water i.e. moist sawdust in this case.

Chemical coordination takes place in animals through Hormones. Hormones are chemical messengers released by the endocrine system that move through the blood stream and can reach every cell in the body. They help to maintain a constant environment inside the body, and control cellular activities by entering the cell and influencing its activities by sending commands to chemical messengers within cell.

Lack of iodine in diet leads to deficiency of thyroxin hormone which results in a condition known as simple goitre. It is a swelling of the thyroid gland without any over secretion sign of thyroid hormone. If the iodine deficiency is moderate, it leads to high concentrations of Thyroid Stimulating Hormone which leads to swelling of the glands. For these reasons it is advisable to take iodine in diet because it stimulates the thyroid gland to produce thyroxin hormone and thus prevents from such disorders.

Adrenaline is a hormone secreted by the adrenal glands in case of flight situation/ emergency. When adrenaline is secreted into the blood, it-

• Speeds up the heartbeat, thus providing more oxygen to the limbs.

• Increases the rate of blood circulation thus resulting in an increase in blood pressure.

• Increases the blood supply to limbs and face.

• Stimulates the liver to put more glucose into the blood.

All these characteristics that occur on adrenaline secretion prepare the organism for flight from danger.

A person suffers from diabetes when his/her body fails to produce adequate amount of Insulin.

Insulin is a hormone secreted by pancreas that helps in regulating the blood glucose level. If insulin is not produced in sufficient amount in blood, the level of glucose in the blood increases which leads to various serious conditions like retinopathy, blindness, fatigue, excessive urination and other serious complications too. So in order to maintain the insulin level in the blood of a diabetic person, insulin injections are administered artificially into them.

Cytokinins are plant growth hormones that Control cellular division in root and shoot, also called as antiaging hormones.

Synapse is the gap between two neurons that passes chemical or electrical signals from one neuron to another.

Brain is divided into many parts- cerebrum, cerebellum, hypothalamus, medulla oblongata, pons,

Cerebrum is concerned with thinking. Midbrain, pons and medulla are concerned with regulating the heartbeat. Cerebellum helps in balancing the body.

A receptor is a protein molecule that receives chemical signal from outside and interprets them. On receiving these signals the receptors bring about cellular responses. There are receptors in nose, tongue, ear, eye etc.

If receptors do not work properly then the information sent by the chemical signals will not be interpreted and perceived. Suppose the receptors found on our tongue, gustatory receptors do not work, an organism will not be able to perceive the taste of things one puts on tongue or eats. If the receptor in eye, say rod, does not work properly then an organism will not be able to perceive vision at night because rods function in less intense lights; so if rods will not function the person will not be able to perceive vision at night. Similarly, If in a situation the receptors in nose, i.e. the olfactory receptors fail to function properly, then the signals sent to brain regarding any smell will not be perceived and an organism will not be able to smell.

A neuron consists of a cell body which gives off a variable number of processes. They give off several short branching processes called dendrites and one longer process known as axon.

Neurons transmit chemical and electric signals in the brain. The ends of axons possess bulb like structures which have neurotransmitters in them, these bulbs connect with the dendrite of another neuron and form synapses. These neurotransmitters transmit signals from one end of neuron to the dendrites of another neuron, thus conducting the chemical impulse. Electrical signals also occur in neurons but they are comparatively slower.

Phototropism are curvature movements that occur when a plant is provided with artificial, natural light just from one direction. Plant parts that show a bending towards the source of light are said to be positively phototropic, whereas plant parts that bend/ grow away from light source are said to be negatively phototropic.

This curvature / bending of parts usually stem is due to unequal distribution of auxin under the influence of light. Auxins accumulate on side away from light. So wherever auxin concentration will be high, the stem will promote growth on that side.

In case of a spinal cord injury, the signals coming from nerves and signals coming to the receptors will be disrupted, also disturbing the reflex and involuntary actions.

Chemical coordination occurs in plant with plant hormones. Plant hormones are synthesized at places away from where they act and diffuse to the area of action. Different plant hormones help to coordinate growth and development. For example, auxins and gibberellins. Gibberellins help in growth of the stem. Abscisic acid, another plant hormone, inhibits growth in plants.

• There are various organs and organ systems in an organism.
• To allow proper functioning and survival of an organism they need to be coordinated and controlled.
• In human beings nervous system and endocrine system work together to control and coordination.