Nervous System
* The nervous system is made up of the brain, spinal cord and a huge network of nerves that thread through our body.
* The nervous system is responsible for sending, receiving and processing nerve impulses.
* Neurons are the fundamental unit of the nervous system. The axons of the nervous bundle together to form nerve fibre that run throughout our body.
* Nerves carry information in the form of electrochemical signals called impulses, which travel from the brain and spinal cord to the nerves located throughout the body.
* Reflex action is an involuntary action by the body or an action by the body on which we do not have our control.
* The nervous system is functionally organised into-a central, a peripheral and an automatic nervous systems.
* The human brain is a part of the central nervous system and has three major parts – the fore brain, mid brain and hind brain.
* The spinal cord extends from the medulla of the brain through the whole length of the vertebral column.
* The peripheral nervous system includes the cranial and spinal nerves.
* Cranial nerves originate from the brain while the spinal nerves originate from the spinal cord.
Hormones in Animals
* The endocrine system is made up of the endocrine glands that secrete hormones.
* Hormones bring about changes that help coordinate body systems in a general way.
* Endocrine glands are ductless glands; they secrete hormones directly into the blood stream.
* Hormones are known as chemical messengers as they modify and regulate the activity of the target tissues or organs.
* There are eight major endocrine glands throughout the body – pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovary and testis.
* Also present are the hypothalamus and the parathyroid glands.
* Deficiency or an increase in hormone secretion leads to harmful effects. Hence the timing and amount of hormones released are regulated by feedback mechanisms in the body.
* Iodine is essential for the synthesis of thyroxine, produced by the thyroid gland. A deficiency of iodine in our diet may lead to goitre.
Insulin, secreted by the pancreas, regulates the sugar level in our blood. A deficiency of insulin may lead to a disease called diabetes.
Coordination in Plants
* Plants show two different types of movement – one independent of growth and the other dependent on growth.
* Plant growth in the direction of stimulus is defined as tropic movement.
* The movement of a plant part in response to light is called phototropism.
* The movement of a plant part in response to gravity is called geotropism.
* The movement of a plant part in response to chemicals is called chemotropism.
* The movement of a plant part in response to water is called hydrotropism.
* The directional growth movement of a plant part in response to the touch of an object is called thigmotropism.
* Plants have different hormones which help coordinate growth development and responses to the environment.
* A nastic response is not a directional movement of the plant part with respect to the stimulus.
* Auxins are plant hormones that promote and regulate the growth and development of plants.
* Gibberellins are plant hormones that help in the elongation of internodes.
* Cytokinins are plant hormones that promote cell division. They also promote the closing of the stomata.
* Abscisic acid is a plant hormone that inhibits growth. Its effects include wilting of leaves.