Stimulation And Reaction

The environmental change that brings about a response in the organism is called stimulus. For e.g.: Removal of hand from a hot thing.

The response of the organism to the stimulus is called reaction. For E.g. closing the leaflets to touch me not plant.

Taxis: The movement of the organism in the response of the stimulus by changing the location is called taxis.

Phototaxis: It is the movement of the organism under the influence of the light. E.g. earthworm

Chemo taxisIt is the movement of the organism under the influence of the chemicals.eg antheroziods of ferns moves towards the malic acid

Tropism: The movement of parts of plants (roots, steam or leaves) in response to an external stimulus is called tropism. It is a directional movement of the plant caused by their growth. 

Phototropism: The movement of the parts of the plants in response to the stimulus of the light is known as phototropism. Example: movement of the shoot towards the light and roots away from the light.

Geotropism: The movement of the parts of plants in response to the stimulus of gravity is known as geotropism. Example: The stem grows upward i.e. Negative geotropism.

Hydrotropism: The movement of the parts of the plants in response to the stimulus of water is known as hydrotropism. Example: Roots of the plants grow in the direction of water.

Chemotropism: The movement of the parts of the plants in response to the stimulus of chemical is known as chemotropism. Example: Pollen tubes moves towards style because of positive chemotropism.

Thermo tropism: Movement of the parts of the plants in the response to the heat.

Nervous system

The system of the body that receives the information from the surroundings and transmits to the other parts of the body to show the corresponding effects is called nervous system.

Neurons: Neurons or nerves cell are the cells that transmits the message from one parts of the body to another.

The structures of neuron are:

Afferent or sensory nerves: They carry impulses from various parts of the body to the brain or to the spinal cord.

Efferent or motor nerves: They carry impulses from the brain or the spinal cord to various parts of the body.

Mixed nerves: Sometimes axons of both motor and sensor neurons from a nerve which is called mixed nerves. All the spinal nerves are of mixed type.

Parts of nervous system

Central nervous system

It is the controlling centre of the body which consists of brain and spinal cord

It is composed of three membranes together called meninges. The brain is located in sub arachnid cavity. This cavity is filled with the spinal fluid that protects the brain from shocks.

The three parts of brain are:

Cerebrum

It is the centre of intelligence, memory, imagination and emotions.

It controls the functions of other part of the brain.

Cerebellum

It maintains the equilibrium and controls the posture of the body.

It makes body movement smooth, steady and coordinate.

 Brain stem

Brain stem connects the cerebrum and spinal cord. The bottom of the brain stem is medulla oblongata.

The functions of Medulla Oblongata are:

It receives and integrates signal from the spinal cord and sends resulting impulses to the cerebrum and cerebellum.

It contains different centers that regulate heart beat rate, blood pressure, breathing, vomiting and some involuntary action.

Spinal cord

Spinal cord is protected cylindrical structure that arises from the medulla oblongata and passes through the neural canal of the vertebral column. Spinal cords acts as link between spinal nerves and brain. It is the main centre of the reflex action.

The involuntary action performed by the muscles under the control of spinal cord without the involvement of brain is called reflex action.

Peripheral nervous system

The peripheral nervous system consists of spinal and cranial nerves.

The spinal nerves arises from the spinal cord and spread to different parts of the body. There are thirty-one pairs of spinal nerves in the human beings. Out of them 8 pairs are cervical, 12 pairs are thoracic, 5 pairs are lumbar, 5 pairs are sacral and one pair is coccygeal. They are mainly responsible for reflex actions of the body.

The cranial nerves arise from the brain and terminate inside I, except the vagus. The vagus is connected to the alimentary canal. There are 12 pairs of cranial nerves in human being. They control the activities of eyes, ears, tongue etc. Three pairs are cranial nerves are sensory, 5 pairs are motor and four pairs are of mixed types.

Autonomous nervous system

This nervous system maintains and regulates the internal environment by controlling the involuntary actions of the internal organs. It is divided in to sympathetic and parasympathetic.

Exocrine glands are ducted glands. The secret juices like mucus, saliva, tear etc. Their secretions are related life processes like respiration, digestion etc.

Endocrine are ductless glands. The secret juices like mucus, saliva, and tear etc.They secrete hormones. Their secretions are responsible for control and coordination of growth.

Hormones

Hormones are the chemical substance secreted by endocrine and heterocrine glands. Theyare chemical messenger of the body because it carries chemicals to all parts of the body through blood circulation to bring about the harmonious working of the body.

The functions of hormones are as follows:

They stimulate and control various physiological and metabolic activities of the body.

They regulate growth and reproduction.

Some of the major glands and their functions:

Thyroid gland: It is situated in the neck. Its function is to secrete thyroxin which contains iodine which controls general metabolism.

Pancreas:  It is found in alimentary canal. It secretes insulin and glucagon. Insulin maintains sugar level in the blood and glucagon supplies sugar in the blood.

Pituitary gland: It is found in the skull. It secretes growth hormone and stimulating hormone. Growth hormone controls the growth of the body and stimulating hormone controls and stimulates in the secretion of the other glands.

Gonads: Male gonads are found in the scrotum. It secretes testosterone, which develops and maintains male secondary characters. It is also responsible for production of sperms.

Female gonads are found in the female reproductive system. It secretes Oestrogen and Progesterone. Oestrogen controls the growth of mammary gland as well as development of female secondary characters. Progesterone prepares uterus suitable for the development of embryo.

Adrenal gland: Adrenal gland is situated on the top of each kidney. Adrenalin hormone secreted by the adrenal gland at the time of emergency prepares the body face and emergency situation for flight, fright or fight. So adrenalin is called an emergency hormone.

Parathyroid gland: They are located on the thyroid gland. They secrete parathormone, which controls the calcium metabolism of the body and helps in normal growth of bones and tissues