Chapter 7 control & coordination class 10th

 Stimuli

The changes in the environment or environmental factors to which the organisms respond and react are called stimuli.

Coordination

The working together of the various organs of an organism in a systematic manner so as to produce a proper reaction to the stimulus, us called coordination.

System functions by the release of chemical messengers -- the hormones and is called endocrine system and the other works by the Conduction of nerve impulses like the Conduction of an electric current and is called nervous system.

ANIMALS-- NERVOUS SYSTEM

The system by which controls and coordinates all the activities of various parts in response to external and internal stimuli by the Conduction of nerve impulses is called nervous system.

Sense organs

Name of receptors     stimulus    location

Photoreceptors             light             Eyes

Phonoreceptors            sound          Inner ears

Olfactoryreceptor         smell            nose 

Gustatoreceptors          Taste             Tongue

Thermoreceptors         heat/cold       skin

Tangoreceptors              Touch           skin

 1. Functional unit of Nervous system-- Neuron

• structure of Neuron

  Neurons are the structural and functional unit of Nervous syste.

It is the longest cell of human body. It consists three parts:

1. Cyton

        The main part of the neuron is cell body called cyton. It is bounded from outside by a simple cell membrane. 

Its cytoplasm is called neuroplasm

2.  Dendrites

       These are highly branched small projections arising from the cyton. These are one to many in number. They conduct impulses towards the cyton, hence, called afferent process.

3. Axon

        From the cyton arises always one very long process called axon. It may be microscopic to one metre in length. The axon carries impulses away from the cyton, hence, called as efferent process. 

The axon traverse through the nerve fibres aa neuraxis. Dendrites and axon are collectively known as neurites. 

The terminal arborization of axon of one neuron is very closely placed to the dendrites of another neuron without any physical or protoplasmic contact. 

This close proximity is known as synapse.

An axon of neuron covered by one or two sheaths is called nerve fibre.

• Type of Nerve fibres

The nerve fibres are of two types:

1. Medullated Nerve fibres

     In these nerve fibres the axon of neuron is surrounded by two sheaths, i.e inner sheath called medullary or merylin sheath and the outer sheath called neurilemma. 

The unmyelinated gaps or constrictions in these axons are called nodes of Raniver.

2. Non- medullated Nerve fibres

    In these fibres the neuraxis is covered by only one sheath i.e. neurilemma.

• Classification of Neurons 

According to their functions, the neurons are categorised into the following three types:

1. Sensory (Afferent) Neurons 

     These Neurons carry sensory impulses from the sense organs to the central nervous system.

2. Motor (Efferent) Neurons 

    These Neurons transmit messages or impulses from the central nervous system to the effectors i.e muscles or glands.

3. Association (connector) Neurons

     These Neurons are present in the central nervous system and connect sensory neurons to motor neurons.

How animals Respond to stimuli?

All information of the environment is detected by specialized tips of nerve cells. These receptors are usually present in the sense organs. This information sets off a chemical reaction that creates an electrical impulse. 

This impulse moves from dendrite to cyton and then from cyton along axon to the terminal arborizations. On reaching the terminal arborizations, the impulse releases small amount of chemical into the gap. 

The chemicals cross the gap and starts a similar impulse in the dendrite of the next neuron. The impulse again follows the same path in the second neuron. The impulse passes through a number of neurons in this way until it reaches other cells, such as muscles or glands. This impulse cause muscle to contact or glands to secrete some chemical