Draw the structure of a neuron and explain its function.
The nervous system consists of two types of cells:- Neurons and Neuroglia. Neurons are the basic structural and functional unit of the nervous system. They respond to the specific physical or chemical stimuli and conduct nerve impulses and release neurotransmitters. Whereas neuroglial cells are the glial cells which support, nourish and protect the neurons.
Neurons possess the ability to respond to a stimulus and convert it into the action potential. An action potential is an electrical signal that travels along the plasma membrane of a neuron and these nerve impulses travel at the speed ranging from 0.5 to 130 meters per second. On the basis of structure and functions neurons are classified into various types.
Structural:- Multipolar contains many dendrites and one axon; Bipolar contains dendrite and axon with a cell body; Unipolar possess extension of cell body which divides into two branches.
Functional:- afferent or sensory neurons carry nerve impulses from peripheral sensory receptors to the CNS; efferent or motor neurons transmit nerve impulses from the CNS to effector organs; and Interneurons are located within the CNS in which they form connection between afferent or efferent neuron.
Neurons are consisted of cell body, dendrites, axon, myelin sheath and their functions are as follows:-
1. Cell body:- also known as perikaryon and contains a nucleus which is surrounded by cytoplasm. cytoplasm contains cell organelles like lysosome, mitochondria etc. it contains free ribosomes and the cell body in the peripheral nervous system usually occurs in the cluster form known as Nissl bodies.
2. Dendrites:- Dendrites are the receiving or input portion of the neurons. They are short, hair- like or tightly branched.
3. Axon:- it is a long, thin, cylindrical projection which joins the cell body to the cone shaped structure called axon hillock. Axon propagates nerve impulses towards other neurons and then muscles or gland cells.
4. Myelin sheath:- axons are covered by a protective myelin sheath and this sheath is interrupted by gaps called Nodes of Ranvier. Myelin sheath serves as an excellent insulator.
Diagram:
Draw the structure of a neuron and explain its function.
Which signals will get disrupted in case of a spinal cord injury?
How does chemical coordination take place in animals?
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Why is the use of iodised salt advisable?
The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
How do we detect the smell of an agarbatti (incense stick)?
How do auxins promote the growth of a tendril around a support?
Which part of the brain maintains posture and equilibrium of the body?
How does our body respond when adrenaline is secreted into the blood?
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Why should a magnesium ribbon be cleared before burning in air?
Define the principal focus of a concave mirror.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Name some sources of direct current.
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Draw magnetic field lines around a bar magnet.
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
What is geothermal energy?
The change in focal length of an eye lens is caused by the action of the
(a) pupil. (b) retina.
(c) ciliary muscles. (d) iris.
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
How would you distinguish experimentally between an alcohol and a carboxylic acid?