s this point from the end suspended between your fingers?
2 cm up (nearly at the end of the scale).
- Why did this happen?
Because it is the sudden action. To hold it fastly. The exact point went up.
- How fast do you think the process was?
The process was so fast in a fraction of a second.
- What makes this kind of communication possible?
Rapidity of response indicates an efficient communication system linking those parts that pick up stimuli that trigger a response by the nervous system.
Activity – 2
Observe the permanent slide of nerve cell or neuron under microscope and try to find out its parts. Compare with the following diagram.
Structural unit of the nervous system is the nerve cell or neuron. Neuron is highly specialised cell. Neurons carry impulses or messages. New nerve cells are not produced to replace the damaged or destroyed nerve cell. A neuron has three parts. They are
- axon and
1. The cyton:
- It is also called the cell body.
- It has a large and round nucleus.
- In the cytoplasm of the cyton, nissl granules are present.
- It is the long and cylindrical process that arises from the cyton.
- In some nerve cells, axon is surrounded by a layer of fatty material known as myelin sheath.
- The myelin sheath is not continuous throughout length of the axon.
- It is broken at regular intervals.
- These broken spots are called as nodes of Ranvier.
3. Dendrites: Arise from the cyton they are much branched, when compared to axon.
Activity – 3
What is knee jerk reflex?
Cross the legs, in a seated position, so that the lower half of the uppermost leg hangs freely over the other. Strike the area below the knee cap sharply, while firmly grasping the front part of the thigh with the other hand. Note the changes in shape of the thigh muscles.
- What changes do you observe in the thigh muscle?
The thigh muscles get contracted and becomes short.
- What do we call this type of response?
This type of responses are called involuntary actions. Such type of actions in the body are carried by without our involvement and our knowledge.
- What do we call the action of kicking a foot ball?
Kicking of a foot ball is a voluntary action’ These actions are within our control.
- How is the knee jerk action takes place?
In the knee jerk action a nerve pathway was involved.
v) Do you think most of the functions in our body go about in an involuntary manner? Why ? Why not ?
Most of our body functions are done without the involvement of our knowledge. For example, heart beating, respiration, digestion, etc., are the involuntary actions which are carried by our body.
Activity – 4
Touch the leaves of Mimosa pudica (athipathi, touch me not) plant and observe the response of leaves.
- Are they folding?
When the leaves of Mimosa are touched the leaves get folding. Touching the leaves is the stimulus and folding is the response.
- In which direction the folding of the leaves take place?
The folding of the leaves take place inward direction.
- Give some examples of situations in plants responding to a certain stimulus.
Examples: The sun flower turning to the direction of sun, the bending response of the plant when it is kept in the dark. Some of leaves of the trees opens at the day time and closes after sun set.
Phototropism of stem and geotropism of roots, hydrotropism of roots of plants growing towards water and thigmotropism where the creepers like cucumber, bitter – gourd takes the help of tendrils and wind around the support are some of the examples of response to stimulus in plants.
Activity – 5
Take a glass jar and fill with soil. Sow a bean seed near the wall of the jar. After 4 – 5 days you will notice seed germination. Keep the jar under the sun. Observe how root and shoot grows. Then tilt the glass jar and keep the plant horizontally. Observe the direction of the root and shoot growth for more than a week.
- Does the shoot take a horizontal tilt after a week?
After a week the shoot takes a horizontal tilt.
- Which side of the shoot may have grown more and which side less to bring about this effect?
The shoot grown more towards the light