Class 10 (biology) Science Control and coordination

Spinal cord

The spinal cord is a long unsegmented cord like structure. It extends from medulla of brain through vertebral canal of vertebral column of backbone. Like brain it is also protected by three meanings and cerebrospinal fluid. 

The spinal cord is hollow from inside and contains a cavity called central canal.

Functions

  • It conducts impulses to and from the brain.

  • It acts as reflex centre which controls all the spinal reflexes.

Peripheral Nervous system

All the whitish, thread like nerves which connects the various body parts with central nervous system, collectively constitute the peripheral Nervous system. 

It consists of cranial and spinal nerves.

1. Cranial Nerves  

        Those nerves which arise from the brain are called cranial or cerebral nerves. 

In men there are 12 pairs of cranial Nerves.

They leave the cranium through apertures and innervate may be sensory, motor or mixed in nature. 

2. Spinal Nerves 

      Spinal nerves arise from spinal cord and these are 31 pairs in number. These nerves after their origin leave the vertebral canal through apertures present in the adjacent vertebrate. Spinal nerves are mixed in nature.

Autonomic Nervous system

Autonomic Nervous system is that part of the peripheral Nervous system which lies outside parallel to the central nervous system.

It controls the activities of the organ inside our body automatically even without thinking about them.

The autonomic Nervous system can be subdivided into two subdivisions.

• Sympathetic Nervous system

• Parasympathetic Nervous system

The sympathetic nervous system and parasympathetic nervous system have opposite effects on internal organs of body. If one system exerts stimulatory effect on an organ, then the other system exerts an inhibitory effect on the same organ.

How are these Tissues protected ?

Brain is the control centre of human body. It regulates almost all the processes taking place in the body. But it is very delicate and vital organ. The protection provided by a bony box called cranium in which the brain sits. 

The bony box protecta from external shocks.

 

Brain is covered by three membranes called mennings. The space between the menings is filled by cerebrospinal fluid. This fluid protects from shocks and mechanical injury.

Spinal cord is also a vital organ. It also needs protection. The spinal cord is enclosed in hard vertebral column or backbone which protects it from external injuries.

Reflex action

  The word reflex refers to sudden action in response to something in environment.

Such a spontaneous involuntary, automatic, machanical response to any stimulus without the will of the animal is known as reflex action and the path followed by the impulse during reflex actions is known as reflex arc. 

Reflex actions are of two types : unconditioned reflexes and conditioned reflexes. 

Unconditioned reflexes are inborn. They do not require any training, learning, etc. They are protective in function.

Examples :

• salivation on smelling a favourite food. 

• withdrawal of hand on touching fire.

• sneezing, coughing, vomiting etc

Conditioned reflexes are not inborn. They are acquired by learning, training, etc.

Examples : 

• Learning of cycling 

• Wild animals of circus trained to perform strange acts. 

• salivation of mouth on hearing the bell of lunch break.

Coordination in plants 

Plants lack a specialised nervous system for controlling and coordinating the activities of the body. 

Plants are fixed and they cannot move from one place to another. They respond to stimuli by the movements of their parts.

Plants shows two types of movements :

• Movements independent of growth:

  The drooping of leaves of chui-mui plant is an example of such type of movement. 

No growth is involved in this type of movement. 

• Movements dependent on growth :

   When a seed germinate, the root goes down and the stem goes up into the air. 

These movements are caused by growth and can be stopped by preventing the growth.

Response to stimulus  

When touch a toch-me-not plant, its leaves droop. The point of movement of leaf is different from the point of touch. 

It means that there is a system which communicates the information of touch from the point of touch to the point of movement. But like animals, plants do not have a specialised tissue for conduction of information.

The plants use electrical-chemical means to conduct information from cell to cell. 

The drooping of leaf of touch-me-not plant is due to loss of water from the cells present in the lower half of the leaf base as a result of which the cells become flaccid and the leaf droops down. 

Plant Movements 

 The Movements of plants parts in response to external stimuli can be broadly classified into two types :

(a) Tropic Movements 

    Directional induced movements generally found in cylindrical organs where the direction of movement is related to the direction of stimulus are called Tropic movements. 

They are slow. The movements are either towards or away from the stimulus. 

The phenomenon of such movements is called tropism.

If the movement of the plant is towards the stimulus it is termed as positive tropism while when it takes place away from the stimulus, it is termed as negative tropism. 

   The type of stimulus, tropisms are of the types :

1. Phototropism

    The growth of plant or its parts in response to an external light stimulus is called phototropism and the movements aasociated with it are termed phototropic movements. 

Shoot of the growing plants bends towards light and thus shows positive phototropism. 

Roots of the plant move away from light and thus show negative phototropism.

2. Geotropism

      The growth of plant or its parts in response to gravity is called geotropism and the movements associated with it are called geotropic movement.

3. Hydrotropism

       The growth of plant or its parts in response to an external water stimulus is called hydrotropism and the movements associated with it are called hydrotropic movements.

4. Chemotropism

       The growth of plant or its parts in response to chemicals is called chemotropism.

 The growth of pollen tubes towards ovules is an example of chemotropism.

5. Thigmotropism

      It is the response to contact with some physical object. The coiling of tendrils around some support is an example of thigmotropism.