CLASS-X NERVOUS SYSTEM EPISODE – 7 STATE SYLLABUS

REFLEX ACTIONS

If you touch a hot object, you will with draw the hand immediately. A sudden gust of wind blows and dust raises, you blurt sneezing. If any substance like a tiny grain of rice or even smaller than that enters the wind pipe, you cough till the foreign substance is thrown out of wind pine. You close your eyes when bright light is focused on to you eyes.

Show animation A 1) A man touching hot flame 2) Remove it immediately B 1) A man on a dusty road 2) SneezesC 1) A woman eating food 2) Action of Cooking 3) Severe coughing. All the above actions are called REFLEX ACTIONS or REFLEXES. Reflexes are fast, immediate, automatic and involuntary responses of the body. The structural and functional unit that carries out reflexes is REFLEX ARC.

What are the actions of a reflex arc?

Animate reflex arcA reflex arc has

a) A RECEPTOR which is the place where the sensory cells generate the nerve impulse. They receive information about stimuli and generate the nerve impulse. They receive information about stimuli and generate electric potential.

b) Sensor or afferent nerve which carries messages from receptor to spinal cord.

c) Relay neurons which transmit impulses from the afferent to the efferent neurons in spinal cord.

d) Motor neurons which carry impulses from the spinal cord to the effector organs like muscles or glands or organs.

Animate fig 6.10 ICSE PAGE 871. Touching flame 2. Transmission of electric current through sensory neuron to spinal

cord.3. Transmission of electric current to muscle by motor neuron.4. Muscle contracts.5. Hand is removed

How many types of reflexes occur?The reflexes are of two types.1).Unconditional reflex, 2).Conditional reflex.

What is unconditional reflex?The unconditional reflexes are inborn. They are unconscious response to a given stimuli. A new born baby has the natural reflex to suckle mother’ s breast. One blinks when are object is brought very close to the eye. These reflexes are inherited. They are transmitted to next generation.Animate 1. A person with eyes open 2.Bring an object close to his eye suddenly 3.The person blinks closes eyes momentarily

What is conditional reflex?Conditional reflex - The response is experienced and learned during the life time.

If you rip hot milk your tongue is burnt. Will you repeat the same thing next time? The famous story of Tenali Rama Krishna and the cat given by the king serves as a best example for unconditional reflexes. Tenali Rama Krishna was not willing to part with the milk. He fed the cat with hot milk in the first serving. The cat eagerly put its mouth in the milk and burnt its mouth. From that day the cat never went near the milk even if it was cold. The response was recorded in its mind of hot milk. This is a conditional response.

Conditional responses however can be permanent once learned or can be forgotten or change the response according to situation or environmental conditions.

Our habits, likes, dislikes, prejudices, love, hatred, etc are conditional reflexes. The animals in the circus are trained to perform acts. They do it show after show.

A Russian scientists Ivan Pavlov’ s experiment proved that sight and smell of food caused salivation in a hungry dog. Does your mouth water when you see your favorite dish or when you get the smell of it.Look at this animation

Pavalov’ s experience:-(1) He rang a bell(2) There was no response from the dog.(3) Then he placed dog food(4) He repeated the same again and again(5) After some time the dog salivated at the ring of the bell even is

absence of food. We can understand that the dog at the first bell was not interested. But when it knew that a ring of bell is followed by food it responded to the ring of the bell. The sound of the bell is the stimulus and salivation a conditioned response.

The conditioned or acquired reflexes in man area) Learning processb) Playing musical instrumentsc) Typingd) Standing in attention when National anthem is played.

Dear students with this episode we conclude our sessions on Control and coordination. You must now be having a very clear idea of the different constituents of the Control and Coordination and their functions.