blog10d2: August 2013

CLASS WORK-2

CLASSX D&H BIOLOGY

7/8/2013 CONTROL AND COORDINATION (COND)

REFLEX ACTION AND REFLEX ARC

REFLEX ACTION – It is defined as a spontaneous automatic and mechanical response to a stimulus by an organ or a system of organs controlled by the spinal cord without the involvement of brain. For example

1) Constriction of pupil in bright light.

2) Pulling away of the hand on touching a hot object

3) Watering of mouth at the thought of good food or at the sight of tasty food

4) Playing a musical instrument

NEED OF REFLEX ACTION:- Reflex actions are quick and show immediate response to stimuli without being processed by the brain. To understand the need of reflex action let us consider a situation when we touch something very hot we move our hand away immediately without thinking and so we are able to save ourselves. On the other hand, if this response involves thinking process then, the information of touching a hot body will be sent to brain that lies in the forward end of the skull. The brain will process the information and respond through motor nerves. It may take enough time for us to get burnt.

So to avoid such situations, these actions are completed quickly with the help of the spinal cord, although the information also goes on to reach the brain.

MECHANISM OF REFLEX ACTION:- It involves the following steps

(i) Receptor organ receives the stimulus and activates the sensory nerve impulse.

(ii) The message is passed on to the spinal cord in the form of sensory impulse

(iii) The neurons in the spinal cord transmit the sensory nerve impulse to motor neuron.

(iv) Motor nerve conducts the impulse to the effecter muscle or gland which shows appropriate response.

REFLEX ARC:- The pathway followed by sensory and motor nerves in a reflex action is called the Reflex Arc.

COMPONENTS OF REFLEX ARC

FOUR MAIN COMPONENTS

· Receptor or sensory organ to perceive the stimulus

· Sensory neuron which carries the message from receptor to the spinal cord.

· Relay neuron of the spinal cord which transmit impulse from sensory neuron to the motor neuron

· Motor neuron which carries the message from the spinal cord to the muscles or

glands.

HOW DOES THE NERVOUS TISSUE CAUSE ACTION:- Nervous coordination takes place with the help of nerve cells. Nerve cells carry nerve impulses. From the axon of one cell to dendrites of the next nerve cell, transmission occurs through chemicals called neurotransmitters. Ultimately the nerve impulse reaches the muscle. Muscle cells have special contractile proteins that change their shape and arrangement in response to nervous electrical impulses when the muscle cells attain a new shape, they contract and bring about movement. So a coordinated behavior has stimulus, receptor organs, sensory neuron, coordinator, motor neuron, effectors organ and response.

II] PERIPHERAL NERVOUS SYSTEM:- The peripheral nervous system includes the nerves that arise from brain (cranial nerves) and spinal cord (spinal nerves). These nerves carry impulses to and from the CNS. These are 12 pairs of cranial nerves and 31 pairs of spinal nerves.

II] AUTONOMIC NERVOUS SYSTEM:- ANS also known as visceral nervous system. It consists of special set of peripheral nerves that control and coordinate the activities of internal organs like heart muscles, glands, & smooth muscles (muscles of blood vessels). It is involuntary in action and controls heart beat, peristaltic movements etc. It is formed by the pair of chain of ganglia found on both side of the vertebral column.

‘CHEMICAL COORDINATION’

NEED FOR A CHEMICAL COORDINATION: One drawback of the nervous system is that the electrical impulses generated reach only those cells which are connected by nervous tissue and not each and every cell. Second drawback is that the cells that receive an impulse will take some time to reset to generate and transmit impulses. So animals have chemical coordination to overall these two drawbacks. Chemical coordination takes place in animals with the help of hormones secreted by the endocrine glands.

Endocrine glands are ductless glands that pour their secretion (hormones) directly into the blood. Blood carries the hormone to the target organ which shows a response to that hormone.

Features of Hormones:-

1) They are secretion of endocrine glands

2) They are directly poured into the blood stream

3) They are required in small quantity

4) They act on particular organs called target organs.

5) Chemically they may be proteins or steroids

6) They are very specific in function

S. No.	Name Glands	Location	Hormone and their features/functions
1	Hypothalamus	Lower side of brain	Releases hormone to regulate secretion of hormones by pituitary gland
2	Pituitary	Lower side of brain attached to hypothalamus	1) Growth hormone (GH) it regulates growth and development of the body. Over secretion causes gigantism and under secretion causes dwarfism 2) TSM –Thyroid stimulating hormone
3	Thyroid	In the throat part	Secretes thyroxin which regulates metabolism of carbohydrates, fats and proteins. Thyroid gland needs iodine to make thyroxin hormone. Iodine deficiency causes goitre i.e. swelling of thyroid gland in the neck region (for this reason we are advised to take iodised salt)
4	Parathyroid	Near thyroid	Calcitonin- Regulates calcium and phosphate levels in blood
5	Pancreas	In the abdomen	1) Insulin- Decreases blood glucose level. In case of under activity sugar level in the blood rises causing diabetes.(causes restlessness, nervousness, excretion of glucose in urine) These patients take insulin injections 2) Glucagon – It increases the glucose level in blood. Regulates conversion of glycogen back to glucose
6	Adrenal glands (a pair)	Just above each kidney	Adrenalin- It acts on heart which beats faster to supply more oxygen to muscles. The breathing rate increases to enable the body to deal with the emergency situation. It prepares us to meet any emergency
7	A pair of ovaries in females	In the lower abdomen	Estrogen– Development of female sex organs and secondary sexual characteristics like growth of mammary glands Progesterone- Release of ovum and maintaining pregnancy
8	A pair of testes in males	Outside the body in the scrotum	Testosterone- Development of male sex organs and secondary sexual characteristics like growth of beard moustache etc.

FEED BACK MECHANISM:- It is important that hormones should be secreted in precise quantities therefore the timing and amount of hormone released are regulated by feedback mechanism.

Example – When we eat food, the blood glucose level rises, so information is sent to the cells of the pancreas which respond by producing more insulin to lower down the glucose level. As the blood sugar level becomes normal, insulin secretion is automatically reduced.

EXERCISE-2

1) Draw a diagram of ‘reflex arc’ and label in it sensory neuron, motor neuron, relay neuron and receptors.

2) What is the role of brain in reflex action?

3) How does chemical coordination take place in animals?

4) What is the difference between reflex action and walking?

5) Why is the use of iodised salt advised?

6) Why are some patients of diabetes treated by giving injections of insulin?

7) Which signals will get disrupted in case of a spinal injury?

8) How are involuntary actions and reflex actions different from each other?

9) What is the need for a system of control and coordination in an organism?

10) Identify the gland that secrete

I) Insulin

II) Thyroxin

11) Explain with an example how the timing and amount of hormone secreted are regulated in human body?

12) How does our body respond when adrenal gland secretes its hormone?

Seema Misra

blog10d2

Friday 23 August 2013

Wednesday 21 August 2013

Thursday 15 August 2013

Wednesday 14 August 2013

Monday 12 August 2013

Tuesday 6 August 2013

Monday 5 August 2013