Introduction To Neurons

• Neurons are the structural and functional unit of nervous system.

• Control and coordination is managed by both nervous and muscular tissues.

• Receptors :

1. Olfactory: smell
2. Gustatory: taste

Pathway Of Transmission Of Nerve Impulse

Reflex Arc

• Reflex is a neurological mechanism or pathway that controls reflex.

• Reflex or reflex action refers to the instantaneous response to the stimuli without thinking.

• In reflex arc as soon as the spinal cord receives a signal the response will be seen even before the brain gets the signal.

• Whenever we touch any hot object the immediate response seen is an example of a reflex action.

• NOTE : Of course, reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. In fact many animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes.

Figure showing Pathway of transmission of nerve impulse

Nervous System

• Human Brain

Functions Of Different Parts Of Brain

• The brain is the main coordinating centre of our body.

• The communication between the central nervous system and the body is coordinated by the peripheral nervous system.

• The forebrain is the main thinking part of the brain.

• Separate areas are there in the forebrain for hearing, smell and sight.

• There are few association areas too in the brain which are clearly neither sensory nor motor.

• Most of the involuntary actions are controlled by the midbrain and the hindbrain.

• Medulla of hindbrain controls the following:

1. Salivation
2. Vomiting
3. Blood pressure

• Cerebellum of hindbrain controls the following:

1. Posture of the body
2. Balance of the body
3. Other associated voluntary actions

• NOTE : Brain is protected inside a bony box known as cranium or skull and inside this box brain is surrounded by a fluid filled balloon like structure known as cerebrospinal fluid which protects brain from any kind of shock or mechanical damage .

Coordination In Plants

TROPISM	Negative response	Positive response
Hydrotropism (response to water)	Shoot system	Root system
Geotropism (response to gravity)	Shoot system	Root system
Phototropism (response to light)	Root system	Shoot system
Thigmotropism (response to touch)
Chemotropism (response to chemicals)

• A tropism is the innate ability of an organism to turn or move in response to a stimulus.

• Example of plant responding to thigmotropism : Mimosa pudica ( touch-me-not-plant)

• Example showing response to chemotropism: germination of the pollen tube.

• Communication between the living cells is coordinated chemically.
• Communication coordinated electrically only to those cells that are connected to nervous tissue.
• Chemical coordination is slower whereas electrical coordination is much faster.

Functions Of Plant Hormone

1. Auxin : It is a light detecting hormone . It is synthesized at the shoot tips.  It stimulates the cells to grow longer on the side of the shoot which is away from light.
2. Gibberellins : Stimulates growth in stem.
3. Cytokinin : Promotes cell division. Present in areas of rapid cell division such as fruits and seeds.
4. Abscisic acid : It inhibits growth and also lead to wilting of leaves. Promote dormancy.
5. Ethylene : It stimulates ripening of fruits.

Hormones In Animals

HORMONE	ENDOCRINE GLAND	FUNCTIONS
Growth hormone	Pituitary gland	Stimulates growth in all organs
Thyroxine	Thyroid gland	Regulates metabolism for body growth
Insulin	Pancreas	Regulates blood sugar level
Testosterone	Testes	Development of male sex organs, stimulation of male secondary growth like growth of beards and moustaches, chest hair etc.
Estrogen & Progesterone	Ovaries	Development of female sex organs, and regulation of menstruation.
Adrenaline	Adrenal glands	It is also known as “fight and flight hormone” it increases the heart beat, blood pressure seeing any danger and again put the body back to normal conditions.

• Iodine is necessary for the thyroid gland to make thyroxine hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth.
• Iodine is essential for the synthesis of thyroxine.
• Iodine deficiency can lead to goitre.
• One prominent symptom of goitre is swollen neck.
• Growth hormone is one of the hormones secreted by the pituitary.
• Growth hormone regulates growth and development of the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism.
• Various changes during the puberty stage (ie. between 12-13 years of age) is due to the secretion of testosterone in males and estrogen in females.