CLASS 10 SCIENCE NOTES: CHAPTER - CONTROL AND COORDINATION

Coordination means working together of the various organs of an organism to adjust various activities of life.

Control & coordination ensures:

1. Correct movement for each specific change (stimulus).
2. No wrong or unnecessary actions.

Stimulus (Stimuli): Any change in the environment (internal or external) that produces a response in an organism. Example: Light, sound, smell, touch, temperature.

Receptors: Receptors are specialized structures that can convert various types of energy (stimuli) into the electrical signals (nerve impulses) used by the nervous system

Nervous System: The nervous system is composed of specialized tissues, called nervous tissue. The nerve cell or neuron is the functional unit of the nervous system.

Functions of the nervous system:

1. To receives information from the environment through sense organs.
2. To act according to through muscles and glands.

A neuron is the structural and functional unit of the nervous system.

Synapse: The gap between the terminal branches of axon of one neuron with the dendrite of another neuron is called synapse. Across this gap, the electrical impulse from the first neuron is converted into a chemical signal, which crosses the gap and starts a similar electrical impulse in the next neuron.

Neuromuscular Junction (NMJ): NMJ is the point where a muscle fibre comes in contact with a motor neuron carrying nerve impulse from the control nervous system.

Transmission of nerve impulse: Nerve impulses travel in the following manner from one neutron to the next.

Stimulus → Receptors → Dendrites of sensory neurons → Cell body → Axon → Synapse → Dendrites of relay neurons → Central Nervous System(CNS) → Dendrites of motor neurons → Cell body → Axon → Effector

Neuromuscular Junction:

It is the point where muscle fibre comes in contact with the motor neuron carrying a nerve impulse from the Central Nervous System (CNS). It works exactly the same way as impluses are transmitted across a synapse between two neurons.

Limitations to the use of electrical impulse:

1. The electrical impulse(signal) will reach only those cells that are linked through nerve tissue, not every cell in the animal's body.
2. After a nerve cell sends an electric impulse (signal), it needs some time to get ready again before it can send another signal.

Reflex Action:

A reflex action is a quick and automatic response to a stimulus, like when your hand quickly moves back after touching something hot.
It helps protect the body from harm and happens without thinking.
In a reflex action, the message goes directly from the sensory neuron to the motor neuron through a relay neuron.
Reflex actions are mainly controlled by the spinal cord, not the brain, because the brain would take more time to react.

Reflex Arc:

The pathway taken by nerve impulses in a reflex action is called reflex arc.

Components of Reflex Arc

1. Sense organs which receive the stimulus.
2. Sensory neurons conveys the stimulus to spinal cord
3. Spinal cord interprets the stimulus and gives command to motor neurons.
4. Motor neuron conveys the motor command to effectors (muscles).
5. Effectors or muscles execute the effect by neuromuscular movements.

The flowchart showing reflex arc is given below:

Stimulus(heat) → Receptors (Sense organs) → Sensory neuron → Spinal cord (Relay neuron) → Motor neuron → Effector organ (muscles) → Action (response)

Importance of reflex action

1. Provides immediate and automatic response to harmful stimuli. 
2. Protects the body from injury (e.g., withdrawing hand from hot object). 
3. Saves time by avoiding delay of thinking in the brain. 
4. Helps in survival and safety by giving quick reactions in emergencies.

Divisions of Nervous System

The human nervous system comprises of two major sub systems i.e. Central Nervous System (CNS) and Peripheral Nervous System (PNS)

CENTRAL NERVOUS SYSTEM (CNS)

It is the centre of control and coordination of all body activities. It comprises of brain and spinal cord. 

Human Brain:

The main coordinating centre of the body, which enables an organism to think and take decisions. 

Forebrain: It is the largest, most developed and main thinking part of the brain. It also controls the voluntary actions.

It comprises of:

1. Cerebrum: It acts as the main thinking part of the body. It controls intelligence, memory, learning, emotions, and voluntary movements.
2. Thalamus: It acts as a relay station, directing sensory signals to the cerebrum.
3. Hypothalamus: It regulates hunger, thirst, sleep, body temperature, and emotions. It also controls the pituitary gland (involved in hormone secretion).

Midbrain: It is the middle part of brain.

Functions of midbrain:

1. Controls the movement of head, neck.
2. Connects forebrain to hindbrain.
3. Controls reflex movements of eye muscles, pupil size etc.
4. Helps in processing sensory information and keeps the body alert.

Hindbrain: It is the lower part of the brain. It provides connection between spinal cord and rest of the brain. It consists of three parts:

1. Cerebellum: It is responsible for mantaning posture and coordination of the body movements.
2. Pons: It lies above the medulla. It helps in relaying signals between different parts of the body. It also takes part in respiration.
3. Medulla oblongata: It is the lower part of the brain. It controls involuntary actions like heartbeat, breathing, blood pressure, vomiting, salivation etc. 

Midbrain and hindbrain together forms the brain stem, i.e. central trunk of the brain and is connected to spinal cord.

Protection of the Brain:

1. The brain is protected by the bony skull (cranium).
2. A fluid called cerebrospinal fluid (CSF) surrounds it, which acts as a shock absorber and protects it from injury.

Protection of Spinal Cord

1. The spinal cord is protected by the vertebral column (backbone).
2. Cerebrospinal fluid (CSF) around the spinal cord provides cushioning and prevents damage.

Glands

Glands are special organs in our body that make and release substances like hormones, enzymes, sweat, or saliva.

There are two types of glands: exocrine glands and endocrine glands.

Exocrine Glands	Endocrine Glands
They have ducts and pour secretions to a specific organ or surface.	They are ductless glands and release hormones directly into the blood.
They secrete substances like enzymes, saliva, sweat, mucus etc.	They only secrete hormones.
They act local, meaning their influence is limited to the immediate area where the duct opens.	They act on distant target organs or tissues throughout the body with the help of blood.
Examples are salivary glands, sweat glands, and tear glands.	Examples are Pituitary gland (growth hormone), Thyroid gland (thyroxin), Adrenal gland (adrenaline), Pancreas (insulin), Testis (testosterone), Ovary (oestrogen).

Hormones

• They are chemical messengers secreted by endocrine glands, transported by blood to target organs.
• They provide control and coordination along with the nervous system.

                                    Endocrine glands in male          Endocrine glands in female

Gland	Hormone	Description
Hypothalamus	Growth hormone releasing hormone (GHRH)	Stimulates pituitary gland to release hormones
Pituitary gland	Growth hormone	Body growth, development of bones and muscles. Excess of growth hormone causes Gigantism. Deficiency of growth hormone causes Dwarfism
Thyroid gland	Thyroxine	Location below Larynx Regulates carbohydrate, protein, fat metabolism.  Deficiency of iodine causes Goitre (hypothyroidism)
Pancreas	Insulin	Control blood sugar levels.  Deficiency of insulin creates diabetes
Adrenal gland	Adrenaline	Prepare body to cope with emergency situations Also known as Fight or Flight Hormone Increases heartbeat (more supply of oxygen to muscles) Blood to the digestive system and skin is reduced Increased blood to skeletal muscles Breathing rate increases
Testes in males	Testosterone	Development of secondary male characters like deep voice, beard, and sex organs
Ovaries in females	Oestrogen	Development of secondary female characters like mammary glands, menstrual cycle and sex organs

Feedback mechanism - The timing and amount of hormone released are regulated by feedback mechanism. 

E.g.

• Blood sugar levels increase $\to$ pancreas produces more insulin. (positive feedback)
• Blood sugar levels decrease $\to$ insulin secretion is reduced. (negative feedback)

COORDINATION IN PLANTS

Plants do not have nervous system or muscle tissue like animals. However, they still show movement and response to stimuli. 

These movements of plants are broadly classified into two main types:-

Nastic movements	Tropic movements
Growth independent movements	Growth dependent movements
Non directional movements	Directional movements with respect to stimulus
Temporary and reversible	More or less permanent and irreversible
Found only in a few specialized plants	Found in all plants
Immediate action	Slow action

Types of tropical movements:

Types	Description	Example
Phototropism	Growth toward or away from light	A plant's stem bends to grow toward the sun.
Geotropism / Gravitotropism	Growth toward or away from gravity (straight down).	A plant's roots always grow down into the soil.
Hydrotropism	Growth toward or away from water.	Roots grow toward water in the soil.
Chemotropism	Growth toward or away from chemicals.	A pollen tube grows toward the right chemical signal to fertilize a flower.
Thigmotropism	Growth toward or away from touch or contact.	Tendrils (like on a pea plant) curl and wrap around a fence or stake for support.

Functions of Plant Hormones

Plant Hormone	Key Functions
Auxin (Growth Promoter)	Promotes cell elongation. Present at the tip of shoot and root. Directs growth towards light (phototropism) and against gravity. Helps fruit develop after flowering.
Gibberellins (Growth Promoter)	Helps in seed germination by breaking dormancy and getting seeds to sprout. Present at stem regions. Helps in the development of fruits and flowers.
Cytokinin (Growth Promoter)	Promotes cell division for overall growth and forming new tissues Delays the aging of leaves. Found in high concentration in fruits and seeds (rapid growth regions).
Abscisic Acid (Growth inhibitor)	Causes the tiny pores (stomata) on leaves to close to conserve water (stress response) Keeps seeds dormant (asleep) until conditions are right. Causes the wilting and shedding of leaves. Acts as a stress hormone.
Ethylene (Gaseous Hormone)	Stimulates the ripening of fruits (like bananas turning yellow). Promotes the natural shedding of leaves and fruits.