Control and Coordination

 Control and Coordination 

Introduction

All living organisms need control and coordination to respond to changes in their environment (stimuli).

• Control → Regulation of body activities.

• Coordination → Linking of different body parts to work together efficiently.

In humans, nervous system and endocrine system work together for control and coordination.
In plants, control and coordination are done by hormones and growth responses.

Human Nervous System

The nervous system controls and coordinates all voluntary and involuntary actions.

Main Parts:

1. Central Nervous System (CNS) → Brain + Spinal cord

2. Peripheral Nervous System (PNS) → Nerves from CNS to body

3. Autonomic Nervous System (ANS) → Involuntary activities (e.g., heartbeat, digestion)

Neuron (Structure and Function)

• Neuron = Basic unit of the nervous system.

• It transmits messages in the form of electrical impulses.

Structure:

1. Cell body (Cyton) – Contains nucleus.

2. Dendrites – Receive impulses from other neurons.

3. Axon – Long fibre that carries impulses away from cell body.

4. Axon terminals – Pass impulses to next neuron or muscle.

Direction of impulse:
Dendrite → Cell body → Axon → Axon terminal

Reflex Action

Reflex action: Sudden, involuntary, and automatic response to a stimulus.
Example: Withdrawal of hand from a hot object.

Pathway of reflex (Reflex arc):
Stimulus → Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector (muscle)

Importance:

• Protects the body from injury.

• Saves time as it does not involve the brain initially.

Human Brain

The brain is the main coordinating centre of the body, protected by:

• Cranium (skull) – hard outer covering

• Meninges – protective membranes

• Cerebrospinal fluid (CSF) – shock absorber

Parts of Brain and Their Functions:

Part	Location	Functions
Cerebrum	Largest part, upper region	Controls intelligence, memory, learning, voluntary actions, thinking
Cerebellum	Below cerebrum, back side	Maintains posture, balance, coordination
Medulla oblongata	Brainstem	Controls involuntary actions (heartbeat, breathing)
Pons	Bridge between cerebrum and cerebellum	Involved in respiration
Midbrain	Between forebrain and hindbrain	Controls reflexes of eyes and ears

Coordination Between Brain and Spinal Cord

• Spinal cord: Controls reflex actions and relays messages between body and brain.

• Brain: Controls complex voluntary actions and higher mental activities.

Coordination in Animals

Animals coordinate through:

1. Nervous system (fast, electrical impulses)

2. Endocrine system (slow, hormonal messages)

Control and Coordination in Plants

Plants lack a nervous system.
They respond to stimuli through hormones and tropic movements.

Plant Movements

1. Tropic Movements

→ Directional growth movements of plants in response to external stimuli.

Type	Stimulus	Example
Phototropism	Light	Shoot bends towards light
Geotropism	Gravity	Roots grow downward
Hydrotropism	Water	Roots grow towards moisture
Chemotropism	Chemicals	Growth of pollen tube towards ovule
Thigmotropism	Touch	Tendrils coil around support

2. Nastic Movements

→ Non-directional responses to stimuli (independent of direction).
Example: Folding of leaves in Touch-me-not (Mimosa pudica).

Plant Hormones (Phytohormones)

Hormone	Function	Example of Action
Auxin	Cell elongation, phototropism	Bending of shoots towards light
Gibberellin	Stem elongation, germination	Growth of sugarcane
Cytokinin	Cell division, delay ageing	Found in coconut milk
Abscisic acid (ABA)	Inhibits growth, causes wilting	Closing of stomata during drought
Ethylene	Fruit ripening, leaf fall	Ripening of banana, mango

Chemical Coordination in Animals (Endocrine System)

The endocrine system uses hormones for slow and long-term coordination.

Major Endocrine Glands and Their Functions

Gland	Hormone	Function
Pituitary gland (Master gland)	Growth hormone, TSH, etc.	Controls other glands, growth
Thyroid gland	Thyroxine	Regulates metabolism
Parathyroid glands	Parathormone	Regulates calcium levels
Adrenal glands	Adrenaline	Prepares body for emergencies (“fight or flight”)
Pancreas	Insulin, Glucagon	Controls blood sugar level
Testes (in males)	Testosterone	Controls male sexual traits
Ovaries (in females)	Estrogen, Progesterone	Controls female sexual traits
Pineal gland	Melatonin	Controls sleep cycles

Difference Between Nervous and Hormonal Control

Nervous Control	Hormonal Control
Fast and short-term	Slow and long-term
Electrical impulses	Chemical messengers (hormones)
Conducted through neurons	Transported by blood
Immediate response	Delayed response

Important Questions

1. What is a reflex arc?
   → Pathway of impulse during reflex action.

2. Name the largest part of the human brain.
   → Cerebrum.

3. Which hormone regulates sugar level in blood?
   → Insulin.

4. Which plant hormone helps in fruit ripening?
   → Ethylene.

5. Which movement is shown by touch-me-not plant?
   → Nastic movement.

6. Which part of the brain controls balance and posture?
   → Cerebellum.

7. What is the function of thyroxine hormone?
   → Regulates metabolism.

Summary Points

• Neuron is the structural and functional unit of the nervous system.

• Reflex action is a rapid and involuntary response.

• Brain is divided into forebrain, midbrain, and hindbrain.

• Plants respond to light, gravity, water, and touch.

• Hormones coordinate growth and development in both animals and plants.