Chapter 6 - Control and Coordination

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 Chapter: Control and Coordination

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1. Nervous System

The nervous system is responsible for controlling and coordinating various activities of the body. It helps the body to respond to external and internal stimuli quickly by transmitting electrical impulses.

➤ Parts of the Nervous System:

1. Central Nervous System (CNS)
• Brain
• Spinal cord
  
  
2. Peripheral Nervous System (PNS)
• Nerves arising from the brain and spinal cord.
  Connects CNS to the rest of the body.

 

 2. Neuron – Structure & Diagram

A neuron is the structural and functional unit of the nervous system. It is a nerve cell that transmits messages in the form of electrical signals.

Structure of a Neuron:

1. Dendrites – Receive messages.
2. Cell body (Cyton) – Contains nucleus.
3. Axon – Long extension that carries impulses away.
4. Axon terminals – Pass the message to the next neuron or muscle.

Draw Labelled Diagram of a Neuron:

(Image reference: textbook image, draw with clear labels – Dendrites, Cell Body, Nucleus, Axon, Axon Terminal, Myelin sheath)

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 3. Types of Neurons & Functions

Type of Neuron	Function
Sensory Neuron	Carries impulses from sense organs to CNS
Motor Neuron	Carries impulses from CNS to muscles/glands
Interneuron/Relay Neuron	Connects sensory and motor neurons in CNS

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 4. Transmission of Nerve Impulse

1. A stimulus is received by dendrites.
2. It is converted into an electrical signal.
3. Signal travels through axon as nerve impulse.
4. At axon terminals, it releases chemicals (neurotransmitters).
5. These chemicals pass the impulse to the next neuron or muscle cell.

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 5. Pathway Followed by Nerve Impulse in Body

Sense organ → Sensory neuron → Brain/Spinal Cord → Motor neuron → Effector (muscle/gland)

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 6. Neuromuscular Junction

• A neuromuscular junction is the synapse (connection) between a motor neuron and a muscle fiber.
• Here, the neurotransmitters are released by the neuron to make the muscle contract.

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7. Limitations to the Use of Electrical Impulses

• Electrical impulses are short-lived and cannot be used for long-term responses.
• They require a network of neurons.
• Not suitable for growth-related or slow body responses.
• Hence, the body also uses chemical coordination (hormones) for slower processes.

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8. Reflex Action – Definition & Examples

Reflex action is a sudden, automatic response to a stimulus that does not involve thinking.

Examples:

• Pulling hand away from hot object.
• Blinking eyes when an object comes close.
• Sneezing due to dust.

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 9. Why Are Some Decisions Taken by Spinal Cord?

• For quick responses, the spinal cord acts without waiting for the brain.
• This helps in saving time and protecting the body from harm.
• Brain is informed later (after action).

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10. Reflex Arc – Definition with Image

A reflex arc is the pathway followed by nerve impulses during a reflex action.

Draw  Labelled Diagram of Reflex Arc:

(Textbook image style – draw and label: Receptor, Sensory Neuron, Spinal Cord, Motor Neuron, Effector)

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11. Components of Reflex Arc

1. Receptor – Detects stimulus (e.g., skin).
2. Sensory Neuron – Carries impulse to spinal cord.
3. Interneuron – In spinal cord, processes impulse.
4. Motor Neuron – Sends command to effector.
5. Effector – Muscle/gland that acts (e.g., hand pulls back).

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12. Importance of Reflex Action

• Quick response to danger.
• Protects the body from injury.
• Works even without conscious thought.
• Helps in survival.

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 Human Nervous System 

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 1. Central Nervous System (CNS)

The Central Nervous System consists of:

• Brain
• Spinal Cord

It controls most functions of the body and mind, including thoughts, movement, emotions, and sensations.

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2. Human Brain

The brain is the main control center of the body. It is soft, moist, and weighs about 1.3–1.4 kg in adults. It is enclosed in a bony skull (cranium) and protected by meninges and cerebrospinal fluid (CSF).

Parts of the Brain

The human brain is divided into three major parts:

A. Forebrain (Most developed & largest part)

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i) Cerebrum

• Largest part of the brain.
• Divided into two hemispheres (right and left).
• Surface is folded (to increase area).
• Functions:
• Intelligence, memory, learning.
• Voluntary actions (e.g., writing, walking).
• Thinking and decision-making.
• Sensory areas interpret signals from eyes, ears, skin, etc.

ii) Olfactory Lobes

• Small pair of lobes beneath cerebrum.
• Function: Detect and interpret smell.

iii) Hypothalamus

• Below the thalamus in the forebrain.
• Functions:
• Controls hunger, thirst, emotions.
• Regulates body temperature.

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🔷 B. Midbrain

• Located between the forebrain and hindbrain.
• Functions:
• Controls reflex movements of the head, neck, and eyes in response to light and sound.
• Controls eye movement and pupil size.

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🔷 C. Hindbrain

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i) Cerebellum

• Located under the cerebrum.
• Functions:
• Maintains posture and balance.
• Coordinates voluntary movements (like walking in a straight line).

ii) Pons

• Rounded structure above the medulla.
• Functions:
• Connects different parts of the brain.
• Assists in controlling breathing.

iii) Medulla Oblongata

• Lowest part of the brain, connects brain to spinal cord.
• Functions:
• Controls involuntary actions such as heartbeat, breathing, digestion, blood pressure, coughing, sneezing.

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Draw Diagram of Human Brain

(Draw or refer to a labelled textbook diagram with: Cerebrum, Cerebellum, Medulla, Pons, Midbrain, Hypothalamus, Olfactory lobes)

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🔹 3. Functions of the Brain

Brain Part	Functions
Cerebrum	Thinking, memory, learning, voluntary actions, sensory processing
Olfactory lobes	Detecting smells
Hypothalamus	Hunger, thirst, emotions, body temp, hormonal control
Midbrain	Reflexes for sight and sound
Cerebellum	Balance and coordination of movement
Pons	Breathing coordination
Medulla oblongata	Involuntary actions: heartbeat, breathing, swallowing

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4. Spinal Cord

• A long, cylindrical structure made of nerve tissues.
• Extends from the medulla oblongata to the lower back inside the vertebral column.
• Protected by vertebrae.
• Controls reflex actions and carries signals to and from the brain.

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Structure of Spinal Cord

• Surrounded by vertebral column (bony protection).
• Covered by meninges.
• Contains a central canal filled with cerebrospinal fluid (CSF).
• Gray matter inside, white matter outside.

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5. Protection of Brain and Spinal Cord

Organ	Protection
Brain	1. Skull (cranium)

            2. Meninges (3-layered membranes) 

            3. Cerebrospinal Fluid (CSF) – absorbs shocks and provides nutrition               |

| Spinal Cord|         1. Vertebral column (backbone)
                                2. Meninges
                                3. CSF |

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6. Peripheral Nervous System (PNS)

The Peripheral Nervous System includes all nerves outside the brain and spinal cord.

Types of Nerves in PNS:

Type of Nerve	Function
Cranial Nerves	Arise from the brain (12 pairs), control senses and facial muscles
Spinal Nerves	Arise from the spinal cord (31 pairs), control body muscles and skin
Visceral Nerves	Connect to internal organs; control activities like heartbeat, digestion

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Summary Table: Human Nervous System

Component	Details
CNS	Brain and Spinal Cord
Brain	Forebrain, Midbrain, Hindbrain
Spinal Cord	Reflex center, connects brain with body
PNS	Cranial, Spinal, and Visceral Nerves
Protection	Skull, vertebrae, meninges, and cerebrospinal fluid (CSF)

1. Coordination in Plants

Unlike animals, plants do not have a nervous system, but they do respond to stimuli such as light, gravity, water, touch, etc.

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Immediate Response to Stimuli in Plants

Some plants show quick movements when touched (e.g., Mimosa pudica or "touch-me-not"). These are nastic movements, which are not dependent on direction of stimulus.

Example:

• In Mimosa pudica, leaves droop quickly when touched.

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Means to Convey Messages in Plants

1. Electrochemical Means

• Plant cells use electrical and chemical signals to communicate between different parts.
• No specialized tissues like nerves in animals, but signals travel cell to cell.

2. Change in Cell Shape

• Response is brought about by changing the amount of water in plant cells.
• Cells either swell or shrink due to water movement, causing movement in plant parts.

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Tropic Movements in Plants

Tropic movements are directional movements in response to external stimuli.

Types of Tropic Movements:

Type	Stimulus	Movement Toward/Away	Example
Phototropism	Light	Toward (positive)	Shoot bends toward sunlight
Geotropism	Gravity	Root – Positive, Shoot – Negative	Roots grow downward, shoots upward
Hydrotropism	Water	Positive	Roots grow towards water
Chemotropism	Chemicals	Positive	Pollen tube grows towards ovule in flowers

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🌞 Phototropism (with Diagram)

• Shoots bend towards light = Positive phototropism
• Roots may bend away from light = Negative phototropism

Draw Diagram - Description:

• Draw a potted plant with a window on one side.
• Show the shoot bending toward the light.
• Label: Light source, shoot, root, direction of growth.

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Chemical Communication in Plants

Plants use hormones to regulate growth and responses to the environment.

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Plant Hormones (Phytohormones)

Hormone	Function
Auxins	Promote cell elongation, root growth, and phototropism
Gibberellins	Stimulate stem elongation, seed germination, and flowering
Cytokinins	Promote cell division, delay leaf aging, found in growing tissues
Abscisic Acid	Inhibits growth, causes stomatal closure during stress, induces dormancy

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Coordination in Animals – Hormonal Control

Animals use hormones produced by endocrine glands to regulate body functions.

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Glands

Endocrine Glands (Ductless)

• Release hormones directly into the bloodstream.
• Example: Thyroid, Pituitary, Adrenal, Pancreas (endocrine part), Testes, Ovaries

Exocrine Glands (With Ducts)

• Release enzymes or secretions through ducts.
• Example: Salivary glands, sweat glands, pancreas (exocrine part)

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Major Hormones and Their Functions

Hormone	Gland	Function
Adrenaline	Adrenal glands	Fight-or-flight response; increases heart rate, BP, energy
Thyroxine	Thyroid gland	Controls metabolism
Growth Hormone	Pituitary gland	Controls body growth; too much = gigantism, too little = dwarfism
Insulin	Pancreas	Regulates blood sugar level
Testosterone	Testes (males)	Male secondary sexual traits
Oestrogen	Ovaries (females)	Female secondary sexual traits and reproductive cycle

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Hormonal Disorders

Disorder	Cause
Dwarfism	Deficiency of Growth Hormone (GH)
Gigantism	Excess Growth Hormone during childhood
Goitre	Iodine deficiency → Thyroxine deficiency
Diabetes Mellitus	Deficiency of Insulin → High blood sugar

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Feedback Mechanism

• Regulation of hormone secretion is controlled by a mechanism called the feedback mechanism. It regulates the time and amount of secretion of hormones, e.g increased blood sugar levels are detected by the β-cells of pancreas, which responds by producing more insulin

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Quick Summary

Topic	Key Points
Plant Coordination	Uses hormones and cellular responses, no nerves
Immediate Response	Due to turgor changes; seen in touch-me-not plant
Tropic Movements	Directional, based on stimulus (light, gravity, water, chemicals)
Plant Hormones	Auxins, gibberellins, cytokinins, abscisic acid
Animal Hormones	Secreted by endocrine glands; control body functions
Hormonal Disorders	Dwarfism, gigantism, goitre, diabetes
Feedback Mechanism	Maintains hormone levels using signals and negative feedback