NCERT Exemplar Solutions
Class 10 - Science - CHAPTER 7: Control and Coordination

Long Answer Questions

Structure of a Neuron

A neuron consists of three main parts:

1. Cell body (Cyton): Contains the nucleus and cytoplasm. It performs metabolic activities of the cell.
2. Dendrites: Short, branched extensions that receive impulses from other neurons or receptors.
3. Axon: A long, cylindrical projection that carries impulses away from the cell body to other neurons, muscles or glands.

Functions of a Neuron

1. Receives information through dendrites.
2. Processes information in the cell body.
3. Transmits nerve impulses along the axon.
4. Transfers the signal to the next neuron, muscle or gland through synapses using chemical messengers.

The brain is divided into three major parts:

1. Forebrain:
   • Controls intelligence, memory, learning and emotions.
   • Processes sensory information such as smell, touch, taste, vision and hearing.
2. Midbrain:
   • Acts as a relay centre for auditory and visual reflexes.
3. Hindbrain:
   • Cerebellum: Maintains posture, balance and coordination.
   • Pons: Helps in regulating breathing.
   • Medulla: Controls involuntary activities like heartbeat, blood pressure, swallowing and vomiting.

Central Nervous System (CNS):

The CNS consists of the brain and spinal cord.

Peripheral Nervous System (PNS):

The PNS includes all nerves that connect the CNS to different parts of the body.

Protection of CNS

1. Brain box (cranium): A bony structure that protects the brain.
2. Vertebral column: Protects the spinal cord.
3. Meninges: Three membrane layers that cover and protect the CNS.
4. Cerebrospinal fluid (CSF): Cushions the CNS and absorbs shocks.

(a) Thyroxin: Regulates carbohydrate, protein and fat metabolism.

(b) Insulin: Regulates blood sugar levels.

(c) Adrenaline: Increases heart rate and supply of blood to organs during emergency situations.

(d) Growth hormone: Regulates growth and development of the body.

(e) Testosterone: Controls the changes of body features associated with puberty in males.

Plant Hormones and Their Functions

• Auxins: Promote cell elongation and root growth.
• Gibberellins: Stimulate stem growth and seed germination.
• Cytokinins: Promote cell division and delay ageing in leaves.
• Abscisic acid (ABA): Induces dormancy and causes falling of senescent leaves.

Reflex Actions

Reflex actions are automatic, quick responses to stimuli that do not involve conscious thought.

Examples:

• Withdrawing hand from a hot object.
• Knee-jerk reflex.

Reflex Arc

A reflex arc is the pathway through which nerve impulses travel during a reflex action.

1. Receptor detects stimulus.
2. Sensory neuron carries impulse to spinal cord.
3. Interneuron processes the information.
4. Motor neuron carries impulse to effector.
5. Effector produces a response.

Coordination by Nervous System

The nervous system coordinates body activities through electrical impulses. It involves dendrites, axons, synapses and neurotransmitters. It controls actions of muscles and glands.

Coordination by Hormonal System

Endocrine glands secrete hormones that are released into the bloodstream. Hormones reach specific target tissues where they trigger biochemical changes.

Combined Coordination

• Nervous system provides quick responses.
• Hormonal system provides slow but long-lasting control.
• Together they maintain balance and ensure proper functioning of the body.

Different endocrine glands secrete hormones, which are chemical messengers. These hormones are released into the blood and transported to target tissues or target organs.

In the target tissues, hormones trigger specific biochemical or physiological activities such as growth, metabolism, reproduction and development.

When an electrical signal reaches the axonal end of a neuron, it releases chemical substances (neurotransmitters). These chemicals cross the synapse and initiate an electrical signal in the dendrite of the next neuron.

The dendritic end does not release these chemicals; therefore, the reverse conversion from dendrite to axon cannot occur. Hence, signal transmission is unidirectional.