The Nervous System

ICSE Class 10 Biology • Chapter 08

1. The Neuron (Nerve Cell)

Neuron: The structural and functional unit of the nervous system needed to receive and transmit stimuli.

Parts of a Neuron:

Cyton (Cell Body): Contains nucleus and cytoplasm.
Dendrites: Short, branched processes that receive impulses towards cyton.
Axon: Long process that carries impulses away from cyton.
Myelin Sheath: Insulating fatty layer over axon. Speed up impulse. (White Matter).
Synapse: The junction between two neurons. Neurotransmitters (Acetylcholine) help in transmission.

Practice Q1: Neuron Structure

CONCEPT CHECK Which part of the neuron accelerates impulse transmission?

Ans: Myelin Sheath (Insulates the axon and allows saltatory conduction).

2. Divisions of Nervous System

CNS (Central)	PNS (Peripheral)	ANS (Autonomic)
Brain and Spinal Cord.	Nerves arising from Brain (Cranial) and Spinal Cord (Spinal).	Sympathetic and Parasympathetic systems.

3. The Brain

Cerebrum: Largest part. Seat of intelligence, memory, consciousness. Two hemispheres connected by Corpus Callosum.
Cerebellum: Maintains body balance and coordination.
Medulla Oblongata: Controls involuntary activities like heartbeat, breathing.

4. The Spinal Cord

A cylindrical structure extending from Medulla. Protected by Vertebral Column.

Structure: Outer White Matter, Inner Gray Matter (H-shaped).
Function: Controls Reflex Actions below the neck. Conducts impulses to/from brain.

5. Reflex Action and Reflex Arc

Reflex Action: An immediate, automatic, involuntary response to a stimulus without consulting the brain (e.g., withdrawing hand from hot object).

Reflex Arc (Pathway):

Stimulus $\rightarrow$ Receptor $\rightarrow$ Sensory Neuron $\rightarrow$ Spinal Cord (Association Neuron) $\rightarrow$ Motor Neuron $\rightarrow$ Effector (Muscle) $\rightarrow$ Response.

Practice Q2: Pathway

BOARD QUESTION Arrange the following in the correct order of a reflex arc: Effector, Receptor, Motor Neuron, Sensory Neuron, Spinal Cord.

Ans: Receptor -> Sensory Neuron -> Spinal Cord -> Motor Neuron -> Effector.

6. Sense Organs: The Eye

Focusing (Accommodation): Ability of the lens to change its curvature to see near and far objects clearly.

Defects of Vision:

Myopia (Near-sightedness): Cannot see far objects. Image forms in front of retina. Correction: Concave Lens.
Hypermetropia (Far-sightedness): Cannot see near objects. Image forms behind retina. Correction: Convex Lens.

7. Sense Organs: The Ear

Cochlea: For Hearing.
Semicircular Canals: For Dynamic Balance (spinning).
Vestibule: For Static Balance.

Exam Practice Questions

Practice Q3: The Eye

APPLICATION A person can read a book clearly but cannot see the blackboard in class. Name the defect.

Ans: Myopia (Near-sightedness). Corrected by Concave lens.

Q1: Differentiate between White Matter and Gray Matter.

Ans: White matter contains Myelinated axons (Outer part of Spinal Cord). Gray matter contains Cytons/Cell bodies (Inner part of Spinal Cord).