ICSE Class 10 Biology: Nervous System — Complete Notes 2026

Organisation of the Nervous System

• CNS: brain + spinal cord; PNS: cranial and spinal nerves
• Somatic NS: voluntary control of skeletal muscles; Autonomic NS: involuntary (sympathetic and parasympathetic)
• Nervous system works via electrochemical impulses; endocrine system via hormones

Neuron — Structure and Types

• Parts: dendrites (receive signals), cell body (nucleus), axon (transmit signals), myelin sheath, Schwann cells, nodes of Ranvier, axon terminals
• Types: sensory (afferent), motor (efferent), interneuron (relay/connector)
• Myelin sheath increases speed of impulse conduction (saltatory conduction)

Nerve Impulse

• Resting potential: inside −70 mV relative to outside (K⁺ inside, Na⁺ outside)
• Action potential: Na⁺ rushes in → depolarisation → K⁺ rushes out → repolarisation
• Impulse travels in one direction along neuron; synapse ensures directionality

Synapse and Neurotransmitters

• Synapse: gap between axon terminal of one neuron and dendrite of next
• Neurotransmitter (e.g., acetylcholine) released from pre-synaptic knob → diffuses across cleft → binds receptor
• After signal: neurotransmitter broken down by enzymes (e.g., acetylcholinesterase)

Reflex Action and Reflex Arc

• Reflex: rapid, involuntary response to a stimulus; protective in nature
• Reflex arc: receptor → sensory neuron → spinal cord (interneuron) → motor neuron → effector
• Examples: knee-jerk (monosynaptic), withdrawal reflex; spinal cord is control centre

Brain — Parts and Functions

• Cerebrum: largest; voluntary movements, intelligence, memory, speech, sensation
• Cerebellum: coordinates balance and fine motor movements
• Medulla oblongata: controls involuntary activities — breathing, heart rate, swallowing

ICSE Exam — Nervous System

• Draw a labelled diagram of a motor neuron
• Describe the sequence of events in a reflex arc with an example
• State two differences between a reflex action and a voluntary action