Class 10

Human Nervous System: Neuron Structure & Reflex Action (Class 10 Notes)

📅 Sunday, 18 January 2026 📖 3-5 min read

Nervous System: Neuron, Synapse and Reflex Action

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Definition: Control and Coordination is the ability of an organism to detect changes in the environment (stimuli) and produce an appropriate response to maintain homeostasis. In animals, this is achieved by the Nervous System and the Endocrine System.

All living organisms respond and react to changes in the environment around them. These changes in the environment to which organisms respond are called stimuli (e.g., heat, cold, sound, smell, touch). In humans, the nervous system provides a rapid means of communication using electrical impulses.

1. The Neuron (Structural Unit)

The Neuron or nerve cell is the fundamental unit of the nervous system. It is specialized to detect, receive, and transmit information. A neuron consists of three main parts:

  • Cell Body (Cyton): Contains the nucleus and cytoplasm. It maintains the growth of the cell.
  • Dendrites: Short, branched projections that acquire information (signal) and conduct it towards the cell body.
  • Axon: A long single fiber that conducts impulses away from the cell body to the next neuron.
  • Nerve Ending: The terminal part of the axon where the electrical impulse is converted into a chemical signal.
Cell Body Dendrite Axon Nerve Ending
Fig 1: Structure of a Neuron.
(Schematic representation; not to scale)

The Synapse (The Gap)

Neurons are not connected physically. There is a microscopic gap between the nerve ending of one neuron and the dendrite of the next neuron. This gap is called a Synapse.

  • Mechanism: At the nerve ending, the electrical impulse sets off the release of some chemicals (neurotransmitters).
  • These chemicals cross the gap (synapse) and start a similar electrical impulse in the dendrite of the next neuron.

2. Reflex Action

A Reflex Action is a sudden, automatic, and involuntary response to a stimulus. It is not under the conscious control of the brain. Example: Pulling back your hand immediately upon touching a hot object.

Reflex Arc (The Pathway)

The pathway taken by nerve impulses in a reflex action is called a Reflex Arc. Reflex arcs are formed in the Spinal Cord (although the information eventually reaches the brain).

A relay neuron (interneuron) inside the spinal cord connects the sensory neuron to the motor neuron, ensuring rapid transmission of impulses.

Receptor (Skin) Spinal Cord Sensory Neuron Motor Neuron Effector (Muscle)
Fig 2: Reflex Arc Pathway.
Stimulus → Receptor → Sensory Neuron → Spinal Cord → Motor Neuron → Effector
Common Mistake: Reflex actions are controlled by the spinal cord, not by the brain.

Points to Remember for Exam

  • Unit: Neuron is the structural and functional unit of the nervous system.
  • Direction: Nerve impulses travel in only one direction: Dendrite → Cell Body → Axon → Nerve Ending.
  • Impulse Flow: Impulse always travels from the axon of one neuron to the dendrite of the next neuron.
  • Speed: Electrical impulses are faster than chemical signals but cannot reach cells that are not connected by nervous tissue.
  • Center: The main center for reflex action is the Spinal Cord.

Chapter Assessment

A. Very Short Answer Type Questions (1 Mark)

  • Q1. What is the gap between two neurons called?
    Ans: Synapse.
  • Q2. Which part of the neuron acquires information?
    Ans: Dendrite.
  • Q3. Identify the effector in a reflex arc involving touching a hot plate.
    Ans: Muscle in the arm.
  • Q4. In which form does information travel through the axon?
    Ans: Electrical impulse.
  • Q5. Name the part of the neuron where information is converted into a chemical signal.
    Ans: Nerve ending.
  • Q6. Define receptors.
    Ans: Receptors are specialized cells in sense organs that detect stimuli.
  • Q7. Which system provides control and coordination in animals alongside the nervous system?
    Ans: Endocrine System (Hormonal System).
  • Q8. Where are gustatory receptors located?
    Ans: On the tongue (detect taste).
  • Q9. Where are olfactory receptors located?
    Ans: In the nose (detect smell).
  • Q10. Is reflex action voluntary or involuntary?
    Ans: Involuntary.

B. Short Answer Type Questions (2-3 Marks)

Q11. What happens at the synapse between two neurons?
At the synapse, the electrical impulse generated at the nerve ending of one neuron triggers the release of chemicals (neurotransmitters). These chemicals cross the gap and start a similar electrical impulse in the dendrite of the next neuron. This ensures the signal travels in one direction.
Q12. Why is the flow of signals in a synapse unidirectional?
The flow is unidirectional because the chemicals (neurotransmitters) are produced only at the nerve endings (axon tip) and the receptors to detect them are present only on the dendrites of the next neuron. Thus, the signal can only go from Axon to Dendrite.
Q13. Differentiate between Sensory Neuron and Motor Neuron.
Sensory NeuronMotor Neuron
Carries impulses from receptors (sense organs) to the brain/spinal cord.Carries impulses from the brain/spinal cord to effectors (muscles/glands).
Q14. Draw a flowchart of the path of a reflex arc.
Stimulus → Receptor → Sensory Neuron → Spinal Cord (Relay Neuron) → Motor Neuron → Effector (Muscle) → Response.
Q15. Why are reflex arcs evolved in animals?
Reflex arcs have evolved as an efficient way of functioning in the absence of a true thinking process. Thinking is a complex and slow process. To protect the body from sudden danger (like burning), a quick mechanism (reflex) was required which bypasses the thinking process of the brain.

C. High Order Thinking Skills (HOTS)

Q16. If the cerebellum is not functioning, what will happen?
The cerebellum controls voluntary movements, balance, and posture. If it is damaged, the person will not be able to maintain body balance, walking in a straight line will be difficult, and precision in movements (like picking up a pen) will be lost.
Q17. "All involuntary actions are reflexes, but all reflexes are not involuntary." Is this statement true?
No, this statement is confused. The correct concept is: All reflexes are involuntary actions, but not all involuntary actions are reflexes. For example, heart beating and digestion are involuntary but they are not sudden responses to external stimuli, so they are not reflexes.
Reference: NCERT Science Textbook Class X (Chapter 7: Control and Coordination).
Last Updated: January 2026
Reviewed under Sarkari Service Prep Academic Policy.

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