Human Anatomy — Nervous System
Introduction
The nervous system coordinates and controls all body activities through electrical signals (nerve impulses). In ICSE Class 10 Biology, you study the structure of the brain and spinal cord, the reflex arc mechanism, and the sense organs (eye and ear).
Neuron (Nerve Cell)
The neuron is the structural and functional unit of the nervous system.
| Part | Function |
|---|---|
| Dendrites | Receive impulses from other neurons or receptors |
| Cell body (soma) | Contains nucleus and organelles |
| Axon | Carries impulses away from the cell body |
| Myelin sheath | Fatty insulating layer (speeds up impulse conduction) |
| Axon terminals (synaptic knobs) | Transmit impulses to next neuron/effector |
Types of Neurons
| Type | Function |
|---|---|
| Sensory (afferent) | Carry impulses from receptors to CNS |
| Motor (efferent) | Carry impulses from CNS to effectors |
| Interneurons (relay) | Connect sensory and motor neurons (in CNS) |
Brain
The brain is protected by the skull and three meninges (dura mater, arachnoid mater, pia mater).
| Part | Location | Function |
|---|---|---|
| Cerebrum | Forebrain (largest part) | Voluntary actions, intelligence, memory, speech, senses |
| Cerebellum | Hindbrain (below cerebrum) | Balance, coordination of movement, posture |
| Medulla oblongata | Hindbrain (lowest part) | Involuntary actions (heartbeat, breathing, blood pressure) |
Other Important Parts
| Part | Function |
|---|---|
| Hypothalamus | Body temperature, hunger, thirst, hormone control |
| Pituitary gland | Master gland — controls other endocrine glands |
Spinal Cord
- Extends from the medulla to the lower back.
- Protected by the vertebral column.
- Functions:
- Transmits impulses between brain and body.
- Controls reflex actions (without involving the brain).
Reflex Arc
The pathway followed by a nerve impulse during a reflex action.
Sequence: Receptor → Sensory neuron → Spinal cord (relay neuron) → Motor neuron → Effector (muscle/gland)
Example (knee jerk): Tapping the patellar tendon stretches the quadriceps muscle → sensory neuron → spinal cord → motor neuron → quadriceps contracts (leg kicks).
Importance: Reflexes are quick and automatic — protect the body from harm without waiting for the brain to process.
Sense Organs
Eye (Vision)
| Part | Function |
|---|---|
| Cornea | Transparent front — refracts light |
| Iris | Controls the size of the pupil |
| Pupil | Opening through which light enters |
| Lens | Focuses light on the retina |
| Retina | Contains light-sensitive cells (rods and cones) |
| Optic nerve | Carries impulses to the brain |
Rods: Dim light vision (black and white). Cones: Bright light vision (colour).
Ear (Hearing and Balance)
| Part | Function |
|---|---|
| Pinna (outer ear) | Collects sound waves |
| Ear drum (tympanum) | Vibrates on receiving sound |
| Hammer, Anvil, Stirrup (ossicles) | Amplify vibrations |
| Cochlea (inner ear) | Contains auditory receptors — converts vibrations to impulses |
| Auditory nerve | Carries impulses to the brain |
| Semicircular canals | Maintain body balance |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Confirming cerebellum with cerebrum | Cerebrum = thought/speech; Cerebellum = balance/coordination |
| Thinking all actions involve the brain | Reflex arcs bypass the brain (through spinal cord) |
| Mixing rods and cones | Rods = dim light; Cones = colour/ bright light |
| Forgetting the pinna in the ear diagram | Pinna is the visible outer part that collects sound |
ICSE Exam Focus
This chapter carries 6–8 marks. Key topics: brain diagram and functions, reflex arc, neuron structure, eye and ear diagrams.
Marks Blueprint: Brain structure — 2 marks, Neuron/Reflex arc — 2 marks, Eye — 2 marks, Ear — 2 marks.
Self-Test Questions
-
Draw a labelled diagram of the brain showing the cerebrum, cerebellum, and medulla.
-
What is a reflex arc? Draw and label its pathway.
-
Draw a labelled diagram of a neuron and explain the function of each part.
-
Describe the accommodation of the eye to see near and distant objects.
-
How does the ear help in hearing and maintaining balance?
-
Differentiate between rods and cones in the retina.
