Nervous System
1. Functions of the Nervous System
The nervous system is the BODY'S control and communication network.
| Function | Description |
|---|---|
| SENSORY input | DETECTS changes (stimuli) from inside and outside the body |
| INTEGRATION | PROCESSES and interprets sensory information |
| MOTOR output | SENDS signals to muscles and glands to RESPOND |
| COORDINATION | Coordinates ACTIVITIES of different body parts |
| HIGHER functions | Thinking, MEMORY, emotions, learning |
2. The Neuron — Basic Unit
A neuron is a specialised cell that transmits ELECTRICAL signals.
Structure
| Part | Function |
|---|---|
| Cell body (soma) | Contains NUCLEUS. Controls cell activity |
| DENDRITES | BRANCH-LIKE extensions. RECEIVE signals from other neurons |
| AXON | LONG fibre that CARRIES signals AWAY from the cell body |
| Myelin sheath | INSULATING layer around the axon. Speeds up signal transmission |
| Axon terminals | ENDINGS that release NEUROTRANSMITTERS to pass signals to NEXT neuron |
Types of Neurons
| Type | Function |
|---|---|
| SENSORY (afferent) | Carry IMPULSES from sense organs → brain/spinal cord |
| MOTOR (efferent) | Carry IMPULSES from brain/spinal cord → muscles/glands |
| INTERNEURONS | CONNECT sensory and motor neurons (in spinal cord and brain) |
3. Central Nervous System (CNS)
Brain
Located inside the SKULL. Protected by MENINGES (membranes) and CEREBROSPINAL FLUID.
| Part | Location | Function |
|---|---|---|
| CEREBRUM | Forebrain (LARGEST part) | HIGHER functions: thought, memory, reasoning, speech, voluntary movements, SENSORY perception |
| CEREBELLUM | Hindbrain (below cerebrum) | BALANCE, POSTURE, COORDINATION of voluntary movements |
| MEDULLA OBLONGATA | Brainstem (lowest part) | INVOLUNTARY actions: breathing, heart rate, digestion, blood pressure |
Cerebral cortex: The OUTER layer of the cerebrum — folded (convolutions) for INCREASED surface area.
Spinal Cord
- A LONG, CYLINDRICAL bundle of nerves running through the VERTEBRAL COLUMN
- CONNECTS the brain to the REST of the body
- Controls REFLEX actions
- Protected by VERTEBRAE
4. Peripheral Nervous System (PNS)
Nerves that connect the CENTRAL nervous system to the rest of the body.
| Division | Function |
|---|---|
| Somatic nervous system | CONTROLS voluntary movements (skeletal muscles) |
| Autonomic nervous system | CONTROLS involuntary functions (heart, digestive system, glands) |
| — SYMPATHETIC | 'Fight or flight' — ACTIVE during stress |
| — PARASYMPATHETIC | 'Rest and digest' — ACTIVE during relaxation |
5. Reflex Arc
The SIMPLEST nerve pathway. A RAPID, AUTOMATIC response to a stimulus WITHOUT involving the brain (initially).
Example — Touching a hot object:
- Stimulus (HEAT) → Sensory receptors in skin
- Sensory neuron → Spinal cord (INTERNEURON)
- Motor neuron → Muscle in HAND
- Response: Hand PULLS AWAY
'This entire reflex happens in FRACTIONS of a second — much FASTER than waiting for the brain to process. The brain gets the information LATER (you 'feel' pain after pulling away).'
6. Sense Organs
| Sense Organ | Sense | Stimulus | Receptors |
|---|---|---|---|
| EYES | Sight | LIGHT | Photoreceptors (rods and cones in RETINA) |
| EARS | Hearing, Balance | SOUND waves, Gravity | Mechanoreceptors (cochlea, semicircular canals) |
| NOSE | Smell | CHEMICALS in air | Olfactory receptors |
| TONGUE | Taste | CHEMICALS in food | Taste buds (sweet, sour, salty, bitter, umami) |
| SKIN | Touch, Pressure, Pain, Temperature | Mechanical, thermal, pain | Various receptors |
7. Common Disorders
| Disorder | Description |
|---|---|
| PARALYSIS | LOSS of movement and sensation in a body part (due to nerve/brain damage) |
| EPILEPSY | Abnormal electrical activity in the brain → SEIZURES |
| ALZHEIMER'S disease | Progressive brain disorder → MEMORY loss |
| PARKINSON'S disease | Dopamine deficiency → TREMORS, stiffness |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| 'The cerebrum controls balance' | The CEREBELLUM controls balance and coordination. The CEREBRUM controls THOUGHT and voluntary actions |
| 'Reflexes involve the brain' | Reflex arcs go through the SPINAL CORD (not brain initially). The brain is informed AFTERWARDS |
| 'Neurons can be regenerated easily' | Most neurons CANNOT regenerate when damaged (unlike skin cells). Spinal cord injuries are PERMANENT |
| 'The medulla controls thinking' | The medulla controls INVOLUNTARY functions (breathing, heart rate). Thinking is a function of the CEREBRUM |
ICSE Exam Focus (6–8 marks)
- 2-mark questions: Parts of a neuron, parts of the brain
- 3-mark questions: Functions of cerebrum, cerebellum, and medulla
- 4-mark questions: Reflex arc — labelled diagram and explanation
- 6-mark questions: Types of neurons or sense organs and their functions
Self-Test
Q1. Name the three main parts of the brain and state their functions. A1. (1) CEREBRUM — thought, memory, voluntary movement, sensation. (2) CEREBELLUM — balance, coordination, posture. (3) MEDULLA — involuntary actions (breathing, heart rate).
Q2. What is a reflex arc? Describe with an example. A2. A reflex arc is the SIMPLEST nerve pathway for a RAPID, automatic response. Example: Touching a hot object → sensory neuron → spinal cord (interneuron) → motor neuron → hand pulls away.
Q3. Draw and label the structure of a neuron. A3. Key parts: Dendrites (receive signals), Cell body (nucleus), Axon (carries signals), Myelin sheath (insulation), Axon terminals (release neurotransmitters).
Q4. What is the function of the spinal cord? A4. The spinal cord CONNECTS the brain to the rest of the body. It CARRIES nerve impulses to and from the brain and controls REFLEX actions.
Q5. Name the five sense organs and their corresponding senses. A5. Eyes (sight), Ears (hearing and balance), Nose (smell), Tongue (taste), Skin (touch, pressure, pain, temperature).
Q6. What is the difference between the sympathetic and parasympathetic nervous systems? A6. The SYMPATHETIC system prepares the body for 'fight or flight' (increases heart rate, dilates pupils). The PARASYMPATHETIC system promotes 'rest and digest' (slows heart rate, stimulates digestion).
