Control, Coordination and Hormones
Nervous system
- Neuron is the unit: dendrites (receive), cell body, axon (carries away). Synapse is the gap between two neurons; neurotransmitters (acetylcholine) pass the impulse.
- Central nervous system (CNS): brain and spinal cord. Peripheral: cranial and spinal nerves. Autonomic nervous system controls involuntary actions (sympathetic and parasympathetic).
| Brain part | Function |
|---|---|
| Cerebrum | Largest part; thinking, memory, intelligence, speech, voluntary actions; seat of consciousness |
| Cerebellum | Balance, posture, coordination |
| Medulla oblongata | Involuntary actions: breathing, heartbeat, blood pressure, vomiting, swallowing |
| Hypothalamus | Body temperature, hunger, thirst, sleep; links nerves and hormones |
| Pituitary | Master gland (attached below the brain) |
- Adult human brain weighs about 1.3 to 1.4 kg and is protected by the skull and meninges, with cerebrospinal fluid.
- Reflex action: a sudden, automatic response (touching a hot object, blinking, sneezing, knee jerk) controlled by the spinal cord through the reflex arc: receptor, sensory neuron, spinal cord, motor neuron, effector. It is faster than a voluntary action.
- Twelve pairs of cranial nerves and 31 pairs of spinal nerves in humans.
Sense organs
| Organ | Facts |
|---|---|
| Eye | Vision; see the Light topic |
| Ear | Hearing and balance (semicircular canals for balance) |
| Nose | Smell (olfactory receptors) |
| Tongue | Taste: sweet, salty, sour, bitter and umami. Older books show a tongue map with separate zones, but all tastes can be sensed over the whole tongue |
| Skin | Touch, pain, pressure, temperature |
Endocrine system and hormones
Hormones are chemical messengers released directly into the blood by ductless (endocrine) glands; they act slowly but for longer than nerves.
| Gland | Hormone | Function / disorder |
|---|---|---|
| Pituitary ("master gland") | Growth hormone, FSH, LH, TSH, ACTH, prolactin, oxytocin, ADH | Dwarfism (low GH), gigantism (excess in childhood), acromegaly (adult) |
| Thyroid | Thyroxine (needs iodine) | Controls metabolism; goitre (iodine lack), cretinism (child), hypo- and hyperthyroidism |
| Parathyroid | Parathormone | Calcium level in blood |
| Pancreas | Insulin (lowers blood sugar), glucagon (raises it) | Diabetes (low insulin) |
| Adrenal | Adrenaline | "Fight, flight or fright" hormone; emergency; raises heartbeat |
| Testes | Testosterone | Male sex characters |
| Ovaries | Oestrogen, progesterone | Female sex characters, pregnancy |
| Pineal | Melatonin | Sleep cycle |
| Thymus | Thymosin | Immunity (shrinks with age) |
- Pancreas is both exocrine and endocrine. Insulin was discovered by Banting and Best.
- Feedback mechanism keeps hormones balanced.
- Pheromones are chemicals used for communication between members of a species (insects).
- Diabetes mellitus: high blood sugar from low insulin; treated by insulin injections and diet.
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from the NCERT Science textbooks for Classes 6 to 10 and standard sources. Space missions, awards and records change, so check official sources for recent facts. Found a mistake? Tell us.