Control and Coordination — Detailed Notes

Chapter 6 | NCERT Class 10 Science

6.1 Animals — Nervous System

Controlled movement is a response to recognised environmental change. Multicellular animals use specialised nervous and muscular tissues.

Detecting information

Specialised tips of nerve cells — receptors — in sense organs detect stimuli. Examples: gustatory receptors (taste), olfactory receptors (smell).

Neuron and impulse

Diagram — neuron:

dendrites (receive) → cell body → long axon → axon endings. At the axon end, chemicals are released across the **synapse** (gap) to start an impulse in the next neuron, or to stimulate muscle/gland cells (**neuromuscular junction**).

Path: dendritic tip → chemical reaction → electrical impulse → cell body → axon → chemical signal at synapse → next cell.

Nervous tissue is an organised network of neurons specialised for conducting information via electrical impulses.

6.1.1 Reflex Actions

A reflex is a sudden response without conscious control (pulling hand from flame; watering mouth). Thinking in the brain involves complex networks and takes time — too slow for urgent danger.

Reflex arc: sensory input connected more directly to motor output in the spinal cord, where nerves meet on the way to the brain. Information still reaches the brain, but the quick motor response need not wait for full conscious thought. Reflex arcs remain efficient even in animals with complex brains.

Sequence example (bright light on eye): receptors in eye → sensory neurons → (spinal/brainstem reflex pathways) → motor neurons → muscles of iris/eyelid → pupil/eye protective response (trace similarly for heat).

Diagram — reflex arc:

receptor → sensory neuron → spinal cord relay → motor neuron → effector (muscle).

6.1.2 Human Brain

Central nervous system (CNS): brain + spinal cord — receive and integrate information.
Peripheral nervous system (PNS): cranial nerves (from brain) + spinal nerves (from spinal cord) — link CNS to the body.

Voluntary actions (writing, talking, moving a chair): brain decides and sends messages to muscles.
Involuntary actions (heart beat, breathing, digestion, salivation, vomiting, blood pressure): mid-brain and especially medulla (hind-brain).
Cerebellum (hind-brain): precision of voluntary actions; posture and balance (walking straight, cycling).

Fore-brain: main thinking region; specialised sensory areas (hearing, smell, sight, etc.); association areas interpret and store information; motor areas control voluntary muscles; hunger centre also in fore-brain.

Diagram — human brain:

cerebrum (fore-brain) large and folded; mid-brain central; hind-brain with cerebellum (dorsal, wrinkled) and medulla merging into spinal cord.

6.1.3 Protection

Brain inside a bony box (cranium); further protected by a fluid-filled cushion. Spinal cord protected by vertebral column (backbone).

6.1.4 How Nervous Tissue Causes Action

Muscle cells shorten by changing shape. Special proteins in muscle cells change shape and arrangement when a nerve impulse arrives, producing contraction. Voluntary vs involuntary muscles differ in control (conscious vs not).

Better Method / Strategy

For any nervous question, write the chain: stimulus → receptor → neuron path → effector.

Reflex ≠ “no brain involvement forever”; say arc in spinal cord; brain also receives input.

6.2 Coordination in Plants

Plants have no nervous system or muscles, yet respond to stimuli.

Two movement types:

Independent of growth — e.g. Mimosa (touch-me-not) leaves fold quickly
Dependent on growth — directional growth of seedling parts; if growth stops, movement stops

6.2.1 Immediate Response to Stimulus

Touch at one point; movement at another → information must be communicated. Plants use electrical–chemical signals cell to cell without specialised nerve tissue. Cells change shape by changing water content (swell/shrink), not by animal-type muscle proteins.

6.2.2 Movement Due to Growth

Tendrils (e.g. pea): touch-sensitive; contact side grows slower than opposite side → tendril coils around support.

Tropic movements: directional growth toward or away from a stimulus.

Tropism	Stimulus	Typical response
Phototropism	Light	Shoots toward light; roots often away
Geotropism	Gravity	Roots down; shoots up
Hydrotropism	Water	Growth toward water
Chemotropism	Chemicals	e.g. pollen tube toward ovules

Diagram — phototropism setup:

seedlings in a box open on one side; shoots bend to light, roots away; after rotating flask, new growth reorients.

Plant hormones

Electrical impulses are fast but limited: they reach only connected cells and cells need reset time between impulses. Hormones diffuse more widely and act steadily.

Plant hormones are made in one place and diffuse to sites of action.

Hormone	Main role
Auxin	Made at shoot tip; promotes cell elongation; accumulates on shady side → shoot bends to light
Gibberellins	Help stem growth
Cytokinins	Promote cell division; high in fruits/seeds
Abscisic acid	Inhibits growth; involved in wilting of leaves

Auxin and phototropism: light from one side → auxin diffuses to shady side → those cells elongate more → shoot bends toward light. Tendril coiling uses differential growth (auxin-related growth differences around support).

Better Method / Strategy

First ask: is growth involved? Then name tropism or “nastic/sensitive” style quick response.

For phototropism answers, always mention unequal auxin → unequal elongation.

6.3 Hormones in Animals

Chemical signals reach all cells via blood — useful when many tissues must prepare together (e.g. escape).

Adrenaline (adrenal glands)

Secreted into blood in scary/emergency situations. Effects: heart beats faster → more O₂ to muscles; blood diverted from digestive system/skin to skeletal muscles; breathing rate increases. Prepares body to fight or flee.

Other important hormones

Hormone	Gland	Function / note
Growth hormone (GH)	Pituitary	Stimulates growth; childhood deficiency → dwarfism
Thyroxin	Thyroid	Regulates carb/protein/fat metabolism for balanced growth; needs iodine; deficiency → goitre (swollen neck)
Insulin	Pancreas	Lowers/regulates blood sugar; deficiency → diabetes (may need insulin injections)
Testosterone	Testes	Male puberty changes; linked to sperm formation regulation
Oestrogen	Ovaries	Female sex organ development; menstrual cycle regulation
Releasing hormones	Hypothalamus	Stimulate pituitary to release hormones (e.g. GH releasing factor)

Diagram — endocrine glands:

Endocrine glands — Main endocrine glands in humans

Feedback mechanisms

Timing and amount of hormone release are regulated by feedback. Example: blood sugar rises → pancreas secretes more insulin → sugar falls → insulin secretion reduced. Hypothalamus monitors and can stimulate pituitary when GH is low.

Better Method / Strategy

Hormone answers: gland + target effect + deficiency disease (if any).

Compare systems: nerves = fast, local, electrical; hormones = slower, widespread, chemical, longer-lasting.

Chapter Closing Strategy

Master neuron + reflex arc diagrams in words.
Drill brain part → function pairs.
Learn one full phototropism paragraph with auxin.
Complete hormone table from memory thrice.

Deep Dive Add-On — Hormones Table (Expanded)

Hormone	Gland	Target / effect	Deficiency or excess note	Board phrase
Adrenaline	Adrenal glands	Heart rate ↑, breathing ↑, blood to skeletal muscles, digestion reduced	Surge in emergency (fight or flight)	Prepares body to face danger
Growth hormone (GH)	Pituitary	Overall body growth	Childhood deficiency → dwarfism	Pituitary master growth signal
Thyroxin	Thyroid	Carb / protein / fat metabolism for balanced growth	Iodine lack → less thyroxin → goitre	Needs dietary iodine
Insulin	Pancreas	Lowers / regulates blood glucose	Deficiency → diabetes mellitus	Feedback with sugar level
Testosterone	Testes	Male secondary sexual characters; helps regulate sperm formation	Puberty changes in boys	Male sex hormone
Oestrogen	Ovaries	Female secondary characters; helps regulate menstrual cycle	Linked to puberty / cycle	Female sex hormone
Releasing hormones	Hypothalamus	Stimulate pituitary to release hormones (e.g. GH releasing factor)	Timing of pituitary output	Brain–pituitary link

Feedback worked mini-example (insulin):
Blood glucose rises after a meal → pancreas releases more insulin → cells take up / use glucose → blood glucose falls → insulin release is reduced. This negative feedback keeps sugar in a safe range.

Nerves vs hormones (must-compare):

Feature	Nervous control	Hormonal control
Signal type	Electrical impulse (+ chemical at synapse)	Chemical (hormone in blood)
Speed	Very fast	Relatively slower
Reach	Specific connected pathway	Widespread to many tissues
Duration	Short-lived unless repeated	Often longer-lasting
Example	Reflex withdrawal	Adrenaline preparedness

Deep Dive Add-On — Reflex vs Voluntary vs Involuntary

Feature	Reflex action	Voluntary action	Involuntary action
Conscious control	No (sudden)	Yes (will / decision)	No (automatic ongoing)
Typical path	Receptor → sensory → spinal cord → motor → effector	Fore-brain decides → motor path to muscles	Mid-brain / medulla centres
Speed need	High (protection)	Can be planned / slower	Continuous life support
Examples	Hand from flame; knee-jerk; pupil to light	Writing, talking, picking a book	Heartbeat, breathing, blood pressure, peristalsis
Brain role	Arc may complete in spinal cord; brain still informed	Fore-brain thinking + motor areas	Medulla (and related) without conscious effort
Cerebellum link	Not the reflex “decision maker”	Precision / balance of voluntary movement	—

Reflex arc must-sequence (write in order):

Stimulus detected by receptor
Impulse in sensory neuron
Processing / relay in spinal cord (CNS)
Impulse in motor neuron
Response by effector (muscle or gland)

Common exam trap: “Reflex means brain is not involved at all.”
Better line: The quick motor response is organised via the spinal reflex arc so it need not wait for full conscious thought; information still reaches the brain.

Plant quick response vs tropism (extra clarity):

	Mimosa-type folding	Phototropism / geotropism
Growth needed?	No (immediate)	Yes (directional growth)
Mechanism idea	Cell water content / chemical signals	Unequal growth (e.g. auxin)
Stops if growth stops?	Not a growth movement	Yes