Cheatsheet — Control and Coordination

🧠 Overview — Control & Coordination

⚡ Nervous System

Medium: Electrical impulse via neurons

Speed: Very fast (milliseconds)

Duration: Short-lived

Scope: Specific — through nerves

Components: CNS + PNS

Response: Immediate, precise

💊 Endocrine System

Medium: Chemical hormones via blood

Speed: Slow (seconds to minutes)

Duration: Long-lasting

Scope: Broad — via bloodstream

Components: Glands + hormones

Response: Diffuse, sustained

🔬 Neuron — Structural Unit

Part	Function
Dendrites	Receive impulses; carry toward cell body
Cell Body (Cyton)	Nucleus + organelles; metabolic centre
Axon	Carry impulses away from cell body
Myelin Sheath	Fatty insulation by Schwann cells; speeds conduction
Nodes of Ranvier	Unmyelinated gaps; saltatory conduction
Axon Terminals	Release neurotransmitters at synapse

Synapse: ~20 nm gap between neurons. Signal crosses via neurotransmitters (acetylcholine, dopamine). Unidirectional.

Types: Sensory (Afferent) Relay (Interneuron) Motor (Efferent)

⚡ Reflex Action & Reflex Arc

Rapid, involuntary response to stimulus. Signal does NOT go to brain — processed in spinal cord. Brain informed after response.

Pathway:

🖐 Receptor

→

Sensory Neuron

→

Relay Neuron
(spinal cord)

→

Motor Neuron

→

💪 Effector

Type	Centre	Example
Spinal	Spinal cord	Touch hot object, knee-jerk
Cranial	Brain	Pupil dilation, blinking
Conditioned	Brain (learned)	Pavlov's salivation experiment

🧬 Human Brain

Protection: Cranium → Meninges (3 layers: Dura, Arachnoid, Pia) → Cerebrospinal Fluid (CSF)

Region	Division	Key Functions
Cerebrum	Forebrain	Voluntary actions, memory, thought, speech, emotions
Cerebellum	Hindbrain	Balance, posture, coordination of voluntary movements
Medulla Oblongata	Hindbrain	Heartbeat, breathing, BP, swallowing — ALL involuntary
Hypothalamus	Forebrain	Thermoregulation, hunger, thirst, pituitary control
Thalamus	Forebrain	Relay station — routes sensory signals to cerebrum
Pons	Hindbrain	Bridge between cerebellum and cerebrum; sleep

Cerebrum = 85% of brain weight. Two hemispheres joined by corpus callosum. Left hemisphere controls right side of body.

💊 Endocrine Glands & Hormones

Gland	Location	Hormone(s)	Function	Deficiency/Excess
Pituitary	Base of brain	GH, TSH, ACTH, LH, FSH, ADH, Oxytocin	Master gland — controls all other glands	Excess GH → Gigantism; Deficiency → Dwarfism
Thyroid	Front of neck	Thyroxine (needs iodine)	Metabolism, growth, development, protein synthesis	Deficiency → Goitre; Cretinism (in children)
Adrenal	On kidneys	Adrenaline (Epinephrine)	Fight-or-flight: ↑HR, ↑BP, dilates pupils	"Hormone of emergency" — stress response
Pancreas	Behind stomach	Insulin (β cells), Glucagon (α cells)	Blood sugar regulation — insulin ↓, glucagon ↑	Insulin deficiency → Diabetes mellitus
Testes	Scrotum	Testosterone	Male secondary sexual characters, sperm production	Deficiency → delayed puberty, reduced fertility
Ovaries	Pelvic cavity	Oestrogen, Progesterone	Female characters, menstrual cycle, pregnancy	Imbalance → menstrual disorders

Negative Feedback: Blood sugar ↑ → Insulin released → Glucose stored → Blood sugar ↓ → Insulin stops. Maintains homeostasis.

🌿 Plant Hormones (Phytohormones)

Auxin (IAA)

Type: Promoter
Cell elongation, phototropism, apical dominance
Tip: Shoot bends toward light

Gibberellin

Type: Promoter
Stem elongation, seed germination, fruit growth
Tip: Dwarf plants grow tall

Cytokinin

Type: Promoter
Cell division, delays leaf senescence
Tip: Keeps cut flowers fresh

Abscisic Acid

Type: Inhibitor
Stomatal closure, seed dormancy, wilting
Tip: Stress hormone of plants

🌱 Tropisms

☀️

Phototropism

Stimulus: Light
Shoot: +ve (toward)
Root: −ve (away)
Auxin → shaded side

⬇️

Geotropism

Stimulus: Gravity
Root: +ve (downward)
Shoot: −ve (upward)

💧

Hydrotropism

Stimulus: Water
Root: +ve (toward)
Helps roots find water

🌀

Thigmotropism

Stimulus: Touch
Tendrils coil around support
e.g. Pea, cucumber

Phototropism mechanism: Light → Auxin migrates to shaded side → More cell elongation → Shoot bends toward light. Darwin (1880) → Went (1926, named auxin).

Nastic movements (non-directional): Mimosa pudica — leaves fold on touch. Venus flytrap — snaps shut. Not tropism — no growth involved.

💡 Memory Tricks & Quick Facts

DAMN Mnemonic

Dendrites — Axon — Myelin — Nodes. The four structures of a neuron in signal order.

Brain Divisions

Fore = Think/Feel (Cerebrum, Hypothalamus, Thalamus)
Hind = Move/Live (Cerebellum, Medulla, Pons)

Reflex vs Voluntary

Reflex → Spinal cord (fast). Voluntary → Brain (slow). You feel pain after withdrawing hand.

Plant Hormones AGCA

Auxin, Gibberellin, Cytokinin = PROMOTERS. Abscisic Acid = INHIBITOR.

Endocrine Memory

Pituitary = MASTER (controls all). Adrenal = EMERGENCY. Thyroid = METABOLISM. Pancreas = SUGAR.

Medulla = Vital

Controls heartbeat, breathing, BP. Even slight damage → death. Never confuse with adrenal medulla (produces adrenaline).

⭐ High-Yield CBSE Points

Neuron is the structural and functional unit of the nervous system.
Myelin sheath speeds up nerve impulse by saltatory (jumping) conduction at Nodes of Ranvier.
Reflex arc does not involve the brain — processed at spinal cord. Brain informed after.
Cerebrum = largest brain part (~85%). Controls all voluntary and conscious activities.
Medulla oblongata = controls ALL involuntary vital functions. Critical for survival.
Hypothalamus = thermoregulation centre AND controls the pituitary gland (links NS + endocrine).
Pituitary = master gland. All other endocrine glands are under its control.
Adrenaline = "hormone of emergency". Prepares body for fight-or-flight.
Insulin deficiency → Diabetes mellitus. Insulin lowers blood sugar; glucagon raises it.
Thyroxine requires iodine. Deficiency → Goitre (swollen neck).
Auxin causes phototropism — migrates to shaded side, causes elongation → bending toward light.
Abscisic Acid (ABA) = only inhibitory plant hormone. Causes stomatal closure during drought.
Plants do NOT have nervous system — coordination only through phytohormones.
Negative feedback maintains hormonal homeostasis — rising hormone level suppresses further secretion.
Conditioned reflex (Pavlov) = learned reflex. Example: salivation at bell sound.