Neural Control and Coordination - Complete NEET Biology Notes

Neural Control and Coordination is one of the most important and high-weightage chapters, contributing 5-7 questions in NEET annually. This comprehensive guide covers all NCERT concepts.

Introduction to Neural System

Definition: The system that controls and coordinates body activities through rapid electrical signals.

Organization of Neural System

Central Nervous System (CNS):

Brain
Spinal cord

Peripheral Nervous System (PNS):

Cranial nerves (12 pairs)
Spinal nerves (31 pairs)

Neuron - Structural and Functional Unit

Structure of Neuron

Three Main Parts:

1. Cell Body (Soma/Cyton)

Contains nucleus and most organelles
Nissl granules (rough ER) - protein synthesis
Site of metabolic activity

2. Dendrites

Short, branched processes
Receive signals from other neurons
Conduct impulse toward cell body

3. Axon

Single, long process
Conducts impulse away from cell body
May be myelinated or unmyelinated
Ends in terminal buttons (synaptic knobs)

Myelin Sheath

Feature	Myelinated	Unmyelinated
Myelin	Present	Absent
Nodes of Ranvier	Present	Absent
Conduction	Saltatory (faster)	Continuous (slower)
Speed	100-120 m/s	0.5-2 m/s
Location	White matter, PNS	Gray matter

Myelin in CNS: Oligodendrocytes Myelin in PNS: Schwann cells

Types of Neurons

Type	Structure	Function
Sensory (Afferent)	Long dendrite, short axon	Carry impulse to CNS
Motor (Efferent)	Short dendrite, long axon	Carry impulse from CNS
Interneurons	Short processes	Connect neurons within CNS

Based on Processes	Number of Processes
Unipolar	1 (axon only)
Bipolar	2 (1 dendrite, 1 axon)
Multipolar	3+ (many dendrites, 1 axon)

Nerve Impulse

Resting Membrane Potential

Value: -70 mV (inside negative relative to outside)

Maintenance:

Na⁺/K⁺ ATPase pump: 3 Na⁺ out, 2 K⁺ in
High K⁺ inside, High Na⁺ outside
K⁺ leak channels maintain negativity

Generation of Action Potential

Stimulus → Threshold (-55 mV) → Action Potential

Phase	Events	Potential
Resting	Na⁺/K⁺ pump maintains gradient	-70 mV
Depolarization	Na⁺ channels open, Na⁺ rushes in	-70 → +30 mV
Repolarization	Na⁺ channels close, K⁺ channels open	+30 → -70 mV
Hyperpolarization	K⁺ channels slow to close	Below -70 mV
Return to resting	Na⁺/K⁺ pump restores gradient	-70 mV

Properties of Action Potential

All-or-None Law: Action potential either occurs fully or not at all; no partial response.

Refractory Period:

Absolute: No stimulus can generate another AP
Relative: Only strong stimulus can generate AP

Conduction of Nerve Impulse

Type	Mechanism	Speed
Continuous	Sequential depolarization	Slower
Saltatory	Jumps between Nodes of Ranvier	Faster

Synapse

Definition: Junction between two neurons where signal transmission occurs.

Types of Synapses

Type	Mechanism	Speed
Electrical	Gap junctions, direct ion flow	Very fast
Chemical	Neurotransmitter release	Slower

Structure of Chemical Synapse

Presynaptic terminal: Contains synaptic vesicles with neurotransmitters
Synaptic cleft: 20-40 nm gap
Postsynaptic membrane: Contains receptors

Synaptic Transmission

Action potential reaches axon terminal
Ca²⁺ channels open, Ca²⁺ enters
Synaptic vesicles fuse with membrane
Neurotransmitter released into synaptic cleft
NT binds to receptors on postsynaptic membrane
Ion channels open/close on postsynaptic neuron
NT removed (reuptake, enzyme degradation, diffusion)

Common Neurotransmitters

Neurotransmitter	Location	Effect
Acetylcholine	NMJ, brain	Excitatory/Inhibitory
Norepinephrine	Sympathetic NS	Excitatory
Dopamine	Brain	Pleasure, movement
Serotonin	Brain	Mood, sleep
GABA	Brain	Inhibitory
Glutamate	Brain	Excitatory

Central Nervous System

Brain

Weight: ~1400 g Protection: Skull, meninges, CSF

Meninges (Three Layers)

Layer	Location	Characteristics
Dura mater	Outermost	Tough, fibrous
Arachnoid	Middle	Web-like, CSF beneath
Pia mater	Innermost	Delicate, on brain surface

CSF (Cerebrospinal Fluid):

Volume: ~150 mL
Functions: Protection, nutrient supply, waste removal

Parts of Brain

1. Forebrain

A. Cerebrum (Largest Part - 80%)

Lobe	Location	Function
Frontal	Front	Motor control, thinking, speech (Broca's area)
Parietal	Top	Sensory processing, spatial awareness
Temporal	Side	Hearing, memory, speech comprehension (Wernicke's area)
Occipital	Back	Vision

Cerebral Cortex:

Gray matter on surface (6 layers)
White matter inside (myelinated fibers)
Corpus callosum connects two hemispheres

Association Areas:

Higher mental functions
Memory, reasoning, judgment

B. Thalamus

Relay center for sensory information
All sensory signals (except smell) pass through

C. Hypothalamus

Controls autonomic functions
Regulates: Temperature, hunger, thirst, sleep, emotions
Controls pituitary gland (master of master gland)

D. Limbic System

Hippocampus: Memory formation
Amygdala: Emotions, especially fear

2. Midbrain

Contains cerebral peduncles
Superior colliculi: Visual reflexes
Inferior colliculi: Auditory reflexes
Contains substantia nigra (dopamine, Parkinson's disease)

3. Hindbrain

A. Cerebellum (Little Brain)

Second largest part
Coordination of voluntary movements
Balance and posture
Motor learning

B. Pons

Relay center between cerebrum and cerebellum
Contains pneumotaxic center (breathing)

C. Medulla Oblongata

Controls vital functions: Breathing, heart rate, blood pressure
Contains reflex centers: Vomiting, swallowing, coughing, sneezing

Brain Stem: Midbrain + Pons + Medulla

Spinal Cord

Location: Within vertebral column Length: ~45 cm Structure:

Gray matter (H-shaped) inside
White matter outside (opposite of brain)

Functions:

Conducts impulses between brain and body
Center for spinal reflexes

Peripheral Nervous System

Cranial Nerves (12 pairs)

Number	Name	Type	Function
I	Olfactory	Sensory	Smell
II	Optic	Sensory	Vision
III	Oculomotor	Motor	Eye movement
IV	Trochlear	Motor	Eye movement
V	Trigeminal	Mixed	Face sensation, chewing
VI	Abducens	Motor	Eye movement
VII	Facial	Mixed	Facial expression, taste
VIII	Vestibulocochlear	Sensory	Hearing, balance
IX	Glossopharyngeal	Mixed	Taste, swallowing
X	Vagus	Mixed	Visceral organs
XI	Accessory	Motor	Neck muscles
XII	Hypoglossal	Motor	Tongue movement

Mnemonic: On Old Olympus Towering Tops, A Finn And German Viewed Some Hops

Spinal Nerves (31 pairs)

Region	Number
Cervical	8
Thoracic	12
Lumbar	5
Sacral	5
Coccygeal	1

Autonomic Nervous System (ANS)

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar	Craniosacral
Ganglion location	Close to spinal cord	Near/in target organ
Neurotransmitter	Norepinephrine	Acetylcholine
General effect	Fight or flight	Rest and digest
Pupil	Dilates	Constricts
Heart rate	Increases	Decreases
Digestion	Inhibits	Stimulates
Bronchi	Dilates	Constricts

Reflex Action

Definition: Automatic, involuntary response to a stimulus.

Reflex Arc

Components (in order):

Receptor: Detects stimulus
Sensory (afferent) neuron: Carries impulse to CNS
Integration center: Interneuron in spinal cord
Motor (efferent) neuron: Carries impulse to effector
Effector: Muscle or gland that responds

Types of Reflexes

Type	Example	Integration Center
Spinal	Knee jerk, withdrawal	Spinal cord
Cranial	Pupillary reflex	Brain
Conditional	Salivation to bell (Pavlov)	Brain
Unconditional	Salivation to food	Brain

Sensory Reception

Eye - Photoreception

Structure:

Sclera (white), Cornea (transparent front)
Choroid (vascular), Iris (colored, controls pupil)
Retina (photoreceptors)

Photoreceptors:

Type	Shape	Pigment	Function	Sensitivity
Rods	Rod-shaped	Rhodopsin	Dim light, peripheral vision	High
Cones	Cone-shaped	Photopsins	Color, bright light, acuity	Low

Fovea: Maximum cone density, sharpest vision Blind spot: Where optic nerve exits, no receptors

Ear - Hearing and Balance

Three Parts:

Part	Structures	Function
Outer ear	Pinna, ear canal, tympanic membrane	Sound collection
Middle ear	Malleus, Incus, Stapes	Sound amplification
Inner ear	Cochlea, vestibular apparatus	Hearing, balance

Organ of Corti: Contains hair cells (auditory receptors) in cochlea

Previous Year NEET Questions

Q1 (NEET 2023): Resting membrane potential of neuron is:

(a) +70 mV
(b) -70 mV ✓
(c) +30 mV
(d) -30 mV

Q2 (NEET 2022): The part of brain responsible for balance is:

(a) Cerebrum
(b) Cerebellum ✓
(c) Medulla
(d) Hypothalamus

Q3 (NEET 2021): Saltatory conduction occurs in:

(a) Unmyelinated neurons
(b) Myelinated neurons ✓
(c) All neurons
(d) Dendrites only

Q4 (NEET 2020): Hypothalamus controls:

(a) Body temperature ✓
(b) Voluntary movements
(c) Balance
(d) Hearing

Q5 (NEET 2019): Which neurotransmitter is released at neuromuscular junction?

(a) GABA
(b) Dopamine
(c) Acetylcholine ✓
(d) Serotonin

Quick Revision Points

Functional unit: Neuron
Resting potential: -70 mV
Action potential peak: +30 mV
Myelination in CNS: Oligodendrocytes
Myelination in PNS: Schwann cells
Largest brain part: Cerebrum
Second largest: Cerebellum
Master of master gland: Hypothalamus
Relay center: Thalamus
Memory formation: Hippocampus
Vital functions: Medulla oblongata
Fight or flight: Sympathetic NS
Rest and digest: Parasympathetic NS
Number of cranial nerves: 12 pairs
Number of spinal nerves: 31 pairs

FAQs

Q: Why is the resting potential negative? A: The Na⁺/K⁺ pump creates an ionic gradient (3 Na⁺ out, 2 K⁺ in). Additionally, K⁺ leak channels allow K⁺ to diffuse out, leaving the inside more negative relative to outside.

Q: What is the advantage of saltatory conduction? A: In myelinated neurons, action potential jumps between Nodes of Ranvier instead of traveling continuously. This is faster (100 m/s vs 1 m/s) and more energy-efficient.

Q: Why is the cerebellum called the "little brain"? A: It has a similar folded structure to the cerebrum but is smaller. Despite being only 10% of brain volume, it contains more neurons than the rest of the brain combined.

Q: What happens if the corpus callosum is cut? A: This procedure (commissurotomy) prevents communication between hemispheres. Patients can function normally in daily life but show "split-brain" effects in specific tests.

Q: Why does Parkinson's disease cause tremors? A: Parkinson's involves death of dopamine-producing neurons in the substantia nigra. Dopamine is essential for smooth, coordinated movements, so its deficiency causes tremors and rigidity.

Key Takeaways

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