# Neural Control and Coordination (NEET Biology Class 11): Nerve Impulse, Synapses & the Brain Source: https://tracknation.in/story/neural-control-and-coordination-neet-biology-class-11-nerve-impulse-synapses-the-brain (TrackNation β€” free UPSC notes with PYQs) > NEET Class 11 Neural Control and Coordination, mined from NCERT: the divisions of the human neural system in a table (CNS, PNS, afferent/efferent, somatic/autonomic), the neuron and its three types with locations, myelinated vs unmyelinated fibres, resting potential (with the 3 Na+/2 K+ pump ratio), the action potential and impulse conduction, an electrical-vs-chemical synapse comparison table, and the central neural system β€” the meninges plus a full forebrain/midbrain/hindbrain function table, ## Divisions of the Neural System & the Neuron πŸ“Œ **NEET priority: Important.** *3–4 questions a year. The **resting/action potential mechanism** (especially the Na⁺/K⁺ pump ratio) and **which brain part does what** are the two reliable scorers β€” both tabulated below.* The **neural system** gives point-to-point connections for **quick** coordination; the **endocrine system** gives chemical integration through hormones. Neural organisation is simplest in **Hydra** (just a network of neurons), better in insects (brain + ganglia), most developed in vertebrates. ### Divisions of the human neural system | **Division** | **What it includes** | **Role** | | Central Neural System (CNS) | Brain and spinal cord | Site of information processing and control | | Peripheral Neural System (PNS) | All nerves associated with the CNS | Carries impulses to and from the CNS | | β€” Afferent fibres | Part of PNS | Transmit impulses FROM tissues/organs TO the CNS | | β€” Efferent fibres | Part of PNS | Transmit regulatory impulses FROM the CNS TO peripheral tissues/organs | | β€” Somatic neural system | PNS subdivision | Relays impulses from CNS to SKELETAL muscles | | β€” Autonomic neural system | PNS subdivision β€” further split into SYMPATHETIC and PARASYMPATHETIC | Relays impulses from CNS to INVOLUNTARY organs and smooth muscles | ### The neuron β€” structural and functional unit - Three parts: **cell body** (contains **Nissl's granules**), **dendrites** (short, branched, also contain Nissl's granules β€” carry impulses **TOWARDS** the cell body), and the **axon** (long fibre carrying impulses **AWAY**; ends in a **synaptic knob** with **synaptic vesicles** containing neurotransmitters). | **Neuron type** | **Structure** | **Where found** | | Multipolar | One axon and two or more dendrites | Cerebral cortex | | Bipolar | One axon and one dendrite | Retina of the eye | | Unipolar | Cell body with one axon only | Usually the embryonic stage | - **Myelinated axons** are enveloped by **Schwann cells** forming a **myelin sheath**; the gaps between adjacent sheaths are the **nodes of Ranvier**. Found in **spinal and cranial nerves**. **Unmyelinated** fibres have a Schwann cell that does NOT form a sheath β€” found in the **autonomic and somatic** neural systems. ## Resting Potential, Action Potential & Synapses ### Resting potential β€” why a neuron is polarised - At rest, the axonal membrane is **more permeable to K⁺** and **nearly impermeable to Na⁺**, and impermeable to the negatively charged proteins in the axoplasm. - Result: **inside the axon = high K⁺, high negative protein, low Na⁺**; **outside = low K⁺, high Na⁺**. This gradient is maintained by the **sodium-potassium pump, which transports 3 Na⁺ OUT for every 2 K⁺ IN**. - So the **outer surface is POSITIVE and the inner surface NEGATIVE** β€” the membrane is **polarised**. This potential difference is the **resting potential**. ### Action potential β€” the nerve impulse - A stimulus at site A makes the membrane **freely permeable to Na⁺** β†’ **rapid influx of Na⁺** β†’ **polarity REVERSES** (outer surface becomes negative, inner positive) β€” the membrane is **depolarised**. This potential difference is the **action potential = the nerve impulse**. - Current then flows between site A and the still-polarised site B, reversing polarity there too β€” and the sequence repeats along the axon, **conducting the impulse**. - The rise in Na⁺ permeability is **extremely short-lived**, quickly followed by a rise in **K⁺ permeability**. K⁺ diffuses out, **restoring the resting potential** (repolarisation), and the fibre becomes responsive again. ### Synapses β€” electrical vs chemical | **Feature** | **Electrical synapse** | **Chemical synapse** | | Membrane arrangement | Pre- and post-synaptic membranes in very close proximity | Separated by a fluid-filled SYNAPTIC CLEFT | | How the impulse crosses | Electrical current flows DIRECTLY from one neuron to the other | Via chemical NEUROTRANSMITTERS released from synaptic vesicles | | Speed | FASTER β€” similar to conduction along a single axon | Slower | | Occurrence in our system | RARE | The normal type | - At a chemical synapse: the arriving impulse moves synaptic vesicles to the membrane, which **fuse and release neurotransmitters** into the cleft. These bind **specific receptors on the post-synaptic membrane**, **opening ion channels** and generating a new potential β€” which may be **either excitatory or inhibitory**. ## The Central Neural System & Why This Matters for NEET ### The brain β€” protection and three divisions - The brain is the **'command and control system'**, protected by the skull and by **cranial meninges** β€” three layers: outer **dura mater**, very thin middle **arachnoid**, inner **pia mater** (touching the brain tissue). - Three major parts: **forebrain, midbrain, hindbrain**. | **Division** | **Parts** | **Functions** | | FOREBRAIN | Cerebrum, thalamus, hypothalamus | Cerebrum: the major part, split into two hemispheres joined by the CORPUS CALLOSUM. Thalamus: major coordinating centre for SENSORY and MOTOR signalling. Hypothalamus: controls body TEMPERATURE, urge for EATING and DRINKING; contains neurosecretory cells making hypothalamic hormones | | MIDBRAIN | Located between thalamus/hypothalamus and pons; the CEREBRAL AQUEDUCT passes through it | Its dorsal portion has four round swellings β€” the CORPORA QUADRIGEMINA | | HINDBRAIN | Pons, cerebellum, medulla (medulla oblongata) | Pons: fibre tracts interconnecting brain regions. Cerebellum: very convoluted surface for more neurons. Medulla: connects to the spinal cord; contains centres for RESPIRATION, CARDIOVASCULAR REFLEXES and GASTRIC SECRETIONS | The **brain stem** = **midbrain + pons + medulla oblongata**, forming the connection between brain and spinal cord. ### Cerebral cortex β€” grey matter vs white matter - The **cerebral cortex** is the cell layer covering the hemispheres, thrown into prominent folds. It is called **GREY MATTER** because **neuron cell bodies** are concentrated there. - The inner part, made of fibre tracts covered with **myelin sheath**, looks opaque white β€” hence **WHITE MATTER**. - The cortex contains **motor areas, sensory areas**, and **association areas** (neither clearly sensory nor motor) responsible for **intersensory associations, memory and communication**. - The inner cerebral hemispheres plus deep structures like the **amygdala and hippocampus** form the **limbic lobe / limbic system**. With the hypothalamus it regulates **sexual behaviour, emotional reactions** (excitement, pleasure, rage, fear) **and motivation**. ### Why this matters for NEET - High-value one-liners: Na⁺/K⁺ pump moves **3 Na⁺ out for 2 K⁺ in**; resting membrane is **outside positive, inside negative**; meninges order **dura β†’ arachnoid β†’ pia**; the two hemispheres are joined by the **corpus callosum**; midbrain has the **corpora quadrigemina**; medulla controls **respiration and cardiovascular reflexes**; grey matter = **cell bodies**, white matter = **myelinated fibres**. - **Trap:** at rest the membrane is more permeable to **K⁺**, NOT Na⁺ β€” Na⁺ permeability only spikes during the action potential. Also, **electrical synapses are FASTER but RARE** in humans; the common type is chemical. And **dendrites carry impulses TOWARDS** the cell body while **axons carry them AWAY** β€” a direction students routinely invert. ## Test Yourself: MCQs, PYQs & Active Recall Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one. ## Practice Questions **Q1.** The neural system of Hydra is composed of: - (a) A brain with ganglia - (b) A spinal cord - (c) Only a nerve ring - (d) A network of neurons **Answer: (d)** β€” Neural organisation is very simple in lower invertebrates β€” in Hydra it is just a network of neurons. **Q2.** Afferent nerve fibres transmit impulses: - (a) From tissues and organs to the CNS - (b) Only within the brain - (c) From the CNS to organs - (d) Only to skeletal muscles **Answer: (a)** β€” Afferent fibres carry impulses from tissues/organs TO the CNS; efferent fibres carry regulatory impulses away from it. **Q3.** The somatic neural system relays impulses from the CNS to: - (a) Smooth muscles - (b) Cardiac muscle only - (c) Skeletal muscles - (d) Endocrine glands **Answer: (c)** β€” The somatic neural system relays impulses to skeletal muscles; the autonomic system serves involuntary organs and smooth muscles. **Q4.** Granular bodies present in the cell body and dendrites of a neuron are called: - (a) Schwann cells - (b) Nissl's granules - (c) Nodes of Ranvier - (d) Synaptic vesicles **Answer: (b)** β€” Nissl's granules are present in the cytoplasm of the cell body and also in the dendrites. **Q5.** Bipolar neurons, with one axon and one dendrite, are found in the: - (a) Embryonic stage - (b) Spinal cord - (c) Cerebral cortex - (d) Retina of the eye **Answer: (d)** β€” Bipolar neurons occur in the retina; multipolar neurons are in the cerebral cortex and unipolar in the embryonic stage. **Q6.** The gaps between two adjacent myelin sheaths along an axon are called: - (a) Nodes of Ranvier - (b) Sutures - (c) Cerebral aqueducts - (d) Synaptic clefts **Answer: (a)** β€” Nodes of Ranvier are the gaps between adjacent myelin sheaths formed by Schwann cells. **Q7.** At rest, the axonal membrane is: - (a) More permeable to Na+ than K+ - (b) Impermeable to both - (c) More permeable to K+ and nearly impermeable to Na+ - (d) Equally permeable to both **Answer: (c)** β€” At rest the membrane is comparatively more permeable to potassium ions and nearly impermeable to sodium ions. **Q8.** The sodium-potassium pump transports: - (a) 3 K+ out for 2 Na+ in - (b) 1 Na+ out for 1 K+ in - (c) 2 Na+ out for 3 K+ in - (d) 3 Na+ out for 2 K+ in **Answer: (d)** β€” The sodium-potassium pump transports 3 Na+ outwards for every 2 K+ into the cell, maintaining the ionic gradient. **Q9.** In a resting neuron, the outer surface of the axonal membrane carries: - (a) No charge - (b) A negative charge - (c) A positive charge - (d) A variable charge **Answer: (c)** β€” The outer surface possesses a positive charge and the inner surface a negative charge β€” the membrane is polarised. **Q10.** Depolarisation during an action potential is caused by: - (a) Rapid influx of Na+ - (b) Influx of Cl- - (c) Rapid efflux of K+ - (d) Efflux of proteins **Answer: (a)** β€” A stimulus makes the membrane freely permeable to Na+, causing rapid influx and reversal of polarity. **Q11.** The resting potential is restored at the site of excitation by: - (a) Protein influx - (b) Further Na+ influx - (c) Chloride influx - (d) K+ diffusing outside the membrane **Answer: (d)** β€” The short-lived rise in Na+ permeability is followed by a rise in K+ permeability; K+ diffuses out, restoring the resting potential. **Q12.** Which of the following is true of electrical synapses? - (a) They have a wide synaptic cleft - (b) They use neurotransmitters - (c) They are the common type in humans and are slow - (d) They are rare in our system but faster than chemical synapses **Answer: (d)** β€” Electrical synapses are rare in our system, but impulse transmission across them is always faster than across a chemical synapse. **Q13.** The three layers of the cranial meninges, from outside inwards, are: - (a) Dura mater, arachnoid, pia mater - (b) Pia mater, arachnoid, dura mater - (c) Arachnoid, dura mater, pia mater - (d) Dura mater, pia mater, arachnoid **Answer: (a)** β€” From outside in: dura mater (outer), arachnoid (very thin middle), pia mater (inner, contacting the brain). **Q14.** The two cerebral hemispheres are connected by a tract of nerve fibres called the: - (a) Corpora quadrigemina - (b) Cerebral aqueduct - (c) Corpus callosum - (d) Brain stem **Answer: (c)** β€” The corpus callosum is the tract of nerve fibres connecting the left and right cerebral hemispheres. **Q15.** The cerebral cortex is called grey matter because: - (a) It is covered with myelin - (b) It is made of fibre tracts - (c) It contains no neurons - (d) Neuron cell bodies are concentrated there **Answer: (d)** β€” Neuron cell bodies concentrated in the cortex give it a greyish appearance; myelinated fibre tracts inside form the white matter. **Q16.** The four round swellings on the dorsal portion of the midbrain are called: - (a) Corpora quadrigemina - (b) Limbic lobes - (c) Corpus callosum - (d) Cerebral peduncles **Answer: (a)** β€” The dorsal portion of the midbrain has four round swellings called corpora quadrigemina; the cerebral aqueduct passes through the midbrain. **Q17.** The centres controlling respiration, cardiovascular reflexes and gastric secretions lie in the: - (a) Cerebrum - (b) Thalamus - (c) Medulla - (d) Cerebellum **Answer: (c)** β€” The medulla oblongata contains the centres controlling respiration, cardiovascular reflexes and gastric secretions. **Q18.** Which part of the brain controls body temperature and the urge for eating and drinking? - (a) Thalamus - (b) Pons - (c) Cerebrum - (d) Hypothalamus **Answer: (d)** β€” The hypothalamus contains centres controlling body temperature and the urge for eating and drinking, plus neurosecretory cells. **Q19.** In the neuron shown in the figure, the gap in the myelin sheath marked D is called the - (a) Axon hillock - (b) Synaptic cleft - (c) Node of Ranvier - (d) Neurilemma **Answer: (c)** β€” The myelin sheath is interrupted at regular intervals; these uninsulated gaps are the nodes of Ranvier, where the impulse jumps from node to node (saltatory conduction), making conduction faster. **Q20.** In the figure, which labelled part receives impulses from other neurons and conducts them towards the cell body? - (a) E - (b) C - (c) F - (d) A **Answer: (d)** β€” A is a dendrite β€” the short, branched processes that carry impulses towards the cell body (soma, B). The axon [C] carries impulses away; E is the axon terminal and F is the myelin sheath. **Q21.** The sheath marked F around the axon of a peripheral nerve fibre is formed by - (a) Astrocytes - (b) Microglia - (c) Schwann cells - (d) Oligodendrocytes **Answer: (c)** β€” In the peripheral nervous system the myelin sheath is formed by Schwann cells; in the central nervous system it is formed by oligodendrocytes. ### NEET Previous Year Questions (PYQs) *Real NEET previous-year questions on this chapter, with explanations in our own words.* **Q22.** The brain stem is made up of: (NEET PYQ) - (a) Midbrain, pons and medulla oblongata - (b) Only the medulla - (c) Cerebellum and cerebrum - (d) Cerebrum, thalamus and hypothalamus **Answer: (a)** β€” Three regions make up the brain stem: midbrain, pons and medulla oblongata, forming the connection between brain and spinal cord. **Q23.** The limbic system, involved in regulating emotions and sexual behaviour, includes: (NEET PYQ) - (a) Cerebellum and medulla - (b) Corpora quadrigemina - (c) Amygdala and hippocampus - (d) Corpus callosum and pons **Answer: (c)** β€” The inner cerebral hemispheres plus deep structures such as the amygdala and hippocampus form the limbic lobe or limbic system. **Q24.** The electrical potential difference across the resting neural membrane is called: (NEET PYQ) - (a) Action potential - (b) Resting potential - (c) Synaptic potential - (d) Threshold potential **Answer: (b)** β€” The potential difference across the resting plasma membrane of a neuron is the resting potential. **Q25.** Myelinated nerve fibres are typically found in: (NEET PYQ) - (a) Only the retina - (b) Spinal and cranial nerves - (c) Only in the embryonic stage - (d) The autonomic neural system **Answer: (b)** β€” Myelinated nerve fibres are found in spinal and cranial nerves; unmyelinated fibres are common in autonomic and somatic systems. **Q26.** The major coordinating centre for sensory and motor signalling in the brain is the: (NEET PYQ) - (a) Hypothalamus - (b) Thalamus - (c) Cerebellum - (d) Pons **Answer: (b)** β€” The cerebrum wraps around the thalamus, which is a major coordinating centre for sensory and motor signalling. **Q27.** Neurotransmitters at a chemical synapse are contained in: (NEET PYQ) - (a) Synaptic vesicles in the axon terminal - (b) Nissl's granules - (c) Nodes of Ranvier - (d) Schwann cells **Answer: (a)** β€” The axon terminals contain synaptic vesicles filled with neurotransmitters, released into the synaptic cleft on arrival of an impulse. **Q28.** The association areas of the cerebral cortex are responsible for: (NEET PYQ) - (a) Reflex actions - (b) Intersensory associations, memory and communication - (c) Only motor control - (d) Only sensory reception **Answer: (b)** β€” Association areas are neither clearly sensory nor motor, and handle complex functions like intersensory associations, memory and communication. **Q29.** The canal passing through the midbrain is called the: (NEET PYQ) - (a) Central canal - (b) Neural canal - (c) Cerebral aqueduct - (d) Synaptic cleft **Answer: (c)** β€” A canal called the cerebral aqueduct passes through the midbrain. ### Active Recall Prompt Write everything you can recall about **Neural Control and Coordination**, naming each part first: the **divisions of the human neural system** (CNS, PNS, afferent/efferent, somatic/autonomic); the **neuron** (its three parts, the three neuron types with locations, myelinated vs unmyelinated); **resting potential** (permeabilities, ionic distribution, the sodium-potassium pump ratio); **action potential** and how the impulse is conducted; **synapses** (electrical vs chemical); and the **central neural system** β€” the meninges, and the forebrain, midbrain and hindbrain with every part and its function, plus grey vs white matter and the limbic system. Begin each fact with its topic and end it with a full stop.