Nervous System — Set 1

Correct Answer: B. Cerebellum

• **Cerebellum** = The cerebellum, located at the rear of the brain, coordinates voluntary muscle movements and maintains balance and posture by processing input from the eyes, ears, and muscles. • **Alcohol test** — Alcohol preferentially impairs the cerebellum first, which is why intoxicated people lose coordination and walk unsteadily — this is the basis of the roadside sobriety walk test. • The cerebellum does not initiate movement; it fine-tunes it, acting like an auto-correction system for the body. • 💡 Option A (Medulla) controls heartbeat and breathing; Option C (Cerebrum) handles thought and sensory perception; Option D (Pons) relays signals between brain regions.

Correct Answer: B. Neuron

• **Neuron** = A neuron is the specialized cell that forms the entire nervous system — it receives, processes, and transmits electrical and chemical signals throughout the body. • **Three parts** — Every neuron has a cell body (soma) that contains the nucleus, dendrites that receive incoming signals, and an axon that sends signals forward; all three must work together for communication. • The human brain alone contains approximately 86 billion neurons, making it the most complex biological structure known. • 💡 Option A (Axon) is only the signal-sending arm of a neuron, not the whole unit; Option C (Nephron) is the filtering unit of the kidney; Option D (Dendrite) is only the receiving arm.

Correct Answer: A. Medulla Oblongata

• **Medulla Oblongata** = The medulla oblongata sits at the base of the brainstem where the brain meets the spinal cord, and it houses the cardiac centre, respiratory centre, and vasomotor centre that regulate heartbeat, breathing, and blood pressure automatically. • **Life-critical location** — Any injury to the medulla is immediately life-threatening because it controls functions the body cannot survive without even for a few minutes. • The medulla also controls reflexes like coughing, sneezing, swallowing, and vomiting, acting as the autonomic emergency manager. • 💡 Option B (Thalamus) relays sensory signals to the cortex; Option C (Hypothalamus) maintains homeostasis like temperature and hunger; Option D (Cerebellum) coordinates balance.

Correct Answer: B. Synapse

• **Synapse** = A synapse is the microscopic junction between two neurons where communication occurs — the electrical impulse from the first neuron triggers the release of chemical messengers (neurotransmitters) that carry the signal across the gap to the next neuron. • **One-way communication** — Signals at a synapse travel in only one direction (from axon terminal to dendrite), which ensures precise and controlled neural signalling without backward interference. • The human brain contains an estimated 100 to 500 trillion synapses, and strengthening synaptic connections is the physical basis of learning and memory. • 💡 Option A (Axon terminal) is the end bulb of the first neuron before the gap; Option C (Ganglion) is a cluster of nerve cell bodies outside the CNS; Option D (Node of Ranvier) is a gap in the myelin sheath along an axon.

Correct Answer: D. Neurotransmitter

• **Neurotransmitter** = Neurotransmitters are endogenous chemical molecules released by the axon terminal into the synaptic cleft; they bind to receptors on the next neuron and either excite or inhibit its firing. • **Famous examples** — Acetylcholine (muscle activation), Dopamine (reward and motivation), Serotonin (mood regulation), and GABA (calming inhibition) are all neurotransmitters whose imbalance underlies disorders like depression, Parkinson's, and anxiety. • Most psychiatric drugs work by increasing or decreasing the availability of specific neurotransmitters at synapses, not by creating new ones. • 💡 Option A (Vitamin) is a dietary micronutrient with no direct signalling role; Option B (Enzyme) is a biological catalyst that speeds chemical reactions; Option C (Hormone) travels through the bloodstream and acts over longer distances.

Correct Answer: C. 12 pairs

• **12 pairs** = There are exactly 12 pairs of cranial nerves that emerge directly from the brain (mostly the brainstem) rather than from the spinal cord, controlling sensory and motor functions of the head, neck, and some thoracic and abdominal organs. • **Longest cranial nerve** — The vagus nerve (Cranial Nerve X) is the longest, travelling from the brainstem all the way into the abdomen to regulate heart rate, digestion, and breathing — the only cranial nerve to leave the head and neck region. • Cranial nerves are numbered I to XII using Roman numerals; Nerve I (Olfactory) handles smell and Nerve II (Optic) handles vision. • 💡 Option A (10 pairs) is an undercount with no anatomical basis; Option B (31 pairs) is the count of spinal nerves, not cranial; Option D (24 pairs) is incorrect.

Correct Answer: A. Dura mater

• **Dura mater** = The dura mater (Latin for 'tough mother') is the thick, leathery outermost layer of the meninges — the three protective membranes that surround the brain and spinal cord to shield them from physical impact. • **Three-layer sandwich** — Moving inward from the skull: Dura mater (tough outer) → Arachnoid mater (middle, spider-web-like) → Pia mater (thin inner layer directly on brain tissue), with cerebrospinal fluid filling the space between arachnoid and pia. • Subdural haematoma (bleeding between dura and arachnoid) is a dangerous condition after head injuries because blood accumulates and compresses the brain. • 💡 Option B (Arachnoid mater) is the middle membrane; Option C (Pia mater) is the innermost layer directly touching the brain; Option D (Pericardium) is the protective sac around the heart, not the brain.

Correct Answer: A. Sympathetic system

• **Sympathetic system** = The sympathetic nervous system is the division of the autonomic nervous system that activates the body during stress or danger — it increases heart rate, dilates pupils, redirects blood to muscles, and releases adrenaline to prepare the body to fight or flee. • **SLUDD reversal** — Sympathetic activation reverses the parasympathetic SLUDD functions: it inhibits salivation, tears, urination, and digestion while maximising muscle and brain blood flow. • Chronic sympathetic overactivation (perpetual stress) damages the heart and immune system because the body was designed for short bursts of this response, not sustained activation. • 💡 Option B (Central system) is the brain + spinal cord and does not directly trigger fight-or-flight; Option C (Somatic system) controls voluntary skeletal muscles; Option D (Parasympathetic system) is the opposite — it calms the body down.

Correct Answer: D. Cerebrum

• **Cerebrum** = The cerebrum is the largest and most developed part of the human brain, occupying about 85% of its total weight — it is responsible for conscious thought, language, memory, emotions, sensory perception, and voluntary movement. • **Two hemispheres, four lobes** — The cerebrum is divided into left and right hemispheres, each with frontal, parietal, temporal, and occipital lobes handling different functions; the left hemisphere controls the right side of the body and vice versa. • Humans have a proportionally larger cerebrum than any other animal, which accounts for our superior intelligence, complex language, and abstract reasoning abilities. • 💡 Option A (Cerebellum) coordinates movement and balance, not intelligence; Option B (Midbrain) processes eye movement and auditory reflexes; Option C (Hindbrain) handles basic survival functions like breathing.

Correct Answer: C. Myelin sheath

• **Myelin sheath** = The myelin sheath is a white, fatty insulating coating produced by Schwann cells (in the peripheral nervous system) that wraps around axons in segments, dramatically increasing the speed of nerve impulse conduction. • **Saltatory conduction** — Electrical impulses jump between the exposed gaps in the myelin sheath called Nodes of Ranvier instead of travelling the entire length, allowing signals to travel at up to 120 metres per second instead of just 1 metre per second in unmyelinated fibres. • Multiple Sclerosis (MS) is a disease in which the immune system attacks the myelin sheath, disrupting nerve signals and causing numbness, weakness, and coordination loss. • 💡 Option A (Sarcolemma) is the plasma membrane surrounding muscle fibres; Option B (Cytoplasm) is the fluid inside the cell body; Option D (Neurilemma) is the outer nucleated layer of Schwann cells — it exists only in peripheral nerves.