Nervous System — Set 2

Correct Answer: A. Dendrite

• **Dendrite** = Dendrites are the branching, tree-like extensions of a neuron that act as the primary antennae — they receive electrochemical signals from the axon terminals of neighbouring neurons and channel them toward the cell body for processing. • **More dendrites = more connections** — A single neuron can have thousands of dendritic branches, allowing it to receive input from thousands of different neurons simultaneously, which is why the brain can integrate enormous amounts of information at once. • The word 'dendrite' comes from the Greek word for tree, reflecting their characteristic branching appearance under a microscope. • 💡 Option B (Axon) transmits signals away from the cell body to the next neuron; Option C (Nucleus) stores DNA and controls cell metabolism; Option D (Mitochondria) generates ATP energy for the neuron.

Correct Answer: D. Brain and Spinal cord

• **Brain and Spinal cord** = The Central Nervous System (CNS) consists exclusively of the brain and the spinal cord — these two structures together receive all sensory information, process it, and issue motor commands to the rest of the body. • **Protected by bone** — The defining feature of the CNS is that both its components are encased in bone: the brain is protected by the skull (cranium) and the spinal cord is protected by the vertebral column, reflecting how critical they are for survival. • The CNS is distinguished from the Peripheral Nervous System (PNS), which consists of all the nerves that branch out from the brain and spinal cord to reach every part of the body. • 💡 Option A (Spinal cord and Nerves) incorrectly pairs nerves — nerves belong to the PNS; Option B (Brain and Cranium) confuses the cranium (a bone) with a nervous system component; Option C (Brain and Nerves) also mixes CNS and PNS components.

Correct Answer: B. Hypothalamus

• **Hypothalamus** = The hypothalamus is a small but powerful region at the base of the brain that maintains the body's internal balance (homeostasis) by controlling body temperature, hunger, thirst, sleep, and sexual behaviour. • **Neuro-endocrine bridge** — The hypothalamus directly controls the pituitary gland (master gland) by releasing hormones into it, making the hypothalamus the critical link between the nervous system and the endocrine (hormone) system. • Damage to the hypothalamus can cause extreme obesity, inability to regulate body temperature, or chronic insomnia because these functions lose their central controller. • 💡 Option A (Cerebrum) handles thought, memory, and conscious perception; Option C (Pituitary gland) secretes hormones but is controlled by the hypothalamus — it is the tool, not the thermostat; Option D (Thalamus) relays sensory signals to the cortex.

Correct Answer: C. Reflex action

• **Reflex action** = A reflex action is a rapid, automatic, involuntary response to a stimulus that is processed entirely within the spinal cord (not the brain), allowing the body to react before conscious thought can occur to prevent injury. • **Reflex arc** — The pathway is: Receptor → Sensory neuron → Spinal cord interneuron → Motor neuron → Effector muscle; the brain is informed after the action is complete, which is why you jerk your hand back from fire before you feel pain. • Knee-jerk reflex (patellar reflex), blinking when an object approaches the eye, and pupil constriction in bright light are classic reflex actions tested in medical examinations. • 💡 Option A (Voluntary action) requires conscious decision-making through the cerebrum; Option B (Muscular action) is a general term for any muscle movement; Option D (Cerebral action) is a non-standard term implying brain-controlled movement.

Correct Answer: C. Optic nerve

• **Optic nerve** = The optic nerve (Cranial Nerve II) is a bundle of over one million nerve fibres that transmits electrical impulses generated by photoreceptors in the retina to the visual cortex in the occipital lobe of the brain for processing. • **Blind spot** — Where the optic nerve exits the retina, there are no photoreceptors — this is called the blind spot (optic disc). Your brain fills in this gap using information from the other eye, so you normally don't notice it. • Both optic nerves partially cross at the optic chiasm, allowing each hemisphere to receive visual input from both eyes, which enables depth perception and three-dimensional vision. • 💡 Option A (Olfactory nerve) is Cranial Nerve I and carries smell signals; Option B (Trigeminal nerve) is Cranial Nerve V and handles facial sensation and chewing; Option D (Auditory nerve/Vestibulocochlear nerve) is Cranial Nerve VIII for hearing and balance.

Correct Answer: C. Cerebrospinal fluid

• **Cerebrospinal fluid (CSF)** = Cerebrospinal fluid is a clear, colourless liquid that fills the subarachnoid space between the arachnoid mater and pia mater, acting as a shock absorber that prevents the brain from crashing into the skull during physical impacts. • **Dual function** — Beyond cushioning, CSF supplies nutrients and removes metabolic waste products from the brain, since most of the brain lacks direct lymphatic drainage — it essentially serves as the brain's own waste-clearance system. • A lumbar puncture (spinal tap) samples CSF to diagnose meningitis, multiple sclerosis, and brain haemorrhages without directly touching the brain. • 💡 Option A (Synovial fluid) lubricates joints like knees and hips; Option B (Lymph) flows through the lymphatic system to carry immune cells; Option D (Plasma) is the liquid component of blood.

Correct Answer: A. Synaptic cleft

• **Synaptic cleft** = The synaptic cleft is the tiny physical nanometre-wide gap (about 20–40 nanometres) within the synapse that separates the pre-synaptic axon terminal from the post-synaptic dendrite — neurotransmitters must diffuse across this gap to transmit the signal. • **Why the gap matters** — The cleft prevents direct electrical conduction between neurons, ensuring signal transmission is chemical and therefore controllable; this is the precise point where drugs, toxins, and learning alter brain function. • Enzymes in the synaptic cleft rapidly break down or reuptake neurotransmitters after use, resetting the synapse for the next signal — drugs like SSRIs block this reuptake to increase serotonin availability. • 💡 Option B (Bridge) is an informal term not used in neuroscience for this structure; Option C (Cell body) is the soma of the neuron containing the nucleus; Option D (Node) refers to Nodes of Ranvier — gaps in the myelin sheath.

Correct Answer: D. Corpus Callosum

• **Corpus Callosum** = The corpus callosum is the largest white matter structure in the brain — a thick band of over 200 million nerve fibres that connects the left and right cerebral hemispheres, allowing them to share information and coordinate complex tasks. • **Split-brain experiments** — When the corpus callosum is surgically cut (a rare treatment for severe epilepsy), each hemisphere loses awareness of the other's actions, producing the famous 'split-brain' phenomenon where the left hand literally does not know what the right hand is doing. • The corpus callosum continues developing until a person's mid-20s, which partly explains why adolescents have less coordinated decision-making — the two hemispheres are not yet fully integrated. • 💡 Option A (Medulla) is the brainstem region controlling vital functions; Option B (Thalamus) is a sensory relay station deep in the brain; Option C (Pons) is a brainstem bridge relaying signals between upper and lower brain regions.

Correct Answer: B. Autonomic Nervous System

• **Autonomic Nervous System (ANS)** = The autonomic nervous system is the division of the peripheral nervous system that operates without conscious control — it regulates smooth muscles of blood vessels and organs, cardiac muscle, and all glands to maintain vital functions like digestion, heart rate, and breathing. • **Two sub-divisions** — The ANS has two antagonistic branches: the sympathetic (accelerates functions during stress — fight or flight) and the parasympathetic (decelerates functions during rest — rest and digest), which balance each other to maintain internal stability. • You cannot voluntarily control your digestion, pupil size, or heart rate under normal conditions because these are governed by the ANS, not the somatic system. • 💡 Option A (Peripheral Nervous System) is the broader category containing both the ANS and somatic system; Option C (Central Nervous System) is the brain and spinal cord; Option D (Somatic Nervous System) controls voluntary skeletal muscle movements.

Correct Answer: A. Glial cells

• **Glial cells** = Glial cells (neuroglia) are the non-neuronal support cells of the nervous system — they outnumber neurons roughly 10:1 and provide physical scaffolding, supply nutrients, remove waste, form myelin sheaths, and regulate the immune defence of the brain. • **Can cause cancer, cannot transmit signals** — Unlike neurons, glial cells retain the ability to divide; when this division becomes uncontrolled, it causes glioma (brain cancer), which is why most brain tumours originate from glial cells, not neurons. • Recent research shows glial cells are not passive supporters — astrocytes actively modulate synaptic transmission and participate in memory formation alongside neurons. • 💡 Option B (Red blood cells) carry oxygen in the bloodstream and play no structural role in the nervous system; Option C (Epithelial cells) form body surface linings; Option D (Muscle cells) are contractile cells unrelated to neural support.