97 Fun Facts About Nervous System

In vertebrates the nervous system has two main parts: the central nervous system and which other?

Peripheral nerves link the brain and spinal cord to the rest of the body, and unlike those two they can often regrow after being cut.

Neurons are typically sorted into three functional types: sensory neurons, motor neurons and what?

Interneurons are the ones in between: they pass signals from sensory neurons to motor neurons and to each other, forming the circuits that process information along the way.

Which part of a neuron carries impulses away from the cell body, sometimes for a metre or more?

It leaves the cell body at a swelling called the axon hillock. Dendrites, by contrast, branch profusely but only reach a few hundred micrometres.

Which nerve, the largest in the body, runs from the lower spine down the back of each leg to the foot?

The sciatic nerve is about 2 cm wide, and a slipped disc pressing on its roots is the most common cause of sciatica, pain that shoots from the buttock down the leg.

Along with neurons, the nervous system is built from support cells known collectively as what?

Glia take their name from the Greek for 'glue' because they were long thought merely to hold neurons together; in fact they insulate, feed and defend them.

Which cells, named after a German physiologist, form the myelin sheath outside the brain and spinal cord?

Schwann cells, named after Theodor Schwann, also help a severed nerve fibre regrow, one reason nerves in the limbs recover from injury far better than those of the brain and spinal cord.

What are the gaps in the myelin sheath, between which nerve impulses appear to jump, called?

Nodes of Ranvier let an impulse leap from gap to gap instead of creeping along every bit of the fibre, which is why insulated nerves conduct so much faster than bare ones.

Which ion floods into a neuron to trigger the rising phase of an action potential?

Voltage-gated channels open at a threshold, the interior turns positive, then potassium flows out to restore the resting state. Local anaesthetics work by blocking those sodium channels.

The fastest myelinated nerve fibres conduct impulses at roughly what speed?

120 metres per second, about 430 km/h, is reached only by the thickest insulated fibres, such as those reporting muscle position; bare fibres carrying dull, lingering pain are far slower, so that ache arrives last.

The adult spinal cord is much shorter than the spine, so where does it end?

The lower back is where the cord stops, near the first lumbar vertebrae, because the spinal column keeps growing after the cord has finished; only a bundle of nerve roots runs on below.

What does cauda equina, the name of the nerve-root bundle below the spinal cord, mean in Latin?

A horse's tail is what the fanned-out nerve roots resemble; squeezing them, as a slipped disc can, may cut off bladder control, which is why it is treated as a surgical emergency.

Which region of the spine has seven vertebrae but eight pairs of spinal nerves?

Cervical nerves number eight because the first leaves above the top neck vertebra and the eighth below the seventh; they are among the 31 pairs that branch off the spinal cord in all.

Which cranial nerves partly cross so each brain half sees the opposite side?

The optic nerves cross right beside the pituitary gland, so a tumour swelling there presses on the crossing fibres and wipes out the outer edges of vision in both eyes.

Which cranial nerve, the tenth, takes its name from the Latin for 'wandering'?

The vagus nerve wanders from the brainstem to the gut and slows the heartbeat, which is why it overreacting to pain, heat or the sight of blood can make a person faint.

Which cranial nerve, the fifth, carries feeling from the face and powers the chewing muscles?

The trigeminal nerve splits into three branches for the forehead, cheek and jaw, which is why a dentist can numb half the lower teeth with one injection beside its lowest branch.

The facial nerve also carries which sense from the front two-thirds of the tongue?

Taste fibres travel in a branch called the chorda tympani, which crosses the middle ear on its way to the brain, so ear infections or ear surgery can dull taste on one side of the tongue.

Doctors test which cranial nerve, the twelfth, by asking a patient to stick out their tongue?

Hypoglossal means 'under the tongue', and because the nerve on each side pushes the tongue forward, damage to one makes it swing toward the injured side when stuck out.

Which cranial nerve, the shortest of all, runs only from the lining of the nose to the brain just above?

Olfactory nerve endings line the roof of the nose, and a cold, flu or COVID-19 can knock out the sense of smell; it often returns within a few weeks or months.

The knee-jerk reflex is the classic example of which kind of reflex arc?

Monosynaptic means a single junction: the stretch-sensing fibre connects straight to the motor neuron in the spinal cord, so the leg kicks without any signal having to reach the brain first.

Why can a reflex like the knee-jerk fire faster than a deliberate movement?

The brain still receives the input, but it analyses the signal after the reflex has already happened.

Which division of the autonomic nervous system is built into the walls of the gut?

The enteric system can keep the gut churning and moving food along even when cut off from the brain and spinal cord, which is how it earned the nickname 'second brain'.

Which branch of the autonomic nervous system drives the 'fight or flight' response?

Sympathetic nerves speed the heart, widen the pupils and open the airways within seconds, while putting digestion on hold until the danger has passed.

Luigi Galvani found in the 1780s that an electric spark made the legs of which dead animal twitch?

A frog's leg kicking on his bench convinced Galvani that nerves and muscles run on 'animal electricity', and his name survives in the verb galvanise.

Roughly how many neurons does the human gut's own 'second brain' contain?

That is about 0.5% of the brain's count but five times the spinal cord's. It signals with acetylcholine, dopamine and serotonin, just like the brain.

Inflammation of the three protective membranes that wrap the brain and spinal cord is called what?

Meningitis can be life-threatening if not treated quickly; its warning signs include a stiff neck, a dislike of bright light and a rash that does not fade when a glass is pressed against it.

Which clear liquid, made inside the brain's ventricles, lets the brain float within the skull?

Cerebrospinal fluid gives a brain of about 1.4 kg an effective weight of only 25 to 50 g, which keeps its own mass from pressing on the tissue and blood vessels at its base.

Which injection delivers anaesthetic into the space just outside the tough membrane sheathing the spinal cord?

An epidural numbs the nerves from just outside the sac of fluid around the cord, so a woman in labour can stay awake while the pain is blocked; a spinal block goes one layer deeper, into the fluid itself.

Which part of the brainstem controls breathing, heart rate, blood pressure and vomiting?

The medulla oblongata keeps breathing and heartbeat going without conscious thought, which is why an opioid overdose that dulls its breathing centres can stop a person breathing altogether.

Which small brain structure regulates body temperature and hunger and controls the pituitary gland?

The hypothalamus works like a thermostat for body heat, and during an infection chemicals called pyrogens push its setting upward, which is what a fever is.

Which brain structure, Latin for 'little brain', fine-tunes coordination and timing of movement?

The cerebellum does not start movements but corrects them as they happen, and thanks to its tiny granule cells it holds more than half of the brain's neurons in a small fraction of its volume.

Grey matter, unlike white matter, is made up mostly of what?

Neuron cell bodies do the processing, while white matter is the cabling between them; the fatty insulation on that cabling looks pale, which is where the two names come from.

A knot of nerve-cell bodies lying outside the brain and spinal cord is called what?

A ganglion beside the spinal cord is where the chickenpox virus lies dormant for decades before travelling back down one nerve to cause the painful band of rash called shingles.

Which nerve, arising from C3 to C5 in the neck, provides the sole motor control of the diaphragm?

The phrenic nerve is the diaphragm's only motor supply, hence the students' rhyme 'C3, 4 and 5 keep the diaphragm alive': a spinal injury above that level can stop a person breathing unaided.

Hitting your 'funny bone' actually strikes which nerve against the elbow?

The ulnar nerve crosses the elbow with only skin over it, so a knock squashes it against the bone and sends tingling to the little finger; 'funny' is said to be a pun on humerus, the upper-arm bone.

Carpal tunnel syndrome is caused by compression of which nerve at the wrist?

The median nerve shares the cramped carpal tunnel with the tendons that bend the fingers, so swelling there numbs the thumb and the next fingers while leaving the little finger alone.

Which autoimmune disease strips the insulation from nerve fibres in the brain and spinal cord, slowing or blocking their signals?

Multiple sclerosis leaves hardened, scarred patches wherever the insulation is destroyed; because these can form anywhere, early symptoms range from blurred vision to numb limbs.

Parkinson's disease involves the loss of dopamine-producing neurons in which brain region?

The substantia nigra, Latin for 'black substance', is named for its dark colour; by the time symptoms appear, at least half of its dopamine-producing cells have usually already been lost.

Amyotrophic lateral sclerosis is popularly named after which baseball star?

Lou Gehrig played 2,130 consecutive games for the Yankees before the disease forced him to retire in 1939, when he told the crowd he was 'the luckiest man on the face of the earth'.

Which viral disease strikes sooner after a bite to the face than the foot, because it creeps to the brain along nerves?

Rabies travels so slowly along the nerves that a vaccine given soon after the bite can stop it before it reaches the brain; once symptoms appear it is almost always fatal.

Which bacterial infection, nicknamed lockjaw, enters through wounds and locks the muscles in painful spasms?

Tetanus bacteria live in soil and manure and get in through cuts; their toxin acts on the nerves that control the muscles, so the spasms usually begin in the jaw and neck.

Which syndrome, usually triggered by an infection, has the immune system attack the body's nerves so weakness climbs up from the feet?

Guillain-Barré syndrome can paralyse the breathing muscles within days, yet most people recover, even from severe cases; three French doctors described it in 1916.

Which sea animals, among the simplest alive, have no neurons or nervous system at all?

Sponges lack neurons entirely, yet they carry many of the genes other animals use to build synapses, a hint that the nervous system's toolkit is older than nerves themselves.

Cnidarians such as jellyfish and hydras have which simplest form of nervous system?

A diffuse nerve net spreads a signal in all directions from the spot touched, so a hydra responds the same way wherever the contact is and cannot tell where it came from.

Which tiny animal's usual adult form has just 302 neurons, all named and mapped?

A roundworm, C. elegans, is a soil worm about a millimetre long whose wiring was pieced together from electron micrographs of thin slices, in a study published in 1986.

Which giant 'command neurons' in a fish's brainstem trigger its C-shaped escape reflex?

Every fish has two, one on each side; a single action potential from one makes the fish curve into a C-shape within milliseconds.

An injury low on the spinal cord typically paralyses the legs but spares the arms, a condition called what?

Paraplegia follows damage lower down because the nerves to the arms leave the cord at the neck; an injury up there can paralyse all four limbs.

Which birth defect arises when the embryo's neural tube, the forerunner of the central nervous system, fails to close along the back?

Spina bifida arises in the first month of pregnancy, often before a woman knows she is pregnant, which is why folic acid is advised before conception: it prevents most such defects.

In which animal does the nerve to the voice box take a detour of about 4.6 metres via the chest?

The giraffe inherited the route from fish-like ancestors, in which the nerve ran straight past the heart to the gills. As necks grew longer, the nerve stayed hooked under an artery in the chest.

Which fish, served in Japan as the delicacy fugu, carries a toxin that shuts down nerve signals?

Pufferfish organs hold tetrodotoxin, which stops nerves from firing, so a victim can lie fully paralysed yet conscious. Chefs in Japan train for years to earn the licence needed to prepare it.

Which farm bird, nicknamed Mike, lived 18 months after a 1945 beheading spared most of the brain stem?

The chicken kept breathing and walking because a bird's brain stem runs its heartbeat, breathing and most reflexes. Mike's owner fed him milk and water with an eyedropper and toured him in sideshows.

Which childhood illness leaves a virus hiding in nerve cells for decades, able to return as shingles?

Chickenpox virus stays dormant in nerve cells beside the spinal cord long after the spots fade. When it wakes it travels along one nerve to the skin, so a shingles rash forms a stripe on one side of the body.

Which wrinkle-smoothing injection works by stopping nerve endings from telling muscles to contract?

Botox is a heavily diluted dose of botulinum toxin, considered the deadliest natural substance known. It blocks the chemical message that passes from nerve to muscle, so the muscle under a wrinkle relaxes.

Which animal has the heaviest brain known in any living or extinct creature?

The sperm whale has a brain more than five times heavier than a human's. Measured against its vast body, though, that brain is small, and many dolphins score higher on brain-to-body size.

Which sea animal keeps two-thirds of its neurons in its limbs rather than in its brain?

The octopus runs a thick nerve cord down each arm, and those cords hold most of its neurons. Its arms can move and sense largely on their own, without orders from the brain.

What do doctors call the vivid sensation, common after amputation, that a lost arm or leg is still there?

Phantom limb was named in the 1870s by the physician Silas Weir Mitchell, who called it a 'sensory ghost' of the lost part. Most amputees feel one, and for many it hurts.

Which Russian physiologist showed reflexes can be learned by training dogs to drool at a metronome's tick?

Ivan Pavlov won his 1904 Nobel Prize for work on digestion, not behaviour. He noticed conditioning when his dogs began to drool at the mere sight of the technician who usually fed them.

Which medical emergency are people taught to spot with the acronym FAST: face, arms, speech, time?

Stroke cuts or blocks the blood flow to part of the brain, and the cells there start to die. FAST was devised in the UK in 1998 to train ambulance crews to recognise one quickly.

Which lobe of the brain was wrecked when an iron rod shot through railway foreman Phineas Gage's head?

The frontal lobe on Gage's left side took the blow, yet he lived for more than a decade afterwards. Friends found him so altered that they called him 'no longer Gage', an early hint that this region shapes personality.

Which bridge between the brain's halves was cut in the 'split-brain' patients studied by Roger Sperry?

The corpus callosum was severed as a last resort to stop violent seizures spreading across the brain. Sperry found that each half then had its own perceptions, and only the left could put them into words.

Which brain operation, now discredited, won Portuguese neurologist Egas Moniz a share of the 1949 Nobel Prize?

Lobotomy severed connections at the front of the brain to quieten psychiatric patients, and its champion Walter Freeman spoke of a 'surgically induced childhood'. Critics have urged that the prize be rescinded.

Which test, first run on a human in 1924 by Hans Berger, records the brain's electrical waves through the scalp?

EEG is short for electroencephalogram, a word Berger coined himself. He also discovered the brain's alpha rhythm, which for a time was known as the Berger wave.

Which Italian scientist found in the 1780s that an electrical spark makes a dead frog's leg muscles twitch?

Luigi Galvani took the twitch as proof of an 'animal electricity' running through nerve and muscle. His rival Alessandro Volta rejected the idea, yet coined the word galvanism in his honour.

Which B vitamin do women take before and during early pregnancy to protect a baby's developing spinal cord?

Folic acid lowers the risk of neural tube defects such as spina bifida, which arise in the first weeks of pregnancy. Spina bifida births in the United States fell after grain products were fortified with it.

Which condition did the ancient Greeks call the 'sacred disease', believing its sudden fits had a divine origin?

Epilepsy was no more divine than any other illness, argued a treatise in the Hippocratic collection, which traced it to the brain. That turn from gods to nature is counted a breakthrough in the history of medicine.

Which ancient disease damages nerves so that sufferers injure numb hands and feet without noticing?

Leprosy does not make fingers and toes drop off by itself; they are lost to wounds and infections that go unfelt once the nerves stop reporting pain. Roughly 30% of patients suffer nerve damage.

Which sea animal's giant nerve fibre, up to 1.5 mm thick, let Hodgkin and Huxley work out how nerves fire?

The squid uses that outsized fibre to trigger its jet-propelled escape, and its width let the two scientists slip electrodes inside. Their measurements of its electrical pulses won them a Nobel Prize.

Which sea animals have no central brain, only a nerve ring around the mouth and a nerve along each arm?

Starfish let their arms take turns in charge: whichever arm detects something attractive becomes dominant and overrides the others to lead the way. The ring around the mouth links the arms together.

Which brain structure was found to be enlarged in taxi drivers who had memorised the streets of London?

The hippocampus, which handles spatial memory, was larger at the back in cabbies who had passed the test known as The Knowledge. The longer they had driven, the bigger that part had grown.

Which relay station deep in the brain passes on signals from every sense except smell to the cortex?

The thalamus keeps a separate cluster of cells for each sense it forwards, from sight and hearing to touch. It also helps to regulate sleep, alertness and consciousness.

Which small structure in the middle of the brain did René Descartes call the 'principal seat of the soul'?

The pineal gland stood out to Descartes because it was the only part of the brain he found single rather than paired. Its real job is to release melatonin, the hormone that sets sleep patterns.

Which French surgeon tied speech to one region of the brain after examining a patient who could say only 'tan'?

Paul Broca opened the dead man's brain in 1861 and found a lesion on the left side. The patient had understood everything said to him for 21 years while losing the power to answer.

Which sense of body position lets a sober person touch their own nose accurately with both eyes closed?

Proprioception draws on sensors in the muscles, tendons and joints that report where each limb is. American police use the nose-touch test at the roadside because alcohol blunts the sense.

Which part of the eye grows out of the embryonic brain and counts as central nervous tissue?

The retina and the optic nerve both begin as outgrowths of the developing brain, so anatomists class the light-catching layer as brain tissue rather than as a separate sense organ.

Which arrow poison of South American hunters paralyses prey by blocking the signal from nerve to muscle?

Curare does nothing when swallowed and works only once it reaches the blood through a wound, so the hunters could eat their catch. In the 1850s Claude Bernard showed that it strikes where a nerve meets its muscle.

Which natural painkillers does the brain release during hard exercise, blocking pain much as morphine does?

Endorphins take their name from a contraction of 'endogenous morphine', meaning morphine made within the body. As well as dulling pain, they raise feelings of well-being.

Which drug did Karl Koller bring into medicine in 1884 as a local anaesthetic to numb the eye for surgery?

Cocaine was already known to Koller's colleague Sigmund Freud as a painkiller, but it was Koller who saw that it could numb living tissue. Dentists took up the idea soon afterwards.

Which term describes nerve fibres that carry signals from sense receptors toward the brain and spinal cord?

Afferent comes from the Latin for 'carrying toward', while its opposite, efferent, means 'carrying away' and describes the fibres that take orders back out to muscles.

Which branching parts of a neuron, named from the Greek for 'tree', receive signals from other nerve cells?

Dendrites give a neuron an enlarged surface on which to collect incoming signals. A single neuron may carry many of these branching trees.

Which hormone do glands above the kidneys release on a signal from nerves, readying the body for 'fight or flight'?

Adrenaline is called epinephrine in the United States, where 'Adrenalin' was registered as a trademark for an extract patented in 1901. The cells that release it are modified nerve cells.

Which chemical messenger did Otto Loewi identify using two beating frog hearts, in an experiment he first dreamed?

Acetylcholine seeped from the first heart's nerve into the surrounding fluid, and that fluid alone slowed the second heart. It proved that nerves signal with chemicals, and won Loewi a 1936 Nobel Prize.

Which sugar is the main fuel of the human brain, an organ that burns about a fifth of the body's energy?

Glucose powers the brain even though the organ makes up only about 2% of body weight. When the sugar runs short, as in fasting, the brain switches to burning ketone bodies instead.

Which support cells wrap their 'end-feet' around the brain's capillaries and help to maintain the blood–brain barrier?

Astrocytes are named for their star shape, from the Greek words for 'star' and 'cell'. They also supply nutrients to nerve tissue and help to scar over the brain after an injury.

Which compound makes chilli peppers burn by switching on a nerve sensor that also responds to heat?

Capsaicin has no such effect on birds, whose version of the sensor ignores it, so they eat chillies freely and scatter the seeds. Research into how it works fed into the 2021 Nobel Prize in medicine.

Which Spaniard, whose detailed drawings of brain cells are still used in teaching, shared a 1906 Nobel Prize?

Ramón y Cajal shared it with Camillo Golgi, whose staining method he had used to show that nerve tissue is made of separate cells. Golgi disagreed, holding that it was one continuous network.

Which division of the nervous system, the counterpart of the autonomic, gives conscious control of skeletal muscles?

Somatic nerves link the brain and spinal cord to the skeletal muscles, and also bring in signals from sensory receptors in the skin. The autonomic system, by contrast, works without conscious effort.

Which disease, first described in 1906 by a German psychiatrist, clogs the brain with protein 'plaques' and 'tangles'?

Alzheimer's disease is named after that psychiatrist, Alois Alzheimer, and accounts for around 60–70% of dementia cases. Its most common early symptom is difficulty remembering recent events.

Which nerve agent did the Aum Shinrikyo cult release on the Tokyo subway in a 1995 attack?

Sarin blocks the enzyme that clears away a nerve's signal to contract, so muscles are driven without rest. German chemists discovered it in 1938 while trying to make stronger pesticides.

Which kind of conduction, named from the Latin for 'leap', carries impulses rapidly along insulated nerve fibres?

Saltatory conduction lets an impulse skip from gap to gap in a fibre's fatty coating instead of crawling along its whole length. It also saves energy, because fewer ions need pumping back afterwards.

Which metal, once used to turn fur into felt, gave hat-makers tremors often linked to the phrase 'mad as a hatter'?

Mercury vapour left hatters shaky, irritable and painfully shy, a condition doctors call erethism. Lewis Carroll's Mad Hatter, though, is often said to have been modelled on an eccentric furniture dealer.

Which word names the band of skin supplied by one spinal nerve, the strip that a shingles rash typically follows?

Dermatome bands run around the chest and abdomen like a stack of discs, each fed by a different spinal nerve. A virus lying dormant beside one nerve therefore erupts in a single stripe.

Which Montreal neurosurgeon mapped the body onto the brain's surface by electrically probing patients who were awake?

Wilder Penfield used only local anaesthetic, so his patients could describe what they felt as he touched each spot. His maps became the 'homunculus', a distorted figure with huge hands, lips and face.

Which neurotransmitter, the brain's chief 'brake' on nerve activity, is boosted by tranquillisers such as Valium?

GABA quietens nerve cells instead of exciting them, and the benzodiazepine family of drugs works by enhancing its effect. That is why those drugs sedate, ease anxiety and relax muscles.

Which form of paralysis did Superman actor Christopher Reeve live with after a riding accident at a 1995 competition?

Quadriplegia, also called tetraplegia, is the loss of movement or feeling in all four limbs, usually after damage to the spinal cord in the neck. Reeve relied on a ventilator for the rest of his life.

Which mood-regulating neurotransmitter is about 90% made in the gut, where it controls the movements of the intestines?

Serotonin is released by cells lining the gut when food arrives. If the meal contains an irritant, those cells release more of it to hurry everything through.

Which Paris-born neurologist gave his name to the upward flick of the big toe when the sole is stroked?

Joseph Babinski reported the sign in 1896 in a presentation just 26 lines long. In an adult it points to damage in the brain or spinal cord, but in infants it is a normal primitive reflex.

Which infectious misfolded proteins, named by Stanley Prusiner in 1982, cause mad cow disease and its human form, CJD?

Prions take their name from a blend of 'protein' and 'infection'. Prusiner won the 1997 Nobel Prize for his research on them, and the cattle form is thought to reach people through infected meat.

Whose brain did pathologist Thomas Harvey remove in 1955, cut into about 240 blocks and keep for decades?

Albert Einstein's brain weighed 1,230 grams when Harvey removed it. Its sections then spent more than twenty years preserved in alcohol in two mason jars inside a cider box.