100 Fun Facts About Nervous System

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

The peripheral half is not shielded by the skull, the vertebral column or the blood-brain barrier, which makes it more vulnerable to injury and toxins.

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

They connect neurons to other neurons within the same region. Sensory neurons carry signals in from the sense organs; motor neurons carry orders out to muscles and glands.

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.

The body's longest axons belong to which nerve, running from the spine's base to the big toe?

It is also the widest single nerve in the body, formed from the L4 to S3 spinal roots. Most axons are only about a micrometre across.

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

They provide structural and metabolic support. Star-shaped astrocytes are the most abundant kind in the brain, and microglia act as its resident immune cells.

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

Theodor Schwann is the namesake. Inside the brain and spinal cord the same wrapping job is done by different cells, the oligodendrocytes.

Impulses in myelinated axons seem to jump between gaps in the sheath. What are those gaps called?

The leaping style is called saltatory conduction, from the Latin for 'jump'. Louis-Antoine Ranvier described the gaps in the 1870s.

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?

That is about 432 km/h, glacial next to electricity in a wire but far quicker than blood flow. The slowest unmyelinated fibres crawl along at about half a metre per second.

Jens Christian Skou, who discovered the neuron's three-out, two-in ion pump in 1957, was of which nationality?

He collected a Nobel Prize for it forty years later. The pump burns one ATP molecule per cycle and keeps every animal cell electrically ready to fire.

Roughly how long is the adult human spinal cord?

It is much shorter than the spinal column that protects it, ending between the first and second lumbar vertebrae before tapering into a bundle of nerve roots.

The nerve-root bundle below the spinal cord takes its Latin name from its resemblance to what?

The cauda equina consists of the lower lumbar, sacral and coccygeal nerve pairs. Compressing it is a surgical emergency.

How many pairs of spinal nerves branch off the human spinal cord?

Eight cervical, twelve thoracic, five lumbar, five sacral and one coccygeal. The cervical nerves are numbered by the vertebra below them, the rest by the one above.

Conventionally, how many pairs of cranial nerves do humans have?

They are labelled with Roman numerals I to XII. Only the first two emerge from the cerebrum; the other ten arise from the brainstem.

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

It is the longest nerve of the autonomic system, reaching from the brainstem to the gut, and it drives the 'rest and digest' response that slows the heart.

Which cranial nerve, the fifth, serves facial sensation and chewing and is named for its three branches?

Its ophthalmic, maxillary and mandibular divisions converge just before entering the pons. It is often called the most complex of the cranial nerves.

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

A branch called the chorda tympani carries the taste fibres. Damage to this nerve on one side is what causes the drooping of Bell's palsy.

The hypoglossal nerve, cranial nerve XII, which drives the muscles of the tongue, is which type of nerve?

Its name means 'under the tongue'. Doctors test it by asking a patient to stick their tongue out and watching for it to deviate to one side.

Which is the shortest of the twelve cranial nerves, and unusually can regenerate after damage?

It carries the sense of smell and, like the optic nerve, does not come off the brainstem. Regeneration is rare among nerve tracts of the central nervous system.

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

A tap below the kneecap stretches the quadriceps spindle, the signal loops through L3-L4 in the spinal cord and back, and the leg kicks before the brain hears about it.

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.

What is the third division of the autonomic nervous system, which runs the gut, called?

Often called the 'second brain', it holds five times as many neurons as the spinal cord and can operate independently of the brain.

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

Its nerves emerge from the thoracic and lumbar spinal cord, and the adrenal medulla behaves like one of its ganglia, pumping out adrenaline.

With nerves emerging from the brainstem and sacral spinal cord, the parasympathetic system has what kind of 'outflow'?

The fight-or-flight system, by contrast, has thoracolumbar outflow. Parasympathetic fibres travel in the oculomotor, facial, glossopharyngeal and vagus nerves.

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.

How many layers of meninges surround the brain and spinal cord in mammals?

From outside in: the tough dura mater, the web-like arachnoid mater and the delicate pia mater. Cerebrospinal fluid fills the space under the arachnoid.

Cerebrospinal fluid is mostly produced by which structures inside the brain's ventricles?

Harvey Cushing demonstrated this in 1914. About 125 mL is present at any moment, but roughly 500 mL is made every day and absorbed back into the blood.

A lumbar puncture, or spinal tap, was first introduced in 1891 by which German physician?

The needle goes into the lower back below where the spinal cord ends, to draw cerebrospinal fluid or inject drugs and anaesthetics.

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

It is the lowest part of the brain and continues directly into the spinal cord through the foramen magnum.

Which almond-sized brain structure controls temperature and hunger and links to the pituitary gland?

It secretes releasing hormones that switch pituitary hormones on and off, and it also governs circadian rhythms and sleep.

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

It does not initiate movement but corrects it. Thanks to its tiny granule cells it packs more neurons than the rest of the brain combined into 10% of the volume.

Grey matter looks grey mostly because it contains lots of what?

White matter is the opposite: mostly long myelinated axons, whose fatty insulation gives it the pale colour. In the spinal cord the grey matter forms a butterfly shape in the centre.

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

Dorsal root ganglia sit just outside the spinal cord. The chickenpox virus hides in such ganglia for decades before re-emerging as shingles along a single nerve's skin territory.

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

Medical students remember 'C3, 4, 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?

It runs exposed behind the medial epicondyle of the humerus. The name is thought to be a pun on 'humerus' and 'humorous'.

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

It is the only nerve that passes through the carpal tunnel, squeezed in alongside nine flexor tendons under the flexor retinaculum.

Multiple sclerosis is an autoimmune disease in which the immune system attacks what?

French neurologist Jean-Martin Charcot first described it in 1868. Damaged insulation means signals in the central nervous system slow down or fail.

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

The Latin name means 'black substance'. Levodopa, MAO-B inhibitors and dopamine agonists are the usual first treatments.

Amyotrophic lateral sclerosis is popularly named after which baseball star?

It is the most common motor neuron disease. Charcot linked the symptoms to the underlying nerve damage in 1869 and coined the name in 1874.

Why does the incubation period of rabies vary with where on the body a person is bitten?

A bite on the face reaches the brain far sooner than one on the foot. The old name hydrophobia comes from the throat spasms triggered by trying to swallow liquids.

Which bacterial infection, nicknamed lockjaw, causes muscle spasms violent enough to break bones?

Clostridium tetani produces a toxin that blocks the nerve signals which normally relax muscles. Spasms can continue for three to four weeks.

Bell's palsy, sudden one-sided facial paralysis, results from dysfunction of which cranial nerve?

It is named for the Scottish surgeon Charles Bell and accounts for about 70% of one-sided facial nerve paralysis.

Guillain-Barré syndrome is caused by the immune system attacking which part of the nervous system?

Weakness usually starts in the feet and hands and climbs. Three French doctors described it in 1916.

The name of the disease poliomyelitis literally refers to inflammation of what?

From Greek polios (grey) and myelos (marrow). The virus destroys motor neurons, and in about 1 in 200 to 1,000 cases the result is flaccid paralysis.

Which are the only multicellular animals with no nervous system at all?

Jellyfish and their relatives do have one, though it is about as simple as a nervous system gets, with nothing that could be called a brain.

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

It lets them respond to contact but with no central processing, so a hydra reacts the same way wherever it is touched. Comb jellies share the same arrangement.

Exactly how many neurons does a hermaphrodite of the roundworm C. elegans have?

Its nervous system is the first to be fully mapped as a connectome; males of the species have exactly 383 neurons.

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.

What is the rule that a neuron releases the same neurotransmitters at all its synapses called?

It has only a few known exceptions, and a neuron can still affect targets differently because the effect depends on the receptors activated.

Which two embryologists showed that nervous tissue is 'induced' by signals from an organizer region?

Their early-20th-century experiments posed a puzzle about neural induction that was only solved by genetic approaches in the 1990s.

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.