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Brain Quiz

  • 1. How much does a normal adult human brain weigh?
    • Answer: Normal range 1100-1700g; av. 1400g
  • 2. Approximately how many neurons are there in the human brain?
    • A. 1 million (10^6)
    • B. 100 million (10^8)
    • C. 1 billion (10^9)
    • D. 100 billion (10^11)
    • E. 1000 billion (10^12)
    • Answer: D. Half that number are granule cells in a single layer of the cerebellum!
  • 3. What are glial cells?
    • Glial cells are misleadingly referred to as the supporting cells of the nervous system, whereas in reality they have a large variety of active and unique functions. They have extremely close interactions with neurons, wrapping over every part of their surface not otherwise involved in synapses, and modulate the activity of large groups of neurons.
    • Glial cells control the extracellular environment of the brain, buffer many of the biochemical processes which occur in neurons, process energy sources for neurons, and are involved in the cleanup and reprocessing of neurotransmitters at every synapse. Microglia can respond to injury by ingesting foreign matter and dead cells. Astrocytes also wrap around the capillaries of the brain to form a major component of the blood-brain barrier.
  • 4. Approximately how many glial cells does the human brain contain?
    • A. 100 million (10^8)
    • B. 1 billion (10^9)
    • C. 10 billion (10^10)
    • D. 100 billion (10^11)
    • E. 1000 billion (10^12)
      • Answer: 1000 billion (10 to every neuron)
  • 5. If you took a cubic millimetre of grey matter from the cerebral cortex (about the size of a poppy seed), approximately how many neurons would it contain?
    • A. 250
    • B. 5000
    • C. 40,000
    • D. 250,000
    • E. 1 million
      • Answer: About 40 000 neurons, or at least their cell bodies

  • 6. In that same cubic millimetre of grey matter, if you took all the axons and dendrites in it, including those passing through, what would be their total length? (I.e. if you joined them end to end)
    • A. 5 mm
    • B. 1 cm
    • C. 10 cm
    • D. 100 m
    • E. 5 km
      • Answer: 5 km. Every cubic millimetre of cerebral cortex has about 5km of dendrites and axons woven into it. The processes are extremely thin – about 0.1 µm for a typical dendrite – and are packed absolutely solid (1 mm3 = one million µm3). Grey matter is mostly dendrites, with cell bodies dotted throughout, and of course hundreds of thousands of glia would also be present in the same cubic millimetre.
      • The scale becomes even more staggering when you consider that the cortex is about 4-6 mm thick, and the hemispheres flattened out would have a combined area of about 2200 cm2 (a square just under 50cm on a side). If you multiply it out we each have over a million kilometres of dendrites just in the cortex alone – i.e. if you joined the dendrites of one adult brain end to end, they would wrap around the earth more than 30 times, or reach to the moon and back. Such figures are not easily comprehended, and give an idea of the degree of complexity of the brain.
  • 7. How does activity pass from one neuron to another?
    • Generally by the release of chemical neurotransmitters into a fluid-filled gap where cells are almost touching, which then causes a response in the postsynaptic cell (chemical synapse). Less common, but also very important, are electrical couplings between neurons via gap junctions, thought to synchronise rhythmic activity across large groups of neurons.
  • 8. (i) How big is the gap between two neurons at a chemical synapse?
    • The gap at a synapse (synaptic cleft) is small – about 20 nm, or 1/50 of a micron (1 nm = 10-6 mm)
    • (ii) How does this compare with the thickness of a cell membrane?
    • Cell membrane 8-10 nm
  • 9. How many separate synaptic inputs can a single neuron receive?
    • A. usually only one
    • B. up to 100
    • C. up to 1000
    • D. up to 50,000
    • E. up to 250,000
      • Answer: E. up to 250,000. Most large neurons in the cerebral cortex have about 60 000 synapses, but Purkinje cells of the cerebellum receive up to 250 000 per cell.
  • 10. How long is the longest neuron in an adult human?
    • Many first-order sensory neurons that innervate the toes and feet have processes that run from the toe, past the cell body in the lumbar part of the spinal cord, all the way up to the brain stem – a distance of about 1.4-1.6 m spanned by a single cell, whose action potentials (impulses) start at one end and reach the other end with great reliability.
  • 11. Estimate the fastest speed at which a neuron can transmit an impulse in the human.
    • A. 0.1 ms-1
    • B. 1 ms-1
    • C. 25 ms-1
    • D. 80 ms-1
    • E. 250 ms-1
      • Answer: D. 80ms-1 (approximately 300 km.h-1)
  • 12. Pain fibres conduct relatively slowly (around 1 ms-1 or slower). How long would it take a 4m tall giraffe to notice that it has stepped on a thorn?
    • Assuming 1 ms-1 conduction speed and a 4m tall giraffe, it might take 4 seconds for the “sharp” pain information to arrive, and a few tens of ms after that for it to be processed. Burning or “slow” pain could take up to 40 s to be received by the brain – some fibres conduct at 0.1 ms-1.

  • 13. Roughly how many neurons do you think it would take to transmit sensory information from the toe to the brain?
    • Some senses, such as touch and joint sensation are transmitted by a single neuron from the receptor (in the skin), right up to the dorsal column nuclei in the brain stem. Other sensations, such as pain and temperature, take at least two neurons to reach the brainstem. It usually takes a chain of 3-4 neurons to transmit sensory information from the skin to the cerebral cortex.
  • 14. If you enlarged the axon of a motor neuron running from the brain down the spinal cord so that it was as thick as a garden hose (1 cm), how long would it be?
    • A. 1 mm
    • B. 1 cm
    • C. 10 m
    • D. 1 km
    • E. 10 km
      • Answer: D. 1 km. The axon is about 10µm thick, so enlarging it to the thickness of a 1 cm garden hose is scaling it up by 1,000. Its typical 1 m length would scale up to 1 km. The cell body would be about the size of a softball. It’s worth emphasising that the action potentials travel along the axon with essentially perfect reliability, despite its immense length.
  • 15. Is the male or female brain proportionally larger (in relation to body weight)?
    • Even when you correct for body weight the male brain is larger than the female brain, on average. There is little difference in overall anatomical organisation – it took hundreds of years of study before reliable anatomical differences were found between the brains of men and women, and nobody knows what they really mean. Some are related to parenting and reproduction-related parts of the hypothalamus.
  • 16. Does the male or female brain make more synaptic connections?
    • Per unit volume, the female brain has more synapses. If you consider connections to be the unit of brain capability, this means that women use their brains more efficiently.
    • Females typically use more of their brains for a given task, meaning that multiple abilities may be tapped simultaneously.
  • 17. At what stage in our lives do we have the maximum number of neurons? What happens to them?
    • Just before birth is when the number of neurons is at its peak. During development many die off, as we maximise the efficiency of connections and the organisation of the brain. Some neurons continue to be generated in specialised parts of the brain throughout our lifetime – most of them are to replenish the turnover in the hippocampus, a structure related to memory formation and awareness of surroundings, and the olfactory bulb, where many die due to exposure to the outside environment. Whether they reach the other parts of the brain, and what they might do there, are highly contentious issues.
  • 18. What makes the brain grow in size during childhood?
    • Mostly the growth of dendrites, with some growth of axons and a lot of myelination by proliferating glial cells to increase conduction speed. Dendrites form the bulk of grey matter expansion because each neuron has dozens or hundreds of them, but only one axon plus its branches.
  • 19. Does brain weight correlate with intelligence?
    • No. There is also no well-accepted definition of intelligence itself, so the question is not really answerable. As far as the most common measures of intelligence are concerned, there is little to no correlation between brain size and test results.
  • 20. Compared to other mammals, what is unique about the human brain?
    • In particular, speech and language areas. Other parts of the brain are remarkably similar to other animals. At the cellular level it would be difficult to distinguish sections of human brain tissue from that of mice, rats or cats, which is why they are commonly employed as experimental animals in neuroscience. Primate cortex is extremely similar, and the overall anatomy of the brain of a chimpanzee is very close to that of a human. They are relatively smaller with respect to body size, but that’s not always an indicator, since small birds have a higher brain-to-body-weight ratio than we do.

UNSW TV video of neurological examination (Leon)

  • Leon exam
  • 1996, suddenly can’t walk, right leg can’t move, 24 hours, right arm
    • speech, eyes fine, face fine
    • BP problems (high)
      • Cholesterol high
      • Diabetes
      • Non-smoker
      • No arrhythmia
  • Gait
    • Right arm flexed
    • Highstepping; right foot drop
    • Right foot has a fast drop
    • Right side has wasting and stiffening; spasticity of right leg too
  • 68 years old
  • Minimental
    • Age/month
    • Eye exam, fingers (see CCS guide)
  • Hands, right arm, incoordination and drift
    • Normal tone in the left, right has a spastic catch
    • Incoordination in right arm
    • Right wrist has increased tone
    • Power
      • Weak in the right shoulder
    • Reflexes
      • More brisk in the right
  • Legs
    • Nonsustained clonus in left leg, which is normal; no clonus in right leg
    • Tone increased on the right
    • Strength, decreased on the right
    • Reflexes more brisk on the right
    • Sensation fine (no sensory neglect)
    • Plantar up on right (extensor plantar reflex = Babinski reflex)
    • Weakness of dorsiflexion of the right foot
    • Incoordination of shin on knee testing on the right side
  • Diagnosis:
    • Hemiplegic gait, upper motor neuron problem on the right (no sensory or cortical problems, just motor)
      • R hemiparesis, vascular event: stroke in the left hemisphere
      • Subcortical area
      • CT scan confirms: region of low attenuation; no sensory or cortical signs

Neurological testing

  • Reference: http://www.neuroexam.com/
  • During this task students will get the opportunity to try out a number of simple neurological tests that are used in a standard neurological examination.

Test 1

Ask the subject their name and where they are now, the day of the week, date, month and year. Result of test:

  • What is this test telling the examiner?
    • Whether or not the subject is alert, attentive, cooperative and oriented in time, place and person.
    • Checking for delirium (acute) or dementia (chronic)

Test 2

  • Tell the subject “I’m going to give you three words to remember. I’ll ask you for them later so please try to remember them. The words are rose, umbrella and fear”. You may use other words but make sure they are not related (such as big, deep, lake) since they can be stored as a single item. Then distract the subject for at least two minutes by asking them to count backwards from100 by 7’s (e.g. 100, 93, 86 etc) or, get them to do a few simple mathematical calculations (e.g. add 53 and 12, or subtract 9 from 25). Immediately after this ask the patient “What did I ask you to remember earlier?” Do not use hints or multiple choice.
  • Result of test:
  • What is this test telling the examiner?
    • This test is telling the examiner whether or not memory for recent events is normal and if the structures involved in the formation of new memories are intact. A normal subject should be able to repeat at least two of the words they were given earlier. The counting distraction also tests ability to do simple calculations.
    • Where in the brain do you think memories for facts and figures are formed and stored?
    • In the cerebral cortex. More specifically there is a region of the brain known as the hippocampus, located inside the temporal lobe, which is vital for the formation of new memories. The hippocampus is the most sensitive part of the brain to oxygen deprivation (hypoxia). Patients who have suffered prolonged periods of hypoxia often present with normal ability to recall long-term memories but can’t form new ones, i.e. recent memory is impaired. This will be revisited later in this course.

Test 3

  • Ask the subject to close their eyes and say ‘yes’ when you touch them. Touch the subject lightly on each side of the face and on each arm (not necessarily in that order). [In a full neurological test you would also test each lower limb and each side of the trunk.]

Test 4

  • With their eyes still closed touch them on the skin with a metal object (such as a key or pen) and ask whether it feels, warm, normal or cool. Like the previous test, this one would normally be done on a number of different regions of the body.
  • What do these last two tests tell the examiner?
  • Whether or not skin sensation for light touch and temperature is normal.
  • Try to guess the nervous system structures that are being tested here:
  • Structures involved in transmitting somatosensory information from the skin to the brain, i.e. peripheral sensory neurons and central ascending pathways.
  • Light touch = dorsal column; deep touch is closer to pain, so it runs through a different pathway.
    • Therefore need to do higher
    • Sensory neurons are a single neuron from target to thalamus

Test 5

  • (i) Get the subject to position their hand with the palm facing up, and close their eyes. Draw a number on the palm of their hand with your finger and ask them what the number was.
  • (ii) Get the subject to close their eyes. Place an object in their hand and ask them to identify it.
    • Result of tests:
  • What does this test tell the examiner?
    • This test tells the examiner whether or not the subject is able to recognise letters, numbers or shapes based on sensory stimuli. In order to do this, the incoming sensory information must be integrated with previously learned information (recognition), a process which occurs in the cerebral cortex. It is thus a test of higher level sensory processing.

Test 6

  • Ask the subject to try to relax one forearm. Now, you move their limb for them (while they keep their arm as relaxed as possible) - flex and extend their elbow, wrist and fingers and observe/feel whether or not there is any resistance to the movement.
  • What does this test tell the examiner?
  • Whether or not the resting level of muscle activity (known as muscle tone) is normal. If muscle tone is normal you should only be able to feel slight resistance to the passive movement. Increased resistance (hypertonia) occurs when messages from the brain can’t reach the spinal cord motor neurons. Decreased resistance, (limb/muscles are floppy - hypotonia), may indicate damage to the motor neuron carrying messages to the muscle or to its connection with the with altered muscle tone and if so, when and why they think it happens.

Test 7

  • Get the subject to sit on the table with their legs hanging down. Using the tendon hammer, gently tap the quadriceps tendon, just below the kneecap, and observe the response. If there is no response, try distracting the subject with another motor task for the upper limbs e.g. get them to interlock their fingers and push them together. This way they won’t be concentrating on what is happening in their leg and you should see a response to the tendon tap. You could also try this test on another muscle if you are having difficulty getting a response – get the subject to kneel on a chair with their feet hanging down. Using the tendon hammer try tapping the Achilles tendon on one side and watch the foot to see if there is a response.
  • Describe the response:
    • The quadriceps muscle contracts causing the knee to extend (straighten) – known as the knee jerk. At the ankle, the foot should be seen to plantar flex, i.e. bend toward the back of the leg).
  • This response is a type of reflex. In general terms, what is a reflex?
    • A reflex is an automated (standardised) response to a particular stimulus. The reflex being tested here is the simplest of all reflexes and involves only two neurons – a sensory neuron (transmitting the stimulus to the spinal cord) and a motor neuron which transmits a message to the muscle, telling it to contract in response to the stimulus.
  • What nervous system structures do you think this reflex tests?
    • This reflex tests the integrity of both peripheral sensory and motor neurons, since both must be intact to bring about the reflex. Peripheral motor neurons are known as lower motor neurons. The way in which a motor neuron responds to the stimulus is influenced by descending messages from the brain to the motor neurons. Neurons carrying these descending messages are known as upper motor neurons. If these descending messages are interrupted but the peripheral nerves are intact the reflex becomes exaggerated.

Test 8

  • Ask the subject to hold one arm out so it is at the same level as the shoulder. Now get them to try to push the arm up further while you push down on it. Are they able to resist (oppose) your downward push, i.e. how much power do they show in this movement? Repeat the test on the other side. Repeat this test for elbow flexion - get the subject to flex (bend) their elbow to a right angle. Place your hand on front of their forearm and ask them to try to flex it further while you pull against it. Once again, feel for resistance. *Repeat on the other side.
  • What is this testing?
    • Muscle strength
  • Why would you perform the tests first on one side and then on the other?
    • It enables the examiner to compare muscle strength on the two sides. This is particularly important if the patient has a lesion affecting one side of the body, in which case the strength of muscles on the affected side can be compared with that on the normal side. Similarly muscle tone and reflexes should also be compared on both sides. Start on normal and then do abnormal.
  • This is a reflex arc - only a lower motor neuron pathology will show up.
    • Upper motor neuron lesion = hyperreflexive
    • Lower motor neuron lesion = hyporeflexive
    • If you know someone has a lower motor lesion, then check the reflexes from above down, then you'll find that at some point there will be hyporeflexiveness

Test 9

  • Get the subject to stand with their feet together. Observe if they sway sideways at all. Then ask them to close their eyes and look for sideways movement. Ask them to lift one leg and make the same observation.
  • What does this test tell the examiner?
    • Whether or not the structures involved in the control of balance are intact and normal. If any of these structures are damaged the patient will be seen to sway to one side, either when their eyes are open (typically due to cerebellar or vestibular problems) or only when their eyes are closed (typically due to problems with proprioception, i.e. detection of the position of the limbs in space).
  • How are we able to detect body position?
    • Receptors in the ear (vestibular receptors) detect head position and movement and receptors in the muscles and joints (proprioceptors) provide feedback on limb position.
  • Why is it important for the subject to close their eyes during this test?
    • The eyes need to be closed because visual cues significantly influence both body position and balance and it’s important to make sure that the vestibular system and proprioception are examined in isolation.
  • What part of the brain controls balance?
    • Cerebellum


  • This Rhomberg's sign. Bad balance: ataxic. See wikipedia:Rhomberg's test
  • Coordination: clapping game, alternating hand on other hand

Test 10

  • With eyes open get the subject to first touch your finger, then touch their own nose. Repeat this sequence, moving your finger between touches. Observe if movements are smooth and accurate
  • What does this test tell the examiner?
    • Whether or not movements (the timing and force of muscle contractions) are properly coordinated
  • What major brain region is being tested here?
    • Cerebellum
  • 11. Position yourself about a metre in front of the subject, either both of you sitting or both standing. Hold your hands about 60 cm apart, exactly half way between you and the subject. Ask the subject to look into your eyes and to maintain their gaze. Examine each eye separately. Get the subject to cover one eye with their hand and to fixate the other eye on your eyes. Be sure they maintain this fixation and try not to let their eyes wander. Start with your finger outside of their field of vision and gradually move your hand inwards. Ask the subject to tell you when they first see it. Start by bringing your finger in from one side, then the other, the from above and below. Now repeat the test on the other eye.
  • What does this test tell the examiner?
    • Whether or not the range of vision (visual field) is normal in each eye.
  • Other tests of cranial nerve 2: optic nerve
    • Direct and indirect light reflex
    • Accommodation
  • 12. Now hold up your index finger in front of the subject and ask them to follow it with their eyes as you move it up, down, to the right and to the left and observe their eye movements. Are they smooth? Are the movements of the two eyes well-coordinated?
  • What is this test telling the examiner?
    • Whether or not the eye muscles and the nerves that supply them are functioning normally.

Other notes

  • Upper motor neuron: hyperreflexia and increased tone (inhibitory signals stopped)
  • Lower motor neuron: flaccid paralysis
  • When you know something from history, you know which side is normal (compare normal to abnormal)
  • Be clear on the commands you give

Mini mental test

Leon exam

  • 1996, suddenly can’t walk, right leg can’t move, 24 hours, right arm
    • speech, eyes fine o BP problems
      • Cholesterol high
      • Diabetes
      • Non-smoker
  • Gait
    • Highstepping
    • Right foot has a fast drop
    • Right side has wasting and stiffening
  • Minimental
    • Age/month
    • Eye exam, fingers
  • Hands, right arm, incoordination and drift
    • Normal tone in the left, right has a spastic catch o Wrist has increased tone
    • Power
      • Weak in the right o Reflexes
      • More brisk in the right
  • Legs
    • Tone increased on the right
    • Strength, decreased on the right o Reflexes more brisk on the right o Sensation fine
    • Plantar up on right
  • Diagnosis:
    • Hemiplegic gait, upper motor neuron problem on the right
    • R hemiparesis, vascular event: stroke in the left hemisphere
    • Subcortical area
    • CT scan confirms