trivia Flashcards
sensory neurons
none
motor neurons
none
interneurons
These are by far the most numerous (in the
human brain)
glial cells
long thought to have a purely
supporting function to the neurons
cerebral cortex
cortical tissue is the most highly
developed area of the brain in humans - four times bigger
than in gorillas
lateralization of the brain
Many of the cortex’s functions are carried out by
both sides of the brain, but some are largely lateralised to
one cerebral hemisphere or the other. Areas concerned with
some of these higher functions, such as speech (which is
lateralised in the left hemisphere in most people), have been
identified.
On the receiving side of the cell, the dendrites have close
contacts with incoming axons of other cells, each of which is
separated by a miniscule gap of __. These junctional spots are
named __, from __ words that mean “__”.
On the receiving side of the cell, the dendrites have close
contacts with incoming axons of other cells, each of which is
separated by a miniscule gap of about 20 billionths of metre. These junctional spots are
named synapses, from classical Greek words that mean “to
clasp together”.
Cajal
Ramon Y Cajal, father of modern neuroscience. photograph shows him in 1890.
Hodjkin
Alan Hodgkin and Andrew Huxley won the Nobel Prize for discovering the mechanism of transmission of the nerve impulse. They used the "giant axon" of the squid in studies at the Plymouth Marine Biology Laboratory
Huxley
Alan Hodgkin and Andrew Huxley won the Nobel Prize for discovering the mechanism of transmission of the nerve impulse. They used the "giant axon" of the squid in studies at the Plymouth Marine Biology Laboratory
action potential speed
in myelinated neurons,
action-potentials can race along at 100 metres per second!
action potential frequency
The most efficient axons can
conduct action potentials at frequencies up to 1000 times
per second.
synaptic cleft
20 nanometer gap that the chemical messenger diffuses across
excitatory and inhibitory neurotransmitters
The main excitatory neurotransmitter in the brain is
glutamate. There are
two inhibitory neurotransmitters – GABA and glycine.
synaptic transmission time
Synaptic transmission is a very rapid process: the time
taken from the arrival of an action potential at a synapse to
the generation of an epsp in the next neuron is very rapid -
1/1000 of a second.
alcohol dependency
about one in ten of regular drinkers will become dependent
alcoholics
alcohol deaths
More than 30,000
people die every year in Britain from alcohol-related diseases.
pregnancy and alcohol
Pregnant mothers who drink run the risk of having
babies with damaged brains and low IQ’s.
smoking deaths
More than
100,000 people die every year in Britain from smoking-related
diseases.
cannabis dependency
About one in ten users may become
dependent
cannabis and mental illness
Although not yet proven,
there is some evidence that heavy use by young people might
trigger the mental illness schizophrenia in
susceptible individuals.
“mid-week blues”
Animal experiments have shown that Ecstasy can
cause a prolonged, perhaps permanent reduction of
serotonin cells. This might account for the “mid-week blues”
suffered by weekend ecstasy users. Every year, dozens of
young people die after taking it
amphetamines and mental illness
Frightening schizophrenialike
psychosis can happen after Dexedrine and Speed.
amphetamines
man-made chemicals that include
“Dexedrine”, “Speed”, and the methamphetamine derivative
called “Ecstasy”. also d-LSD
heroin
a man-made chemical derivative of the plant
product morphine. a very dangerous drug that can kill in even
modest overdose (it suppresses breathing reflexes).
cocaine
plant-derived chemical which can cause
intensely pleasurable sensations as well as acting as a
powerful psychostimulant.
receptive field size
Pacinian corpuscles have
much larger receptive fields than Meissner’s corpuscles
animal experiments on the pain threshold
Animal experiments have revealed that electrical stimulation
of brain areas such as the aqueductal gray matter causes a
marked elevation in the pain threshold and that this is
mediated by a descending pathway from the midbrain to the
spinal cord.
example of endogenous opioid
met-enkaphalin
hyperalgesia
enhanced pain. There is a lowering of the pain threshold, an
increase in the intensity of pain, and sometimes both a
broadening of the area over which pain is felt or even pain in
the absence of noxious stimulation. This can be a major
clinical problem. Hyperalgesia involves sensitisation of the
peripheral receptors as well as complex phenomena at
various levels of the ascending pain pathways.
science behind acupuncture
Forty years ago, a research laboratory was set up in China to
find out how it works. Its findings reveal that electrical
stimulation at one frequency of vibration triggers the
release of endogenous opoiods called endorphins, such as
met-enkephalin, while stimulation at another frequency
activates a system sensitive to dynorphins.
how do photoreceptors work?
respond to the
light that hits them by generating tiny electrical potentials.
These signals pass, via synapes through a network of cells in
the retina, in turn activating retinal ganglion cells whose
axons collect together to form the optic nerve. These enter
the brain where they transmit action potentials to different
visual regions with distinct functions.
photoreceptor light sensitivty comparison
rods are about 1000 times more sensitive to light than the other,
less numerous category called cones.
genetic basis of colorblindness
due to the absence
of certain visual pigments
types of retinal ganglion cells
About 90% of these cells are very small, while another
5% are large M-type or magnocellular cells. We shall see
later that abnormalities in the M-Type cells may underlie
certain cases of dyslexia
where are internal “representations” of visual space around us are
created?
cerebral cortex
number of cortical layers
six
decision making brain region
cerebral cortex
behavior of V5 neurons
(V5 = MT)
It turns out that activity of cells in
V5 accurately reflects the strength of the movement signal.
Neurons here respond selectivity to particular directions of
movement, increasing their activity systematically and
accurately when the proportion of dots moving in their
preferred motion direction increases.
17th C neuro metaphor
In the 17th C,
Descartes used a hydraulic metaphor to explain how the
“humours” of the brain moved the muscles - a metaphor
borrowed from the water engineering he saw in the gardens
of French chateaux.
20th C neuro metaphor
At the turn of the 20th C, reflecting
the industrial age, neurophysiologists described the
intricate wiring of the brain as “an enchanted loom” or later
as a giant “telephone exchange”.
21st C neuro metaphor
Now, at the start of the
21st C, computational metaphors abound, such as the
fanciful speculation that “the cerebral cortex operates not
unlike a private world wide web”.
Parkinson’s and animal research
the use of
L-DOPA to treat Parkinson’s disease emerged from Nobel
Prize winning work on the rat brain.
2 replacement techniques (3 Rs)
tissue culture, computational modelling
seizure and brain waves
During a generalised
seizure, the normal alpha rhythym of the
electroencephalogram (EEG) is replaced by large, slow,
synchronous waves of electrical activity in both
cerebral hemispheres.
normal headache cause
Usually this
is caused by muscle tension and is nothing serious to worry
about.
serious headache cause
In these conditions the pain comes not from the brain itself, but from irritation or stretching of the meninges - the lining of the brain.
migraine cause
sensations coming from
cerebral blood vessels. Brain imaging reveals increased
activity in these regions at the start of a migraine. In
response, there is a brief increase in local blood supply (which
brings on symptoms like flashing lights), immediately followed
by reduced blood flow (reflected in temporary weakness).
migraine meds
A new class of drugs was
discovered which activated a particular subgroup of
serotonin (5-HT) receptors. These drugs – triptans - are very
effective at stopping a migraine headache in its tracks.
sign of stroke
sudden weakness down one side of the body (interruption of fuel to opposite side of the brain)
stroke cause
What has gone wrong has to do with prolonged interruption of the energy supply (blood supply) that the brain needs to function.
molecular basis of stroke
In the
absence of ATP, cells cannot maintain homeostasis and they
may swell up and burst. Neurons may also spontaneously
depolarise, releasing potentially toxic neurotransmitters
such as glutamate. And glial cells, that normally mop up
excess glutamate through an ATP-dependent pump, also
stop working.
new stroke meds
block
neurotransmitters including glutamate that accumulate to
toxic levels during a stroke. These drugs can either block
glutamate receptors themselves or the intracellular
signalling pathways that are turned on by glutamate.
Many such drugs are in development. Sadly, none has yet
had an impact on stroke.
Huntington’s disease naming
named after the doctor who first
described the condition.
du Pre
Jacqueline du Pré – a well
known musician who
suffered from multiple
sclerosis
Guillain Barre syndrome
condition that occurs when the immune system attacks the nerves as they emerge from the
spinal cord.
dementia age
affects approximately 5% of 65 years olds and 25% of those
aged 85 or older.
depression meds
Antidepressant
drugs, which enhance the effects of neuromodulatory
transmitters such as serotonin and noradrenaline can
rapidly (within weeks) treat
the illness.
depression rate
The condition is surprisingly common – 1 in 5 may suffer at some time in their lives from some degree of depressive disorder.
schizophrenia rate
affects 1 in 100
Broca
idneitifed the speech areas of the brain. correlated oddities of mind/behavior w/ measurements of brain structure at postmortem.
PET disadv
There are several disadvantages of
PET, the major one being that it requires the injection of
radioactive tracers. This means that many people cannot
have a PET scan, such as children and women of child-bearing
age, and the number of measures taken during a scan
are limited.
MRI length
30min - 1hr
Beatles
The profits made by E.M.I. from the sale of records by ‘The Beatles’ helped to pay for the development of the first brain
scanners.
energy consumption in the brain
About 50-80% of the total energy consumption of the brain
is consumed in the conduction of action potentials along
nerve fibres and in synaptic transmission. The rest is taken in
manufacturing and maintenance.
Gardner
an American teenager called Randy Gardner
resolved to try and win his place in the Guinness book of
Records by going without sleep for the longest period ever
recorded. His ambition was to last 264 hours without sleep -
and he did it! It was a carefully controlled experiment supervised by doctors in the American Navy.
sleep rhythm research animal
A big leap forward has come from neurogenetics. Various
genes have been identified that, like the cog-wheels and
escapement of a clock, are the molecular components of
rhythmical pacemakers. Much of this work has been done in
Drosophila (fruit flies) where it has been found that two
genes - per and tim - produce proteins that interact
together to regulate their own synthesis.
sleep rhythms and neurotransmitters
research has revealed a brain-stem activating system involving various
neuromodulatory transmitters, including one called adenosine, in a kind of molecular chain reaction that takes
us through the various sleep stages. Synchronisation
mechanisms enable networks to pass from one sleep state
to another.
activation of immune system
triggers cells called leucocytes and
macrophages, and acute phase proteins that travel to the
site of attack, to identify, kill and then remove invading
pathogens. In addition, the acute phase response generates
the symptoms we have all felt (fever, aches and pains,
sleepiness, loss of appetite, disinterest)
where are acute phase proteins produced
liver
when were cytokines discovered, what are they, how many are there
20 yrs ago, they are a group of proteins, 100+
examples of cytokines
They include interferons, interleukins, tumour
necrosis factors and chemokines.
cytokine amounts
These proteins are normally produced in the body at very low
levels, but are switched on quickly in response to disease or
injury. Many are produced
locally within damaged tissues and act on cells nearby, but
some enter the blood stream where they send signals to
distant organs including the brain.
cytokine effects
It is cytokines that cause
most of the responses to disease and infection. stimulate the
immune system and the key components of inflammation
such as swelling, local changes in blood flow, and the release
of a second wave of inflammatory molecules. They act on
almost all physiological systems, including the liver where
they stimulate the acute phase proteins.
cytokine production regulation
triggers: include bacterial or viral
products, damage to cells or threats to cell survival such as
toxins or low levels of oxygen.
Another important regulator
of cytokine production is the brain that, through neural
signals to tissues (mainly via the sympathetic nervous
system) or hormones (such as cortisol from the adrenal
gland), can switch cytokines on or off.
fight or flight response physical effects
initial tingling sensation, sweating, heightened
awareness, rapid pulse rate, higher blood pressure and
general feelings of fear
fight or flight response physical effects: why do they occur
These changes
happen because of receptors that are found on blood
vessels, causing them to constrict and so our blood pressure
to shoot up, and in the heart, causing it to accelerate and
produce the pounding sensation in the chest known as
palpitations. There are also receptors in the skin causing
hairs to erect (goosebumps) and in the gut causing those
disconcerting abdominal sensations that we all sense as
stress. These changes are there to prepare us to fight or to
flee - and to concentrate blood flow to vital organs, the
muscles and the brain.
fight/flight and neurotransmitters
sympathetic nervous system is activated. After receiving a stressful challenge and
computing the right response, the brain rapidly activates
nerves originating from control centres in the brainstem.
These cause the release of noradrenaline in a variety of
structures and of adrenaline from the adrenal glands
(situated just above the kidney).
2 major neuroendocrine responses to stress
- activation of HPA axis
- activation of sympathetic nervous system
brain region and HPA axis (stress)
The hypothalamus is the key brain area regulating many of
our hormones. It has strong inputs from areas of the brain
processing emotional information, including the amygdala,
and from regions of the brainstem controlling sympathetic
nervous responses. It integrates these to produce a
co-ordinated hormonal output (corticotrophin releasing factor, CRF) that stimulates the next part
of the circuit - the pituitary gland. In turn, this releases a
hormone called adrenocorticotrophin (ACTH) into the blood.
ACTH then stimulates a part of the adrenal gland to
secrete cortisol.
cortisol feedback to the brain
The last step of the circuit is cortisol
feedback to the brain. The highest density of cortisol
receptors is in the hippocampus, a key structure for learning
and memory, but cortisol also acts on the amygdala, which
processes fear and anxiety. The net effect is to turn on the
amygdala - to allow learning of fear-related information; and
to turn off the hippocampus - to ensure that resources are
not wasted on more complex but unnecessary aspects of
learning.
cortisol feedback
steroid. raises blood sugar and other metabolic fuels such as fatty
acids. This often occurs at the expense of proteins that are
broken down into fuels required immediately - instant
‘chocolate bars’ for the muscles and brain. Cortisol also
helps adrenaline to raise blood pressure and, in the short
term, makes you feel good. Cortisol also
turns off growth, digestion, inflammation, sex, even woundhealing.
brain region and cortisol
the hippocampus has high levels of the 2 receptors for cortisol, low MR and high GR. The low MR receptor is activated by the normally
circulating levels of cortisol in the bloodstream highway of
the HPA axis. This keeps our general metabolism and brain
processing ticking over nicely. However, as cortisol
levels begin to rise, particularly in the morning, the high GR
receptor becomes progressively more occupied. When we
become stressed, cortisol levels become very high indeed,
activation of this receptor is sustained and the
hippocampus is then shut down by a genetically controlled
program. –> bell-shaped stress curve
cytokine: negative
Recent research has shown that many of the defence
molecules such as cytokines are also active contributors to
brain diseases such as multiple sclerosis, stroke and
Alzheimer’s. It seems that over production of such
molecules within the brain itself can damage neurons -
particularly certain cytokines.
working memory brain regions
frontal and pareital lobes (auditory parts are lateralized to the left)
long term memory brain regions
Long-term memory is also sub-divided into different
systems located in widely dispersed networks of the brain.
The different networks do very different jobs. Broadly
speaking, information enters sensory systems and then
passes down pathways that provide increasingly specialised
processing.
visual memory path
information entering the visual
system passes down a so-called ventral pathway from the
striate cortex to the medial temporal lobe through a
cascade of networks that work out shape, colour, object
dentity, whether the object is familiar or not, until finally,
some kind of memory is formed of this particular object and
when and where it has been seen.
episodic memory brain regions
the perirhinal cortex which mediates the sense of
familiarity about the past and the hippocampus
which encodes events and places.
semantic dementia
type of Alzheimer’s. Early on, patients will be quite capable of telling you
that the pictures they are being shown in an experiment are
of a cat, or a dog, or of a car, or a train. Later on in the
disease, they may hesitate to call a picture of a mouse a
mouse, saying instead that it is a dog. What this confirms is
that factual information is organised categorically, with
animate information stored together in one place well away
from inanimate information.
Baddeley
Alan Baddeley
who developed the idea
of working memory, which consists of
a number of different interacting systems.
dyslexia rate
As many as 1 in 10 of us may have had this
condition
control of reading
Visual control of the eye movement system is dominated by
a network of large neurons known as the magnocellular
system. It gets this name because the neurons (cells) are
very large (magno). It is
specialised to respond particularly well to moving stimuli and
it is therefore important for tracking moving targets.
dyslexics vs normal readers
- impaired visual magnocellular system
- less steady control of the eye
- altered patterns of function activation in brain regions sensitive to visual motion (poor sensitivity to visual motion)
dyslexia types
different forms of the acquired
condition, known as surface and deep dyslexia, which may
require different kinds of treatment.
4 dyslexics mentioned
Leonardo da
Vinci, Hans Christian Andersen, Edison and Einstein
Watkins
Jeffery Watkins a medicinal chemist who transformed the study of excitatory transmission in the brain by developing drugs like AP5 (below) that act on specific glutamate receptors
neuromodulator release and states of mind
- acetyclholine: during heightened attention
- dopamine, noradrenaline, steroid hormones (such as cortisol): novelty, stress, anxiety
NMDA receptor situation 1
If the synapse is
activated quite slowly (glutamate binding to NMDA receptors), the NMDA receptors play little or no
role. This is because as soon as NMDA receptors open their
ion channels these channels become plugged by another ion
present in the synapse – magnesium (Mg2+).
NMDA receptor situation 2
But, when
synapses are activated by several pulses very quickly to a
set of inputs on to a neuron, the NMDA receptors
immediately sense this excitement. This greater synaptic
activity causes a large depolarisation in the postsynaptic
neuron and this dispels the Mg2+ from the NMDA ion
channels by a process of electrical repulsion. NMDA
receptors are then immediately able to partake in the synaptic communication.
how do neurons partake in synaptic communication?
the postsynaptic neurons’ NMDA receptors do this in 2 ways: first, and
just like AMPA receptors, they conduct Na+ and K+ which
adds to the depolarisation; second, they allow calcium (Ca2+)
to enter the neuron. In other words, NMDA receptors sense
strong neuronal activity and send a signal to the neuron in
the form of a surge of Ca2+.
length of Ca2+ surge
This Ca2+ surge is also brief,
lasting for no more than about a second while glutamate is
bound to NMDA receptors.
Blakemore
Colin Blakemore has contributed to understanding how the visual system develops. This includes pioneering studies using cell-culture to study interactions between different parts of a pathway in the embryonic brain.
how many genes in the genome
40,000
zebrafish adv
The zebrafish embryo is transparent -
allowing each cell to be watched under the microscope as it
develops.
mouse adv
The mouse breeds rapidly - its genome has been
mapped and almost completely sequenced.
chick adv
less amenable to genetic studies, but their large embryos
allow microsurgical manipulations - such as examining what
happens when cells are moved to abnormal positions.
frog adv
less amenable to genetic studies, but their large embryos
allow microsurgical manipulations - such as examining what
happens when cells are moved to abnormal positions.
