fitb Flashcards
The nervous system consists of__. It is made up of __.
The nervous system consists of the brain, spinal cord and
peripheral nerves. It is made up of nerve cells, called
neurons, and supporting cells called glial cells.
There are three main kinds of neurons
sensory, motor, interneurons
The receptors sensitive to changes in ___ subserve the sensory
modalities of vision, hearing, touch, smell and taste.
The receptors sensitive to changes in light,
sound, mechanical and chemical stimuli subserve the sensory
modalities of vision, hearing, touch, smell and taste.
The brain and spinal cord are connected to __ through __
The brain and spinal cord are connected to sensory
receptors and muscles through long axons that
make up the peripheral nerves.
These basic structures of the nervous system are the same
in all vertebrates. What distinguishes the human brain is __. This is due to __
These basic structures of the nervous system are the same
in all vertebrates. What distinguishes the human brain is its
large size in relation to body size. This is due to an enormous
increase in the number of interneurons over the course of
evolution, providing humans with an immeasurably wide choice
of reactions to the environment.
The brain consists of __
The brain consists of the brain stem and the cerebral
hemispheres.
The brain stem is divided into __
The brain stem is divided into hind-brain, mid-brain and a
‘between-brain’ called the diencephalon.
The diencephalon is divided into __
The diencephalon is divided into two very different areas
called the thalamus and the hypothalamus
The cerebral hemispheres consist of __
The cerebral hemispheres consist of a core, the basal
ganglia, and an extensive but thin surrounding sheet of
neurons making up the grey matter of the cerebral cortex.
The different parts of a neuron are __. The dendrites __, and the
axons __
The different parts of a neuron are in constant motion, a
process of rearrangement that reflects its own activity and
that of its neighbours. The dendrites change shape,
sprouting new connections and withdrawing others, and the
axons grow new endings as the neuron struggles to talk a bit
more loudly, or a bit more softly, to others.
Inside neurons are __. These
consist of __
Inside neurons are many inner compartments. These
consist of proteins, mostly manufactured in the cell body,
that are transported along the cytoskeleton
Most of the synapses on cells in the __ are located on the __ that
stick out like __.
Most of the synapses on cells in the cerebral cortex are located on the dendritic spines that
stick out like little microphones searching for faint signals.
The axons of neurons __. These travel along __ rather like __. This works because __. When channels open, the Na+ or K+ ions flow down __, in and out of the cell, in response to __ of the membrane.
(3 Na+ out for every 2 K+ in)
The axons of neurons transmit electrical pulses called action potentials. These travel along nerve fibres rather like a wave travelling down a skipping rope. This works because the axonal membrane contains ionchannels, that can open and close to let through electrically charged ions. When channels open, the Na+ or K+ ions flow down opposing chemical and electrical gradients, in and out of the cell, in response to electrical depolarisation of the membrane.
When __ stimuli to the __
exceed a certain intensity, they can cause __
and __
When mechanical, thermal or chemical stimuli to the skin
exceed a certain intensity, they can cause tissue damage
and a special set of receptors called nociceptors are
activated; these give rise both to protective reflexes and to
the sensation of pain
The pathways from the __ to the __ and
from __ to the __ __. Thus movements of the right side of the body are
controlled by the left side of the cortex (and vice versa).
Similarly, the left half of the body sends sensory signals to
the __ such that, for example, sounds in the
left ear mainly reach the right cortex.
The pathways from the sensory receptors to the cortex and
from cortex to the muscles cross over from one side to the
other. Thus movements of the right side of the body are
controlled by the left side of the cortex (and vice versa).
Similarly, the left half of the body sends sensory signals to
the right hemisphere such that, for example, sounds in the
left ear mainly reach the right cortex.
When the dendrite receives __, __. These are usually __, or they may be
__. All these
positive and negative waves of current are accumulated in
the dendrites and they spread down to the __. If they
don’t add up to very much activity, __. However, if the currents
add up to a value that crosses a threshold, __.
When the dendrite receives one of the chemical messengers
that has been fired across the gap separating it from the
sending axon, miniature electrical currents are set up inside
the receiving dendritic spine. These are usually currents
that come into the cell, called excitation, or they may be
currents that move out of the cell, called inhibition. All these
positive and negative waves of current are accumulated in
the dendrites and they spread down to the cell body. If they
don’t add up to very much activity, the currents soon die
down and nothing further happens. However, if the currents
add up to a value that crosses a threshold, the neuron will
send a message on to other neurons.
When an action potential starts at the __, the first
channels to open are __ channels. A pulse of __ ions
flashes into the cell and __ is established
within a __. In a trice, the transmembrane voltage
switches by about __ mV. It flips from an inside membrane
voltage that is negative (about __ mV) to one that is
positive (about __ mV). This switch opens __ channels,
triggering a pulse of __ ions to flow out of the cell,
almost as rapidly as the __ ions that flowed inwards, and
this in turn causes __. The actionpotential
is over within less time than it takes to flick a
domestic light switch on and immediately off again.
When an action potential starts at the cell body, the first
channels to open are Na+ channels. A pulse of sodium ions
flashes into the cell and a new equilibrium is established
within a millisecond. In a trice, the transmembrane voltage
switches by about 100 mV. It flips from an inside membrane
voltage that is negative (about -70 mV) to one that is
positive (about +30 mV). This switch opens K+ channels,
triggering a pulse of potassium ions to flow out of the cell,
almost as rapidly as the Na+ ions that flowed inwards, and
this in turn causes the membrane potential to swing back
again to its original negative value on the inside. The actionpotential
is over within less time than it takes to flick a
domestic light switch on and immediately off again
Remarkably few ions traverse the cell membrane to do this,
and the concentrations of Na+ and K+ ions within the
cytoplasm do not change significantly during an action
potential. However, in the long run, __ by __ whose job is to __. This happens in much the same way that a small leak in
the hull of a sailing boat can be coped with by baling out
water with a bucket, without impairing the overall ability of
the hull to withstand the pressure of the water upon which
the boat floats.
Remarkably few ions traverse the cell membrane to do this,
and the concentrations of Na+ and K+ ions within the
cytoplasm do not change significantly during an action
potential. However, in the long run, these ions are kept in
balance by ion pumps whose job is to bale out excess sodium
ions. This happens in much the same way that a small leak in
the hull of a sailing boat can be coped with by baling out
water with a bucket, without impairing the overall ability of
the hull to withstand the pressure of the water upon which
the boat floats.
Much of this has been known for 50 years based on
wonderful experiments conducted using __. The __ enabled
scientists to __
Much of this has been known for 50 years based on
wonderful experiments conducted using the very large
neurons and their axons that exist in certain
sea-creatures. The large size of these axons enabled
scientists to place tiny electrodes inside to measure the
changing electrical voltages.
An analogy that might help you think about the conduction
of action potentials is the movement of energy along a
firework sparkler after it is lit at one end. The first ignition
triggers very rapid local sparks of activity (equivalent to __), but the overall progression of the sparkling
wave spreads much more slowly.
An analogy that might help you think about the conduction
of action potentials is the movement of energy along a
firework sparkler after it is lit at one end. The first ignition
triggers very rapid local sparks of activity (equivalent to the
ions flowing in and out of the axon at the location of the
action potential), but the overall progression of the sparkling
wave spreads much more slowly.
synaptic vesicles reform when
Synaptic vesicles reform when
their membranes are swallowed back up into the nerve ending
where they become refilled with neurotransmitter, for
subsequent regurgitation in a continuous recycling process.
how are neurotransmitters cleared from the synapse?
1) Glial cells are also lurking all around the synaptic cleft. Some of these have miniature
vacuum cleaners at the ready, called transporters, whose
job is to suck up the transmitter in the cleft. This clears the
chemical messengers out of the way before the next action
potential comes. But nothing is wasted - these glial cells
then process the transmitter and send it back to be stored
in the storage vesicles of the nerve endings for future use.
2) Sometimes the nerve cells pump the transmitter molecules
back directly into their nerve endings.
3) In other cases, the
transmitter is broken down by other chemicals in the
synaptic cleft.
Typically, __
converge on a neuron and, at any one moment, some are
active and some are not. If __, __ and signals are passed down the axon of the receiving neuron.
Typically, a large number of synapses
converge on a neuron and, at any one moment, some are
active and some are not. If the sum of these epsps reaches
the threshold for firing an impulse, a new action potential is
set up and signals are passed down the axon of the receiving
neuron
When a neurotransmitter is
recognised and bound by a metabotropic receptor, __. Binding of the
transmitter to a metabotropic recognition site can
be compared to an ignition key. It doesn’t __, as ionotropic receptors do, but
instead __. The metabolic engine of the neuron then revs up and
gets going.
When a neurotransmitter is
recognised and bound by a metabotropic receptor, bridging
molecules called G-proteins, and other membrane-bound
enzymes are collectively triggered. Binding of the
transmitter to a metabotropic recognition site can
be compared to an ignition key. It doesn’t open a door for ions in the membrane, as ionotropic receptors do, but
instead kick-starts intracellular second messengers into
action, engaging a sequence of biochemical events. The metabolic engine of the neuron then revs up and
gets going.
The effects of neuromodulation include __. These changes are __ and __ than those triggered by the
__ and their effects
__.
The effects of neuromodulation include changes
in ion channels, receptors, transporters and even the expression
of genes. These changes are slower in onset and more
long-lasting than those triggered by the
excitatory and inhibitory transmitters and their effects
extend well beyond the synapse.
Among the many messengers acting on G-protein coupled
receptors are __. Neurons that release these transmitters not only __, but their anatomical organisation is
also remarkable because __. These neuromodulatory transmitters do not __, but __
Among the many messengers acting on G-protein coupled
receptors are acetylcholine, dopamine and noradrenaline. Neurons that release these transmitters not only have a
diverse effect on cells, but their anatomical organisation is
also remarkable because they are relatively few in number but
their axons project widely through the brain. These neuromodulatory transmitters do not send out
precise sensory information, but fine-tune dispersed
neuronal assemblies to optimise their performance.
Drugs differ in their dependence
liability - ranging from high risk in the case of __ to lower risk in the case of __.
Drugs differ in their dependence
liability - ranging from high risk in the case of cocaine, heroin
and nicotine to lower risk in the case of alcohol, cannabis,
ecstasy and amphetamines.
physical effects of cannabis
Cannabis is an intoxicant which can
be pleasurable and relaxing, and it can cause a dream-like
state in which one’s perception of sounds, colours and time
is subtly altered. No-one seems to have died from an overdose,
although some users may experience unpleasant panic
attacks after large doses.
amphetamines and neurotransmitters
These drugs act in the brain by causing the
release of two naturally occurring neurotransmitters. One is
dopamine - which probably explains the strong arousal and
pleasurable effects of amphetamines. The other is serotonin
- which is thought to account for their ability to cause a
sense of well-being and a dream-like state that can include
hallucinations. Dexedrine and Speed promote mainly
dopamine release, Ecstasy more serotonin. The even more
powerful hallucinogen d-LSD also acts on serotonin
mechanisms in the brain.
Arrays of
receptors throughout our bodies are tuned to different
aspects of the somatosensory world – __ - with yet others for the sensations of
pain.
touch, temperature
and body position
Embedded in the dermal layers of the skin, beneath the
surface, are several types of tiny receptors. Named after the
scientists who first identified them in the microscope,
__ sense different aspects of touch. All these
receptors have __ that __ in response to
__, triggering __ that can
be recorded experimentally by __. Some amazing
experiments were conducted some years ago by
scientists who experimented on themselves, by __.
Embedded in the dermal layers of the skin, beneath the
surface, are several types of tiny receptors. Named after the
scientists who first identified them in the microscope,
Pacinian and Meissner corpuscles, Merkel’s disks and Ruffini
endings sense different aspects of touch. All these
receptors have ion channels that open in response to
mechanical deformation, triggering action potentials that can
be recorded experimentally by fine electrodes. Some amazing
experiments were conducted some years ago by
scientists who experimented on themselves, by inserting
electrodes into their own skin to record from single sensory
nerves.
which subsurface dermal receptors respond best to what?
Pacinian and Meissner corpuscles: adapt quickly and so respond best to rapidly changing indentations
(sense of vibration and flutter).
Merkel’s disks: responds well to a sustained indentation of the skin (sense
of pressure)
Ruffini endings: respond to slowly changing
indentations.
Once they detect a stimulus, the receptors in turn \_\_. The \_\_ connecting \_\_ to the \_\_ are \_\_ that convey information from the \_\_ towards the \_\_ extremely rapidly
Once they detect a
stimulus, the receptors in turn send impulses along the sensory
nerves that enter the dorsal roots of the spinal cord.
The axons connecting touch receptors to the spinal cord are
large myelinated fibres that convey information from the
periphery towards the cerebral cortex extremely rapidly
__, __ and __ (stmuli) are detected by __ with
__, which transmit more __. Temperature
receptors also show __
Cold, warmth and pain are detected by thin axons with
“naked” endings, which transmit more slowly. Temperature
receptors also show adaptation
There are relay stations for touch in the \_\_ and the \_\_, before projection on to the \_\_ in the \_\_ called the \_\_ cortex. The nerves cross the midline so that \_\_
There
are relay stations for touch in the medulla and the thalamus,
before projection on to the primary sensory area in
the cortex called the somatosensory cortex. The nerves
cross the midline so that the right side of the body is
represented in the left hemisphere and the left in the right.
Skin is sensitive enough to
measure
a raised dot that is less than 1/100th of a
millimetre high – provided you stroke it as in a blind person
reading Braille.
Functional brain imaging suggests
that the identification of textures or of objects by touch
involves
diff regions of cortex
Molecular biological techniques have now revealed the
structure and characteristics of a number of nociceptors.
They include receptors that respond to (3)
heat above 460 C,
to tissue acidity and - again a surprise - to the active
ingredient of chilli peppers.
Two classes of
peripheral afferent fibres respond to noxious stimuli:
relatively fast myelinated fibres, called Αδ fibres, and very
fine, slow, non-myelinated C fibres.
the pathway for the emotional aspect of pain projects to quite different areas than
the somatosensory cortex, including
the anterior cingulate
cortex and the insular cortex.
which brain imaging technique was used to study pain sensation vs pain ‘unpleasantness’?
PET
during changes in experienced pain intensity there was
activation of the __, whereas the
experience of pain unpleasantness was accompanied by
activation of the __.
during changes in experienced pain intensity there was
activation of the somatosensory cortex, whereas the
experience of pain unpleasantness was accompanied by
activation of the anterior cingulate cortex.
Light enters the eye through the __ and is focused, by the
__ and the __, on to the __ at the back of the eye.
The pupil is surrounded by __
Light enters the eye through the pupil and is focused, by the
cornea and the lens, on to the retina at the back of the eye.
The pupil is surrounded by a pigmented iris that can expand
or copntract, making the pupil larger or smaller as light levels
vary.
If overexposed
to one colour of light,
the pigments in the cones
adapt and then make a lesser contribution to our perception
of colour for a short while thereafter
3 Rs
reduction, refinement, replacement
what happens during seizures?
there is an increase
in the firing of action potentials by neurons followed by a
period of reduced excitability. This cyclical process is
modulated by inhibitory (GABA) and excitatory (glutamate)
neurotransmitters. When the reduction in excitability is
incomplete, seizures may be triggered by the uncontrolled
recruitment of neighbouring neurons. This recruitment may
be localised (causing a partial seizure), or may spread to the
entire cortex (a generalized seizure). `
In people with epilepsy,
attacks may be provoked by
tiredness, missed meals, low
blood sugar, alcohol, or flickering television screens.
Very occasionally - especially if the headache __, or is associated with a __ or with
___ – there can be a serious underlying cause.
Very occasionally - especially if the headache comes
on very quickly, or is associated with a skin rash or with
vomiting – there can be a serious underlying cause.
a migraine is characterized by
migraine is common cause of headache. As well as a sore head (often on one side), people feel sick, find bright lights or loud noises discomforting, and experience a migrainous aura consisting of flashing lights or jagged lines. The aura generally precedes the headache.
how is fuel delivered to neurons and glia?
That fuel is
delivered through the four major blood vessels that supply
the brain. The most important fuels are oxygen, and
carbohydrate in the form of glucose; together these provide
the raw materials to make ATP - the energy currency of cells.
This energy is necessary for driving
the flow of charged ions that underlie the electrical activity
of neurons.
TIA
transient ischaemic attack. the
blood supply to a part of the brain fails and the supply of ATP
is interrupted. Neurons cannot recharge their ionic
gradients and so can no longer conduct action potentials. If the obstruction passes quickly,
neurons can again make ATP, recharge their membranes and
normal function will resume. Fortunately, no permanent
damage occurs in TIA.
Doctors have long recognised and diagnosed brain disease
according to the region affected. For many diseases, the
name is
a description of what appears to be wrong and the
part of the brain involved, often dressed up in Latin or Greek,
such as “parietal apraxia”.
Multiple sclerosis is caused by
inflammation in the nervous
system that flares up and then settles down again.
If the immune system attacks the myelin that wraps
around neurons,
there will be a local area of inflammation
that causes demyelination.
Some early onset forms of Parkinson’s
disease are due to
problems in genes coding for Parkin.
genetics has provided a handle to get us started in understanding Alehzimer's – pointing to mutations in genes that encode (2)
amyloid precursor protein (from which amyloid
is made) and the presenilins (which encode enzymes that
break the precursor protein down).
when chronically activated, stress hormones may actually
damage brain cells, particularly in which regions?
the frontal and temporal
lobes of the brain
It has recently been found that
antidepressant drugs promote
the integrity of brain cells
and increase the rate at which new neurons are produced in
the hippocampus.
what is happening as Alzheimer’s develops?
brain cells die, the cortex things, the ventricles (fluid-filled spaces in the brain) enlarge
core symptoms of shcizophrenia
delusions
(abnormal beliefs – commonly bizarre ideas which are often
persecutory in nature) and hallucinations (disorders of
perception where sufferers experience abnormal sensory
impressions).
what have post-mortem studies revealed about schizophrenia?
the way that neurons have connected up
during development may be abnormal, and that other
neurotransmitter systems, such as glutamate, may be
malfunctioning
last great frontier
Our efforts to understand the nature of mental disorders
represents the last great frontier for medical neuroscience.
phrenologists
thought they could understand the brain by
examining the bumps on the surface of the skull.
Structural brain imaging techniques began to be developed how long ago?
30 yr ago
Our brain contains roughly __ nerve cells, __ of ‘wires’, __ connections, all
packed into a volume of __, but weighing only __ and
consuming a mere __. If we tried to build such a brain
using silicon chips, it would consume about __, i.e.
enough electricity to __
Our brain contains roughly 100 billion nerve cells, 3.2
million kilometers of ‘wires’, a million-billion connections, all
packed into a volume of 1.5 litres, but weighing only 1.5 kg and
consuming a mere 10 watts. If we tried to build such a brain
using silicon chips, it would consume about 10 megawatts, i.e.
enough electricity to power a town.
However, compared to the speed of
digital computers, the speed of nerve impulses is
very
slow - only a few metres per second.
__. In this way,
silicon engineers can begin to emulate the connectivity of
biological networks.
the impulses from many
silicon neurons can be ‘multiplexed’ - a process of carrying
many different messages along the same wire.
how is the suprachiasmatic nucleus unusual?
(controls sleep cycle)
just above optic chasm; the neurons here are unusual in having lots of synapses btwn their dendrites to synchronize their firing together
If people are woken during REM sleep,
they almost
invariably report dreaming.
how many episodes of REM sleep do we have?
In fact, most of us will have about 4 to 6
short episodes of REM sleep each night. Babies have a bit
more REM sleep and even animals show REM sleep. .
how do clock prteins work?
mRNA and protein
synthesis begins early in the day, the proteins accumulate,
link up together and this linkage then stops their own
synthesis. Daylight helps to degrade the proteins whose
level eventually drops to a point where the genes that make
PER and TIM protein get going again.
Our defences work in many ways. The first
is locally within
the tissue that is infected, injured or inflamed, causing
swelling, pain, changes in blood flow and release of local
inflammatory molecules.
The brain receives signals from injured or infected tissues
that may be __ or __ in origin. Neural signals seem to be via
neural or humoral (via circulating molecules) in origin.
C-fibers
vagus nerve from the liver
signals from injured/infected tissues from the brain include
prostaglandins (which are inhibited by aspirin),
and complement proteins (a cascade of proteins important
in killing invader cells); most important signals are cytokines
heat-shock proteins
special
molecules called heat-shock proteins guide damaged
proteins to where they can be repaired or harmlessly
degraded, thus protecting cells from toxicity or dysfunction.
in severe depression __ is
over-produced and recent work suggests that the
__ also shrinks in this condition.
in severe depression cortisol is
over-produced and recent work suggests that the
hippocampus also shrinks in this condition.
Anti-depressant
drugs often help to normalise
the overactive HPA axis. One
idea is that they do so, in part, by adjusting the density of
MR and GR receptors in the brain, particularly in the
hippocampus.
MRI images
are very fine-grained.
How did working-memory evolve?
Studies with young children point to a critical role for workingmemory
in learning language, suggesting that this memory
system may have co-evolved with speech. The precision
required for keeping track of words and their order in a
sentence is critical for accurately working out the correct
meaning.
Downstream of the receptors activated during
imprinting or the tasting of food,
a cascade of secondmessenger
chemicals transmit signals to the nucleus of
brain cells where genes are activated to make special
proteins that can literally fix the memory.
How are space maps and other memory traces formed?
One emerging view is that synaptic plasticity based on
NMDA receptors is involved. Learning about
places is impaired when a drug that blocks NMDA receptors is applied to the hippocampus.
Having said that, really serious forgetfulness might be
alleviated by drugs that
make NMDA or AMPA receptors
work better, or drugs to stimulate the cascade of secondmessenger
signals that studies of learning in young animals
have identified.
When researchers
put experienced taxi drivers in a brain scanner and asked
them to imagine a trip from Marble Arch to Elephant and
Castle, they saw greater activation in the
right
parahippocampal cortex
It may only have been __ ago that
communities in scattered parts of the world realised that
the thousands of spoken words are made up of a smaller
number of separate sounds (__ in English) and
that these can be represented by an even smaller number
of visual symbols.
It may only have been a thousand years ago that
communities in scattered parts of the world realised that
the thousands of spoken words are made up of a smaller
number of separate sounds (44 phonemes in English) and
that these can be represented by an even smaller number
of visual symbols.
reading depends on (2)
- orthography
- hearing the separate sounds in words in their right order``
what exactly do dyslexics have problems with
What the eyes see
has to be integrated with motor signals from the eye
movement system; and it is with this visuomotor integration
that many dyslexics have problems.
motion error signal
impt feature of magnocellular system. it generates
motion signals, during reading, when the eyes move off
letters they are meant to be fixating. This motion error
signal is fed back to the eye-movement system to bring the
eyes back on target.
It is important to stress that dyslexics may be slightly
better than even good readers at
some perceptual
judgements such as colour distinctions and global, rather
than local, shape discriminations
There are various
mechanisms of plasticity, of which the most important is
synaptic plasticity – the science of how neurons alter their
ability to communicate with one another.
Neuroscientists are particularly interested in long-lasting
changes in synaptic strength that can be produced by
brief
periods of neuronal activity, notably in two processes called
long-term potentiation (LTP), which enhances their
strength, and long-term depression (LTD), which
depresses them.
AMPA receptors
are fastest into the act. Once glutamate
is bound to these receptors, they rapidly open their ion
channels to produce a transient excitatory postsynaptic
potential. The glutamate
is only bound to AMPA receptors for a fraction of a second
and, once it leaves and is removed from the synapse, the ion
channels close and the electrical potential reverts to its
resting state. This is what happens when neurons in the
brain send information to each other quickly.
what’s the result of NMDA receptor activation?
it triggers plastic changes in the connectivity of neurons
Changes in the functioning of AMPA receptors are not the
whole story. As memories become more permanent,
structural alterations occur in the brain:
Synapses with
more AMPA receptors inserted following the induction of LTP
change their shape and may grow bigger, or new synapses
may sprout out from the dendrite so that the job of one
synapse can now be done by two. Conversely, synapses that
lose AMPA receptors following the induction of LTD may
wither and die.
how is muscle movement cotrolled?
the axons of motor neurons project out and form specialized contacts w/ individual muscle fibers at the neuromuscular junction. Each action potential in a motor
neuron causes the release of neurotransmitter (ACh) from nerve
endings and generates a corresponding action potential in
the muscle fibres. This causes Ca2+ ions to be released from
intracellular stores inside each muscle fibre. This in turn
triggers contraction of the muscle fibres, producing force
and movement.
Here is a complete map of the body: nerve
cells that cause movements in different limbs (via connections
onto the motor neurons in the spinal cord) are
topographically arranged. By using a recording electrode,
neurons may be found in any part of this map that are active
about __ before activity in the appropriate
muscles
100 milliseconds
where exactly is the problem in Parkinson’s?
The problem is the degeneration of neurons in an
area of the brain called the substantia nigra (so-called
because it is black in appearance) whose long, projecting
axons release the neurotransmitter dopamine into the basal
ganglia .
Amazingly, many of our genes are shared with
fruit fly Drosophila
Neuroscientists studying brain development examine a wide
variety of animals:
zebrafish, frog, chick and mouse
