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.
