function Flashcards
sensory neurons
coupled to receptors specialised to detect and
respond to different attributes of the internal and external
environment.
motor neurons
control the activity of muscles, are
responsible for all forms of behaviour including speech.
interneurons
mediate simple reflexes as well
as being responsible for the highest functions of
the brain
glial cells
make
an important contribution to the development of the
nervous system and to its function in the adult brain.
While much more numerous, they do not transmit
information in the way that neurons do.
axons
one of the two ‘processes’ of the neuron. their job is
to transmit information from the neuron on to others to
which it is connected. axons and dendrites both participate in the specialised contacts called synapses.
dendrites
one of the two ‘processes’ of the neuron. their job is to receive the information being transmitted by
the axons of other neurons. axons and dendrites both participate in the specialised contacts called synapses.
spinal cord
has two
functions: it is the seat of simple reflexes such as the knee
jerk and the rapid withdrawal of a limb from a hot object or a
pinprick, as well as more complex reflexes, and it forms a
highway between the body and the brain for information
travelling in both directions.
hind-brain
contains networks of
neurons that constitute centres for the control of vital
functions such as breathing and blood pressure. Within
these are networks of neurons whose activity controls these
functions
cerebellum
plays an absolutely central role in the
control and timing of movements
mid-brain
contains groups of neurons, each of which seem
to use predominantly a particular type of chemical
messenger, but all of which project up to cerebral
hemispheres. It is thought that these can modulate the
activity of neurons in the higher centres of the brain to mediate such functions as sleep, attention or reward.
thalamus
The thalamus
relays impulses from all sensory systems to the cerebral
cortex, which in turn sends messages back to the thalamus.
This back-and-forward aspect of connectivity in the brain is
intriguing - information doesn’t just travel one way.
hypothalamus
controls functions such as eating and
drinking, and it also regulates the release of hormones
involved in sexual functions.
basal ganglia
play a central role in the initiation and
control of movement.
cerebral cortex
The cortical tissue is divided into a large number of discrete
areas, each distinguishable in terms of its layers and
connections. The functions of many of these areas are
known - such as the visual, auditory, and olfactory areas, the
sensory areas receiving from the skin (called the
somaesthetic areas) and various motor areas. The cerebral cortex is required for voluntary actions,
language, speech and higher functions such as thinking and
remembering.
polarization
Roughly speaking, the dendrite receives, the cell-body
integrates and the axons transmit - a concept called
polarization because the information they process
supposedly goes in only one direction.
dendritic spines (and proteins)
These are where incoming axons make
most of their connections. Proteins transported to the
spines are important for creating and maintaining neuronal
connectivity. These proteins are constantly turning over,
being replaced by new ones when they’ve done their job.
growth factors
The
end-points of the axons also respond to molecules called
growth factors. These factors are taken up inside and then
transported to the cell body where they influence the
expression of neuronal genes and hence the manufacture of
new proteins. These enable the neuron to grow longer
dendrites or make yet other dynamic changes to its shape
or function.
synaptic transmission
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.
Communication between nerve cells at these contact points
is referred to as synaptic transmission.
patch-clamping
Nowadays, a modern electrical
recording technique called patch-clamping is enabling
neuroscientists to study the movement of ions through
individual ion-channels in all sorts of neurons, and so make
very accurate measurements of these currents in brains
much more like our own.
refractory period
The marvellous feature of
nerve fibres is that after a very brief period of silence (the
refractory period) the spent membrane recovers its
explosive capability, readying the axon membrane for the next
action potential.
myelin sheath
New research is telling us about the proteins that make up
this myelin sheath. This blanket prevents the ionic currents
from leaking out in the wrong place but, every so often the
glial cells helpfully leave a little gap. Here the axon
concentrates its Na+ and K+ ion channels. These clusters of
ion channels function as amplifiers that boost and maintain
the action potential as it literally skips along the nerve
all-or-nothing
Action potentials have the distinctive characteristic of being
all-or-nothing: they don’t vary in size, only in how often they
occur. Thus, the only way that the strength or duration of a
stimulus can be encoded in a single cell is by variation of the
frequency of action potentials.
neurotransmitters
The electrical currents responsible for the
propagation of the action potential along axons cannot
bridge the synaptic gap. Transmission across this gap is
accomplished by chemical messengers called
neurotransmitters.
calcium
The arrival of an action potential leads
to the opening of ion-channels that let in calcium (Ca++).
This activates enzymes that act on a range of presynaptic
proteins given exotic names like “snare”, “tagmin” and “brevin”. Neuroscientists have only just discovered
that these presynaptic proteins race around tagging and
trapping others, causing the releasable synaptic vesicles to
fuse with the membrane, burst open, and release the
chemical messenger out of the nerve ending.
ionotropic receptors
The attachment of the
transmitter (the key) to the receptors (the lock) generally
causes the opening of an ion channel; these receptors are called ionotropic receptors. If the ion channel
allows positive ions to enter, the inflow of
positive current leads to excitation. This produces a swing in the membrane potential called an excitatory post-synaptic potential (epsp).
inhibition
The great precision of nervous activity requires
that excitation of some neurons is accompanied by
suppression of activity in other neurons. This is brought
about by inhibition.
inhibitory synapses
At inhibitory synapses, activation of
receptors leads to the opening of ion channels that allow the
inflow of negatively charged ions giving rise to a change in
membrane potential called an inhibitory post-synaptic
potential (ipsp) (see Figure). This opposes membrane
depolarisation and therefore the initiation of an action
potential at the cell body of the receiving neuron.
metabotropic receptors
These receptors
don’t contain ion channels, are not always localised in the
region of the synapse and, most importantly, do not lead to
the initiation of action potentials. We now think of these
receptors as adjusting or modulating the vast array of
chemical processes going on inside neurons, and thus the
action of metabotropic receptors is called neuromodulation.
noradrenaline
is released in response to various forms of
novelty and stress and helps to organise the complex
response of the individual to these challenges
dopamine
makes certain situations rewarding for
the animal, by acting on brain centres associated with
positive emotional features
acetylcholine
acts on both
ionotropic and metabotropic receptors. uses ionic mechanisms to signal across the neuromuscular junction from motor neurons to striated muscle fibres. It can also function as a neuromodulator. It does this, for example, when you want to focus attention on something - fine-tuning neurons in the brain to the task of taking in only relevant information.
alcohol
Alcohol acts on neurotransmitter systems in the brain to
dampen down excitatory messages and promote inhibition of
neural activity
nicotine
Nicotine is the active ingredient in all tobacco products.
Nicotine acts on brain receptors that normally recognise the
neurotransmitter acetylcholine; it tends to activate natural
alerting mechanisms in the brain.
cannabis
acts on an
important natural system in the brain that uses neurotransmitters
that are chemically very like cannabis. This system
has to do with the control of muscles and regulating pain
sensitivity
heroin
Like cannabis, heroin hijacks a system in
the brain that employs naturally occurring neurotransmitters
known as endorphins. These are important in pain
control - and so drugs that copy their actions are very
valuable in medicine.
cocaine
Like the amphetamines, cocaine
makes more dopamine and serotonin available in the brain.
endogenous analgesics
- Under conditions of likely injury, such as soldiers
in battle, pain sensation is suppressed to a surprising degree
– presumably because these substances are released. - a key function of pain is to inhibit activity, the rest that allows healing to occur after tissue damaged. but in some situations, it’s important that activity and escape reactions aren’t inhibited.
acupuncture
This involves fine
needles, inserted into the skin at particular positions in the
body along what are called meridians, which are then rotated
or vibrated by the person treating the patient. for pain relief.
phototransduction
the conversion
of light into electrical signals in the rods and cones
binocularity
the neural representation of the visual world has inputs from each eye and so the cells in
the visual areas at the back of the brain (called area V1, V2
etc.) can fire in response to an image in either eye. This is
called binocularity.
neuroethics
the
intersection of neuroscience, philosophy and ethics.
smart drugs
may help us remember better. Some
might think about designing neurotoxins (nerve agents) that
disrupt this critical process, such as enzyme inhibitors that
are but a step from the agents of biological warfare
reductionist agenda
For some molecular neurobiologists, ultimate truth lies
embedded in the molecular constituents of the nervous
system - with new DNA and proteomic technologies
promising fuller explanations of the brain that will finesse the
problems faced by other neuroscientists. This is the reductionist
agenda, whose full philosophical and
technological flowering is so often celebrated in media
accounts.
interactionist neuroscientists
argue for a more eclectic approach to modern
neuroscience, an approach that explores its interaction with
the social sciences as well.
emergent property
a property which a collection or complex system has, but which the individual members do not have.
ATPase
About two thirds of a neuron’s energy is used to
fuel an enzyme called Sodium/ Potassium ATPase which
recharges the ionic gradients of sodium and potassium after
an action potential has occurred.
spinocerebellar ataxia
Some people inherit a problem with the fine control of
movements that makes them increasingly unsteady on their
feet as the years go by. we now know the precise gene defects that
cause it.
autoimmune diseases
Our immune system is designed to fight infections caused by
bacteria or viruses. Sometimes it gets confused and starts
attacking parts of us instead. We call such conditions
autoimmune diseases and they can affect almost any
tissue.
DTI
a recent development called
diffusion tensor imaging (DTI) permits detailed images of
the white matter tracts of fibres that connect brain regions.
working-memory
holds
information in your mind for a short time in an active
conscious state.
long-term memory
the much larger, more passive storehouse
of information is called
central executive system
controls the flow of information,
supported by two additional memory stores: phonological store (alongside silent rehearsal loop) + visual sketchpad
phonological store
There is a
phonological store alongside a silent rehearsal loop - the bit
of your brain that you use to say things to yourself. Even if
you read words or numbers visually, the information will be
transcribed into a phonological code and stored for a short
while in this two-part system.
visual sketchpad
can hold on to images of objects for long
enough for you to manipulate them in your mind’s eye.
perceptual representation
there are areas in the cortex that extract a
perceptual representation of what we are looking at.
This is used to store and later recognise things around us.
Our ability to identify familiar people in newspaper cartoons,
such as politicians, reflects this system
semantic memory
very closely related to the system that stores perceptual representations. semantic memory - the vast
storehouse of factual knowledge that we have all accumulated
about the world
conditioning
skill learning: basal ganglia and cerebellum
emotional learning: amygdala
imprinting
Neuroscientists now believe that many aspects of the
fine-tuning of neural connections in the developing brain are
also used during early learning. The attachment that
develops between an infant and its mother has been studied
in young chicks in a process called imprinting.
place cells
Place cells are another important discovery. These are
neurons in the hippocampus that fire action-potentials only
when an animal explores a familiar place. Different cells code
for different parts of the environment such that a
population of cells is involved in mapping a whole area. Other
cells in a nearby brain area code for the direction the animal
is moving in. (so it’s map of space + sense of direction)
synaptic strength
The normal electrical response
to neurotransmitter release is a measure of synaptic
strength. This can vary and the change may last for a
few seconds, a few minutes or even for a lifetime.
Glutamate
a common amino acid used throughout our
bodies to build proteins. You may have come across it as the
flavour enhancer called mono-sodium glutamate. It is the
neurotransmitter that functions at the most plastic
synapses of our brains - those that exhibit LTP and LTD.
ionotropic glutamate receptors
use
their ion channels to generate an excitatory post-synaptic
potential (epsp)
metabotropic glutamate
receptors
modulate the size and nature of epsp response.
memory molecules
all glutamate receptor types are important for synaptic plasticity, but it is the
AMPA and NMDA receptors about which we know the most
and that are often thought of as memory molecules.
Ca2+
Ca2+ is a crucial
molecule as it also signals to the neuron when NMDA
receptors have been activated. Once inside the neuron, the Ca2+ binds to proteins located
extremely close to the synapses where the NMDA receptors
were activated. Many of these proteins are physically
connected to the NMDA receptors in what constitutes a
molecular machine. Some are enzymes that are activated by
Ca2+ and this lead to chemical modifications of other
proteins within or close to the synapse.
EMG
The electrical events in the muscles of the arm can be
recorded with an amplifier, even through the skin, and these
electro-myographic recordings (EMGs) can be used to
measure the level of activity in each muscle.
mirror neurons
Striking new findings include the discovery of mirror neurons
in monkeys that respond both when the monkey sees a hand
movement and when the animal performs that same movement.
Mirror neurons are likely to be important in imitating
and understanding actions.
parietal neglect
Damage to the parietal cortex for example, after a stroke, can cause misreaching for objects or even
neglect or denial of parts of the world around us. Patients
with so-called parietal neglect fail to notice objects (often
on their left side) and some even ignore the left side of their
own body
spina bifida
Failure of
the neural tube to close results in spina bifida, a condition
that is usually confined to the lower spinal cord. While
distressing, it is not lifethreatening.
anencephaly
failure of
closure at the head end can result in the complete absence
of an organised brain, a condition known as anencephaly.
