neurons ch3 Flashcards
overall goal of nervous system is
enable organism, to move its body appropriately to succeed at 4 fours - feeding, fleeing, fighting and reproducing
uses predictions of what is going inside and outside the body to make predictions about and act accordingly
neurons communicate via __ and __ signals
chemical and electrical
neurons have same organelles as other cells, what makes them different
what makes them able to do this
they can transmit electrical signals fast over long distances - when they arrive at destination they trigger a specialized form of chem signaling
because of the proteins on their membranes
summarize the neurons 1st zones of importance
dendrite - branching extensions from cell body that collect info from lots of tiny chem signals they receive along their extent. collect info and pass it on to soma
summarize the neurons 2nd zones of importance
soma or cell body - key feature is Nucleus, control centre, integrates (sums up) signals coming in from the dendrites
summarize the neurons 3rd zones of importance
3 ways it differs from dendrite
axon - nerve fiber, reaches long distances, cable to conduct signals rapidly,
differs: only on axon, can be many branches of dendrites, axons remain constant length and dendrites are tapered, axons are a lot longer
summarize the neurons 4th zones of importance
axon terminals - axons brach into 10k terminals at end. have small swellings at each tip, which contain packages of chemicals that can be released into the space between cells
synapse is the gap between axon terminals and dendrites or somas of others cell, how does this differ in cns vs pns
synapse links to other neurons in Central NS
synapse links to other neurons, muslces, or glands in Peripheral NS
what are en passant synapses
although most synapses occur at axon terminals, they can also exist along axon itself - en passant synapses
4 critical functions of neuron
collect
integrate
conduct
output
what categories do we get when we classify neurons by function
Sensory - directly respond to signals from outside environment (light waves, sound, odour)
Motor - have direct output to muscles or glands - final step for signals to exit nervous system
Interneurons - not beginning or end, inbetween sensation of singal and action at other end. most neurons are this type
what roles do glial clells play in the nervous system
speed up signalling,
regulate concentrations of extracellular (outside cell) chemicals,
determine the extent to which networks of neurons can modify their connections
list 4 types of glial cells
Oligodendrocytes
Schwann Cells
Astrocyte
Microglia
what do Oligodendrocytes Glial cells do
found only where
large cells that wrap around axons (myelination) to speed signals. one oligodendrocytes can wrap axons of 50 diff neurons
only in Central NS
what do Schwann Cells Glial cells do
found only where
wrap around axons (myelination) to speed signals. can only fit around one axon unlike Oligodendrocytes
peripheral NS
what are the gaps between myelin sheaths called
nodes of ranvier
not all axons become myelinated - which do which don’t
subcortical (deep brain structures) and peripheral axons are myelinated
those in the cortex (outer layer of brain) often are not myelinated
neurotransmission
cells communications across small gulfs of space to other targets
neurotransmitters
the chemicals released from one cell to another to send a message by changing chemical concentration at target
space between pre and post synaptic cells is called?
how does its small space help
synaptic cleft
small only 20-50 nanometers
this small distance allowed the [ ] of neurotransmitters to rise and decay rapidly
in presynaptic cell - where are neurotransmitters packaged before release
small spherical packages called Synaptic Vesicles
how is released of presynaptic chemicals done
synaptic vesicles (contain neurotransmitters) fuse with the outer membrane causing molecules to spill out into the cleft
what are the 4 categories of Neurotransmitters?
not a neurotransmitter - but what else can carry signals, how do they enter post cell. why do we say they work in opposite way. they are called ________ transmitters
Acetylcholine - used in frog experiment - stands in category of its own. excitatory - causes muscle contractions
Monoamines - large molecules: dopamine, epinephrine, norepinephrine, serotnin and melatonin
Amino Acids - smaller, building blocks of proteins,
Peptides - short strings of amino acids,
gasses like nitric-oxide and carbon monoxide which diffuse directly into cell membrane. opposite because they are produced in dendrites 1 cell and cross synapse backwards to axons of post cell. so they are called Retrograde Transmitters
most neurosn will release one peptide neurotransmitter in addition to 1 or a few smaller enurotreansmitters - what is the rule of order here?
release smaller neurotransmitters first and only start to release the larger peptide neurotransmitters after they have ben stimulated repeatedly
when chemicals are relased into synapse from pre cell how do they enter post cell
bind to Receptors: specialized proteins in the membrane of post synaptic cell
when reached the post cell there are two receptor types which let in transmitters transmit a signal to another cell: they __ or __
Ionotropic Receptors: located n an ion channel. quick response, cause a direct flow of Ions into or out of the cell
Metabotropic Receptors: not on ion channels, own unit in membrane, when nt binds to it, iniates more indirect changes inside the cell by a cascade of signals eventually leading to ion channel opening, longer process, they stay open longer
how do IonoTropic Receptors work to cause a direct flow of ions into or out of the cell
there are diff [ ] of ions (charged particles) inside and outside a cell, if you were to poke a hole in the membrane, ions would tend to flow out or in. ionotropic receptor is like poking a temporary hole in membrane.
when closed, the protein blocks entrance.
open: protein changes its shape to allow a hole,
many only allow a particular ion to flow through
how do MetaboTropic receptors work? Using the specific G Protein receptor as an example
the g proteins are in the inside of postsynaptic membrane, they relay info from neurotransmitter receptors to other proteins in the cell, these in turn relay, amplify, and transform the signal
signaling cascades integrate several signals from the outside
the ‘Second Messengers’ triggered. by metabotropic receptors serve many diff functions
what second messages can be triggered by metabotropic receptors
modulating activity of neighbouring ion channels
activate or deactivate enzymes in cell
change which genes are expressed
when neurotransmitters bind to receptors, they do not stay there long, they are ‘cleaned up’ by 3 different ways:
which is most common for small neurotransmitters
Degradation - the neurotransmitter is broken apart by other molecules
Diffusion - it moves out of the synapse down chemical [ ] gradient
Reuptake - specialized protein transporters in membrane selectively pull the neurotransmitter back inside the cell either presynaptically, postsynapticaly, or into neighbouring cells
reuptake is most common for small neurotransmitters
what causes the original voltage/potential difference across the membrane
normally - which side is more positive and which is more negative
diff concentrations of ions inside and outside the cell cause the potential difference
normally the outside is more positive, inside is more negative
difference between excitatory post synaptic potential and inhibitory post synaptic potential
EPSP - positive ions enter cell making the difference betwen the inside and otuside smaller
IPSP - negative ions make the inside MORE negative making the difference between the two sides larger than before. can happen by negative ions entering or positive ions leaving cell
what changes do excitatory or inhibitory cause
what makes this change
excitatory - positive
inhibitory - negative
it is not the the neurotransmitter molecule itself that is excitatory or inhibitory - it is the action of receptor that determines the effect
electrical synapses also exist but way less common, what are they also known as
gap junctions
agonists vs antagonists
agonists - can functionally change a target - like ssri’s prevent reuptake of serotonin
antagonists - block receptor from functioning
what is a spike/action potential/nerve impulse
neuron’s membrane suddenly reverses than right after it is restored
all or nothing - always same size
how to epsp’s and ipsp’s add up
2 epsp will make larger voltage charge, 1 epsp and 1 ipsp will cancel themselves out and equal 0, 2 ipsp will make larger negative charge
because soma receives lots of signals at any given moment, the total voltage of cell is not determined by _________, it is determined by ______
because soma receives lots of signals at any given moment, the total voltage of cell is not determined by any one incoming singal, it is determined by overall pattern of all inputs received all over the cell - epsp and ipsp
how are action potentials generated and where
if the number of excitatory psp’s overwhelms the number of inhibitory psp’s the voltage of cell is driven towards more positive values, making it more DePolarized
if it reaches a threshold the action potential is generated at the Axon Hillock - the part of axon that connects to the soma
where is the axon hillock
part of axon that connects to the soma
most excitable part of the neuron
where is most excitable part of neuron - where the action potential is initiated
axon hillock - where axon connects to the soma
what 2 ions play a key role in making an action potential
sodium Na+ and potassium K+
where are sodium ions and potassium ions when a cell is at rest
more Na+ on outside and lower concentration on inside
more K+ on inside and lower concentration on the outside
what does the membrane potential trigger when it rises beyond a certain point
triggers the opening of voltage gated ion channels, Na+ for example comes into cell driven in by Concentration Gradient (goes to where there are less of it) as well as the Electrical Gradient (the inside is negative so it attracts the positive Na+ ions)
what happens after the Na+ comes into cell and depolarizes the cell
the influx of Na+ depolarizes the membrane further, which triggers opening of K+ channels - there are more K+ ions on outside of cell so by the concentration gradient they leave the cell
inside of cells becomes more negative and Repolarizes and shuts the Na+ gates and ends the swing in voltage
how does the action potential travel down the length of the axon from the initial spike
rapid voltage change gives just enough time and spreads far enough down the membrane for neighbouring voltage gated Na+ channels to open up, causing the same cycle of ion exchange to happen nearby
in this wya it moves down the axon - mousetrap effect
what stops the action potential from moving in both ways in mousetrap analogy
because there is a short refractory period after an action potential - during which the Na+ channels are more resistant to opening (take time for mousetrap to reset)
what point in axon can ions most easli flow in and out
nodes of ranvier - gaps in myelination
explain Saltatory Conduction
hard for ions to move across the myelinated sections of axon, so they leap from Node to Node (of ranvier)
thsi increases speed of action potentials, saves energy too
once action potential have reached axon terminals - how are they released - explain system
the sudden voltage change in terminal causes opening of voltage gated calcium channels - causes rapid entry of calcium ions from outside
calcium ions cause the vesicles packed with enurotransmitter to fuse with terminal membrane - causes nuerotransmitter molecules to spill out into synatiptic cleft - move onto next set of dendrites
why does sending of electrical signals so costly to the brain - what part of it
the maintenance of chemical gradients (more sodium on outside and more potassium on side)
reset the traps after, neuron expends energy to push Na+ ions back out and pull K+ ions back in
what is the idea that neurons encode stimuli by the number of action potentials per a unit of time
Rate Coding
why do neurons send a train of spikes and not just one - two reasons the textbook mentions are
the train of spikes for each stimulus is variable in pattern - says the firing is ‘probabilistic’
secondly, neurons fire even without stimulus called ‘noise’ so a single strike is not sufficient
why does it argue that rate coding. may not be the right framework for encoding stimuli that changes quickly
because in the time needed to reach enough signals to breach the threshold, the environment may have already changed - severely limits how fast animal can act to environment
what is temporal structure coding
hypothesis that a stimulus may be represented from the pattern of individual spikes - arranged precisely in time - pattern is important.
what does idea of local coding say
each stimuli in environemnt is represented by a neuron
grandma neuron,
two problems with the local coding hypothesis
brain cells die naturally through life - we would notice this if the hypothesis were true
there aren’t enough neurons for each stimuli we encounter if a lifetime
what does idea of population coding suggest
a coalition of hundreds of neurons work together to encode each stimuli, neurons can help encode lots of different stimuli when placed in different coalitions
2 theories on how coalitions of neurons are activated
neurons become active in a way that excites other neurons because they are connected - temporary coalitions
time domain - these neurons all fire at once to work as a team
4 important actions of a neuron
input integration, conduction and output.
how do we measure the potential difference between a cell and outside it
in a lab we could take a volt meter with two electrodes, stick it in a cell and one in extracellular fluid - measure that difference - use volts as a unit of measure.
-70 mv is usually the resting potential - more negative inside the cell
difference between ion channels or ion pumps
pumps are actively pushing ions from one side to another and channels are not.
As a result, as it is active it needs energy ATP. adenosine triphosphate.
how does the Nernst equation work
shows when equilibrium will happen. you plug in the ion concentration outside the cell and inside the cell and plug in a few other values like charge of time, temp, constants. Calculates diff in electrical potential between inside and outside of the cell at which this system will be in equilibrium.
number you get is a reasonable approximation of the membrane potential of a neuron.
main source of the membrane potential is due to Potassium In neurons
what 4 things classifies smth as a neurotransmitter
made and found in presyn neurons in terminal bouton
released by presyn’s when ap’s occur
postsyn neurons contain receptors specific to it
a mechanism exists to remove it after it is released
another name for ionotropic receptors, why
Ligand Gated Ion Channels
because the nt is the ‘ligand’ binding to channel
