2 - Sept.20&23 - Neurons pg. 400-412 & 414-425 Flashcards
What do neurons uses changes in their membrane for?
as communication signals to receive, integrate and send information
how is membrane potential changed
by anything that produces change in ion concentration on two sides of the membrane or by changing membrane permeability to ions
what’s most important for transferring information?
permeability changes
changes in membrane potential creates what types of signals
graded potential and action potential
graded potential
usually incoming signals operating over short distances that are short-lived and can be either depolarizing or hyper polarizing
action potential
long-distance signals of axons, it’s a brief reversal or membrane potential with total change in voltage
depolarizing and hyper polarizing terms describe changes in the membrane that is relative to?
the resting membrane potential
depolarization
a decrease in membrane potential - the inside of membrane becomes less negative (moves closer to 0) than the resting potential
what is another event that includes depolarization?
membrane potential reversed and moves above 0 to become positive
hyper polarization
increase in membrane potential - inside of membrane is more negative than resting membrane potential
what increases the probability of producing nerve impulses?
depolarization
how does graded potential affect current flow?
by creating current flows that decrease in magnitude with distance
why is graded potential called graded
because their magnitude varies directly with stimulus strength
the stronger the stimulus is for graded potential..?
the more voltage changes and the farther the current flows
what triggered graded potential
by some change in the neurons environment that opens gated ion channels
what are other names for graded potentials?
receptor/generator potential and postsynaptic potential
receptor(generator) potential is the graded potential when
when the receptor of a sensory neuron is excited by some form of energy
postsynaptic potential is the graded potential of
when the stimulus is a neurotransmitter released by another neuron - the neurotransmitter is related into a fluid filled gap and influences the neuron beyond the synapse
grade potentials are essential for initiating
action potential
why does graded potential last a short distance?
due to leaky plasma membrane, the current is lost through distance
how does depolarization spread?
opposite charges attract each other and creates local currents that depolarize adjacent membrane areas
what type of cells can generate action potential?
cells with excitable membranes
what cells have excitable membranes?
neurons and muscle
depolarization is followed by —————- and often a short period of —————
depolarization, hyperpolarization
action potential generation and transmission is identical between
neurons and skeletal muscle cells
in a neuron, action potential is also called
nerve impulse
where is AP typically generated in a neuron
in axon
action potential is created by
adequate stimulation that’s usually started by graded potential
where does transition from local graded potential to long-distance action potential take place
axon hillock
where is action potential generated In sensory neurons
peripheral process (axonal)
threshold
when depolarization reaches a certain critical level to where it becomes self-generating through positive feedback
what creates the upward spike of action potential
the rapid depolarization and polarity reversal of Na reaching +30mV in the cell
true or false, can membrane potential depend on membrane permeability and membrane permeability depend on membrane potential?
yes true because both statements establish a positive feedback loop
what is the purpose of repolarization
restoring the internal negativity of the resting neuron
what is happening in permeability of the membrane during repolarization
decline in permeability of Na and increase in permeability of K
repolarization only restores resting ——- conditions, not resting ——- conditions
electrical, ion
action potential is what type of phenomena
all-or-none, happens completely or it desist happen at all
how is action potential propagated
more voltage-gated Na+ channels open as the depolarization spreads
if action potential is similar to the domino effect within the cell, what else is doing the domino effect behind the depolarization wave going down the axon?
repolarization wave
if action potential is similar to the domino effect within the cell, what else is doing the domino effect behind the depolarization wave going down the axon?
repolarization wave
what expression for AP is appropriate
propagation of a nerve impuse
AP is —— ——- at each membrane patch, and every subsequent AP is —— to the one that was generated initially
regenerated anew, identical
once generated all AP are independent on
stimulus strength
how is stimulus intensity coded within the body
by how often it generates in a time frame (frequency)
when a neuron is in response to AP and has Na channels opens, can it respond to any other signal?
no, regardless of strength
what does the absolute refractory period ensure?
that each AP is separate, all or none event and forces one way transmission of AP
what does the absolute refractory period look like on a graph
it is the 1 ms peak of the AP
what happens in relative refractory period
Na channels have reset back to normal, some K channels are open and repolarization is occurring
during what period can a strong stimulus retriever more frequent AP by intruding?
relative refractory period
during the relative refractory period, what happens with the AP threshold?
threshold is higher, although can be reached and generate AP by a strong stimulus
rate of impulse propagation in a neuron depends on what
axon diameter and degree of myelination
axon diameter size for impulse speed
larger the diameter, the faster the impulse speed due to lack of resistance to the flow of local currents which brings adjacent membranes to threshold more quickly
continuous conduction - nonmyelinated axons
channels are immediately adjacent to each other but continuous conduction is slow
the presence of myelin sheath on neurons that are sending impulses, cause what’s?
dramatic increase of AP propagation
how does myelin sheath help as a conductor in propagating AP
the sheath prevents leakage of ions
what happens to the local depolarizing current in myelinated axons during AP
current is maintained and moves rapidly to next myelinated sheath gap where AP is triggered
saltatory conduction
when action potential is only triggered at the gaps
saltatory conduction is ——— than continuous conduction
faster
nerve fibres can be classified by
diameter, degree of myelination and conduction speed
group a fibers
mostly somatic sensory and motor fibres serving the skin, skeletal muscles and joints - they have larges diameter and thickest myeline sheath and conduct impulse speeds up to 150m/s
group b fibers
lightly myelinated fibres of intermediate diameter with conducting speed of 15m/s
group c fibers
smallest diameter with no myelination and incapable of saltatory conduction and conduction speed is 1m/s
Group B and C fibres include locations in
the autonomic nervous system motor fibres serving visceral organs, visceral sensory fibres
synape
junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell
axodendritic synapse
synapses between the axon endings of one neuron and the dendrites of another neuron
axosomatic synapse
synapse between the axon endings of one neuron and cell bodies of another neuron
axoaxonal
synapses between axons
dendrodendritic
synapses beween dendrites
somatodendritic
synapse between cell bodies and dendrites
presynaptic neuron
neuron that conducts impulses toward the synapse
postsynaptic neuron
neuron that conducts the electrical signal way from the synapse
most neurons function as both ——- and ——— neuron
presynaptic and postsynaptic neuron
outside the CNS, the postsynpasitc cell may be either
another neuron or an effector cell (muscle or gland)
electrical synapses are —— common variety
less
electrical synapse
specialized connections between neurons that facilitate direct ionic and small metabolite communication
connexons
protein channels found in electrical synapses
electrical synapse are neurons that are —— coupled, and transmission is ———-
electrically, rapid
through development —— synapses replaces ——- synapses
chemical, electrical
during development, electrical synapses help by
being guiding cues in early neuroscience development so connection between neurons are proper
chemical synapses
specialized to allow the release and reception of chemical neuortransmitters
what is a typical chemical synapses made up of
a knob like axon terminal of the presynaptic neuron and a neurotransmitter receptor region on the postsynaptic neuron membrane
what does the knob like axon terminal on a chemical synapse have?
synaptic vesicles that each contain thousands of neurotransmitter molecules
where is the neurotransmitter receptor region located ?
on dendrite or cell body
how are presynaptic and postsynaptic region separated
synaptic cleft
synaptic cleft
fluid filled space - similar to a lake size division
the synaptic cleft prevents what during transmission
direct transmission
how are impulses transmitted from one to another
via chemical event
what does a chemical event rely on?
the release, diffusion and receptor binding of the neurotransmitter molecules, which results in unidirectional communication
what signal is transmitted through the neuron
electrical
what type of signal is communication made between two neurons
chemical
chemical signalling is then converted to what when reached the postsynaptic neuron
electrical
three ways neurotransmitters are terminated
reuptake, degradation, diffusion
reuptake of neurotransmitters
re absorption by astrocytes or presynaptic terminal, where the neurotransmitter is stored or destroyed by enzymes and norepinephrine
degradation of neurotransmitters
broken down enzymes associated with the post-synaptic membrane or present in the synapse with acetylcholine
diffusion of neurotransmitters
done away from the synapse
synaptic delay
the time interval between inward current through the presynaptic membrane and commencement of inward current through the postsynaptic membrane - meaning that the process of chemical communication will and needs to be slower
chemical synapses are either
excitatory or inhibitory
excitatory synapses
Depolarization that spreads to axon hillock and moves membrane potential toward threshold for generating another action potential
inhibitory synapses
binding of neurotransmitters reduces a postsynaptic neurons ability to generate an AP - membrane potential is moved away from threshold
excitatory postsynaptic potential (EPSP)
a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential at the axon hillock of postsynaptic neuron
EPSP - how is AP generated
if currents reaching hillock are strong enough to depolarize the axon to threshold
how do most inhibitory neurons work
hyper polarize the postsynaptic membrane by making it more permeable to K or Cl
how does inhibitory neurons decrease the chance of AP
by increasing membrane potential and creating a larger and larger need for depolarization to generate AP
Inhibitory postsynaptic potentials (IPSP)
hyper polarizing changes in potentials
a single event of SPSP ——— induce an AP in the postsynaptic neuron
cannot
what are the two types of summation
temporal and spatial
temporal summation
occurs when one or more presynaptic neurons transmit impulses in rapid fire order and bursts of neurotransmitters are related in quick succession
temporal summation causes the postsynaptic membrane
to depolarize much more than it would from a single EPSP
spatial summation
occurs when the postsynaptic neuron is stimulated simultaneously by a large number of terminals from one or many presynaptic neurons
spatial summation causes
dramatic depolarization
what happens to transmitters in spatial summation
huge numbers of receptors bind with neurotransmitters and simultaneously initiate EPSP
how does EPSP get triggered in temporal summation
first impulse causes a small EPSP then before it dissolves the successive impulses trigger more EPSP
EPSP and IPSP both summate
temporally and spatially
what keeps a running account of all the signal a neuron recieves
axon hillock
T/F IPSP and EPSP summate with each other
true
facilitated neurons
partially depolarized and closer to threshold
where do inhibitory synapses occur most often
on the cell body
where do excitatory synapses occur most often
the dendrites
EPSP and IPSP are graded potentials that
decay over distance
the most effect synapses are the ones closest to
axon hillock
synaptic potentiation
is a persistent increase in synaptic efficacy that can be quickly induced through repeated or continuous use of synapse
higher Ca concentrations mean what for the neuron and transmission
triggers more neurotransmitter release and produces larger EPSP
presynaptic inhibition - how it happens
occurs when the release of excitatory neurotransmitter by one neuron is inhibited by another neurons activity via an axoaxonal synapse
presynaptic inhibition definition
decreases the excitatory stimulation of the postsynaptic neuron
difference of post synaptic inhibition IPSP and presynaptic inhibition
IPSP decreases the excitability of postsynaptic neuron VS decrease of excitatory stimulation
neurotransmitters are classified by
chemical and function
classification of neurotransmitters based on chemical structure
acetylcholine, biogenic amines, amino acids, peptides, purines, gases and lipids
biogenic amine neurotransmitter examples
norephiephine, dopamine, serotonin, histamine
catecholamines examples
norephiephine and dopamine
indolamine examples
serotonin and histamine
peptide neurotransmitter example
endorphines
purine neurotransmitter example
ATP
the function of a neurotransmitter is dependent on
the receptor to which it binds to
functions of neurotransmitters
effect - inhibitory or excitatory
actions - direct or indirect
direct neurotransmitters
those that bind to and open ion channels - they provoke rapid responses in postsynaptic cells by altering the membrane potential
indirect neurotransmitters
promote broader, longer-lasting effects by acting through intracellular second-messenger molecules
what is typically used as a second messenger in indirect neurotransmitters
g-protein pathways
indirect neurotransmitters example
hormones
neuromodulator
to describe a chemical messenger released by a neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission
how would a neuromodulator work presynaptically
it may act presynaptically to influence the synthesis, release, degradation or reuptake of neurotransmitter
how would a neuromodulator work postsynaptically
by altering the sensitivity of the postsynaptic membrane to neurotransmitter
the activity mediated by g protein-linked receptors is
indirect, complex and slow and often prolonged
function of neuronal pools
functional groups integrate incoming information received from receptors or other pools and then forward the processed information to other destinations
what is the periphery of the neuronal pool called
facilitated zone
what is the discharge zone in the neuronal pool
postsynaptic neurons that receive more synapses and are more likely to discharge (aka create AP)
circuits
the pattern of synaptic connections in neuronal pools
circuits determine
the pools functional capabilities
4 basic circuit patters
diverging, converging, reverberating and parallel after-discharge
patterns of neural processing
serial and parallel
input processing is both
serial and parallel
serial processing
the input travels along one pathway to a specific destintion
parallel processing
input travels along several different pathways to be integrated in different CNS regions
the brain derives its power from its ability to process
in parallel
reflexes
automatic and rapid responses to stimuli
simple reflex arc steps
receptor, sensory neuron, integration centre, motor neuron and effector (effector is muscle or gland)
diverging circuit
one input, many output - amplifying circuit
converging circuit
many inputs, one output - concentrating circuit
reverberating circuit
signal travels through a chain of neurons with the feeding of the previous neuron - oscillating circuit and controls rhythmic activity
parallel after-discharge circuit
signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell - called after-discharge since output cell receives input at different times
what is parallel processing important for
higher-level mental functioning
how did the nervous system originate
from a dorsal neural tube and the neural crest, formed from surface ectoderm
three step process of differentiation
1 - they proliferate to produce enough cells for nervous system development
2 - the potential neurons (neuroblasts) become amitotic and migrate into their characteristic positions
3 - the neuroblasts sprout axon to connect with their functional targets and doing so become neurons
growth cone
the growing tip of an axon
How do neurons know where to go?
extracellular and cell surface proteins provide anchor points for growth cone
neurotropins
chemical signals that tell the growth cone where to go
netrin tells growth cone
come this way
ephrin tells growth cone
go away
semaphorin tells growth cone
stop here
throughout development, what needs to be present to keep neuroblast alive
neurotropic factors like nerve growth factor
how does neuroblast know what target cell to form a synapse with
special cell adhesion molecules couple then generate intracellular signals to recruit vesicle containing preformed synaptic components
dendrites and astrocytes and cholesterol are active partners in the process of
synapse formation
