Unit 2: Neurophysiology Flashcards
What types of cells make up the nervous system?
neurons
[the functional cell of the NS]
Define “nerve impulse” (describe the different forms of “nerve impulse”).
an electrical signal
- graded potential
- action potential
Describe the basic structural divisions of the neuron.
Describe the myelin sheath
Myelin = insulating layer/sheath that forms around nerves
~allows electrical impulses to transmit quickly and efficiently along the nerve cells.
~If myelin is damaged, these impulses slow down
What does the term “saltatory conduction” mean?
the rapid method by which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier
Going from slow action potential to very fast electrical transmission to slow AP to fast ET to slow AP , back and forth
Jumping back and forth in between these 2 modes = saltatory conduction [characteristic of a myelinated axon]
textbook definition: jump of action of AP from node to node
Describe the distribution of ions across the cell membrane at rest. How does the cell maintain a “resting potential”?
More potassium inside cell; more sodium outside cell
Cell maintains a resting potential with
~leak channel
~sodium potassium pump [leaky potassium pushed in, sodium kept higher outside cell]
Where in the neuron do you find graded/local potentials?
in dendrites & cell bodies
Compare and contrast the absolute refractory period and the relative refractory period.
When do they occur, what is responsible for their occurrence, and what is the effect of their occurrence?
Absolute RP-
-first half- stage 2 (channels open, inactive)
-2nd half- stage 3 (channels closed, inactive)
~so it is impossible to stimulate another AP bc impossible to stimulate the voltage-gated sodium channels.
Relative RP-
~sodium channel is in its active phase (1), so it is possible to produce a voltage stimulus to open the sodium channel; but also, cell is hyperpolarizing and potassium channels are open; as a consequence, any voltage applied has to overcome potassium’s effect
5 steps of synaptic conduction
1) an AP depolarizes the axon terminal
2) this opens voltage-gated calcium channels and calcium enters the cell
3) calcium entry triggers exocytosis of synaptic vesicle contents
4) NT diffuses across the synaptic cleft and binds with receptors on the post synaptic cell
5) NT binding initiates response in the post-synaptic cell
Compare and contrast the post-synaptic events of primary and second messenger systems
1] receptor channel
~direct or indirect channel
~most common in synapse
direct receptor: NT binds to receptive site on ion channel protein [ion channel is receptor and transporter] protein shape change and opens
indirect channel: the molecule that binds to NT is not the same protein as ion channel [G protein-coupled receptor] Alpha sub unit attaches to channel, opening it.
2] 2nd messenger
~commonly uses cAMP as 2nd messenger; cAMP relays message
Compare and contrast receptor and synaptic potentials.
Receptor potentials
~All properties of graded potential, BUT they are always depolarizing
~graded potentials in dendrites
Synaptic potentials
~When AP arrives at the terminal, there is synaptic communication and a graded potential in the dendrite (this is the synaptic potential- still a graded potential).
~Can be depolarizing/excitatory [can stimulate voltage gated channels to open] [EPSP] or hyperpolarizing/inhibitory [cannot stimulu voltage gated channels to open] [IPSP]
Compare and contrast “EPSP’ and “IPSP”.
2 types of synaptic graded potentials
EPSP- excitatory- depolarizing post synaptic potential
~creates a ripple effect through cell; if at initial segment, amplitude is large enough = action potential
IPSP- inhibitory- hyperpolarizing PSP
~decreases potential that other stimuli will trigger an AP
Define “spatial summation”. Provide an example.
when 2 graded potentials occur at 2 different locations, they are added together at the axon hillock
Define “temporal summation”. Provide an example.
a graded potential is produced, and shortly after another is produced, adding on top of the first one
[separated by time]
What is the significance of the initial segment to summation? What is the significance of summation?
Electrical summation takes place at the initial segment
the deciding point about whether AP occurs or not
_________ do the communication, integration, decision making, memory generating process in the NS
Neurons
The neuron can generate:
a nerve impulse
[electrical signal]
One type of nerve impulse is a graded potential; it is restricted to :
dendrites and cell body of the neuron and does not have transmission capability
A type of nerve impulse, _________________, is the typical example; associated with axons down to terminals; a true transmission form of electrical change/excitation of cell
an action potential
Describe the 3 signaling formats within the NS
cell bodies/ dendrites: graded potential
axons: action potential [rapidly travels down axon]
terminal: neurotransmitter- chemical messengers [no physical contact w/ next neuron]
Describe the center of the neuron
center with nucleus
metabolic cell center = cell body/ soma
the _______________ AKA receivers/receiving end are the input point for signals coming from other cells or from the environment
dendrites
All of the information induced in the dendrites when they receive an input is relayed to
the cell body
> sends out the info in a single axon
Action potentials will travel:
very rapidly down the length of the axon to the terminals
Describe the basic functional divisions of the neuron.
The NS has 2 main components:
Central NS: brain, brainstem, spinal cord
Peripheral NS: all the nerves outside of the CN
Interneurons, AKA association neurons:
~enclosed within the CNS
~mostly multi-polar
~make up the majority of neurons in the NS
Interneurons are usually structurally:
multipolar
Efferent neurons are almost always structurally:
multipolar
Afferent neurons are sometimes bipolar, but mostly structurally are
Pseudo unipolar
The neuron is dependent on a support structure which is formed by
neuroglial cells
Neuroglial cells carry out several roles allowing the neuron to be very -
specialized
Neurons cannot be
reproduced/generated more of
Neuroglial cells can form an association with a neuron acting like a
bodyguard around the neuron
The neuroglial cell found in the peripheral NS is the
Schwann cell [loosely wraps, acts as a bodyguard]
Neuroglial cells can wrap the neurons very tightly to:
form a myelin sheath, allowing the nueron to transmit action potentials quickly
Neuroglial cells can form a path for the lengthening of an axon in case of :
axonal damage.
[If axon is damaged, neuron cannot reproduce, but it can re-grow pieces of itself]
________________ can form a myelin sheath around more than 1 axon at the same time, creating a bridge between axons
Oligodendrocytes - in CNS
[CNS]
A neuron has a resting potential of about
-70 Mv
The cell maintains a higher conc. of _____1____ ions inside the cell, and higher conc. of ____2______ outside the cell
1- potassium
2- sodium
this leads to charge difference = resting potential
The 2 categories of ion channels responsible for producing excitation/membrane potential changes are:
1- leak channels [maintains resting membrane potential]
2- gated channels [lead to change, open and close]
3 types of gated channels are-
1- chemically/ligand gated channel
2- mechanically gated
3- voltage gated
Gated channels exhibit 2 types of specificity:
1- specific to what moves through them
2- what specifically acts as the key to open the gate
the myelin sheath __________ the speed that nerve impulses can be conducted
increases
The multiple thin, branched structures on a neuron whose main function is to receive incoming signals are the
dendrites
The resting membrane potential results from:
-activity of the sodium & potassium pump
-uneven distribution of ions across the cell membrane
-greater membrane permeability to K+ compared to Na+
Neurotransmitter is released from _______1_________ into the _____________2__________
1- axon terminals
2-synaptic cleft
The gap of exposed axon in the myelin sheath is the________.
node of Ranvier
Based on structural classifications, which neuron types is the most common?
multipolar neurons
Interneurons are distinguished by the fact that they are found
in the brain and spinal cord only
Peripheral neurons that transmit nerve impulses towards the central nervous system are:
afferent
Which ion(s) is/are higher in concentration inside the cell compared to outside?
potassium
In a neuron at rest, potassium is _______ permeable across the membrane than sodium
more
The sodium-potassium pump is actively using __________ to transport sodium and potassium ions across the membrane
ATP
the __________ is the receptive end of the cell
dendrite
what portion of the neuron forms sensory receptors and the portion on to which another neuron relays a message at the synapse?
dendrite
Graded potentials are properties of specific ion channels -
[chemically/ ligand or mechanical gated channel]
The amplitude of graded/local potentials are
variable [where the graded potential gets its name from]
depends on the # of chemical or mechanical gated channels that open
Are graded potentials localized?
yes
[no propagation]
the stimulus is specific to a single group of channels, so only those channels open.
the graded/local potential has a ____________ range, meaning the effect of the graded localized potential, has a ripple effect detectable at a distance, but the further away it is, the less detectable it is [detecting an electrical potential change].
decremental
definition- gradual decrease
How many chemical or mechanically gated channels open determines what?
the amplitude of the electrical change of the graded potential
[change is localized to the site where channels open]
If the ion that moves through the channel causes the inside of the cell to become less negative, or maybe even positive, that is called a
depolarizing graded potential
[excitation]- ability to generate/trigger action potential
If the ion that moves through the channel caused the inside of the cell to become more negative, it is called
hyperpolarizing graded potential [becoming more polar]
[inhibitory]
~potassium/chloride channels would do this
Graded potentials can add together, which is called
Summation
[2 types, spatial or temporal]
The amplitude of the local/graded potential is proportional to-
the amplitude of the original stimulus that triggered the membrane channels to open
[bigger stimuli = more channels open = more ion movement across membrane = bigger amplitude grade potential— could be depolarizing or hyperpolarizing]
The axon hillock/initial segment is the beginning of the axon and that is where graded potentials add together and serve to initiate the other form of excitation-
the action potential
in dendrites and cell bodies, there are no voltage-gated ion channels, only
chemical and mechanical gated ion channels
In the axon, you find _______ gated ion channels
voltage
Because of the characteristic of voltage gated channels, axons produce:
action potentials
Voltage-gated ion channels open in response to
a voltage stimulus
ex) voltage being generated by graded potential acting on the initial segment
Once you open up a voltage-gated ion channel, it will allow ions to move across the membrane. when the ions move across the membrane, that produces a membrane potential change measured as a-
voltage
~large enough voltage to serve as stimulus triggering another voltage gated channel to open, can keep going, triggering more and repeating down the length of the axon.
end result = every single voltage-gated channel ends up opening each time
The amplitude of action potentials is
constant [all or none]
Action potentials are ______ ___________ , meaning once the process starts, it will keep itself going until the end, from one end of the axon to the other end.
self-propagating
Once the action potential starts, it will not get any weaker with distance, it is ________________
non-decremental
[no reduction/decay in intensity depending on location]
Action potentials are always :
[membrane potential]
depolarizing
~followed by repolarization [moves back to polarized state]
Can action potentials summate?
No
[all or nothing]
Because of _____1____, an action potential will always start with depolarization, followed by repolarization and hyperpolarization interval because of _______2_______.
1- sodium
2- potassium
The frequency of action potentials is proportional to
the original stimulus
Location of action potentials:
axons all the way down to terminals
Location of graded potentials:
cell bodies and dendrites
[stage 1 of AP] At resting membrane potential, the channel is
Closed
(active)- it is able to be stimulated to open by voltage stimulus
[stage 2 of AP] When a voltage is applied, the channel will
open by depolarization [action potential]
inactive- it cannot respond to voltage since it is already open
Stage 3 of action potentials; when sodium reaches the peak of diffusion, the inactivation gate :
swings closed
ion channels are closed [inactive] cannot respond to a voltage.
action potentials only travel in 1 direction, they are
unidirectional
The unidirectionality of action potentials is a consequence of
the 3 phases of the sodium channel
The segment with a myelin sheath is called
an internode
In between the myelin sheath segments is called
nodes of Ranvier
During the refractory period, it is impossible or more difficult to trigger:
another action potential
A graded potential will degrade with
distance
action potentials occur in the :
axon and axon terminal only
_______ ________ are always depolarizing
Action potentials
Are action potentials all or none?
yes
The absolute refractory period prevents:
bidirectional transmission of action potentials
temporal summation of action potentials
Voltage gated sodium (Na+) channels have two gates (an activation and an inactivation gate) and three different states (closed/active, open/inactive, and closed/inactive). Which gate is closed during the “closed/active” state?
activation gate is closed
During which time interval(s) is the neuron non-responsive to additional stimuli and incapable of producing another action potential?
both A and B
[absolute refractory period]
During the relative refractory period, the stimulus required to initiate an action potential:
just must have a higher amplitude
The membrane potential change during interval A is due to _______ and is called _________.
sodium ions diffusing into the cell
depolarization
Action potentials convey information about the amplitude of a stimulus by:
action potential frequency is proportional to the amplitude of the initiating stimulus
2 forms of synapses are
electrical (rare)
chemical (NTs)
The “contact point” between one neuron and the cell its relaying a message to is the
synapse
Very rarely, the synapse is electrical, meaning it is composed of
Gap junctions
The main type of synapse is the
Chemical synapse
Chemical synpase uses what to relay a message between one cell and the next?
chemical signal
[neurotransmitters for neurons]
The bulging end of the neuron is the
axon terminal
Within the axon terminal, you will find
vesicles filled with neurotransmitter molecules
On the arrival of the action potential, some of the vesicles will migrate to the membrane and :
fuse by exocytosis, releasing NTs into the synaptic cleft space
[will diffuse across into receptors of the post synaptic cell]
If the ion movement across the membrane is occurring in response to a chemical binding to this channel, what type of membrane potential change is produced?
graded potential
[chemical gated channel]
The most common way to eliminate neurotransmitters is
~enzymatically break down the NT making it non-functional [enzymatic degradation]
[can also simply diffuse into the synaptic cleft]
The portion of the pre-synaptic neuron where the exocytosis is taking place is called the
pre-synaptic membrane
The portion of the post-synaptic neuron that has the actual receptors for the NT is
postsynaptic membrane
NTs bind to receptors on the post-synaptic membrane, and this causes attached ion channels to open; This may __________________ the receiving cell
excite or inhibit
In the post-synaptic cell, the receptors, ligand-gated channel, and the enzyme can all be-
one single protein that serves all 3 purposes
or can each be a different protein working together
After the action potential is gone, it will need to :
turn off the signal at the synapse
EPSP is a response to a stimulus where the membrane potential shifts upwards towards:
threshold (making it excitatory)
if reaches threshold, AP is triggered
IPSP will result in drop in membrane potential, moving :
further away from threshold
graded potentials can summate to produce
bigger amplitude/voltage changes measured as graded potentials
Spacial summation - 2 neurons are both stimulating post synaptic cell at :
2 different locations at the same time
= action potential
Temporal summation - one graded potential occurs, and the next one :
piggybacks off the first one, hitting threshold and leading to an action potential
spatial summation of IPSP and EPSP produces
a smaller amplitude graded potential bc they cancel each other out
Describe the sequence of membrane permeability changes that occur through the complete course of an action potential beginning with the stimulus that initiates it
1- resting membrane potential
2-depolarizing stimulus
3- membrane depolarizes to threshold; voltage gated K and Na channels start to open
4- rapid Na entry depolarizes cell
5- Na channels close; slower K channels open
6- K moves from cell to extracellular fluid
7- K channels remain open and more K leaves cell > hyperpoarizing cell
8- Voltage gated K channels close, less K leaks out cell
9- cell returns to resting membrane potential
Where are “leak” channels found and what is their significance?
leak channels are found throughout the neuronal membrane
allow potassium and sodium to leak in such a way that maintains resting potential.
~essential for establishing & maintaining resting membrane potential
~role is to allow the passive movement of ions, particularly potassium, to counteract any changes in membrane potential and help keep the neuron in a state of readiness for generating action potentials when needed
Which of the following determines the “content” of the synaptic message – the identity of the neurotransmitter or the receptor? Explain.
Receptor
- having or not having a receptor [if no receptor, no message]
- which transduction pathway is triggered—depends on which kind of channel is connected to the receptor.
Describe how the location of an applied stimulus and its identity are determined by the nervous system
NS determines the location of an applied stimulus by analyzing the activation of specific sensory receptors and their respective locations in the body.
~ ex) touch receptor: each receptor in a unique location, has a discrete pathway that ends in a unique termination point in the brain
location: continuity between receptor and specific region of the brain
which receptors are stimulated?
identity of stimulus : which receptor responds
How is the intensity of a stimulus represented by the nerve impulse within the dendrites and cell body, within the axon, and across the synaptic cleft?
the intensity of a stimulus is represented by
~the strength of graded potentials in the dendrites and cell body
~the frequency of action potentials in the axon,
~quanity of NT the synapse.
Stimulus strength is proportional to the amplitude of the :
graded potential
stimulus amplitude is proportional to the frequency of the :
action potential
Calcium channels in the axon terminal allow calcium ions into the terminal in response to arrival of :
an action potential at the axon terminal
The mechanism of action of neurotransmitters in the synaptic cleft is the same as the mechanism of action of cellular signals described in the cell signaling section of the course.
True or false?
true
When two different neurons (E1 and E2) synapse on a single postsynaptic neuron and simultaneously stimulate the postsynaptic neuron, the result is called:
spatial summation
Neurotransmitters are released from the presynaptic cell by _______ in response to influx of _______ into the axon terminal
exocytosis; calcium ions
Both of the terms “receptor potential” and “postsynaptic potential” name types of:
graded potentials.
When a single neuron (E1) synapses on a postsynaptic neuron and stimulates the postsynaptic neuron multiple times in a row, the result is called:
temporal summation
The final integration of postsynaptic potentials that determines whether an action potential is generated occurs within what region of a neuron?
initial segment
agonist VS antagonist
agonist: molecule that enhances/mimics the effects of NT when it binds to receptor.
In the context of synapses/receptors, an agonist increases the response initiated by the NT
antagonist: molecule that inhibits/ blocks the effects of a NT when it binds to receptor.
In the context of synapses/receptors, an antagonist decreases/prevents the response initiated by the NT
_______________ form myelin sheath in the CNS
oligodendrocytes
____________ form myelin sheath in the PNS
Schwann cells
