c2.2 (neural signalling) Flashcards
for a neuron to send an impulse, the neuron membrane must be “polarized.” what is a polarized membrane?
a membrane that has a positive electrical charge on one side and a negative charge on the other side
how can the amount of polarization of a cell be measured? what is it called?
why is it generally a negative value?
voltage difference between the inside and outside of the cell membrane. known as membrane potential
inside of cells is generally negatively charged, so the membrane potential is expressed as a negative value
when not sending an impulse the neuron is said to be “at rest.” what is the resting membrane potential of a neuron?
-70mV
3 factors contribute to the negative charge of the resting potential:
sodium-potassium pump actively transports three sodium ions (Na+) out of the cell for every two potassium ions (K+) it brings in; it pumps more positive ions out than it brings in, leaving the inside of the cell relatively negative compared to the outside
K+ ions can leak out through the cell membrane, leaving the cell and further increasing the charge imbalance
negatively charged proteins within the neuron also contribute to the charge imbalance
define action potential
the electrical signal that a neuron generates to transmit information along its cell membrane from the dendrite to the synaptic terminal
stages of an action potential x6
resting potential
stimulus
threshold
depolarization
repolarization
refractory
how are action potentials propagated along neurons?
the movement of Na+ that depolarizes one part of the membrane triggers depolarization in the neighboring part of the neuron membrane
factors which adjust speed of the neural impulse as it is propagated along an axon x3
the body size of the animal (larger animals experience longer delays)
the axon diameter size (larger diameter axons have a faster conduction velocity)
whether or not the axon is myelinated (myelination increases the speed of neuron impulses)
why do larger diameter axons have a faster conduction velocity? provide a case study example
a larger axon experiences less resistance to ion flow, facilitating faster propagation of the action potential
the giant axon in a giant squid allows for a very fast escape response
what are nodes of ranvier
gaps between the schwann cells
why does myelination increases the speed of neuron impulses?
the impulse can jump from one node of ranvier to the next, speeding the transmission
as height increases, the conduction
velocity tends to decrease. why does this occur?
change in height of the limb causes gradual tapering of nerve with decrease in diameter and myelination, both of which will decrease neuron conduction velocity
three main types of synapses & definitions
synapse between a sensory cell (such as a photoreceptor in the eye or a hair cell in the ear) and a sensory neuron
synapse between neurons, where a one neuron transmits a signal to another neuron
synapse between a motor neuron and a muscle or gland, where the neuron triggers contraction. this is called a neuromuscular junction
why are muscles and glands are referred to as “effector” cells?
because they carry out the effect/response to a stimulus
types of neurotransmitters & one example each x5
amino acids (i.e. glutamic acid)
amines (i.e. dopamine)
peptides (i.e. endorphins)
esters (i.e. acetylcholine)
gasses (i.e. carbon monoxide)
steps of release of a neurotransmitter from presynaptic cell x5
nerve impulse arrives at the axon terminal of the presynaptic cell
depolarization of the presynaptic cell membrane causes voltage gated calcium (Ca2+) channels in the axon terminal to open
calcium moves into the cell through facilitated diffusion
increase in calcium concentration causes vesicles containing neurotransmitters to move towards the end of the axon terminal
neurotransmitters fuse with the presynaptic cell membrane to release the neurotransmitter into the synaptic gap via exocytosis
often, the neurotransmitter receptor is a what?
ligand-gated channel
binding of the neurotransmitter to the receptor leads to what?
the opening of an ion channel within the postsynaptic cell membrane
depending on which ions move when the receptor is activated, the neurotransmitter can either have an excitatory or inhibitory effect.
what do these mean and how are they generated?
excitatory effect: influx of positive ions (such as Na+) will depolarize the cell, triggering an action potential in the postsynaptic cell membrane
inhibitory effect: influx of negative ions (such as Cl-) will hyperpolarize the cell, preventing an action potential
acetylcholine (Ach) is one of the most common neurotransmitters in both invertebrates and vertebrates. acetylcholine forms in the presynaptic neuron when what occurs?
acetic acid binds with choline
how does acetylcholine create an excitatory effect? x3 steps
what happens after threshold potential is reached?
acetylcholine binds to the acetylcholine receptor in the postsynaptic cell membrane
acetylcholine receptor is a ligand-gated channel so when the neurotransmitter binds, the Na+ channel opens and Na+ moves into the cell through facilitated diffusion
if the threshold potential is reached with the influx of Na+, an action potential will be triggered and propagated as an impulse in the postsynaptic cell
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enzyme (acetylcholinesterase) in the synaptic gap rapidly breaks down the acetylcholine into choline & acetate, where choline is then recycled back to the presynaptic cell and the acetate is excreted as waste
the threshold potential is the minimum membrane potential value at which a neuron will fire an action potential. what value does this typically sit at?
-55 mV
in depolarization, entry of positively charged sodium ions (Na+) causes the inside of the membrane to become positively charged relative to the outside, raising the membrane potential to about what value?
+30 mV
once the membrane potential of depolarization is reached, voltage-gated potassium channels open. the exit of positively charged potassium ions (K+) causes the inside of the membrane to again become more negatively charged relative to the outside, dropping the membrane potential to what?
-70 mV
the refractory period is the brief period of time during which the membrane is incapable of repeating an action potential. why does this occur?
concentration gradients of sodium and potassium must be restored by the Na/K pump
how does the electrical impulse always move in one direction?
the region of the membrane that has just had an action potential will not be able to depolarize again for a brief moment of time (it is hyperpolarized in the refractory period)
define local current
the process by which sodium ions move within the neuron to generate action potentials in neighboring regions of the membrane
what is an oscilloscope?
what does the Y and X axes measure?
an instrument that graphically displays electrical signals as waveforms, creating visualization of the change of voltage over time
y = voltage measurement
x = time
how can membrane potentials in neurons can be measured? what does the oscilloscope display?
placing electrodes connected to an oscilloscope on either side of the membrane.
displays the change in charge between the electrodes during resting and action potentials in a section of neuron cell membrane
look at c2.2 slides 60 and 61
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define saltatory conduction
a process by which nerve impulses travel rapidly down a myelinated axon, jumping from one node of ranvier to the next
depolarization and repolarization only occur at _______. why?
the nodes
it is more energy effective
define exogenous chemicals
substances that enter an organism from an external source, not produced naturally within the body
some exogenous chemicals alter synaptic transmission by stimulating (⬆) or inhibiting (X) components of the synapse. for example, different exogenous chemical might: (list a few)
⬆ cause the synthesis of a neurotransmitter
X prevent the synthesis of a neurotransmitter
X prevent the storage of the neurotransmitter in vesicles
⬆ over stimulate the release of neurotransmitters
X inhibit the release of neurotransmitters
⬆ bind to and stimulate neurotransmitter receptors
X bind to and inhibit neurotransmitter receptors
X block the enzymatic digestion of neurotransmitters
X block the reuptake of neurotransmitters
how do neonicotinoids (insecticide) affect synapses in insects?
why does it lead to paralysis and death in insects?
binding to acetylcholine receptors, inhibiting acetylcholine from binding, thus depolarization does not occur and the postsynaptic cell will not fire an action potential
binding of the neonicotinoid to the receptor is irreversible
how does cocaine affect synapses?
binding to the dopamine reuptake transporter, causing dopamine to accumulate and continue to activate the postsynaptic cell
hyperpolarization occurs when a cell’s membrane potential becomes what?
more negative than its resting potential
how can hyperpolarization occur? x2 ways
channels allow positive ions to flow out of the cell (such as K+ during refractory of an action potential
neurotransmitter binding opens ligand-channels that allow negative ions (such as Cl-) to flow into the cell.
what is inhibitory postsynaptic potential (IPSP)?
how do inhibitory neurotransmitters function?
a response to a neurotransmitter that decreases the likelihood of a neuron firing an action potential
causing the membrane potential to become hyperpolarized, which makes it harder for the neuron to reach the threshold required to generate an action potential
what is gamma-aminobutyric acid (GABA)? what does it do?
what is it thought to be able to do to affect daily life? x3
the most common inhibitory (binds to receptor to let in Cl- ions) neurotransmitter in the brain. lessens the ability of a nerve cell to receive, create or send chemical messages to other nerve cells
reduce stress
relieve anxiety
improve sleep
define postsynaptic potential
a temporary change in the membrane potential of a region of cell membrane due to the binding of a neurotransmitter at a synapse
what are excitatory postsynaptic potentials (EPSP) due to? what effect does it have on threshold potential?
the binding of excitatory neurotransmitters
increase the membrane potential making it easier for the neuron to reach the threshold required to generate an action potential
what are inhibitory postsynaptic potentials (IPSP) due to? what effect does it have on threshold potential?
the binding of inhibitory neurotransmitters
decrease the membrane potential, making it harder for the neuron to reach the threshold required to generate an action potential
what is summation (in relation to synapses)?
where does it occur?
the combined effect of all input to the postsynaptic cell
axon hillock (cone-shaped region at the end of the cell body where the axon originates)
three general classes of pain stimuli
mechanical
thermal
chemical
