Nerve impulse long note

Question 1

Phase 1 (13)
describe the state of the resting membrane? what is it permeable to?

what occurs when an electric current stimulates the nerve?

what is depolarization and how does this affect the charge within the axon

what follows this process

what follows this process

what helps restore the old conditions and what does this use and what is the process called

what is action potential ( 2 points)

how long does one action potential take

is the voltage change or electrical potential same for all neurons?

what about the recovery time?

Answer 1

 The resting membrane is charged, and is called a polarized membrane
(negative inside compared to outside), and is more permeable to potassium than
sodium
 when an electrical current stimulates the nerve, voltage-gated ion channels
open allowing sodium ions into the cell
 the flood of sodium ions wipes out the voltage difference, called depolarization
 the inside begins to develop a positive charge with respect to the outside
 following depolarization the sodium channels begin to close, called channel
inactivation
 Potassium gated channels open and the movement of potassium ions outwards
helps to reestablish the voltage difference and return to resting potential
 a sodium-potassium pump in the cell membrane helps restore the original
condition of the resting membrane by pumping 3 Na + ions out of the neuron for
every 2 K + ions into the neuron (uses ATP) and is called repolarization
 depolarization and return to resting potential is called an action potential
 action potential is all or nothing, the amount of stimulation required is the
threshold value
 one action potential takes 5 milliseconds
 the electrical potential or voltage change is the same for all neurons
 the recovery time is also the same
 the accumulation of sodium within the cell is reduced by the Na-K pump

Question 2

Phase 2: Transmission

when does the site of stimulation have less charge then the membrane surrounding it?

what does this potential difference create

what is the refractory period and what does this allow

what is always the same in depolarization and what is different?

what do the myelin sheath of the Schwan n cells prevent

where are voltage gated cells concentrated?

the electric current jumps from ________ to _________ causing depolarization

what does this allow?

Answer 2

 during the few milliseconds of depolarization, when sodium ions move in and
before the gates are closed, the site of stimulation has less charge than the
membrane surrounding it
 the potential difference creates a small, localized current which influences nearby voltage-gated sodium channels to open, permitting sodium ions to enter the cell and depolarizing these sites
 during the time required for the voltage-gated sodium channels to recover from
their inactive state another action potential cannot occur, this is called the
refractory period
 this allows for the movement of the nerve impulse away from the stimulus site

 the amplitude of depolarization is always the same, the number or frequency of
firings can change
 the myelin sheath of the Schwann cells prevent the movement of ions across the
neuron membrane
 voltage-gated channels are concentrated in the Nodes of Ranvier
 the electrical current jumps from node to node causing depolarization
 allows the signal to move faster and conserves energy

Question 3

Phase 3: Transfer
7 POINTS

Answer 3

 the action potential passing along the axon eventually reaches the end, often
branched, called the terminus or presynaptic membrane
 could be associated with dendrites of another neuron, a muscle cell or a
secretory gland
 passage across the gap is chemical
 wave of depolarization stimulates the release of neurotransmitters into the
synaptic cleft
 chemicals rapidly pass to the other side where they combine with receptor
molecules in the membrane of the target cell (postsynaptic membrane)
 the binding of the neurotransmitters to the receptor causes chemically-gated ion
channels to open
 over 60 neurotransmitters are used for a variety of messages, also the
chemically gated channels can be different

Question 4

Phase 4: Effect on Target

WHAT IS THE TARGET

WHAT IS THE NEUROTRANSMITTER and what does it generally do

what does the ion flow into the muscle cell do

WHAT HAPPENSE NEXT

what must be destroyed

what enzyme is present in cleft

what does it do

Answer 4

Neuromuscular Junctions  target cell is muscle
 neurotransmitter is acetylcholine
 acetylcholine binds to receptors opening chemically-gated sodium ion channels
 ion flow into the cell depolarizes the postsynaptic muscle cell membrane which
contains voltage-gated sodium ion channels
 a wave of depolarization passes down the muscle cell permitting calcium ions
into the muscle cell which triggers contraction
 necessary to destroy residual(old) neurotransmitter in the synaptic cleft otherwise the postsynaptic membrane would remain depolarized
 enzyme called acetylcholinesterase is present in the cleft
 it inactivates one acetylcholine molecule every 40 microseconds, permitting as
many as 1000 impulses per second to be transmitted across the neuromuscular
junction

Question 5

Neural synapse

what does it target

what can it cause a postsynaptic cell to be

diff neurotransmitters have a specific what?

what type of neurons can they be

Answer 5

Neural Synapses  target cell is another neuron
 postsynaptic cell could be depolarized or hyperpolarized
 different neurotransmitters each have a specific receptor
 these neurons can be excitatory neurons or inhibitory neurons

Question 6

excitatory neurons

 inhibitory neurons

Answer 6

 excitatory neurons are neurons that release neurotransmitters that target receptors connected to Na+ channels to depolarize the postsynaptic membrane to
cause an action potential
 inhibitory neurons are neurons that release neurotransmitters that target receptors connected to K+ channels to hyperpolarize the postsynaptic membrane
to prevent an action potential

Question 7

how does hyperpolarization inhibit action potential ex(inhibitory neurons)

Answer 7

It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.

Question 8

Nerve Summation

Answer 8

 more than one neuron can synapse with the same post-synaptic neuron
 nerve summation involves combining the effects of excitatory and inhibitory neurotransmitters to determine whether the threshold of excitation is reached in the postsynaptic neuron.
 Summation allows for prioritizing of information and coordinating of muscle movements.

Question 9

What are some real-world applications of this?

Answer 9

 Some nerve poisons (e.g., scorpion venom) open Na+ channels and shut
K+ channels & disrupts any action potentials.
 Local anesthetic drugs (Novocain, Xylocaine) block the Na+ channels and
prevent action potentials along sensory neurons.
 General anesthetics used in hospitals (ether, chloroform) open some K+
channels in the brain a bit wider than usual. This counter-acts the effects of
Na+ channels being opened and prevents action potentials from
propagating, too.