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22 Cards in this Set

  • Front
  • Back
SEQUENCE of ELECTROCHEMICAL changes propagated ALONG the plasma membrane of a neuron or the sarcolemma of a muscle fiber.
NERVE IMPULSE
Occurs when a part of the membrane is NOT CONDUCTING a nerve impulse. The transmembrane potential is -70MV during this time

Characteristics:

1. OUTSIDE of the membrane has a POSITIVE electric charge and the INSIDE has a NEGATIVE electric charge.

2. Na+ concentration is GREATER on the OUTSIDE of the membrane and K+ concentration is GREATER on the INSIDE of the membrane. This maintained by the Na+ - K+ pump.

3. The membrane is SLIGHTLY PERMEABLE to Na+ 's and much more permeable to K+ 's.
RESTING POTENTIAL
When a part of the membrane is STIMULATED (usually by a neurotransmitter substance), the membrane at the stimulated area becomes more permeable to Na+ 's.

This results in a net MOVEMENT of Na+ 's across the membrane from the outside to the inside.

As the Na+ 's move in, the inside of the membrane becomes less negative and is described as being DEPOLARIZED.

However if the depolarization is SLIGHT { that is if only a few Na+ 's move in } a transient local depolarization called a graded potential will occur at the stimulated area and the stimulated area will return to the resting potential WITHOUT a nerve impulse being generated.
DEPOLARIZATION
If the STIMULUS to the stimulated area is of sufficient intensity the depolarization at the stimulated area REACHES a CRITICAL LEVEL called threshold. { transmembrane potential changes from -70mv to between -60mv to -55mv }

Once threshold is reached voltage regulated Na+ CHANELS open.

Very quickly enough Na+ 's move these channels to cause a reversal of the charge at the stimulated area; that is it becomes POSITIVE on the INSIDE and NEGATIVE on the OUTSIDE..

The transmembrane potential changes to +30 mv.
CLOSE. Thus at this point Na+ 's no longer going in but K+ 's are going out.

This results in restoring the resting potential ; that is the INSIDE becomes NEGATIVE
and OUTSIDE becomes POSITIVE. The transmembrane potential again becomes
-70mv, and the membrane is said to be REPOLARIZED.
This rapid sequence of events involving depolarization to threshold ,then reversal of charge, and then repolarization is called an action potential.It takes about 1 msec.
ACTION POTENTIAL
The reversal of charge at the stimulated area during an action potential results in a
local current flowing to the membrane adjacent to the stimulated area.

This local current opens voltage regulated Na+ channels causing an action potential to develop on that part of the membrane.
The action potential continues to propagate itself in this manner along the membrane.
The action potential propagating itself along the membrane results in a current flowing along the membrane called a nerve impulse.

Hint: PAP
PROPAGATION OF THE ACTION POTENTIAL
The TIME when part of the membrane will respond to a stimulus by generating a nerve impulse {action potential}. This is from the time an action potential begins until the resting potential is RESTORED. This is about 1 msec.
The refractory period
The speed of a nerve impulse varies from as slow as a few _______ to a maximum speed of __________.
mm/sec
130 meters/sec.
3 factors that effect the speed of a nerve impulse:

HINT: T D M
1. Temperature - the higher the temperature the greater the speed.

2. Diameter of the nerve fiber - the thicker the fiber the greater the speed.

3. If the fiber is myelinated or nonmyelinated - nerve impulses move faster along a myelinated fiber.
How the all- or - none effect relates to nerve impulse conduction.
In regards to the intensity or strength of the nerve impulse nerve fibers obey the all or none effect. That is a stimulus will either cause the maximum strength nerve impulse { action potential} or none at all.
Only occurs along myelinated fibers.Due to the insulation effect of the myelin sheath the action potentials {nerve impulse} jump from 1 node of RANVIER to the next.

Because of SALTORY nerve impulses move a much greater speed along myelinated fibers.
Saltory conduction
STEPS in Nerve Impulse Transmission:

An action potential reaches the synaptic knob and ____________ its membrane.

This causes voltage regulated Ca++ channels to _____ and Ca++ 's flow into the ________ ________.

The ____________ cause the release of neurotransmitter molecules from the synaptic vesicles.

The _______________ ____________ diffuse across the synapse and attach to receptor sites on the postsynaptic membrane where they cause a graded potential called an
_______ ________ _______ _______ { EPSP } to develop.

Each _______ is subthreshold (produces a depolarization of about 0.5 mv)

So for action potential to develop on the initial segment of the ______ __________ of EPSP's required to reach threshold depolarization. (that is lower the depolarization by 15 - 20 mv)

Once there is enough summation of ______ to reach threshold depolarization the voltage regulated Na+ channels on initial segment ______ and an _______ ________ develops.

This action potential propagates itself along the ______ of the _________ _______.
STEPS:
An action potential reaches the synaptic knob and DEPOLARIZES its membrane.

This causes voltage regulated Ca++ channels to OPEN and Ca++ 's flow into the SYNAPTIC KNOBS.

The Ca++ 's cause the release of neurotransmitter molecules from the synaptic vesicles.

The NEUROTRANSMITTER MOLECULES diffuse across the synapse and attach to receptor
sites on the postsynaptic membrane where they cause a graded potential called an
excitatory postsynaptic potential { EPSP } to develop.

Each EPSP is subthreshold { produces a depolarization of about 0.5 mv }

So for action potential to develop on the initial segment of the AXON SUMMATION of EPSP's required to reach threshold depolarization. { that is lower the depolarization by 15 - 20 mv }

Once there is enough summation of EPSP's to reach threshold depolarization the voltage regulated Na+ channels on initial segment OPEN and an ACTION POTENTIAL develops.

This action potential propagates itself along the AXON of the POSTSYNAPTIC NEURON.
The 2 main neurotransmitters that act as excitatory substances { that is cause EPSP 's to develop on postsynaptic membrane} at synapses within the CNS are _______________ and ______________.
acetylcholine and
norepinephrine.
The neurotransmitter molecules CAN"T BE ALLOWED to accumulate at ___________ because they
would cause __________ and/or continuous ___________ of the postsynaptic membrane.

This is prevented by ________ of an _______ by the postsynaptic membrane that breaks down the _____________ ____________.

For example, if the neurotransmitter is _____________ the enzyme _____________ is released and it breaks down the ______________.
The neurotransmitter molecules can't be allowed to accumulate at SYNAPSE because they would cause OVERSTIMULATION and/or continuous DEPOLARIZATION of the POSTSYNAPTIC membrane.

This is prevented by RELEASE of an ENZYME by the postsynaptic membrane that breaks down the NEUROTRANSMITTER MOLECULES.

For example, if the neurotransmitter is ACETYLCHOLINE the enzyme CHOLINESTERASE is released and it breaks down the ACETYLCHOLINE.
INHIBITION AT SYNAPSES:

Not all __________ ________ release neurotransmitters that act as excitatory substances and result in EPSP's.

Some release ________________ that act as inhibitory substances causing
an _____________ of __________ ___________ across the synapse.

They do this by _____________ the
postsynaptic membrane ; that is making the __________ more ___________ and the _________ more ___________.{ they do this by opening chemically gated K+ channels but not the Na+ channels }

This means that even more _______ would have to move through the membrane to reach ______________ depolarization and trigger an __________ _______ on the initial segment.

That is it would require a greater summation of ________'s.

We say that an __________ _______ __________ or IPSP is developed on the postsynaptic membrane.
INHIBITION AT SYNAPSES:

Not all synaptic vesicles release neurotransmitters that act as excitatory substances and result in EPSP's.

Some release neurotransmitters that act as inhibitory substances causing
an inhibition of nerve impulses across the synapse.

They do this by hyperpolarizing the
postsynaptic membrane ; that is making the inside more negative and the outside more positive.{ they do this by opening chemically gated K+ channels but not the Na+ channels }

This means that even more Na+ 's would have to move through the membrane to reach threshold depolarization and trigger an action potential on the initial segment.

That is it would require a greater summation of EPSP's.

We say that an inhibitory
postsynaptic potential or IPSP is developed on the postsynaptic membrane.
enzyme that breaks down acetylcholine preventing its accumulation at synapses and neuromuscular junctions.
cholinesterase
The terminal filament of a _______ ________ and the muscle fiber innervate at the __________ _____________.
The terminal filament of a motor axon and the muscle fiber innervate at the neuromuscular junction.
2 parts of neuromuscular junction :

HINT: NT& MEP
Nerve Terminal
Motor End Plate
Axons of motor NEURON branch into TERMINAL filaments.

Each terminal filament ends on a muscle fiber.

The end of each terminal filament forms a flattened structure called a ________ ___________. { like a expanded synaptic knob }

It contains vesicles which contain the neurotransmitter
acetylcholine.
Nerve Terminal
The sarcolEMma Portion of the neuroMuscular junction.

It is foldEd to increase surface area.
Motor End Plate
Steps of Neuromuscular Transmission: Hint: ACH

The arrival of the action potential at the ______ __________ causes the release of ___________ from the vesicles into the gap.

The __________ diffuses across the gap and attaches to __________ _________ on the sarcolemma.

This causes _______ channels to open causing a depolarization called an _____ ______ ________ or EPP to develop on this part of the sarcolemma.

Each EPP is of threshold value; so it causes an action potential to develop on the _________ and __________ itself along the sarcolemma and the T- tubules.

So no summation of EPP's is required; so there is a _____ stimulus response ratio - ____ nerve impulse arriving at nerve terminal causes ___ nerve impulse to move along the
sarcolemma causing _____ contraction of the muscle fiber.

The buildup of ______ at the neuromuscular junction is prevented by the ____________ releasing cholinesterase which breaks down the ______.
Steps of Neuromuscular Transmission:
The arrival of the action potential at the nerve terminal causes the release of acetylcholine from the vesicles into the gap.
The ach. diffuses across the gap and attaches to receptor sites on the sarcolemma.
This causes Na+ channels to open causing a depolarization called an end plate potential or EPP to develop on this part of the sarcolemma.
Each EPP is of threshold value; so it causes an action potential to develop on the sarcolemma and propagate itself along the sarcolemma and the T- tubules.
So no summation of EPP's is required; so there is a1:1 stimulus response ratio - 1
nerve impulse arriving at nerve terminal causes 1 nerve impulse to move along the
sarcolemma causing 1 contraction of the muscle fiber.

The buildup of ach. at the neuromuscular junction is prevented by the sarcolemma releasing cholinesterase which breaks down the ach.
List 3 ways that synaptic transmission and neuromuscular transmission are alike.

HINT: NT # EP
1. They both include the release of a neurotransmitter substance into the gap.

2. They are both characterized bY 1-way conduction across the gap.

3. They both result in a change in the electrical potential of membrane across the gap.
List 2 differences between Synaptic transmission and neuromuscular transmission.

HInt: SS & NS AND SI & NI
1. Synaptic transmission requires summation; neuromuscular transmission does not require summation.

2. May get inhibition at synapses{IPSP}; no inhibition at the neuromuscular junction.