The Action Potential and
Neurotransmission
MARION COPELAND AND LYNNETTE LACEK
FIRST YEAR MEDICAL STUDENTS
PENN STATE HERSHEY COLLEGE OF MEDICINE
Review
● What are the major components of the nervous
system? (different categories)
● What are the main structures of a nerve cell?
● What happens at the nerve axon terminal?
Review
Learning Objectives
1.
Students will review the properties of the neuronal
membrane and explain the role of inward and
outward flow of ions (current) in creating membrane
potentials.
1.
Students will understand how the depolarization of
the neuronal membrane contributes to generating an
action potential. Students will understand that the
action potential is an all or nothing response.
The Membrane
jd
Integral Proteins are Important in the nerve and sending signals
GATED ION CHANNEL= one type that we are going to talk about today
❖ There is a lot of stuff in the
membrane of cells
➢ Peripheral Proteins
➢ Globular Protein
➢ Integral Protein
➢ Cholesterol
❖ Important to know:
➢ Integral Protein
■ span the
membrane from
the Extracellular
fluid to the
cytoplasm
Why do we need proteins in the membrane?
●The cell membrane is impermeable to charged
molecules
●Proteins allow the cell a way to let these charged
molecules inside
● The proteins help pick and choose which molecules
are allowed into the cell
●Proteins that do this are called transporters and
channels
Lets Watch the Channel Function
Before we do : what does the membrane channel do?
https://www.youtube.com/watch?v=Mc0rRLlVi6w
What Drives the Movement of Ions Across the Membrane
Two forces move ions across the
membrane
1. Concentration Gradient : Diffusion
a. Ions move from high concentration
to low concentration
2. Voltage or potential difference across
the membrane
a. You can calculate this driving force
with an equation
● The combination of these two forces
drives ions across the membrane through
the channel proteins
● This is known as the Electrochemical
gradient
NEURON AT REST
❖ Key Players:
Sodium (Na+)
Potassium (K+)
❖ Sodium (Na+) is in high
concentrations outside of
the neuron
❖ K+ is high inside the
neuron
When the channel
opens what ions moves
where?
Membrane Potential
● When the cell is at rest the
concentration of the ions on
either side of the membrane
creates a resting membrane
potential
● This is -70mV
● At rest the ion channels are
closed = no ion movement
Action Potential 1
Cell receives an excitatory stimulus
Na+ Channels Open reaches Threshold Potential (1)
Na+ Rushes into the cell causing depolarization (1,2,3)
K+ channels begin to open and K+ leaves out of the cell (2)
Na+ Channel gates close no more Na+ can enter the cell (3)
K+ channels fully open - K+ leaves the cell (4)
K+ channels close and Na+ Channels Reset
Action Potential 2
★ Depolarization : when the
membrane potential is increasing
○ Becoming MORE POSITIVE
○ WHY?
★ Repolarization : When the
membrane potential is decreasing
○ Becoming MORE NEGATIVE
○ WHY?
★ Hyperpolarization: When the
membrane potential dips below the
resting potential
○ Why?
Refractory Periods
Absolute Refractory Period
● Sodium (Na+) Channels Inactivate
when the membrane becomes
depolarized
● CANNOT be activated again and
another Action Potential cannot be
generated until membrane potential
goes negative to de-inactivate
Why is this important?
Action Potential is initiated at the
Axon Hillock
● Signal travels down axon
all the way to the axon
terminals
What do you remember ?
What does the letter A represent?
A. Hyperpolarization
B. Threshold potential
C. Resting Membrane Potential
D. Depolarization
What do you remember ?
Letter C represents __________
and the ______ gate is open.
A. Hyperpolarization, Na+
B. Repolarization, K+
C. Hyperpolarization, K+
D. Depolarization, Na+
What do you remember ?
The cell receives a depolarizing
stimulus at C what will happen
next?
A. The cell will depolarize and the
Na+ channels will open.
B. The cell will do nothing with
this new stimulus.
C. The stimulus will cause
hyperpolarization.
D. The stimulus will add to the
current action potential
creating a stronger signal
Learning Objectives
1.
Students will review the importance of the schwann cell and
their role in myelin production and synaptic transmission.
1.
Students will be introduced to the synapse and the different
types of synapses in the nervous system.
Schwann Cells
●How cells and structures help action potential
travel down the nerve axon?
○ Myelin
○ Oligodendrocyte
sSchwann Cells
○ Nodes of Ranvier
What happens when the signal reaches the Axon terminal?
●Once the action potential reaches the Axon
terminal, the “message” must be transmitted to
another structure.
●What structures do nerves send signals to?
○ Muscles, other nerves, blood vessels
●The synapse is the structure that allows a nerve to
pass an electrical or chemical signal to another
neuron
Components of the Synapse
● Presynaptic membrane
● Synaptic Cleft
● Post Synaptic membrane
● Neurotransmitters
● Receptors
Neurotransmission
● Synaptic vesicles hold
neurotranmitters in the
presynaptic neuron
● Voltage-gated Ca2+
channel is closed at rest
● Receptors and enzymes
on the postsynaptic
membrane are
unoccupied
Neurotransmission
1. Action potential reaches
Axon terminal
2. Voltage-gated Ca2+
channel opens, allowing
Ca2+ to flow into the
presynaptic neuron
3. Ca2+ binds to synaptic
vesicles containing
neurotranmitters,
ushering them towards
the presynaptic
membrane
Neurotransmission
4. Synaptic vesicles fuse with
the presynaptic
membrane, releasing
neurotransmitters into the
synaptic cleft
5. Neurotransmitter binds to
receptor on postsynaptic
membrane, causing a
response
6. Neurotransmitter binds
and is degraded by an
enzyme on the
postsynaptic membrane
Neurotransmission
7. Some molecules of
neurotransmitter
are reabsorbed into
the presynaptic
neuron
8. Other molecules of
neurotransmitter
diffuse away from
the synaptic cleft
Learning Objectives
1.
Students will be able to identify several types of excitatory
and inhibitory neurotransmitters, including glutamate,
GABA, norepinephrine, glycine, and acetylcholine.
1.
Students will understand the concept of a receptor and be
introduced to different types.
Receptors
★ Where : Postsynaptic Cell Membrane
○ What part of the neuron receives
these signals?
★ What: Integral Membrane proteins that are
specific for a certain ligand
★ How: Based on their fit, think of a lock and
key model
★ Why: different molecules and different
receptor will cause different downstream
effects in the cell
★ How do they elicit an action potential?
Response to Neurotransmitters
Excitatory
Inhibitory
● Opening of ligand-gated
sodium channels on the
postsynaptic membrane.
● Allows sodium ions to flow
into the cell, making the
interior less negative
● Exitatory Postsynaptic
Potential (EPSP)
● Opening of potassium
channels on the postsynaptic
membrane
● Allows potassium ions to flow
out of the cell, making the
interior more negative
● Inhibitory Postsynaptic
Potential (IPSP)
Neurotransmitters
Exitatory
●Acetylcholine
●Norepinephrine
●Glutamate
●Aspartate
Inhibitory
●GABA
●Glycine
●Serotonin
Summary
●Explain to someone sitting next to you what creates
the membrane potential
Summary-Membrane Potential
●Created by the different concentrations of the ions
(Na+ and K+) on different sides of the membrane.
Summary
●Talk with a different partner and summarize how a
gated channel works.
Summary - Gated Channel
●Ligand binds the receptor causing a conformational
change ( a change in its structure) that allows the
ions to pass through
Summary
●Explain to someone sitting next to you the role of
neurotransmitters.
Summary-Neurotransmitter
Neurotransmitters are released into the synaptic cleft
to transmit the “message” to the next nerve.
They bind to receptors on the postsynaptic membrane
and either signal an exitatory or inhibitory response
Summary
Talk with a neighbor about the difference between
exitatory and inhibitory neurotransmitters
Summary- Neurotransmitters
●Excitatory neurotransmitters bind to receptors and
cause the opening of Sodium channels which elicits
an action potential in the postsynaptic neuron
●Inhibitory neurotransmitters bind to receptors and
cause the opening of Potassium channels which
hyerpolarize the cell membrane of the postsynaptic
neuron
Learning Objectives … Again
1. Properties of the neuronal membrane and the role of ion movement in
creating the membrane potential
2. Understand how an action potential is generated
3. Review the importance of the schwann cell and their role in myelin
production and synaptic transmission.
4. Understand the components of a synapse and how neurotransmission
occurs.
5. Identify types of excitatory and inhibitory neurotransmitters, including
glutamate, GABA, norepinephrine, glycine, and acetylcholine.
6. Understand the role of a receptor and the different types