Tricky Topics: Synaptic Transmission
Summary
TLDRThis script delves into the intricacies of neuronal communication via synaptic transmission. It explains how neurons, with their billions of connections, communicate using electrical signals and chemical messengers like neurotransmitters. The process involves graded potentials and action potentials, with neurotransmitters playing a crucial role in message transmission across synapses. The script also distinguishes between excitatory and inhibitory postsynaptic potentials, triggered by different ion channel receptors, ultimately leading to action potentials if a threshold potential is reached.
Takeaways
- π§ The nervous system is composed of billions of neurons that communicate constantly, even during sleep.
- π Neuronal communication is facilitated by electrical signals and chemical messengers called neurotransmitters.
- π‘ Neurons have two primary functions: transmitting messages across a synapse and carrying messages along their axon.
- π Graded potentials are electrical signals that can be either excitatory or inhibitory, depending on the type of ion channel receptor activated.
- π¬ If graded potentials are of the right size and type, they can trigger action potentials, which are necessary for message transmission along the axon.
- π΄ The presynaptic neuron sends signals, while the postsynaptic neuron receives them, with synapses forming the connection points.
- π§ Synaptic vesicles contain neurotransmitters that are released into the synaptic cleft to communicate with the postsynaptic neuron.
- π Binding of neurotransmitters to receptors on the postsynaptic neuron can lead to either depolarization (excitatory) or hyperpolarization (inhibitory).
- π Glutamate is an example of an excitatory neurotransmitter that, when bound to its receptor, allows sodium ions to enter the neuron, causing depolarization.
- β GABA is an inhibitory neurotransmitter that, when bound to its receptor, allows chloride ions to enter the neuron, causing hyperpolarization.
- π If the sum of EPSPs and IPSPs reaches a threshold, voltage-dependent sodium channels open, initiating an action potential and allowing the neuron to transmit its message.
Q & A
How do neurons communicate with each other?
-Neurons communicate with each other through a process called synaptic transmission, which involves the use of electrical signals and chemical messengers called neurotransmitters.
What is the role of neurotransmitters in synaptic transmission?
-Neurotransmitters act as messengers that transmit messages across a synapse from the presynaptic neuron to the postsynaptic neuron.
What are the two important jobs of a neuron?
-A neuron's two important jobs are to transmit a message to a target across a synapse using neurotransmitters and to carry the message along the length of its axon to its target using an action potential.
What is a graded potential?
-A graded potential is a type of electrical signal that results when neurotransmitters bind to receptors on the postsynaptic neuron, causing a change in the neuron's membrane potential without necessarily generating an action potential.
What is an action potential?
-An action potential is a type of electrical signal that allows the neuron to send its message to its targets when the membrane potential reaches a threshold, typically around -55 millivolts.
What is the difference between a presynaptic and a postsynaptic neuron?
-The presynaptic neuron is the sending neuron that releases neurotransmitters into the synapse, while the postsynaptic neuron is the receiving neuron that has receptors for these neurotransmitters.
What are synaptic vesicles and what do they contain?
-Synaptic vesicles are small bubbles within the presynaptic neuron that contain neurotransmitter molecules, which are released into the synaptic cleft to transmit signals.
How do neurotransmitters create a graded potential in the postsynaptic neuron?
-Neurotransmitters create a graded potential by binding to receptors on the postsynaptic neuron, which can be gated to ion channels. This binding allows ions to flow across the membrane, creating a change in potential.
What is the role of ion channels in generating graded potentials?
-Ion channels play a crucial role in generating graded potentials by allowing certain ions to flow across the neuronal membrane when they are opened by neurotransmitter binding, thus changing the neuron's membrane potential.
What is an excitatory postsynaptic potential (EPSP)?
-An EPSP is a type of graded potential that occurs when neurotransmitters, such as glutamate, bind to their receptors and cause positive ions like sodium to enter the neuron, making it less negative and more likely to fire an action potential.
What is an inhibitory postsynaptic potential (IPSP)?
-An IPSP is a type of graded potential that occurs when neurotransmitters, such as GABA, bind to their receptors and cause negative ions like chloride to enter the neuron, making it more negative and less likely to fire an action potential.
How does the type of ion channel receptor activated determine the type of graded potential?
-The type of ion channel receptor activated determines whether the graded potential is excitatory (depolarizing) or inhibitory (hyperpolarizing), based on whether positive or negative ions are allowed to enter the neuron.
Outlines
π§ Understanding Neuronal Communication
This paragraph explains the fundamental process of synaptic transmission, which is crucial for neuronal communication. It highlights that the nervous system contains billions of neurons that communicate through synapses. Neurons have two main functions: transmitting a message across a synapse using neurotransmitters and carrying the message along the axon using an action potential. The paragraph introduces the concepts of graded potentials and action potentials, which are electrical signals that facilitate communication. It also describes the roles of presynaptic and postsynaptic neurons and delves into the structure of synapses, including synaptic vesicles and neurotransmitter release. The paragraph concludes with an overview of how neurotransmitters initiate graded potentials by binding to receptors on the postsynaptic neuron.
π¬ Excitatory and Inhibitory Graded Potentials
This paragraph delves into the specifics of excitatory and inhibitory graded potentials. It explains how different types of ion channel receptors can lead to either depolarization (excitatory) or hyperpolarization (inhibitory) of the postsynaptic neuron. An excitatory neurotransmitter, like glutamate, causes sodium ions to enter the neuron, leading to a depolarization and an excitatory postsynaptic potential (EPSP). Conversely, an inhibitory neurotransmitter, like GABA, allows chloride ions to enter, causing hyperpolarization and an inhibitory postsynaptic potential (IPSP). The paragraph also discusses the role of voltage-dependent sodium channels, which, when activated by the sum of EPSPs and IPSPs reaching a threshold, initiate an action potential. This potential is critical for the neuron to transmit its message to its targets, illustrating the complexity and importance of synaptic transmission in neuronal communication.
Mindmap
Keywords
π‘Neurons
π‘Synaptic Transmission
π‘Graded Potential
π‘Action Potential
π‘Presynaptic Neuron
π‘Postsynaptic Neuron
π‘Neurotransmitters
π‘Synaptic Cleft
π‘Depolarization
π‘Hyperpolarization
π‘Ion Channels
Highlights
Neurons communicate through synaptic transmission.
The nervous system has billions of neurons.
Each neuron can have hundreds or thousands of contacts.
Neurons are in constant communication even during sleep.
Neuronal communication is facilitated by electrical signals and chemical messengers.
Neurons have two key functions: transmitting messages across synapses and carrying messages along their axons.
Graded potentials are electrical signals resulting from neurotransmitter release.
Action potentials are electrical signals that carry messages along the axon.
The axon terminals of one neuron form synapses with the dendrites of another.
Neurons can act as both presynaptic (sending) and postsynaptic (receiving) cells.
Synaptic vesicles contain neurotransmitter molecules.
Neurotransmitters are released into the synaptic cleft and bind to receptors on the postsynaptic neuron.
Binding of neurotransmitters opens ion channels, generating graded potentials.
Graded potentials can be either depolarizing (excitatory) or hyperpolarizing (inhibitory).
Glutamate is an example of an excitatory neurotransmitter.
GABA is an example of an inhibitory neurotransmitter.
Depolarization makes the neuron's inside more positive, while hyperpolarization makes it more negative.
Excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) sum up to determine neuronal activity.
If the membrane potential reaches a threshold, voltage-dependent sodium channels open, creating an action potential.
Synaptic transmission is a fundamental process for neuronal communication.
Transcripts
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to understand how neurons communicate
with one another it is vital to
understand the basics of synaptic
transmission the nervous system has
billions of neurons in each of them can
have hundreds or thousands of contacts
these neurons are in constant
communication even when we're sleeping
this sheer amount of activity is truly
remarkable
despite this neuronal communication is
made possible by couple different types
of electrical signals which are linked
by chemical messengers let's zoom in for
a closer look
neurons have two important jobs one is
to transmit a message to a target across
a synapse using neurotransmitters as
messengers the type of electrical signal
resulting from this is called a graded
potential if the graded potentials the
right size and type then it allows the
neuron to do its second important job
which is to carry the message along the
length of its axon to its target using a
type of electrical signal called an
action potential when an action
potential reaches the axon terminals it
triggers once again neurotransmitter
release which continues the cycle of
producing a graded potential and then
action potential and the next targeted
neurons this continuous cycle of
communication is running all the time in
your nervous system for this tricky
topic we'll focus on the events at the
synapse and learn how synaptic
transmission plays a role in neuronal
communication we're going to start our
journey to the synapse with a bird's eye
view the axon terminals of the neuron on
the Left shown here in red form synapses
with the dendrites of the neuron on the
right although most neuronal axon
terminals synapse on dendrites like you
see here keep in mind they can also form
synapses on other parts of the targeted
neuron
such as the soma and the axon the
sending neuron on the left is referred
to as the presynaptic neuron and the
receiving neuron on the right is
referred to
the postsynaptic neuron keep in mind
these are relative terms most neurons
act as senders and receivers of
information so they're both presynaptic
and postsynaptic depending on which
event were referring to let's pick this
particular synapse and zoom in for a
little more detail at this magnification
we can see little bubbles called
synaptic vesicles and inside these we
can see neurotransmitter molecules these
vesicles here are releasing their
neurotransmitter contents into the
synaptic cleft once released into the
synapse the neurotransmitters can travel
the short distance to the postsynaptic
neuron once they reach the other side
these neurotransmitters bind to
receptors on the postsynaptic neuron
there are lots of different types of
receptors but the simplest ones are
gated to ion channels like shown here
once the neurotransmitter binds it opens
the ion channel part of the receptor
allowing certain ions to travel across
the neuronal membrane along their
electrochemical gradient this influx a
positive current in the form of positive
ions is what generates graded potentials
in the postsynaptic neuron thus through
the binding of postsynaptic ion channel
receptors synaptic neurotransmitters
initiate postsynaptic graded potentials
let's review the steps so far first
neurotransmitter is released from the
presynaptic terminal second that
neurotransmitter binds to receptors
opening their ion channels on the
postsynaptic side what happens next in
the postsynaptic neuron depends on the
type of ion channel receptor that is
activated as different receptors are
permeable to different types of ions the
type of ion channel receptor that is
activated will then determine the type
of graded potential that is initiated if
the channel opens and positive ions
enter through the channel then the
inside of the neuron will become less
negative for example the potential of
the neuron might rise from its resting
potential of minus 70 millivolts to
minus 55 millivolts this is referred to
as a depolarization and is considered
excitatory if instead negative ions
enter through the channel then the
inside of the neuron will become more
negative
for example the potential of the neuron
might decrease from its resting
potential of minus 70 millivolts to
minus 90 millivolts this is referred to
as a hyper polarization and is
considered inhibitory let's look at some
examples of different types of receptors
which produce either excitatory or
inhibitory graded potentials first let's
look at depolarization a
neurotransmitter that is always
excitatory at the synapse is glutamate
so we can pretend that the orange
diamonds are glutamate molecules and the
white circles in the synapse are sodium
ions when glutamate binds to its
receptor the channels open in sodium
ions are driven by their electrochemical
gradient to enter the neuron when sodium
moves into the cell through the receptor
ion channel it brings its positive
charge with it making the cell more
positive which is called a
depolarization if the channel remains
open for longer more sodium will flow in
making the cell even more positive
this type of graded potential is called
an excitatory postsynaptic potential or
epsp for short what about
hyper-polarization a neurotransmitter
that's almost always inhibitory at its
synapse is gaba and it's receptor
channel is permeable to negatively
charged chloride ions shown here as
black circles when gaba binds to its
receptor the channel opens and chloride
ions are driven into the postsynaptic
neuron because of their concentration
when chloride moves into the cell
through the GABA receptor ion channel it
brings its negative charge with it
making the cell more negative which is
called a hyper polarization if the
channel remains open for longer more
chloride will flow in making the cell
even more negative
this type of graded potential is called
an inhibitory postsynaptic potential or
IPSP for short so why does this matter
well if the postsynaptic neuron adds up
all its epsps
and ipsps and the membrane potential
reaches a threshold of minus 55
millivolts a different type of ion
channel comes into play one that is
opened by a change in voltage the ion
channels we've learned about so far are
opened by neurotransmitter binding but
these voltage dependents sodium channels
are sensitive to changes in charge at
resting conditions say minus 70
millivolts these channels are closed and
sodium ions cannot pass through them
into the cell however when the sum of
all ipsps and ipsps raises the neurons
potential to are above minus 55
millivolts the voltage dependent sodium
channels open allowing sodium ions to
flow into the cell
when these voltage dependent sodium
channels open they create an action
potential which allows the neuron to
send its message to its targets overall
synaptic transmission may seem quite
tricky but it's actually quite simple
once you know the basics
you
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