topic 6.5 neurons & synapses - sciencestephenson.com
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TOPIC 6.5 – NEURONS & SYNAPSES
6.5 – A - Neurons
INTRO
IB BIO – 6.5 The nervous system is the
organ system that carries
signals throughout the body.
It is divided into two sections:
• Central nervous system –
nerve tissue in the brain and
spinal cord
• Peripheral nervous system –
nerve tissues outside the
central nervous system
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https://ka-perseus-images.s3.amazonaws.com/f7fa1bdddc896c2c635a1929c6578b745a6030c2.png
Understandings
U1: Neurons transmit electrical impulses.
IB BIO – 6.5
Key Terms
Neurons
The nervous sytem is made up of cells called neurons, which
transmit electrical impulses. The general structure of is
shown here. Key structures include…
4
https://denisezannino.files.wordpress.com/2014/09/neuron1.jpg
Understandings
U1: Neurons transmit electrical impulses.
IB BIO – 6.5
Key Terms
Axon
Dendrites
• Axon – a long, narrow
‘arm’ that carries electric
signals (like wires)
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https://askabiologist.asu.edu/sites/default/files/resources/plosable/Brain_Speed/connected-neurons.jpg
• Dendrites – short, branched
fibers that transmits signals
to other cells
Understandings
U1: Neurons transmit electrical impulses.
IB BIO – 6.5
Key Terms
Cell Body
• Cell Body – contains the nucleus and majority of the
organellels and cytoplasm
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https://upload.wikimedia.org/wikipedia/commons/e/ed/Neuron_Cell_Body.png
Understandings
U2: The myelination of nerve fibers allows for saltatory conduction.
IB BIO – 6.5
Key Terms
Myelin
Nodes of Ranvier
Nerve fibers function by transmitting
signals over long distances very
quickly.
To facilitate this, some nerve axons
are covered by a myelin sheath
which is produced by Schwann cells.
Gaps between the myelin sheaths
are called nodes of Ranvier.
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https://classconnection.s3.amazonaws.com/811/flashcards/141811/jpg/neuron21320853416098.jpg
Understandings
U2: The myelination of nerve fibers allows for saltatory conduction.
IB BIO – 6.5
Key Terms
Nodes of Ranvier
Saltatory Conduction
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http://antranik.org/wp-content/uploads/2012/04/conduction-in-a-myelinated-nerve-fiber-saltatory-conduction.jpg
Electric impulses traveling down
the axon are able to jump
between the nodes.
This ‘skipping’ is called saltatory
conduction and allows impulses
to travel up to 100 m/s.
Understandings
U3: Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
IB BIO – 6.5
Key Terms
Na+/K+ Ion Pump
Sodium/Potassium ion pumps are embedded in the membrane of
axons and move ions against their concentration gradient using ATP.
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http://reader14.docslide.net/store14/html5/392015/5571ffce49795991699e26b8/bg12.png
• THREE Na+ ions are
pumped out of the cells
• TWO K+ ions are pumped
into the cells
Understandings
U3: Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
IB BIO – 6.5
Key Terms
Na+/K+ Ion Pump
After being pumped, Na+ ions and K+ ions are able to diffuse
across the membrane. However, K+ diffuses much more quickly
than Na+.
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http://slideplayer.com/slide/7069457/24/images/10/Figure+11.8:+The+basis+of+the+resting+membrane+potential,+p.+399..jpg
As a result:
• The Na+ gradient
is much is greater
than the K+
gradient.
• A charge imbalance
is created across
the membrane
Understandings
U3: Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
IB BIO – 6.5
Key Terms
Resting potential
This imbalance of of charges results in a potential difference
(voltage) across the membrane. This is called resting potential and
has a value of approx. -70 mV.
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http://slideplayer.com/slide/7069457/24/images/10/Figure+11.8:+The+basis+of+the+resting+membrane+potential,+p.+399..jpg
VID
EO
SIB BIO – 6.5
• Crash Course – The Nervous System, Pt 1https://www.youtube.com/watch?v=qPix_X-9t7E
• 2-Minute Neuroscience – The Neuronhttps://www.youtube.com/watch?v=6qS83wD29PY
• Khan Academy – Resting Potentialhttps://www.youtube.com/watch?v=4htSVI5E9AQ
12
REVIE
WIB BIO – 6.5 1. Outline the role of the nervous system and its
primary subdivisions.
2. Identify the following structures:
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https://s3.amazonaws.com/classconnection/399/flashcards/2562399/png/1280px-neuronsvg-151C0DCC5994F4DC02E.png
REVIE
WIB BIO – 6.5 1. Outline the role of the nervous system and its
primary subdivisions.
2. Identify the following structures:
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https://s3.amazonaws.com/classconnection/399/flashcards/2562399/png/1280px-neuronsvg-151C0DCC5994F4DC02E.png
REVIE
WIB BIO – 6.5 3. Describe nodes of Ranvier and their role in
transmitting impulses.
4. State the number of K+ and Na+ ions transported
by Na+/K+ pumps.
5. Outline how the resting potential is formed.
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https://s3.amazonaws.com/classconnection/399/flashcards/2562399/png/1280px-neuronsvg-151C0DCC5994F4DC02E.png
6.5 – B – Action Potential
INTRO
IB BIO – 6.5 Recall that neurons have axons that are able to transmit signals in
the form of electrical impulses. These signals travel in the form of
action potentials.
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https://s-media-cache-ak0.pinimg.com/originals/b0/61/7c/b0617c59b5b5dc7bcd4760f3447349d4.jpg
INTRO
IB BIO – 6.5 Na+ and K+ voltage-gated ion channels are embedded in
the membrane of the axon. When open, these allow ions to diffuse
across the membrane. This affects the local potential.
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https://cnx.org/resources/09ab17c9199ed6fb925c5fae201df4bcfac9b846/Figure_35_02_01.jpg
Understandings
U4: An action potential consists of depolarization and repolarization of the neuron.
IB BIO – 6.5
Key Terms
Action potential
Polarization
Repolarization
Action potentials occur when there is a rapid change in the
membrane potential. In has two phases as shown here:
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https://s-media-cache-ak0.pinimg.com/originals/f9/53/59/f95359a8d685edcaaaaae66d6e43c510.jpg
1
2
1. Depolarization –
Na+ channels open,
allowing Na+ to diffuse
inside the neuron. The
Potential becomes +30mV
2. Repolarization –
Na+ channels close and
K+ channels open. K+
diffuses outwards. The
potential returns to
-70 mV
Understandings
U4: An action potential consists of depolarization and repolarization of the neuron.
IB BIO – 6.5
Key Terms
Action potential
Polarization
Repolarization
Repolarization happens quickly after depolarization. The diffusion
of K+ changes the potential from positive to negative, often
overshooting the resting potential. This is hyperpolarization.
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https://s-media-cache-ak0.pinimg.com/originals/f9/53/59/f95359a8d685edcaaaaae66d6e43c510.jpg
Understandings
U5: Nerve impulses are action potentials propagated along the axons of neurons.
IB BIO – 6.5
Key Terms
In order to communicate
with other cells, action
potentials are propagated
along axons.
Nerve impulses travel in one
direction from the receiving
terminal to the other end.
The propagation of action
potentials has many steps…
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http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-13/13_11.jpg
Understandings
U6: Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.
IB BIO – 6.5
Key Terms
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https://s-media-cache-ak0.pinimg.com/736x/36/16/fb/3616fb33b2765be22faaec1bffd52679.jpg
Propagation
1. Membrane is at resting
potential.
2. An action potential causes Na+
channels to open and Na+
diffuses into the cell.
Na+ inside the cell diffuses
toward the neighboring region.
3. When the threshold potential is
reached, nearby Na+ channels
open, resulting in
depolarization.
Understandings
U6: Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.
IB BIO – 6.5
Key Terms
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https://s-media-cache-ak0.pinimg.com/736x/36/16/fb/3616fb33b2765be22faaec1bffd52679.jpg
Propagation
4. K+ ion channels open in the
original region, allowing K+
ions to diffuse outward.
This repolarizes the local
region, which returns to the
resting potential.
5. This process repeats allowing
the action potential to move
forward.
Understandings
U6: Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.
IB BIO – 6.5
Key Terms
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https://s-media-cache-ak0.pinimg.com/736x/36/16/fb/3616fb33b2765be22faaec1bffd52679.jpg
Action Potential Propagation
Understandings
S1: Analysis of oscilloscope traces showing resting potentials and action potentials.
IB BIO – 6.5
Key Terms
Oscilloscope
Oscilloscopes are devices
that can visualize oscillations
in electric potential.
To do this, they have two
electrodes that can be placed
on each side of the
membrane.
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Skills
S1: Analysis of oscilloscope traces showing resting potentials and action potentials.
IB BIO – 6.5
Key Terms
Oscilloscope
As shown here, oscilloscopes can be used to observe changes in
membrane potential as an action potential is propagated.
A narrow spike from -70mV to +30mV is seen during depolarization.
Then, the potential quickly drops back during repolarization.
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https://online.science.psu.edu/sites/default/files/biol141/Propagation_of_Action_Potential.jpg
VID
EO
SIB BIO – 6.5
• Crash Course – The Nervous System, Pt 2https://www.youtube.com/watch?v=OZG8M_ldA1M
• 2-Minute Neuroscience – Action Potentialhttps://www.youtube.com/watch?v=W2hHt_PXe5o
27
REVIE
WIB BIO – 6.5 1. Define action potential.
2. Identify the types of ion channels embedded in the
axon membrane.
3. Differentiate between depolarization and
repolarization.
4. Outline the propagation of an action potential down
an axon.
28
REVIE
WIB BIO – 6.5 Action Potential Graph
Draw the graph of an action potential (potential vs.
time). Be sure to:
- Label the x and y axis
- Include specifica potential values
- Label regions of the graph correspond to:
- Depolarization
- Repolarization
- Hyperpolarization
29
REVIE
WIB BIO – 6.5 Action Potential Graph 30
https://opentextbc.ca/anatomyandphysiology/wp-content/uploads/sites/142/2016/03/1221_Action_Potential.jpg
6.5 – C - Synapses
INTRO
IB BIO – 6.5 Recall that the role of the nervous system is to carry signals
throughout the body. To do this, neurons must be able to pass
signals (action potentials) between them.
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https://denisezannino.files.wordpress.com/2014/09/simple-network.jpg
Understandings
U7: Synapses are junctions between neurons and between neurons and receptor or effector cells.
IB BIO – 6.5
Key Terms
Synapse
Neurotrans-mitter
Synapses are the junctions
between neurons or between
neurons and receptor/effector
cells.
They are the places where signals
are transferred through chemicals
called neurotransmitters.
The gap between cells
is called the synaptic
clef.
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https://www.ncbi.nlm.nih.gov/projects/pmh/PMH_Authoring/media/Images/originals/Fig8.1Neurons.jpghttps://www.ncbi.nlm.nih.gov/projects/pmh/PMH_Authoring/media/Images/originals/Fig8.1Neurons.jpg
Understandings
U8: When presynaptic neurons are depolarized they release a neurotransmitter
into the synapse.
IB BIO – 6.5
Key Terms
Pre-synaptic
Post-synaptic
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http://openneuronproject.org/wp-content/uploads/2016/08/synapse.png
When a signal is being passed
between neurons, two types of cells
are involved:
• Presynaptic cell – the neuron
transitting a signal and releasing
neurotransmitters into the
synaptic cleft
• Post-synaptic cell – the neuron
receiving the signal by detecting
the presence of
neurotransmitters
Understandings
U8: When presynaptic neurons are depolarized they release a neurotransmitter
into the synapse.
IB BIO – 6.5
Key Terms
Synapse
Synaptic Cleft
When an action potential
reaches a dendrite, it
depolorizes the area
This causes the release of
neurotransmitter into
the synaptic cleft.
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https://cnx.org/resources/75ab19a5b7c2945555083964780a2159caa68856/1225_Chemical_Synapse.jpghttps://cnx.org/resources/75ab19a5b7c2945555083964780a2159caa68856/1225_Chemical_Synapse.jpg
Understandings
U8: When presynaptic neurons are depolarized they release a neurotransmitter
into the synapse.
IB BIO – 6.5
Key Terms
Synapse
Synaptic Cleft
Synaptic Transmission 36
http://www.mrhorrocks.com/wp-content/uploads/2016/02/synaptic_transmission_med.jpg
1. An action potential propagate down an axon and reaches the
synapse.
2. Depolarization causes
Ca2+ ions to open, which
allows Ca2+ to diffuse
into the cell.
3. Vesicles containing
neurotransmitters
merge with the cell
membrane
This releases the
neurotransmitter into
the synaptic cleft.
Understandings
U8: When presynaptic neurons are depolarized they release a neurotransmitter
into the synapse.
IB BIO – 6.5
Key Terms
Synapse
Synaptic Cleft
Synaptic Transmission 37
http://www.mrhorrocks.com/wp-content/uploads/2016/02/synaptic_transmission_med.jpg
4. Neurotransmitters diffuse across the synaptic cleft towards the
post-synaptic cell.
5. Neurotransmitters bind
to receptors on the
post-synaptic cell.
This opens Na+ ion
channels and causes
depolarization and
triggers an action
potential.
6. This potential propagates
down the cell towards
the cell body.
Understandings
U9: A nerve impulse is only initiated if the threshold potential is reached.
IB BIO – 6.5
Key Terms
Threshold potential
In order for an action potential to be propagated in a post-
synaptic neuron, the threshold potential must be reached.
This is the potential at which voltage-gated ion channels open. The
graph above shows two failed attempts before the threshold is met.
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http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_07_17_labeled.jpg
Understandings
U9: A nerve impulse is only initiated if the threshold potential is reached.
IB BIO – 6.5
Key Terms
Threshold potential
When neurotransmitters bind to recepters on the post-synaptic
neuron, the influx of Na+ ions increases the membrane potential.
If the threshold potential is not reached, an actional potential will
not be initiated and propagated.
39
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_07_17_labeled.jpg
Understandings
U9: A nerve impulse is only initiated if the threshold potential is reached.
IB BIO – 6.5
Key Terms
Threshold potential
When the threshold potential is reached, the action potential is
propagated down the post-
synaptic cell and the signal is carried.
40
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_07_17_labeled.jpg
REVIE
WIB BIO – 6.5 1. Define synapse.
2. Differentiate between pre-synaptic and post-
synaptic cells.
3. Outline the process of how a signal is transmitted
between two neurons (synaptic transmission).
4. Define the threshold potential.
41
6.5 – D - Acetylcholine
INTRO
IB BIO – 6.5 Recall that pre-synaptic cells release neurotransmitters in
order to communicate with other neurons or effector cells.
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http://www.compoundchem.com/wp-content/uploads/2015/07/Chemical-Structures-of-Neurotransmitters-2015.png
Applications
A1: Secretion and reabsorption of acetylcholine by neurons at synapses.
IB BIO – 6.5
Key Terms
Acetylcholine
Acetylcholine is a neurotransmitter used in many synapses, most
notably between neurons and muscle fibers. After it is secreted, it
diffuses towards receptors on the post-synaptic cell.
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http://www.nature.com/nature/journal/v436/n7050/images/436473a-f1.2.jpg
Applications
A1: Secretion and reabsorption of acetylcholine by neurons at synapses.
IB BIO – 6.5
Key Terms
Acetylcholine
Acetylcholine molecules only
bind for a short period of time
and only cause one action
potential in the post-synaptic
cell.
While in the synaptic cleft, it is
broken down by
acetylcholinesterase.
The products of this are choline
and acetate molecules.
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https://classconnection.s3.amazonaws.com/801/flashcards/3736801/jpg/ace_enzy-1446A6ABC875C206CE2.jpg
Applications
A1: Secretion and reabsorption of acetylcholine by neurons at synapses.
IB BIO – 6.5
Key Terms
Acetylcholine
The choline and acetate molecules are reabsorbed by the pre-
synaptic cell via endocytosis. Inside the cell, they are converted
back into acetycholine by recombining with an acetyl group.
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http://www.dokimiscience.com/uploads/4/6/9/2/46925269/939160450.gif
Applications
A2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
IB BIO – 6.5
Key Terms
Neonicitonoids
Neonicotinoids are synthetic molecule that can bind to acetylcholine
receptors in the central nervous system of insects. It is not broken
down by acetylcholinesterase and so does not unbind from
receptors.
47
https://upload.wikimedia.org/wikipedia/commons/thumb/2/26/R-nicotine.svg/2000px-R-nicotine.svg.png
Applications
A2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
IB BIO – 6.5
Key Terms
Neonicitonoids
Since the binding is irreversible, neonicitinoids block synaptic
transmissions in cholinergic synapes. This cause paralysis and
death, making it an effective pesticide.
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https://oregonsustainablebeekeepers.files.wordpress.com/2013/03/bad.jpg
Applications
A2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
IB BIO – 6.5
Key Terms
Neonicitonoids
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http://www.compoundchem.com/wp-content/uploads/2015/04/Neonicotinoid-Pesticides-Their-Effect-on-Bee-Colonies-The-Facts.png
REVIE
WIB BIO – 6.5 50U1: Neurons transmit electrical impulses.
U2: The myelination of nerve fibers allows for saltatory conduction.
U3: Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
U4: An action potential consists of depolarization and repolarization of the neuron.
U5: Nerve impulses are action potentials propagated along the axons of neurons.
U6: Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.
U7: Synapses are junctions between neurons and between neurons and receptor or effector cells.
U8: When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.
U9: A nerve impulse is only initiated if the threshold potential is reached.
A1: Secretion and reabsorption of acetylcholine by neurons at synapses.
A2: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
S1: Analysis of oscilloscope traces showing resting potentials and action potentials.
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