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6.5 neurons and synapses (chris paine)
1. Essential idea: Neurons transmit the
message, synapses modulate the message.
6.5 Neurons and synapses
By Chris Paine
https://bioknowledgy.weebly.com/
The image shows a tiny segment of a human brain the lines
show neurons and the dots show synapses. The image is
intended to illustrate both the how complex even a small
mammal's brain is and additionally how important the synapses
between neurons are; it is the synapses that drive
communication and conscious thought. With the exception of
the memory centre the number of cells in the human brain does
not increase after birth, what increase is the number of
connections and hence synapses between neurons.
http://med.stanford.edu/mcp/_jcr_content/hero/hero_banner/images/ima
geSlide8.img.620.high.jpg
2. Understandings
Statement Guidance
6.5.U1 Neurons transmit electrical impulses.
The details of structure of different types of
neuron are not needed.
6.5.U2
The myelination of nerve fibres allows for
saltatory conduction.
6.5.U3
Neurons pump sodium and potassium ions
across their membranes to generate a resting
potential.
6.5.U4
An action potential consists of depolarization
and repolarization of the neuron.
6.5.U5
Nerve impulses are action potentials propagated
along the axons of neurons.
6.5.U6
Propagation of nerve impulses is the result of
local currents that cause each successive part of
the axon to reach the threshold potential.
6.5.U7
Synapses are junctions between neurons and
between neurons and receptor or effector cells.
Only chemical synapses are required, not
electrical, and they can simply be referred to
as synapses.
6.5.U8
When presynaptic neurons are depolarized they
release a neurotransmitter into the synapse.
6.5.U9
A nerve impulse is only initiated if the threshold
potential is reached.
3. Applications and Skills
Statement Guidance
6.5.A1
Secretion and reabsorption of acetylcholine by
neurons at synapses.
6.5.A2
Blocking of synaptic transmission at cholinergic
synapses in insects by binding of neonicotinoid
pesticides to acetylcholine receptors.
6.5.S1
Analysis of oscilloscope traces showing resting
potentials and action potentials.
5. 6.5.U5 Nerve impulses are action potentials propagated along the axons of neurons.
http://outreach.mcb.harvard.edu/animations/actionpotential_s
hort.swf
6. 6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials.
https://phet.colorado.edu/en/simulation/neuron
Use the PhET simulation to
build an understanding of
resting and action
potentials and how they
relate to the voltage
changes in the axon
membrane.
The neuron lab worksheet
activity acts as a guide for
the investigation:
https://phet.colorado.edu/en/cont
ributions/view/3608
Investigate how neurons generate electrical impulses
7. 6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
Plasma membrane is 50 times
more permeable to K+ ions
than Na+
n.b. proteins inside the nerve fiber are negatively charged which increases the charge imbalance.
-70mV
8. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
The sodium-potassium
pump (Na+/K+ pump)
maintains the
electrochemical gradient of
the resting potential. Some
K+ leaks out of the neuron
(making the membrane
potential negative, -70mv).
1 In response to a stimulus (e.g. change in membrane
potential) in an adjacent section of the neuron some
voltage gated Na+ channels open and sodium enters
the neuron by diffusion. If a sufficient change in
membrane potential is achieved (threshold
potential) all the voltage gated Na+ channels open.
The entry of Na+ causes the membrane potential to
become positive (depolarisation)
http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg
2
Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane
potential as an impulse travels along it.
9. Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane
potential as an impulse travels along it.
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
The depolarisation of the
membrane potential causes the
voltage gated Na+ channels to close
and the voltage gated K+ channels
open. K+ diffuses out of the neuron
rapidly and the membrane
potential becomes negative again
(repolarisation)
3
http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg
4 Before the neuron is ready to propagate another impulse the
distribution of Na+ (out) and K+ (in) needs to be reset by
the Na+/K+ pump, returning the neuron to resting potential. This
enforced rest (refractory period) ensures impulses can only travel in a
single direction.
10. Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane
potential as an impulse travels along it.
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg
From McGraw Hill:
http://goo.gl/tI2MD
http://www.wiley.com/WileyCDA/
11. http://highered.mheducation.com/ol
c/dl/120107/bio_d.swf
6.5.U6 Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to
reach the threshold potential.
Propagation of a nerve impulse in un-myelinated axons
http://cnx.org/resources/0d4d8e978090c5adf07cc1661372b69be3496ec6/Figure_35_02_04.png
Cell body
12. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
http://www.psych.ualberta.ca/~ITL/ap/ap.htm
http://www.mrothery.co.uk/images/nerveimpulse.swf
More action potential resources:
http://www.sumanasinc.com/webco
ntent/animations/content/actionpot
ential.html
http://highered.mheducation.com/olc/dl/12
0107/anim0013.swf
13. 6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
http://cnx.org/resources/1a264d4943c1148665b7216c649d72ad774fc80b/Figure_35_02_05.jpg
http://antranik.org/wp-content/uploads/2012/04/conduction-in-a-myelinated-nerve-fiber-saltatory-conduction.jpg
myelination and saltatory conduction
*The jump along the axon is actually just the
very rapid conduction inside the myelinated
portion of the axon.
As myelin acts as an insulator myelinated
axons only allow action potentials to occur
at the unmyelinated nodes of Ranvier.
This forces the the action potential to jump* from
node to node (saltatory conduction).
The result of this is that the impulse travels much more
quickly (up to 200 m/s) along myelinated axons compared to
unmyelinated axons (2 m/s).
Saltatory conduction from node to node also
reduces degradation of the impulse and hence
allows the impulse to travel longer distances
than impulses in unmyelinated axons.
The myelin sheath also reduces energy expenditure over the
axon as the quantity of sodium and potassium ions that
need to be pumped to restore resting potential is less than
that of a un-myelintated axon
14.
15.
16. 6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells.
To function the nervous system needs to receive input/stimuli
and then to coordinate a response to it.
For this to happen impulses need to travel from sensory
receptor cells via a series of nerve cells to effectors, which
are commonly muscles and glands.
There are junctions between each cell called
synapses across which impulses cannot travel.
A special group of molecules called neurotransmitters move
across the synapse to effect an impulse in the adjacent cell.
18. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9
A nerve impulse is only initiated if the threshold potential is reached.
19. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9
A nerve impulse is only initiated if the threshold potential is reached.
20. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9
A nerve impulse is only initiated if the threshold potential is reached.
21. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9
A nerve impulse is only initiated if the threshold potential is reached.
22. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9
A nerve impulse is only initiated if the threshold potential is reached.
23.
24.
25. 6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses.
http://faculty.pasadena.edu/dkwon/chap%208_files/images/image61.png
Acetylcholine is a neurotransmitter used in many synapses through the nervous system
One use is at the neuromuscular junction, i.e. it is the molecule that motor neurons
release to activate muscles. Interfering with the action of acetylcholine can cause a
range of effect from paralysis to convulsions.
26. 6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides
to acetylcholine receptors.
27. 6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides
to acetylcholine receptors.
28. Nature of science: Cooperation and collaboration between groups of scientists - biologists are contributing to
research into memory and learning. (4.3)
Gero Miesenböck FRS
Waynflete Professor of
Physiology, Wellcome
Investigator
Martin Booth
Professor of
Engineering Science
Tim Vogels
Sir Henry Dale Fellow
(physicsist)
Stephen Goodwin
Professor of
Neurogenetics,
Wellcome Investigator
Korneel Hens
Group Leader
(Biochemist)
Scott Waddell
Professor of
Neurobiology,
Wellcome Trust Senior
Research Fellow in
Basic Biomedical
Sciences
http://www.cncb.ox.ac.uk/team/
Nowadays scientists often work in
multidisciplinary teams for example the Centre for
Neural Circuits and Behaviour (CNCB)
The aim of the CNCB is to understand how
intelligence emerges from the physical interaction
of nerve cells.
Studying the brain
from this top-
down approach to
answer such
fundamental
questions requires
techniques and
understanding
from a range of
disciplines.
