6.5 Neurons and Synapses
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6.5 Neurons and Synapses
Essential idea
Neurons transmit the message, synapses modulate the message.
6.5 Neurons and Synapses
Understandings
Syllabus Reference
| 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. | |
6.5 Neurons and Synapses
Applications and Skills
Syllabus Reference
| 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. | |
6.5 Neurons and Synapses
Vocabulary
6.5 Neurons and Synapses
6.5.U1 Neurons transmit electrical impulses.
1.
2.
3.
4.
5.
6.
6.5 Neurons and Synapses
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
There are 3 types of neurons, specific for their function
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
Which one is faster?
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
6.5 Neurons and Synapses
Which one is faster?
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
6.5 Neurons and Synapses
Which one is faster?
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
6.5 Neurons and Synapses
Which one is faster?
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
6.5 Neurons and Synapses
Cells called neurons can carry rapid electrical impulses.
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
Cells called neurons can carry rapid electrical impulses.
6.5.U1 Neurons transmit electrical impulses.
6.5 Neurons and Synapses
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
The Myelin layer prevents the movement of Na+ and K + ions through the axon membrane.
The impulse jumps from node to node – a process called saltatory conduction
As a result signals travel more quickly down myelinated neurons.
6.5 Neurons and Synapses
Draw and label a motor neuron showing the direction of the nervous impulse (4)
6.5.U2 The myelination of nerve fibres allows for saltatory conduction.
Award [1] for each of the following clearly drawn and correctly labelled.
cell body — complete with nucleus and dendrites;
axon—shown longer than the longest dendrite, with the membrane drawn as a continuous line;
myelin sheath — surrounding the axon, showing nodes of Ranvier;
motor end plates — not covered by myelin sheath and ending in a button / dot;
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What is wrong with these diagrams?
6.5 Neurons and Synapses
Guiding Questions
Name three different roles of integral proteins in cell membranes.
How can integral proteins in a neuron plasma membrane cause an electrical potential across the membrane?
What do these proteins do to carry the nerve impulse along the neurone axon?
6.5 Neurons and Synapses
6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
6.5 Neurons and Synapses
Annotate the graph and membrane
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
Sodium Potassium Pump
Voltage-gated Sodium Channel
Voltage-gated Potassium Channel
Leakage Potassium Channel
Extracellular (outside axon)
Intracellular (inside axon)
6.5 Neurons and Synapses
Membrane proteins
6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
6.5 Neurons and Synapses
Membrane proteins
6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
Facilitated Diffusion - passive process
e.g. large polar molecules (glucose) and ions (Cl-, Na+)
Active Transport - requires ATP
Against the concentration gradient
e.g. Na+/K+ pumps
6.5 Neurons and Synapses
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Neurons have an electrical potential (voltage) across the cell membrane, i.e. membrane is polarised.
The inside of the cell is more negative than the outside
This is called the Resting Membrane Potential = 70mV
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
ATP
Na+
Na+
Na+
K+
K+
Inside of the axon has a Resting Potential of -70mv
Inside the axon
Outside the axon
To maintain the Resting Membrane Potential of -70mv a sodium-potassium pump is used (active)
Na+
Na+
Na+
K+
K+
Na+
Na+
Na+
K+
K+
Na+
Na+
Na+
K+
K+
Notice the high concentration of Na+ outside of the axon
Notice the high concentration of K+ inside of the axon
6.5 Neurons and Synapses
Animations to help you
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Resting potential - the electrical potential across the cell membrane of a cell that is not conducting an impulse
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
K+
K+
If there the Resting Membrane Potential is too positive, K can leave through the Leakage Potassium Channel
K+
K+
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
-70mv
-55mv
+20mv
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Action potential arrives at the voltage gated Sodium Channel
The Sodium Channel Opens
Sodium rushes into axon
The inside of the axon becomes extremely positive (+20mv)
The is called depolarisation
The Na+ channel closes quickly
6.5 Neurons and Synapses
Action Potential Profile
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
-70mv
-55mv
+20mv
Depolarisation
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Action potential arrives at the voltage gated Potassium Channel
The Potassium Channel Opens
Potassium rushes out of the axon
The inside of the axon becomes negative again (-70mv)
The is called repolarisation
6.5 Neurons and Synapses
Action Potential Profile
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
-70mv
-55mv
+20mv
Depolarisation
Repolarisation
6.5 Neurons and Synapses
Create a GIF for Mr Trent to use next year,
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
The Potassium Channel is slow to close
Potassium continues moving out of the axon
The inside of the axon becomes negative again (-90mv)
The is called hyperpolarisation
6.5 Neurons and Synapses
Action Potential Profile
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
-70mv
-55mv
+20mv
Depolarisation
Repolarisation
Hyperpolarisation
The sodium potassium pump restores the axon to resting membrane potential
Refractory Period
6.5 Neurons and Synapses
6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials.
Action potential - is the reversal (depolarisation) and restoration (repolarisation) of the electrical potential across the plasma membrane as an impulse passes along a neuron
6.5 Neurons and Synapses
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
6.5 Neurons and Synapses
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
Na+ move in
K+ move out
Na+/K+ exchanged in a ratio of 3:2
More Na+ outside
More K+ inside
6.5 Neurons and Synapses
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
6.5 Neurons and Synapses
6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials.
6.5 Neurons and Synapses
6.5 Neurons and Synapses
6.5 Neurons and Synapses
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).
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)
6.5 Neurons and Synapses
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).
6.5 Neurons and Synapses
6.5.U4 An action potential consists of depolarization and repolarization of the neuron.
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.
6.5 Neurons and Synapses
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
Concentration of K+ is high inside the neuron
Concentration of Na+ is high outside the neuron
Membrane is more permeable to K+ than Na+
Concentration of K+ inside 20x greater so K+ ions rapidly diffuse out until equilibrium reached
This results in the inside being more negative than outside
Difference in concentration of ions maintained by active transport against concentration gradient
Sodium/potassium cation pumps transport Na+ out and K+ in
This requires ATP
6.5 Neurons and Synapses
Depolarization only occurs in the gaps between myelin sheath cells.
These gaps are called, nodes of Ranvier
6.5 Neurons and Synapses
6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells.
6.5 Neurons and Synapses
Synapses occur where neurons meet
6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells.
6.5 Neurons and Synapses
Explain the principles of synaptic transmission
Pre-synaptic membrane
Post-synaptic membrane
Synaptic Cleft
6.5 Neurons and Synapses
Explain the principles of synaptic transmission
Pre-synaptic membrane
Post-synaptic membrane
Synaptic Cleft
Action potential arrives on pre-synaptic membrane
This causes voltage gated Ca2+ channels to open
This causes a vesicle containing a neurotransmitter to fuse with the pre-synaptic membrane (exocytosis)
6.5 Neurons and Synapses
Explain the principles of synaptic transmission
6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses.
Pre-synaptic membrane
Post-synaptic membrane
Synaptic Cleft
The neurotransmitter diffuses across the synaptic cleft
The neurotransmitter attaches to receptors on the post-synaptic membrane
This causes the sodium channels on the post synaptic membrane to open
This causes depolarization on the post-synaptic membrane
6.5 Neurons and Synapses
Explain the principles of synaptic transmission
6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses.
Pre-synaptic membrane
Post-synaptic membrane
Synaptic Cleft
The neurotransmitter is broken down by an enzyme
The calcium is pumped out via active transport
The NT fuses with the pre-synaptic membrane membrane to be packaged in a vesicle (endocytosis)
Acetylcholine is broken down by acetylcholinesterase into Acetate and Choline
6.5 Neurons and Synapses
Explain the principles of synaptic transmission
6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses.
6.5 Neurons and Synapses
Outline the use of four methods of membrane transport in nerves and synapses (8)
6.5 Neurons and Synapses
6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.
6.5 Neurons and Synapses
Explain how is used neonicotinoid used to maintain insect’s population. You may like to include a diagram to support your explanation
6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
6.5 Neurons and Synapses
Research and answer the neurotransmitter related questions below
6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.
6.5 Neurons and Synapses
Checkpoint
6.5 Neurons and Synapses
Kahoot