Nerve Impulses Flashcards
What is found between the sensory neuron and relay neuron
Synapse
What is found between the sensory neuron and relay neuron
Synapse
What is found on the cell surface membrane of the dendrites?
Receptors
Receptors
Receptors
Specialised cell that produces the myelin sheath
Schwann cell
Biological molecule found in myelin sheath
phospholipids
Myelin also contains cholesterol, so similar to cell surface membrane.
Released by axon terminals
neurotransmitters
Process at nodes of ranvier
saltatory conduction
Stages of an action potential
Resting potential,
(Threshold potential),
Depolarisation,
Repolarisation,
Hyperpolarisation,
Re-establish resting potential.
Resting potential in mV
-70mV
Channel proteins found in axon cell surface membrane
Voltage-gated sodium ion channels
Voltage-gated potassium ion channels
Explain how a resting potential is maintained across the axon membrane in a neurone (3 marks).
- Sodium ions actively transported OUT and potassium ions IN;
- LESS permeable to sodium ions as voltage-gated channels closedOR membrane MORE permeable to potassium ions as some voltage-gated channels open;
- Higher concentration of potassium ions inside AND higher concentration of sodium ions outside the axon
The sodium potassium ion pump establishes an ________________ gradient.
electrochemical gradient
i.e., higher sodium ion concentration outside the axon, lower inside.
Threshold potential in mV
-55mV
Channel open at -55mV
Voltaged-gated sodium ion channels
The all-or-nothing principle
An action potential is only generated/produced when threshold stimulus is reached (-55mv)
OR
An action potential is not generated/produced until/unless threshold stimules is reached (-55mv);
If stimulus reached, voltage-gated sodium ion channels open
Sodium and potassium ions can only cross the axon membrane through channel proteins. Explain why (2 marks).
- Cannot pass through phospholipid bilayer
(via simple diffusion) - because they are NOT lipid soluble
OR because they are charged;
A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.
Explain why (3 marks).
- No/less ATP produced;
- No/less active transport
OR fewer sodium ions moved out.
OR Sodium/potassium pump inhibited; - Electrochemical gradient not maintained
OR same concentration of sodium and potassium ions either side of axon membrane
Sodium ions diffusing into the axon via open voltage-gated channels leads to___________________.
depolarisation
Why does the graph increase from -55mV to +40mV?
image
- Voltage-gated sodium ion channels are open
- Sodium ions diffuse into the axon via faciliated diffusion (DOWN an electrochemical gradient)
- Inside of the axon MORE positive
What happens at +40mV?
image
Voltage-gated sodium ion channels CLOSE
AND
Voltage-gated potassium ion channels OPEN
Why does the graph decrease after +40mV during repolarisation?
image
- Voltage-gated potassium ion channels are open (& voltage-gated sodium ion channels are closed).
- Potassium ions rapidly diffuse OUT of the axon via faciliated diffusion (DOWN an electrochemical gradient)
- Inside of the axon LESS positive
Hyperpolarisation in mV
-90mV
What causes hyperpolarisation?
- Voltage-gated potassium ion channels stay open;
- Potassium ions diffuse out of axon;
- Inside of axon becomes even LESS positive (decreasing from -70mV to -90mV).
Channels closed at -90mV
Voltage-gated potassium ion channels (close at -90mV)
Voltage-gated sodium ion channels (already closed during repolarisation)
Explain how the resting potential is re-established (2 marks).
- Sodium potassium pump uses energy from ATP hydrolysis;
- Sodium ions actively transported OUT and potassium ions IN.
Both ions move AGAINST their concentraton gradient from low to high.
Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon (3 marks).
- Myelination provides insulation;
- In myelinated axon saltatory conduction occurs
OR In myelinated axon depolarisation only occurs at nodes of Ranvier;
- In non-myelinated axon, depolarisation occurs along whole length of axon;
Refractory period
- Time during which a new action potential cannot be generated;
- It lasts from the threshold potential until the resting potential has been re-established;
Importance of the refractory period
- Action potentials occur in one direction
- Each impulse / action potential is discrete
- Number of action potential is limited
Factors affecting speed of impulse conductance along an axon
Myelination
Temperature
Axon diameter
explain how myelination affects conductance of an impulse
insulates axon;
Depolarisation only occurs at nodes of Ranvier;
Leads to salatory conduction (action potential ‘jumps’ between nodes of Ranvier);
Impulse / action potential moves FASTER along axon;
Explain how increasing temperature affects conductance of an impulse
More kinetic energy;
Faster rate of diffusion of sodium and potassium ions DOWN electronchemical gradient;
Faster rate of diffusion of sodium ions within axon;
Impulse / action potential moves FASTER along axon
Explain how increasing axon diameter affects conductance of an impulse
- Larger surface area so more cell-surface membrane for voltage-gated sodium/potassium ion channel proteins;
- Less resistance to flow ions within the axon;
Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed.
Explain how this results in slower responses to stimuli (2 marks).
- Less / no saltatory conduction / action potential / impulse unable to ‘jump’ from node to node;
- More depolarisation over length of membranes;
