ORTCITIAEE: Nerve impulses Flashcards
Define neurones:
Specialised animal cells that pass on nerve impulses.
Name the basic components (structure) of a myelinated motor neurone:
- Dendrites
- Cell body (containing nucleus)
- Axon
- Axon terminal
- Myelin sheath
- Nodes of Ranvier
What cells are is the myelin sheath made from?
Schwann cells
To get a response from an effector, the receptor first detects a ______.
Stimulus
In an axon a nerve impulse is a moving area of ______.
Charge
Nerve impulses always travel away from a receptor and to an ______.
effector
What are the two main ions involved in establishing a resting potential?
- Sodium ions
- Potassium ions
Sodium and potassium ions can be found inside and outside of an _____- with the majority of them being found on the ____ of it.
Axon
Outside
The outside of a neurone’s axon is generally more ______ charged than inside the axon.
positively
What causes the difference in charge between the outside and inside of a neurone?
Concentration of sodium and potassium ions
There is usually a higher concentration of sodium ions _____ the axon, and potassium ions _____ the axon.
Outside
Inside
What is a nerve impulse?
A moving area of charge
By what process do sodium and potassium ions move across membranes?
Facilitated diffusion
What are ion channels?
Channel proteins that specifically transport ions.
Sodium and potassium ions are transported by facilitated diffusion via ____ channels.
Ion
An ion channel that transports sodium is called a ______ channel.
Sodium
An ion channel that transports potassium is called a ______ channel.
Potassium
What is an electrochemical gradient?
The difference in concentration and charge across the membrane.
overtime why does the inside of the axon become more positive?
sodium ions move down their electrochemical gradient into the inside of the axon.
Overtime, the charge of the outside of the axon changes. It is first positive and then it becomes negative and then positive again- why?
- Positive at first due to higher concentration of sodium ions outside of axon
- Then becomes negative as sodium ions are transported from the outside of the axon to the inside of the axon via sodium channels + facilitated diffusion
- Becomes positive again as potassium ions pre-existing inside the axon repel the sodium ions and are transported outside the axon via potassium channels + facilitated diffusion.
A ___-______ protein can transport BOTH sodium and potassium ions.
Co-transporter.
A co-transporter protein/sodium-potassium pump binds to 3 sodium ions and one molecule of ____.
ATP
Co-transporter proteins/sodium-potassium pump bind to one molecule of ATP. What does this do?
Allows for ATP to be hydrolysed to produce on molecule of ADP and an inorganic phosphate ion.
When a phosphate ion and three sodium ions are all bonded to the carrier protein, they trigger a series of reactions that cause the sodium-potassium pump to change ______.
shape
The sodium-potassium pump changes shape as it is triggered by the binding of 3 sodium ions and a Pi. Where does the energy come from for it to be able to change shape?
The breaking of the bond between the Pi and ADP
Yes- it is ADP not ATP. It is the actual bond separation of the Pi from the ADP that provides the energy.
The sodium-potassium pump changes shape as it is triggered by 3 sodium ions and ATP. What does the change in shape do?
Provides 2 binding sites for potassium
When the phosphate ion is released from the sodium-potassium pump, the sodium-potassium pump reverts to its ______ shape.
original
What happens when the Pi molecule is removed from the sodium-potassium pump?
The sodium-potassium pump reverts back to its original shape- ‘dropping’ the potassium ions on the other side (inside the axon)
What is the co-transporter protein actually called?
Sodium-potassium pump
The sodium-potassium pump moves ___ potassium ions into the axon, and ___ sodium ions out of the axon.
2
3
The sodium-potassium pump maintains a more positive charge ______ the axon, and a less positive charge ______ the axon
Outside
Inside
The sodium-potassium pump allows for ions to be transported _____ their concentration gradient.
Against
(an example of active transport)
What is the overall purpose of the sodium-potassium pump?
Maintain a more positive charge outside of the axon, and a less positive charge inside the axon
Inside an axon a nerve impulse appears as a ____ charge.
Positive
What is the resting potential?
When a neurone maintains a less positive charge inside of an axon, maintained by the sodium-potassium pump.
What does it mean if the neurone is ‘at rest’?
It is not exposed to a stimulus.
Why is the establishment of a resting potential important for neurones?
It allows for neurones to respond to any nerve impulses arriving at its axon.
A nerve impulse causes the inside of the axon to become ____ positively charged than the outside of the axon.
More
What is a voltage-gated ion channel?
An ion channel that opens in response to the positive charge of a nerve impulse.
When a nerve impulse appears next to a voltage-gated ion channel, it causes the inside of the axon to become _____ positively charged.
more
Explain the establishment of an action potential:
- The outside of an axon is more positive than the inside because there are more sodium and potassium ions outside.
- A nerve impulse will enter the inside of an axon and make it slightly more positively charged.
- This causes some voltage-gated sodium channels to open, allowing for some sodium ions to diffuse into the inside of the axon.
- The movement of sodium ions makes the inside even more positive, allowing for even more voltage-gated sodium channels to open, and more sodium ions to diffuse inside the axon.
- The inside of the axon will become more positively charged than outside the axon
- A high number of sodium ions inside the axon will allow it to reach its action potential.
When is an action potential reached?
When the inside of an axon has reached its maximum positive charge.
What is hyperpolarisation?
when the inside of an axon reaches its minimum positive charge
How is a resting potential REestablished?
- Voltage-gated sodium channels close which reduces the number of sodium ions diffusing into the axon.
- Voltage-gated potassium channels open, allowing potassium ions to diffuse out of the axon, causing the overall charge inside the axon to become less positive.
- The voltage-gated potassium channels remain open, allowing even more potassium ions to diffuse out of the axon, causing the overall charge inside of the axon to become temporarily even less positive (hyperpolarisation).
- Sodium ions diffuse into the axon through sodium ion channels down their electrochemical gradient.
- The sodium-potassium pump restores the electrochemical gradients of sodium and potassium ions by actively transporting 3 sodium ions out of the axon, and 2 potassium ions into the axon.
- The inside of the axon is less positive than outside of the axon.
