Module 5: Nervous Transmission Flashcards
When an axon membrane is at resting potential , is the outside or the inside of the neuron more positively charged?
At resting potential , the membrane is said to be …
What is the potential difference of an axon membrane when its at resting potential?
the outside of the membrane
polarised
approxiametly -70mV
Describe the transport of sodium and potassium ions in and out of the axon membrane , what mechanism controls this?
What does this movement result in?
1-Na2+ ions are actively transported out the axon and K+ ions are actively transported into the axon via the sodium potassium pump
2-this results in their being more sodium ions outside the axon than in and more potassium ions in the axon cytoplasm than outside the axon , therefore sodium ions diffuse back into the axon and potassium ones diffuse out
How many Na2+ ions are transported out and how many K+ ions are transported in at a time in the sodium potassium pump ….
3 Na2+
2 K+
Name the type of gradient used when referring to ion movement
electrochemical gradient
Describe the first 2 stages involved in the generation of an action potential
Refer to the state of the neuron and which ion channels are open and closed
1) The neuron is at resting potential
some potassium ion channels are open but sodium VG ion channels are closed
the sodium potassium pump is open
2)The energy of the stimulus triggers the sodium VG ion channels to open so sodium ions diffuse into the axon down their EC gradient
this makes the inside of the neuron less negative-depolarisation
Describe the next 2 stages involved in the generation of an action potential
3)the change in charge causes more sodium ion channels to open so more sodium ions diffuse into the axon
4)when the potential difference of the membrane reaches approxiametly +40mV the sodium ion VG channels close and potassium ion VG channels open
The process of more VG sodium ion channels opening when theres a change in charge is an example of what type of feedback?
positive feedback
Describe the final 2 stages involved in the generation of an action potential
5)potassium ions diffuse out the axon down their EC gradient , this decreases the charge in the axon (inside becomes more negative)-this is repolarisation
6)initially lots of potassium ions diffuse out causing the inside of the axon to be more negative than its resting potential-hyperpolarisation
VG potassium ion channels close and the sodium potassium pump causes sodium to leave the cell and potassium to enter which returns the axon to its resting potential
Why does hyperpolarisation occur?
because the VG potassium ion channels are slow to close
Describe the process of action potential propagation
make 3 points
1-the initial stimulus triggers an action potential in the sensory receptor
2-this causes the first region of the axon membrane to depolarise
3-this depolarisation acts as a stimulus for the depolarisation of the next region
The short period of time after an action potential where the axon can’t be excited again is the …
refractory period
What is the purpose of the refractory period?
2 points
prevents propagation of an action potential backwards along the axon
ensures action potentials don’t overlap and occur as discrete impulses
Why do myelinated neurons transfer impulses much faster then unmyelinated neurons?
make 2 points
What does this result in?
because depolarisation can only occur at the nodes of Ranvier
the sodium ions then pass through the membrane here causing longer localised circuits to arise between the nodes
results in the action potential ‘jumping’ from one node to the next
The two other factors that affect the speed an action potential travels are…
axon diameter and temperature
How does axon diameter affect the speed of action potential travel?
it increases speed as there is less resistance to the flow of ions in the cytoplasm
