CNS and Response exam questions Flashcards
Why must organisms respond to changes in their environment
in order to survive
What does an organism need to respond to changes
requires detection
What is detection
stimulus is detected by receptor cell
Why is ATP required to maintain the resting potential
The sodium-potassium pump requires ATP for the active transport of sodium ions out of the axon and potassium ions into the axon
Explain how the refractory period ensures the unidirectional flow of a nervous impulse in a neurone
-Sodium channels are closed during hyperpolarisation
-depolarisation cannot occur in that region again until the resting potential has been restored
-As a result, the membrane can only be depolarised ahead of an action potential
Three features of a neurone that influence the speed of conduction
-Diameter of the axon
-Myelination OR the presence of Schwann cells
-Temperature
Why can axons with a wider diameter can transmit an action potential more quickly
-the axon membrane has a greater surface area (for the diffusion of ions) SO the rate of diffusion is faster
-a faster rate of depolarisation / action potential propagation
-a greater volume of cytoplasm containing ions SO there is less electrical resistance
-the action potential can move through to the next section of the axon more quickly
How is a nerve impulse generated in the postsynaptic neurone
1) The neurotransmitter diffuses across the synaptic cleft
2) then binds to receptors on the postsynaptic membrane
3) Causing Na+ channel proteins to open
4) Na+ move into the postsynaptic neurone
5) causes depolarisation of the membrane
6) Leading to an action potential in the postsynaptic neurone if the threshold value is achieved
When is the refractory period
Short time after action potential has been generated in axon membrane
What happens to sodium ion channel proteins in refractory period
Na+ channels cant open and depolarise, so ap travels in only one direction, producing discrete impulse limiting frequency of impulses
What happens to potassium ions in refractory period
axon membrane open
diffusion of potassium ions out of the axon
down their concentration gradient
What effect do the sodium and potassium ions have
gradually returns the potential difference to normal (repolarisation)
Describe whole refractory period process before and after summarisation
1) stimulus occurs
2) depolarisation as NA+ ions enter, voltage increases action potential occurs
3) Repolarisation as K+ exit, voltage decreases
4) As K+ exit refractory period occurs, hyperpolarisation
5) Resting state
Why is the refractory period important
-ensures that action potentials are discrete events, stopping them from merging into one another
-ensures that ‘new’ action potentials are generated ahead
-impulse can only travel in one direction
-minimum time between action potentials occurring at any one place along a neurone
-length of the refractory period is key in determining the maximum frequency
What is the refractory period definition?
period of hyperpolarisation in an action potential
How does the unmyelinated neurone change the speed of impulse
myelin sheath is formed from Schwann cells
depolarisation cannot occur where the mylein sheath is as the myelin sheath stops the diffusion of sodium ions and potassium ions
action potentials ‘jump’ from one node to the next (saltatory conduction)
So impulse travels faster
How does the diameter of the axon change the speed of impulse
Thicker axons have an axon membrane with a greater surface area over which the diffusion of ions can occur
increases the rate at which depolarisation and action potentials
AND
greater volume of cytoplasm reduces their electrical resistance so that an action potential can push into the next section faster
Why can damage to the myelin sheaths of neurones can lead to problems controlling the
contraction of muscles
Action potentials travel more slowly
So delay in muscle contraction
OR
Action potentials ‘leak’ to adjacent neurones
So wrong muscle (fibres) contract
When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction
Prevents influx of calcium ions
vesicles don’t release
neurotransmitter
Neurotransmitter does not diffuse across synapse
No action potential preventing influx of sodium ions
Explain how the resting potential of –70 mV is maintained in the sensory neurone
when no pressure is applied.
Membrane more permeable to potassium ions and less permeable to sodium
ions
Sodium ions actively transported / pumped out and potassium ions in
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.
impulse unable to
‘jump’ from node to node
More depolarisation over length of membranes
Why does a shoot grow to one side (other than light)
Tip produces IAA
IAA diffuses into shoot
(More) elongation of cells on one side (than other)
