5.3 - Neuronal Communication Flashcards
1
Q
How receptors respond to pressure
A
- receptors distorted
- Sodium ion channels open
- Sodium ions enter
- And depolarisation the membrane
- Is the threshold potential is met or exceeded
- And action potential is generated
2
Q
Events in the neurone as an action potential is generated -
Resting potential
A
- about -60mV –> -70mV (-65mV on graph)
- the membrane is polarised
- when neurone is at rest (no stimulus)
- sodium/potassium ion pumps actively pump 3 sodium ions out for every 2 potassium ions in to
maintain resting potential - K ions ‘leak’ (diffuse) out of neurone
3
Q
Events in the neurone as an action potential is generated - Depolarisation
A
- Voltage gated sodium ion channels open and sodium ions diffuse into axon
- This is an example of positive feedback – the presence of sodium ions cause the opening of
more voltage gated sodium ion channels and so the influx of more sodium ions - Potential difference increases from -65mV to 40mV
- the membrane is depolarised
- at 40mV, the sodium ion channels close (an action potential is transmitted along axon)
4
Q
Events in the neurone as an action potential is generated -
Repolarisation
A
- Voltage gated potassium ion channels open
- Potassium diffuse out of axon
- This is an example of positive feedback – this causes more potassium ion channels to open and
so more potassium ions to diffuse out - The membrane is depolarised
- The membrane becomes hyper polarised
- Potential difference falls from 40mV to -70mV
5
Q
All or nothing response
A
If the stimulus is not strong enough the threshold value will not be reached and there will be
6
Q
Transmission of action potential along neurone (myelinated)
A
- Distortion of receptors produces a generator potential
- Sodium ions diffuse into axon…
- Causes depolarisation of the membrane
- If the depolarisation exceeds the threshold value…
- More voltage gated sodium ion channels will open causing more sodium ions to diffuse in…
- And an action potential will be produced and transmitted down the axon.
- Sodium ions diffuse along axon…
- Creating local currents
- Due to the myelin sheath, the action potential moves by salatatory conduction…
- Where the action potential ‘jumps’ from one node of Ranvier to the next
- The presence of sodium ions cause voltage gated sodium ion channels to open so more sodium
ions diffuse into the axon – positive feedback - The transmission can only move in one direction…
- Due to the refractory period where voltage gated sodium ion channels behind the action
potential to allow resting potential to be restored
7
Q
Difference between structures of motor neurone and sensory neurones
A
- Sensory neurone cell body not in CNS, motor neurone’s is
- Cell body of sensory neurone in middle of neurone, motor neurone’s is at the end
- The dendrites of the sensory neurone are at the end of the axon but they connect directly to
the cell body in the motor neurone - Sensory neurone has a shorter axon then the motor neurone
- Dendron present in sensory neurone but no Dendron in motor neurone
8
Q
Difference between functions of motor neurone and sensory neurones
A
- Sensory neurone carries action potential from receptor to relay neurone in CNS
- Motor neurone carries action potential from relay neurone in CNS to effector (muscle/gland)
9
Q
Structure of myelin sheath
A
- Consists of Schwann cells wrapped around axon
- Except at the nodes of Ranvier where there are gaps in the myelination
10
Q
Function of myelin sheath
A
- Acts as an electrical insulator
- Myelinated neurones conduction action potentials faster than non-myelinated neurones
- Depolarisation can only occur where sodium ion channels are present
- There are no voltage gated sodium ion channels in the myelinated regions so ion movement
can only take place at the nodes - Causes salutatory conduction where the action potential jumps from one node of Ranvier to
the next - Which means longer local currents (than in non-myelinated neurones)
11
Q
Refractory period and its importance
A
- Follows an action potential
- During which time an action potential cannot be generated (absolute refractory period)
- Voltage gated sodium ion channels are closed
- Allows resting potential to be restored in axon
- Ensures impulses are separated
- Ensures impulses on travel in one direction along axon
12
Q
What happens at the synapse
A
- Action potential arrives at pre synaptic knob and causes voltage gated calcium ion channels to
open - Calcium ions diffuse into presynaptic knob
- Calcium ions causes vesicles containing acetylcholine (neurotransmitter) to move towards and
fuse with the presynaptic membrane - Acetylcholine is released into synaptic cleft by exocytosis
- Acetylcholine diffuses across synaptic cleft
- Acetylcholine binds to receptors on sodium ion channels on the post synaptic membrane
- Sodium ions diffuse into post synaptic membrane and generate new action potential
- Acetylcholine is hydrolysed by acetylcholinesterase
13
Q
Role of acetylecholinesterase
A
- Hydrolyses acetylecholine into acetic acid and choline
- Unblocks receptors and so allows sodium ion channels to close on post synaptic knob
- Stops continuous production of action potentials in post synaptic neurone
- Allows repolarisation of post synaptic membrane
14
Q
Role of synapse
A
- Allows for communication between neurones
- Ensures transmission between neurones is only in one direction
*Vesicles containing acetylcholine are only found in presynaptic knob
*Receptors for acetylcholine are only found on postsynaptic knob - Allows convergence – impulses from more than one neurone to pass into a single neurone and
allows divergence – impulses from a single neurone to be passed to more than one neurone - Filters found low level stimuli
- Prevents overstimulation and fatigue of neurone
- Allows many low level stimuli to be amplified
