5.3: Neuronal communication (new) Flashcards
1
Q
What is resting potential?
A
State at which the cell can be stimulated
-60mV
2
Q
What happens in resting potential?
4 steps
A
- Na/K pump moves 3Na ions out and 2K ions in by ATP
- Sodium ion voltage gated channels are closed to prevent re-entry of the Na
- Potassium ion channels are opened to show K ions to leave the cell by facilitated diffusion
- Permenant negative ions stay inside the cell
3
Q
What is action potential?
A
State at which the membrane is stimulated
4
Q
What are the stages that make up action potential
A
- Depolarisation
- Repolarisation
- Hyperpolarisation
5
Q
What happens at depolarisation?
5 steps
A
- High concentration of Na due to resting potential
- The sodium channels open and Na ions enter
- Membrane is depolarised to -50mV (threshold potential)
- 2nd sodium channels open and there is a big influx of Na ions
- Happens until it reaches +40mV
6
Q
What happens at repolarisation?
3 steps
A
- Na/K pumps reopen and 3Na leave and 2K ions enter
- Na channels close at 40mV
- Voltage gated K channels open at 40mV
7
Q
What is hyperpolarisation?
A
Potential difference is lower than resting potental
8
Q
What makes up a neuron?
A
- Dendron - sends impulse to cell body
- Cell body - releases neurotransmitters
- Axon - sends impulse away from cell body
- Myelin sheath - layers of plasma membranes (lipids and glycolipids) and cholesterol
8
Q
What is the role of the myelin sheath?
A
Acts as an insulating layer
- Speeds up nerve impulse transmission (saltatory conduction) at nodes of Ranvier
9
Q
What are sensory receptors?
A
- Specific to one type of stimulus
- Acts as transducers - turn stimulus into electrical impulse (generator potential)
10
Q
What are the four types of sensory receptors?
A
- Mechanoreceptors - sensitive towards pressure and movement
- Chemoreceptors - senses chemicals (smell and taste)
- Thermoreceptors - senses heat and temperature changes
- Photoreceptors - sense light
11
Q
What makes up the pacinian corpsucle?
A
Connective tissue
- Helps transmit vibrations better
Sensory neurones
Stretch mediated sodium ion channels
- Sensitive to changes in physical structure
- At normal resting state they are closed
12
Q
What happens at the pacinian corpsucle?
4 steps
A
- At normal resting state, stretch mediated Na+ channels are closed, maintaining resting potential, with higher Na+ concentration outside the neurone
- When pressure is applied, the corpsucle changes shape, causing the neurone membrane to stretch as well, which opens the stretch mediated Na+ channels
- Na+ diffuse into sensory neurone through the channels down an electrochemical gradient
- This depolarises the membrane, initiates generator potential, which leads to an action potential to be propgated down the neurone
13
Q
What is involved in the synapse?
A
- Voltage gated Ca2+ channels
- Calcium ions
- Synaptic vesicles
- ACh
- Na+
- Choline
- Acetate
14
Q
What are the steps involved in cholegernic synapses?
10
A
- The action potential arrives at the presynaptic neurone, causing the voltage gated calcium ion channels to open
- Calcium ions diffuse into the presynaptic neurone, down the electrochemical gradient
- Calcium ions cause the synaptic vesicles with ACh to move and fuse with the presynaptic membrane
- ACh is released into the synaptic cleft by exocytosis and diffuses across the synapse towards the postsynaptic neurone
- ACh binds to receptor sites on postsynaptic Na+ channels, causing them to open
- Na+ diffuse into the postsynaptic neurone, down the electrochemical gradient causing the depolarisation of postsynaptic membrane and creating a generator potential
- If sufficent GP combine then potential across postsynaptic membrane reaches threshold potential and a new AP is created
- Na+ channels close, preventing continuous AP generation
- Acetylcholinesterase (enzyme) hydrolyses acetycholine to ethanoic acids and choline - synapse stops producing action potentials
- ATP from mitochondria in presynaptic membrane can combine them back to ACh
15
Q
What is the role of synapse?
A
- Unidirectional transmission
- Can converge
- Can diverge
16
Q
What is summation?
A
The effect of the build up of neurotransmitters in the synapse
- A new action potential can only be triggered if the neurotransmitters have built up to a threshold level
17
Q
What is spatial summation?
A
More than one presynaptic neurone release neurotransmitters to trigger new action potential in one post synaptic neurone
18
Q
What is temporal summation?
A
Summation resulted from several action potential in the same presynaptic neurone
19
Q
How is an action potential generated?
all stages 10 steps
A
- Energy from stimulus triggers voltage gated sodium ion channels to open
- Sodium now rapdily diffuse into the axon down their electrochemical gradient which makes the inside of the axon less negative
- Change in voltage causes more voltage gated ion channels to open and more sodium diffuse into the axon
- Membrane depolarises and the inside reaches potential of +40mV
- Triggers voltage gated sodium channels to close and potassium channels to open
- Sodium ions stop diffusing into the axon and potassium ions now diffuse out down electrochemical gradient
- Repolarisation: inside of axon switches from positive to negative
- Hyperpolarisation: large amount diffuse out, inside becomes more negative than resting potential
- Voltage gated potassium channels close
- Resting potential is restarted as potassium/sodium pump pumps sodium out of and potassium into the axon
20
Q
What is generator potential?
A
Causes a wave of depolarisation to pass down the sensory neurone to the CNS
This wave of depolarisation is now an action potential
21
Q
What is the all or nothing principle?
A
- The threshold phenomenon - Once the threshold potential is reached, an action potential is always triggered, regardless of the stimulus’ strength.
- No partial response - Without reaching the threshold potential, no action potential is initiated.
- Action potentials are always the same size - A stronger stimulus doesn’t increase the size of the action potential, but it does increase the frequency of action potentials generated.
22
Q
What is the tranmission of an action potential along a non-myleinated axon?
6 steps
A
- Opening of Na+ channels causes local depolarisation, allowing positive ions to spread sideways
- Adjacent voltage gated Na+ channels open in response to this change
- This action leads to the depolarisation of nearby membrane areas
- As each patch of membrane activates the next, an advancing wave is formed
- Areas of the membrane that have just experienced depolarisation are in the refactory period and repolarise (K+ exits the axon and Na+ channels are closed)
- This ensures that the wave moves in one direction, preventing backflow of the nerve impulse
23
Q
What is the refactory period?
A
Neurone’s membrane cannot generate another action potential, this is because sodium ion channels remain closed during repolarisation
24
What is the role of the refactory period?
* Ensures action potential do not overlap
* Limiting the frequency at which impulses are transmitted
* Guaranteeing that impulses travel in only one direction
25
What happens in saltatory conduction?
| 5 steps
1. Voltage gated Na+ channels now open in the membrane at node A so Na+ diffuse down the electrochemical gradient
2. This depolarises the axon at node A
3. Localised electrical circuit is created as Na+ are attached sideways towards the negative charges at node B
4. Triggers voltage gated Na+ channels at node B to open and Na+ diffuse which depolarises node B
5. Localised electrical circuits form between node C and B which causes C to depolarises
26
What are advantages of saltatory conduction?
Only nodes need to be repolarised
* Requires ATP for the action of K+/Na+ pump
* Less ATP is required to repolarise a myelinated axon
Increases the speed of transmission of an action potential
27
What increases the speed of transmission in saltatory conduction?
Speed of transmission is greater in axons with a wider diameter
* Less resistant to ion flow within the cytoplasm
Warmer temperatures also increase the speed of transmission
* Ions diffuse faster at warmer temperatures
* Only applies to below 40 degreees celsius
* Proteins denature (ion channels and sodium/potassium pump)
28
What is GABA?
Inhibitory neurotransmitter that is found in the brain
29
What happens in a inhibitory synapse?
| 5 steps
1. When an action potential arrives at a presynaptic neurone, GABA is released into the synaptic cleft
2. It diffuses across and binds with Cl- channels on the postsynaptic membrane
3. Cl- channels open and it diffuses into the postsynaptic neurone
4. Potassium channels are also triggered to open and potassium diffuses out of the postsynaptic neurone
5. This hyperpolarises the interior of the postsynaptic membrane
30
What does a hyperpolarisation in the inhibitory synapse do?
Makes it less likely that an action potential will be generated in the postsynaptic neurone
31
What is EPSP?
Excitatory post-synaptic potential
* Causes summation
* Takes several to reach threshold potential and cause action potential
32
What is IPSP?
Inhibitory post synaptic membrane
* Can reduce the effect of summation and prevent action potential in post synaptic membrane
* Can prevent EPSP from producing an action potential
* Makes it more negative
33
What is divergence?
Presynaptic neurone may diverge
* Allows one action potential to be transmitted to several parts of the nervous system
34
What is convergence?
Presynaptic neurone may converge
* Allows action potential of different parts of the nervous system to contribute to generating an action potential in one post synaptic neurone
35
What is temporal summation - filtering?
Synapses filter out unwanted low level signals
* Low level stimulus causes action potential that cannot properly pass across synapse
36
What is temporal summation - summation?
Low level action potentials amplified by summation
* If low level stimulus is persistent this generates several successive action potentials in presynaptic neurone
37
What is habituation?
Nervous system no longer responds to the stimulus
May also help to avoid overstimulation of an effector
