5.1.3 - NEURONAL COMMUNICATION Flashcards
1
Q
What are the THREE main types of neurones?
A
- Sensory
- Motor
- Relay (Intermediate)
2
Q
What is a transducer?
A
Something that converts one form of energy into another
E.g. pacinian corpuscle converts pressure into electrical impulses
3
Q
What common features do the three neurones have?
A
- Cell body
- Dendrons
- Axons
4
Q
What are dendrons?
A
Carry the action potentials to surrounding cells
5
Q
What are axons?
A
Conductive, long fibres that carry the nervous impulse along the motor neurone
6
Q
What is the myelin sheath?
A
- A lipid wrapped around the axon made from Schwann cells
- Insulated
7
Q
What are the gaps between the myelin sheath called?
A
Nodes of Ranvier
8
Q
What is saltatory conduction>
A
- Action potential jumps from node to node
^— means action potential travels along the axon faster as it doesn’t have to generate an action potential along the entire length
9
Q
Describe the role of the sensory neurone
A
Carry electrical impulses from the sensory receptor cell to the relay neurone
10
Q
Describe the structure of the sensory neurone
A
- Has a long dendron which carries the impulse from teh sensory receptor cell to the cell body of the neuron
- An axon to carry the impulse from the cell body to the next neurone
11
Q
Describe the role of the relay neurone
A
- Carries impulses between the sensory + motor neurones
12
Q
Describe the structure of the relay neurone
A
- Multiple short axons + dendrons
13
Q
Describe the role of the motor neurone
A
- Carries the impulse from a relay or sensory neurones to the effector (muscle of gland)
14
Q
Describe the structure of the motor neurone
A
- One long axons
- Multiple short dendrites
15
Q
List the three types of sensory receptor
A
- Photoreceptors (light)
- Thermoreceptors (skin)
- Mechanoreceptors (pressure)
16
Q
Give an example of a photoreceptor
A
- Rods
- Cone cells
17
Q
Give an example of a thermoreceptor
A
Skin
18
Q
Give an example of a mechanoreceptor
A
Pacinian corpuscle
19
Q
What is the pacinian corpuscle?
A
Pressure receptor located deep in skin, mainly fingers + feet
20
Q
What happens to the pacinian corpuscle when pressure is applied?
A
- Stretch-mediated sodium channels in the membranes open and allow sodium to enter the sensory neurones only when they are stretched + deformed
^— when this occurs, it deforms the neurone plasma membrane, stretches and widens the sodium channels so sodium diffuses in which leads the establishment of a generator potential
21
Q
What is a resting potential?
A
- Has a value of around -65mV to -70mV
22
Q
Describe how a resting potential is produced
A
- In either side of the members are sodium ions move + potassium ions
- Sodium-potassium pump actively transports sodium ions OUT of the axon and potassium ions INTO the axon
^— higher conc. of potassium ions inside than outside membrane
^— higher conc. of sodium ions outside than inside membrane - For every 3 sodium ions transported out, only 2 potassium ions are transported in
^—therefore, number of positive ions outside the membrane is greater than inside - establishes membrane potential - Here is an electrochemical gradient
- Ion channels in the membrane switch between open and closed (SODIUM MAINLY CLOSED - low diffusion rate of sodium into axon | POTASSIUM MAINLY OPEN - high diffusion rate of potassium out of axon)
^— therefore inside of membrane more negative than outside
MORE POSITIVELY CHARGED IONS OUTSIDE THAN INSIDE AXON - PRODUCING MEMBRANE POTENTIAL
23
Q
What is a generator potential?
A
The nervous impulse the pacinian corpuscle produces in response to pressure
24
Q
Describe the structure of the pacinian corpuscle
A
- In the centre, the end of the sensory neurone
^— surrounded by many layers of connective tissue with a layer of gel between each
25
What does it mean if the membrane of a neurone is polarised?
The inside of the membrane is negative with respect to the outside
(RESTING POTENTIAL)
26
Explain how the pacinian corpuscle generates a nerve impulse in response to pressure
- Sodium channels in the corpuscle membrane are stretch-mediates sodium channels (normally too narrow for sodium ions to diffuse through)
- When pressure is applied, shape of the corpuscle changes, causing the membrane to stretch
^— causes the stretch-mediated sodium channels to widen
- Sodium ions diffuse through the channels into the neurone
^— INTERIOR BECOMES POSITIVELY CHARGED (DEPOLARISED)
^— the effect of this is called the generator potential —> causes a wave of depolarisation to pass down the sensory neurone to the CNS (ACTION POTENTIAL)
27
What is the action potential?
How a nerve impulse is transmitted
28
What are voltage-gated ion channels?
Only open when the membrane potential reaches a certain value
29
What are the stages a membrane enters as an action potential travels?
- Resting potential
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Resting potential
30
Describe what happens during detection of a stimulus (neurones)
- Receptor detects a stimulus
- Energy of the stimulus triggers voltage-gated sodium channels to open
^— sodium ions rapidly diffuse into the axon down their electrochemical gradient
- Inside of axon becomes less negative
31
Describe what happens during depolarisation of an axon
- Inside of axon is less negative
- Change in voltage bow triggers more voltage-gated sodium channels to open
^— allows more sodium ions to diffuse into the axon (POSITIVE FEEDBACK)
- Potential of +40mV
- Voltage-gated sodium channels close + voltage-gated potassium ion channels open
- Sodium ions stop diffusing into the axon
32
Describe what happens during repolarisation of an axon
- Potassium ions diffuse out of the axon down electrochemical gradient
^— meanwhile inside of axon switches from positive to negative
33
Describe what happens during hyperpolarisation of an axon
- Because large amount of potassium ions diffuse out of the axon, the inside become more negative than the resting potential
- Voltage-gated potassium ion channels close
34
Describe how the resting potential is restored after hyperpolarisation
- Sodium-potassium pump pumps sodium ions out of the axon + potassium ions into the axon
35
What is the all or nothing principle?
- Action potential is only generated if the stimulus is greater than a certain threshold
^— If below, no action potential is generated
- if the stimulus is greater than the threshold, action potential generated
- Size of the action potential does not depend on the strength of the stimulus (weaker stimulus will generate same potential as a stronger one)
^— stronger stimulus produces a greater frequency of action potentials than a weaker stimulus
36
describe how an action potential is transmitted along a non-myelinated axon
- Resting state: more sodium ions outside membrane than inside | higher conc. of potassium ions inside than inside | Inside membrane as a negative charge relative to the outside of the membrane
- A stimulus causes the beginning of the membrane to depolarise, causing voltage-gated sodium ion channels to open + allow sodium channels inside axon down electrochemical gradient
- Sodium ions move sideways to next region, attracted to negative charge (LOCALISED ELECTRICAL CIRCUIT)
^— causes voltage-gated sodium ion channels to open in second region —> sodium ions diffuse in (depolarises)
- In first region, voltage-gated sodium ion channels close + voltage-gated potassium ion channels open
- Potassium ions diffuse out of axon in first region (A) - beginning to REPOLARISE
- Localised electrical circuits form between region B and C
^— action potential continues to propagate down the axon
- Meanwhile, region A is negative inside + positive outside | sodium ions actively transported out of axon in region A by S-P pump (now back to RESTING POTENTIAL)
- Wave of depolarisation down axon, + previously depolarised areas have to repolarise
37
What is the refractory period?
Once a region of the membrane has transmitted an action potential, there is a short period where it cannot transmit another action potential
38
Why is there a refractory period?
1. After a wave of depolarisation, the membrane has to repolarise (reestablish the electrochemical gradient for sodium + potassium ions)
2. Once voltage-gated sodium ion channels have closed, they cannot open again for a short period of time
39
Give 3 reasons why the refractory period is important
- Because the axon membrane enters the refractory period once it transmits an action potential —> ensures that the potential can only travel in one direction
- this period means that a. potentials are clearly separated from each other and cannot overlap
- Time delay between a. potentials limits the number of them that can be transmitted during a time period (creates a maximum frequency of action potentials in all-or-nothing principle - max stimulus strength)
40
Describe the process of saltatory conduction
- e.g. stimulus triggers depolarisation of left part of axon
^— voltage-gated sodium ions actively channels open in the membrane at the first node (of Ranvier)
- Sodium ions diffuse into axon down electrochemical gradient at first node, depolarisation axon at node a and making it positive
^— positive sodium ions attracted sideways towards negative charges at second node (LOCALISED ELECTRICAL CIRCUIT between 1st & 2nd node)
^— triggers voltage-gated sodium ion channels at 2nd node to open + sodium ions diffuse into axon (DEPOLARISATION)
- LOCALISED ELECTRICAL CIRCUIT forms between 2nd & 3rd node (3rd node depolarises)
41
Give two advantages of saltatory conduction
- Transmission is much faster
- Because depolarisation only takes place @ Nodes of Ranvier, only these regions need to be repolarised (less ATP required to repolarise a myelinated axon at voltage-gated sodium ion channels)
42
Describe the structure of the synapse
- In synaptic knob, contains large number of vesicles contains neurotransmitters
- Synaptic cleft (space between presynaptic and postsynaptic neurone)
- Synaptic knob (end of action potential) - contains mitochondria + endoplasmic reticulum to produce neurotransmitter
43
What is a cholinergic synapse?
- An excitatory synapse - transport of neurotransmitter acetylcholine
44
What is an excitatory synapse?
- Triggers an action potential in the postsynaptic neurone
45
What is an inhibitory synapse?
- Prevents an action potential in the postsynaptic neurone
46
Describe what happens during synaptic transmission
- Action potential arrives at the presynaptic neurone - triggers voltage-gated calcium ions actively channels channels to open
- Calcium ions diffuse into synaptic knob, triggers vesicles to fuse with the presynaptic membrane
^— acetylcholine released into synaptic cleft + diffuse across cleft, binding with sodium ions actively channels channels on postsynaptic membrane
^— triggers sodium ion channels to open
- Sodium ions diffuse into postsynaptic neurone, triggering action potentials in postsynaptic neurone
- if acetylcholine remains attached to channels, could trigger multiple action potentials
- Enzyme acetylcholinesterase hydrolyses acetylcholine to choline + ethanoic acid
^— choline + ethanoic acid reenter presynaptic neurone where energy from ATP turns them to acetylcholine
47
Describe the functions of synapses
- Synapses ensure that transmission takes place in one direction only
^— neurotransmitter can only be released from PRESYNAPTIC membrane + neurotransmitter receptors are only found on POSTSYNAPTIC neurone (UNIDIRECTIONAL)
- One neurone can form synapses with a large number of other neurones
^— likewise, several different neurones can form synapses with one neurone
48
Describe temporal summation
- Action potential arrives at neurone A and triggers the release of a neurotransmitter, but insufficient neurotransmitter was released for neurone B to reach the threshold to trigger an action potential
^— neurotransmitter is now broken down + recycled back in presynaptic neurone
- Another action potential arrives at neurone A and the neurotransmitter is released, however another a. potential arrives and more neurotransmitter is released
^— conc. in synaptic cleft is enough to trigger an action potential in neurone B
- Effects of multiple action potentials acting over time can add together
- only works if incoming a. potentials are close together in time
49
Describe spatial summation
- Action potentials arrive at two presynaptic neurones that have synapses with one postsynaptic neurone
^— individually, neither releases a bough neurotransmitter to trigger an action potential on the postsynaptic neurone
- Here, the effects of the two neurones add together
^— combined effect of the neurotransmitter released from both separate neurones reach the threshold in the shared neurone and trigger an action potential
50
Describe the synaptic transmission of inhibitory synapses
- E.g. GABA (in the brain) is released into the synaptic cleft
^— diffuses across the synaptic cleft + binds with chloride ion channels on the postsynaptic membrane
^— causes chloride ion channels to open + chloride ions diffuse into postsynaptic neurone
- Potassium ion channels also triggered to open and diffuse OUT of postsynaptic neurone
^— hyperpolarisation interior of postsynaptic neurone (MORE NEGATIVE THAN RESTING POTENTIAL) - -80mV
LESS LIKELY ACTION POTENTIAL IS GENERATED
