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B5 > Neural communication > Flashcards

Neural communication Flashcards

1
Q

What are sensory receptors?

A
  • specialised cells that detect stimuli and generate an action potential.
  • most are transducers - convert one form of energy to another (electrical impulse).
  • transducers adapted to detect a change in a particular form of energy.
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2
Q

What are Pacinian corpuscles?

A
  • pressure receptors that detect changes in pressure on the skin.
  • rings of connective tissue wrapped around the end of a nerve cell.
  • rings deformed when skin is under pressure which push against nerve ending.
  • when pressure is constant they stop responding.
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3
Q

How do Pacinian corpuscles work?

A
  • Na/K pumps actively pump 3Na+ out for every 2K+ in, conc gradient created across membrane.
  • cell is -vely charged inside compared to outside.
  • membrane is more permeable to K+, some leak out. Few Na+ leak in.
  • Na+ and K+ channels are voltage gated
  • when membrane is deformed by changing pressure, Na channels open, allowing Na+ to diffuse into cell producing a generator potential.
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4
Q

How are nerve impulses generated (in Pacinian corpuscles)?

A

1) cell membrane in polarised when cell is inactive, -vely charged inside compared with outside.
2) Na channels open, Na+ diffuse down their conc gradient into the cell.
3) this movement creates a change in potential difference across the membrane.
4) inside cell becomes less -ve (compared to outside) than usual. this is depolarisation (of cell membrane).
5) change in potential difference across receptor membrane is called a generator potential.
6) small stimuli, few Na channels open. Larger stimulus, more gated channels open.
7) If enough gates open and enough Na+ enter cell, pot diff across cell membrane changes significantly and will initiate an action potential (impulse).

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5
Q

function of sensory neurones

A

carry ac pot from sensory receptor to CNS

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6
Q

function of relay neurones

A

connect sensory and motor neurones

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7
Q

function of motor neurones

A

carry ac pot from CNS to effector (muscle or gland)

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8
Q

structure (specialised features) of neurones

A
  • long so they can carry ac pot over a long distance.
  • many gated Na+, K+ channels in plasma membrane.
  • Na/K pumps use ATP to actively transport 3 Na+ out and 2 K+ in.
  • neurones maintain a pot diff across plasma membrane.
  • cell body contains nucleus, many mitochondria + ribosomes.
  • axon carries impulses away from cell body. Dendron carries impulses to cell body.
  • surrounded by fatty layer (Schwann cells), insulating cell from the electrical activity in other nerve cells nearby.
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9
Q

How are motor neurones different?

A

have their cell body in the CNS and have a long axon that carries ac pot out to the effector.

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10
Q

How are sensory neurones different?

A

have a long dendron carrying ac pot from sensory receptor to cell body (outside CNS). they then have a short axon carrying ac pot into CNS

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11
Q

What are myelinated neurones?

A

neurones wrapped in several layers of membrane and thin cytoplasm from the Schwann cells.

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12
Q

What are non-myelinated neurones?

A

neurones not wrapped in myelin sheath.

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13
Q

Which type of neurone aren’t myelinated?

A
  • those in CNS aren’t.
  • peripheral are
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14
Q

What are the gaps in myelin sheath?

A

nodes of Ranvier

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15
Q

What does the myelin sheath prevent?

A

movement of ions across membrane, leads to saltatory conduction where impulse jumps from one node to the next for faster conduction.

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16
Q

How do non myelinated neurones transmit impulses?

A

as waves

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17
Q

What are the advantages of myelination?

A
  • ac pot transmitted more rapidly
  • faster response to stimuli
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18
Q

Why are faster transmission speeds not important non-myelinated neurones?

A
  • neurones are shorter and carry ac pot over a short distance.
  • Often used is coordinating body functions like breathing, action of digestive system.
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19
Q

What does it mean when a neurone is at rest?

A
  • polarised
  • not transmitting an ac pot
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20
Q

Describe function of neurone at rest

A
  • plasma membrane actively pumping 3Na+ out for every 2K+ in.
  • pot diff across membrane is about -60mV (resting potential).
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21
Q

What’s an action potential?

A

action potential is a brief reversal of the pot diff across membrane causing a peak of +40mV compared to resting pot of -60mV.

22
Q

What’s positive feedback?

A

a mechanism that increases a change, taking it away from the optimum.

23
Q

How is an ac pot self-perpetuating?

A

once it starts at a point on a neurone, it will continue along to the end of neurone.

24
Q

What are the stages in creating an ac pot?

A

1) membrane starts in its resting state - polarised with the inside of cell being -60mV compared to the outside. Higher conc of Na+ outside than inside and higher conc of K+ inside than outside.
2) Na+ channels open and some Na+ diffuse into the cell.
3) membrane depolairses (becomes less -ve) compared to outside and reaches the threshold value of -50mV.
4) +ve feedback causes nearby voltage-gated Na+ channels to open and many Na+ diffuse in. As more enter, cell becomes more +vely charged inside compared to outside.
5) pot diff across plasma membrane reaches +40mV. Inside of cell is +vely charged inside compared with outside.
6) Na+ channels close, K+ open.
7) K+ diffuse out of cell bringing the pot diff back to -ve inside compared with outside (repolarisation).
8) pot diff overshoots slightly, making cell hyperpolarised.
9) the original pot diff is restored so that the cell returns to its resting state.

25
Q

What’s the refractory period?

A
  • After an ac pot, conc of Na+ and K+ are in the wrong places.
  • conc of these must be restored by Na/K ion pumps.
  • impossible to stimulate cell mebrane to reach another ac pot for short time after each ac pot.
  • ensures ac pot are transmitted in one direction only.
26
Q

What are local currents?

A
  • depolarisation causes local currents in cytoplasm of neurone.
  • Na+ move along neurone towards regions where its conc is lower.
  • local currents cause a slight depolarisation of the membrane and cause Na+ channels further along membrane to open (+ve feedback).
27
Q

Steps in formation of local currents + transmission of nerve impulse:

A

1) When an ac pot occurs, Na+ channels open at that point in neurone.
2) Na+ diffuse across membrane down its conc gradient. Conc of Na+ inside neurone rises at the point where the Na+ channels are open.
3) Na+ continue to diffuse sideways along neurone (creates local currents).
4) local currents opens voltage- gated Na+ channels allowing rapid influx of Na+ causing depolarisation (ac pot) further along neurone.
5) direction of ac pot won’t reverse as conc of Na+ behind ac pot is still high.

28
Q

What happens when stimulus is at higher intensity?

A
  • more Na channels are opened in sensory receptor, producing more generator potentials.
  • there are more frequent ac pots in the sensory neurone.
  • more frequent ac pots enter CNS.
  • a higher freq of ac pots means a more intense stimuli.
  • magnitude doesn’t change
29
Q

What’s a neurotransmitter?

A

chemical used as signalling molecule between two neurones in a synapse

30
Q

What’s a cholinergic synapse?

A

synapse that uses acetylcholine as its neurotransmitter

31
Q

What’s a synapse?

A

junction between 2 or more neurones

32
Q

What’s a synaptic cleft?

A

small gap between 2 neurones

33
Q

What’s the pre-synaptic bulb/knob?

A

swelling at the end of a neurone

34
Q

What are the specialised features of the pre-synaptic bulb?

A
  • many mitochondria (for ATP for exocytosis)
  • large amount of smooth ER which package neurotransmitter into vesicles
  • large no of vesicles containing acetylcholine
  • voltage gated Ca2+ channels on plasma membrane
35
Q

specialised features of the post-synaptic membrane

A
  • contain Na+ channels that respond to neurotransmitter
  • receptors specific to Ach on Na channels (complementary).
  • Na+ channel open when Ach binds to receptors
36
Q

How does transmission across synapse happen?

A

1) ac pot arrives at synaptic bulb.
2) voltage gated Ca2+ channels open.
3) Ca2+ diffuse into the synaptic bulb.
4) Ca2+ cause synaptic vesicles to move to and fuse with pre-synaptic membrane.
5) Ach released by exocytosis
6) Ach diffuses across synaptic cleft
7) Ach binds to receptor sites on the Na+ channels in the post-synaptic membrane.
8) Na+ channels open
9) Na+ diffuses across post-synaptic membrane into post-synaptic neurone
10) a generator potential/ excitatory post-synaptic potential (EPSP) is created
11) if sufficient gen pots combine then potential across the post-synaptic membrane reaches the threshold potential.
12) A new ac pot is created in post-synaptic neurone.
- once ac pot is achieved, it will pass down the post-synaptic neurone.

37
Q

Role of acetylcholinesterase

A
  • hydrolyses Ach into ethanoic acid and choline which are recycled by re-entering synaptic bulb by diffusion and are recombined using ATP. Ach stored.
  • transmission signal stopped, synapse doesn’t continue to produce ac pots in post-synaptic neurone.
38
Q

What’s summation?

A
  • occurs when the effect of several EPSPs (excitatory post-synaptic potentials) are added.
  • increases depolarisation of membrane until it reaches the threshold.
39
Q

What’s the post-synaptic neurone responding to neurotransmitter an example of?

A

cell signalling

40
Q

What are the different types of nerve junctions?

A
  • several neurones converging on one neurone.
  • one neurone sending signals to several neurones that diverge to different effectors. May also allow ac pots to be transmitted to parts of the several nervous system, useful in reflex arc.
41
Q

why is it unlikely that a post-synaptic action potential will occur?

A
  • relatively small no of Ach diffusing across cleft produces a small depolarisation (EPSP).
  • Won’t be sufficient to cause an ac pot in post- synaptic neurone.
42
Q

What’s spatial summation?

A

ac pots arriving from different pre-synaptic neurones at one neurone.

43
Q

Why is spatial summation useful?

A

useful where several diff stimuli are warning us of danger

44
Q

How can summation be prevented from producing an ac pot?

A

Inhibitory post-synaptic potentials (IPSP) produced by neurones reduce effect of summation.

45
Q

How is transmission in one direction ensured?

A

only pre-synaptic bulb has vesicles of Ach

46
Q

Why are low level stimuli unlikely to create an ac pot?

A

several Ach vesicles must be released to create ac pot in post-synaptic neurone.

47
Q

How are low level stimuli amplified?

A
  • by summation.
  • if low level stimulus is persistent, several successive ac pots generated in pre-synaptic neurone.
  • release of many Ach vesicles over short time period allows post-synaptic EPSPs to combine to produce ac pot.
48
Q

What happens when a synapse runs out of neurotransmitter?

A
  • synapse fatigued as a result of repeated stimulation
  • Nervous system doesn’t respond to stimulus- has become habituated to it.
  • Helps avoid overstimulation of effector which could cause damage.
49
Q

How can post- synaptic membrane be made more sensitive?

A

adding more receptors specific to neurotransmitter.

50
Q

What’s temporal summation ?

A

Where multiple ac pots from a single pre-synaptic neurone occur in succession and are transmitted to post synaptic neurone

B5 (8 decks)

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