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A-Level Biology > 5.3 Neuronal communication > Flashcards

5.3 Neuronal communication Flashcards

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1
Q

stimulus definition

A

change in energy levels in environment

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2
Q

receptors definition

A

specialised cells that detect stimulus

transducers

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3
Q

why receptors are transducers

A

converts one type of energy into another

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4
Q

different receptors and energy

A

rods and cones (in eyes): light -> electrical
specialised hairs in ears: kinetic -> electrical
chemoreceptors in taste buds: chemical -> electrical
olfactory chemoreceptors in nose: chemical -> electrical

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5
Q

how touch receptors work

A 
Pacinian corpuscles 
pressure on skin causes connective tissue deforming it
sodium ion channels distort and open
sodium ions diffuse into axon
produced a.p.
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6
Q

sensory neurone function

A

carries action potential from sensory receptor

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7
Q

sensory neurone structure

A

long dendron

short axon

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8
Q

relay neurone structure

A

short dendrites
no dendron
short axon

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9
Q

relay neurone function

A

connects sensory and motor neurones

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10
Q

motor neurone function

A

carried action potentials from CNS to effector

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11
Q

motor neurone structure

A

short dendron

long axon

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12
Q

neurone general structure

A

can be long (transmit a.p. long distances)
plasma membrane gated ion channels (uses ATP to pump ions in and out to maintain potential difference across plasma membrane)
cell body (contains nucleus, lots of mitochondria, ribosomes)
dendrites and dendron (connect to other neurones, carry a.p. towards cell body)
axon (carries a.p. away from cell body)
myelin sheath around axon and dendron (series of Schwann cells)

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13
Q

myelinated neurones features

A

myelin sheath
series of Schwann cells associated and wrapped tightly around neurone
nodes of Ranvier (2-3um gaps every 1-3mm along neurones
wider neurone

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14
Q

why myelination speeds up transmission of a.p.

A

myelin sheath wrapped tightly around neurone
prevents movement of ions across neurone plasma membrane
ion can only move across at nodes of Ranvier
impulse jumps from one node to the next (saltatory conduction)
conduction is more rapid

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15
Q

non-myelinated neurone features and why they are slower at transmission

A

Schwann cells associated
several neurone enshrouded in one loosely wrapped Schwann cell
a.p. travels along neurone in wave instead of jumping from node to node (local currents)
narrower

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16
Q

advantages of myelination

A

myelinated neurones able to carry a.p. over long distances more quickly
enables faster response to stimulus

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17
Q

where non-myelinated neurones tend to be used

A

shorter distances
occurs in neuronal body cells and dendrites (grey matter)
coordination body functions e.g. breathing, digestive system where speed of transmission not so important

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18
Q

normal resting state of axon

A

resting potential
when neurone is at rest (no stimulus)
p.d. = -70mv
membrane is polarised

19
Q

potential difference definition

A

difference in electrical charge

20
Q

how resting potential is established

A

sodium-potassium ion pumps 3 Na+ out, 2K+ in
K+ leaks out through open potassium ion channels
anions are also inside of axon
membrane polarised

21
Q

depolarisation method

A

axon is stimulated
Na+ channels open (becomes permeable to Na+)
influx of Na+ diffuses into axon
causes inside of axon to become more positive (depolarises)
potential difference reaches -55mV (threshold is met)
potential difference reaches +35 mV (with the help of positive feedback causing nearby voltage-gated Na+ channels to open)
action potential moves along axon
Na+/K+ pump keeps operating

22
Q

repolarisation method

A

0.5 ms after depolarisation
voltage-gated Na+ channels close
voltage-gated K+ channels open
membrane impermeable to Na+ and permeable to K+
K+ flood out of axon
inside of axon becomes negative again compared to outside

23
Q

hyperpolarisation method

A

K+ channels remain open

inside temporarily becomes too negative until resting potential is reached

24
Q

refractory period

A

follows a.p. along neurone
in absolute refractory period, no impulse can be generated
in relative refractory period, impulse can only be generated if stimulus more intense than normal threshold level
voltage-gated Na+ channels close (stops another impulse from being generated) so resting potential can be restored
ensures impulses are separated, only pass in one direction along axon

25
Q

all-or-nothing response

A

if threshold value met, action potential is generated

if not, generator potential is generated

26
Q

threshold value

A

-55mV

27
Q

why hyperpolarisation occurs

A

K+ channels close too slowly

too much K+ diffuse out

28
Q

generator potential

A

generated when threshold value is not met (-55mV)

29
Q

how action potentials are transmitted (local currents)

A

stimulus causes opening of Na+ channels
Na+ diffuses into neurone
a.p. generated, disrupts resting potential ion balance
higher conc of Na+ where they enter neurone, lower conc of Na+ to the side
Na+ ions diffuse sideways towards negative region
movement of ion = local current
continues along neurone

30
Q

how voltage-gated sodium ion channels work

A

Na+ diffuse along membrane
reduces p.d. across membrane
causes voltage-gated sodium ion channels to open
causes more Na+ to enter membrane (example of positive feedback)

31
Q

saltatory conduction definition

A

when impulses jump from one Node of Ranvier to another

32
Q

excitatory neurotransmitter features

A

result in depolarisation of post synaptic neurone
if threshold reached in postsynaptic neurone, a.p. is triggered
e.g acetylcholine

33
Q

inhibitory neurotransmitter features

A

results in hyperpolarisation of post synaptic membrane
prevents action potential from being triggered
e.g. GABA

34
Q

transmission of impulses across synapse method

A

a.p. arrived at pre-synaptic neurone
causes Ca+ channels to open, Ca+ diffuse into pre-synaptic knob
causes synaptic vesicles to move to pre-synaptic membrane
vesicles fuse with membrane, releases acetylcholine into synaptic cleft via exocytosis
acetylcholine diffuses across synaptic cleft
binds to receptors on post-synaptic membrane
Na+ channels open on post-synaptic membrane, Na+ diffuses into post-synaptic membrane
causes it to be depolarised , a.p. generated at post-synaptic neurone

35
Q

acetylcholinesterase definition

A

enzyme that hydrolyses acetylcholine into acetic acid and choline in synaptic cleft

36
Q

why acetycholine in hydrolysed

A

stops continuous production of action potential in post-synaptic neurone
enables repolarisation of post synaptic membrane by unblocking receptors (stops Na+ channels from staying open)
recycles acetylcholine

37
Q

what happens after hydrolysis of acetylcholine

A

acetic acid and choline diffuse back into pre-synaptic knob
combined back into acetylcholine using ATP
stored into vesicles

38
Q

where myelinated neurone used and why

A

voluntary muscles

occurs along long axons within nervous system (white matter)

39
Q

role of synapse

A

transmit information between neurones
ensure one way transmission of impulses (vesicles with Ach only in presynaptic knob, receptors for Ach only on post-synaptic membrane)
acclimatisation (fatigue and stop responding to stimulus as it runs out of neurotransmitters, helps avoid overstimulation of effectors that may cause damage)
divergence of nervous pathways

40
Q

why 1 action potential in pre-synaptic neurone may not result in action potential in post-synaptic neurone

A

low level stimulus may generate a.p.
may not cause release of enough ach vesicles to cause a.p. in post synaptic neurone
just causes generator potential (excitatory post-synaptic potential = EPSP)
won’t reach threshold value
helps avoid overstimulation

41
Q

how a.p. is generated in post-synaptic neurone when only low level stimulus present

A

several a.p. generated in short time
causes more vesicles of ach to be released
in post-synaptic neurone, several EPSPs combine to produce a.p.

42
Q

temporal summation definition

A

several generator potentials come from same pre-synaptic neurone to create action potential in postsynaptic neurone

43
Q

spatial summation definition

A

many a.ps arrive from converting pre-synaptic neurones causes few vesicles each to be released into same synapse, causing a.p. in postsynaptic neurone

A-Level Biology (24 decks)

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