5.3 Neuronal communication Flashcards by M3MES bigbrain

stimulus definition

change in energy levels in environment

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receptors definition

specialised cells that detect stimulus

transducers

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why receptors are transducers

converts one type of energy into another

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different receptors and energy

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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how touch receptors work

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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sensory neurone function

carries action potential from sensory receptor

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sensory neurone structure

long dendron

short axon

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relay neurone structure

short dendrites
no dendron
short axon

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relay neurone function

connects sensory and motor neurones

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motor neurone function

carried action potentials from CNS to effector

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motor neurone structure

short dendron

long axon

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neurone general structure

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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myelinated neurones features

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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why myelination speeds up transmission of a.p.

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

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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advantages of myelination

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

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where non-myelinated neurones tend to be used

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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normal resting state of axon

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

potential difference definition

difference in electrical charge

how resting potential is established

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

depolarisation method

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

repolarisation method

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

hyperpolarisation method

K+ channels remain open

inside temporarily becomes too negative until resting potential is reached

refractory period

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

all-or-nothing response

if threshold value met, action potential is generated | if not, generator potential is generated

threshold value

-55mV

why hyperpolarisation occurs

K+ channels close too slowly | too much K+ diffuse out

generator potential

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

how action potentials are transmitted (local currents)

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

how voltage-gated sodium ion channels work

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)

saltatory conduction definition

when impulses jump from one Node of Ranvier to another

excitatory neurotransmitter features

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

inhibitory neurotransmitter features

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

transmission of impulses across synapse method

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

acetylcholinesterase definition

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

why acetycholine in hydrolysed

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

what happens after hydrolysis of acetylcholine

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

where myelinated neurone used and why

voluntary muscles | occurs along long axons within nervous system (white matter)

role of synapse

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

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

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

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

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.

temporal summation definition

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

spatial summation definition

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