Neuronal communication Flashcards
5.1.3
name all 3 neurones found in the body
sensory
relay
motor
what do all 3 neurones have in common?
cell body
contains organelles including nucleus
axons
conductive, long fibre that carries nerve impulse along motor neurone
dendrites
carries AP to surrounding cells
features of the myelin sheath
made up of Schwann cells wrapped around axon
is a lipid
so no charged ions can pass through
gaps in the myelin sheath are called Nodes of Ranvier
what is saltatory conduction?
when the action potential jumps from node to node
this helps the AP travel faster
as it only has to generate AP at the nodes
instead of down the whole sheath length
features of the sensory neurone
carries electrical impulses to relay/motor neurone or brain
long dendron
carries impulse from sensory receptor cell (these detect stimulus)
to sensory cell body
then axon carries impulse from there to next neurone
features of the relay neurone
carries impulses from sensory to motor
lots of short axons
and dendrons
features of motor neurone
carries impulses from sensory/relay to effector (muscles/glands)
one long axon
multiple short dendrites
features of sensory receptors
detects stimuli
convert them into electrical impulses (transducer)
photoreceptors (rods and cones cells) detect light
thermoreceptors (skin) detect heat
mechanoreceptor (Pacinian corpuscle in skin) detect pressure
features of Pacinian corpuscle
located deep in skin of fingers and feet
sensory neurone membrane has stretch-mediated Na+ channels
allowing Na+ to enter sensory neurone only if its stretched
when pressure applied
deforms neurone plasma membrane
stretches and widens Na+ channels
Na+ diffuses in
establishes generator potential
what is resting potential?
when neurone is not conducting an impulse
there’s a difference between electrical charge inside and outside the neurone
establishing a resting potential
maintained by Na+ and K+ pump
requires ATP and active transport
pump moves 2 K+ ions IN
3 Na+ ions OUT
creates electrochemical gradient
causing K+ to diffuse OUT
and Na+ to diffuse in
membrane more permeable to K+
what is an AP?
neurone’s voltage increases beyond a set point from resting potential
generates nervous impulse
what is depolarisation?
increase in voltage
due to the membrane becoming more permeable to Na+
explain what is meant by the ‘all-or-nothing principle’
if depolarisation doesn’t exceed -55mV
AP and impulse aren’t produced
but any stimulus that triggers depolarisation past -55mV
will always peak at the same max voltage
bigger stimuli increase the frequency of APs
important because it makes sure animals respond to large enough stimuli
what happens at the refractory period?
after AP generated
membrane cannot be stimulated
as Na+ channels are recovering and cant be opened
why is the refractory period essential?
ensures discrete impulses are produced
so each AP is separate
ensures they go in 1D
if they go in 2 directions it prevents a response
limits no of impulse transmissions
so prevents over-reaction to stimuli
function of a synapse
impulse arrives at synaptic knob
depolarisation of knob leads to Ca2+ channels opening and Ca2+ diffusing in
neurotransmitter vesicles fuse with pre-synaptic membrane
diffuse across cleft down conc gradient
NT vesicles complementary bind to receptors on post synaptic cleft
Na+ channels on post-synaptic neurone open
so Na+ diffuse in
if enough NT, enough Na+ diffuse in above threshold
Post-synaptic neurone becomes depolarised
Na+ channels close
post-synaptic neurone can establish resting potential
NT degraded and releases from receptor
goes back to pre-synaptic neurone to be recycled
what is meant by ‘summation’?
rapid build up of NT in synapse to help build up an AP
describe spacial summation
many different neurones collectively trigger a new AP
by combining NT they release
to exceed threshold value
describe temporal summation
one neurone releases NT repeatedly
over a short period of time
to accumulate enough to exceed threshold value
what do inhibitory synapses do?
causes Cl- ions to move into post-synaptic neurone
and K+ ions to diffuse out
membrane potential decreases to -80mV
hyperpolarisation
makes it difficult to generate an AP
