Neurophysiology revision Flashcards
what happens to info in a neuron
info arrives at cello body (where it is processed) via dendrites
processed info digitised into APs transmitted along axon
info passed to target at bouton
where to action potentials start
axon hillocks
how are action potentials graded
all or none response
but increasing frequency increases intensity
why does the inside of a neuron have a negative potential and what is it
-70mV (resting membrane potential)
3Na out
2k in for each atp consumed
describe to action potential
stimulus causes the potential to push to the threshold (-55mV)
membrane depolarises, Na channels open and flows in
peaks
na channels become refractory
k channels open and k flows out therefore becomes more negative
hit absolute refractory period (all na channels closed) and relative refractory period (some na channels open but more k open-need large stimulus)- so only 1 direction and stimulates the next one
vectoial transmission
what happens when voltage gated sodium channels close
resting potential na channels and activation gate is closed
depolarisation opens activation gate and causes a conformational change
blocking of channel by inactivation gate
repolarisation of cell resets gates to their equilibrium
what increases efficiency of conduction
myelin sheath
increased diameter
where are oligodendrocytes found
cns
what is saltatory conduction
describes the way an electrical impulse skips from node to node down the full length of an axon
flows rapidly inside axon to node
ap takes place (only a few ions are needed- energy saving)
normal conduction velocity
50-60 metres/second
fastest alpha motor neurons 120m/s
are neurons hard wired
no they are separate entities
are neurons elongated secretory cells
yes and they are polaried
secretion at bouton
exocytosis occurs
explain vesicle docking
v-snare on vesicle complexes and t-snare at pre-synaptic membrane
allow vesicle to dock by drawing them close to membrane
exocytosis clamped by complexin
ap triggers calcium influx at end bulb, induces synaptotagmin (displaces complexin and causes exocytosis
what does botulinum toxin do
inactivates snare and therefore ach process
what is clostridium botulinum
bacteria that releases the toxin botulinum
what are the two receptors
ionotropic
metabotropic
can be excitatory or inhibitory
how to visualise opening of pores
cryo-electron microscopy
what are post synaptic responses
excitatory or inhibitory post synaptic responses
EPSP AND IPSP
Single ones rarely result in ap
therefore add multiple
how do epsp and ipsp work together
spatial and temporal summation
spatial- add together
temporal-ap separate
what does summation lead to
integration of information
sensory receptors need to reach threshold
how to sensory receptors respond
slowly adapting from constant input then constant output
rapidly adapting respond when it is changing then falls off (only respond on up phase)
one to change and one to extent of change
what is a stretch reflex there for
stabalising effect
prevent damage to muscle by activating reflexes via spindle fibre mechanisms
feedback info on stretch
contraction therefore controlled by output of stretch recpetors
what does gamma motor neuron efferent from spinal cord do
regulate degree of contraction
what does sensory afferent to spinal cord do
gives info on stretch
what do grp 1a and grp 2 outputs do
give cns different info
1a rapdily adapting
2 respond to length
give info on rate and extent of shortening
how is reflex protective
feedback to same muscle group
and feedbacks inhib way to antagonist muscle
therefore control extent of movement around joint
how to measure nerve conduction
we measure the sum not individual action potentials in a nerve
or
resulting stimulus detected in target cell eg. skeletal muscle
compare latency (gap between stimulation and what happens in muscle)
difference in latency gives speed of conduction
what does reduced amplitude in a nerve conduction exam mean
less axons
what does slowed conduction velocity mean in nerve conduction study
or increase latency
less myelin
what is CMAP
Compound muscle action potential
stimulate into a muscle and measure potential changes in target muscle cells
what is snap
sensory nerve action potential
record from superficial radial nerve
ring electrodes placed around the thumb and recorded using surface electrodes at the wirst
what are neuropathies
damage or dysfunction of one or more nerves that typically results in numbness, tingling, muscle weakness and pain in the affected area
what are neuropathies
what happens in carpal tunnel syndrome
median nerve is compressed
amplitude is reduced
latency not changed
what are channelopathies
defect in channels
what are the different types of channelopathies
inherited
autoimmune
name inherited channelopathies
calcium, chloride potassium, sodium, glycine, gaba, ach
neurological
cardiac
what are autoimmune channelopathies
myasthenia gracis
lambert-eaton myasthenic syndrome
limbic encephalitits
What is myasthenia gravis
autoimmune condition related to nmj mechanism
pplus also mutation/genetic assocations
antibodies to enzyme which degrade ach
itll downregulate the ability of ach to stiumlate its target
tired by end of day
eyelid droop
treat with supplements of NT
