neurones communication booklet (laake) PART 2 Flashcards
describe resting potential
- membrane is polarised
- stimulus caused
describe depolarisation
- Na+ channels open and Na+ diffuse in
- potential difference becomes less negative
- if threshold reached, positive feedback occurs = voltage gated sodium channels open
- many na+ diffuse in = depolarisation and potential difference reaches peak (action potential)
describe repolarisation
-voltage gated Na+ channels close and
-voltage gated K+ channels open
- K+ diffused out down electrochemical gradient
- voltage decreases = repolarisation
describe hyperpolarisation
- voltage goes below the resting potential (original)
describe how the neurone combats hyperpolarisation
Na+/K+ pumps actively transports 3Na+ and 2K+ in to restore the original resting potential = voltage becomes less negative
after an axon has transmitted an impulse why can it not transmit another straight away?
-membrane needs to be repolarised
- resting distribution of ions needs to be restored
what is the absolute refractory period
no additional stimulus, no matter how great can cause an action potential. (Conc of Na+ is high in the axon and Na+ channels still open).
relative refractory period
only a more intense stimulus can cause an action potential => increasing frequency of action potential
what is the importance of refractory period
- action potentials only propagated forwards (unidirectional)
- separates AP’s as by the time 2nd AP generated, the 1st has passed further down = setting up frequency limit
role of synapses (give each title)
- allow neurones to communicate
- ensure one way transmission between neurones
- divergence
- summation
-spatial summation (convergence)
-temporal summation - memory and learning
why are synapses useful
- memory and learning
- synaptic fatigue
- allow weak background stimuli to be filtered out as only stimulation strong enough is passed on
why is saltatory conduction more efficient?
uses less energy as less Na+ and K+ channels are needed as these are only found at nodes
how do synapses ensure one way transmission?
vesicles only found on presynaptic, receptors only found on post synaptic ensuring one way system
what is divergence
one presynaptic neurone diverges to many post synaptic neurones so one action potential can be transmitted to several parts of brain/body
example of divergence
muscle contraction - when moving/exercising
explain synaptic fatigue and how it prevents over stimulation
synaptic transmission progressively weaker with increase excitations = reduction in neurotransmitter release from synapse = synapse fatigues and becomes habituated.
spatial summation (convergence)
post synaptic neurone receives excitatory and inhibitory from many presynaptic neurones. Summates all the stimuli from all neurones to produce coordinated response
action potential in spatial summation will only be generated if…
EPSP overcomes the sum of IPSP
if IPSP over comes EPSP then…
membrane will hyper polarise the threshold potential not reached so AP not generated
describe temporal summation
repeated stimulation of same synaptic ending in succession may occur until sufficient neurotransmitter is released to allow EPSP to combine to reach threshold = AP. ensures only stimulation that is strong enough will pass on.
explain synapses in terms of memory and learning
strengthening of specific pathways in nervous system is basis of memory - when brain processes new information it is said that new synapses form
describe how weak background stimuli can be filtered out with neurones
background stimuli filtered out as only changes in intensity of stimuli are significant.
- low level stimulus unlikely to cause AP in post synaptic neurone as several vesicles of neurotransmitter must be released for this to occur.
difference between divergence and convergence
divergence is one presynaptic neurone diverging into many post synaptic neurones (muscle contraction)
convergence is multiple presynaptic neurone converging into one post synaptic neurone (brain signal)
what is myelin useful for other than increasing speed of conduction
prevents Na+ leakage = decrease dissapation
