neurones communication booklet (laake) PART 2

Question 1

describe resting potential

Answer 1

• membrane is polarised
• stimulus caused

Question 2

describe depolarisation

Answer 2

• 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)

Question 3

describe repolarisation

Answer 3

-voltage gated Na+ channels close and
-voltage gated K+ channels open
- K+ diffused out down electrochemical gradient
- voltage decreases = repolarisation

Question 4

describe hyperpolarisation

Answer 4

• voltage goes below the resting potential (original)

Question 5

describe how the neurone combats hyperpolarisation

Answer 5

Na+/K+ pumps actively transports 3Na+ and 2K+ in to restore the original resting potential = voltage becomes less negative

Question 6

after an axon has transmitted an impulse why can it not transmit another straight away?

Answer 6

-membrane needs to be repolarised
- resting distribution of ions needs to be restored

Question 7

what is the absolute refractory period

Answer 7

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).

Question 8

relative refractory period

Answer 8

only a more intense stimulus can cause an action potential => increasing frequency of action potential

Question 9

what is the importance of refractory period

Answer 9

• 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

Question 10

role of synapses (give each title)

Answer 10

1. allow neurones to communicate
2. ensure one way transmission between neurones
3. divergence
4. summation
   -spatial summation (convergence)
   -temporal summation
5. memory and learning

Question 11

why are synapses useful

Answer 11

• memory and learning
• synaptic fatigue
• allow weak background stimuli to be filtered out as only stimulation strong enough is passed on

Question 12

why is saltatory conduction more efficient?

Answer 12

uses less energy as less Na+ and K+ channels are needed as these are only found at nodes

Question 13

how do synapses ensure one way transmission?

Answer 13

vesicles only found on presynaptic, receptors only found on post synaptic ensuring one way system

Question 14

what is divergence

Answer 14

one presynaptic neurone diverges to many post synaptic neurones so one action potential can be transmitted to several parts of brain/body

Question 15

example of divergence

Answer 15

muscle contraction - when moving/exercising

Question 16

explain synaptic fatigue and how it prevents over stimulation

Answer 16

synaptic transmission progressively weaker with increase excitations = reduction in neurotransmitter release from synapse = synapse fatigues and becomes habituated.

Question 17

spatial summation (convergence)

Answer 17

post synaptic neurone receives excitatory and inhibitory from many presynaptic neurones. Summates all the stimuli from all neurones to produce coordinated response

Question 18

action potential in spatial summation will only be generated if…

Answer 18

EPSP overcomes the sum of IPSP

Question 19

if IPSP over comes EPSP then…

Answer 19

membrane will hyper polarise the threshold potential not reached so AP not generated

Question 20

describe temporal summation

Answer 20

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.

Question 21

explain synapses in terms of memory and learning

Answer 21

strengthening of specific pathways in nervous system is basis of memory - when brain processes new information it is said that new synapses form

Question 22

describe how weak background stimuli can be filtered out with neurones

Answer 22

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.

Question 23

difference between divergence and convergence

Answer 23

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)

Question 24

what is myelin useful for other than increasing speed of conduction

Answer 24

prevents Na+ leakage = decrease dissapation