nervous and synaptic impulses

Question 1

what do dendrites do

Answer 1

carry nerve impulses to the body

Question 2

what does does the cell body of a nerve cell contain

Answer 2

organelles - lots of rough er and mitochondria

Question 3

what is the axon

Answer 3

long fibres that carry impulses away from the cell body

Question 4

what are schwann cells and what do they do

Answer 4

wrap around axon many times forming the myelin sheath and are rich in lipids

providing insulation

Question 5

what are the nodes of ranvier

Answer 5

gaps between schwann cells

Question 6

what is the resting potential

Answer 6

the potential difference (voltage) across the membrane of a neurone when not transmitting an impulse

Question 7

what do the sodium potassium pumps do maintain resting potential

Answer 7

actively transports 3 sodium ions (Na⁺) out of neurone and 2 potassium ions (K⁺) into neurone

Question 8

what ion is the membrane more permeable to

Answer 8

K+ ions

Question 9

why does a neuron have an overall negative charge

Answer 9

potassium diffuses out quicker that sodium diffuses in

because the membrane is more permeable / has more ion channels
for potassium

Question 10

what is the voltage of resting potential

Answer 10

~ -70mV

Question 11

what are the intrinsic membrane proteins in the membrane of a neuron

Answer 11

sodium potassium pumps
leak channels
gated channels

Question 12

how is the resting potential established

Answer 12

active transport of 3Na+ out and 2K+ in by sodium potassium pumps

membrane more permeable to K+

K+ diffuse back out faster than Na+ back in

membrane is polarised

Question 13

what is action potential

Answer 13

when a stimulus caused a temporary reversal in the charges and the axon is depolarised

Question 14

what are the stages of causing action potential

Answer 14

stimulus
depolarisation
repolarisation
hyperpolarisation
refractory period
resting state

Question 15

what happens in depolarisation

Answer 15

stimulus causes gated sodium ion channels to open
influx of Na+ ions into axon
potential difference increases to +40mV
gated sodium ion channels close

Question 16

what happens in repolarisation

Answer 16

gated potassium ion channels open

K+ ions diffuse rapidly out of axon

Question 17

what is hyperpolarisation

Answer 17

so many K+ ions diffuse out that the axon becomes more negatively charged than normal

Question 18

what restored the resting potential

Answer 18

sodium potassium pump restored the concentration gradients of Na+ and K+

Question 19

what is the all or nothing principle

Answer 19

if the stimulus is large enough, action potential is generated at a constant size and speed

increasing initial stimulus will not produce a larger or faster action potential

Question 20

what is the refractory period

Answer 20

a short period where axon recovers from its depolarisation

gated channels can’t be opened

Question 21

what does the refractory period ensure

Answer 21

this ensures action potentials are discrete and unidirectional

Question 22

what factors affect the speed of conduction of impulses

Answer 22

myelination / saltatory conduction
axon diameter
temperature

Question 23

why is conduction slow in unmyelinated neurones

Answer 23

depolarisation occurs along entire length of axon membrane

Question 24

why can’t depolarisation and action potentials occur in myelinated neurones

Answer 24

myelin sheathstops diffusion of sodium and potassium ions

Question 25

what is saltatory conduction and what does it mean for impulses

Answer 25

depolarisation can only occur at the nodes of Ranvier (gaps between Schwann cells) so action potentials ‘jump’ from one node to the next meaning impulses travels faster 

Question 26

what does the presynaptic neurone contain

Answer 26

synaptic vesicles containing acetylcholine (ACh) mitochondria (to provide ATP for neurotransmitter synthesis and vesicle movement) gated Ca²⁺ channels in presynaptic membrane

Question 27

what is the synaptic cleft

Answer 27

the gap between the presynaptic and postsynaptic neurone

Question 28

what does the postsynaptic neurone contain

Answer 28

specific receptors for acetylcholine Na⁺ channels that open in response to ACh binding acetylcholinesterase (enzyme) embedded in membrane

Question 29

what does the arrival of action potential at the presynaptic terminal cause

Answer 29

gated calcium channels to open and an influx of calcium ions

Question 30

what does the influx of Ca2+ ions into presynaptic neurone cause

Answer 30

synaptic vesicles to fuse with presynaptic membrane, which release acetylcholine (ACh) via exocytosis into the synaptic cleft

Question 31

what does ACh do once released by synaptic vesicle

Answer 31

diffuses across synaptic cleft and binds to specific receptors on sodium channels of postsynaptic membrane

Question 32

what does binding of the ACh to receptors in the postsynaptic membrane cause

Answer 32

Na⁺ channels to open so Na⁺ diffuses into the neurone, causing depolarisation if threshold is reached, action potential generated

Question 33

how is the initiation of more action potentials prevented

Answer 33

ACh hydrolysed by acetylcholinesterase into choline and ethanoic acid

Question 34

what happens to the ethanoic acid and choline

Answer 34

reabsorbed into presynaptic neurone to resynthesise acetylcholine using ATP

Question 35

what is unidirectionality in relation to synaptic transmission

Answer 35

action potential occurs in one direction

Question 36

what is summation in relation to synaptic transmission

Answer 36

multiple nerve impulses combine their effects at a synapse to increase chance that postsynaptic neurone reaches threshold initiating action potential

Question 37

what is spatial summation

Answer 37

multiple presynaptic neurones release neurotransmitters at same time onto one postsynaptic neurone combined neurotransmitter effect may be enough to stimulate action potential

Question 38

what is temporal summation

Answer 38

one presynaptic neurone releasing neurotransmitters in quick succession if impulses arrive closely enough in time, neurotransmitter builds up and may stimulate action potential

Question 39

what can neurotransmitters be

Answer 39

excitatory or inhibitory

Question 40

what do stimulants do and how

Answer 40

generate/make it easier to generate action potential by mimicking neurotransmitter → similar shape or causing the release of excess neurotransmitter or reducing activity of enzyme which breaks it down increase number of impulses sent along a neurone

Question 41

what are examples of stimulants

Answer 41

caffeine, nicotine

Question 42

what do inhibitors do and how

Answer 42

cause fewer action potentials in the post synaptic neurone by inhibiting the release of neurotransmitters or blocking the receptors for neurotransmitter on the postsynaptic membrane reduces the number of impulses sent along a neurone

Question 43

what are examples of inhibitors

Answer 43

alcohol, cannabis

Question 44

how do inhibitory neurotransmitters work

Answer 44

certain neurotransmitters open calcium channels in postsynaptic membrane, causing influx of negative calcium ions into post synaptic knob hyper-polarisation occurs so less likely for action potential to be generated

Question 45

how do excitatory neurotransmitters work

Answer 45

cause depolarisation of the postsynaptic neurone

Question 46

what are neuromuscular junctions

Answer 46

synapse between presynaptic neurone and muscle

Question 47

how are neuromuscular junctions different to other synapses

Answer 47

postsynaptic membrane folded into clefts which store enzyme acetylcholinesterase, acetylcholine always an excitatory neurotransmitter postsynaptic membrane contains higher number of receptors