Transmission across synapse

Question 1

what effects the speed of nerve impulse

Answer 1

myelin sheath- more nodes of ranvier, faster
axon diameter- quicker along bigger axon bc less resistance to flow of ions in cytoplasm. less leakage
temp- speed increases as temp does.diffusion and enzymes faster

Question 2

nerve impulse detected by

Answer 2

larger stimulus- more impulses

diff neurones with diff thresholds

Question 3

what is the refractory period

Answer 3

na-k vg channels closed
action potentials dont overlap - discreet
one direction

Question 4

spatial summation

Answer 4

diff presynaptic neurones release enough nt to exceed threshold and trigger action potential

Question 5

temporal summation

Answer 5

single presynaptic neurone releases nt lots

Question 6

inhibitory nt

Answer 6

pre sn binds to cl protein channels on post sn
cl- channels open and facilitated diffuse, k+ move out of post into synapse.influx of cl- and out of k+ hyperpolarises. na+ cant influx in so no action potential

Question 7

node of ranvier

Answer 7

increase impulse spped. ap along myelinated faster than unmyelinated as depolarisation occurs along whole length of axon. ap jumps from node to node-saltatory conduction

Question 8

myelinated neurone

Answer 8

lots of rough er to maked nt

long thin

Question 9

schwaznn cellls

Answer 9

wrap around axon as electrical insulation

Question 10

transmission across synapse

Answer 10

ap arrives at knob of presn. vg ca2+ open and diffuse into knob. synaptic vesicles fuse w presn releasing ach into cleft. ach diffuses short path and binds w receptors on na+ channels on membrane of post sn. na channels open and na+ diffuses along conc grad and depolarisation and ap generated.
achesterase enzyme hydrolyses ach and diffuses it back into pre sn( why ap is discreet). atp puts it back in vesicles.

Question 11

neuromuscular junction

Answer 11

uses ach
post sn lots of folds that store achesterase
post sn lots of receptors
ach always excitatory

Question 12

resting potential

Answer 12

na k pump actively transports 3na+ out for every 2k in, so outside more positive. membrane permeable to k so more k down conc gradient
-65mv

Question 13

depolarisation

Answer 13

ap opens vg na+ channels so influc of na+ in axon so more pos than outside. depolarisation spreads.
-65mv to +40mv

Question 14

repolarisation

Answer 14

once reached +40, vg na+ close and vg k+ open. more k move out and na+ stop coming in. so axon gets neg
+40mv to -65mv

Question 15

hyperpolarisation

Answer 15

too many k+ go out but pump gets it back to -65mv

-80mv

Question 16

roles of pump and channels

Answer 16

na-k pump maintain and resztore rp
vg na+ open at depolarisation
vg k+ open at repolarisation