nerves

Question 1

what does speed of propigation depend on?

Answer 1

• axon diameter
• insulataion(myelin sheath)
• temperature

Question 2

what does a myelin sheath allow

Answer 2

for sodium ions to diffuse across the neurone during the action potential, it allows an A/P to jump across the axon

Question 3

what is myelin made of

Answer 3

oligodendroglia cells and schawnn cells

Question 4

what is a local current?

Answer 4

the flow of Na+ ions down the concentration gradient which slightly depolarises the membrane from left to right

Question 5

what is the 1st part of A/P propigation

Answer 5

A/P is generated in 1 part of the axon

Question 6

what is the 2nd part of A/P propigation

Answer 6

Na+ ions flow left and right down the concentration gradient

Question 7

what is the 3rd part of A/P propigation

Answer 7

the membrane is slightly depolarised from left to right

Question 8

what is the 4th part of A/P propigation

Answer 8

voltage gated Na+ ion channels open and so on-new A/P

Question 9

what is the 5th part of A/P propigation

Answer 9

-membrane behind in refractory period therefore A/P travels oneway this happens until the end of the axon

Question 10

how is a resting potential maintaned

Answer 10

Membrane more permeable to potassium ions and less permeable to sodium ions;
Sodium ions actively transported and potassium ions in.

Question 11

What is the resting potential

Answer 11

-60mV

Question 12

What is the threshold for an action potential

Answer 12

-50mV

Question 13

what is the all or nothing principle

Answer 13

once threshold is reached an action potential will occur a larger stimulus will not cause a greater action potential

Question 14

what are nodes of ranvier

Answer 14

nodes in a myelinated neuron that contain sodium ion channels so a A/P can occur there

Question 15

why are impulses unidirectional

Answer 15

as the receptors are on postsynaptic membranes

Question 16

what is a synapse

Answer 16

a junction between two neurons or between a neuron and an effector cell

Question 17

what is acetylcholine

Answer 17

its is a neurotransmitter in cholinergic synapses

Question 18

what enzyme breaks down acetylcholine

Answer 18

acetylcholinesterase

Question 19

what is the 1st stage in nerve impulses travelling across a synapses

Answer 19

arrival of the action potential

Question 20

what are the key points of arrival of the action potential

Answer 20

A/P arrives in presynaptic knob
Voltage gated Ca2+ ion channels open
influx of Ca2+ ions into presynaptic knob

Question 21

what is the second stage in nerve impulses travelling across synapses

Answer 21

fusion of vesicles

Question 22

what are the key points of fusion of vesicles

Answer 22

influx of Ca2+ ions Mobilises vesicles
they fuse with membrane
releasing neurotransmitter into synaptic cleft by exocytosis

Question 23

what is the third stage of nerve impulses travelling across synapses

Answer 23

diffusion of (excitatory) neurotransmitter

Question 24

what are the key points of diffusion of (excitatory) neurotransmitter

Answer 24

transmitter diffuses across cleft binds to receptors on Na+ ion channels
Na+ ion channels open influx of Na+ new A/P occurs in post synaptic membrane if threshold is reached
neurotransmitter released from receptor and is broken down by enzyme and then reabsorbed by presynaptic neuron to make more neurotransmitter

Question 25

what do inhibitory neurotransmitters do to the post synaptic membrane

Answer 25

they hyperpolarise it preventing an action potential from firing

Question 26

what is an inhibitory synapse

Answer 26

a synapse where inhibitory neurotransmitters are released from the presynaptic membrane

Question 27

what is spatial summation

Answer 27

where two or more presynaptic neurones release their neurotransmitters at the same time onto the postsynaptic neurone

Question 28

describe the key points of salatory conduction

Answer 28

action potential only occurs at nodes of ranvier where Na+ ion channels are concentrated
neurones cytoplasm conducts enough electrical charge to depolarise next node so impulse jumps from node to node