nerves Flashcards
what does speed of propigation depend on?
- axon diameter
- insulataion(myelin sheath)
- temperature
what does a myelin sheath allow
for sodium ions to diffuse across the neurone during the action potential, it allows an A/P to jump across the axon
what is myelin made of
oligodendroglia cells and schawnn cells
what is a local current?
the flow of Na+ ions down the concentration gradient which slightly depolarises the membrane from left to right
what is the 1st part of A/P propigation
A/P is generated in 1 part of the axon
what is the 2nd part of A/P propigation
Na+ ions flow left and right down the concentration gradient
what is the 3rd part of A/P propigation
the membrane is slightly depolarised from left to right
what is the 4th part of A/P propigation
voltage gated Na+ ion channels open and so on-new A/P
what is the 5th part of A/P propigation
-membrane behind in refractory period therefore A/P travels oneway this happens until the end of the axon
how is a resting potential maintaned
Membrane more permeable to potassium ions and less permeable to sodium ions;
Sodium ions actively transported and potassium ions in.
What is the resting potential
-60mV
What is the threshold for an action potential
-50mV
what is the all or nothing principle
once threshold is reached an action potential will occur a larger stimulus will not cause a greater action potential
what are nodes of ranvier
nodes in a myelinated neuron that contain sodium ion channels so a A/P can occur there
why are impulses unidirectional
as the receptors are on postsynaptic membranes
what is a synapse
a junction between two neurons or between a neuron and an effector cell
what is acetylcholine
its is a neurotransmitter in cholinergic synapses
what enzyme breaks down acetylcholine
acetylcholinesterase
what is the 1st stage in nerve impulses travelling across a synapses
arrival of the action potential
what are the key points of arrival of the action potential
A/P arrives in presynaptic knob
Voltage gated Ca2+ ion channels open
influx of Ca2+ ions into presynaptic knob
what is the second stage in nerve impulses travelling across synapses
fusion of vesicles
what are the key points of fusion of vesicles
influx of Ca2+ ions Mobilises vesicles
they fuse with membrane
releasing neurotransmitter into synaptic cleft by exocytosis
what is the third stage of nerve impulses travelling across synapses
diffusion of (excitatory) neurotransmitter
what are the key points of diffusion of (excitatory) neurotransmitter
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
what do inhibitory neurotransmitters do to the post synaptic membrane
they hyperpolarise it preventing an action potential from firing
what is an inhibitory synapse
a synapse where inhibitory neurotransmitters are released from the presynaptic membrane
what is spatial summation
where two or more presynaptic neurones release their neurotransmitters at the same time onto the postsynaptic neurone
describe the key points of salatory conduction
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
