Topic 6 B Flashcards
(49 cards)
What is the voltage at resting potential?
-70mV
What do the sodium potassium pumps use to transport the sodium ions out of the neurone?
Active transport
How many sodium ions are transported for how many potassium ion?
Three sodium ions for 2 potassium ions
What is the electrochemical gradient?
Sodium ions move out of the membrane, but can’t move back in as it isn’t permeable to the ions. There are more positive sodium ions outside the cell than inside
How does an action potential occur?
Stimulus, depolarisation, depolarisation, hyperpolarisation, resting potential
What happens when a stimulus occurs? (Action potentials)
Voltage gated sodium channels open allowing, sodium ions to flood into the axon, making it more positive
What happens during depolarisation? (Action potential)
Threshold is reached -55mV, more voltage gated sodium channels open causing a rapid influx of sodium ions
What happens during repolarisation? (Action potentials)
At +40mV, Voltage gated sodium channels close and the voltage gated potassium ions open, causing potassium ions to diffuse out of the cell, making the inside more negative
What happens during hyperpolarisation? (Action potentials)
Potassium ions close too slowly so too much moves out, called refractory period, they eventually cloe
What happens during the resting potential? (Action potential)
Ion channels are reset and sodium potassium pump returns membrane to its resting potential
What happens during the refractory period? (Action potentials)
When the ion channels are recovering and can’t open again, acts as a time delay between action potentials
What is the all or nothing principle?
If a threshold is reached, an action potential will fire, if it isn’t then it won’t
What increased the speed of conduction along the neurone?
Myelination (electrical insulator made of Schwann cells) , axon diameter (bigger diameter quicker action potentials) and temperature (higher the temp, higher the speed)
What is saltatory conduction?
The neurone conducts enough electrical charge to depolarise the next node of rangier do the impulse can jump to it
What is the effect of an action potential?
It causes neurotransmitters to be released into the synaptic cleft and diffuse across the postsynaptic membrane where they bind to receptors, triggering an action potential in another neurone. Impulse are unidirectional
What happens to neurotransmitters at the synaptic cleft?
Removed so response doesnt keep happening
What receptors does acetylcholine bind to?
Cholinergic receptors, and diffuse across cholinergic synapses
How are impulses transmitted across the cholinergic synapses?
Action potential arrives at synaptic knob, stimulating voltage gated calcium ion channels in the presynaptic neurone to open. Calcium ions diffuse into synaptic knob, influx causes synaptic vesicles to fuse with presynaptic membrane releasing acetylcholine into the synaptic cleft by exocytosis. ACH diffuse across and binds to cholinergic receptors on post synaptic neurone. Sodium ion channels open causing an influx of sodium ions, causing depolarisation, If threshold is reached an action potential is generated. ACh is removed from cleft and is broken down by acetylcholinesterase and are reabsorbed by presynaptic neurone to remake ACh
What do excitatory neurotransmitters do?
Depolarise postsynaptic membrane making it fire an action potential if threshold is reached
What do inhibitory neurotransmitters do?
Hyperpolarise postsynaptic neurone preventing it from firing an action potential
What is spatial summation?
Two or more presynaptic neurones release transmitters at the same time
What is temporal summation?
Two or more nerve impulses arrive in quick succession from the same presynaptic neurone
Why are neuromuscular junctions different from cholinergic synapses?
Post synaptic membrane has lots of folds that form clefts which store AChE
Post synaptic membrane has more receptors
ACh is always excitatory, it normally triggers a response in muscle cells
What does smooth muscle do?
contracts without conscious control, in walls of internal organs
