Muscles, Synapses And Nerves Flashcards
What is resting potential
Imbalance in K+ and Na+ that gives the axon a value of -70mV.
Caused by polarisation.
How’s resting potential maintained
ATP used to swap 3Na+ ions out and 2K+ ions in through NA/K pump by active transport.
The membrane is less permeable to Na+ but more permeable to K+ so some of the K+ moved back out by facilitated diffusion as the K+ channels are partially open and Na+ channels shut.
Action potential
Upon stimulation, axon membrane depolarised because the voltage across the axon membrane changed so voltage gated Na+ channels open and Na+ move in.
If threshold reached Na+ diffused rapidly into axon down electrochemical gradient making the inside less negative.
Repolaristaion
Membrane potential = 0
K+ channels open, K+ diffuses out of the cell making it more negative
Hyperpolaristaion
K+ channels open until -70mV reached, when -80mV reached they close.
NA/K pump helps return this back to -70mV.
Salatory conduction
Occurs in myleniated axons, exchange occurs between ranvier and Schwann.
Action potential at 1 node.
Influx of Na+ displaces the K+ down the axon.
As K+ diffused down axon it makes the next node more positive so it depolarises until threshold reached.
Impulse jumps from node to node.
What effects speed of impulse
Myelin sheath - allows for saltatory conduction, increases speed.
Diameter of axon - larger diameter = faster.
Temperature - higher temperature means faster ion diffusion, increased respiration, more ATP fir Na/K pump.
All or nothing response
Threshold must be reached for change to occur.
Size of impulse after thresholds been reached does not affect the action potential size - all the same.
Refractory period
Time which the neurone membrane cannot be excited as Na channels enter recover stage - ensures action potential can only go in 1 direction.
Synaptic transmission
Action potential arrives at synapse.
Ca2+ ions diffuse into the presynaptic membrane as Ca2+ channels open.
Ca2+ ions cause the fusion of synaptic vesicles.
Molecules of neurotransmitter diffuse across the gap (pre —> post) and bind to receptors on the post synaptic membrane.
Permeability of post synaptic neurone changes.
Na+ ions flow in = EPSP / +ve charge build up in the post synaptic membrane .
If threshold reached, action potential made in the post-synaptic membrane.
Name a neurotransmitter
Acetylcholine
Synapse roles
Prevents action potential going the wrong direction - neurotransmitter only in PreSN and receptors only on PostSN.
Amplify low frequency action potentials - summation (temporal and spatial).
Some synapses are inhibitory = prevent action potential movement.
Temporal vs Spatial summation
Temporal - quick succession same preSN
Spatial - same time
Skeletal muscle
Voluntary
Fast contraction
Movement + posture
Smooth muscle
Tubular organs
Slow contraction
Peristalsis
