Muscles, Synapses And Nerves Flashcards
(25 cards)
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
Cardiac muscle
Involuntary
Fast contraction
Never fatigue
Pumping
Sarcomere structure
Actin outside
Myosin inside
Actin - thin / light band
Myosin - thick / H zone
Overlapping - dark zone
Define troponin
Small globular proteins - when activated move tropomyosin
Define tropomyosin
Long thin proteins which cover the myosin active sites on actin
Muscle contraction
Impulse reaches synapse, release acetylcholine.
Acetylcholine fits into receptor in muscle fibre.
Wave of depolarisation passes along myofibril and sarcomere that contains Ca2+.
Ca2+ binds to troponin activating it.
Troponin moves tropomyosin which exposes myosin binding sites on the actin.
Myosin head attached to binding site and cross bridge is formed.
ATP attached to myosin head, splits and releases energy.
This causes myosin head to detach from actin, recock its head and reattach further along the actin (power stroke).
ATP energy source stage 1
ATP already in muscles (lasts 3 seconds).
Immediately re-synthesised by creatine.
Anaerobic fast twitch.
ATP energy source stage 2
ATP from first stage respiration (glycolysis) - lasts 10-60seconds.
Lactate builds up causing fatigue.
Anaerobic fast twitch.
ATP energy source stage 3
ATP from full aerobic respiration, provides energy as long as there’s substrate.
Aerobic slow twitch.
Fast twitch
Rapid release of energy - intense short bursts.
Thick and numerous myosin filaments.
High glycogen concentration.
High enzyme concentration - ATP generated rapidly.
