Y2: Nervous coordination and muscles Flashcards
How is a resting membrane potential established?
4
- The sodium-potassium pump actively transports 3 Na+ out of the axon per 2 K+ in
- Sets up electrochemical gradient
- Sodium channels are mostly closed and potassium channels mostly open
- Means the inside of the axon is more negative than outside the membrane
- Sets up potential difference/ axon is polarised
Action potential steps? Full
8
- Neuron is at resting membrane potential
- A stimulus depolarises the nerve to threshold and Na+ moves in by facilitated diffusion
- Voltage-gated Na+ Channels open
- Na+ floods in and the membrane potential depolarises
- Voltage-gated K+ Channels open
- Potassium floods out of the cell (repolarisation)
- The membrane potential falls past the threshold (hyperpolarisation) and the voltage gated K+ channels close
- The membrane potential is restored to resting by the sodium-potasssium pump
Action potential steps? brief
7
- Resting membrane potential
- Threshold
- Depolarisation
- Peak
- Repolarisation
- Hyperpolarisation
- Recovery/ resting membrane potential
What is the all or nothing principle?
3
- An impulse has to surpass a threshold value to generate action potential
- size/strength of stimulus does not affect size/strength of impulse
- However, stronger impulses lead to significantly more frequent stimulations.
What is the refractory period?
5
- After action potential
- Where inward movement of Na+ ions is prevented
- Na+ voltage gated channels closed
- Impossible for another action potential to be generated
- however, huge stimulus can stimulate action potential in refractory period
Propagation/ unmyelinated axon: how is action potential conducted/ propagated? full
8
- Resting potential- more positive inside
- Stimulus causes influx of Na+ and depolarisation of first region
- Voltage-gated Na+ channels allow influx of Na+ in next region depolarising next region
- Voltage-gated Na+ channels in first region close and voltage gated K+ channels open and K+ leave
- The second region induces depolarisation in the next region
- First region hyperpolarises
- Third region induces depolarisation in next region
- First region returns to resting membrane potential
What is important about the all or nothing principle?
3
- Action potentials can only be propagated in one direction
- Produces discrete impulses (no overlap)
- Limits number of action potentials
Saltatory conduction in myelinated axons: steps?
3
- Action potentials occur at nodes of ranvier
- Localised circuits occur between adjacent nodes of ravier,
- Causes electrical charge to ‘jump’ from one node to the other.
Which is better saltatory conduction or propagation? Why?
Saltatory conduction
It is faster
Factors in the speed of an impulse?
-Myelin sheath
-Diameter of axon- bigger means membrane potentials
are easier to maintain, so less leakage of ions, so faster
speed of conduction
-Temperature- enzymes, diffusion, rate
Synapses part 1?
Up to synaptic cleft
5
- Resting- Ca2+ actively transported out of synapse
- Depolarisation- voltage gated Ca2+ ion channels open and Ca2+ enter
- Calcium causes vesicles containing neurotransmitters to travel to the pre-synaptic membrane
- Vesicles fuse w/ pre-synaptic membrane
- Release neurotransmitters into synaptic cleft by exocytosis
Synapses: two options after neurotransmitters released into synaptic cleft?
Excitatory- depolarises next neuron
Inhibitory - hyperpolarises next neuron
Excitatory synapse steps?
5
- NT diffuses from pre-synaptic membrane to post-synaptic membrane
- NT binds to Na+ ion channels on postsynaptic membrane
- Opens the Na+ ion channels
- Na+ enter down electrochemical gradient
- If enough enter, generates action potential in postsynaptic neuron
Inhibitory synapse steps?
6
- NT diffuses from presynaptic membrane to postsynaptic membrane
- NT binds to Cl- or K+ ion channels on postsynaptic membrane
- Channels open
- Cl- enter or K+ leave –> makes membrane potential more -ive
- Makes it more difficult to meet threshold for an action potential
- Lots of Na+ need to enter
What happens to the neurotransmitters after synapse stuff?
3
- They must be removed
- Then hydrolysed and recombined so can be used again
- Taken up by presynaptic membrane and reused
Why is summation needed?
Frequency of action potentials can be too low to release enough NT to depolarise post-synaptic membrane
-Need to increase amount of NT in cleft
What are the two ways to increase amount of NT in synaptic cleft? ie: summation
Temporal
Spatial
What is temporal summation?
4
- Increase frequency of AP’s in one neuron
- Constant stimulus
- More NT released
- More Na+ channels open so more Na+ into postsynaptic membrane
What is spatial summation?
3
- Multiple neurons release NT together on one postsynaptic membrane (into synaptic cleft)
- Enough Na+ channels open on postsynaptic membrane
- To trigger opening of voltage-gated Na+ channels so more Na+ enters
What is the terminal bouton?
Axon terminal
Neuromuscular junction steps? Remember different names
Cholinergic receptor
6
- Action potential depolarises neuron
- Voltage gated Ca2+ channels open and Ca+ enters
- Ca2+ causes vesicles containing acetylcholine move to presynaptic membrane
- Vesicle fuses w/ membrane and releases acetylcholine into synaptic cleft by exocytosis
- Acetylcholine binds to voltage gated Na+ channels on sarcolemma
- If enough Na+ enters into the sarcoplasm depolarises so causes sarcoplasmic reticulum to release calcium ions- for muscle contraction
What are the three types of muscle?
- Skeletal- move bones/ whole limbs, antagonistic pairs
- Cardiac- heart
- Smooth- lines tubes
Structure of skeletal muscle?
5
-Surrounded by a membrane called the sarcolemma
-Have thousands of myofibrils that are made up of thick
and thin filaments
-Myofibrils are divided into sarcomeres
-Have cytoplasm called sarcoplasm
-Have a specialized network of tubules that store calcium
called sarcoplasmic reticulum
Structure of muscle fibres?
3
- Multi-nucleiated
- Bundles of fibres
- Myofibrils
