Spread Of Nerve Impulse Flashcards
What do nerves use to communicate electrically?
Ion fluxes
What’s involved with CNS?
Brain
Cranial nerve II and retina
Spinal cord
What’s involved with PNS?
Everything outside dura mater
Sensory receptors
Peripheral portions of spinal + cranial nerves
Peripheral options of autonomic nervous system
How does PNS send signals to CNS?
Sensory (afferent) nerves
How does CNS send signals to PNS?
Motor (efferent) nerves
What happens to electrical signal when transducer down length of axon?
Converted to chemical signal + passed to target cell via nerve terminals
What are the different types of neuron?
Unipolar
Pseudo-unipolar
Bipolar
Multipolar
What happens when signal arrives at dendrites?
If greater than threshold, action potential is generated + transducer along axon to nerve terminal
How do nerves transmit electrical signals?
Movement of ions
In what ways can electrical charge be conducted?
Passively and actively
What happens in active conduction?
Action potentials are generated due to opening of ion channels
What happens if axon has larger diameter?
Lower resistance
Faster passive current flow
What’s a capacitor?
2 conducting regions separated by an insulator
E.g. extracellular and intracellular fluid and cell membrane
What must happen for a current to pass along a nerve?
Must overcome membrane capacitance e.g. stored charge
What do ions require to cross plasma membranes?
Membrane proteins inc. ion channels
Passive ion channels:
Always open
Leak channels
Ligand-gated channels:
Require ligand binding to open
Voltage-gated channels:
Require specific membrane voltage to open
What generates electrochemical gradients across plasma membrane?
Asymmetrical distribution of ions
What do neurons exhibit?
Electrical excitability
What is resting membrane potential?
-60 to -70 mV
What happens if inside of cell becomes more positive?
Depolarisation (excitatory)
What happens if inside of cell becomes more negative?
Hyperpolarisation (inhibitory)
What are channels like in neuron at rest?
Voltage gated Na+ channels inactive
Leak K+ channels open
What happens when signal arrives from another nerve terminal?
Some voltage gated Na+ channels open
Na+ enters cell body —> depolarisation
What effects do small signals produce?
Small effects - graded potentials
What are graded potentials like?
They decay (temporarily and spatially)
Na+ disperses in cytoplasm and pumped out by Na+/K+ ATPase
What happens when a larger of multiple signals arrive at neuron?
Many voltage gated sodium channels open
Cell depolarises + membrane potential crosses threshold
What happens once threshold is reached?
Rapid depolarisation occurs by voltage gated Na+ channels opening
What causes repolarisation?
Voltage-gated Na+ channels inactive rapidly
Voltage-gated K+ channels open + allow K+ to exit cell
What causes hyperpolarisation?
Voltage-gated K+ channels are slow to close
K+ continue to leave cell down electrochemical gradient
What causes membrane potential to reach back to resting potential?
Voltage-gated K+ channels close
Resting potential is reached due to action of K+ leakage channels and Na+/K+ ATPase pumps
What is initial depolarisation due to?
Rapid opening of voltage-gated Na+ channels
What is repolarisation due to?
Closing of voltage-gated Na+ channels
Opening of voltage-gated K+ channels
K+ moving through K+ leakage channels
Nature of action potentials:
All-or-none
Only fired when threshold is reached
Can only move away from stimulus due to refractory period
Voltage-gated Na+ channels at rest:
Closed
Voltage-gated Na+ channels at depolarisation:
Fully open
Voltage-gated Na+ channels at repolarisation:
Second gate shuts (not fully closed nut non Na+ going through)
Voltage-gated Na+ channels at hyperpolarisation:
Initial gate closes (fully shut)
Voltage-gated K+ channels at rest:
Closed
Voltage-gated K+ channels at depolarisation:
Closed
Voltage-gated K+ channels at repolarisation:
Open
Voltage-gated K+ channels at hyperpolarisation:
Open
Why isn’t it possible to generate second action potential immediately after first?
Absolute refractory period due to inactivation of voltage-gated Na+ channels
Takes time for inactivated channels to return to closed state
Why is it more difficult to elicit second action potential?
Due to relative refractory period (need much greater threshold to elicit action potential)
What is the significance of refractory period?
Action potential only travels away from stimulus
What can a sustained stimulus that crosses the threshold produce?
Continuous firing of action potentials
What helps speed up neuronal transmission?
Myelin sheath
What can demyelination get diseases cause?
Impaired conduction as peripheral or central axons affected
What is multiple sclerosis?
Autoimmune disease affecting oligodendrocytes
How much can myelination speed up propagation?
Up to 10 fold
What are gaps between insulated sections called?
Nodes of Ranvier - where voltage-gated Na+ channels are found
What is saltatory conduction?
When action potentials jump at high speed from one gap to the next
