Physiology of neurons Flashcards
What are the properties of electrical synapses?
Faster than chemical
no plasticity so no learning
don’t release neurotransmitter so no amplification
signal always weakened as its transmitted
signal won’t transmit if post synaptic cell much bigger than pre synaptic
excitatory pre-synaptic signal can’t inhibit post-synaptic cell
Define spatial summation
neuron fires based on converging signal from multiple neurons synapsing onto it. If many small depolarisations can reach threshold
Define temporal summation
input neuron firing fast enough repeatedly so receiving neuron adds together many tiny signals to reach threshold
What channels are open when membrane is at rest?
Inward rectifier K+ channels
What channels open upon initial depolarisation
voltage gated Na channels
what are the 2 delayed events that happen during repolarisation?
- sodium channels close
2. delayed K+ rectifier channels open
What is the after hyperpolarisation period?
at the end of the action potential where voltage goes more negative than at rest followed by return to resting membrane potential
What channels open when membrane goes below -60mb during after hyperpolarisation?
Inward K+ rectifier channels
What is the refractory period?
Period of time when neuron is incapable of regenerating new action potential. refractory period occurs during hyperpolarisation
How is the intensity of neurons coded?
Increased threshold = decreased firing frequency
Increased excitatory synaptic activity = increased firing frequency
Define excitability
how easy to start nervous signalling.
decreased threshold = decreased excitability
What occurs when Na channels are open?
Na flows into the cell and membrane becomes more positive on the inside
What occurs when K channels are open
K flows out of the cell and membrane becomes more negative on the inside
What occurs when Ca channels are open
Ca flows into the cell and membrane becomes more positive on the inside
What is lidocaine and how does it work?
local anaesthetic. blocks Na channels in pain neurons, raises threshold and decreases excitability to stop action potentials locally
What is quinidine and how does it work?
antiarrythmic drug. decreases conduction velocity which extends the refractory period
What is carbamazepine and how does it work?
Anticonvulsant. Inactivates Na channels, raises AP threshold so decreases excitability. Has a weak effect
What is Tetrolotoxin?
Fugu fish poison. Blocks all Na channels.
What is the chemical force acting on ions?
Also called the diffusional force. Is the mass of ion. Based upon difference in concentration across the membrane
What is the electrical force acting on ions?
Depends on the Vm (membrane potential at rest) which varies. If positive charge separate from negative charge= powerful electrical field
What are equilibrium potentials?
The more permeable the cell is to a certain ion, the more the membrane potential approaches its equilibrium
What are the membrane potentials of the following? ENa EK ECa ECl
ENa: +60
EK: -90
ECa: +123
ECl: -40
Properties of graded action potentials
decrease as they move along electrically localised last long time much flatter in shape conducted almost instantly in receptor cells (rods and cones)
Properties of Action potentials
stereotyped electrical signal
short duration
in most neurons, skeletal and cardiomyocytes
A spike
always the same ‘all or nothing’
require time to start due to conformational changes
How do graded potentials transmit signals?
changes in membrane potential don’t propagate very far via passive electrical forces.
graded potentials transmit signals along length of axon
the action potential is a way for re-amplifying the signal
Describe saltatory conduction
when action potential jumps from node to node. Net effect= faster conduction velocity. Electronic jumps between nodes are very fast.
What is conduction velocity and what affects it?
Signal transmission along length of axon
faster when myelinated and large diameter
100 m/s for alpha motor fibres (myelin)
1 m/s for c nociceptive fibres (no myelin)
