Cell physiology of neurones Flashcards
- Recite the equilibrium potentials for a the main ions involved in neural activity. - Explain the actions of ionic and molecular contributors to the action potential, the equilibrium potential, graded potentials, electrotonic conduction, conduction velocity and synaptic transmission. - Derive the effects and explain the rationale for changes to excitability caused by changes in electrolyte concentrations and drugs that affect ionic conduction. - Explain the mechanisms of synaptic transmissio
Electrical synapse
A bidirectional synapse that is coupled by gap junctions.
Faster that chemical synapses
Does not have plasticity or amplification- always excitatory.
Amplification in electrical synapses
Signals are always weakened as it moves from pre-synaptic to post-synaptic neurone.
Signal will not transmit if the post-cell is larger.
Spatial summation
The sum of signals from several pre-synaptic neurone dictates a neurone’s response.
- Can be excitatory or inhibitory.
Example of convergent neuronal signalling.
Temporal summation
The pre-synaptic neurone fires several signals fast enough for the post-synaptic neurone to not recover and receive another signal.
Refractory period
Period of time when a neurone is incapable of starting a new action potential.
Coding of intensity by neurones
Increased firing frequency = increased intensity of activity.
Higher threshold voltage= decreased firing frequency, thus intensity of activity is lower.
Increased excitatory synaptic activity= increased firing frequency.
Different neurones for different strength stimuli
Accommodation
Changes in the face of continued stimulation.
Lengthy small synaptic currents increase threshold potential for AP generation.
- Na+ channels are inactivated
Excitability of neurones
How easily a neurone starts an AP.
Increased threshold potential = lower excitability.
Excitability can be changed by pharmacological agents.
Inactivated vs closed ion channel
Inactivated= Channel is non-conducting when the membrane potential is positive on the inside.
Closed= Channel is non-conducting when membrane potential is negative.
Lidocaine/ Lignocaine
Local anaesthetic applied topically.
Mechanism:
Blocks Na+ channels in pain neurones by raising threshold potential
Carbamazepine
Anticonvulsant drug.
- Neuropathic pain and seizure disorders.
Mechanism:
- Inactivates Na+ channels by raising AP threshold.
Quinidine
Class 1 Anti arrhythmic drug
Mechanism:
- Blocks Na+ channels
- Lowers conduction velocity
- Increases refractory period
Equilibrium potential
When the Electrical force and the chemical force of an ion is equal
- Voltage flowing in is equivalent to voltage out.
Ek of Na+
+60mV
Ek of K+
-90mV
