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
Ek of Ca2+
+123mV
Ek of Cl- in neurons
- 40mV
- 65mV in neurons
Graded potentials
Electrical potentials that can occur anywhere.
- Transmits APs
Potential decreases as it conducts.
Varies in duration and voltage and lasts longer than APs.
Electrically localised potential.
Examples: In receptor cells like rods and cones.
Graded potentials vs APs
APs are much shorter than GPs.
GPs can occur anywhere, APs are limited to neurones, skeletal cells and cardiomyocytes.
GPs voltage decreases further from the source, APs are the same “all or none”.
Factors that affect conduction velocity
Myelination
- Saltatory conduction
Large diameter
- Lower resistance
Electrical vs chemical synapse
Speed: Electrical is faster
Direction: Electrical is bidirectional, chemical is unidirectional
Gap: Electrical has 10-fold thinner gap
Amplification: Electrical has no amplification, chemical can have summation etc.
Plasticity: Electrical has no plasticity
