Action Potential Flashcards
What does the potential in skeletal muscle change from and to?
-90mV -> +40mV
What does the potential at the SAN change from and to?
-60mV -> +30mV
What does the potential in a cardiac ventricle change from and to?
-90mV -> +30mV
Describe the ARP
Most Na+ channels are inactivated
Cannot fire another AP no matter how strong the stimulus
Describe the RRP
Na+ channels are recovering therefore many in the closed state ready to be opened again
AP may be fired with a strong enough stimulus
What does accommodation mean?
The longer the stimulus lasts, the more sodium channels will be in the inactivated state. This means a larger depolarisation is necessary to initiate AP and the amplitude of the AP will be reduced.
Describe the Na+ channels
1 polypeptide 4 sets of repeated sequence Each sequence has 6 TMDs Pore at the H5 region Voltage sensor is the 4th domain Has an inactivation particle that blocks the pore
Describe the K+ channels
4 individual polypeptides
4 alpha subunits
6 TMDs per polypeptide
4th TMD is the voltage sensor
How do many local anaesthetics work?
Block Na+ channels
Give the order in which local anaesthetics block particular axons
- Small, myelinated
- Unmyelinated
- Large, myelinated
Name 2 diseases that attack the myelin sheath of the CNS
Multiple sclerosis
Devic’s disease
Name 2 diseases that attack the myelin sheath of the PNS
Landry-Guillain-Barre Syndrome
Charcot-Marie-Tooth Disease
What are the 4 classes of peripheral axons?
A alpha
A delta
B
C
Which axons will be A alpha and are they fast or slow?
Fast
Sensory fibres from muscle spindle
Motor neurones to skeletal muscle
Which axons will be A delta?
Sensory fibres from pain and temperature receptors (sharp, localised pain)
Which axons will be B?
Preganglionic neurones of ANS
Which axons will be C?
Sensory fibres from pain, temperature and itch receptors (diffuse pain)
Which class of peripheral axon has the slowest conduction?
C
Define capacitance
Ability to store charge
What does the spread of local current depend on?
Resistance
Capacitance
Does a larger diamter cause faster or slower conduction?
Faster
What is the approximate distance between the nodes of Ranvier?
1mm
How does a myelin sheath change resistance and capacitance?
Increases resistance
Reduces capacitance
In myelinated axons, how do conduction velocity and diameter relate?
Conduction velocity is proportional to diameter
In unmyelinated axons, how do conduction velocity and diameter relate?
Conduction velocity is proportional to the square root of the diameter
When are unmyelinated axons faster than myelinated?
When the diameter is less than 1 micrometer
What does the potential in an axon change from and to?
-70mV -> +30mV
