Excitable Tissues

Question 1

What is the resting membrane potential of a neuron?

Answer 1

-70mV

Question 2

What is the resting membrane potential of skeletal muscle?

Answer 2

-85mV

Question 3

What is the resting membrane potential of cardiac muscle?

Answer 3

-90mV

Question 4

What does the drug Oubain do?

Answer 4

Binds to Na+/K+ pump and stops it working so intracellular Ca2+ rises
Leads to vomiting, convulsions, cardiac arrest and death

Question 5

What establishes the membrane potential?

Answer 5

ATPase Na+/K+ pump at 3 Na+ outside vs 2K+ inside

Question 6

What is the Nernst Equation?

Answer 6

Calculates electrical equilibrium potential when membrane is permeable to a single ion
Veq = (RT/zF) * ln ([X]out/[X]in)

Question 7

What is the Goldman equation?

Answer 7

Resting membrane potential when permeable to Na, K and Cl ions

Question 8

Where do chemical gated ion channels exist?

Answer 8

Synapses, neuromuscular junctions, dendrites and cell bodies

Question 9

Where do voltage gated ion channels exist?

Answer 9

Axons (uni/multi-polar), sacrolemma, T tubules, cardiac muscle

Question 10

What is a graded potential?

Answer 10

A local change in the plasma membrane potential which radiates in all directions but the amplitude decreases exponentially with distance and time

Question 11

What does Tetrodoxin do?

Answer 11

Plugs Na+ channels on nerve axons preventing conduction

Results in tingling, paralysis, warmth, nausea, tremors and eventually PNS shutdown

Question 12

What is the order of events of action potential generation?

Answer 12

-70mV resting state
Na channels open, K channels begin to open
Na channels close at 30mV, K channels all open
K gates slowly close, Na inactivation gates open
K channels close and resting potential re-established

Question 13

Describe the relative permeability of the cell membrane to Na and K during the generation of an action potential

Answer 13

Higher permeability to Na than K
Na permeability onset first
K permeability onset delayed, but slower decline

Question 14

What maintains the directional control of action potential propagation?

Answer 14

The absolute refractory period

Question 15

What does conduction velocity depend on?

Answer 15

Square root of axon diameter
Speed of depolarisation
- Amount of current
- Membrane capacitance
- Internal resistance

Question 16

Describe Type A neurons and where they are found.

Answer 16

Large (4-20um)
Fast (140m/s)
Somatic sensory or motor neurons

Question 17

Describe Type 2 neurons and where they are found.

Answer 17

Small (2-4um)
Slow (18m/s)
Autonomic sensory and preganglionic neurons

Question 18

Describe Type 3 neurons and where they are found.

Answer 18

Very small (2um)
Very slow (1-2.5m/s)
Somatic sensory and autonomic sensory nerves

Question 19

What makes a neuron more sensitive?

Answer 19

Smaller diameter

Question 20

Which are blocked first, myelinated or non myelinated nerves?

Answer 20

Myelinated

Question 21

How is insulin release triggered?

Answer 21

ATP closes K+ gates, to intracellular K+ rises
Depolarisation triggers opening of Ca2+ gates
Influx of Ca2+ triggers insulin release