Question

Compare and Contrast the Neuronal Action Potential vs Cardiac Action Potential. Focus on the steps of the both action potentials and identify the difference(s).
What is the significance and involvement of Calcium ions in the cardiac action potentials? Why are Calcium ions not necessary in the neuronal action potentials, but are essential in the myocardial AP?

Answer 1

Neurons make use of sodium channels to create the action potential and potassium channels to restore the resting potential. The stimulation of skeletal muscle to contract and influx of sodium ions depolarizes the skeletal muscle and stimulates the release of calcium from the endoplasmic reticulum.

In cardiac muscle, the calcium ion release from the sarcoplasmic reticulum is stimulated by the influx of calcium ions into the cell through the voltage gated calcium channels on the outer membrane. This process is called as calcium induced calcium release and increases the myoplasmic free calcium concentration resulting in muscle contraction.The restoration of resting potential also happens with the potassium channels in cardiac muscle.

In both skeletal and cardiac muscles, after the absolute refractory period, potassium channels open and the ions flow out of the cell resulting in repolarization to the resting stage. A specific difference between cardiac and skeletal muscles is that how each of them enhance the calcium ions to stimulate contraction.

Compare action potentials in neurons, skeletal muscle, and cardiac muscle

Similarities	neurons	skeletal muscle	cardiac muscle
Role or function	cell-to-cell communication by providing for the propagation of signals along the neuron's axon towards ends of axon which can then connect with other neurons at synapses,	Ca+2 binds to troponin C and initiate muscle contraction	Ca+2 binds to troponin C and initiate muscle contraction
action potentials prorogated along	Axon	T tubules	T tubules
Resting membrane potential	-70mV	-90mV	-90mV
Platue	Present	Present	Present
cations and anions are involved in this type of action potentials	Yes	Yes	Yes

Differences	neurons	skeletal muscle	cardiac muscle
role	in cell-to-cell communication by providing for the propagation of signals along the neuron's axon towards ends of axon which can then connect with other neurons at synapses, or to motor cells or glands.	is to activate intracellular processes and it is the first step in the chain of events whihc leads to contraction	an initial fast sodium spike provides a "primer" to provoke the rapid onset of a calcium spike, which then produces muscle contraction
Action potential duration	2-4 ms	2-4 ms	2-4 ms
	Acetylcholine binds and then it produces an action potential	Acetylcholine binds to muscle membrane and then it produces an action potential	It transmits to the contractile muscle via gap junction
Excited by	Signals from pre existing neurons	motor nerve	own excitability ( SA / AV node , Bundle of His
absolute refractory periods duration	1-2 ms	1-3 ms	200 ms