What is the primary difference between cardiac nodal cells and neurons?

What is the primary difference between cardiac nodal cells and neurons?

• A. Nodal cells can reach threshold without stimulation, while neurons require neurotransmitters.
• B. Nodal cells rely on more abundant mitochondria than neurons.
• C. Neurons can reach threshold without stimulation, while nodal cells require input from neurons.
• D. Nodal cells have no voltage-gated channels.

Answer: (A)

Automaticity is the key idea here. Cardiac nodal cells, like those in the SA node, can spontaneously depolarize and reach the threshold without any external stimulation, thanks to pacemaker currents that cause a slow, gradual depolarization toward threshold. When they hit threshold, voltage-gated calcium channels open to produce the action potential, driving the rhythmic heartbeat. Neurons, in contrast, typically stay at a resting potential and need depolarizing input from synaptic neurotransmitters to reach threshold before firing. Once threshold is reached in neurons, fast voltage-gated sodium channels open to generate the spike. So the defining difference is automatic, self-initiated activity in nodal cells versus stimulus-dependent activation in neurons. The other statements don’t fit: nodal cells do have voltage-gated channels and do not require input from neurons to reach threshold, and mitochondria abundance isn’t the main distinguishing feature.

Automaticity is the key idea here. Cardiac nodal cells, like those in the SA node, can spontaneously depolarize and reach the threshold without any external stimulation, thanks to pacemaker currents that cause a slow, gradual depolarization toward threshold. When they hit threshold, voltage-gated calcium channels open to produce the action potential, driving the rhythmic heartbeat. Neurons, in contrast, typically stay at a resting potential and need depolarizing input from synaptic neurotransmitters to reach threshold before firing. Once threshold is reached in neurons, fast voltage-gated sodium channels open to generate the spike. So the defining difference is automatic, self-initiated activity in nodal cells versus stimulus-dependent activation in neurons. The other statements don’t fit: nodal cells do have voltage-gated channels and do not require input from neurons to reach threshold, and mitochondria abundance isn’t the main distinguishing feature.