Biological Systems MCAT Practice Exam

Where is the axon hillock located and what is its significance?

1. At the synapse; it releases neurotransmitters

2. At the cell body; it contains ribosomes

3. At the junction of dendrites and the axon; highest concentration of Na+ channels

4. At the base of the axon; it provides insulation

The correct answer is: At the junction of dendrites and the axon; highest concentration of Na+ channels

The axon hillock is a critical region of a neuron located at the junction of the cell body and the axon. This area is significant because it is where the decision to initiate an action potential occurs. The axon hillock has the highest concentration of voltage-gated sodium channels compared to other parts of the neuron. When the neuron receives sufficient excitatory signals, the membrane potential at the axon hillock can reach the threshold level needed to trigger an action potential. The influx of sodium ions through these channels facilitates the rapid depolarization of the neuron that constitutes the action potential, allowing for the propagation of the signal down the axon. This location and function play a pivotal role in neuronal communication, as it determines whether a signal will be transmitted further along the axon or if it will die out at the dendrites or cell body. The high density of sodium channels in this specific area is crucial for the rapid and efficient transmission of electrical impulses in the nervous system.