**Question:** Specialized cell membrane structures that decrease electrical resistance between the cells allowing action potentials to pass efficiently from one cell to adjacent cells are the

A. Dendrites
B. Myelinated axons
C. Nerve terminals
D. Astrocytes

**Correct Answer:** B. Myelinated axons

**Core Concept:** Action potentials are rapid, transient depolarizations that propagate along the plasma membrane of excitable cells, such as neurons and muscle cells, facilitating the transmission of nerve impulses and muscle contraction, respectively. These action potentials enable organisms to transmit information and coordinate physiological responses.

**Why the Correct Answer is Right:** Myelinated axons are specialized cellular structures found primarily in the peripheral nervous system. They consist of a series of tightly packed, myelin sheaths surrounding individual axons. The myelin sheaths are formed by the oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). Myelin sheaths decrease electrical resistance between cells, thereby reducing the time and energy required for an action potential to propagate along the axon. This efficient transmission of action potentials is crucial for maintaining the integrity of the nervous system and ensuring proper cellular communication.

**Why Each Wrong Option is Incorrect:**

A. Dendrites are branched extensions of a neuron that receive and integrate synaptic inputs. They are not involved in the propagation of action potentials.

B. Unmyelinated axons, such as axons of neurons in the CNS, also transmit action potentials, but myelinated axons are more efficient due to their reduced electrical resistance.

C. Nerve terminals are specialized regions where neurons synapse with other neurons or effector cells, facilitating neurotransmitter release and communication. They are not involved in the propagation of action potentials.

D. Astrocytes are supportive cells in the CNS that help maintain the blood-brain barrier and provide structural support, not involved in the propagation of action potentials.

**Clinical Pearls:**

1. Understanding the structure and function of myelinated axons is crucial for understanding neuronal communication and the efficiency of the nervous system.
2. The presence of myelination allows for faster and more efficient propagation of action potentials, which is essential for maintaining proper neuronal function and overall physiological integrity.
3. In the CNS, unmyelinated axons (axons of neurons) are responsible for transmitting action potentials, but the efficiency of these axons is lower compared to myelinated axons due to their higher electrical resistance.