Understanding Neurons

Neurons have many dendrites, one cell body, and a single axon with several terminal branches. A dendrite receives an external stimulus and causes an electrical disturbance in the cell body. This electrical disturbance is transmitted to the axon, where an action potential is generated if the stimulus is large enough. The action potential is propagated through the axon and is transmitted to a neighboring neuron at the synapse.

A large enough electrical disturbance will generate an action potential in the axon, but no magnitude of stimulus can create an action potential in the dendrites. Neurons do contain multiple dendrites, but they only contain one cell body and one axon. Finally, neurons transmit electrical signals to other neurons at the synapse, not at the cell body.

The correct answer is Schwann cells. Schwann cells are cells that produce the myelination present on the outer covering of the axon of the neuron. This lipid-rich material helps facilitate the movement of the action potential along the axon from the axon hillock to the axon terminal branches.

There are two types of synapses: chemical and electrical. Chemical synapses use chemical signals called neurotransmitters to transmit nerve signals between neurons, whereas electrical synapses use electrical signals. These electrical signals are transmitted through a gap junction that connects adjacent neurons. Intercalated discs in cardiac muscle contain gap junctions for the purpose of propagating electrical signals to cause systole.

A neuron receives input from other neurons at the dendrites. Neurotransmitters released by other neurons bind to receptors on the dendrites, which carry the signal to the cell body. The signal is then amplified in the cell body before being transferred to the axon. Once the signal transitions to the axon, it is considered an action potential. The signal eventually reaches the end of the axon, where the synaptic vesicles are located, and stimulates release of neurotransmitters to the next neuron's dendrites.

While both oligodendrocytes and Schwann cells produce myelin sheaths that insulate nervous system signals, only the Schwann cells are found in the peripheral nervous system.

All other cells listed are found only in the central nervous system. Microglia act as immune cells within the cerebrospinal fluid, since lymphocytes are barred entry by the blood-brain barrier. Astrocytes support the neural cells and provide nutrients. Ependymal cells are responsible for secreting cerebrospinal fluid.

Neurotransmitters from presynaptic cells are received by the dendrites of postsynaptic cells. There are myriad dendrites on each neuron that then propagate this signal to the soma (or cell body), allowing the signal to be passed down the axon to another neuron.

The axon carries action potentials away from the cell body of a neuron via a sequence of continuous depolarization. The cell body, or soma, however, is the site of neurotransmitter production and the location of the nucleus and other organelles. Every single neuron contains only one axon.

Schwann cells produce myelin for neurons of the peripheral nervous system, while oligodendrocytes produce myelin for neurons of the central nervous system.

The tiny gaps in between myelin sheaths are referred to as nodes of Ranvier. The action potential will jump from node to node as it moves down the axon.

If an axon existed without these gaps (the entire length was covered in myelin), it would be unable to conduct an action potential.