The nervous system coordinates every function in the human body, from basic breathing to complex sensory processing. In midwifery, understanding this system helps explain how mothers sense uterine contractions and how neonates respond to touch and pain. The structural and functional unit of this vast communication network is the neuron.
Neurons consist of three primary parts:
Axons are often wrapped in a fatty insulating substance called myelin, produced by specialized cells like Schwann cells in the peripheral nervous system. Gaps in this myelin sheath are known as nodes of Ranvier. These structural features determine how fast and efficiently nerve messages travel through the body.
Before a nerve can transmit a message, it must maintain a state of readiness called the resting membrane potential. In a resting neuron, the inside of the cell membrane is negatively charged compared to the outside, typically measuring around -70 millivolts.
This electrical difference is maintained through a careful distribution of ions across the cell membrane:
Because the membrane is slightly permeable to potassium through leak channels, potassium tends to drift outward down its concentration gradient, leaving behind trapped intracellular proteins that carry a negative charge. This baseline electrical charge is essential because it stores potential energy, ready to be released the moment the neuron is stimulated.
When a stimulus reaches a neuron and depolarizes the membrane to a specific threshold—usually around -55 mV—an action potential is triggered. This event is an all-or-none electrical impulse that travels rapidly down the axon.
Voltage-gated sodium channels suddenly fly open, allowing a rush of positively charged sodium ions to flood into the cell. This rapid influx causes the inside of the membrane to briefly become positive, a phase called depolarization. As the electrical peak is reached, these sodium channels snap shut and voltage-gated potassium channels open, allowing potassium ions to rush outward, restoring negative internal charges during repolarization.
Following an action potential, the neuron undergoes a brief recovery phase known as the refractory period. This phase is divided into two parts:
These refractory periods ensure that nerve impulses travel in only one direction—away from the cell body and toward the axon terminal. They also prevent signals from merging together or traveling backward.
Nerve impulses travel much faster down myelinated axons than unmyelinated ones. Because myelin blocks ion movement across most of the axon surface, the action potential cannot occur smoothly along the entire length of the fiber. Instead, the electrical signal leaps from one node of Ranvier to the next. This jumping form of transmission is called saltatory conduction, derived from the Latin word meaning to leap.
This mechanism conserves cellular energy because ion pumps only need to work at the exposed nodes rather than across the entire axon membrane. Conditions that damage myelin, such as multiple sclerosis, slow down this conduction and disrupt neural communication.
When an action potential reaches the end of an axon, it cannot jump directly across the physical gap—called the synaptic cleft—to the next cell. Communication becomes chemical across this junction.
Common neurotransmitters include acetylcholine at neuromuscular junctions and norepinephrine in the autonomic nervous system. Once their job is finished, enzymes break them down or neighboring cells reabsorb them to clear the channel.
Understanding nerve impulse transmission directly supports safe and effective midwifery practice, particularly during labor pain management and nervous system complications.
Recognizing how chemical and electrical blocks alter nerve conduction helps midwives monitor patients receiving regional anesthesia and manage obstetric emergencies safely.