Which of the following nerves are NOT blocked by spinal or epidural anesthesia?
A. Motor
B. Sensory
C. Sympathetic
D. Parasympathetic
The correct answer and explanation is:
The correct answer is D. Parasympathetic.
Spinal or epidural anesthesia is a commonly used technique to provide regional anesthesia for surgeries, particularly in the lower abdomen, pelvis, and legs. This type of anesthesia works by blocking nerve signals in a specific region of the body, typically targeting the nerve fibers that transmit pain, motor, and sympathetic signals.
Spinal and epidural anesthesia primarily works by injecting a local anesthetic into the epidural space or subarachnoid space surrounding the spinal cord. This prevents nerve signals from traveling along the sensory (pain), motor, and sympathetic fibers.
- Motor nerves: Motor nerve fibers are responsible for muscle control, and these are usually blocked by spinal or epidural anesthesia. This is why patients undergoing surgeries like cesarean sections or lower abdominal surgeries often experience paralysis or loss of muscle movement below the level of anesthesia.
- Sensory nerves: These fibers transmit sensory information, including pain, temperature, and touch. Local anesthetics effectively block sensory nerve transmission, providing pain relief or complete numbness during surgery.
- Sympathetic nerves: The sympathetic nervous system controls functions such as blood vessel constriction, heart rate, and sweating. Spinal and epidural anesthesia can block these nerves, which often results in a drop in blood pressure and a feeling of warmth or sweating in the patient, especially if the anesthesia is administered at a higher dose or higher level of the spine.
- Parasympathetic nerves: Unlike the other nerve types, parasympathetic nerves are generally not blocked by spinal or epidural anesthesia. The parasympathetic nervous system is primarily involved in “rest and digest” activities such as slowing the heart rate, promoting digestion, and regulating certain glandular functions. These nerve fibers are less affected by local anesthetics compared to sympathetic and sensory nerves.
In summary, while motor, sensory, and sympathetic nerve signals are effectively blocked by spinal or epidural anesthesia, parasympathetic fibers are typically not directly affected, meaning the parasympathetic system continues to function even during regional anesthesia.