Final answer:
The nerve fibers that sense dull pain and warmth in the lateral dorsal horn of the spinal cord are slow, unmyelinated C fibers. These fibers are part of the spinothalamic tract and convey pain and temperature sensations to the brain.
Step-by-step explanation:
The type of nerve fibers that sense dull pain and warmth in the lateral dorsal horn of the spinal cord are typically slow, unmyelinated fibers known as C fibers. These fibers are part of the spinothalamic tract, which is responsible for conveying pain and temperature sensations to the brain. C fibers carry the sensation of dull pain and warm temperatures, while sharper pain and cold temperatures are typically conveyed by slightly faster, thin, myelinated A-delta fibers. Both types of fibers enter the spinal cord through the dorsal nerve root. C fibers are characterized as being thin and unmyelinated, which contributes to their slower conduction velocity compared to myelinated fibers.
In the spinothalamic tract, sensory information from these fibers decussates, or crosses over, to the opposite side of the spinal cord from which they entered. This information then travels up to the brain, where it reaches the thalamus and ultimately projects to the somatosensory cortex.