Final answer:
Large bundles of axons and dendrites visible to the unaided eye are known as nerves. These are made up of neurons, which have axons sometimes insulated by a myelin sheath that speeds up nerve impulse transmission.
Step-by-step explanation:
The large bundles of axons and dendrites that are visible to the unaided eye are called nerves. Nerves consist of many axons, which are the long thin extensions of neurons that transmit nerve impulses away from the neuron's cell body. These axons can often be wrapped in an insulating layer known as the myelin sheath. This insulating sheath enhances the speed of impulse transmission across nerve fibers and is essential for the proper functioning of the nervous system. Neurons are the cells responsible for receiving sensory input from the external world, sending motor commands to our muscles, and transforming and relaying the electrical signals at every step in between.