In Chapter 4 we learned that the peripheral nervous system contains nerve fibers (bundles of axons and sometimes dendrites). Most of these nerves enter and leave the spinal cord, but the cranial nerves connect directly to the brain

Describe the role played by the cranial nerves that are involved in the senses of vision, hearing, and smell.

What will be an ideal response?

Answer: A good answer will include the following key points.
• The cranial nerves are part of the somatic division of the peripheral nervous system.
• There are 12 pairs of cranial nerves connected directly to the brain.
• The function of the cranial nerves for vision, hearing, and smell is to carry information to the brain from the eyes, the ears, and the nose.
• The optic nerve is made up of axons of ganglion cells that receive information from the rods and cones by way of the bipolar cells.
• The auditory nerve is made up of axons of auditory nerve cells that receive their input from the hair cells in the cochlea.
• The olfactory nerve carries information from olfactory receptors in the nasal cavities to the brain's olfactory bulb.
• The optic and auditory nerves direct the information to the thalamus and it is sent on to the cortex by cells in the thalamus.
• Olfactory information is sent directly to the cortex from the olfactory bulb, the only sensory system to bypass the thalamus.