Final answer:
Cranial nerves are categorized based on sensory, motor, or mixed functions. There are twelve cranial nerves with varied functions including the senses, muscle movement, and autonomic control. Spinal nerves contain both sensory and motor fibers, which form plexuses except in the thoracic region.
Step-by-step explanation:
Function of Cranial Nerves
The twelve cranial nerves have various functions, including sensory, motor, and both. The olfactory (CNI), optic (CNII), and vestibulocochlear (CNVIII) nerves are purely sensory, responsible for smell, vision, and hearing and balance, respectively. The oculomotor (CNIII), trochlear (CNIV), and abducens (CNVI) nerves, as well as the spinal accessory (CNXI) and hypoglossal (CNXII) nerves, are motor nerves that control eye movements and muscles of the neck. The trigeminal (CNV), facial (CNVII), glossopharyngeal (CNIX), and vagus (CNX) nerves include both sensory and motor functions, with the trigeminal nerve carrying somatic sensations from the head and the others involved in taste, facial muscle control, salivation, and visceral responses.
Autonomic Functions of Cranial Nerves
Three of the cranial nerves contain autonomic fibers: the oculomotor nerve initiates pupillary constriction, the facial and glossopharyngeal nerves stimulate salivation, and the vagus nerve primarily targets autonomic ganglia in the thoracic and upper abdominal cavities.
Sensory and Motor Components of Spinal Nerves
Spinal nerves are mixed nerves, containing both sensory and motor fibers. They merge into plexuses which organize the nerves to serve different body parts. Thoracic spinal nerves do not form a plexus and directly give rise to intercostal nerves.