Anatomy & Physiology

Anatomy & Physiology Study Guide Beta waves are typical of individuals who are either concentrating on a task, under stress, or in a state of psychological tension. Theta waves may appear transiently during sleep in normal adults, but are most often observed in children and in intensely frustrated adults. The presence of theta waves may also signal pathology, as it may indicate the presence of a brain disorder, such as a tumor. Delta waves are very-large-amplitude, low-frequency waves. They are normally seen during deep sleep in individuals of all ages. A seizure is a temporary cerebral disorder accompanied by abnormal movements, unusual sensations, inappropriate behavior, or some combination of these symptoms. 12.14 Cranial Nerves Cranial nerves are PNS components that connect directly to the brain. The twelve pairs of cranial nerves are visible on the ventral surface of the brain, and each has a name related to its appearance or its function. The number assigned to a cranial nerve roughly corresponds to the position of the nerve along the longitudinal axis of the brain, beginning at the cerebrum. Roman numerals preceded by the letters CN are usually used. Each cranial nerve attaches to the brain near the associated sensory or motor nuclei. The sensory nuclei act as switching centers, with the postsynaptic neurons relaying the information to other nuclei or processing centers in the cerebral or cerebellar cortex. Similarly, the motor nuclei receive convergent inputs from higher centers or from other nuclei along the brain stem. Cranial nerves can be classified as primarily sensory, special sensory, motor, or mixed (sensory and motor). Sensory nerves carry somatic sensory information, including touch, pressure, vibration, temperature, or pain. The sensations of smell, sight, hearing, and balance are carried by special sensory nerves . Motor nerves are dominated by the axons of somatic motor neurons; mixed nerves have a mixture of sensory and motor fibers. The Olfactory Nerves (I) The first pair of cranial nerves carries special sensory information responsible for the sense of smell. Axons from these sensory neurons collect to form 20 or more bundles that penetrate the cribriform plate of the ethmoid bone. Almost at once these bundles enter the olfactory bulbs , neural masses on either side of the crista galli. The Optic Nerves (II) The optic nerves carry visual information from special sensory ganglia in the eyes. These nerves contain about one million sensory nerve fibers. The optic nerves pass through the optic canals of the sphenoid. Then they converge at the optic chiasm . At the optic chiasm, fibers from the nasal half of each retina cross over to the opposite side of the brain. The Oculomotor Nerves (III) The mesencephalon contains the motor nuclei controlling the third and fourth cranial nerves. Each oculomotor nerve (III) innervates four of the six extra-ocular muscles that move the eye, and the levator palpebrae superioris muscle, which raises the upper eyelid. Achieve Page 136 of 368 ©2018