Lecture 18Outline of Last Lecture I. MentencephalonII. The PonsIII. MyelencephalonIV. Cerebrospinal Fluid Outline of Current LectureI. Cranial NervesII. Names of the Cranial NervesIII. Functional Grouping of Cranial NervesIV. Visceral Sensory ComponentsV. Visceral Motor FibersVI. Comparing Cranial Nerves and Spinal NervesVII. The Autonomic Nervous SystemCurrent LectureI. Cranial Nerves- Introductiona. We have 12 pairs of cranial nervesb. Attach to the brain c. Innervate the structures of the headd. Part of the peripheral nervous system e. Carry out both sensory and motor functionsII. Names of the Cranial Nervesa. Names and numbers- ordered from the forebrain to the hindbrain I. Olfactory (smell)II. Optic (visual)III. Oculomotor (innervates 4 of the muscles that move the eye)IV. Trochlear (innervates an eye moving muscle, the superior oblique, formed by looping ligament in the orbit)V. Trigeminal (has 3 big branches)VI. Abducens (innervates an eye muscle, lateral rectus, which abducts the eye, turning it laterally)VII. Facial (innervates the muscles of facial expression)VIII. Vestibulochoclear (carries information on senses of balance and hearing)IX. Glossopharyngeal (innervates the tongue and throat)X. Vagus (wanders through the head, thorax, and abdomen)XI. Accessory (an accessory part of the vagus, attaches the cervical part of the spinal cord as well as to the brain)XII. Hypoglossal (innervates the tongue moving muscles and runs inferior to thetongue)b. Attachments to the brain i. The olfactory nerves (I)1. Enter telencephalon @ olfactory bulbs2. Many thin, separate filaments makeup each olfactory nerve BIOL_315 1nd Editiona. These filaments run superiorly from a special olfactory epithelium in the nasal cavity b. Through the cribriform plate of the ethmoid bone to attach to the olfactory bulbii. The optic nerves (II)1. Enter at the diencephalon2. Really outgrowths of the braina. They are brain tracts not true nervesb. The retina of the eye is a brain nucleus that migrated out during the development, to the body surface, where light strikesiii. The oculomotor nerve (III)1. Exits at the midbrain iv. The trochlear nerve exits at the midbrain-metencephalon border v. The trigeminal, abducens, and facial attach to the ponsvi. Vestibulochoclear attaches to the pons-medulla bordervii. The other cranial nerves attach to the medulla but some of the rootlets of the accessory nerve attach to the cervical spinal cord as well viii. Most cranial nerves attach to the ventral side of the brain1. Only trochlear attaches dorsally III. Functional grouping of the cranial nervesa. Some cranial nerves are purely sensory, some are almost entirely motor, and some are mixed nerves that contain both sensory and motor fibersb. Purely sensory i. Olfactory (I)ii. Optic (II)iii. Vestibulocochlear (VIII)c. Almost purely motori. Oculomotor (III)ii. Trochlear (IV)iii. Abducens (VI)iv. Hypoglossal (XII)d. Mixed sensory and motor:i. Trigeminal (V)ii. Facial (VII)iii. Glossopharyngeal (IX)iv. Vagus + Accessory (X + XI)IV. Visceral Sensory Componentsa. General visceral sensory:i. Mixed nerves convey general sensations from different parts of the mouth, pharynx, and nasal cavityii. The more rostral of these nerves innervate regions farther forward in the mouth and pharynxiii. Oddly, the facial nerve of humans, has no general visceral sensory fibers, although it does have special visceral sensory fibers, for taste.b. Special visceral sensory (taste)i. With exception of trigeminal, all the mixed cranial nerves carry taste fibersii. Fibers in the facial nerve innervate taste buds on the anterior 2/3 of the tongue iii. The glossopharyngeal fivers innervate taste buds on the posterior 1/3 of the tongueiv. Fibers from the vagus innervate taste buds on the epiglottis V. Visceral Motor Fibersa. General visceral motori. The general visceral motor output of the body innervates all smooth muscle, cardiac muscle, and glands, and it is collectively called the autonomic nervous systemii. The facial, glossopharyngeal, and vagus all have general visceral motor fibers, which together belong to something called the cranial part of the parasympathetic division of the ANSiii. 2 exceptions to the rule that mixed cranial nerves carry autonomic nerve fibers:1. The trigeminal is a mixed nerve but it has NO autonomic fibers of its own2. The oculomotor nerve which is not a mixed cranial nerve, contains autonomic fibersb. Special visceral motor (branchial motor)i. Innervation of the pharyngeal arch musculature, which is the skeletal musculature derived from the embryonic pharynxii. All the mixed cranial nerves, without exception, have special motor fibers that innervate pharyngeal arch muscles iii. The trigeminal nerve innervates the chewing muscles iv. The facial nerve innervates the muscles of facial expression; that is, the muscles that make you blink, smile, and flare your nostrils v. The glossopharyngeal innervates a single muscle in the superior part of the pharynx vi. The vagus innervates the majority of the muscles of the pharynx as well as some muscles of the voice boxvii. The accessory nerve contains only special visceral motor fibersVI. Comparing Cranial Nerves and Spinal Nervesa. Relative to the brain, the purely motor cranial nerves occupy the same positions as do ventral roots relative to the spinal cord, in that both attach to the far ventral part of the CNSb. Ventral roots and motor cranial nerves correspond to one anotherc. A difference: the ventral roots contain both visceral and somatic motor fibers , but the motor-cranial nerves contain only somatic motor fibersd. Mixed cranial nerves, resemble dorsal roots off of the spinal cord i. But differ in containing the visceral motor fibersii. Mixed cranial nerves Resemble dorsal rootsiii. Purely motor cranial nerves resemble ventral rootsVII. The Autonomic Nervous Systema. Definitioni. The autonomic nervous system (ANS): part of the peripheral nervous system that innervates the smooth muscle and cardiac muscle of the body, plus the body’s glands1. Strictly a motor system, all the body’s general visceral motor neurons ii. Autonomic neurons have cell bodies in the visceral motor regions of the gray matter of the brain and spinal cordiii. INVOLUNTARY SYSTEM1. Normally operates below the level of our consciousnessiv. The CNS and smooth muscle or gland being innervated there are always 2 autonomic motor neurons1. 1st neuron signaling the second2. 2nd neuron