Cranial Nerves PDF

13 The Peripheral Nervous System (PNS) Part A  Peripheral Nervous System (PNS) PNS – all neural structures outside the brain and spinal cord Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings Provides links to and from the external env...

13 The Peripheral Nervous System (PNS) Part A  Peripheral Nervous System (PNS) PNS – all neural structures outside the brain and spinal cord Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings Provides links to and from the external environment  Structure of a Nerve Nerve – cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue Connective tissue coverings include: – Endoneurium – loose connective tissue that surrounds axons – Perineurium – coarse connective tissue that bundles fibers into fascicles – Epineurium – tough fibrous sheath around a nerve Structure of a Nerve Figure 13.3b  Classification of Nerves Sensory and motor divisions Sensory (afferent) – carry impulse to the CNS Motor (efferent) – carry impulses from CNS Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve  Peripheral Nerves Mixed nerves – carry somatic and autonomic (visceral) impulses The four types of mixed nerves are: – Somatic afferent and somatic efferent – Visceral afferent and visceral efferent Peripheral nerves originate from the brain or spinal column  Cranial Nerves Twelve pairs of cranial nerves arise from the brain They have sensory, motor, or both sensory and motor functions Each nerve is identified by a number (I through XII) and a name Four cranial nerves carry parasympathetic fibers that serve muscles and glands Cranial Nerves Figure 13.5a Summary of Function of Cranial Nerves Figure 13.5b  Cranial Nerve I: Olfactory Arises from the olfactory epithelium Passes through the cribriform plate of the ethmoid bone Fibers run through the olfactory bulb and terminate in the primary olfactory cortex Functions solely by carrying afferent impulses for the sense of smell Cranial Nerve I: Olfactory Figure I from Table 13.2  Cranial Nerve II: Optic Arises from the retina of the eye Optic nerves pass through the optic canals and converge at the optic chiasm the X-shaped structure formed at the point below the brain where the two optic nerves cross over each other They continue to the thalamus where they synapse From there, the optic radiation fibers run to the visual cortex Functions solely by carrying afferent impulses for vision Cranial Nerve II: Optic Figure II Table 13.2  Cranial Nerve III: Oculomotor Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape Parasympathetic cell bodies are in the ciliary ganglia Cranial Nerve III: Oculomotor Figure III from Table 13.2  Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle Primarily a motor nerve that directs the eyeball Cranial Nerve IV: Trochlear Figure IV from Table 13.2  Cranial Nerve V: Trigeminal Composed of three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3) Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3) Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication Cranial Nerve V: Trigeminal Figure V from Table 13.2  Cranial Nerve VI: Abdcuens Fibers leave the inferior pons and enter the orbit via the superior orbital fissure Primarily a motor nerve innervating the lateral rectus muscle Figure VI from Table 13.2  Cranial Nerve VII: Facial Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face Mixed nerve with five major branches Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands Sensory function is taste from the anterior two- thirds of the tongue Cranial Nerve VII: Facial Figure VII from Table 13.2  Cranial Nerve VIII: Vestibulocochlear Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border Two divisions – cochlear (hearing) and vestibular (balance) Functions are solely sensory – equilibrium and hearing Cranial Nerve VIII: Vestibulocochlear Figure VIII from Table 13.2  Cranial Nerve IX: Glossopharyngeal Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat Nerve IX is a mixed nerve with motor and sensory functions Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx Cranial Nerve IX: Glossopharyngeal Figure IX from Table 13.2  Cranial Nerve X: Vagus The only cranial nerve that extends beyond the head & neck Fibers emerge from the medulla via the jugular foramen The vagus is a mixed nerve Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs Its sensory function is in tastes Cranial Nerve X: Vagus Figure X from Table 13.2  Cranial Nerve XI: Accessory Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord The spinal root passes upward into the cranium via the foramen magnum The accessory nerve leaves the cranium via the jugular foramen  Cranial Nerve XI: Accessory Primarily a motor nerve – Supplies fibers to the larynx, pharynx, and soft palate – Innervates the trapezius and sternocleidomastoid, which move the head and neck Cranial Nerve XI: Accessory Figure XI from Table 13.2  Cranial Nerve XII: Hypoglossal Fibers arise from the medulla and exit the skull via the hypoglossal canal Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech Cranial Nerve XII: Hypoglossal Figure XII from Table 13.2