Detron M. Brown, MPH SUMMER PBP PROGRAM: STRUCTURE AND FUNCTIONS – PHYSIOLOGY DIVISION OF NERVOUS SYSTEM AND CRANIAL NERVES

Central Nervous System (CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Sensory Neurons Motor Neurons Somatic Nervous System voluntary movements via skeletal muscles Somatic Nervous System voluntary movements via skeletal muscles Autonomic Nervous System organs, smooth muscles Autonomic Nervous System organs, smooth muscles Sympathetic - “ Fight-or-Flight ” responses Sympathetic - “ Fight-or-Flight ” responses Parasympathetic - maintenance Parasympathetic - maintenance THE NERVOUS SYSTEM The Nervous System

DIVISIONS OF THE AUTONOMIC NERVOUS SYSTEM The sympathetic division is the nervous system that prepares the body for action. The Parasympathetic part of the systems allows it to return to a resting state.

Action/Rest

Sensory (Afferent) vs. Motor (Efferent) e.g., skin e.g., muscle Gray ’ s Anatomy sensory (afferent) nerve motor (efferent) nerve Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS Neurons that transmit from the CNS to the muscles, glands, and organs

THE WITHDRAWAL REFLEX

The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb. Olfactory receptors in the olfactory mucosa in the nasal cavity receive information about smells which travel to the brain through the cranial nerve which extend from the olfactory epithelium to the olfactory bulb. Olfactory receptor neurons continue to be born throughout life and extend new axons to the olfactory bulb. OLFACTORY (I) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The optic nerve is considered part of the central nervous system.The myelin on the optic nerve is produced by oligodendrocytes rather than Schwann cells and it is encased in the meningeal layers instead of the standard endoneurium, perineurium, and epineurium of the peripheral nervous system. The optic nerve travels through the optic canal, partially decussates in the optic chiasm, and terminates in the lateral geniculate nucleus where information is transmitted to the visual cortex. Axons responsible for reflexive eye movements terminate in the pretectal nucleus. OPTIC (II) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The oculomotor nerve is the third paired cranial nerve. The oculomotor nerve contains two nuclei, including the Edinger-Westphal nucleus, which supplies parasympathetic nerve fibers to the eye to control pupil constriction and accommodation. The oculomotor nerve originates at the superior colliculus and enters through the superior orbital fissure to control the levator palpabrae superioris muscles, which hold the eyelids open. OCULOMOTOR NERVE

The trochlear nerve innervates the superior oblique muscle of the eye. The trochlear nerve contains the smallest number of axons of all the cranial nerves and has the greatest intracranial length. The two major clinical syndromes that can arise from damage to the trochlear nerve are vertical and torsional diplopia. TROCHLEAR (IV) NERVE

The sensory function of the trigeminal nerve is to provide the tactile, motion, position, and pain sensations of the face and mouth.The motor function activates the muscles of the jaw, mouth, and inner ear. The trigeminal nerve has three major branches on each side, the opthalmic nerve, maxillary nerve, and mandibular nerve, which converge on the trigeminal ganglion. The trigeminal ganglion is analogous to the dorsal root ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body. TRIGEMINAL (V) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The abducens nerve exits the brainstem at the junction of the pons and the medulla and runs upward to reach the eye, traveling between the dura and the skull. The long course of the abducens nerve between the brainstem and the eye makes it vulnerable to injury at many levels. In most mammals besides humans, it also innervates the musculus retractor bulbi, which can retract the eye for protection. ABDUCENS (VI) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The facial nerve (cranial nerve VII) is responsible for the muscles that determine facial expression as well as the sensation of taste in the front of the tongue and oral cavity. The facial nerve's motor component begins in the facial nerve nucleus in the pons and the sensory component begins in the nervus intermedius.The nerve then runs through the facial canal, passes through the parotid gland, and divides into five branches. Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (inability to do so is called lagophthalmos), pursing the lips, and puffing out the cheeks, all test the facial nerve. FACIAL (VII) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The vestibulocochlear nerve comprises the cochlear nerve which transmits hearing information and the vestibular nerve which transmits balance information. The cochlear nerve travels away from the cochlea of the inner ear where it starts as the spiral ganglia. The vestibular nerve travels from the vestibular system of the inner ear. VESTIBULOCOCHLEAR (VIII) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The glossopharyngeal nerve (cranial nerve IX) is responsible for swallowng and gagging, along with other functions. The glossopharyngeal nerve receives input from general and special sensory fibers in the back of the throat. The glossopharyngeal nerve has five components: branchial motor, visceral motor, visceral sensory, general sensory, and special sensory components. GLOSSOPHARYNGEAL (IX) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

The vagus nerve (cranial nerve X) sends information about the body's organs to the brain and carries some motor information back to the organs. The vagus nerve has axons which originate from or enter the dorsal nucleus of the vagus nerve, the nucleus ambiguus, and the solitary nucleus in the medulla. The vagus nerve is responsible for heart rate, gastrointestinal peristalsis, sweating, to name a few. VAGUS (X) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

Cranial nerve XI is responsible for tilting and rotating the head, elevating the shoulders, and adducting the scapula. Most of the fibers of the accessory nerve originate in neurons situated in the upper spinal cord.The fibers that make up the accessory nerve enter the skull through the foramen magnum and proceed to exit the jugular foramen with cranial nerves IX and X. Due to its unusual course, the accessory nerve is the only nerve that enters and exits the skull. ACCESSORY (XI) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves

It controls tongue movements of speech, food manipulation, and swallowing. While the hypoglossal nerve controls the tongue's involuntary activities of swallowing to clear the mouth of saliva, most of the functions it controls are voluntary, meaning that the execution of these activities requires conscious thought. Proper function of the hypoglossal nerve is important for executing tongue movements associated with speech.Many languages require specific uses of the nerve to create unique speech sounds, which may contribute to the difficulties some adults encounter when learning a new language. HYPOGLOSSAL (XII) NERVE The Peripheral Nervous System (PNS) > Cranial Nerves