Brain and Cranial Nerves PDF

The Brain and Cranial Nerves Lecture slides prepared by Curtis DeFriez, Weber State University Copyright © John Wiley & Sons, Inc. All rights reserved. Copyright © John Wiley & Sons, Inc. All rights reserved. ...

The Brain and Cranial Nerves Lecture slides prepared by Curtis DeFriez, Weber State University Copyright © John Wiley & Sons, Inc. All rights reserved. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Human Brain ❖ Copyright © John Wiley & Sons, Inc. All rights reserved.  The Human Brain ❖ The human brain, compared to all other animals’ brains, is marked by the highest ratio of brain to body size - thought to directly correlate with our higher level of intelligence. ▪ Most of the expansion is manifest in man’s large cerebral cortex. Especially expanded are the frontal lobes which are associated with higher (executive) functions such as self-control, planning, reasoning, and abstract thought. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Development ❖ During the first 3 weeks of gestation, the human embryo's neural tube flexes as it grows, forming the three primary brain vesicles colloquially called the forebrain, midbrain, and hindbrain. The 1st and 3rd vesicles further divide forming 5 secondary brain vesicles in a process called encephalization. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Development ❖ The major parts of the adult brain are directly derived from the 2o brain vesicles: From the crescent-shaped cerebral hemispheres of the telencephalon to the inferiorly placed brain stem formed from the metencephalon and myelencephalon Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Development ❖ The brain grows at an amazing rate during development; at times, as many as 50,000 neurons are added each second! ❖ At birth, the neonatal brain looks very much like that of an adult and almost all the neurons the brain will ever have are already present. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Organization ❖ The brain stem is the continuation of the spinal cord and consists of the medulla oblongata, pons and midbrain. ❖ The cerebellum is the second largest part of the brain. ❖ The diencephalon gives rise to the thalamus & hypothalamus. ❖ The cerebrum is the newest (evolutionarily) and largest part of the brain as a whole. ▪ It is in the cerebral cortex that perception, thought, imagination, judgment, and decision making occur. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Organization ❖ The major parts of the adult brain are shown here Copyright © John Wiley & Sons, Inc. All rights reserved.  Protective Coverings ❖ The cranial meninges are continuous with the spinal meninges and mirror their structure and function – they also bear the same names: ▪ a tough outer dura mater ▪ a spidery arachnoid mater ▪ and a thin, delicate pia mater Copyright © John Wiley & Sons, Inc. All rights reserved.  Protective Coverings ❖ The cranial dura mater, however, has two layers – an external periosteal layer and an internal meningeal layer; the spinal dura mater has only one. ▪ In the brain, extensions of the dura mater form hard, non-compliant membranes that divide the intracranial vault in various ways:. ▪ The 3 important dural extensions are the falx cerebri, the falx cerebelli, and the tentorium cerebelli. Copyright © John Wiley & Sons, Inc. All rights reserved.  Protective Coverings ❖ The falx cerebri is a strong sickle-shaped fold of dura mater which descends vertically in the longitudinal fissure and separates the two cerebral hemispheres. ❖ The falx cerebelli is a small triangular process that separates the two cerebellar hemispheres. Copyright © John Wiley & Sons, Inc. All rights reserved.  Protective Coverings ❖ Clinically, the tentorium cerebelli is important because brain tumors are often characterized as supratentorial (above the tentorium) and infratentorial (below the tentorium). Most childhood tumors are infratentorial, while most adult tumors are supratentorial. ▪ Since the tentorium is a hard structure, if there is any brain swelling the brain can get partly pushed down and herniate through the tentorium, which becomes a life- threatening event. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Blood Flow ❖ The brain represents only 2 percent of total body weight, but receives about 20% of the body’s blood supply and consumes 20% of the O2 and glucose (even when resting). ❖ Anteriorly, the internal carotid arteries supply blood to the brain; the posterior blood supply is via the vertebral arteries. ❖ The internal jugular veins are the venous return Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Blood Flow ❖ The vascular endothelium around brain capillaries differs from most other organs of the body in that it forms tight junctions with the end-feet of nearby astrocytes. ▪ As a result of this unusual architecture, a blood brain barrier (BBB) is formed that serves to isolate the parenchyma of the brain from many substances in the blood that would normally be able to gain access. Encyclopedia of Life Sciences, © Wiley Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Blood Flow ❖ The BBB protects the brain from some harmful substances (like bacteria), but at a cost: ▪ For one thing, certain molecules needed to meet metabolic needs (such as glucose) must be actively transported across the barrier using specific transport proteins and energy. ▪ Another aspect of the BBB is that if a brain infection were to develop, antibiotics (and many other drugs) have difficulty crossing into the brain tissues and reaching therapeutic levels. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Blood Flow ❖ The BBB can be used advantageously in certain pharmacological situations. For example, it is well known that certain older antihistamine drugs readily cross the BBB and cause sedation. This makes these drugs not very good antihistamines, but very helpful in cough and cold medications to induce sleep (NyQuil). ▪ Drugs companies have devoted enormous resources to the development of newer 2nd and 3rd generation antihistamines that do not cross the BBB, and don’t (usually) cause somnolence – they also charge you accordingly. Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF ❖ Cerebral spinal fluid is a clear fluid that circulates through the internal cavities in the brain (called brain ventricles) and spinal cord (the central canal) and also flows over and around the brain and cord in the subarachnoid space. In essence, the brain "floats" in it. ▪ CSF absorbs shock and protects the brain and the cord. It also helps transport nutrients and wastes between blood and nervous tissues. Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF The Irrigation System of the fluid filled brain showing the circulating CSF. Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF ❖ The majority of CSF production - 80 to 150 mL at any given time in an adult - comes from ependymal cells in the choroid plexuses (networks of blood capillaries that line the ventricles). ❖ The pathway CSF follows from the internal ventricles to the SAS is given in the following sequence: lateral ventricles ⇨ interventricular foramina ⇨ third ventricle ⇨ cerebral aqueduct ⇨ fourth ventricle ⇨ median aperture (of Magendie ) and the lateral apertures (of Luschka ) ⇨ SAS Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF ❖ The choroid plexuses can be seen in this superior view of a transverse section through the brain: Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF ❖ Once in the SAS, CSF flows continuously between the pia mater covering the brain and the arachnoid that is tightly adhered to the outer dura. ❖ Pressure remains constant in the head because the rate of fluid reabsorption closely matches fluid formation at approx. 20 mL/h. Copyright © John Wiley & Sons, Inc. All rights reserved.  Production and Flow of CSF ❖ CSF is gradually reabsorbed back into the blood through the arachnoid villi (finger-like projections that extend into the dural sinuses). ❖ In this graphic, the arachnoid villi are seen projecting into the superior sagittal sinus. A cluster of arachnoid villi is called an arachnoid granulation. Copyright © John Wiley & Sons, Inc. All rights reserved.  Production _________ and___ Flow ___of__CSF ❖ Failure of CSF to form and drain normally results in a buildup of pressure called hydrocephalus. ▪ Hydrocephalus occurs with congenital abnormalities, head injury, meningitis, and episodes of bleeding into the brain. Copyright © John Wiley & Sons, Inc. All rights reserved. Parts of the Brain Copyright © John Wiley & Sons, Inc. All rights reserved.  The Brain Stem ❖ The brain stem is superior to, but continuous with, the spinal cord. Developmentally, it does not represent a single structure, but rather a group of anatomical components considered collectively. ▪ It is made up of the midbrain, pons, and medulla oblongata. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Medulla Oblongata ❖ Copyright © John Wiley & Sons, Inc. All rights reserved.  The Medulla Oblongata ❖ It has two external bulges called the pyramids formed by the largest motor tracts in the body. ❖ Axons from the left pyramid cross over to the right and axons on the right cross over to the left (decussation of pyramids) – so that the left hemisphere of the brain controls the right side muscles, while the right hemisphere controls the left side. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Medulla Oblongata ❖ Vital functional centers regulated by the medulla include: ▪ The cardiovascular center – controls the rate and force of heartbeat, and the diameter of blood vessels ▪ The respiratory rhythmicity center – controls the rate and rhythm of breathing ▪ The vomiting, coughing, and sneezing centers ❖ The nuclei associated with 5 of the 12 cranial nerves originates in the medulla (CN VIII – XII). ❖ A portion of the 4th ventricle extends to the medulla. Copyright © John Wiley & Sons, Inc. All rights reserved. The Medulla Oblongata Three cranial nerves emerge from the medulla. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Pons ❖ The pons lies directly above the medulla and anterior to the cerebellum (2.5 cm). It acts as a bridge connecting the spinal cord with the brain and parts of the brain with each other. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Pons ❖ Together with the medulla, areas in the pons help control breathing (inhalation and exhalation). ❖ The pontine respiratory group is normally inactive during quiet breathing. This group of neurons acts like an “off- switch” to terminate medullary inspiratory activity. ▪ Early termination of inspiration leads to an increase in the rate of breathing (which is why this center was formerly know as the “pneumotaxic center” - taxic meaning fast). Copyright © John Wiley & Sons, Inc. All rights reserved.  The Pons ❖ The pons contains the nuclei associated with 4 pairs of cranial nerves: V - VIII ▪ Cranial nerve V emerges directly from the pons. ▪ VI, VII, and VIII emerge from the space between the pons and the medulla. CN V exits the pons, while 3 others come from the medullary pontine angle. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Midbrain ❖ The midbrain extends from the pons to the diencephalon. ▪ The cerebral aqueduct passes through the midbrain connecting the 3rd ventricle above with the 4th ventricles below (both locations of CSF formation and circulation.) Copyright © John Wiley & Sons, Inc. All rights reserved.  The Midbrain ❖ On the anterior part of the midbrain are found the “little feet” of the cerebral peduncles. ▪ The peduncles contain axons of the corticospinal, corticobulbar, and corticopontine tracts which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla, and pons, respectively. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Midbrain ❖ On the posterior part of the midbrain are four rounded elevations known as the superior and inferior colliculi which serve as reflex centers for certain visual and auditory reflexes, and also the startle reflex. ❖ It is the origin of cranial nerves III and IV. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Midbrain ❖ The midbrain contains several other nuclei, including the darkly pigmented. Neurons that release dopamine, extending from the substantia nigra, help control subconscious muscle activities; loss of these neurons is associated with Parkinson disease. ❖ The red nucleus helps control voluntary movements of the limbs. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Reticular Formation ❖ In addition to the well-defined nuclei already described, much of the brain stem consists of a netlike arrangement of neuronal cell bodies and small bundles of myelinated axons known as the reticular formation. ▪ The ascending portion of this network is called the reticular activating system (RAS), and consists of sensory axons that project to the cerebral cortex. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Reticular Formation ❖ The RAS functions to maintain consciousness, a state of wakefulness in which an individual is fully alert, aware, and oriented. Inactivation of the RAS produces sleep, a state of partial consciousness from which an individual can be aroused. ▪ It also prevents sensory overload by filtering out insignificant information. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebellum ❖ The cerebellum, or “little brain”, is the second largest part of the brain and lies inferior to the cerebrum and posterior to the brain stem. ▪ It is separated from the cerebrum by the transverse fissure (in which the falx cerebelli is located). Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebellum ❖ The cerebellum’s central constricted area is the vermis and the lateral “wings” or lobes are the cerebellar hemispheres. ▪ The cerebellum compares intended movements with what is happening with skeletal muscles, and regulates posture, equilibrium, and balance. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Diencephalon ❖ The diencephalon is located near the midline of the brain, above the midbrain. Like the cerebral cortex, the diencephalon develops from the forebrain vesicle (the prosencephalon) - yet it is more primitive than the cerebral cortex, and lies underneath it. ▪ The diencephalon surrounds the 3rd ventricle and contains the thalamic structures. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Diencephalon ❖ The thalamus functions as a relay station for all sensory impulses to the cerebral cortex (except smell, which belong to the hypothalamus). Pain, temp, touch, and pressure are all relayed to the thalamus en route to the higher centers of the cerebral cortex. ❖ While not precisely localized here (that occurs in the cerebral cortex), all of these peripheral sensations are processed in the thalamus in conjunction with their attendant memories and the emotions they evoke. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Diencephalon ❖ The epithalamus is superior and posterior to the thalamus. ▪ It consists of the pineal gland (secretes melatonin) and habenular nuclei (emotional responses to odors). ▪ More melatonin is secreted in darkness epithalamus thalamus than light, and it is thought to promote sleepiness and help regulate our biological clocks. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Diencephalon ❖ The hypothalamus controls many homeostatic functions: ▪ It controls the Autonomic Nervous System (ANS). ▪ It coordinates between NS and endocrine systems. ▪ It controls body temperature (measured by blood flowing through it). ▪ It regulates hunger/thirst thalamus and feelings of satiety. ▪ It assists with the internal circadian clock by regulating biological activity. hypothalamus Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The cerebral cortex is the “seat of our intelligence”– it’s because of neurons in the cortex that we are able to read, write, speak, remember, and plan our life. ❖ The cerebrum consists of an outer cerebral cortex, an internal region of cerebral white matter, and gray matter nuclei deep within the white matter. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ During embryonic development, the grey matter of the brain develops faster than the white matter - the cortical region rolls and folds on itself. Convolutions and grooves are created in the cortex during this growth process. ▪ The folds are called gyri, the deepest of which are known as fissures; the shallower grooves between folds are termed sulci. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The prominent longitudinal fissure separates the cerebrum into right and left cerebral hemispheres. The central sulcus further divides the anterior frontal lobe from the more posteriorly situated parietal lobe. ▪ Note the precentral gyrus and postcentral gyrus of those two lobes. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The precentral gyrus - located immediately anterior to the central sulcus in the anterior lobe - contains the primary motor area of the cerebral cortex. Another major gyrus, the postcentral gyrus, which is located immediately posterior to the central sulcus in the parietal lobe, contains the primary somatosensory area of the cerebral cortex. ❖ The parieto-occipital sulcus separates the parietal lobe from the posterior-most occipital lobe. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The lateral cerebral sulcus (fissure) separates the frontal lobe from two laterally placed temporal lobes, hanging like ear muffs off the sides. A fifth part of the cerebrum, the insula, cannot be seen at the surface of the brain because it lies within the lateral cerebral sulcus, deep to the parietal, frontal, and temporal lobes. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The lobes of the cerebrum correspond to the bones of the braincase which bear the same names. parietal frontal parietal frontal temporal temporal occipital occipital parietal frontal occipital temporal Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ Brodmann’s areas are numbered regions of cortex that have been “mapped” to specific cognitive functions. ▪ Sensory areas of cerebral cortex are involved in perception of sensory information. ▪ Motor areas control execution of voluntary movements. ▪ Association areas deal with more complex integrative functions such as memory, personality traits, and intelligence. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum Brodmann’s areas: Numbered Regions of Cortical tissue. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The primary somatosensory area (areas 1, 2, and 3 – located in the postcentral gyrus of each parietal lobe) receives nerve impulses for, and consciously perceives the somatic sensations of touch, pressure, vibration, itch, tickle, temperature (coldness and warmth), pain, and proprioception (joint and muscle position). ▪ Each point within the area “maps” impulses from a specific part of the body (depending on the number of receptors present there rather than on the size of the body part). Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum For example, a larger region of the somatosensory area ❖ receives impulses from the lips and fingertips than from the thorax or hip. ▪ This distorted somatic sensory map of the body is known as the sensory homunculus (little man). ▪ This allows us to pinpoint (feel exactly) where somatic sensations originate. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The primary motor area (area 4 – located in the precentral gyrus of the frontal lobe) controls voluntary contractions of specific muscles or groups of muscles. ▪ The motor cortex also has a homunculus map, with more cortical area devoted to muscles involved in skilled, complex, or delicate movement. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The 1o visual area is located at the posterior tip of the occipital lobe mainly on the medial surface ❖ The 1o gustatory area is located just inferior to the 1o somatosensory area ❖ The 1o auditory area is in the superior part of the temporal lobe ❖ The 1o olfactory area is in the inferomedial temporal lobe Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The cerebral white matter consists primarily of myelinated axons in three types of tracts. ▪ Association tracts contain axons that conduct nerve impulses between gyri in the same hemisphere. ▪ Commissural tracts conduct nerve impulses between corresponding gyri from one hemisphere to another. ▪ Projection tracts convey impulses to lower parts of the CNS (thalamus, brain stem, or spinal cord) or visa versa. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The corpus callosum is one of the three important groups of commissural tracts (the other two being the anterior and posterior commissures) – it is a thick band of axons that connects corresponding areas of the two hemispheres. ▪ Through the corpus callosum, the left motor cortex (which controls the right body) is linked to the right motor cortex (which controls the left body). Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The outer surfaces of the gyri are not the only areas of gray matter in the cerebrum. Recall that the telencephalon consists of the cortex, and also the basal nuclei. ▪ The basal nuclei are conspicuous centers of cell bodies deep in the cortex. The 3 basal nuclei help initiate and terminate movements, suppress unwanted movements, and regulate muscle tone. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Cerebrum ❖ The basal nuclei also control subconscious contractions of skeletal muscles. Examples include automatic arm swings while walking and true laughter in response to a joke. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Limbic System ❖ Encircling the upper part of the brain stem and the corpus callosum is a ring of structures on the inner border of the cerebrum and floor of the diencephalon that constitutes the limbic system. Copyright © John Wiley & Sons, Inc. All rights reserved.  The Limbic System ❖ The limbic system does not represent any one part of the brain – it is more a functional system composed of parts of the cerebral cortex, diencephalon, and midbrain. ❖ The limbic system is sometimes called the “emotional brain” because it plays a primary role in promoting a range of emotions, including pleasure, pain, docility, affection, fear, and anger. ▪ Together with parts of the cerebrum, the limbic system also functions in memory. Copyright © John Wiley & Sons, Inc. All rights reserved.  Hemispheric Lateralization ❖ Although the brain is almost symmetrical on its right and left sides and shares performance of many functions, there are subtle anatomical and physiological differences between the two hemispheres. ❖ Each hemisphere specializes in performing certain unique functions, a feature known as hemispheric lateralization. Despite some dramatic differences, there is considerable variation from one person to another. Also, lateralization seems less pronounced in females. Copyright © John Wiley & Sons, Inc. All rights reserved.  Hemispheric Lateralization ❖ In most people, the left hemisphere is more important for reasoning, numerical and scientific skills, spoken and written language, and the ability to use and understand sign language. ❖ Conversely, the right hemisphere is more specialized for musical and artistic awareness; spatial and pattern perception; recognition of faces and emotional content of language; discrimination of different smells; and generating mental images of sight, sound, touch, and taste. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Waves ❖ The billions of communicating brain neurons constantly generate detectable signals called brain waves. Those we can more easily measure are generated by neurons close to the brain surface, mainly neurons in the cerebral cortex. ▪ Electrodes placed on the forehead and scalp can be used to make a record called an electroencephalogram. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Waves ❖ Summing waves of different frequency produces some characteristic, and diagnostic patterns. ▪ Alpha (10–12 Hz (cycles/sec) waves are present when awake but disappear during sleep. ▪ Beta (14–30 Hz) waves are present with sensory input and mental activity when the nervous system is active. ▪ Theta (4–7 Hz) waves indicate emotional stress or a brain disorder. ▪ Delta (1–5 Hz) waves appear only during sleep in adults but indicate brain damage in an awake adult. Copyright © John Wiley & Sons, Inc. All rights reserved.  Brain Waves ❖ Electroencephalograms are useful both in studying normal brain functions, such as changes that occur during sleep, and in diagnosing a variety of brain disorders, such as epilepsy, tumors, trauma, hematomas, metabolic abnormalities, sites of trauma, and degenerative diseases. ▪ The EEG is also utilized to determine if “life” is present, that is, to establish or confirm that brain death has occurred. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial The Twelve NervesNerves Cranial Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves Spinal Cranial C1-8, T1-12, L1-5, S1-5, Roman Numerals Designation Co1 I – XII Number 31 pairs 12 pairs Origin Spinal cord Brain 2 - a dorsal and a ventral Number of roots Single root root Most mixed; some Contents Mixed sensory only All in the Head/Neck Target Limbs/Trunk (vagus n leaves) Spinal and cranial nerves are compared in this table. Copyright © John Wiley & Sons, Inc. All rights reserved. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ The major functions of the 12 pairs of cranial nerves are detailed in the following slides. This is a picture of a masterful dissection, showing the cranial nerves in-situ (as they are “in place”). Copyright © John Wiley & Sons, Inc. All rights reserved. Cranial Nerves ❖ CN I is the olfactory nerve (sense of smell). Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN II is the optic nerve (sense of sight). Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves. ❖ CN III,, and VI innervate the extraocular muscles that allow us to move our eyes. ▪ CN III also supplies motor input to our eyelid muscles and facilitates pupillary constriction. SO4 LR6 Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN V is the trigeminal nerve (the major sensory nerve of the face). ▪ It has three large branches, each of which supplies an area of the face: ophthalmic maxillary mandibular Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN VII is the facial nerve. It has 5 large somatic branches which innervate the muscle of facial expression. It also carries some taste sensations (anterior 2/3 of tongue). ▪ Paralysis of CN VII is called and leads to loss of ability to close the eyes and impairment of taste and salivation. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN VIII is the vestibulo cochlear nerve. From the inner ear, the vestibular component carries information on balance, while the cochlear component enables hearing. ▪ Damage of CN VIII causes vertigo, ringing in the ears, and/or deafness. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN IX is the glossopharyngeal nerve. This nerve carries some taste sensations as well as ANS impulses to salivary glands and the mechanoreceptors of the carotid body and carotid sinus (senses changes in BP). Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN X is the vagus nerve (“the wanderer”), which carries most of the parasympathetic motor efferents to the organs of the thorax and abdomen. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN XI is the spinal accessory nerve. This nerve supplies somatic motor innervation to the Trapezius and Sternocleidomastoid muscles. Copyright © John Wiley & Sons, Inc. All rights reserved.  Cranial Nerves ❖ CN XII is the hypoglossal. This is a very large nerve (a lot of resources) to be devoted solely to the tongue – it takes a lot more coordination than you might guess to chew, talk, and swallow without injuring our tongue. 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