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The 12 Cranial Nerves: Overview and Functions

There are 12 pairs of cranial nerves (CNs), which run from the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification to various parts of the head, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, and trunk. The CNs can be sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology or motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology or both. Some CNs are involved in special senses, like vision Vision Ophthalmic Exam, hearing, and taste, and others are involved in muscle control of the face. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.

Last updated: 29 Apr, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

General Features

Table: Overview of the 12 cranial nerves (CNs)
Nerve CN Function Type
Olfactory I Olfaction Olfaction The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction: Anatomy ( smell Smell The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction: Anatomy) Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology
Optic II Vision Vision Ophthalmic Exam Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology
Oculomotor III Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology
Trochlear IV Eye movement ( superior oblique Superior oblique Orbit and Extraocular Muscles: Anatomy muscle) Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology
Trigeminal V Both
Abducens VI Eye movement ( lateral rectus Lateral rectus Orbit and Extraocular Muscles: Anatomy muscle) Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology
Facial VII
  • Facial movements
  • Taste from anterior ⅔ of tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy ( chorda tympani Chorda tympani A branch of the facial (7th cranial) nerve which passes through the middle ear and continues through the petrotympanic fissure. The chorda tympani nerve carries taste sensation from the anterior two-thirds of the tongue and conveys parasympathetic efferents to the salivary glands. Lips and Tongue: Anatomy)
  • Lacrimation
  • Salivation
  • Eyelid closing
  • Auditory reflex
Both
Vestibulocochlear VIII
  • Hearing
  • Balance
Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology
Glossopharyngeal IX
  • Taste and sensation of posterior ⅓ of tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy
  • Monitoring of carotid body Carotid body A small cluster of chemoreceptive and supporting cells located near the bifurcation of the internal carotid artery. The carotid body, which is richly supplied with fenestrated capillaries, senses the ph, carbon dioxide, and oxygen concentrations in the blood and plays a crucial role in their homeostatic control. Carotid Arterial System: Anatomy and sinus chemoreceptors and baroreceptors Baroreceptors Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls. Diabetes Insipidus
  • Elevation of pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy/ larynx Larynx The larynx, also commonly called the voice box, is a cylindrical space located in the neck at the level of the C3-C6 vertebrae. The major structures forming the framework of the larynx are the thyroid cartilage, cricoid cartilage, and epiglottis. The larynx serves to produce sound (phonation), conducts air to the trachea, and prevents large molecules from reaching the lungs. Larynx: Anatomy
Both
Vagus X
  • Taste from supraglottic region
  • Swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility
  • Soft palate Soft palate A movable fold suspended from the posterior border of the hard palate. The uvula hangs from the middle of the lower border. Palate: Anatomy elevation
  • Speech
  • Cough reflex
  • Parasympathetic innervation to thoracoabdominal viscera → important regulator of the pulmonary, cardiovascular, and GI systems
  • Monitoring aortic arch Aortic arch Mediastinum and Great Vessels: Anatomy chemoreceptors and baroreceptors Baroreceptors Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls. Diabetes Insipidus
Both
Accessory XI
  • Head turning
  • Shoulder shrugging
Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology
Hypoglossal XII Tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy movements Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology
Table: Mnemonics to remember the cranial nerves
Cranial nerve Mnemonic 1 Mnemonic 2 Mnemonic 3
Olfactory Ooh Oh Old
Optic Ooh Once Opie
Oculomotor Ooh One Occasionally
Trochlear To Takes Tries
Trigeminal Touch The Trigonometry
Abducens And Anatomy And
Facial Feel Final Feels
Vestibulocochlear Very Very Very
Glossopharyngeal Good Good Gloomy
Vagus Velvet Vacations Vague
Accessory Ah Are And
Hypoglossal Heaven Heavenly Hypoactive
Cranial nerves

The 12 cranial nerves as they exit from the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification and the primary sites of innervations
n.: nerve

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Location and Function

Cerebral

  • CN I (olfactory)
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology function: olfaction Olfaction The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction: Anatomy (smelling)
    • Damage impairs the sense of smell Smell The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction: Anatomy
    • Pathway (origin → termination): nasal mucosa Nasal mucosa The mucous lining of the nasal cavity, including lining of the nostril (vestibule) and the olfactory mucosa. Nasal mucosa consists of ciliated cells, goblet cells, brush cells, small granule cells, basal cells (stem cells) and glands containing both mucous and serous cells. Nose and Nasal Cavity: Anatomy → olfactory bulbs
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the cribriform plate of the ethmoid bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types
  • CN II (optic)
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology function: transmission of visual information from the retina Retina The ten-layered nervous tissue membrane of the eye. It is continuous with the optic nerve and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the choroid and the inner surface with the vitreous body. The outermost layer is pigmented, whereas the inner nine layers are transparent. Eye: Anatomy to the vision Vision Ophthalmic Exam centers of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
    • Damage causes partial or complete blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity
    • Pathway: retina Retina The ten-layered nervous tissue membrane of the eye. It is continuous with the optic nerve and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the choroid and the inner surface with the vitreous body. The outermost layer is pigmented, whereas the inner nine layers are transparent. Eye: Anatomy thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the optic canal

Midbrain Midbrain The middle of the three primitive cerebral vesicles of the embryonic brain. Without further subdivision, midbrain develops into a short, constricted portion connecting the pons and the diencephalon. Midbrain contains two major parts, the dorsal tectum mesencephali and the ventral tegmentum mesencephali, housing components of auditory, visual, and other sensorimotor systems. Brain Stem: Anatomy

  • CN III (oculomotor)
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology function: movement of the upper eyelid and eye
    • Parasympathetic function:
      • Accommodation Accommodation Refractive Errors (ability to cross eyes)
      • Constriction of the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil’s size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Pupil: Physiology and Abnormalities via the iris Iris The most anterior portion of the uveal layer, separating the anterior chamber from the posterior. It consists of two layers – the stroma and the pigmented epithelium. Color of the iris depends on the amount of melanin in the stroma on reflection from the pigmented epithelium. Eye: Anatomy sphincter muscle 
      • Dilation of the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil’s size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Pupil: Physiology and Abnormalities via the iris Iris The most anterior portion of the uveal layer, separating the anterior chamber from the posterior. It consists of two layers – the stroma and the pigmented epithelium. Color of the iris depends on the amount of melanin in the stroma on reflection from the pigmented epithelium. Eye: Anatomy dilator muscle
    • Damage causes:
      • Drooping eyelids Eyelids Each of the upper and lower folds of skin which cover the eye when closed. Blepharitis
      • Difficulty with certain eye movements
      • Lateral rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays of the eye at rest
      • Dilated pupils/difficulty focusing
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the superior orbital fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes
  • CN IV (trochlear)

Pons Pons The front part of the hindbrain (rhombencephalon) that lies between the medulla and the midbrain (mesencephalon) ventral to the cerebellum. It is composed of two parts, the dorsal and the ventral. The pons serves as a relay station for neural pathways between the cerebellum to the cerebrum. Brain Stem: Anatomy

  • CN V (trigeminal) has 3 branches:
    • Ophthalmic nerve (V1):
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation of the forehead Forehead The part of the face above the eyes. Melasma, eyes, and nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose and Nasal Cavity: Anatomy
      • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the superior orbital fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes
    • Maxillary nerve (V2):
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation of the lower eyelid, teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth: Anatomy, nasal cavity Nasal cavity The proximal portion of the respiratory passages on either side of the nasal septum. Nasal cavities, extending from the nares to the nasopharynx, are lined with ciliated nasal mucosa. Nose and Nasal Cavity: Anatomy, gums of the upper jaw Upper jaw One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy, palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Palate: Anatomy, and tonsils Tonsils Tonsillitis 
      • Autonomic innervation of the lacrimal and nasal glands
      • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the foramen rotundum
    • Mandibular nerve Mandibular nerve A branch of the trigeminal (5th cranial) nerve. The mandibular nerve carries motor fibers to the muscles of mastication and sensory fibers to the teeth and gingivae, the face in the region of the mandible, and parts of the dura. Jaw and Temporomandibular Joint: Anatomy (V3) 
      • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology innervation of the muscles of mastication Mastication The act and process of chewing and grinding food in the mouth. Jaw and Temporomandibular Joint: Anatomy
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology supply of the teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth: Anatomy, gums of the lower jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint: Anatomy, buccal mucosa Buccal mucosa Oral Cancer, dorsum of the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy, and external acoustic meatus External acoustic meatus Ear: Anatomy
      • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the foramen ovale Foramen ovale An opening in the wall between the right and the left upper chambers (heart atria) of a fetal heart. Oval foramen normally closes soon after birth; when it fails to close the condition is called patent oval foramen. Patent Foramen Ovale
    • Damage leads to loss of sensation (any branch) and/or impaired chewing (V3)
  • CN VI (abducens)
  • CN VII (facial)
    • Branches (from superior to inferior) innervating different regions of the face and neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess:Temporal
      • Zygomatic Zygomatic Either of a pair of bones that form the prominent part of the cheek and contribute to the orbit on each side of the skull. Skull: Anatomy
      • Buccal
      • Mandibular
      • Cervical
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology functions: 
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology and parasympathetic functions: 
      • Sense of taste in the anterior ⅔ of the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy ( chorda tympani Chorda tympani A branch of the facial (7th cranial) nerve which passes through the middle ear and continues through the petrotympanic fissure. The chorda tympani nerve carries taste sensation from the anterior two-thirds of the tongue and conveys parasympathetic efferents to the salivary glands. Lips and Tongue: Anatomy branch of the facial nerve)
      • Innervation of the 3 large salivary glands Salivary glands The salivary glands are exocrine glands positioned in and around the oral cavity. These glands are responsible for secreting saliva into the mouth, which aids in digestion. There are 3 major paired salivary glands: the sublingual, submandibular, and parotid glands. Salivary Glands: Anatomy, lacrimal glands Lacrimal Glands Dacryocystitis, and nasal glands 
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the stylomastoid foramen and internal auditory meatus
    • Damage leads to difficulty controlling facial muscles Facial muscles The facial muscles (also called mimetic muscles) control facial expression and are supplied by the facial nerve. Most of them originate from the skull and attach to the skin around the facial openings, which serve as a method to group or classify them. Facial Muscles: Anatomy and abnormal taste (especially sweets)
  • CN VIII (vestibulocochlear)
    • Vestibular nerve: 
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation to vestibule Vestibule An oval, bony chamber of the inner ear, part of the bony labyrinth. It is continuous with bony cochlea anteriorly, and semicircular canals posteriorly. The vestibule contains two communicating sacs (utricle and saccule) of the balancing apparatus. The oval window on its lateral wall is occupied by the base of the stapes of the middle ear. Ear: Anatomy and semicircular canals Semicircular canals Three long canals (anterior, posterior, and lateral) of the bony labyrinth. They are set at right angles to each other and are situated posterosuperior to the vestibule of the bony labyrinth (vestibular labyrinth). The semicircular canals have five openings into the vestibule with one shared by the anterior and the posterior canals. Within the canals are the semicircular ducts. Auditory and Vestibular Pathways: Anatomy 
      • Relays information regarding spatial position and motion
      • Critical for maintaining balance
    • Cochlear nerve: 
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation to the organ of Corti Organ of Corti The spiral epithelium containing sensory auditory hair cells and supporting cells in the cochlea. Organ of corti, situated on the basilar membrane and overlaid by a gelatinous tectorial membrane, converts sound-induced mechanical waves to neural impulses to the brain. Auditory and Vestibular Pathways: Anatomy, which converts sound waves into neural signals within the cochlea Cochlea The part of the inner ear (labyrinth) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the vestibular labyrinth. Ear: Anatomy
      • Critical for hearing
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the internal auditory meatus
    • Damage causes deafness, loss of balance, and nystagmus Nystagmus Involuntary movements of the eye that are divided into two types, jerk and pendular. Jerk nystagmus has a slow phase in one direction followed by a corrective fast phase in the opposite direction, and is usually caused by central or peripheral vestibular dysfunction. Pendular nystagmus features oscillations that are of equal velocity in both directions and this condition is often associated with visual loss early in life. Albinism.

Medulla

  • CN IX (glossopharyngeal) 
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology and parasympathetic functions: 
      • Taste and somatic perception Perception The process by which the nature and meaning of sensory stimuli are recognized and interpreted. Psychiatric Assessment (touch, pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, and temperature) of the posterior ⅓ of the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy
      • Proprioception Proprioception Sensory functions that transduce stimuli received by proprioceptive receptors in joints, tendons, muscles, and the inner ear into neural impulses to be transmitted to the central nervous system. Proprioception provides sense of stationary positions and movements of one’s body parts, and is important in maintaining kinesthesia and postural balance. Neurological Examination of swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility musculature
      • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology innervation of the outer ear Outer ear The outer part of the hearing system of the body. It includes the shell-like ear auricle which collects sound, and the external ear canal, the tympanic membrane, and the external ear cartilages. Ear: Anatomy 
      • Baroreceptors Baroreceptors Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls. Diabetes Insipidus in the carotid body Carotid body A small cluster of chemoreceptive and supporting cells located near the bifurcation of the internal carotid artery. The carotid body, which is richly supplied with fenestrated capillaries, senses the ph, carbon dioxide, and oxygen concentrations in the blood and plays a crucial role in their homeostatic control. Carotid Arterial System: Anatomy assist in blood pressure regulation
      • Chemoreceptors in the carotid body Carotid body A small cluster of chemoreceptive and supporting cells located near the bifurcation of the internal carotid artery. The carotid body, which is richly supplied with fenestrated capillaries, senses the ph, carbon dioxide, and oxygen concentrations in the blood and plays a crucial role in their homeostatic control. Carotid Arterial System: Anatomy monitor O2 and CO2 content of blood as part of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing regulation
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology functions: 
      • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology innervation of the palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Palate: Anatomy and the muscles of the pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy
      • Dilation of the pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy during swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility and speaking 
      • Stimulation of salivation
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the jugular foramen
    • Damage primarily impairs taste and swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility
  • CN X (vagus)
    • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology functions: 
      • Taste and sensation in the epiglottis Epiglottis A thin leaf-shaped cartilage that is covered with laryngeal mucosa and situated posterior to the root of the tongue and hyoid bone. During swallowing, the epiglottis folds back over the larynx inlet thus prevents foods from entering the airway. Larynx: Anatomy and the pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. Pharynx: Anatomy 
      • Baroreceptors Baroreceptors Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls. Diabetes Insipidus in the carotid and aortic bodies assist in blood pressure regulation
      • Monitoring of O2 and CO2 content in blood for control of ventilation Ventilation The total volume of gas inspired or expired per unit of time, usually measured in liters per minute. Ventilation: Mechanics of Breathing 
      • Sensation in thoracic and abdominal organs 
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology functions:
    • Parasympathetic functions: 
      • Contraction and relaxation of the smooth muscles Smooth muscles Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. Muscle Tissue: Histology of the GI tract 
      • Secretion Secretion Coagulation Studies of digestive juices
      • Reduction of the HR
      • Assist in control of renal function
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the jugular foramen
    • Damage results in impaired GI motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility, swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility, and speech (fatal if damage is bilateral)
  • CN XI (spinal accessory) 
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology function: movements of the head and shoulders
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the jugular foramen
    • Damage causes the head to turn towards the damaged side
  • XII (hypoglossal)
    • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology function: movements of the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy
    • Exits the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy via the hypoglossal canal
    • Damage causes the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Lips and Tongue: Anatomy to deviate towards the injured side

Mnemonic to remember the functions of the cranial nerves

Table: Primary functions of the cranial nerves
CN Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology, motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology, or both
I Some
II Say
III Marry
IV Money
V But
VI My
VII Brother
VIII Says
IX B ig Ig X-linked Agammaglobulinemia
X Brains
XI Matter
XII More

Clinical Relevance

  • Acoustic neuroma Acoustic neuroma Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Acoustic Neuroma ( Schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma): benign Benign Fibroadenoma tumor Tumor Inflammation of Schwann cells that involve the CNs within the cranium Cranium The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy. Acoustic neuroma Acoustic neuroma Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Acoustic Neuroma most frequently affects the vestibular branch of CN VIII. The condition often presents with hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss and tinnitus Tinnitus A nonspecific symptom of hearing disorder characterized by the sensation of buzzing, ringing, clicking, pulsations, and other noises in the ear. Objective tinnitus refers to noises generated from within the ear or adjacent structures that can be heard by other individuals. The term subjective tinnitus is used when the sound is audible only to the affected individual. Tinnitus may occur as a manifestation of cochlear diseases; vestibulocochlear nerve diseases; intracranial hypertension; craniocerebral trauma; and other conditions. Cranial Nerve Palsies. Treatment is with surgical resection.
  • Herpes zoster Herpes Zoster Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox ophthalmicus: subtype of shingles Shingles Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox that impacts the trigeminal nerve. Shingles Shingles Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox is due to the varicella zoster virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology (VZV). After exposure Exposure ABCDE Assessment, VZV remains latent in the dorsal root ganglion, where it lives in equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy with the healthy immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs. With age, and immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs decline, VZV can reactivate and cause a painful, vesicular rash Rash Rocky Mountain Spotted Fever called herpes zoster Herpes Zoster Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox. When herpes zoster Herpes Zoster Varicella-zoster virus (VZV) is a linear, double-stranded DNA virus in the Herpesviridae family. Shingles (also known as herpes zoster) is more common in adults and occurs due to the reactivation of VZV. Varicella-Zoster Virus/Chickenpox affects the trigeminal nerve, it can involve the cornea Cornea The transparent anterior portion of the fibrous coat of the eye consisting of five layers: stratified squamous corneal epithelium; bowman membrane; corneal stroma; descemet membrane; and mesenchymal corneal endothelium. It serves as the first refracting medium of the eye. Eye: Anatomy of the eye, which can result in vision Vision Ophthalmic Exam loss.
  • Trigeminal neuralgia Trigeminal neuralgia Trigeminal neuralgia (TN) is an often chronic and recurring pain syndrome involving the sensory distribution of the trigeminal nerve (cranial nerve (CN) V). The pain is typically unilateral and described as an acute, sharp, electric-shock-like pain involving the maxillary or mandibular areas and often associated with spasm of facial muscles. Trigeminal Neuralgia: chronic pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways disorder that affects the trigeminal nerve. Trigeminal neuralgia Trigeminal neuralgia Trigeminal neuralgia (TN) is an often chronic and recurring pain syndrome involving the sensory distribution of the trigeminal nerve (cranial nerve (CN) V). The pain is typically unilateral and described as an acute, sharp, electric-shock-like pain involving the maxillary or mandibular areas and often associated with spasm of facial muscles. Trigeminal Neuralgia can be due to compression Compression Blunt Chest Trauma caused by the superior cerebellar artery Superior cerebellar artery Cerebrovascular System: Anatomy, tumors, aneurysms, or infarcts. The condition typically presents with brief, abrupt episodes of exquisite pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways that is out of proportion to the external stimulus in the regions supplied by the trigeminal nerve.

References

  1. Park, J.K., Vernick, D.M. (2020). Vestibular schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma?search=acoustic%20neuroma
  2. Martin, K.A. Patient education: Vestibular schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma-the-basics?search=acoustic%20neuroma
  3. Kutz, J.W. (2020). Acoustic neuroma: Practice essentials, history of the procedure, epidemiology. Medscape. Retrieved May 23, 2021, from https://emedicine.medscape.com/article/882876-overview
  4. Albrecht, M.A., Levin, M.J. (2021). Epidemiology, clinical manifestations, and diagnosis of herpes zoster. UpToDate. Retrieved April 18, 2021, from https://www.uptodate.com/contents/epidemiology-clinical-manifestations-and-diagnosis-of-herpes-zoster
  5. Albrecht, M.A. (2020). Diagnosis of varicella zoster virus infection. UpToDate. Retrieved April 18, 2021, from https://www.uptodate.com/contents/diagnosis-of-varicella-zoster-virus-infection
  6. Albrecht, M.A. (2020). Treatment of herpes zoster in the immunocompetent host. UpToDate. Retrieved April 18, 2021, from https://www.uptodate.com/contents/treatment-of-herpes-zoster-in-the-immunocompetent-host
  7. Saladin, K.S., Miller, L. (2004). Anatomy and physiology. (3rd Ed. Pp. 547-556).

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