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Peripheral Nervous System Peripheral Nervous System Organization of Nervous System: The peripheral nervous system links the brain to the “real” world Nervous system Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor output Brain Spinal cord Ganglia (neuron cell bodies) Sensory input Motor division Sensory division (efferent) (afferent) Nerve Types: Nerves (bundles of axons) 1) Sensory nerves (contains only afferent fibers) Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle) 2) Motor nerves (contains only efferent fibers) 3) Mixed nerves (contains afferent / efferent fibers) Sensory receptors Most nerves in the human body are mixed nerves Sympathetic division Parasympathetic division Motor output Peripheral Nervous System Peripheral Nervous System Nerve Structure: Endoneurium A. Epineurium: Classification of Nerve Fibers: • Classified according to conduction velocity • Outside nerve covering Perineurium • Dense network of collagen fibers Classification Type Relative diameter Relative conduction velocity A alpha (A) Largest Fastest (120 m / s) Yes A beta (A) Medium Medium Yes A gamma (A) Medium Medium Yes A delta (A) Small Medium Yes B Small Medium Yes C Smallest Slowest (0.2 m / s) No Ia Largest Fastest Yes Myelination B. Perineurium: • Divides nerve into fascicles • Contains blood vessels Epineurium C. Endoneurium: Sensory and Motor • Surrounds individual axons and ties them together (Erlanger & Gasser) Fascicle Ib Largest Fastest Yes Sensory only II Medium Medium Yes (Lloyd & Hunt) III Small Medium Yes IV Smallest Slowest No Marieb & Hoehn – Figure 13.26 Sensory Systems Peripheral Nervous System Organization of Nervous System: “Nothing is in the mind that does not pass through the senses” Nervous system Aristotle (~ 350 B.C.) Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor output Brain Spinal cord Sensory input Motor division Sensory division (efferent) (afferent) Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle) Sympathetic division Parasympathetic division • Sensory receptors provide the only channels of communication from the external world to the nervous system: • Detections: Electrical impulses - triggered by receptor cells • Sensations: Electrical impulses - reach brain via neurons • Perceptions: Interpretation of electrical impulses by brain Subjective Sensations / perceptions are not inherent in stimuli themselves; instead they depend on the neural processing of the stimuli 1 Sensory Systems Sensory Systems Sensory Pathways in NS: Fourth-order neuron midline 1) Receptor: Type of Receptor: • Converts stimuli to electrochemical energy Modality: Category of sensation Sensory Receptors: Modality: Location: Cerebral cortex • Structure variable • Specialized epithelial cells (e.g., vision) • Modified neurons (e.g., olfaction) Third-order neuron • Skin (touch) • Inner ear (audition) • Inner ear (vestibular) Mechanoreceptors 2) First-order afferent neuron: Audition Touch • Cell body located in ganglion (PNS) Vestibular Thalamus Photoreceptors Second-order neuron 3) Second-order afferent neuron: • Eye (vision) Vision • Synapse with first-order neuron at relay nuclei • Many first-order synapse with one second-order Brain stem • Interneurons present (signal processing) Chemoreceptors • Cross at midline (decussate) Taste Olfaction Osmolarity • Tongue (taste) • Nose (olfaction) • Vessels (osmolarity) 4) Third-order afferent neuron: • Reside in thalamus (relay nuclei) 5) Fourth-order afferent neuron: Thermoreceptors Relay nucleus • Interneurons present (signal processing) Temperature Receptor Spinal cord First-order neuron • Reside in appropriate sensory area • Skin (pain) Nociceptors Pain Guyton & Hall – Figure 46.2 / 46.3 Sensory Systems • Skin (temperature) Costanzo – Figure 3.5 / 3.6 Sensory Systems Sensory Receptors: Sensory Receptors: Sensory transduction: The process by which environmental stimuli activates a receptor and is converted into electrical energy Receptor Field: An area of the body that when stimulated results in a change in firing rate of a sensory neuron • Receptor excitation = Change in membrane potential (Receptor potential) Receptor fields may be excitatory or inhibitory Receptor fields exist for first-, second-, third-, and fourth-order neurons (usually via opening of ion channels) Excitatory receptor fields increase firing rate Inhibitory receptor fields decrease firing rate Example: Pacinian corpuscle 1) Pressure causes a change in the membrane properties (e.g., mechanical deformation) Receptor Potential > Threshold Action Potential ( Intensity = Receptor potential = AP frequency) 2) Ion channels open; receptor potential develops • Amplitude correlates with stimulus size 3) Receptor potential triggers action potential The smaller a receptor field, the more precisely the sensation can be localized Sensory Systems Lateral inhibition defines boundaries and provides a contrasting border Sensory Systems Adaptation depends on how quickly receptor potential drops below threshold Sensory Receptors: Sensory Receptors: Sensory coding: Various aspects of perceived stimuli are encoded and sent to the proper location in the CNS Sensory adaptation: When a constant stimulus is applied to a receptor, the frequency of action potentials generated declines over time Features encoded: 1) Modality 2) Location Threshold of Detection: Weakest signal that will produce a receptor response 50% of the time Labeled Line Principle: Receptors respond to single modality Touch receptor Tonic receptors (slowly adapting receptors) 3) Threshold Somatosensory cortex Receptor fields Vision: 1 photon of light Hearing: Bending of hair equal to diameter of H atom 4) Intensity 5) Duration • Number of receptors activated Length of time a sensory neuron fires • Firing rate of sensory neurons • Types of receptors activated Can encode stimulus intensity Will adapt to extinction; may take hours / days Pattern of adaptation differs among different types of receptors During prolonged stimulus, receptors “adapt” to the stimulus • Transmit impulses as long as stimulus present • Keep brain appraised of body status Guyton & Hall – Figure 46.5 Costanzo – Figure 3.7 2 Costanzo – Figure 3.8 Sensory Systems Sensory Receptors: Adaptation depends on how quickly receptor potential drops below threshold Sensory adaptation: When a constant stimulus is applied to a receptor, the frequency of action potentials generated declines over time Sensory Systems Rapid adapters = Change in velocity Somatosensory System: Slow adapters = Intensity; duration • Processes information about touch, position, pain, and temperature Mechanoreceptors: Phasic receptors Two-point discrimination (rapidly adapting receptors) Can not encode stimulus intensity Pattern of adaptation differs among different types of receptors Pacinian corpuscle Meissner’s corpuscle Location = Subcutaneous; intramuscular Detection = Vibration; tapping Adaptation = Very rapidly Location = Non-hairy skin Detection = Tapping; fluttering Adaptation = Rapidly • Transmit impulses only when change is taking place Hair plexus Ruffini’s corpuscle • Important for predicting future position / condition of body Location = Hairy skin Detection = Velocity; movement direction Adaptation = Rapidly Location = Skin; joint capsules Detection = Stretch; joint rotation Adaptation = Slowly Guyton & Hall – Figure 46.5 Costanzo – Figure 3.7 Costanzo – Figure 3.8 / 3.9 Sensory Systems Sensory Systems Rapid adapters = Change in velocity Slow adapters = Intensity; duration Somatosensory System: • Processes information about touch, position, pain, and temperature Somatosensory System: • Processes information about touch, position, pain, and temperature Mechanoreceptors: Nociceptors: • Respond to noxious stimuli that can produce tissue damage Mechanical nociceptors: • Respond to mechanical stimuli Merkel’s receptor / Tactile disc Location = Non-hairy skin / Hairy skin Detection = Vertical indentation Adaptation = Slowly • A delta (A) afferent neurons (myelinated) Polymodal nociceptors: • Respond to multiple stimuli: Thermoreceptors: • High-intensity chemical stimuli • Hot / Cold stimuli • C afferent neurons (unmyelinated) • Slowly adapting receptors; located in skin Process where axons of nociceptors release substances that sensitize the nociceptors to stimuli that were not previously painful • Overlap in response ranges • Do not respond at extreme ranges (nociceptors) Sensory Systems • H+ • K+ • ATP • Prostaglandins • Bradykinins • Substance P Sensory Systems Somatosensory Pathways: Somatosensory Pathways: midline 1) Dorsal column system midline 2) Anterolateral (spinothalamic) system • Information transmitted: • Information transmitted: Cerebral cortex a) Discriminative touch b) Pressure / Vibration c) Two-point discrimination Cerebral cortex a) Pain b) Temperature / Light touch • Consists mainly of groups III and IV fibers • Fast pain (e.g., pin prick) d) Proprioception Thalamus • Consists mainly of groups I and II fibers Thalamus • A delta fibers; group II & group III fibers • Rapid onset / offset; precisely localized • Slow pain (e.g., burn) • Fibers decussate in brain stem (second-order neurons) • Nucleus gracilis = Info from lower body • Nucleus cuneatus = Info from upper body Fasciculus gracilis Chemical cues released at damaged / Intense activity areas include: Hyperalgesia: • Cold receptors vs. warm receptors Brain stem Fasciculus cuneatus • C fibers; group IV fibers Brain stem • Aching / throbbing; poorly localized Lateral spinothalamic (pain / temperature) Receptor Marieb & Hoehn – Figure 12.33 Receptor Spinal cord Ventral spinothalamic Marieb & Hoehn – Figure 12.33 Spinal cord (light touch) 3 Sensory Systems Sensory Systems Somatosensory Pathways: Vision: midline 2) Anterolateral (spinothalamic) system 70% of sensory receptors (~ 1 ml / day) Referred Pain: 50% of cerebral cortex Cerebral cortex Thalamus Brain stem Contained in orbit of skull: 1) Orbital fat (cushions / insulates eye) 2) Extrinsic eye muscles (6) 3) Lacrimal gland: Produces tears Dematomal rule: Sites on the skin are innervated by nerves arising from the same spinal cord segments as those innervating the visceral organs • Lubricates eye Strabismus: • Supplies nutrients / oxygen Receptor Spinal cord A condition in which an eye rotates medially / laterally • Provides antibacterial enzymes Marieb & Hoehn – Figure 14.8 Marieb & Hoehn – Figure 15.3 Sensory Systems Cornea is the only tissue that can be transplanted with limited rejection issues Vision: Layers of the Eye: 1) Fibrous Layer: (outermost) Cornea: Sclera: Transparent window “White of the eye” • Offers structurally support / protection Sclera • Acts as anchoring point for muscles Cornea • Assists in light focusing 2) Vascular Layer: Optic Disk (blind spot): Origin of optic nerve; no photoreceptors present Layers of the Eye: 3) Retina: (innermost) • Pigmented layer (light absorption) Sclera • Neural layer (light detection) Cornea Choroid Choroid (middle) • Contains blood vessels / lymph vessels Iris • Controls shape of lens Iris: Regulates size of pupil radial muscles constrict Fovea Pigmented Layer Incoming light • Regulates light entering eye circular muscles constrict Marieb & Hoehn – Figure 15.4 / 15.6 Sensory Systems Vision: Ciliary body Iris Optic Disk Ciliary body Retina Choroid: Pigmented layer; delivers nutrients to retina Ciliary Body: Parasympathetic Sympathetic Smooth, muscular ring; controls lens shape • Only contain brown pigment Marieb & Hoehn – Figure 15.4 Fovea centralis • Photoreceptors (light detectors) • Rods (light sensitive - ~ 125 million / eye) • Cones (color sensitive - ~ 6 million / eye) Cones clustered in fovea of macula lutea (sharp focus) Sensory Systems Sensory Systems Vision: Posterior segment Lasik eye surgery Vision: Segments of the Eye: For clear vision, light must be focused on the retina Aqueous Humor: Circulating fluid in anterior segment • Nutrient / waste transport • Cushioning of eye • Retention of eye shape Vitreous Humor: Gelatinous mass in posterior segment • Transmits light • Stabilize eye shape • Holds retina firmly in place Anterior segment Close objects = focal distance Canal of Schlemm: Drains aqueous humor Accommodation: 1) Cornea: 85% of refraction (fixed) Intraocular Pressure = 12 – 21 mm Hg Glaucoma: Disease where intraocular pressure becomes pathologically high (~ 70 mm Hg) Rounder lens = focal distance Refraction: The bending of light when it passes between mediums of different density Changing the shape of a lens to keep an image in focus 2) Lens: 15% of refraction (variable) • Composed of lens fibers (cells) Ciliary body produces aqueous humor • Crystallins (1 – 2 l / minute) (transparent proteins) Cataract: (cloudy lens) (constant focal length) Marieb & Hoehn – Figure 15.8 4 Sensory Systems Sensory Systems 20 / 20 = Standard visual acuity Near point of vision: Vision: Inner limit of clear vision Accommodation: Loss of lens elasticity 20 / 200 = Legally blind Vision: When Things Go Wrong: Children = 7 – 9 cm Young Adults = 15 – 20 cm Elderly Adults = 70 – 85 cm tightens suspensory ligaments Near-sighted Far-sighted relaxes suspensory ligaments Emmetropia Lens flattens for distant object focus; Ciliary body RELAXES Myopia Hyperopia Lens bulges for near object focus; Ciliary body CONTRACTS Astigmatism: In Addition: • Pupils constrict • Eyeballs converge Warping of the lens or cornea leading to image distortion Randall et al. – Figure 7.38 Sensory Systems Correct with diverging lens Correct with converging lens Sensory Systems Horizontal cells / Amacrine cells Vision: (facilitate / inhibit serial links – retinal processing) Vision: Retinal Layers: Pigment cell layer • Absorbs stray light • Storage site for retinal (R) = Receptor cells Photoreceptor layer • Rods / cones (H) = Horizontal cells Outer nuclear layer • Nuclei of receptor cells Outer plexiform layer • Synapses between receptors and interneurons Inner nuclear layer • Nuclei of interneurons Inner plexiform layer • Synapses between interneurons and ganglion cells Ganglion cell layer • Nuclei of ganglion cells (B) = Bipolar cells (A) = Amacrine cells Photon: Basic unit of visible light High Energy Low Energy (short wavelength) (long wavelength) Optic nerve layer • Leave eye via optic disc Serial link Costanzo – Figure 3.13 Sensory Systems Sensory Systems Vision: Vision: Retinal Layers: Photoreception: A single photon of light can activate a rod; several hundred photons of light are required to activate a cone (Day vision) (R) = Receptor cells (H) = Horizontal cells (B) = Bipolar cells (A) = Amacrine cells Cones demonstrate high acuity and low sensitivity Rod Structure: Cone Structure: (more abundant In rods) • Only a few cones synapse on a single bipolar cell Light-sensitive photochemicals • In fovea, a single cone synapses on a single bipolar cell Outer segment • A single bipolar cell synapses on a single ganglion cell (Night vision) Rods demonstrate low acuity and high sensitivity Cytoplasm / cytoplasmic organelles • Many rods synapse on a single bipolar cell Inner segment • Light striking any one rod will activate the bipolar cell • Multiple bipolar cells may synapse on a single ganglion cell Costanzo – Figure 3.13 Connection to neural elements Connected via individual cilium Synaptic terminal Costanzo – Figure 3.14 5 Sensory Systems Sensory Systems Vision: Vision: Photoreception: Photoreception: Photochemistry of Vision: Rod Receptor Potential: • Rods and cones contain chemicals that decompose on exposure to light • Rods = Rhodopsin (visual purple) • Cones = Cone pigments (color pigments) Similar compositions • At rest (in dark…), rod receptor potential ~ - 40 mV (receptor average = - 80 / - 90 mV) • Cause: Outer segment highly permeable to Na + Dark Current Rhodopsin decomposition triggers hyperpolarization of receptor cell Example: Rhodopsin Structure: • Opsin = membrane protein • Retinal = light-absorbing pigment Hyperpolarize (aldehyde of vitamin A) The greater the amount of light, the greater the hyperpolarization Two sterically distinct retinal states in the retina Light (photoisomerization) cis-form trans-form constant NT release NT release NT = Glutamate Sensory Systems Sensory Systems Night Blindness: Reduced photosensitivity of eyes Vision: Vision: Photoreception: Photoreception: Rhodopsin Activation: (nutritional deficiency of vitamin A) Regeneration of Rhodopsin: Storage location cGMP no longer present to bind to ion channels 1) Conformational change in opsin (picked up from blood) 4) Closure ion channels (Free of opsin) Trans-retinal detaches Opsin converted to metarhodopsin II 3) Activation of phosphodiesterase (enzyme) Bleaching: The fading of photopigment upon absorption of light 2) Activation of transducin (G protein) Randall et al. – Figure 7.44 Randall et al. – Figure 7.45 Sensory Systems Sensory Systems Vision: Vision: Photoreception: Photoreception: Sex-linked (1% of males affected) 8% of women carriers Very rare (autosomal recessive) Color Vision: • Three classes of cones recognized • Trichromacy Theory • Humans: Blue, Green, Orange • Sensation of color = CNS processing • Color sensitivity depends on opsin structure, not light-absorbing molecule • Humans (~ 50% analogy with a.a. of rods) Normal Protanopia Deuteranopia Tritanopia (lacking red cones) (lacking green cones) (lacking blue cones) Test Yourself… • Blue = autosomal chromosome • Red / Green = X chromosome • similarity (gene duplication) Colorblindness: Defect in cone opsin gene Guyton & Hall – Figure 50.10 6 Sensory Systems Vision: Temporal field Optic Pathways: Martini & Nath – Figure 13.18 Sensory Systems Nasal field L R L R Temporal field Auditory: Auricle Tympanic membrane Hemianopia: Loss of vision in half the visual field of one or both eyes Oval window Inner ear Sensory receptors Semicircular canals / Vestibule (equilibrum) Cochlea (hearing) Optic nerve 1) Visual Field Left Optic chiasma Right 2) External acoustic meatus Optic tract 3) 1) Malleus Incus Lateral geniculate nuclei 2) (thalamus) Middle ear Geniculocalcarine tract Converts sound waves Into mechanical movements (amplification) 3) External ear Auditory tube Collect / direct sound waves = deficit Stapes Primary visual cortex Costanzo – Figure 3.17 Marieb & Hoehn – Figure 15.28 Marieb & Hoehn – Figure 15.30 Sensory Systems Cochlea (“snail”): Spiral-shaped chamber that houses the receptors for hearing Auditory: Sensory Systems Sound: A pressure disturbance produced by a vibrating object Auditory: The Nature of Sound: Cochlear nerve Scala media Scala Vestibuli (contains endolymph) (contains perilymph) High pitch Low pitch Cochlea Frequency: Number of waves passing a given point in a given time Pitch = Sensory perception of frequency Organ of Corti Soft Tectorial membrane Loud Amplitude: Organ of Corti: Intensity of sound Loudness = Sensory perception of amplitude As basilar membrane vibrates, hair cells bump up against tectorial membrane Average human speech = 65 dB Potential damage = > 100 dB Pain = > 120 dB Scala tempani (contains perilymph) Basilar membrane Marieb & Hoehn – Figure 15.31 Marieb & Hoehn – Figure 15.31 Sensory Systems Oscillating NT release produces intermittent firing of afferent nerves Auditory: Amplification of signal: 1) Lever action of ossicles 2) Large window small window Sensory Systems Auditory: Sound waves enter auditory meatus Tympanic membrane vibrates High frequency sounds displace basilar membrane near base Basilar membrane differs in stiffness along length Ossicles vibrate Hearing Range: 20 Hz to 20,000 Hz Oval window vibrates Cochlear microphonic potential Pressure waves exit via round window (most sensitive = 2000 – 5000 Hz) Medium frequency sounds displace basilar membrane near middle Pressure waves develop in scali vestibuli Tonotopic map Hyperpolarization Depolarization • Shear force bends hairs • K+ conductance changes • Depolarization leads to NT release NT Organ of Corti vibrates Low frequency sounds displace basilar membrane near end Conduction Deafness: Sound is not able to be transferred to internal ear Sensorineural Deafness: Damage occurs in neural pathway (e.g., hair cells) 7 Marieb & Hoehn – Figure 15.34 Sensory Systems Sensory Systems Auditory cortex (tonotopic map preserved) Auditory: Vestibule: Region of inner ear housing receptors that respond to gravity sensation / linear acceleration (static equilibrium) Vestibular System: midline Auditory Pathways: Cerebral cortex Medial geniculate nuclei Central lesions do not cause deafness because fibers from each ear are intermixed in CNS • Provides stable visual image for retina • Adjust posture to maintain balance (thalamus) Maculae anatomy: Vestibule Otoliths Thalamus Inferior colliculus nuclei Otolithic membrane (midbrain) Brain stem Cochlear nerve Hair cell Cochlear nuclei Saccule (vertical) Maculae: Sensory receptors for static equilibrium (medulla) Spinal cord Marieb & Hoehn – Figure 15.34 / 15.36 Utricle (horizontal) Sensory Systems Vestibular System: Sensory Systems Semicircular canals: Region of inner ear housing receptors that respond to rotational movements of head (dynamic equilibrium) Analyze three (3) rotational planes (“yes” / “no” / head tilt) Crista ampullaris anatomy: Semicircular canal Head acceleration (e.g, forward) causes otolithic membrane to slide; subsequent bending of hair cells modifies AP firing rate For every position of the head, there is a unique pattern of AP activity for the utricle & saccule Cupula Vestibular System: Modified hair cell Example: Counterclockwise rotation of head 1) Cupula begins to move; endolymph is stationary 2) Eventually, endolymph catches up with cupula (hair cells quiescent) Ampulla 3) When stopped, endolymph briefly moves hair cells in opposite direction Endolymph (fluid) (reverses firing rates) Rotation of head stimulates semicircular cells on same side rotation is occurring Hair cell Crista ampullaris: Sensory receptor for dynamic equilibrium Head rotation (e.g., spinning) causes endolymph to push against cupula; subsequent bending of hair cells modifies AP firing rate (stereocilia bent toward kinocilium) Costanzo – Figure 3.23 Sensory Systems Vestibular Pathways: Nucleus Medial nucleus Superior nucleus Sensory Systems Visual reflexes (e.g., nystagmus) Vestibular System: (stereocilia bent away from kinocilium) Olfaction: midline Olfactory Organ: (nasal cavity) Postural reflexes Input Output Semicircular canals Extraocular muscles Lateral nucleus Vestibule Spinal cord (utricles) (vestibulospinal tract) Inferior nucleus Vestibule / Semicircular canals Cerebellum Basal cell Cerebral cortex Olfactory receptor cell Supporting cell Thalamus Nasal epithelium Brain stem • Olfactory receptor cells (~ 1 million / cm2) Vestibular nerve • Primary afferent neurons (bipolar) • Ciliated (~ 20 cilia / cell) • Odorant-binding proteins Vestibular nuclei (medulla) Vestibulospinal tract • Odorants must by water / lipid soluble Spinal cord • 4 molecules = receptor activation • ~ 1000 receptor types (discriminate ~ 10,000) • Supporting cells • Basal cells (stem cells new receptors) • Continuous neurogenesis 8 Sensory Systems Sensory Systems Across-fiber pattern code: Each odorant produces unique pattern of activity across a population of receptors Olfaction: Olfactory Transduction: Olfaction: • cAMP triggers ligand-gated Na+ midline Olfactory Pathways: • G protein (Golf) coupled to adenylate cyclase • ATP cAMP ~ 1000 receptor cells synapse with a single mitral cell Olfactory cortex Cerebral cortex channels Mitral cells Glomeruli (olfactory tract) (Olfactory bulb) Thalamus Limbic system Cribiform plate Olfactory Encoding: Brain stem We don’t exactly know how… • What is known: Nasal epithelium 1) Olfactory receptors are not dedicated to a single odorant 2) Olfactory receptors are selective (variable response…) Spinal cord 3) Different receptor proteins have different responses to the same odors Marieb & Hoehn – Figure 15.23 Sensory Systems Gustation: Sensory Systems Gustation: Taste bud: (~ 10,000 / tongue) Taste Transduction: Basal cell Taste pore Umami Bitter Sour Salty Sweet transient receptor potential Gustatory cell • Gustatory cells (taste receptors) • Slender microvilli (taste hairs) • 10 day lifespan Taste buds spread across tongue; different thresholds in different regions • Basal cells (stem cells new receptors) • Taste buds on lingual papillae: Circumvallate Fungiform Foliate (majority of taste buds) (anteriorly located) (laterally located) Costanzo – Figure 3.37 / 3.28 Sensory Systems Gustation: midline Taste Pathways: Second-order neurons project ipsilaterally Ventral posteromedial nucleus Taste cortex Cerebral cortex (thalamus) Solitary nucleus Thalamus (medulla) Taste bud Brain stem Posterior 1/3 of tongue (bitter / sour): Glossopharyngeal nerve (IX) Anterior 2/3 of tongue (sweet / salty / umami): Facial nerve (VII) Spinal cord 9