Peripheral Nervous System
Organization of Nervous System:
Nervous system
Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor Sensory output input
Brain Spinal cord Motor division Sensory division (efferent) (afferent)
Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)
Sympathetic division Parasympathetic division
Peripheral Nervous System
The peripheral nervous system links the brain to the “real” world
Ganglia (neuron cell bodies)
Nerve Types: Nerves 1) Sensory nerves (contains only afferent fibers) (bundles of axons) 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
Motor output
Peripheral Nervous System
Nerve Structure: Endoneurium A. Epineurium: • Outside nerve covering • Dense network of collagen fibers Perineurium
B. Perineurium: • Divides nerve into fascicles • Contains blood vessels Epineurium C. Endoneurium: • Surrounds individual axons and ties them together
Fascicle
Marieb & Hoehn – Figure 13.26
1 Peripheral Nervous System
Classification of Nerve Fibers:
• Classified according to conduction velocity
Relative Relative conduction Classification Type diameter velocity Myelination
A alpha (A) Largest Fastest (120 m / s) Yes A beta (A) Medium Medium Yes Sensory and A gamma (A) Medium Medium Yes Motor A delta (A) Small Medium Yes (Erlanger & Gasser) B Small Medium Yes
C Smallest Slowest (0.2 m / s) No
Ia Largest Fastest Yes Ib Largest Fastest Yes Sensory only II Medium Medium Yes (Lloyd & Hunt) III Small Medium Yes IV Smallest Slowest No
Peripheral Nervous System
Organization of Nervous System:
Nervous system
Integration Central nervous system Peripheral nervous system (CNS) (PNS) Motor Sensory output input
Brain Spinal cord Motor division Sensory division (efferent) (afferent)
Autonomic nervous system Somatic nervous system (involuntary; smooth & cardiac muscle) (voluntary; skeletal muscle)
Sympathetic division Parasympathetic division
Sensory Systems
“Nothing is in the mind that does not pass through the senses”
Aristotle (~ 350 B.C.)
• 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 Subjective • Perceptions: Interpretation of electrical impulses by brain
Sensations / perceptions are not inherent in stimuli themselves; instead they depend on the neural processing of the stimuli
2 Sensory Systems
Sensory Pathways in NS: Fourth-order midline neuron 1) Receptor: • Converts stimuli to electrochemical energy • Structure variable Cerebral cortex • Specialized epithelial cells (e.g., vision) Third-order neuron • Modified neurons (e.g., olfaction) 2) First-order afferent neuron: • Cell body located in ganglion (PNS) Thalamus Second-order 3) Second-order afferent neuron: neuron • Synapse with first-order neuron at relay nuclei • Many first-order synapse with one second-order Brain stem • Interneurons present (signal processing) • Cross at midline (decussate) 4) Third-order afferent neuron: • Reside in thalamus (relay nuclei) Relay nucleus • Interneurons present (signal processing)
Receptor 5) Fourth-order afferent neuron: Spinal • Reside in appropriate sensory area First-order cord neuron
Sensory Systems Modality: Category of sensation Sensory Receptors:
Type of Receptor: Modality: Location:
• Skin (touch) Mechanoreceptors • Inner ear (audition) • Inner ear (vestibular) Touch Audition Vestibular
Photoreceptors • Eye (vision) Vision
• Tongue (taste) Chemoreceptors • Nose (olfaction) Taste Olfaction Osmolarity • Vessels (osmolarity)
Thermoreceptors • Skin (temperature) Temperature
Nociceptors • Skin (pain) Pain
Guyton & Hall – Figure 46.2 / 46.3 Sensory Systems
Sensory Receptors:
Sensory transduction: The process by which environmental stimuli activates a receptor and is converted into electrical energy
• Receptor excitation = Change in membrane potential (Receptor potential) (usually via opening of ion channels)
Example: Pacinian corpuscle
1) Pressure causes a change in the membrane properties (e.g., mechanical deformation) Receptor Potential > Threshold Action Potential 2) Ion channels open; receptor potential develops • Amplitude correlates with stimulus size ( Intensity = Receptor potential = AP frequency) 3) Receptor potential triggers action potential
3 Costanzo – Figure 3.5 / 3.6 Sensory Systems
Sensory Receptors:
Receptor Field: An area of the body that when stimulated results in a change in firing rate of a sensory neuron
Receptor fields may be excitatory or inhibitory Receptor fields exist for first-, Excitatory receptor fields increase firing rate second-, third-, and fourth-order neurons Inhibitory receptor fields decrease firing rate
The smaller a receptor field, the more Lateral inhibition defines boundaries precisely the sensation can be localized and provides a contrasting border
Sensory Systems
Sensory Receptors:
Sensory coding: Various aspects of perceived stimuli are encoded and sent to the proper location in the CNS
Features encoded:
1) Modality 2) Location 3) Threshold
Labeled Line Principle: Threshold of Detection: Receptors respond to Weakest signal that will single modality produce a receptor response 50% of the time Touch Somatosensory Hearing: receptor cortex Vision: Bending of hair equal to 1 photon of light Receptor fields diameter of H atom
4) Intensity 5) Duration • Number of receptors activated Length of time a sensory • Firing rate of sensory neurons neuron fires • Types of receptors activated During prolonged stimulus, receptors “adapt” to the stimulus
Sensory Systems Adaptation depends on how quickly receptor potential drops below threshold Sensory Receptors: Sensory adaptation: When a constant stimulus is applied to a receptor, the frequency of action potentials generated declines over time
Tonic receptors (slowly adapting receptors)
Can encode stimulus intensity
Will adapt to extinction; may take hours / days
Pattern of adaptation differs among • Transmit impulses as long as different types of receptors stimulus present • Keep brain appraised of body status
Guyton & Hall – Figure 46.5 Costanzo – Figure 3.7
4 Sensory Systems Adaptation depends on how quickly receptor potential drops below threshold Sensory Receptors: Sensory adaptation: When a constant stimulus is applied to a receptor, the frequency of action potentials generated declines over time
Phasic receptors (rapidly adapting receptors)
Can not encode stimulus intensity
Pattern of adaptation differs among • Transmit impulses only when different types of receptors change is taking place • Important for predicting future position / condition of body
Guyton & Hall – Figure 46.5 Costanzo – Figure 3.7
Costanzo – Figure 3.8 Sensory Systems Rapid adapters = Change in velocity Somatosensory System: Slow adapters = Intensity; duration • Processes information about touch, position, pain, and temperature
Mechanoreceptors: Two-point discrimination
Pacinian corpuscle Meissner’s corpuscle Location = Subcutaneous; intramuscular Location = Non-hairy skin Detection = Vibration; tapping Detection = Tapping; fluttering Adaptation = Very rapidly Adaptation = Rapidly
Hair plexus Ruffini’s corpuscle Location = Hairy skin Location = Skin; joint capsules Detection = Velocity; movement direction Detection = Stretch; joint rotation Adaptation = Rapidly Adaptation = Slowly
Costanzo – Figure 3.8 / 3.9 Sensory Systems Rapid adapters = Change in velocity Somatosensory System: Slow adapters = Intensity; duration • Processes information about touch, position, pain, and temperature
Mechanoreceptors:
Merkel’s receptor / Tactile disc Location = Non-hairy skin / Hairy skin Detection = Vertical indentation Adaptation = Slowly
Thermoreceptors: • Slowly adapting receptors; located in skin
• Cold receptors vs. warm receptors • Overlap in response ranges • Do not respond at extreme ranges (nociceptors)
5 Sensory Systems
Somatosensory System: • Processes information about touch, position, pain, and temperature
Nociceptors: • Respond to noxious stimuli that can produce tissue damage
Mechanical nociceptors: • Respond to mechanical stimuli • A delta (A) afferent neurons (myelinated)
Polymodal nociceptors: • Respond to multiple stimuli: • High-intensity chemical stimuli • Hot / Cold stimuli • C afferent neurons (unmyelinated)
Chemical cues released at damaged / Hyperalgesia: Intense activity areas include: Process where axons of nociceptors release • H+ • Prostaglandins substances that sensitize the nociceptors to • K+ • Bradykinins stimuli that were not previously painful • ATP • Substance P
Sensory Systems
Somatosensory Pathways: midline 1) Dorsal column system • Information transmitted: Cerebral a) Discriminative touch cortex b) Pressure / Vibration c) Two-point discrimination d) Proprioception • Consists mainly of groups I and II fibers Thalamus • Fibers decussate in brain stem (second-order neurons) • Nucleus gracilis = Info from lower body • Nucleus cuneatus = Info from upper body Brain stem Fasciculus Fasciculus cuneatus gracilis
Receptor Spinal cord
Marieb & Hoehn – Figure 12.33
Sensory Systems
Somatosensory Pathways: midline 2) Anterolateral (spinothalamic) system • Information transmitted: Cerebral a) Pain cortex b) Temperature / Light touch • Consists mainly of groups III and IV fibers • Fast pain (e.g., pin prick) • A delta fibers; group II & group III fibers Thalamus • Rapid onset / offset; precisely localized • Slow pain (e.g., burn) • C fibers; group IV fibers Brain stem • Aching / throbbing; poorly localized
Lateral spinothalamic (pain / temperature)
Receptor Spinal Ventral cord spinothalamic Marieb & Hoehn – Figure 12.33 (light touch)
6 Sensory Systems
Somatosensory Pathways: midline 2) Anterolateral (spinothalamic) system
Referred Pain: Cerebral cortex
Thalamus
Brain stem
Dematomal rule: Sites on the skin are innervated by nerves arising Receptor from the same spinal cord segments as those Spinal innervating the visceral organs cord
Marieb & Hoehn – Figure 14.8
Sensory Systems
Vision:
(~ 1 ml / day) 70% of sensory receptors 50% of cerebral cortex
1) Orbital fat (cushions / insulates eye) 2) Extrinsic eye muscles (6) 3) Lacrimal gland: Produces tears • Lubricates eye Strabismus: • Supplies nutrients / oxygen A condition in which an eye rotates • Provides antibacterial enzymes medially / laterally
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: Cornea: Sclera: Transparent window “White of the eye” 1) Fibrous Layer: (outermost) • Offers structurally support / protection Sclera • Acts as anchoring point for muscles Cornea • Assists in light focusing Choroid 2) Vascular Layer: (middle) • Contains blood vessels / lymph vessels • Regulates light entering eye Iris • Controls shape of lens Iris: Ciliary circular Regulates size of pupil radial body muscles muscles constrict constrict 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
7 Marieb & Hoehn – Figure 15.4 / 15.6 Sensory Systems
Vision: Optic Disk (blind spot): Origin of optic nerve; no Layers of the Eye: photoreceptors present 3) Retina: (innermost) • Pigmented layer (light absorption) Sclera • Neural layer (light detection) Cornea Choroid
Incoming
light Pigmented Layer Fovea
Iris Optic Disk
Ciliary
body Retina
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
Vision: Posterior segment Segments of the Eye:
Aqueous Humor: Circulating fluid in anterior segment • Nutrient / waste transport • Cushioning of eye • Retention of eye shape
Vitreous Humor: Anterior Gelatinous mass in posterior segment segment • Transmits light • Stabilize eye shape Canal of Schlemm: • Holds retina firmly in place Drains aqueous humor
Intraocular Pressure = 12 – 21 mm Hg Ciliary body produces Glaucoma: aqueous humor Disease where intraocular pressure (1 – 2 l / minute) becomes pathologically high (~ 70 mm Hg) Marieb & Hoehn – Figure 15.8
Sensory Systems Lasik eye Vision: surgery
For clear vision, light must be focused on the retina
Close objects = focal distance Rounder lens = focal distance Refraction: The bending of light when it passes between mediums of different density Accommodation: 1) Cornea: 85% of refraction (fixed) Changing the shape of a lens 2) Lens: 15% of refraction (variable) to keep an image in focus (constant focal length) • Composed of lens fibers (cells) Cataract: (cloudy lens) • Crystallins (transparent proteins)
8 Sensory Systems Near point of vision: Vision: Inner limit of clear vision
Accommodation: Children = 7 – 9 cm Loss of lens Young Adults = 15 – 20 cm elasticity Elderly Adults = 70 – 85 cm
tightens relaxes suspensory suspensory ligaments ligaments
Lens flattens for distant object focus; Lens bulges for near object focus; Ciliary body RELAXES Ciliary body CONTRACTS
In Addition: • Pupils constrict • Eyeballs converge
Sensory Systems 20 / 20 = Standard visual acuity Vision: 20 / 200 = Legally blind When Things Go Wrong:
Near-sighted Far-sighted
Emmetropia Myopia Hyperopia
Astigmatism: Warping of the lens or cornea leading to image distortion Correct with diverging lens Correct with converging lens
Randall et al. – Figure 7.38 Sensory Systems
Vision:
Photon: Basic unit of visible light
High Energy Low Energy (short wavelength) (long wavelength)
9 Sensory Systems Horizontal cells / Amacrine cells Vision: (facilitate / inhibit serial links – retinal processing) Retinal Layers: • Absorbs stray light Pigment cell layer • Storage site for retinal
(R) = Receptor cells Photoreceptor layer • Rods / cones
(H) = Horizontal cells Outer nuclear layer • Nuclei of receptor cells (B) = Bipolar cells (A) = Amacrine cells • Synapses between receptors Outer plexiform layer and interneurons
Inner nuclear layer • Nuclei of interneurons
• Synapses between interneurons Inner plexiform layer and ganglion cells
Ganglion cell layer • Nuclei of ganglion cells
Optic nerve layer • Leave eye via optic disc Serial link
Costanzo – Figure 3.13
Sensory Systems
Vision: Retinal Layers: (Day vision) Cones demonstrate high acuity and low sensitivity (R) = Receptor cells • Only a few cones synapse on a single bipolar cell (H) = Horizontal cells • In fovea, a single cone synapses on (B) = Bipolar cells a single bipolar cell (A) = Amacrine cells • A single bipolar cell synapses on a single ganglion cell
(Night vision) Rods demonstrate low acuity and high sensitivity • Many rods synapse on a single bipolar cell • Light striking any one rod will activate the bipolar cell • Multiple bipolar cells may synapse on a single ganglion cell
Costanzo – Figure 3.13
Sensory Systems
Vision: A single photon of light can activate a rod; several hundred photons of light are Photoreception: required to activate a cone
Rod Structure: Cone Structure:
(more abundant In rods) Light-sensitive photochemicals
Outer segment
Inner Cytoplasm / segment cytoplasmic organelles Connected via individual cilium
Connection to Synaptic neural elements terminal
Costanzo – Figure 3.14
10 Sensory Systems
Vision: Photoreception:
Photochemistry of Vision: • Rods and cones contain chemicals that decompose on exposure to light • Rods = Rhodopsin (visual purple) Similar compositions • Cones = Cone pigments (color pigments)
Example: Rhodopsin
Structure: • Opsin = membrane protein • Retinal = light-absorbing pigment (aldehyde of vitamin A)
Two sterically distinct retinal states in the retina
Light
(photoisomerization) cis-form trans-form
Sensory Systems
Vision: Photoreception:
Rod Receptor Potential:
• 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
Hyperpolarize The greater the amount of light, the greater the hyperpolarization
constant NT release NT release NT = Glutamate
Sensory Systems
Vision: Photoreception:
Rhodopsin Activation: cGMP no longer present to bind to ion channels 1) Conformational change in opsin 4) Closure ion channels
Trans-retinal detaches
Opsin converted to metarhodopsin II
3) Activation of phosphodiesterase (enzyme)
2) Activation of transducin (G protein)
Randall et al. – Figure 7.44
11 Sensory Systems Night Blindness: Vision: Reduced photosensitivity of eyes (nutritional deficiency of vitamin A) Photoreception:
Regeneration of Rhodopsin: Storage location (picked up from blood)
(Free of opsin)
Bleaching: The fading of photopigment upon absorption of light
Randall et al. – Figure 7.45
Sensory Systems
Vision: Photoreception:
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) • Blue = autosomal chromosome • Red / Green = X chromosome • similarity (gene duplication)
Colorblindness: Defect in cone opsin gene
Guyton & Hall – Figure 50.10
Sensory Systems
Vision: Sex-linked (1% of males affected) Very rare (autosomal recessive) Photoreception: 8% of women carriers
Normal Protanopia Deuteranopia Tritanopia (lacking red cones) (lacking green cones) (lacking blue cones)
Test Yourself…
12 Sensory Systems
Nasal Vision: field Temporal L R L R Temporal Optic Pathways: field field
Hemianopia: Loss of vision in half the visual field of one or both eyes Optic nerve Visual Field 1) Optic chiasma Left Right 2) Optic tract 1) 3)
Lateral geniculate nuclei 2) (thalamus)
Geniculocalcarine tract 3)
= deficit
Costanzo – Figure 3.17 Primary visual cortex
Martini & Nath – Figure 13.18 Sensory Systems
Auditory:
Oval Inner ear Auricle window Tympanic Sensory receptors Semicircular canals / membrane Vestibule (equilibrum)
Cochlea (hearing)
External acoustic meatus Malleus Incus
Middle ear Converts sound waves Into mechanical movements External ear (amplification) Collect / direct sound waves Auditory Stapes tube
Marieb & Hoehn – Figure 15.28 Sensory Systems Cochlea (“snail”): Spiral-shaped chamber that Auditory: houses the receptors for hearing
Cochlear nerve Scala Scala media Vestibuli Cochlea (contains endolymph) (contains perilymph)
Organ of Corti
Tectorial membrane Organ of Corti:
As basilar membrane vibrates, hair cells bump up against tectorial membrane Scala tempani (contains perilymph) Basilar membrane
13 Marieb & Hoehn – Figure 15.30 Sensory Systems Sound: A pressure disturbance produced Auditory: by a vibrating object
The Nature of Sound:
High pitch Low pitch
Frequency: Number of waves passing a given point in a given time Pitch = Sensory perception of frequency
Soft Loud
Amplitude: Intensity of sound Loudness = Sensory perception of amplitude
Average human speech = 65 dB Potential damage = > 100 dB Pain = > 120 dB
Marieb & Hoehn – Figure 15.31 Sensory Systems Oscillating NT release produces Auditory: intermittent firing of afferent nerves Amplification of signal: 1) Lever action of ossicles Sound waves enter auditory meatus 2) Large window small window
Tympanic membrane vibrates
Ossicles vibrate
Oval window vibrates
Cochlear microphonic potential Pressure waves exit Pressure waves develop via round window in scali vestibuli
Hyperpolarization Depolarization Organ of Corti vibrates • Shear force bends hairs NT • K+ conductance changes • Depolarization leads to NT release
Marieb & Hoehn – Figure 15.31 Sensory Systems
Auditory:
High frequency sounds displace Basilar membrane differs basilar membrane near base in stiffness along length
Hearing Range: 20 Hz to 20,000 Hz (most sensitive = 2000 – 5000 Hz) Medium frequency sounds displace basilar membrane near middle Conduction Deafness: Sound is not able to be transferred to internal ear Tonotopic map Sensorineural Deafness: Low frequency sounds displace Damage occurs in neural basilar membrane near end pathway (e.g., hair cells)
14 Sensory Systems Auditory cortex Auditory: (tonotopic map preserved) midline Auditory Pathways:
Medial Cerebral geniculate cortex Central lesions do not cause nuclei deafness because fibers from (thalamus) each ear are intermixed in CNS
Inferior Thalamus colliculus nuclei (midbrain) Brain stem Cochlear nerve
Cochlear nuclei (medulla) Spinal cord
Marieb & Hoehn – Figure 15.34 Sensory Systems
Vestibular System: Vestibule: Region of inner ear housing receptors that respond to gravity • Provides stable visual image for retina sensation / linear acceleration • Adjust posture to maintain balance (static equilibrium)
Vestibule Maculae anatomy: Otoliths
Otolithic membrane
Hair cell Utricle Saccule (horizontal) (vertical)
Maculae: Sensory receptors for static equilibrium Head acceleration (e.g, forward) causes For every position of the head, there is a unique otolithic membrane to slide; subsequent bending pattern of AP activity for the utricle & saccule of hair cells modifies AP firing rate
Marieb & Hoehn – Figure 15.34 / 15.36 Sensory Systems
Vestibular System: Semicircular canals: Region of inner ear housing receptors that respond to rotational Analyze three (3) rotational planes movements of head (“yes” / “no” / head tilt) (dynamic equilibrium)
Crista ampullaris anatomy: Semicircular canal Cupula
Ampulla
Endolymph (fluid)
Crista ampullaris: Hair cell 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
15 Sensory Systems
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) 3) When stopped, endolymph briefly moves hair cells in opposite direction (reverses firing rates)
Rotation of head stimulates semicircular cells on same side rotation is occurring
(stereocilia bent (stereocilia bent toward kinocilium) away from kinocilium)
Costanzo – Figure 3.23
Sensory Systems
Vestibular System: Visual reflexes (e.g., nystagmus) midline Vestibular Pathways: Postural reflexes
Nucleus Input Output Cerebral cortex Medial nucleus Semicircular Extraocular Superior nucleus canals muscles
Lateral nucleus Vestibule Spinal cord (utricles) (vestibulospinal tract) Thalamus
Vestibule / Inferior nucleus Semicircular Cerebellum canals Brain stem
Vestibular nerve
Vestibular nuclei Spinal (medulla) cord
Vestibulospinal tract
Sensory Systems
Olfaction: Olfactory Organ: (nasal cavity)
Basal cell
Olfactory receptor cell
Supporting Nasal cell epithelium
• Olfactory receptor cells (~ 1 million / cm2) • Primary afferent neurons (bipolar) • Ciliated (~ 20 cilia / cell) • Odorant-binding proteins • Odorants must by water / lipid soluble • Supporting cells • 4 molecules = receptor activation • Basal cells (stem cells new receptors) • ~ 1000 receptor types (discriminate ~ 10,000) • Continuous neurogenesis
16 Sensory Systems Across-fiber pattern code: Olfaction: Each odorant produces unique pattern of activity across a Olfactory Transduction: population of receptors
• G protein (Golf) coupled to adenylate cyclase • ATP cAMP • cAMP triggers ligand-gated Na+ channels
Olfactory Encoding:
We don’t exactly know how…
• What is known: 1) Olfactory receptors are not dedicated to a single odorant 2) Olfactory receptors are selective (variable response…) 3) Different receptor proteins have different responses to the same odors
Sensory Systems
Olfaction: midline Olfactory Pathways: Olfactory ~ 1000 receptor cells synapse cortex Cerebral with a single mitral cell cortex
Mitral cells Glomeruli (olfactory tract) (Olfactory bulb) Thalamus Limbic system Cribiform plate Brain stem
Nasal epithelium
Spinal cord
Marieb & Hoehn – Figure 15.23 Sensory Systems
Gustation: Taste bud: (~ 10,000 / tongue)
Basal cell
Taste pore Umami Gustatory Bitter cell Sour Salty Sweet • Gustatory cells (taste receptors) • Slender microvilli (taste hairs) • 10 day lifespan • Basal cells (stem cells new receptors) • Taste buds on lingual papillae:
Circumvallate Fungiform Foliate (majority of taste buds) (anteriorly located) (laterally located)
17 Sensory Systems
Gustation: Taste Transduction:
transient receptor potential
Taste buds spread across tongue; different thresholds in different regions
Costanzo – Figure 3.37 / 3.28
Sensory Systems
Gustation: midline Taste Pathways: Ventral Taste cortex posteromedial Cerebral nucleus cortex Second-order neurons (thalamus) project ipsilaterally
Solitary nucleus (medulla) Thalamus
Brain stem Taste bud Posterior 1/3 of tongue (bitter / sour): Glossopharyngeal nerve (IX)
Anterior 2/3 of tongue (sweet / salty / umami): Facial nerve (VII)
Spinal cord
18