Neuroscience Test 2, Auditory/Vestibular and Thalamus

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Neuroscience Test 2, Auditory/Vestibular and Thalamus
2013-04-04 18:40:22
Neuroscience nMedical School nCarver College Medicine

Flashcards for the neuroscience test 2 over the auditory/vestibular and thalamus lectures
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  1. Bony and membranous labyrinth contents and general location
    • Location: Petrous part of the temporal bone
    • Bony contents: Perilymph, which is high in sodium concentration
    • Membranous contents: Endolymph, which is high in potassium concentration
  2. From the tympanic membrane, movement of fluid occurs through what structures (in order) for hearing?
    • Oval window, scala vestibuli, helicotrema, scala tympani, round window
    • All of these contain perilymph
  3. Tonotopic organization of cochlea
    • High frequencies heard at the base
    • Low frequencies heard at the apex
  4. Inner hair cells versus outer hair cells of Organ of Corti
    • Inner: Sensory
    • Outer: Change their length in the tectorial membrane to allow for tuning
  5. Conductive versus sensorineural hearing loss
    • Conductive: Something is blocking the air transmission of sound to the tympanic membrane or otitis media is blocking middle ear conduction; bone conduction will may still be present
    • Sensorineural: Dysfunction of the inner ear (such as hair cell damage) or higher centers (more common)
  6. Location of the cochlear nuclear complex
    • At the pontomedullary junction
  7. Central auditory pathways
    • From the cochlea, fibers that enter the dorsal cochlear nucleus at the pontomedullary junction decussate and ascend in the lateral lemniscus
    • Fibers that enter the ventral cochlear nucleus can also decussate and synapse at the superior olivary complex before rising in the lateral lemniscus, or can go to the ipsilateral superior olivary complex and ascend
    • All cochlear fibers then synapse in the inferior colliculus, then the medial (music) geniculate body, then to the superior temporal gyrus
  8. Superior olivary complex
    • Found in the pons, it is the location of synapses of cochlear fibers
    • Contains four nuclei
    • Medial superior olive: Gets info from both ears and discriminates the time of arrival
    • Lateral superior olive: Gets info from both ears adn discriminates intensity
    • Nucleus of the trapezoid body:
    • Periolivary nuclei: Source of olivocochlear bundles running back to the ears; the crossed fibers are efferent to control the external hair cell tuning ability; uncrossed fibers are efferent to inner hair cells
  9. Lateral lemniscus
    Carries acoustic information from the superior olivary complex (pontomedullary nuclei) to the inferior colliculus
  10. Inferior colliculus
    Is an integral relay center in the pathway of auditory information; contains a tonotopic organization (and the superior contains a retinotopic organization)
  11. Medial geniculate body
    • Found in the thalamus, this region is a relay of auditory information received via the inferior quadrigeminal branchium pathway from the inferior colliculus
    • From the MGB, axons are sent to the superior temporal gyrus via auditory radiations running in the sublenticular portion of the internal capsule
    • The main part of the MGB that receives this information is the ventral nucleus
    • M = music
  12. Primary auditory cortex
    • Found in the superior transverse temporal gyrus
    • Possesses a complete map of audible frequencies
    • Lesions may lead to a loss of awareness of sound, but reflexes involving sound will remain intact
  13. Kinetic and static labyrinths of the vestibular system
    • Kinetic: Semicircular canals which detect angular acceleration
    • Static: Utricle and saccule (otolithic organs) which detect linear and gravitational acceleration, respectively
  14. Macule
    Found in the otolithic organs (utricle and saccule), covered by an otolithic membrane and otoliths
  15. Ampulla
    • An enlarged region in the semicircular ducts
    • Contains a cupula that has kinocilium and stereocilium embedded
  16. Excitation of hair cells in vestibular system
    • Occurs when stereocilia bend towards the kinocilium to cause depolarization of the cell
    • Increased firing occurs in that system towards which we turn our heads
  17. Afferent inputs to vestibular nuclei
    • There are four vestibular nuclei
    • Otoliths: Go to all nuclei but superior
    • Semicircular ducts: Go to all nuclei but inferior
  18. Outputs from the vestibular nuclei
    • Some fibers go directly from the vestibulocochlear nerve to the flocculonodular node of the cerebellum through the inferior cerebellar peduncle for fine control of balance and eye movements
    • Fibers from the superior vestibular nucleus go to nuclei of III and VI (vestibulo-ocular reflex)
    • Lateral vestibulospinal tract: Fibers from the lateral vestibular nucleus go to the cerebellum and to the vestibulospinal tract to stabilize trunk and limbs
    • Medial vestibulospinal tract: Fibers from the medial vestibular nucleus go to nuclei of III and VI (vestibulo-ocular reflex) and to neck motor neurons (vestibulocollic reflex)
  19. Vestibular reflexes
    • Vestibulospinal: Stabilize limbs and body when perterbed
    • Vestibulocollic: Act on neck to stabilize head
    • Vestibulo-ocular: Maintain stable vision during head motion (ex below with left head turn)
  20. Clinical signs of damage to vestibular system
    VANN (vertigo, ataxia, nausea, nystagmus)
  21. What types of sensory information go through the thalamus to the cerebrl cortex?
    All sensory information except some olfactory and some emotional aspects of pain and visceral sensation
  22. Conscious awareness and attention are controlled by what structure?
    The thalamus--it determines the level and content of consciousness
  23. General symptoms of thalamic lesions
    • Usually, thalamic lesions are caused by lacunar strokes, limited to a few nuclei
    • Symptoms include motor and sensory deficits, aphasia (loss of ability to understand or express speech), memory problems, altered personality and social skills, and altered levels of arousal
    • Persistant vegetative state can result from damage to the thalamus (by inhalation of halothane or IV barbiturates)
  24. Topographical anatomy of the thalamus
    • Massa intermedia (interthalamic adhesion): The bridge of tissue connecting the two halves of the thalamus (the third ventricle is located between them); it is NOT a commissure and contains grey matter
    • Hypothalamic sulcus: Separates the thalamus from the hypothalamus
    • External medullary lamina: Found laterally around the thalamus
    • Thalamic reticular nucleus: Found between the external medullary lamina and the internal capsule of the thalamus
    • Midbrain-diencephalic boundary: Junction of the thalamus to the midbrain tegmentum; marked by a line from the posterior commissure to the mammillary bodies
    • Pulvinar: Overlies the midbrain-diencephalic junction, covering the superior colliculi
    • Medial and lateral geniculate bodies: Small elevations located ventrolateral to the pulvinar
  25. Functional categories of the thalamus
    • Specific
    • Have reciprocal connections with specific regions of the cerebral cortex
    • Maintain the spatial organization of their inputs (retinotopy, somatotopy, etc)
    • Specific thalamic nuclei include MGN, LGN, VPM, VPL, VA, VL, MD, pulvinar, anterior and lateral dorsal nuclei
    • Non-Specific
    • Diffuse sensory inputs with many modalities and strong input from the reticular formation
    • Diffuse and non-reciprocal innervation of cortex (intralaminar does have reciprocal connections with the basal ganglia while midline have less extensive connections)
    • Includes intralaminar (centromedian) and midline nuclei
  26. Sensory specific, motor specific, association (integration), limbic specific, and non-specific thalamic nuclei
    • Sensory: VPM, VPL, VPI, LGN, MGN
    • Motor: VA, VL
    • Association: MD, Pulvinar
    • Limbic: Anterior group, LD
    • Non-specific: Midline and intralaminar
  27. VPM
    • Ventral posterior medial nucleus
    • Input: Somatosensory from the face through the trigeminal lemniscus
    • Reciprocal output: Facial area of postcentral gyrus (corticothalamic)
  28. VPMpc
    • Ventral posterior medial parvocellular nucleus
    • Small-celled part of VPM
    • Input: Pontine and mesencephalic taste relays (from NTS)
    • Reciprocal output: The anterior part of the insula (the primary gustatory area)
  29. VPL
    • Ventral posterior lateral nucleus
    • Input: Somatosensory information from the limbs and trunk through the spinothalamic tract and medial lemniscus (remember, some of the spinothalamic projections do not go through the thalamus and instead go to the medullary reticular formation)
    • Reciprocal output: Non-face parts of postcentral gyrus and a small part to insula (for visceral sensation)
  30. VPI
    • Ventral posterior inferior nucleus
    • Transmits vestibular information to the inferior parietal lobule
  31. LGN
    • Lateral geniculate nucleus
    • Input: Visual input via the optic nerve and tract; has six layers, and the contralateral nasal field goes to layers 1, 4, 5, and the ipsilateral temporal goes to layers 2, 3, 5
    • Reciprocal output: Primary visual areas on both sides of the calcarine fissure in the occipital lobe
  32. MGN
    • Medial geniculate nucleus
    • Input: Auditory information from inferior colliculus
    • Reciprocal output: Primary auditory cortex (superior transverse temporal gyrus)
  33. Summary of sensory specific thalamic nuclei
    • VPM: Sensory from face through trigeminal lemniscus
    • VPL: Sensory from body through DCML and spinothalamic tract
    • VPI:
    • LGN:
    • MGN:
  34. VA
    • Ventral anterior nucleus
    • Input: Motor info from basal ganglia (uncrossed) via thalamic fasciculus
    • Reciprocal output: Premotor cortex (frontal lobe)
  35. VL
    • Ventral lateral nucleus
    • Input: Cerebellum via thalamic fasciculus
    • Reciprocal output: Primary motor cortex (precentral gyrus)
  36. Thalamic fasciculus location and information carried
    • Relays motor information from cerebellum to VL and from basal ganglia to VA
  37. MD
    • Mediodorsal nucleus
    • This is an association-specific nucleus
    • Input: Other thalamic nuclei, allowing for integration
    • Reciprocal output: Mostly association cortices in the frontal lobes
  38. Pulvinar
    • This is an association-specific nucleus
    • Input: Other thalamic nuclei, allowing for integration
    • Reciprocal output: Mostly association cortices in the parietal lobes
  39. Anterior group
    • A limbic-specific group of nuclei
    • Input: From midbrain and from parahippocampal region through the fornix and mammillary bodies through the mammillothalamic tract
    • Reciprocal output: Cingulate gyrus
  40. LD
    • Laterodorsal nucleus
    • A limbic-specific nucleus
    • Input: Parahippocampal region via the fornix
    • Reciprocal output: Retrosplenial cortex in the isthmus region
  41. Korsakoff's syndrome
    • Alcoholics with amnesia
    • A distributed neural system (of anterior group, LD, mammillary bodies, fornix, mammillothalamic tract, and cingulate/retrosplenial cortices) for spatial and context-dependent memory is formed
    • Degenerative changes in the anterior group due to vitamin B deficiency causes this syndrome
    • Mammillary bodies, and anterior, mediodorsal, and midline nuclei affected
  42. Midline nuclei
    • Non-specific nuclei, meaning they have diffuse, multimodal sensory input from locus cerulus, dorsal raphe, and the mesencephalon/pons
    • Output: Diffuse projections to the cortex and to the striatum in order to maintain general arousal
  43. Intralaminar nuclei
    • Main one in humans is centromedian nucleus
    • Non-specific nuclei, meaning they have diffuse, multimodal sensory input from locus cerulus, dorsal raphe, and the mesencephalon/pons
    • Output: Reciprocal to striatum, which is thought to be important in attention to motor tasks
  44. What are ways that global consciousness is achieved through the thalamus?
    • Most thalamic nuclei contain a thalamocortical projection neuron (which is either going to a restricted area of cortex or widespread) and an inhibitory interneuron
    • In general, the restricted thalamocortical neurons fire, and the reciprocal corticothalamic projectionss return to the thalamus and activate the widespread thalamocortical projection neurons, rapidly producing global synchrony
    • The reticular nucleus (TRN) is the principal thalamic structure involved in changing the level of consciousness in waking and sleep states
  45. TRN
    • Reticular nucleus
    • A thin sheet of neurons outside the external medullary lamina that virtually encases the thalamus
    • Consists almost entirely of GABA (inhibitory) neurons innervating the whole thalamus
    • All fibers passing between the cortex and thalamus pass through the reticular nucleus, meaning that all thalamocortico/corticothalamic neurons contact TRN neurons
    • TRN switches the thalamocortical neurons firing patterns from a burst mode (info cannot be sent) to a tonic mode in response to a depolarizing drive (awake)
  46. Thalamic blood supply and lesions
    • Most is derived from the posterior cerebral artery, but small penetrating vessels from the ACA and MCA are present
    • Inferolateral: Ataxia, hemiparesis, hemianesthesia, hemihyperesthesia
    • Paramedian: Hemiparesis, memory/learning problems, apathy
    • Tuberal: Amnesia, language difficulty, euphoria/mood
  47. Dejerine-Roussy syndrome
    • Hyperesthesia (abnormal increased sensitivity to stimuli of sense)
    • Dysesthesia: Unpleasant sensations to light touch and sound
    • Hyperpathia: Very painful reactions to minor stimuli
  48. What symptoms are caused by lesions to what nuclei?
    • VPM/VPL: Contralateral hemianesthesia
    • MGN: Contralateral hemihypoacusis (hearing loss)
    • LGN: Contralateral hemianopsia or quadrantopsia (unable to process vision)
    • VA/VL: Hemiparesis, motor neglect, speech difficulties, abnormal movements
    • Anterior group/MD: Memory impairments
    • Pulvinar: Aphasia (loss of ability to understand or express speech)