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AUDITORY PATHWAY
Receptor: organ of Corti – hair cellsN1 –bipolar cell of ganglion cochleareN2 – cochlear nuclei
N3 – colliculus inferior
N4 – corpus geniculatum mediale
VIII.nerveTrapezoid body
Lateral lemniscus
Radiatio acustica (auditory radiations) ICCGM
BA 41,42
cochlear nucleisuperior olive(lat) superior olive(med)
pons
diencephalon
cortex
cochlea
tuberculum acusticum(upper oblongate)
1.N
4.N
3.N
2.N
BA 41, 42
Receptor: organ of Corti – hair cells
N1 –bipolar cell of ganglion cochleare
N2 – cochlear nuclei
N3 – colliculus inferior
N4 – corpus geniculatum mediale
Relay nuclei:
Ncl. corporis trapeziodei
Ncl. olivaris sup. (sound localization)
Ncl. lemnisci lateralis ventralis et dorsalis
IC
acoustic striaeLateral lemniscus
Brachia colliculi inferioris
Radiatio acustica
trapezoid body
Cochlea
1-ductus cochlearis
2 – scala vestibuli
3 – scala tympani
4 – ganglion spirale cochleae
5 – nervus cochlearis
1-ductus cochlearis
2- scala vestibuli
3 -scala tympani
4 –membrana vestibularis
(Reissneri)
5- membrana basilaris
6- membrana tectoria
7 – stria vascularis
8- ganglion spirale cochleae
9 – lamina spiralis ossea
Cross section of one single turn of cochlea
Radial afferents
Lateral efferents
Spiral afferents
Medial efferents
Bipolar ganglionar cells
32 000
Spiral fiber neurons
Radial fiber neurons
Inner hair cell1-nucleus2-stereocilia3-cuticular plate4- afferent ending5-efferent ending
Outer hair cell6-efferent ending7-afferent ending
3 500
in one row
15 000
in 3 rows
EM scan of hair cells and stereocilia
Mechano – electric transduction
Mediators of hair cells
lemniscus lateralis
lemniscus lateralis
radiatio acustica
41,42
22
transverse temporal gyruses of Heschl
Receptor: organ of Corti – hair cells
N1 –bipolar cell of ganglion cochleare
N2 – cochlear nuclei
N3 – colliculus inferior
N4 – corpus geniculatum mediale
CI
DLFautonomic nerves nuclei
motor nerves nucleiand Ret-Sp tractDLF- dorsal longitudinal fascicle
Tonotopic organisation
• Basilar membrane – base of the cochlea high frequencies, apex cochleae – low frequencies
• Cochlear nuclei – low frequencies ventrally, high dorsally• Inferior colliculus – low frequencies dorsally, high
ventraly• Medial geniculate nucleus – low frequencies laterally,
high medially• Auditory cortex – low frequencies anteriorly
Descending connections in the auditory pathway
tr. cortico-geniculatus
2 - tr. olivo-cochlearis noncruciatus
1 - tr. olivo-cochlearis cruciatus
Afferents and efferents of hair cells
tr. olivo-cochlearis cruciatus
tr. olivo-cochlearis noncruciatus
Vestibular pathway
• Receptor: hair cells in macula sacculi et utriculi• hair cells in cristae ampullares• 1.N. bipolar cell in ggl. vestibulare• 2.N. vestibular nuclei• 3.N. ventral thalamic nuclei• Vestibular cortical area: temporal and parietal
lobe, SI
M
LS
IVestibularnuclei
vestibulocochlear nerve
GM
medialis - Schwalbelateralis - Deiters superior - Bechtěrevinferior - Roller
2.N
3.N Thalmus
1.N Vestibular ganglion
Vestibular tract
Vestibular nucei - efferents
Superior MedialLateral Inferior
Paramedian pontine RF
Thalamus
Cortex
Cerebellum
Spinal cord
Ve-S
Ncl. III., IV., VI.ncl.interstitialis Cajali , ncl.Darkševiči
Lobus nodulofloccularis
Ve-Crbl
Ncl. III., IV., VI.ncl.interstitialis Cajali , ncl.Darkševiči
crossed and with medial lemniscus
uncrossed
crossedand uncrossed
MLF
MLF
MLF- medial longitudinal fascicle
uncrossed
corpus restiforme
Inner ear - schema
Dura mater
utriclesaccule
semicircular duct
endolymphatic duct
cochlear ductuniting duct (ductus reuniens)
vestibulecochlea
endolymphatic sac
scala vestibuli
scala tympani
cochlear duct
Hair cells in the vestibular labyrinth transduce mechanical stimuli into neural signals
macula sacculi
macula utriculi
ampullar crests
Mechanoreceptors for equilibrium. a. Rotational equilibrium. The ampullae of the semicircular canals contain hair cells withstereocilia embedded in a cupula. When the head rotates, the cupula is displaced, bending the stereocilia. Thereafter, nerve impulses travel in the vestibular nerve to the brain.b. Gravitational equilibrium. The utricle and the saccule contain hair cells with stereocilia embedded inan otolithic membrane. When the head bends, otoliths are displaced, causing the membrane to sag and the stereocilia to bend. If the stereocilia bend toward the kinocilium, the longest of the stereocilia, nerve impulses increase in the vestibular nerve. If the stereocilia bend away from the kinocilium, nerve impulses decrease in the vestibular nerve. The difference tells the brain in which direction the head moved.
a bcupulaotolithic membrane
The utricle and the saccule detect linear accelaration
Macula
The axis of mechanical sensivity of each hair cell in the utricle is orientated toward the striola
Orientation of the maculae of the utricle and saccule
• the saccular macula is in a vertical plane aligned anteroposterior.
• The utricular macula is mostly horizontal plane but with a backward tilt..
• A striola (str) divides each macula into two regions of reversed hair-cell polarity, so that when all afferents of a macula are excited or inhibited, the net signal will be determined by the relative weighting of each region. pe, Pars externa; pi, pars interna; pl, pars lateralis; pm, pars medialis. [Adapted from drawings by Spoendlin (93).]
Fitzpatrick and Day (1996)
Function of the horizontal semicircular canals
Vestibulo-ocular reflex
The head impulse test• The head impulse, or head thrust, manoeuvre is a test of vestibular
function that can be easily done during bedside examination. This manoeuvre tests the vestibulo–ocular refl ex (VOR), and can help to distinguish a peripheral process (vestibular neuritis) from a central one (cerebellar stroke).
• With the patient sitting on the stretcher, the physician instructs him to maintain his gaze on the nose of the examiner. The physician holds the patient’s head steady in the midline axis and then rapidly turns the head to about 20o off the midline.
• (A) The normal response (intact VOR), is for the eyes to stay locked on the examiner’s nose.
• (B) An abnormal response (impaired VOR) is for the eyes to move with the head, and then to snap back in one corrective saccade to the examiner’s nose. The test is usually “positive” (ie, corrective saccade is visible) with peripheral lesions (vestibular neuritis), and the test is usually normal in cerebellar stroke. This occurs because the primary VOR pathway bypasses the cerebellum.
optokinetic nystagmus
Vestibulo-nuclear connections
macula sacculi et utriculi – static impulses
cristae ampullares kinetic impulses
Medial longitudinal fascicle
PPRF - Paramedial pontine RF
Interstitial nucleus coordination of the vertical movements of eyes
coordination of the horizontal movements of eyes
Spinal cord - cervical
MLF and Ve-S tract
1.N
Repetition
Sources• Petrovický, Basic Neuroanatomy• Kahle, Frotscher, Color Atlas of Human Anatomy• Gray, Anatomy• Nolte, J. The Human Brain• http://www.iurc.montp.inserm.fr/cric/audition/english/corti/fcorti.htm• http://www.rcsullivan.com/www/ears.htm• http://anatomy.uams.edu/anatomyhtml/neuro_atlas.html• http://anatomy.uams.edu/anatomyhtml/gross.html• http://en.wikipedia.org/wiki/Optokinetic_reflex