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