Visual, Auditory, Vestibular Systems

8/12/2019 Visual, Auditory, Vestibular Systems

1/110


2/110

objectives

Review the function of the auditory, visual and vestibular sy Examine the functional connections of the 3 sensory system

Highlight relevant clinical correlates


3/110

introduction

Sight is dependent not only on a substantial portion of the ce

cortex, but also upon six cranial nerves (IIVII).

Perception is the function of the retina, optic nerve, tract, raand cortex.

The oculomotor, trochlear and abducens nerves move the ey

Eyeball sensations such as pain, touch and pressure are medthe ophthalmic nerve, and the facial nerve innervates orbicumuscle.

70% of all sensory receptors are in the eyes

40% of the cerebral cortex is involved in processing visual inf


4/110

visual system

The eye is the organ of vision; modified to suit its function Neural impulses arise from the eye to the brain via the optic

tract(CNII)

The nerve is in fact a tract of the CNS: Rods and cones Bipolar cells

Ganglion cells

Rods, cones and intrinsically photosensitive retinal ganglion[IPRGCs] are the photosentive cells

The eye also has non-image forming pathways to parts of th


5/110

internal structure of the eye

Fig 16.7


6/110

anterior structures of the eye

Fig 16.8


7/110

retina

a) Light passes outward

through the entirethickness of the retinabefore exciting thephostoreceptor cells; thelectrical signals flowinward from neuron toneuronFig 16.9


8/110

optic chiasma

is a flattened bundle of nerve fibres situated at the junction of thwall and floor of the third ventricle

The superior surface is attached to the lamina terminalis, and infrelated to the hypophysis cerebri, from which it is separated by tdiaphragma sellae.

The anterolateral corners of the chiasma are continuous with the

nerves, and the posterolateral corners are continuous with the oA small recess, the optic recess of the third ventricle, lies on its ssurface.

fibres originating from the nasal half of each retina cross the meat the chiasma to enter the optic tract of the opposite side.


9/110

pathway of transmission of visualimpulses

From the retina the impulses reach the LGN of the thalamus The LGN is a 6 layered structure connected to the superior c

via the superior brachium

Layers 1&2 have giant cells [magnocellular]

Layers 3-6 have small sized cells [parvocellular]

Fibres that would have crossed in the optic chiasma relay in&6

Fibres from the temporal hemi-retina relay in layers 2,3 &5.


10/110

the retinofugal projection

The Optic Nerve, Optic Chiasm, and Optic Tract


11/110


12/110

the lateral geniculate nucleus (LGN

Inputs Segregated by Eye and Ganglion Cell Type


13/110

the lateral geniculate nucleus (LGN Receptive Fields

Receptive fields of LGN neurons: Identical to the gangliocells that feed them

Magnocellular LGN neurons: Large, monocular receptivefields with transient responsegross detail: low acuity,movement, peripheral

Parvocellular LGN cells: Small, monocular receptive fieldwith sustained response fine detail: color, high acuity,foveal


14/110


15/110

the lateral geniculate nucleus (LGN

Nonretinal Inputs to the LGN

Primary visual cortex provides 80% of the synapticinput to the LGN

Brain stem neurons provide modulatory influence onneuronal activity


16/110

geniculocalcarine tract

From LGN the fibres of the optic radiation take 2 courses to occipital lobe via the geniculocalcarine tract

Traverses the sublentiform and retrolentiform parts of intercapsule curving posteriorly towards the calcarine sulcus

Some of the fibres travel or loop over the temporal horn of

ventricle as Meyers Loop These fibres carry fibres from the upper quadrants of the ey

the contralateral eye


17/110


18/110

optic radiations


19/110

the primary visual cortex

Brodmanns area V1 17, V2:association areas 18,19.

Also called the striate cortex

Found on the occipital lope(posterior hemispheric pole)

There is a point to point projection of the retina onto the cacortex


20/110


21/110

anatomy of the striate cortex Retinotopy


22/110

anatomy of the striate cortex

Inputs to the Striate Cortex Magnocellular LGN neurons: Project to layer IVC

Parvocellular LGN neurons: Project to layer IVC

Koniocellular LGN axons: Bypasses layer IV to makesynapses in layers II and III


23/110

stripe/band of Gennari in area 17


24/110

summary of point-point projection

Axons from Rt halves of both retinae terminate in the Rt LGvisual info is relayed to visual cortex of Rt Hemisphere.

Axons from upper quadrants peripheral to the macula end ipart of LGN----- ant 2/3 of visual cortex above calcarine sul

Lower quadrants peripheral to macula project to lateral porLGN----ant 2/3 below the calcarine sulcus.

Macula projects to the large posterior region of the LGN----pof the visual cortex in the region of the occipital pole.


25/110

visual field representation on calcarcortex Left visual fieldrep on Rt LGN and visual cortex of right

Upper half of visual field rep on lat portion of LGN and in thbelow the calcarine cortex

Lower half of visual field projected on the medial portion ofon cortex above calcarine cortex


26/110


27/110


28/110


29/110

non-image forming visual


30/110

non-image forming visualpathways

Other visual pathways include optic tracts tothe:

Superior colliculi to control extrinsic eyemuscles,

Pretectal nuclei in the midbrain to mediatepupillary light reflexes,

Suprachiasmatic nucleusin the hypothalamus toregulate daily biorhythms.

These are referred to as the non-imageforming pathways of the eye.

i f h i l


31/110

connections of the visual system anreflexes LGN connected to sup colliculus via sup brachium---pretecta

EW---CNIII---Sphincter pupillae

Pupillary light reflex/Consensual light reflex Light shone into one eye

retina sends fibres from both eyes to the optic tract

Impulses stimulate olivary pretectal nucleus

Pretectal nucleus sends impulses to both ipsilateral and contralat

EW sends pregang fibres to ciliary ganglion

Destination: sphincter pupillae

Constriction of BOTH PUPILS


32/110

direct and consensual light reflexes

Afferent nervous impulses travel from the retina through the opt

optic chiasma, and optic tract A small number of fibres leave the optic tract and synapse on ne

the pretectal nucleus (close to the superior colliculus).

Impulses are passed by axons of the pretectal nerve cells to theparasympathetic nuclei (Edinger-Westphal nuclei) of CNIII on bot

Here, the fibres synapse, and the parasympathetic nerves travel

CNIII to the ciliary ganglion in the orbit. Postganglionic parasympathetic fibres pass through the short cilto the eyeball and to the constrictor pupillae muscle of the iris. Bconstrict in the consensual light reflex because the pretectal nucfibres to the parasympathetic nuclei on both sides of the midbra


33/110


34/110


35/110


36/110


37/110


38/110

accommodation reflex

When eyes are directed from a distant to a near object, con

the medial recti brings about convergence of the ocular axe

Lens thicken to increase refractive power by contraction of tmuscle,

Pupils constrict to restrict the light waves to the thickest cenof the lens.


39/110

argyll-robertson pupil

Characterised by a small pupil, of fixed size that does not re

Contracts with accommodation

Usually caused by a neurosyphilitic lesion to fibres that run pretectal nucleus to the parasympathetic nuclei (Edinger-Wnuclei) of CNIII on both sides

The fact that the pupil constricts with accommodation implthe connections between the parasympathetic nuclei and thconstrictor muscle of the iris are intact


40/110

horners syndrome

consists of (1) constriction of the pupil (miosis),

(2) slight drooping of the eyelid (ptosis),

(3) enophthalmos,

(4) vasodilation of skin arterioles,

(5) loss of sweating (anhydrosis).


41/110

horners syndrome

symptoms result from an interruption of the sympathetic ne

supply to the head and neck.

Pathologic causes include lesions in the brainstem or cervicathe spinal cord that interrupt the reticulospinal tracts descefrom the hypothalamus to the sympathetic outflow in the lacolumn of the first thoracic segment of the spinal cord.

Such lesions include multiple sclerosis and syringomyelia. Trthe stellate ganglion due to a cervical rib or involvement of tganglion in a metastatic lesion may interrupt the peripheral the sympathetic pathway


42/110

lesions of visual pathway

Optic nerve- Blindness

Chiasmabitemporal hemianopia

Tract- homonymous hemianopia

Geniculocalcarine tract- homonymous hemianopia with macsparing.


43/110


44/110

auditory systemwhen he had said these things, he cried, He that hath ears to hear, let [Luke 8:8 -The Holy Bible; King James Version]


45/110

auditory system

The ear is an organ of hearing and equilibrium adapted to it

Nuclei associated with these functions are found in the brai

The nuclei also project to other areas so as to facilitate refle

Hearing is second in importance among the special senses oyielding first place only to sight.

The auditory system consists of the external ear, middle ear,of the internal ear, cochlear nerve, and pathways in the cennervous system (CNS).


46/110

Outer ear

Middle ear

Inner ear


47/110

four major divisions of auditory syste

1. The outer ear

- pinna- ear canal

- eardrum

2. The middle ear

- three ossicle bones;

(malleus, incus, stapes)

- two major muscles

(stapedial muscle, tensor

tympani)- Eustachian tube

3. The inner ear

- cochlea (hearing)

- vestibular system (balance)

4. The central auditory system



48/110


t


49/110

Three parts of outer ear

1) Pinna

2) Ear canal

3) Ear drum

Major function of outer ear

1) protection

2) amplification

3) sound localization

outer ear

outer ear: pinna (binaural cue to sound


50/110

t Left

t Right

* Different distances from source to each ear

=> different arrival times (Interaural time-difference)

and different sound level (interaural level-difference)

Right

ear

Left

ear

Sound

outer ear: pinna (binaural cue to soundsource location)


51/110

t l d iddl


52/110

external and middle ear

The external ear consists of the auricle or pinna and the ext

acoustic meatus, with the latter being separated from the mby the tympanic membrane.

The function of the external ear is to collect sound waves, wcause vibration of the tympanic membrane.

t l d iddl


53/110


The vibration is transmitted across the middle ear by a chain

ossicles (little bones): the malleus, incus, and stapes. The malleus is attached to the tympanic membrane and art

with the incus, which articulates in turn with the stirrup-shastapes.

The footplate of the stapes occupies the fenestra vestibuli (o

window) in the wall between the middle and internal ears; tthe foot plate is attached to the margin of the fenestra vestithe annular ligament, composed of elastic connective tissue


54/110



55/110


Protection against the effect of sudden, excessive noise is pr

reflex contraction of the tensor tympani and stapedius muscwhich are inserted on the malleus and stapes, respectively.

The tensor tympani is innervated by the trigeminal nerve, astapedius is innervated by the facial nerve


56/110

inner ear cochlea


57/110

perilymph

perilymph

endolymph

inner ear- cochlea


58/110

inner earresonance of basilar


59/110

Fig

membrane


60/110

inner earinner hair cells (IHC) & outer hacells (OHC)


61/110

Inner hair cells: produce sensation of hearing

Outer hair cells: modify BM response and act as amplification system

cells (OHC)


62/110

bony and membranous labyrinth


63/110

bony and membranous labyrinth

The bony labyrinth is located in the petrous part of the temp

bone, which forms a prominent oblique ridge between the mand posterior cranial fossae.

The labyrinth is a system of tunnels within the bone.


64/110

bony labyrinth


65/110

bony labyrinth

Three semicircular canals extend posterolaterally from the v

and the cochlea constitutes the anteromedial part of the bolabyrinth. The cochlea has the shape of a snail shell; its baseagainst the deep end of the internal acoustic meatus, whichinto the posterior cranial fossa.


66/110

membranous labyrinth


67/110


The delicate membranous labyrinth conforms, for the most

the contours of the bony labyrinth. There are two dilations, the utricle and the saccule, in the ve

the bony labyrinth. Three semicircular ducts arise from the

A patch of sensory epithelium is present on the inner surfacutricle, the saccule, and each semicircular duct.

The saccule is continuous with the cochlear duct through a channel known as the ductus reuniens. The cochlear duct coalong its entire length, the organ of Corti.



68/110


Whereas the lumen of the membranous labyrinth is filled w

endolymph, the interval between the membranous and bonlabyrinths is filled with perilymph.

The vestibular part of the membranous labyrinth is suspendthe bony labyrinth by trabeculae of connective tissue.

The cochlear duct is firmly attached along two sides to the b

of the cochlear canal.


69/110


70/110


71/110

cochlea


72/110

The thin unspecialized wall of the cochlear duct apposing the scais called the vestibular or Reissner's membrane, and the thicker w

apposing the scala tympani constitutes the specialized basilar mon which the organ of Corti rests.

The basilar membrane is of special importance in the physiologybecause it responds to vibration of the stapes in the following m

vibration of the foot plate of the stapes produces correspondingthe perilymph, beginning with that of the vestibule. Sound wavepropagate through the scala vestibuli, Reissner's membrane, theendolymph in the cochlear duct, and the basilar membrane to thtympani. These same waves create a vibration of the membranefenestra cochleae at the base of the scala tympani; this is essenteliminate the damping of pressure waves that would otherwise obone-encased fluid.

pathway of audition


73/110

p y

Organ of corti

Cochlea nerve Dorsal and ventral cochlea nuclei

3 acoustic striae

Commisural fibres

Superior olivary body

Lateral lemnsicus

Inferior colliculi

MGN

Auditory cortex


74/110


75/110

Tonotopy!


76/110

pathway of audition


77/110

p y

The last link in the auditory pathway consists of the auditory

in the sublentiform part of the internal capsule, through whmedial geniculate body projects to the primary auditory cortemporal lobe.

pathway of audition


78/110

y

This primary auditory area, corresponding to Brodmann's ar

and 42, is located in the floor of the lateral sulcus, extendingslightly onto the lateral surface of the hemisphere. A landmprovided by the anterior transverse temporal gyri (Heschl'sconvolutions) on the dorsal surface of the superior tempora

pathway of audition


79/110

The area receives afferent fibres from the tonotopically orga

ventral part of the medial geniculate body. The tonotopic pattern in the auditory area is such that wher

for low-frequency sounds end in the anterolateral part of thfibres for high-frequency sounds go to its posteromedial par

pathway of audition


80/110

Projection fibres to the auditory area arise principally in the

geniculate body and form the auditory radiation of the intercapsule. The anterior part of the primary auditory area is cowith the reception of sounds of low frequency, and the postof the area is concerned with the sounds of high frequency.unilateral lesion of the auditory area produces partial deafnboth ears, the greater loss being in the contralateral ear. Thi

explained on the basis that the medial geniculate body recemainly from the organ of Corti of the opposite side as well afibres from the same side.


81/110

projections


82/110

Superior temporal gyrus

Projection fibres to brainstem From inferior colliculus to spinal cord[tectospina tract]


83/110

auditory reflexes


84/110

A few acoustic fibres from the inferior colliculus pass forwar

superior colliculus, which influences motor neurons of the cregion of the spinal cord through the tectospinal tract. The scolliculus also influences neurons of the oculomotor, trochleabducens nuclei through indirect connections in the brain stThese pathways provide for reflex turning of the head and etoward the source of a sudden loud sound.

The tectospinal tract is concerned with reflex postural moveresponse to visual stimuli

auditory reflexes


85/110

Some axons from the superior olivary nucleus terminate in t

nuclei of the trigeminal and facial nerves for reflex contractitensor tympani and stapedius muscles, respectively. Contrathese muscles in response to loud sounds reduces the vibratympanic membrane and the stapes, thereby protecting thestructures in the cochlea from mechanical damage.

high-tone deafness


86/110

Persistent exposure to loud sounds causes degenerative cha

the organ of Corti at the base of the cochlea, causing high-todeafness. This is prone to occur in workers exposed to the scompression engines or jet engines and in those working fohours on farm tractors. High-tone deafness was formerly enmost frequently among workmen in boiler factories and is ssometimes called boilermakers' disease.

disorders of hearing: conductiondeafness


87/110

deafness Conduction deafness

conductive deafness - blockage of sound transmission throuand/or middle ear without damage to cochlea

Sound vibrations cannot be conducted to the inner ear

e.g. in ruptured tympanic membrane, otitis media, otosclero

Conductive deafness may resolve or may be treatable in som

disorders of hearing: conductiondeafness


88/110

deafness

normal tympanic membrane ruptured tympanic membrane otitis me

disorders of hearing: sensorineuraldeafness


89/110

Results from damage to any part of the auditory pathway

loss of auditory function because of loss of cochlear hair celcochlear nerve neurons they connect to

Sensorineural deafness can result from direct damage to thecells, or indirectly from damage to the blood supply.

Sensorineural deafness is not reversible in mammals.

important facts 1


90/110

The ossicles of the middle ear transfer vibrations from the aperilymph. Movement of the ossicles is restrained by the te

tympani and stapedius muscles, innervated by CNV and VII,respectively.

In the cochlea, the oscillations of the basilar membrane are by the inner and outer hair cells of the organ of Corti. The ocells respond with movement, which is transmitted to the temembrane and thence to the inner hair cells, increasing thesensitivity of the latter to sound. The inner hair cells responreleasing their excitatory transmitter and stimulating the seterminals of the cochlear division of CNVIII.

important facts 2


91/110

The primary sensory neurons have their somata in the spiral ganthe cochlea. Their axons end in the dorsal and ventral cochlear n

Axons from the dorsal cochlear nucleus cross the midline, travel the lateral lemniscus, and end in the inferior colliculus.

Axons from the ventral cochlear nucleus end in the superior olivof both sides. The convergence of signals from the left and right allows neurons in the superior olivary nucleus to respond to the

times of arrival of sound in the two ears, thus providing the abilidetermine the direction of the source. The neurons in each supenucleus have axons that travel in the lateral lemniscus and end ininferior colliculus

important facts 3


92/110

The inferior colliculus projects (through the inferior brachiumedial geniculate body, which projects to the primary auditof the cerebral cortex.

The primary auditory cortex is located on the superior surfatemporal lobe. It is connected with auditory association corsuperior temporal gyrus and nearby parts of the parietal lobleft cerebral hemisphere (of most people), these regions are

coextensive with the receptive language area.


93/110


94/110

vestibular systemhe who thinks that he is standing must be afraid of falling.


95/110

The Otolith Organs: Detect changes in head angle, linear acceleration

The Vestibular System


96/110

Found in utricule and saccule

Macular hair cells responding to tilt



97/110

The Semicircular Canal

Structure



98/110

Push-Pull Activation of SemicircularCanals

Three semicircular canals on oneside

Helps sense all possiblehead-rotation angles

Each paired with another onopposite side of head

Push-pull arrangement ofvestibular axons:


99/110

Ascending Pathways

b l


100/110

Vestibular nerve

Vestibular nuclei

Cerebellum

Oculomotor complex CN 3, 4, and 6

Along with vestibulospinal reflexes coordinate head andmovements

Relay Centers

Thalamus


101/110

Connection with vestibular cortex and reticularformation arousal and conscious awareness of

body; discrimination between self movement vs. thatof the environment

Vestibular Cortex Junction of parietal and insular lobe

Target for afferents along with the cerebellumBoth process vestibular information with somatosensory

and visual input


102/110


103/110

The Vestibulo-Ocular Reflex(VOR)


104/110

Vestibular-Ocular Reflex(VOR)


105/110

Causes eyes to move in the opposite directionto head movement

Speed of the eye movement equals that of thehead movement

Allows objects to remain in focus during headmovements

Compensatory Eye Movements

VOR


106/110

VOR

Optokinetic reflex

Smooth pursuit reflex, saccades, vergence

Neck reflexes combine to stabilize object on the same area of the

retina=visual stability


107/110

Purves 2001.

Vestibular ProcessingGain


108/110

Keeps eye still in space while head is moving

Ratio of eye movement to head movement (equal1)

VOR Dysfunction


109/110

Direction of gaze will shift with the head movement

Cause degradation of the visual imageIn severe cases, visual world will move with each head mov

Menieres disease

Vertigo

Nausea

Nystagmus(oscillatory mvmnt of the eyes consisting of fastcomponents)

Concluding Remarks

Hearing and Balance


110/110

Nearly identical sensory receptors (hair cells)

Movement detectors: Periodic waves, rotational,

and linear force

Auditory system: Senses external environment

Vestibular system: Senses movements of itself

Documents

Visual, Auditory, Vestibular Systems