SPLH 620 Exam 2

what is the eighth nerve?

the nerve of hearing and balance

CN Vll

vestibular division and cochlear division

vestibular definition

position and movement of head

Outer ear

Pina and ear canal

middle ear

• tympanic membrane

• ossicles

• air filled

• oval window

Ossicles include

malleus, incus, stapes

inner ear

cochlea and vestibular system

is middle ear air or fluid filled

air filled

is inner ear air or fluid filled

fluid filled

middle ear function

• amplification of signal

• transforms signal

  • acoustic → mechanical

inner ear function

• transforms signal

  • mechanical → chemolectric

• represent sound frequencies

vibrations are transmitted through

the tympanic membrane, middle ear ossicles, and oval window reach the fluid of the inner ear

cochlea is a coiled tube with three chambers

• scala vestibulu

• scala tympani

• scala media

scala vestibuli and scala tympani is

perilymph

scala media is

endolymph

organ of corti

a strip of hair cells that rest on the basilar

• inner and outer hair cells

• 90-95% of all cochlear nerve fiber receives input from IHC

• OHC amplify signal

wave energy from the cochlea causes

the basilar membrane to vibrate, bending hair cells, generating action potential

tonotopic map - high frequency

sounds at the base

tonotopic map - low frequency

sounds at the apex

auditory pathway

1. sounds enters ear and stimulates the auditory nerve (CN Vlll)

2. information is passed through the superior olive, lateral lemniscus, inferior colliculus and thalamus (MGN)

3. auditory cortex receives thalamic input and processes signal

• tonotopic map is preserved in cortex

in the auditory pathway 1st : hair cells →

dorsal and ventral cochlear nuclei

in the auditory pathway 2nd : dorsal cochlear nucleus →

most axons cross over to contralateral inferior colliculus

in the auditory pathway 3rd : ventral nucleus →

axons synapse on the ipsilateral and contralateral superior olivary nucleus

the lateral lemniscus in the auditory pathway is

a large fiber hundle of the ipsilateral and contralateral ventral and dorsal axons

what does the lateral lemniscus do in the auditory pathway

synpases in the inferior colliculus and goes on to the medial geniculate nucleus of the thalamus

• from there to the temporal lobe of the auditory cortex and each hemisphere receives info from both ears

spatial hearing

• our ability to localize sounds in space

• requires signals from both hemispheres

• can be computed from:

  • interaural time differences (ITD)

  • interaural level differences (ILD)

where does the auditory pathway become bilateral?

superior olive

conductive hearing loss

impaired ability of air-borne vibrations to reach the organ of corti

sensorineural hearing loss

impaired ability of hair cells or the cochlear nerve to respond

cochlear implant

• microphone collects sound signals

• processing chip converts sound to coded electrical signal

• transmitter sends signal to implanted receiver

• receiver sends electrical pulses to electrodes

auditory gyri

deep within the lateral sulcus (sylvian fissure)

superior temporal sulcus

divides superior temporal gyrus from middle temporal syrus

inferior temporal sulcus

• not usually very continuous

• divides middle temporal gyrus from inferior temporal gyrus

dual-stream model

ventral stream and dorsal stream

ventral stream

phonological, semantic processing (speech perception)

dorsal stream

• no consensus

• invloved in sensorimotor transforms

• motor → auditory

• auditory → motor

vestibular system

sensory organs of balance are located in the inner ear and travel in the VIIIth CN

two types of vestibular organs

• 3 semicircular canals

• 2 otoliths

the 3 semicircular canals

• anterior (rotation in midsagittal place)

• posterior (roation in coronal plane)

• horizontal (rotation in transverse plane)

semicircular canals

the ducts respond to angular acceleration and deceleration of the head

• ampulla

• cupula

• hair cells

what do the ampulla do in semicircular canals

dilation at the end of the duct

what does the cupula do in the semicircular canals

contains hair cells

what do the hair cells do in semicircular canals

respond to endolymph flow

otolithic organs

• utricule

• saccule

• macula

what is the macula

patch of hair cells

• bottom of the utricule

• walls of the saccule

what do the otolithic organs do

respond to the position of the head with respect to linear acceleration and pull of gravity

• utricule sensitive to linear acceleration on horizontal plane

• saccule sensitive to linear acceleration on sagittal plane

how do we use vestibular pathways

to regulate posture and to coordinate eye and head movement

the vestibular nuclei includes

superior, medial, lateral, inferior

the vestibular pathway includes

• spinal cord

• motor nuclei of extraocular muscles

• cerebellum

• via thalamus to cerebral cortex

vertigo

subtype of dizziness in which a patient inappropriately experiences the perception of motion (usually a spinning motion) due to dysfunction of the vestibular system

peripheral vertigo

inner ear

central vertigo

CNS - cerebellum or brainstem damage

chemoreceptors

taste, smell

photoreceptors

vision

mechanoreceptors

• mechanical pressure or distortion

• hearing, balance

eye & retina concentric tissue layers

• sclera (white), outermost

• choroid, middle - holds iris

• meural retina (innermost)

• filled with vitreous humor

input and output of the eye & retina

input → photoreceptors (rods/cones) synpase on : output → bipolar cells

input → bipolar cells synapse on : output → ganglion cells

how do the horizontal and amacrine cells transfer in the eye and retina

transfer information laterally

where does light pass through in the eye and retina

light passes through all retinal layers BEFORE hitting photoreceptors

rods in the photoreceptors

more sensitive to light and function at low levels of illumination

cones in the photoreceptors

cones are color sensitive, less sensitive to light and require high (daylight) illumination levels, concentrated in the center

vision in the visual field center

• operates best under high illumination

• has the greatest visual acuity and color sensitivity

vision in the peripheral visual field

• is more sensitive to dim light

• operates under low illumination

a small “blindspot” is

• located in the temporal hemifield

• where objects cannot be seen

optic nerve

made from ganglion cells : on-center, off-surround OR off-center, on-surround

ganglion cell activity : on-center

• maximum for stimulus in center

• minimum for stimulus in surround

ganglion cell activity : off-center

• maximum for stimulus in surround

• minimum for stimulus in center

visual pathway

The axons in the optic tract terminate in four nuclei within the brain (lateral geniculate, superior colliculus, pretectum, hypothalamus)

visual pathway - lateral geniculate nucleus

of the thalamus for visual perception

visual pathway - superior colliculus

of the midbrain for control of eye movements

visual pathway - pretectum

of the midbrain for control of the pupillary light reflex

visual pathway - hypothalamus

for control of diurnal rhythms and hormonal changes

visual pathway 1

left visual field → right hemisphere

right visual field → left hemisphere

visual pathway : streams

M & P pathways

M pathway

dorsal stream, motion, location

P pathway

ventral stream, form, color

P ganglion cells

type P retinal ganglion cells are color-sensitive object detectors

• color sensitive

• small concentric receptive field

• insensitive to motion

Insensitive to motion in P ganglion cells

• produces a sustained, slowly adapting response that lasts as long as a stimulus is centered on its receptive field

• produces weak responses to stimuli that move across its receptive field

M ganglion cells

type M retinal ganglion cells are color-insensitive motion detectors

• much larger than P ganglion cells

• color insensitive

• large concentric receptive field

• sensitive to motion

sensitive to motion in M ganglion cells

responds with a transient, rapidly adapting response to a maintained stimulus

integration

the process of combining for adding components to make a unified whole

unimodal / unisensory processing

one sense specific

multimodal / integrative / associative processing

integration of more than one sense

key structures in multisensory integration

subcortical and cortical

subcortical - superior colliculus

• midbrain structure

• superior to the brainstem, inferior to the thalamus

sensori-motor function

reflex orientation to salient, novel, external stimuli

• receives afferent input from the visual cortex, spinal cord and inferior colliculus

• sends feedback/efferent input to the spinal cord, cerebellum, thalamus and the occipital lobe as well as eye muscles for saccadic movement

Cortical - multisensory integration

• multisensory neurons are dispersed throughout the cortex with unimodal neurons

• clusters are often located at the borders of major cerebral lobes

sensory convergence

unisensory information projects to association areas that are related to multiple sensory modalities

principles of multisensory integration

• spatial rule

• temporal rule

• inverse effectiveness rule

spatial rule

integration is more likely or stronger when multiple unisensory signals arise from the same location

temporal rule

integration is more likely or stronger when multiple unisensory signals arise at the same time

inverse effectiveness rule

integration is more likely or stronger when constituent unisensory signals are weak when evaluated in isolation

redundancy gain (RG) effect

organisms respond faster to targets presented in more than one modality (visual cue + auditory or tactile cue)