neural substrates exam #3

hearing

acoustic energy waves are changed into neural impulses that are interpreted by the brain

peripheral auditory system

outer ear, middle ear, inner ear, cranial nerve VIII

central auditory system

brainstem and brain

Nature of sound

sound definition is audible variations in air pressure

Cycle

distance between successive compressed patches

sound frequency

number of cycles per second expressed in units of hertz

pitch is

frequency

loudness is

amplitude and intensity

range of human hearing

20Hz to 20,000 Hz

human ear sensitivity

0-140dB SPL

outer ear

canal lined by skin containing hair follicles, sebaceous glands, and ceruminous glands that produce wax

the cerumen lubricates the skin and coats hairs near the opening to impede the entry of the foreign particles into the ear

tympanic membrane

it is the boundary between the outer and middle ears. it virbates when sound wave entering the external audiotry auditory meatus hit it

a framework of connective fibers convered by skin on the external ear side, and mucous membrane on the side of the middle ear cavity.

perforation may cause transient or permanent hearing impairment

ossicles

transduction of vibratory energy into mechanical energy

malleus (hammer)

attached to the tympanic membrane

incus (anvil)

connectes the malleus to the stapes

stapes (stirrup)

fits into the oval window

attenuation reflex structure

tensor tympani inserts on the alleus stapedius inserts on the stapes

attenuation refelx function

protects the inner ear (cochlea) from damaging vibrations

masks background noise in noisy environments

decrease sensitivity to one’s own voice

Eustachian tube

equalizes pressure in middle ear to atmospheric pressure

ear infections from eustachian tube

more common in children; their eustachian tubes are shorter, narrower, more horizontal than adults, makes movement of air and fluid difficult. bacteria trapped in the eustachian tube (when the tissue of the eustachin tube becomes swollen from colds or allergies) may produce an ear infection that pushes on the eardrum causing it to become sore, red and swollen

inner ear anatomy

the rocking of the stapes in the oval window creates waves in the cochlear fluids.

mechanical energy of ossicular movement has been changed into hydraulic energy

these wave disrupt the hair cells in the organ of the corti causing a third energy change: hydraulic energy changed to electrochemical energy

fluid movement in the cochlea

pressure at the oval window pushes perilymph into scala vestibuli, which then travels around to the scala tympani and causes the round window membrane to bulge out.

basilar membrane

at the apex of the cochlea, the scala media is closed off, and the scala tympani becomes continous with the scala vestibuli at a hole in the membranes called the helicotrema

the response of basilar membrane to sound

stuctural properties: wider to apex, stiffness decreases from base to apex

perilymph movement bends basilar membrane near base, wave moves towards apex

response of the basilar membrane

high frequency sound produces a traveling wave, which dissipates near the narrow and stiff base of the basilar membrane

low frequency sound produces a wave that propagates all the way to the apex of the basilar membrane before dissipating

there is a place code on the basilar membrane for the frequecny that produces the maximum amplitude deflection

why the cochlea is spiral shaped

the spiral shape can affect the wave mechnics that take place inside the cochlea. it increases the strength of vibrations produced by sound waves, especially at low pitch.

bending of stereocillia

a) at rest, the hair cells are held between the reticular lamina and the basilar membrane, adn the tips of the outer hair cell stereocilia are attached to the tectorial membrane

b) when sound causes the basilar membrane to deflect upward, the reticular lamina moves ip and inward the modiolus, causing the sterocilia to bend outward

depolarization of hair cell

a) ion channels on stereocilia tips are opened when the top links joining the stereocilia are stretched

b) the entry of K+ (potassium) depolarizes the hair cell, which opens voltage-gated calcium channels. Incoming Ca2+ leads to the release of neurotransmitter from synaptic vesicles, which then diffuses to the postsynaptic neurite from the spiral ganglion

innervation of hair cells

vast majority of information leaving cochlea comes from INNER hair cells

cochlear amplifier: outer hair cells amplify movement of basilar membrane

outer hair cells amplify the response of basilar membrane → stereocilia on inner hair cell bend more → increased transduction in inner hair cells → greater response in auditory nerve

otoacoustics emissions

ears emit sounds present click → echo that can be recorded w/ mic in auditory canal. normally too faint for us to hear.

auditory pathyway

auditory receptors in cochlea → brain stem neurons → MGN → auditory cortex

cortical processing

primary auditory cortex (area 41; heschl’s gyri), secondary auditory area (area 42; superioir temporal gyrus), asssociation cortex of wernicke (area 22)

hearing disorders, conductive

interrupted sound transmission to cochlea

middle ear pathologies: otitis media (inflammation of middle ear fluid) and ottosclerosis (impeded stapes movement)

symptoms: fluctuating hearing loss, good word speech recognition, mostly softly spoken speech, impaired auditory reflex, and air bone gap

hearing disorders, sensorineural

dysfunction of hair cells and or auditory nerve fibers

ménière’s disease-progressive & fluctuating hearing loss with vertigo & tinnitus

presbycusis: old age induced hearing loss of high frequencies

acoustic neuroma/vestibular schwannoma: hearing impariment and disequilibrium, and ataxic symptoms in later stages

symptoms: difficulty in understanding speech, reduced seld-monitoring in speech, recruitment

hearing disorders, mixed

combination of conductive and sensorineural hearing loss

there may be a problem in the outer or middle ear and in the inner ear or auditory nerve

it can happen after a head injury, long term infection, or because of a disorder that runs in your family

hearing disorders, central

can result from samage to lower brainstem upper brainstem or primary auditory cortex

clinical characteristics: near normal sensitivity to stimuli, impaired processing of linguistic signals

unilateral cortical lesion

normal hearing thresholds with impared perception and discrimination of speechbil

ateral cortical lesion

profound hearing impairment

primary and secondary auditory lesion

acoustic aphasia: imparied discrimination of speech sounds and phonemes skills necessary for learning phonems and understanding language

language association cortex lesion

wernickes aphasia: impaired comprehension fo spoken and written language, word deficit and asemantic word output

right temporal lesion

impaired processing of environmental sounds, nonverbal memory, and musical properties

vestibular system

balance, spatial orientation system that hekps us sit upright

macular hair cells responding to tilt

when the utricular macula is level, the cilia from the hair cells also stnad straight

when the head and macula re tilted, gravity pulls the otoliths, which deform the gelatinous cap, and the cilia bend

semicircular canals

sense rotation of the head

vestibular schwannoma

slwo grouing, unilateral benign tumor on the CN VIII

hearing loss and innitus and vertigo and balance issues

labyrinthitis

infection in ears leading to vertigo, nausea, and vomiting

ménières disease

unknown cause liekly involves both genetic and environmental factors

episodes of feeling like the world is spinning (vertigo), rining in ears (tinnitus), hearing loss and fullness int the ear

motion sickeness

the vestibular system reports no movement but the visual system reports movement which causes nausea

difference between speech and language

speech is the MOTOR act that is verbal expression of language

language is the UNDERLYING STRUCTURE (the grammar of langauge) that specifies phonetics, semantics, pragmatics, syntax, morphology

speech requires

intent, emotion, executive function, motor execution, auditory feedback, respiratory coordination

right hemisphere is involved as the sensory areas

levels of motor speech system

conceptual level → linguistic planning level → motor planning/programming level → → direct motor pathway, indirect motor pathway → final common pathway → speech (→ sensory system ←→ motor control circuits → indirect)

conceptual level

involves our thoughts, feelings, and ideas

prefrontal cortex and limbic system probably have primary role at this level

when we want to express ideas through speech alnguage encoding must take place in upcoming levels

linguistic planning elvel

linguistic planning: language content, form, and use (semantics, grammar, and pragmatics)

motor planning: plans and arrangements of phonemes

premotor cortex (BA 6) important area for planning

speech motor planning/programming level

motor planning: plans and arranfements of phonemes

motor programs involve the execution of specific phonemes in time and space

programs involve discrete movements of tonge, lips, etc

many motor programs make up a motor plans

speech motor programming: direct pathway

prefrontal cortex sends concepts to supplementary motor areas/cortex and premotor cortex and broca’s area

these planning areas then send the plan to the promary motor cortex face area — where the corticobulbar tract originates

speech direct motor pathway: corticobulbar

when the primary motor cortex face area is stimulated it sends information thru the corticobulbar tract UMN’s down thru the internal capsule to the brainstem CN nuclei —mostly bilateral

results of damage to direct pathway on speech

apraxia of speech: searching/groping for articulatory placement, random substitution, errors in articulatory placement

spastic sysarthria: strain/strangled vocal quality

flaccid dysarthria: weak breathy vocal quality

speech motor programming: in-direct pathway

input to primary motor cortex face

area from basal ganglia and cerebellum

Pmfa then sends direct signals to speech musclesx

results of damage to indirect pathway on speech

Hypokinetic dysarthria: reduced vocal volume; small articulatory movements

Hyperkinetic dysarthria: excess articulatory movements

Ataxic Dysarthria: scanning speech, variable rate on DDK tasks

Auditory Comprehension steps

1. Cochlea to cohlear nuclear complex (CNC) via CN VIII

2. CNC to thalamus

   1. Thalamus to primary auditory cortex (41, 42)

   2. Primary auditory to Wernicke’s (22)

3. Wernicke’s to BA 44 pf Broca’s area (syntax)

Visual Comprehension

1. eyes to LGN of thalamus via optic tract

2. visual cortex (17, 18, 19) via geniculocalcarine tract

   1. visual areras to ventral and dorsal strams of vision

verbal production

prefrontal cortex (concepts) → SMA and Premotor Cortex & Broca’s area (planning) → primary motor cortex face area → CN’s for speech → muscles for speech

Global aphasia

not fluent, low comprehension, low repeating

broca’s aphasia

low fluent, high comprehension, low repeating

wernicke’s aphasia

high fluency, low comprehend, low repeat

transcortical motor aphasia

low fluent, high comprehend, high repeat

anomic aphasia

high fluent, high comprehend, high repeat

peripheral alexia

reading difficutly due to visuospatial and attentioal issues, does ont co occur with aphasia

central alexia

reading system damaged, co ourring with aphasia

swallowing stage

oral, pharyngeal, esophagous

nerves in oral

CN chewing V, glands IX, VII

pharyngeal nerves

V soft palate closure and laryngeal elevation, VII laryngeal elevation, X velar closure and pahryngeal constriction, XI soft palate closure, XII laryngeal elevation

esopageal nerves

X UES

glands in oral stage

parotid gland XI, submandibular gland VII, sublingula glands VII

swallowing sensory afferent information

afferent information includes taste and touch as well as respiatory and cardiovasular input

swallowing motor efferent information

motor swallowing center innervates the swallowing muscles via CN iX, X and XII

cortial control

premotor cortex (6): role in planning the swallow

primary motor cortex (4): activates voluntary muscles of swallowing

primary sensory cortex (1, 2, 3): processes sensation of eating

subcortical

anterioir cingulate cortex: provide the attention needed in swallowing

thalamus and basal ganglia: sensory information from blous into swallowing through the structures

neurology of cough response

afferent vagus fibers: convery sensory information from cough receptors in swallowing tract

that infor goes to cough center in brainstem

efferent signals: sent from cough center to respiratory muscles and larynx to generate cough

silent aspiration

ouccurs when the bolus penetrates the airway below the level of the vocal folds

about 1/3 of dysphagic pateints aspirtae without any signs

dyphasia can cause

aspiration pneumonia, malnutrition, dehydration

swallowing probelms associated with neurolgical damage, oral

difficult chewing, food falling out of mouth

food remaining in mouth, difficultuy forming and moving bolus

swallowing problems associated with enurological damage pharyngeal stage

swallow delay, swallow absence, pooling of bolus

swallowing problems associated with enurological damage esophageal stage

bolus staying in esophagus (lack of peristaltic waves)

dysphagia follwing stroke, cortical

weakness or paralysis and loss of sensory information of oral structures

apraxia: an impairment in motor planning for swallowing

dysphagia follwing stroke, subcortical

imparied motor control of oral strucutres

dysphagia follwing stroke, brainstem

impaired center for automatic swallow reponse

dysphagia follwing stroke, cerebellar

loss of coordination s

dyspahgia following TBI

damage often diffuse: depends on location of injury

damamge often to frontal lobe: swallowing impacted by poor safety awareness

cranial nerves may be injured from trauma: oral and pahryngeal pahses may be affected

injury to South or jaw

may have delayed or poorly coordinated pharyngeal phase or absent swallow response

dyspahgia in PD

slwo weak movement in oral stage

slow weak movement in pahryngeal stage (aspiration)

esophageal abnormalities are common

dyspahgia in ALS

early in disease, weight loss and ild difficulty due to weakness of structures

initially will need texture modifications, aspiration risk

weakness becomes severe patient needs feeding tube

eventually patients become unable to handle their own secretion

dyspahgia in demyelinating diseases

guillain-barre: totoal body weakness or paralysis

multiple sclerosis: progressive disease f the myeline

transverse myelitis: affects myelin

weakness causes weak pahses

aspiration always at risk

dyspahgia in muslce diseases

myasthenia gravis: muscle fatigue

muscular dystrophy: progressive muscle weakness

affects the phases