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BAB > Week 4 > Flashcards

Week 4 Flashcards

1
Q

Middle ear

A

Ossicles
Malleus, incus, stapes
Amplification system, amplifies the signals that reach the tympanic membrane

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2
Q

Tensor tympani and stapedius muscle

A

Provide protection
Muscles provide attenuation reflex, if noise is loud they contract and reduce transfer signal from tympanic membrane to inner ear

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3
Q

The inner ear cochlea

A

Drains into 3 compartments
Scala vestibuli
Scala media: auditory organ, organ of cortical
Scala tympani

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4
Q

Function of the inner ear

A

Stapes pushed by air movement into the oval window
Moves liquid into basilar membrane. Endolymph
Basilar membrane made to vibrate, liquid vibrates

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5
Q

Response of the basilar membrane to sound

A

Apex: wide and floppy
Base: narrow and stiff
High frequency sounds, vibrates to base of basilar membrane
Low frequency: only vibrates at apex doesn’t reach base
Frequency producing maximum amplitude, different frequency vibration on different path of membrane

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6
Q

Organ of corti

A

Lies on basilar membrane, so it time membrane moves OOC moves too
Tectorial membrane over it
Sensory neurones: hair cells in organ of corti
-embedded in tectorial membrane attached to side of bony structure
Each time basilar membrane moves tectorial membrane moves up tugs on hair cells-> provides signal transduction

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7
Q

Hair cell receptor potentials

A

Changes and movements in liquid- signals elicit hair cell potential
Mechanically gated K+ channels

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8
Q

Depolarisation of hair cells

A

Stereocilia
Mechanically gated K+ channels
When moved K+ channels open allowing K influx into cells
Moved opposite direction influx stops channels closed
Influx K+, opens voltage gated Ca2+ channels on hair cells influx Ca2+, release excitatory neurotransmitters into synaptic cleft, spiral ganglion neurite, glutamate

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9
Q

The auditory nerve

A

Hearing acuity depends on function inner hair cells
Little signal to the brain from outer hair cells
Inner hair cell and (small bit outer hair cells)-> spiral ganglion cells—> auditory nerve

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10
Q

Amplification by outer hair cells

A

Sound intensity is low, amplification by ossicles
2nd amplification by outer hair cells
-motor proteins make wall of cells less contractable pull tectorial membrane further amplifying movement, increasing signal reaching inner hair cells

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11
Q

characteristic frequency

A

Specific to every hair cell

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12
Q

Tonotopy

A

How different neurones sensitive to different frequencies
Flexibility basilar membrane varies apex to base
Sensitivity to frequency that can move membrane at that segment- characteristic frequency

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13
Q

Cochlear nerve and auditory pathways

A

Both ears send signals to both sides of brain at same time
Spiral ganglion, auditory nerve, dorsal and ventral cochlear nucleus, decussate superior olive, ascend lateral lemniscus, to inferior colliculus, to MGN, to auditory cortex

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14
Q

The auditory cortex

A

Top lateral temporal lobe
Primary auditory cortex - sensitive higher frequencies
Secondary auditory cortex

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15
Q

Phase locking

A

Only possible at relatively low frequency sounds, phase locking has a limit
Peaks ands troughs always coincide with AP response via sensory neurones activated by particular sound
Neurones refractory period- limit on how fast can generate new action potentials so phase locking doesn’t work at higher frequency sounds

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16
Q

Frequency identification

A

How we identify pitch of noises
Very low frequency- phase locking
Intermediate frequency- phase locking and tonotopy
High frequency- tonotopy

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17
Q

Sound intensity

A

Loud or soft noise
When increases deflection of basilar membrane increases
Number of hair cells firing higher. Organ of corti
Firing rate is higher, deflections larger in amplitude

18
Q

Sound localisation interaural delay

A

In superior olive
Parallel pathways both ears
Time lag, sound travels slowly by the time sound reaches the ear slight time delay, signal not completely simultaneous
Delay is perceived in superior olive allows us to localise the signal

19
Q

Sound localisation interaural intensity difference

A

Identification of where sound comes from
Sound intensity difference, sound shadows behind object that’s receiving sound waves
Loss hearing in one ear- lose ability to localise sound because only get signal from one ear, lose interaural delay and interaural intensity difference

20
Q

Other projections of the auditory pathway

A

Inferior colliculus- MGN and superior colliculus: integration of auditory and visual signals
Brainstem neurones- outer hair cells
Auditory cortex- MGN and inferior colliculus

21
Q

Whole mechanism hearing

A

Depends on air ability to move tympanic membrane ossicles and oval window
If anything obstructs this become deaf
Auditory canal- obstructed ear wax, small objects
Ear infections can perforate tympanic membrane

22
Q

Clinical aspects

A

Deafness- conduction of mechanical wave
-obstruction of auditory canal
-otosclerosis - sclerosis ossicles movement restricted- comes with age
- ruptured eardrum
-middle ear infection
-head trauma

23
Q

Deafness- nerve deafness

A

Genetic ->40 genes ~300 syndromes with related hearing loss
-Recessive, dominant or X linked genetic mutations- structure or metabolism of the inner ear
-Some genetic causes give rise to a late onset hearing loss
Congential:
-congenital rubella syndrome
-human cytomegalovirus HCMV
-toxoplasmosis
-hypoplastic auditory nerves or abnormalities of cochlea
Presbycusis: normal progressive age related loss hearing acuity or sensitivity:
-1:3 significant hearing loss by age 65
-1:2 significant hearing loss by age 75
-not preventable or reversible

24
Q

Acquired nerve deafness

A

Noise:
-cochlear damage
-permanent or temporary
-environmental or occupational noise
-acoustic trauma
Diseases:
-inflammatory
-diabetes mellitus
-iodine deficiency/hypothyrodism
-tumours
-meningitis
-viral infections (AIDS, mumps, measles, herpes zoster oticus)
-trauma
-stroke
Ototoxic and neurotoxic drugs
-aminoglycosides, partial recovery. Rare mitochondrial mutation m.1555A>G can increase an individuals susceptibility to the ototoxic effect of aminoglycosides
-methotrexate, not recovered, treatment of autoimmune induced inflammatory HL
-various other medications- reversible HL

25
Q

Perinatal conditions

A

Premature birth
Foetal alcohol syndrome
Syphilis

26
Q

Amplification by outer hair cells clinical aspects

A

Tinnitus
Noisy ear
Tinnitus: Motor proteins compress more and tug hairs, hear noises that aren’t there, annoying for patient and hard to treat

27
Q

Chemical senses

A

Evolutionary preserved
Homeostasis
Chemoreceptors
Diverse functions: location, finding food/mate, avoiding danger

28
Q

Smell and taste

A

Environmental chemical detection
-toxins and poisons
-bitterness- acquire a taste for
nutrition
-contribute to flavour of food
-combined action and texture and temp and vision and sound
-involvement of brain. Neurogastromy

29
Q

Clinical implications

A

Alteration/loss
-hypo/hyper ageusia (taste), anosmia (smell)
-> nutritional/toxicity consequences.
-age >70% of over 80s have diminished taste and smell

30
Q

Alteration/loss of taste and smell

A

Age
Drugs:
-change: ion balance, saliva (level and composition), NT change perception of taste
-chemotherapy: antibiotic, cancer affect taste and smell.
-anti hypertensives can affect ionic distribution in mouth, DHPs some people increase salty taste
-> compliance issues if everything tastes bad
Lesion- periphery or brain:
-smell altered. Smell things that aren’t there
—epilepsy
—damage to olfactory bulb (head trauma)
—Parkinson’s disease: loss neurons involved in smell-> loss of smell, early warning
—major depressive disorder

31
Q

Taste

A

Submodalities: 5 basic tastes: salt, sour, sweet, bitter, umami
Taste cells are on tongue and palate, pharynx
-relative distribution not absolute, highest sensitivity. Sweetness tip of tongue, saltiness- side, sourness- side higher, bitterness- back of tongue
Structural organisation:
-papilla
—taste buds
——taste cells

32
Q

Properties of taste cells

A

Not sensory neurons
Sensory afferents separate cell from taste cells, “synapse” with sensory neurones
Constantly replaced: every 2 weeks, by basal cells that multiply and divide rapid, potential damage, mechanical damage to surface tongue
They detect taste through various transduction mechanisms

33
Q

Detect taste

A

Chemical binds
-transduction
Receptor potential
Voltage gated Ca2+ channels open
Calcium entry
“Neurotransmitter” released
Excited sensory release
Action potential

34
Q

Salt and sour

A

Salt:
-sodium entry (non gated channels)
-depolarisation

Sour:TRP channel
-H+
-entry via TRP/ K+ channel block prevent K+ efflux
-depolarisation

35
Q

Sweet, umami, bitter

A

GPCRs
T1R and T2R family
Different subunits different tastes
Sweet (T1R2, T1R3), umami(T1R1, T1R3), bitter (T2R,T2R)
Receptor distribution:
-individual taste cells respond to individual submodalities, not absolute distribution
-each cell unique only expresses receptor for sweet or bitter or umami not all

36
Q

From tongue to brain

A

Gustatory sensory axons
Cranial nerves: CNVII (front 1/3), CNIX (back tongue), CNX (anywhere else)
Brain stem
Thalamus (terminate VPM)
Primary gustatory cortex: 3rd neurone conveys info here, basic detection of taste
Neural coding of taste: central taste pathways, neural coding of taste, comparison of all inputs
Secondary pathways:
-medulla -gustatory nucleus (taste nucleus)- swallowing, salvation
-hypothalamus- satiety, palatability

37
Q

Smell

A

Smell receptors are in olfactory epithelium
Neurones for CNI
Sensitivity (humans): smell>taste
Can it act alone? Location detection, pheromones

38
Q

Properties of olfactory cells

A

Olfactory cells are neurones, replaced every 4-8 weeks
Come from lining ventricles migrate down to olfactory bulb - interruption of this interrupts smell
Each olfactory cell= one type of chemoreceptor molecule
Each chemoreceptor molecule binds a range of odorants not very specific, many types of chemoreceptors
Population coding: coordinated firing of multiple neurones-> odorant detection

39
Q

Detecting smells

A

Adaptation happens at level of detecting cells and higher up, adapt to smell-> dont notice
Signal transduction: single mechanism for all receptors
-odorant binds to receptor
-G protein mediated events
-intercellular cascade
-depolarisation
-receptor potential -> action potential

40
Q

From nose to brain

A

1st order neurones
-glomerulus . Cells expressing same type of receptor molecule same synapse all synapse onto the 2nd neurone
2nd order neurones

41
Q

Central olfactory pathways

A

Olfactory neurones
Olfactory bulb
Olfactory cortex
-MD thalamus —>orbitofrontal cortex—> RECOGNITION (frontal head trauma can affect smell)
-limbic areas (emotional responses)— ASSOCIATION

BAB (10 decks)

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