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Neuroscience > Week 8: Audition > Flashcards

Week 8: Audition Flashcards

1
Q

What is sound?

A

▪ Changes in air pressure produced by objects that vibrate

▪ Alternating compression and expansion of air molecules

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2
Q

Physical and perceptual dimensions

A

Frequency –> Pitch

Amplitude –> Loudness

Complexity –> Tibre

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3
Q

Outer ear function

A

External ear = pinna

Protects the middle and inner ear

Sound is funnelled through pinna and ear canal

	- Pinna causes spectral modification Amplifies frequency of sound, so easier for inner and middle ear to hear
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4
Q

Middle

A

▪ Middle ear increases efficiency of sound transfer into the cochlea
– impedance matching (sort of a translator to the inner ear)

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5
Q

Middle ear: Area affect & Lever effect

A
  • Area effect: greater pressure is exerted at the oval window (see below) than at the tympanic membrane (eardrum)
      * Lever effect: ossicles act as a lever, amplifying the force exerted on the tympanic membrane

Maximises sound travelled to inner ear so it can be perceived correctly

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6
Q

Middle ear: what percentage of sound is transmitted to the cochlea?

A

74% of the sound energy is transmitted to the cochlea (without impedance matching < 1%)

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7
Q

Middle ear reflex: What and why?

A

▪ Muscles attached to ossicles (3 bones)contract when exposed to intense sounds

▪ Protection from loud sounds and reduction from self-generated sounds (e.g. speech)

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8
Q

Inner ear: Cochlea

A

▪ Three fluid filled canals
* Scala vestibula (upper)
* Scala media (middle)
* Scala tympani (lower)

▪ Receptive organ (aka organ of Corti in diagram below)
	* Basilar membrane
	* Hair cells * Tectorial membrane
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9
Q

Process of hearing summarised

A
  • Soundwaves to tympanic membrane (eardrum) = vibrate
    • Vibrate = movement in the ossicles (3 bones)
    • Then to the oval window (in the wall of the cochlea)
    • Scala vestibulia & Scala tympani hold perilymph fluid, scala media holds endolymph
    • Waves carry through fluid in cochlea
    • Also means the basilar membrane moves as well
      • Organ of corti (above the basilar membrane) is when the wave is transduced into neural activity, which can be sent to the brain (does this as has hair cells on the organ of corti, and the stereocilia move)
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10
Q

Organ of Corti structure

A

▪ 3500 inner hair cells (IHC) arranged in one row
▪ 12000 outer hair cells (OHC) arranged in 3-5 rows

Tectorial membrane (vibration exert stretch on cilia of hair cells)

Amplify movement of basilar membrane

Help transform the vibrations of sound to neurotransmissions, to brain to be perceived

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11
Q

Audition: Auditory Pathways

A

Contains 30000 afferent nerve fibres (outside the brain) that are tonotopically organized
* i.e., different fibres correspond to different frequencies:

▪ Fibres innervating IHC responding to low frequencies are near the centre of the nerve

▪ Fibres innervating IHC responding to high frequencies are near the periphery of the nerve

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12
Q

Auditory cortex

A

Hierarchical arrangement

▪ Core region:

▪ Belt region:

▪ Parabelt region:

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13
Q

Auditory cortex: Core region

A
  • Contains the primary auditory cortex (A1)
  • Tonotopically organized isofrequency bands
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14
Q

Auditory cortex: Belt region

A
  • First level of auditory association cortex
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15
Q

Auditory cortex: Parabelt region

A

Highest level of auditory association cortex

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16
Q

Processing streams: Ventral or Dorsal stream

A

Ventral streams:
Anterior parabelt –> Anterior temporal lobe
WHAT it is you’re hearing

Dorsal streams:
Posterior parabelt –> Posterior parietal cortex
WHERE you’re hearing it from

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17
Q

Perception of loudness

A

▪ Corresponds to physical dimension of amplitude of sound waves (height)

▪ Loudness signalled by the rate of firing in nerve activity

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18
Q

Perception of pitch

A

▪ Corresponds to physical dimension of frequency

Signalled by:
▪ Place coding: information is carried by which neurons fire (where)
▪ Temporal coding: information carried by the timing of the AP fired

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19
Q

How do we locate sound?

A

compare signals coming from each ear

Brain stem analyse intensity & time differences in each ear –> results are sent to auditory cortex = location

20
Q

Vestibular System: Structure

A

▪ In the inner ear

▪ Comprised of:
	* Vestibular sacs
	* Semicircular canals

▪ Each containing hair cells
21
Q

Vestibular system: functions

A
  • Balance
  • Maintenance of head position
  • Eye movements for image stability
22
Q

Vestibular system: Semicircular canals

A

ring-like structures approximate to the 3 major planes of the head:

  • sagittal
  • transverse
  • horizontal
  • receptors in each canal respond to angular acceleration in oneplane
  • movement of the endolymph = movement of cilia = electric signal
23
Q

Vestibular system: Vestibular sacs

A
  • Saccule and Utricle
  • sensitive to the force of gravity and inform about the head’s orientation
24
Q

Somatosensory system

A

▪ Organic senses
* Provide information about pleasant and unpleasant sensations – internal organs

▪ Proprioception and kinesthesia
	* Provide sensory information about body position and movement

▪ Cutaneous sense (skin senses - the focus of today)
	* Commonly referred to as “touch” * Includes perception of temperature and pain
25
Q

Anatomy of the skin

A

▪ Consists of epidermis, dermis and subcutaneous tissue

▪ Variable appearance of skin: mucous membrane, hairy or glabrous (see image on slides)
26
Q

Encapsulated somatosensory receptors

A
  • Ruffini corpuscles
      * Pacinian corpuscles

  * Meissner’s corpuscles
  • Merkel’s disks
27
Q

Perception of touch

A

Touch receptors = mechanoreceptors

▪ Respond to vibration in the skin & changes in pressure against it
	→ movement of dendrites of mechanoreceptors
	→ opening of ion channels: influx/efflux of ions
	→ receptor potential (change in membrane potential) ▪ Use large myelinated Aβ fibres (i.e., high conduction velocity) = quick
28
Q

Touch receptors: Merkel’s disks

A
  • responds to indentation of skin
  • detects pressure; static discrimination of shapes and edges

(slow adapting when the stimulus remains)

29
Q

Ruffini corpuscles

A
  • detect stretching of skin
  • maintain grip to avoid slippage
30
Q

Meissner’s corpuscles

A

respond to light touch & vibration

detect surface roughness when textured movements move across skin

31
Q

Pacininan corpuscles

A
  • respond to high frequency vibrations/ touch

Discrimination of fine surface textures/ moving stimuli

32
Q

Perception of temperature

A

Temperature receptors = thermoreceptors

33
Q

3 types of thermoreceptors (warm or cold)

A

“Warm” receptors
* Located deeply in the skin
* Use unmyelinated C fibres

“Cold” receptors
* Located just beneath the epidermis
* Use unmyelinated C fibres and lightly myelinated Aδ fibres

Some thermoreceptors also respond to chemicals (e.g. menthol in mouthwash can feel cold)

34
Q

Perception of pain

A

Pain receptors = nociceptors (free nerve endings)

Pain information conveyed via:
* Lightly myelinated Aδ fibres
* Unmyelinated C fibres

35
Q

Different types of nociceptors

A

▪ Mechanical nociceptors
* Sensitive to strong pressure (e.g. pinch)

▪ Thermal nociceptors
	* Sensitive to burning heat and extreme cold

▪ Chemical nociceptors
	* e.g. sensitive to histamine

▪ Polymodal nociceptors * Respond to mechanical, thermal and chemical stimuli
36
Q

Why do we itch?

A
  • Allergic reactions, dryness or disease - or random
    • Bugs release anticoagulants = triggers histamine
    • Sensation of itch is created by signals related to pain
    • Evolutionary theory - developed a scratching response to avoid bugs/ harmful touch
      Phantom itching when limbs amputated
37
Q

Somatosenses: Somatosensory pathways

A

Two distinct ascending pathways:

Dorsal column-medial lemniscus pathways

Spinothalamic pathway

38
Q

Dorsal column-medial lemniscus pathways

A

(mediates touch and movement sensation) (in blue)

39
Q

Spinothalamic pathway

A

(mediates pain and temperature sensation) (in yellow)

40
Q

Somatosensory cortex

A

▪ Two main cortical areas – primary (S1) & secondary (S2) somatosensory cortex

▪ Somatotopic representation of the body parts

▪ Amount of somatosensory cortex not proportionate to body surface

41
Q

Pain perception

A

▪ Sensory component (perception of pain intensity) involving pathway to S1 and S2

	 ▪ Immediate emotional component (unpleasantness of stimulus) involving pathways including the insular cortex and anterior cingulate cortex

▪ Long-term emotional component in case of chronic pain involving pathways to the prefrontal cortex

42
Q

Psychological factors influencing pain

A

Previous experience

Percieved self-efficacy

Attention

Anxiety

Depression

Percieved helplessness

43
Q

Olfaction

A

How do we smell?

- Molecules from air
- Olfactory epithelium
- Through olfactory epithelium to the brain 40 million different receptor olfactory neurones = can detect different array of smells
44
Q

Anosmia

A

can’t smell certain / all things

(Taste is related to smell - so if you can’t smell this dulls the flavour)

45
Q

Reading: What can cause hearing loss?

A

Antibiotics (bcus can damage auditory hair cells)

(Note that the highest frequency sounds are first to be lost)

High frequency hearing los can also be caused by exposure to loud sounds.

46
Q

Reading: Cochlea implants

A

Cochlear implants are devices that are used to restore hearing in people with deafness caused by damage to the hair cells.

Neuroscience (22 decks)

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