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PHYL2064 > Sensory System > Flashcards

Sensory System Flashcards

1
Q

What is a sensory receptor?

A

Specialised peripheral endings of afferent neurons.

Each receptor responds to a different type of stimulus whereby it translates the energy from the stimulus into electrical stimulus.

This is termed signal transduction.

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2
Q

What are the two different types of sensory receptors?

A

specialised afferent endings and 2 cell receptors

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3
Q

What is the difference between 1 and 2 cell sensory receptors?

A

specialised afferent endings are continuous with the nerve fibre whereas 2 cell receptors are separate (i.e. receptor cell + nerve ending)

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4
Q

How does signal transduction compare between 1 and 2 cell sensory receptors?

A

a specific stimulus opens stimulus-sensitive channels on both causing Na+ to enter and depolarisation resulting in an AP to propagate along the nerve

2 cell receptors go through extra steps, however:
-depolarisation opens voltage-gated Ca2+ channels
-Ca2+ triggers exocytosis of neurotransmitter
-neurotransmitter opens chemically-gated ion channels at afferent nerve, Na+ enters
-THEN an AP propagates along nerve

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5
Q

Describe the difference between tonic and phasic receptors.

A

tonic= slow adapting, AP’s occur as long as the stimulus is present i.e. nociceptors

phasic= fast adapting, AP’s occur when first stimulated, stop and then again when stimulus is removed i.e. touch receptors

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6
Q

What 4 types of information do sensory nerves convey to the CNS?

A

modality, location, intensity and timing

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7
Q

Define ‘labelled line theory’.

A

This principle states that nerves are modality specific and so they travel to specific regions of the cortex. This is how the brain knows which modality is being perceived.

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8
Q

How can our CNS detect a stimulus of greater intensity?

A

more frequent firing of AP’s or activation of more receptors

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9
Q

Name the encapsulated cutaneous receptors.

A

Pacinian corpuscle, Meissner’s corpuscle, Ruffini endings.

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10
Q

Name the non-encapsulated cutaneous receptors.

A

Merkel’s disc/complex, free nerve endings, hair follicle receptors

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11
Q

What modalities are Pacinian corpuscle receptors sensitive to?

Are they phasic or tonic?

A

vibration & deep pressure

phasic

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12
Q

What modalities are Meissner corpuscle receptors sensitive to?

Are they phasic or tonic?

A

light touch

phasic

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13
Q

What modalities are hair receptors sensitive to?

Are they phasic or tonic?

A

hair movement/light touch

phasic

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14
Q

What modalities are Ruffini corpuscle receptors sensitive to?

Are they phasic or tonic?

A

deep pressure

tonic

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15
Q

What modalities are Merkel’s complex receptors sensitive to?

Are they phasic or tonic?

A

light sustained touch

tonic

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16
Q

What modalities are free nerve endings sensitive to?

Are they phasic or tonic?

A

crude touch, pain & temperature

tonic

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17
Q

Name the 4 types of nociceptors.

A

mechanoreceptors, thermoreceptors, polymodal receptors & silent nociceptors

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18
Q

What are silent nociceptors?

A

nociceptors that are only activated during inflammation

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19
Q

Contrast fast pain and slow pain.

(mechano- & thermoreceptors vs polymodal)

A

fast pain occurs on stimulation of mechano- or thermoreceptors, is carried by small myelinated A-delta fibres, produce a sharp prickling sensation, are easily located and occur first.

slow pain occurs on stimulation of polymodal receptors, is carried by small, unmyelinated C-fibres, produces dull, aching, burning sensation, is poorly localised and occurs second.

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20
Q

What are the two neurotransmitters involved in pain production?

A

Substance P & Glutamate

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21
Q

What is Substance P’s role in pain production?

A

activating ascending pathways that transmit nociceptive signals to higher levels for further processing.

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22
Q

Is Glutamate an excitatory or inhibitory neurotransmitter?

A

excitatory

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23
Q

What is descending inhibition?

A

is the body’s natural analgesic system and works by suppressing transmission in pain pathways as they enter the spinal cord.

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24
Q

What is descending inhibition dependent on?

A

the presence of appropriate opiate receptors for endorphins, enkephalins or dynorphin.

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25
Q

How do endogenous opiates work during descending inhibition?

A

by blocking the release of Substance P or Glutamate at the afferent pain fibre before it can reach the spinal cord.

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26
Q

What are the two major components of the vestibular system?

A

semicircular canals & otolith organs

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27
Q

What movement do the semicircular canals respond to?

A

rotational forces

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28
Q

What movement do the otolith organs respond to?

A

gravitational forces

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29
Q

How do semicircular canals detect rotational movement?

A

the canals are filled with endolymph which move when the head does

this causes the movement of hair cells within the cupula which either become depolarised or hyperpolarised depending on the direction

an AP is then sent via the vestibulo-ocular nerve to the brainstem and cerebellum to produce postural corrections

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30
Q

What makes up a hair cell?

A

each hair cell contains 1 kinocilium & 20-50 stereocilia which are connected by tip links

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31
Q

Does endolymph move in the same or opposite direction to the head?

A

opposite

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32
Q

Does depolarisation occur when movement occurs towards or away from the kinocilium of a hair cell?

A

toward

33
Q

What two components make up the otolith organs?

A

the utricle and saccule

34
Q

How does the orientation of hair cells differ between the utricle and saccule?

A

utricle hair cells vertical, saccule hair cells horizontal

35
Q

Hair cells are anchored in the cupula in the SCC, where are they anchored in the otolith organ?

A

in the maculae

36
Q

What are otoliths? What is their purpose?

A

calcium carbonate crystals

they move according to where the head is in gravity and produce signals to relay to the brainstem and cerebellum

37
Q

Are signals sent from the hair cells during constant movement?

A

no- only when movement starts or stops

38
Q

Describe the pathway of AP’s from the vestibular system to the brain.

A

vestibulocochlear never > vestibular nuclei in the brainstem > cerebellum

39
Q

What does the vestibulo-ocular reflex aim to achieve?

A

maintain visual focus on something while the head is in motion (stabilise the image on the retina) through excitation of extraocular muscles on the opposite side of the face while inhibiting on the same side.

40
Q

What makes up the external ear?

A

pinna, external auditory meatus and the ear drum (tympanum)

41
Q

What is the role of the external ear in hearing?

A

transmitting & amplifying airbourne sound waves to the fluid-filled inner ear

42
Q

What is the role of the middle ear?

A

same as the external ear

43
Q

What makes up the inner ear?

A

cochlear & vestibular apparatus

44
Q

What are soundwaves?

A

the alternating compression and refraction of air molecules as heard in dB

45
Q

What is the hearing threshold for humans?

A

~1dB

normal conversation is ~60dB
jet plan is ~150dB

46
Q

Describe the path that soundwaves take through the ear.

A

soundwaves enter via the external auditory meatus

tympanic membrane (ear drum) vibrates when stuck by soundwaves

the middle ear transmits vibrations through ossicles to the oval window

waves in the cochlear fluid set the basilar membrane in motion

hair cells are bent as basilar membrane is deflected up & down

mechanical deformation of specific hair cells is transduced into neural signals that are then transmitted to the auditory complex in the temporal lobe for sound perception

47
Q

How is frequency perceived in the inner ear?

A

by the location where it is detected by the organ of Corti

high frequencies are detected earlier/closer to the oval window while low frequencies are detected later/further from the oval window

48
Q

How does the function of inner and outer hair cells differ?

A

outer hair cells are for amplifying sound whereas inner hair cells are for sending potentials

49
Q

Which type of hair cell releases prestin?

A

outer hair cells

50
Q

How does the innervation differ between IHC and OHC?

A

IHC are innervated by more afferent nerves than efferent

OHC are innervated by more efferent nerves than afferent

51
Q

Describe the process of depolarisation in hair cells of the ear.

A
  1. tip links stretch and open channels when stereocilia bend towards tallest member
  2. K+ enters, hair cell depolarises
  3. Depolarisation opens voltage-gated Ca2+ channels
  4. Ca2+ entry causes greater release of neurotransmitter
  5. more neurotransmitter leads to higher rate of AP
52
Q

Describe the process of hyperpolarisation in hair cells of the ear.

A
  1. tip links slacken and close channels when stereocilia bend away from tallest member
  2. No K+ enters, hair cells hyperpolarise
  3. Ca2+ channels close
  4. No neurotransmitter is released
  5. No AP occurs
53
Q

What is so interesting about AP’s produced by hair cells in the auditory system?

A

they use potassium channels to depolarise as opposed to sodium channels like much of the rest of the nervous system

54
Q

What are the 2 different types of hearing loss?

A

conductive & sensorineural

55
Q

What is the difference between conductive & sensorineural hearing loss?

A

conductive refers to issues that occur prior to the cochlear i.e. glue ear, foreign material, ostitis media (middle ear infection)

sensorineural refers to issues that occur after the cochlear i.e. presbycusis (age related hearing loss), noise damage, ototoxic drugs

56
Q

What does a Rinne test do?

A

determines the presence of conductive hearing loss

57
Q

What is the procedure of a Rinne test?

A

place a struck tuning fork on the mastoid bone behind the ear and have the patient indicate when sound is no longer heard

Move the fork to beside the ear and ask if it is now audible

58
Q

What would indicate conductive hearing loss in a Rinne test?

A

the patient cannot hear the tuning fork at the ear (bone conduction is stronger than air conduction)

normally, air conduction will be stronger and the patient can still hear the fork at the ear

59
Q

What does a Weber test do?

A

determines the presence of either unilateral conductive or unilateral sensorineural hearing loss

60
Q

What is the procedure of a Weber test?

A

place a struck tuning fork on the forehead, looking for lateralisation of sound

61
Q

What would be normal in a Weber test? What would be abnormal?

A

normal would be no lateralisation of sound

if the issue is unilateral conductive loss the sound will move towards the affected ear

if the issue is unilateral sensorineual loss the sound will move towards the unaffected ear

62
Q

What is accommodation in the visual system?

A

our way of focusing by contracting/relaxing the lens and changing its shape

63
Q

What muscles and ligaments are involved in accommodation?

A

ciliary muscle & suspensory ligaments

64
Q

What is the name given to age-related stiffening of the lens?

A

presbyopia

65
Q

What is happening to the ciliary muscle & suspensory ligaments during sympathetic stimulation? What effect does this have on the lens?

A

the ciliary muscle is relaxed and the suspensory ligaments are taut

the lens is flat

66
Q

What is happening to the ciliary muscle & suspensory ligaments during parasympathetic stimulation? What effect does this have on the lens?

A

the ciliary muscle is contracted and the suspensory ligaments are loose

the lens is rounded

67
Q

What is the cause of myopic vision (near-sighted)?

A

eyeball too long or lens too strong

68
Q

What is the cause of hyperopic vision (far-sighted)?

A

eyeball too short or lens too weak

69
Q

How do you correct myopic vision?

A

with a concave lens

70
Q

How do you correct hyperopic vision?

A

with a convex lens

71
Q

Name the 2 different kinds of photoreceptors in the retina.

A

rods and cones

72
Q

Compare and contrast rods & cones.

A

~120 million rods vs ~6 million cones

rods do black & white while cones do colour vision

rods are located peripherally, cones centrally at fovea

rods have high sensitivity, cones have low

rods have low acuity, cones have high

much convergence with rods, little with cones

73
Q

Where is the fovea located and what is its significance in vision?

A

centre of the retina

it is the point of most distinct vision because it only contains cones (which has high visual acuity)

also, bipolar and ganglion cells are ‘pulled aside’ which means light can strike cones directly

74
Q

Where is the macula lutea located?

Does it have high or low visual acuity?

A

around the fovea

fairly high acuity

75
Q

What kind of vison does macular degeneration cause?

A

‘donut’ vision

76
Q

What is the purpose of the pupillary light reflex?

A

to restrict the amount of light entering the eye in case of damage, and to maintain vision in different levels of lighting.

77
Q

Which nerve supplies afferent information from the retina?

A

optic nerve

78
Q

Which nerve supplies efferent information from the brainstem to the ciliary muscles?

A

oculomotor nerve

79
Q

What is the clinical significance of the pupillary light reflex?

A

It is possible to determine the level of lesion/dysfunction by triggering the pupillary light reflex and watching for the pupils to constrict/dilate.

PHYL2064 (7 decks)

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