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Sophie - The Nervous System - Year 2 > 20.1.1 Somatosensory Pathways - Receptors > Flashcards

20.1.1 Somatosensory Pathways - Receptors Flashcards

1
Q

What are the types of stimuli are detected in the somatosensory system?

A

Touch
Thermal sensation
Proprioception
Nociception
Itch

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2
Q

What are the two types of skin?

A

Hairy
Glabrous - hairless

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3
Q

What is A? What type of stimuli does it respond to?

A

Meissner’s corpsucle - found in the ridges of globrous skin
Flutter touch (light touch)
Changes in pressure
LOW THRESHOLD

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4
Q

What is B? What type of stimuli does it respond to?

A

Merkel’s disk - nerve terminal and a flattened non-neuronal epithelial cell
Respond to light touch

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5
Q

What is C? What does it respond to?

A

Ruffini ending -
Detects skin stretch and deformation within joints and digit proprioception (finger position and movement)

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6
Q

What is D? What does it detect?

A

Pacinian corpuscles
Located deep in the dermis for detection of low frequency vibrations and pressure sense

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7
Q

What is meant by the term ‘rapidly adapting’?

A

Rapidly adapting, or phasic, receptors respond maximally but briefly to stimuli; their response decreases if the stimulus is maintained. Conversely, slowly adapting, or tonic, receptors keep firing as long as the stimulus is present.
ONLY RESPOND WHEN STIMULUS STARTS

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8
Q

Which skin receptors are ‘rapidly adapting’?

A

Meissner’s corpuscle
Pacinian corpuscle
(CORPUSCLES)

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9
Q

Which receptors are mainly present in the finger tips at high densities?

A

Meissner’s corpuscles
Merkel disks
Both responsive to fine details and light touch

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10
Q

Which receptors are slowly adapting?

A

Merkel disks
Ruffini ending

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11
Q

What receptor is found below? What type of receptive field does it have?

A

Meissners corpuscle in the fingertips (found directly beneath the base of the epidermis linked to the basement membrane)
Rapidly Adapting
Small receptive field

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12
Q

What receptor is shown below? What sort of receptive field does it have?

A

Merkel disk
Slowly adapting -generate a sustained response during a long stimulus
SMALL/PRECISE receptive field
Attached to basal epidermis
High density in finger tips

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13
Q

What receptor is shown below? What type of receptive field does it have?

A

Pacinian corpsuscle
Has a diffuse, large receptive field

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14
Q

What type of receptor is shown below?

A

Ruffini ending
Large receptive field
Slowly adapting

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15
Q

Other than the four receptor types, what else is found in the dermis of the skin? What do they detect?

A

Free nerve endings - noxious and thermal stimuli

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16
Q

What are the two major mechanoreceptors in the joints and muscles?

A

Muscle spindles
Golgi tendon organs

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17
Q

What is a muscle spindle?

A

Sensory stretch receptors in skeletal muscle

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18
Q

What are Golgi tendon organs?

A

Located within tendon capsules of the tendons connecting muscle to bone and are adapted to detect tension in the muscle (leading to stretch in the tendon)

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19
Q

What do muscle spindles detect and how?

A

Group Ia sensory nerve fibres (largest and fastest) detect changes in muscle length (stretch) to give an indication on where the muscle is in time and space (proprioception)

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20
Q

How do Golgi tendon organs differ from muscle spindles?

A

Golgi tendon organ are situated in series, innervated by Ib sensory axons and give information on muscle tension
Muscle spindles are situated in parallel with the muscle fibres, innervated by Ia sensory axons and give information on muscle length

21
Q

How do Golgi tendon organs contribute to proprioception?

A

Provide information about spatial information of the limbs deduced from the angle of the joints

22
Q

Which receptors are responsible for pain stimulation?

A

Free unmyelinated C and A delta nerve endings

23
Q

What happens once a receptor has been activated for the signal to be transduced? (mechanoreceptors)

A

MECHANOSENSITIVE ION CHANNELS
Force applied to the channels alter their gating to enhance or decrease channel opening
Ionotropic channels open in response to stretch to allow the influx of cations that depolarises the membrane

24
Q

How are rapidly adapting mechanoreceptors able to be only activated by changes in pressure?

A

Rapidly adapting mechanoreceptors have a large capsule around the nerve ending, formed by multiple foldings of a Schwann cell. These act to absorb a constant pressure, so that rapidly adapting mechanoreceptors are only activated by changes in pressure.

25
Q

Which channel is found in Merkel cells?

A

Piezo2 channel which opens in response to pressure and leads to a Ca2+ influx which depolarises the cell

26
Q

Which family of receptors respond to heat?

A

TRPV channels which have different temperature thresholds

27
Q

What do Pacinian and Meissner’s corpuscles have which ensure they only respond to vibration or changes in stimulation of skin (rapid adaptation)

A

-Multilaminate discs so they respond to on/off pressure only
-lamellar fluid between the laminae and surrounding nerve ending which allows force to be spread out and dispersed so the membranes do not stretch and gated channels remain closed after a constant pressure is applied

28
Q

List the types of nerve axons that transmit sensory information to the CNS and their characteristics

A

A alpha - large diameter (13-20µm), myelinated, with conduction speeds up to 120m/s
A beta - moderate diameter (6-12µm), myelinated, with conduction speeds up between 35-75m/s
A delta - small diameter (1-5µm), myelinated fibres with conduction speeds around 5-30m/s
C - very small diameter (0.2-1µm), unmyelinated fibres with conduction speeds between 0.5-2m/s

29
Q

What type of information is carried by A alpha fibres? Which system do they travel through?

A

Proprioceptive information from muscle spindles and GTOs up through the dorsal column system

30
Q

What type of informaiton is carried by A beta fibres? Which column system do they travel through?

A

Mechanoreceptors of the skin transmit information about touch or vibration up through the dorsal column system

31
Q

What type of information is carried by A delta fibres? Which column system do they eventually travel through?

A

Pain (prickling sensation) and temperature from free nerve endings through spinothalamic tract of anterolateral system

32
Q

Wha type of information is carried by C fibres? Which column transmits this information to the CNS?

A

Temperature, itch and burning sensation of pain through the spinothalamic tract

33
Q

Where do C fibres terminate in the grey matter of the spinal cord?

A

Lamina I and II - marginal zone and substantia gelatininosa

34
Q

Where do A delta fibres synapse in the grey matter of the spinal cord?

A

Lamina II - substantia gelatinosa (bit of III and IV)

35
Q

Where do A beta fibres synapse in the grey matter of the spinal cord?

A

Lamina III and IV - nucleus proprius

36
Q

Where do A alpha fibres synapse in the grey matter of the spinal cord?

A

Lamina V and VI

37
Q

Which fibres carry first pain (sharp) and which carry second pain (longer and duller)?

A

A delta fibres: first pain = fast and sharp
C fibres: longer lasting second pain

38
Q

Where do primary afferent axons enter the spinal cord?

A

Dorsal root with cell bodies in the dorsal root ganglion

39
Q

Which nerves transmit information from the head and neck?

A

Trigeminal
Facial
Glossopharyngeal
Vagus

40
Q

Why do slowly adapting nerve fibres respond with a more constant rate of firing

A

They have a much smaller capsule (fewer foldings) around the nerve ending so less pressure is absorbed and dissipated

41
Q

What neurotransmitter is released by pain afferents?

A

Glutamate and substance P

42
Q

When is substance P released alongside glutamate in pain afferents?

A

During high frequency trains of action potentials to experience moderate to intense pain

43
Q

Which type of neurotransmitter mediates descending control on the substantia gelatinosa (C and A delta fibres)? Why?

A

MONOAMINES
-serotonin
-dopamine
-noradrenaline
-enkephalins
Modulates signals so that noxious signals can be attenuated in situations where debilitating pain is actually likely to be harmful to the individual

44
Q

Where do the primary sensory neurons terminate?

A

Dorsal root ganglion

45
Q

What is touch mediated by?

A

Touch is mediated by mechanoreceptors. In non-glabrous skin, there are four types of mechanoreceptor
In glabrous skin, there are three types of follicle receptor (hair-guard, hair-tylotrich and hair-down receptors) and the same deep receptors as in non-glabrous skin

46
Q

What is temperature sensed by?

A

two types of thermoreceptor, one for heat (responding in the range of 30–45°C) and one for cold (responding in the range of 1–20°C). Cold receptors are also activated by extreme heat (at >45°C), resulting in the sensation of ‘paradoxical cold’.

47
Q

Do groups of hot/ cold thermoreceptors overlap?

A

No

48
Q

What is pain mediated by?

A

nociceptors, which can be mechanical, thermal, or polymodal (mechanical nociceptors that can be activated or sensitized by inflammatory mediators and other indicators of tissue damage such as bradykinin, K+ ions, 5-HT, prostaglandin, and histamine).

Sophie - The Nervous System - Year 2 (46 decks)

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