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Neuro 7: Sensory Pathways > Sensory Pathways > Flashcards

Sensory Pathways Flashcards

1
Q

What are the somatosensory modalities

A

touch, thermosensation, nociception, proprioception

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2
Q

What is proprioception

A

mechanical displacement of muscles, joints

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3
Q

Which receptors have free nerve endings

A

thermoreceptors, nociceptors

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4
Q

Which receptors has enclosed nerve endings

A

mechanoreceptors

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5
Q

What are the 3 types of sensory neurons and what do they differ in

A

Abeta, Adelta, C fibres

they differ in diameter, speed (myelination), function

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6
Q

Describe Abeta fibres

A

largest, thick myelin (fastest), innocuous mechanical stimulation

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7
Q

Describe Adelta fibres

A

has myelin, noxious mechanical + thermal stimulation

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8
Q

Describe C fibres

A

smallest, unmyelinated, noxious mechanical + thermal + chemical stimulation

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9
Q

Sensory receptor definition

A

transducer that converts energy from the environment into neural APs

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10
Q

Describe thermoreceptors

A

Adelta + C fibres, free nerve endings, not uniformly distributed - this affects sensitivity

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11
Q

What are thermoreceptors linked to

A

transient receptor potential (TRP) ion channels

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12
Q

Which TRP ion channels are C fibres associated with

A

C fibres detect heat - so, TRPV1-4

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13
Q

Which TRP ion channels are Adelta fibres associated with

A

Adelta fibres detect cold - so, TRPM8, TRPA1

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14
Q

State the 5 types of mechanoreceptors

A

Merkel cells (light touch, superficial pressure), Pacinian corpuscle (deep pressure, tickling, high frequency vibration), Meissner’s corpuscle (low frequency vibration, fine + discriminative touch), Ruffni endings (continuous pressure, touch, stretch), hair follicles

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15
Q

Describe nociceptors

A

free nerve endings; Adelta for sharp (pin-prick) pain, cold; C fibre for dull aching pain, heat

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16
Q

Stimulus threshold definition

A

point of intensity at which a person can detect presence of stimulus 50% of the time (absolute threshold)

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17
Q

What is stimulus intensity

A

how fast a neutron fires

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18
Q

How do you get high stimulus intensity

A

increased stimulus strength AND duration leads to increased NT release and therefore increased stimulus intensity

19
Q

Name the 2 types of adapting receptors

A

tonic, phasic

20
Q

Describe tonic receptors and give an example

A

detects continuous stimulus strength, adapts v slowly, impulses continuously transmitted to brain as long as stimulus is present; example: Merkel cells

21
Q

Describe phasic receptors and give an example

A

detect change in stimulus strength, adapt quickly, impulse transmitted at start and end of stimulus; example: Pacinian corpuscle: sudden pressure excites receptor and another impulse transmitted when pressure released

22
Q

Receptive field definition

A

region on the skin which causes activation of a single sensory neuron when stimulated

23
Q

3 examples of different receptive fields

A

fingers have densely packed mechanoreceptors with small receptive fields, arm has small receptive fields for detection of fine detail over small area - precise perception, back has large receptive fields for detection of changes over wider area

24
Q

The smaller the receptive field, the … the precision of perception

A

greater

25
Q

What is 2 point discrimination

A

minimum distance at which 2 points are perceives as separate; related to receptor field size

26
Q

Where are cell bodies of the body located

A

dorsal root ganglion

27
Q

Where are cell bodies of the face located

A

trigeminal ganglia

28
Q

Info from lower body received at what spinal level and carried in which tract

A

lumbar level, gracile tract

29
Q

info from upper body received at what spinal level and carried in which tract

A

cervical level, cuneate tract

30
Q

info from face received at what level

A

pons

31
Q

2 types of dorsal horn neurons

A 
projections neurons (going to brain), interneurons (remain in spinal cord)
*Abeta fibres are deep: laminas 3-5; Adelta + C fibres are superficial: laminas 1-2
32
Q

What happens when receptive fields overlap

A

difficult to distinguish between the 2 stimuli locations

33
Q

What prevents the overlap of these receptive fields

A

lateral inhibition; mediated by inhibitory interneurons within dorsal horn of spinal cord, leads to enhanced sensory perception

34
Q

Describe the ascending pathway for touch, proprioception

A

Abeta fibres enter dorsal horn and enter dorsal column pathways. Info from lower/upper limbs travel ipsilaterally along gracile/cuneate tracts. 1st order neurons terminate in gracile/cuneate nucleus in medulla. 2nd order neurons decussate in caudal medulla, forming CONTRALATERAL medial leminscus tract. They terminate in ventral posterior lateral nucleus (VPL) of thalamus. 3rd order neutron projects from VPL to somatosensory cortex

35
Q

What is crude touch

A

sensory modality that allows the subject to sense that something hastouched them, without being able to localise where they weretouched (contrasting finetouch)’’

36
Q

Difference between fine and crude touch in terms of fibres

A

fine touch mediated by Abeta fibres (Meissner’s corpuscle), crude touch mediated by Adelta fibres (free nerve ending)

37
Q

Pain and temperature sensations ascend within which part of the spinothalamic tract

A

lateral

38
Q

Crude touch ascends within which part of the spinothalamic tract

A

anterior

39
Q

Describe the ascending pathway for pain, temperature, crude touch

A

Spinothalamic (anterolateral) pathway.
1st order neurons terminate in the dorsal horn upon entering. 2nd order neurons decussate immediately in spinal cord, forming spinothalamic tract and ascend. The neurons terminate in VPL of thalamus. 3rd order neurons to somatosensory cortex

40
Q

Clinical importance: examples of sensory testing

A

pin pricks to detect sharp vs blunt perception of stimulus; brushing to detect whether innocuous stimuli perceived as painful; graded tuning fork to identify normal/abnormal vibration sensation;

41
Q

What does anterior spinal cord lesion result in

A

blocked anterior spinal artery causes ischaemic damage to anterior part of spinal cord - dorsal columns intact but damaged spinothalamic tract. Pain/temp loss below the level of lesion; retained light touch, vibration, 2-point discrimination

42
Q

Which pathway is associated with sensational pain

A

lateral spinothalamic tract

43
Q

Which pathway is associated with emotional pain

A

spin-reticular tract

44
Q

What is gate control theory

A

when elbow gets hit, you activate C fibres. Rubbing the elbow stimulates Abeta fibres which blocks C fibres by stimulating inhibitory neurons. There is reduced C fibre input to somatosensory cortex, resulting in decreased stimulus intensity.

Neuro 7: Sensory Pathways (1 decks)

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