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The Nervous System: Physiology > Sensory system - including physiology of pain > Flashcards

Sensory system - including physiology of pain Flashcards

1
Q

Each sensory information is associated with a specific receptor type, name 5 receptors

A

Mechanoreceptor - mechanical stimuli

Chemoreceptor - chemical stimuli

Thermoreceptor - sensory temp

Nociceceptor - pain

Proprioceptors - muscle spindles

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2
Q

Define receptve field

A

Response to a stimulus over a specific area

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3
Q

What is the different structures of sensory receptors

A 
Pacinian corpuscle 
(deep pressure)
Messiners corpuscle (light touch)
Free nerve ending (pain)
Ruffin corpuscle (warmth)
Merkels corpuscles (touch)
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4
Q

How do sensory (physiological) receptors work in signal tranductions

A

transduce their adequate stimulus into depolarisation, creating a receptor (generator) potential

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5
Q

What encodes the intensity of stimulus

A

The size of the receptor potential

affecting the frequency of action potentials

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6
Q

What does the receptor potential evoke

A

Firing of action potential for long distance transmission

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7
Q

What is the function of the receptive field

A

Encode location of stimulus

giving info on intensity and modality

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8
Q

What determines acuity

A

Density of innervation, and size of receptive fields,

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9
Q

Cutaneous sensation is mediated by what 3 types of primary afferent fibres

A

Aβ = large myelinated (30-70m/s)

Aδ = small myelinated (5-30m/s)

C = unmyelinated fibres (0.5-2m/s)

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10
Q

What are A alpha fibres responsible for what cutaneous sensation

A

Transmission of touch, pressure, vibration sees

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11
Q

What are A delta fibres responsible for what cutaneous sensation

A

Transmission of cold, “fast” pain, pressure senses

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12
Q

What are C fibres responsible for what cutaneous sensation

A

Transmission of warmth, “slow” pain senses

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13
Q

What two primary afferent fibres are responsible for proprioception

A

A alpha

A beta

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14
Q

Define acuity

A

Ability to locate a stimulus & to differentiate it from one nearby

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15
Q

Where do all primary afferent fibres enter the spinal cord

A

Via the dorsal root ganglia

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16
Q

What is the transmission pathway of mechanoreceptive fibres (Aα & Aβ) to first synapse

A

Project straight up through ipsilateral dorsal column pathway and synapse in cuneate and gracile nuclei of the medulla

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17
Q

Where do second order mechanoreceptive fibres decussate

A

Brain stem

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18
Q

Where does second order mechanoreceptive fibres project and synapse

A

Via the contralateral medial lemniscus

synapsing in the Reticular formation, thalamus

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19
Q

Where does first order thermoreceptive and nociceptive fibres (Aδ & C) synapse

A

In the dorsal horn

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20
Q

Where does second order thermoreceptive and nociceptive fibres (Aδ & C) cross over

A

The midline in the spinal cord

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21
Q

What tract do the second order thermoreceptive and nociceptive fibres project up

A

contralateral spinothalamic (anterolateral) tract

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22
Q

Where do the second order thermoreceptive and nociceptive fibres synapse

A

reticular formation, thalamus

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23
Q

What is the pathway of third order neurone of the mechanoreceptive, thermoreceptive and nociceptive fibres and where do they synapse

A

Ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex

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24
Q

What is the clinical consequence of damage to dorsal columns

A

causes loss of touch, vibration, proprioception below lesion on ipsilateral side

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25
Q

What is the clinical consequences of damed to anterolateral quadrant

A

causes loss of nociceptive & temperature sensation below lesion on contralateral side

26
Q

Where does ultimate termination of sensory information occur

A

somatosensory cortex (S1) of the postcentral gyrus

27
Q

How does the somatosensory cortex produce a sensory homunculus

A

Sensory transmission endings are grouped according to the location of the receptors

extent of sensory representation is related to the density of receptors in each location

28
Q

What allows processing of sensory pathways

A

Adaptation

Convergence

Lateral inhibition

Not all info reaches the brain - filtration

Perception

29
Q

When does adaptation of receptors occurs

A

When receptors are continually stimulated by a maintained stimuli

30
Q

What does adaption result in

A

Receptors become less sensitive, or switch off

31
Q

What is the difference between rapid and slow adapting cutaneous receptors?

A

Rapidly adapting receptors are best at detecting rapidly changing signals, while slowly adapting receptors are capable of detecting a long, continuous signal

32
Q

What stimuli does not trigger adaptation

A

Painful stimuli

33
Q

What is the features of convergence

A

Saves on neurones

Reduces acuity

and can underlie referred pain

34
Q

What occurs in lateral inhibition

A

activation of one sensory input causes synaptic inhibition of its neighbours

35
Q

What is the benefit of lateral inhibition

A

Gives better definition of boundaries - enhances perception

Cleans up sensory information

36
Q

How does perception affect the processing in sensory pathway

A

Importance of inputs varies according to your state of mind

37
Q

What activates signal transduction in nociceptors

A

Low pH
Heat
Local chemical mediators

38
Q

What is the usually cause of referred pain

A

Convergence of visceral pain fibres and skin pain fibres

39
Q

What is the structure of nociceptors

A

Free nerve ending

40
Q

What nociceptors directly respond to damaged stimuli

A

ASIS

VR1

41
Q

What direct nociceptor responds to low pH

A

ASIS

42
Q

What direct nociceptor responds to heat

A

Vr1 receptors

43
Q

What are the indirect hormones released that stimulate noceiceptor

A

Bradykinin, Histamine, Prostaglandins

all released with tissue damage

44
Q

What does stimulation of nociceptors result in

A

Transduction as depolarisation of cells occurs due to the opening of sodium and potassium channels and an AP is fired

45
Q

What nerve fibres does the nociceptive AP travel in

A 
C fibres (slow pain)
A delta fibres (fast pain)
46
Q

Where does C/ A delta fibres synapse

A

In the dorsal route of the spinal cord

47
Q

How is the gate closed in controlling pain in the spinal cord

A

By an Inhibitory interneurone release opioid peptidase and inhibits the release from A delta/C fibres

48
Q

What two controls allow the closing of the gate

A

Segmental

Descending

49
Q

How does segmental control close the gate

A

An active A beta activates inhibitory interneurone

50
Q

How does deadening control close the gate

A

Cell bodies from Periaqueductal Grey Matter (PAG) and Nucleus Raphe Magnus (NRM) - sends axons down the spinal cord and activates inhibitory interneurons

51
Q

How does prostaglandins cause analgesia

A

Sensitises nociceptors to bradkyinin

Activates voltage gates sodium channel

52
Q

How does bradykinin cause analgesia

A

Activates VR1 receptor

53
Q

How does NSAIDS work in treating analgesia

A

because they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins

54
Q

What is the affect of prostaglandin have on the body

A

Inflammation
Pain
Fever

55
Q

How does local aesthetics treat analgesia

A

block Na+ action potential and therefore all axonal transmission

56
Q

What is transcutaneous electrical nerve stimulation

A

Low-voltage electrical current for pain relief

The stimulating pulses across the skin help prevent pain signals from reaching the brain

57
Q

How does opiates work in treating analgesia

A

reduce sensitivity of nociceptors

block transmitter release in dorsal horn (hence epidural administration)

activate descending inhibitory pathways

58
Q

What does the Nucleus Raphe Magnus release when stimulated

A

5-HT (serotonin) released from the raphe nuclei descends to the dorsal horn of the spinal cord

59
Q

What stimulates the nucleus raphe magnus

A

Stimulation of the periaqueductal gray matter of the midbrain activates enkephalin-releasing neurons that project to the raphe nuclei in the brainstem

60
Q

Where is the the periaqueductal gray matter

A

The periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain

The Nervous System: Physiology (15 decks)

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