Sensory system - including physiology of pain

Question 1

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

Answer 1

Mechanoreceptor - mechanical stimuli

Chemoreceptor - chemical stimuli

Thermoreceptor - sensory temp

Nociceceptor - pain

Proprioceptors - muscle spindles

Question 2

Define receptve field

Answer 2

Response to a stimulus over a specific area

Question 3

What is the different structures of sensory receptors

Answer 3

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

Question 4

How do sensory (physiological) receptors work in signal tranductions

Answer 4

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

Question 5

What encodes the intensity of stimulus

Answer 5

The size of the receptor potential

affecting the frequency of action potentials

Question 6

What does the receptor potential evoke

Answer 6

Firing of action potential for long distance transmission

Question 7

What is the function of the receptive field

Answer 7

Encode location of stimulus

giving info on intensity and modality

Question 8

What determines acuity

Answer 8

Density of innervation, and size of receptive fields,

Question 9

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

Answer 9

Aβ = large myelinated (30-70m/s)

Aδ = small myelinated (5-30m/s)

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

Question 10

What are A alpha fibres responsible for what cutaneous sensation

Answer 10

Transmission of touch, pressure, vibration sees

Question 11

What are A delta fibres responsible for what cutaneous sensation

Answer 11

Transmission of cold, “fast” pain, pressure senses

Question 12

What are C fibres responsible for what cutaneous sensation

Answer 12

Transmission of warmth, “slow” pain senses

Question 13

What two primary afferent fibres are responsible for proprioception

Answer 13

A alpha

A beta

Question 14

Define acuity

Answer 14

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

Question 15

Where do all primary afferent fibres enter the spinal cord

Answer 15

Via the dorsal root ganglia

Question 16

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

Answer 16

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

Question 17

Where do second order mechanoreceptive fibres decussate

Answer 17

Brain stem

Question 18

Where does second order mechanoreceptive fibres project and synapse

Answer 18

Via the contralateral medial lemniscus

synapsing in the Reticular formation, thalamus

Question 19

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

Answer 19

In the dorsal horn

Question 20

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

Answer 20

The midline in the spinal cord

Question 21

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

Answer 21

contralateral spinothalamic (anterolateral) tract

Question 22

Where do the second order thermoreceptive and nociceptive fibres synapse

Answer 22

reticular formation, thalamus

Question 23

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

Answer 23

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

Question 24

What is the clinical consequence of damage to dorsal columns

Answer 24

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

Question 25

What is the clinical consequences of damed to anterolateral quadrant

Answer 25

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

Question 26

Where does ultimate termination of sensory information occur

Answer 26

somatosensory cortex (S1) of the postcentral gyrus

Question 27

How does the somatosensory cortex produce a sensory homunculus

Answer 27

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

Question 28

What allows processing of sensory pathways

Answer 28

Adaptation Convergence Lateral inhibition Not all info reaches the brain - filtration Perception

Question 29

When does adaptation of receptors occurs

Answer 29

When receptors are continually stimulated by a maintained stimuli

Question 30

What does adaption result in

Answer 30

Receptors become less sensitive, or switch off

Question 31

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

Answer 31

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

Question 32

What stimuli does not trigger adaptation

Answer 32

Painful stimuli

Question 33

What is the features of convergence

Answer 33

Saves on neurones Reduces acuity and can underlie referred pain

Question 34

What occurs in lateral inhibition

Answer 34

activation of one sensory input causes synaptic inhibition of its neighbours

Question 35

What is the benefit of lateral inhibition

Answer 35

Gives better definition of boundaries - enhances perception Cleans up sensory information

Question 36

How does perception affect the processing in sensory pathway

Answer 36

Importance of inputs varies according to your state of mind

Question 37

What activates signal transduction in nociceptors

Answer 37

Low pH Heat Local chemical mediators

Question 38

What is the usually cause of referred pain

Answer 38

Convergence of visceral pain fibres and skin pain fibres

Question 39

What is the structure of nociceptors

Answer 39

Free nerve ending

Question 40

What nociceptors directly respond to damaged stimuli

Answer 40

ASIS | VR1

Question 41

What direct nociceptor responds to low pH

Answer 41

ASIS

Question 42

What direct nociceptor responds to heat

Answer 42

Vr1 receptors

Question 43

What are the indirect hormones released that stimulate noceiceptor

Answer 43

Bradykinin, Histamine, Prostaglandins all released with tissue damage

Question 44

What does stimulation of nociceptors result in

Answer 44

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

Question 45

What nerve fibres does the nociceptive AP travel in

Answer 45

``` C fibres (slow pain) A delta fibres (fast pain) ```

Question 46

Where does C/ A delta fibres synapse

Answer 46

In the dorsal route of the spinal cord

Question 47

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

Answer 47

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

Question 48

What two controls allow the closing of the gate

Answer 48

Segmental | Descending

Question 49

How does segmental control close the gate

Answer 49

An active A beta activates inhibitory interneurone

Question 50

How does deadening control close the gate

Answer 50

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

Question 51

How does prostaglandins cause analgesia

Answer 51

Sensitises nociceptors to bradkyinin Activates voltage gates sodium channel

Question 52

How does bradykinin cause analgesia

Answer 52

Activates VR1 receptor

Question 53

How does NSAIDS work in treating analgesia

Answer 53

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

Question 54

What is the affect of prostaglandin have on the body

Answer 54

Inflammation Pain Fever

Question 55

How does local aesthetics treat analgesia

Answer 55

block Na+ action potential and therefore all axonal transmission

Question 56

What is transcutaneous electrical nerve stimulation

Answer 56

Low-voltage electrical current for pain relief The stimulating pulses across the skin help prevent pain signals from reaching the brain

Question 57

How does opiates work in treating analgesia

Answer 57

reduce sensitivity of nociceptors block transmitter release in dorsal horn (hence epidural administration) activate descending inhibitory pathways

Question 58

What does the Nucleus Raphe Magnus release when stimulated

Answer 58

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

Question 59

What stimulates the nucleus raphe magnus

Answer 59

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

Question 60

Where is the the periaqueductal gray matter

Answer 60

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