Sensory Systems (Including Physiology of Pain)

Question 1

Each type of sensory information is associated with a specific receptor type responding to a specific sensory modality - name some examples?

Answer 1

mechanoreceptors

chemoreceptors

thermoreceptors

nociceptors

proprioceptors

Question 2

sensory receptors may have free nerve endings or a complex structure, what are examples of each?

Answer 2

nociceptors, cold receptors

Pacininan corpuscle, Meissner’s corpuscle

Question 3

What is the response over a specific area called?

Answer 3

receptive field

Question 4

Image showing the different strucutres of neurons

Some have multiple nerve endings, others have fancy structures attached to the end of them

Answer 4

Question 5

What are the 2 different sensory receptors in the body?

Answer 5

difference between physiological (sensory) receptors vs pharmacological (protein) receptors

Question 6

all sensory receptors transduce their adequate stimulus into a depolarisation, what is i that causes this depolarisation?

Answer 6

the receptor (generator) potential

Question 7

the size of the receptor potential encodes what?

Answer 7

intensity of stimulus

Question 8

receptor potential then evokes firing of _____________ for long distance transmission

Answer 8

action potentials

Question 9

frequency of action potentials encodes ________________

Answer 9

intensity of stimulus

Question 10

What do the receptive fields encode

Answer 10

location of stimulus

Question 11

What does the receptive field give information on?

Answer 11

gives information on the modality, intensity & location of the stimulus

Question 12

Image showing graded and action potentials

Answer 12

Generated potentials are local so don’t reach the end but action potentials reach all the way to the end

Question 13

What determines acuity of a sensory neuron?

Answer 13

density of innervation

size of receptive field

Question 14

Explain this image

Answer 14

Two pointed both activated by the right sensory field - no 2 point discrimination

Question 15

Action potentials are transmitted to the CNS by what?

Answer 15

axons

Question 16

cutaneous sensation is mediated by what 3 types of primary afferent fibres?

Answer 16

Aβ

Aδ

C

Question 17

Are Aβ, Aδ, C fibres myelinated or not?

Answer 17

Aβ - large myelinated (30-70m/s)

Aδ - small myelinated (5-30m/s)

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

Question 18

What is the function of the Aβ, Aδ, C fibres?

Answer 18

Aβ = touch, pressure, vibration

Aδ = cold, “fast” pain, pressure

C = warmth, “slow” pain

Question 19

Proprioception is mediated by what 2 types of primary afferent fibres?

Answer 19

Aα & Aβ

eg muscle spindles, golgi tendon organs etc

Question 20

Where do all primary afferent fibres enter the spinal cord?

Answer 20

all enter spinal cord via the dorsal root ganglia (or cranial nerve ganglia for head)

Question 21

Transition of sensory information is done through what types of fibres?

Answer 21

mechanoreceptive (Aα & Aβ) fibres

thermoreceptive & nociceptive (Aδ & C) fibres

Question 22

What type of fibres are mechanoreceptive fibres?

Answer 22

Aα & Aβ

Question 23

What is the course of mechanoreceptive fibres?

Answer 23

project straight up through ipsilateral dorsal columns

synapse in cuneate & gracile nuclei

the 2nd order fibres cross over midline (decussate) in the brain stem & project to reticular formation, thalamus and cortex

Question 24

What type of fibres are thermoreceptive & nociceptive fibres?

Answer 24

Aδ & C

Question 25

What is the course of thermoreceptive & nociceptive fibres?

Answer 25

synapse in the dorsal horn the 2nd order fibres cross over the midline in the spinal cord project up through the contralateral spinothalamic (anterolateral) tract to reticular formation, thalamus and cortex

Question 26

Is the left or the right: mechanoreceptive (Aα & Aβ) fibres thermoreceptive & nociceptive (Aδ & C) fibres

Answer 26

left - thermoreceptive and nociceptive fibres right - mechanoreceptive fibres

Question 27

different pathways for transmission of sensory information explains consequences of spinal cord injuries What does damage to the dorsal columns lead to?

Answer 27

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

Question 28

different pathways for transmission of sensory information explains consequences of spinal cord injuries What does damage to anterolateral quadrant lead to?

Answer 28

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

Question 29

Where does the transmission of sensory information end?

Answer 29

ultimate termination is in the somatosensory cortex (S1) of the postcentral gyrus

Question 30

How is the sensory information stored and arranged?

Answer 30

endings are grouped according to the location of the receptors extent of representation is related to the density of receptors in each location produces the sensory homunculus

Question 31

Adaptation is one of the processes in the sensory pathway, explain this?

Answer 31

gradual decrease over time in the responsiveness of the sensory system to a constant stimulus usually experienced as a change in the stimulus e.g. if a hand is rested on a table, the table's surface is immediately felt against the skin but the sensation of the table surface against the skin gradually diminishes until it is virtually unnoticeable sensory neurons that initially respond are no longer stimulated to respond; this is an example of neural adaptation

Question 32

Convergenge is another process of the sensory pathway, what is it and its effects?

Answer 32

saves on neurones reduces acuity - as if 2 neurons go onto one then you don’t know where the stimulus is coming from may be the cause of reffered pain in nonspecific ascending pathways, different stimuli can get merged together

Question 33

lateral inhibition is another process in the sensory pathway, what is it?

Answer 33

activation of one sensory input causes synaptic inhibition of its neighbours gives better definition of boundaries, can localize a stimulus on the skin better cleans up sensory information

Question 34

What are 3 main processes that happen in the sensory pathway?

Answer 34

adaptation convergence lateral inhibition

Question 35

What are the 2 different types of pain that can be experienced?

Answer 35

sharp, stabbing vs diffuse, throbbing pain

Question 36

What are the 2 different speeds of pain?

Answer 36

fast (initial) pain vs slow (delayed) pain

Question 37

What are the different lengths of time that pain can persist?

Answer 37

acute vs chronic pain

Question 38

What is visceral pain?

Answer 38

occurs when pain receptors in the pelvis, abdomen, chest, or intestines are activated when our internal organs and tissues are damaged or injured vague, not localized, and not well understood or clearly defined often feels like a deep squeeze, pressure, or aching

Question 39

What is referred pain?

Answer 39

pain percieved in another location form the site of the painful stimulus/origin

Question 40

What is phantom limb pain?

Answer 40

ongoing painful sensations that seem to be coming from the part of the limb that is no longer there the limb is gone, but the pain is real the onset of this pain most often occurs soon after surgery

Question 41

What is responsible for signal transduction in nociceptors?

Answer 41

low pH, heat (via ASIC, TRPV1 etc) local chemical mediators (eg bradykinin, histamine, prostaglandins)

Question 42

How can pain be blocked form nocioceptors?

Answer 42

Nociceptors are the bottom left fibres Gate control theory – can control information through the mechanoreceptor fibres and has an inhibitory interneuron in red, to block the gate in the pain neurons Descending controls form the brain, called the PAG and their neurons activate neurons in the NRM and they travel down the spinal cord and also close the gate in the same exact way Descending control work by inhibiting the same interneurons Descending controls are activated during things like battlefield injuries

Question 43

Slide showing the same as before

Answer 43

SG is the (red) interneuron

Question 44

What is analgesia?

Answer 44

inability to feel pain medicine that acts to relieve pain

Question 45

What is a type of analgesia?

Answer 45

Non-steroidal anti-inflammatory drugs (NSAIDs)

Question 46

How do NSAIDS work?

Answer 46

prostaglandins sensitise nociceptors to bradykinin work by reducing the production of prostaglandins. Prostaglandins are chemicals that promote inflammation, pain, and fever NSAIDs are analgesic (and antipiretic & anti-inflammatory) because they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins so NSAIDs work well against pain associated with inflammation

Question 47

How do local anaesthetics work as analgesics?

Answer 47

block Na+ action potential and therefore all axonal transmission

Question 48

How does trans cutaneous electric nerve stimulation (TENS) work as an analgesic?

Answer 48

electrical stimulus activating the A beta fibres to inhibit the others so electrically rubbing the skin Rubbing the skin activates interneuron

Question 49

How do opiates (eg morphine) work as a analgesic?

Answer 49

reduce sensitivity of nociceptors block transmitter release in dorsal horn (hence epidural administration) activate descending inhibitory pathways (to close the gate) Opiate receptors activate potassium channels to hyperpolarize membrane to stop action potentials being fibres in the first place, also block transmitter release in the dorsal horn