Sensory Systems

Question 1

Physiological receptors are

Answer 1

sensory receptors

Question 2

Pharmacological receptors are

Answer 2

protein receptors

Question 3

All sensory receptors transduce their adequate stimulus into

Answer 3

a depolarisation signal which produces the receptor (generator) potential

Question 4

What type of potential is the receptor potential?

Answer 4

Graded local detrimental potential

Question 5

The size of the receptor potential is related to

Answer 5

the intensity of the stimulus

Question 6

The receptor potential triggers

Answer 6

the firing of action potentials

Question 7

Action potentials are always the same size, so intensity of the stimulus is determined by

Answer 7

the frequency of action potentials rather than their size

Question 8

The receptive field encodes

Answer 8

the location of the stimulus, giving information on the modality, intensity and location of the stimulus

Question 9

Thermoreceptive and nociceptive information travels via what fibres?

Answer 9

A-delta and C fibres

Question 10

Where do A-delta and C fibres synapse?

Answer 10

In the dorsal horn

Question 11

A-delta and C fibres come through the dorsal horn and almost immediately synapse onto

Answer 11

the second order fibre

Question 12

The second order fibres of A-delta and C fibres cross over

Answer 12

in the midline of the spinal cord

Question 13

Once the second order fibres of A-delta and C fibres have crossed over, they

Answer 13

project up through the contralateral spinothalamic (anterolateral) tract to the reticular formation, thalamus and cortex

Question 14

Damage to the spinothalamic (anterolateral) quadrant causes

Answer 14

loss of nociceptive and temperature sensation below the lesion on the contralateral side

Question 15

Mechanoreceptive information travels via what fibres?

Answer 15

A-alpha and A-beta fibres

Question 16

A-alpha and A-beta fibres project

Answer 16

straight up through the ipsilateral dorsal columns of the spinal cord

Question 17

A-alpha and A-beta fibres synapse

Answer 17

on the same side, in the cuneate and gracile nuclei

Question 18

The second order fibres of A-alpha and A-beta fibres cross over

Answer 18

in the midline of the spinal cord and synapse in the brain stem

Question 19

Once the second order fibres of A-alpha and A-beta fibres have synapsed in the brain stem, the information goes to

Answer 19

the reticular formation, thalamus and cortex

Question 20

Signal transduction in nociceptors is activated by

Answer 20

Low pH
Heat
Local chemical mediators

Question 21

When are local chemical mediators released?

Answer 21

When the skin is crushed, leading to depolarisation, action potential firing and excitation of the nociceptors

Question 22

Bradykinin, histamine and prostaglandins are examples of

Answer 22

local chemical mediators

Question 23

How is low pH detected and what does this cause?

Answer 23

an acid sensing ion channel (ASIC) which opens its integral ion channel to cause depolarisation, action potential firing and excitation

Question 24

Noxious heat causes what ion channel to open?

Answer 24

VR1 ion channel

Question 25

Why might pain originating from the viscera cause referred pain to a somatic structure from the same dermatome?

Answer 25

Visceral pain is generally poorly localised | Convergence of sensory fibres - fewer neurones reduces the acuity

Question 26

According to the gate control theory, pain signals

Answer 26

are not free to reach the brain as soon as they are generated at the injured tissue/site

Question 27

Pain signals need to encounter

Answer 27

neurological gates at the spinal cord level which determine whether the pain signals should reach the brain or not

Question 28

Pain is perceived when

Answer 28

neurological gates give way to the pain signals

Question 29

Pain is less intense or not perceived when

Answer 29

the neurological gate closes

Question 30

Peri-aqueductal grey matter cell bodies transmit to the

Answer 30

nucleus raphe magnus

Question 31

Fibres travel from the nucleus raphe magus down what?

Answer 31

The spinal cord and descending tracts

Question 32

Function of peri-aqueductal grey matter cell bodies that transmit to the NRM

Answer 32

Activate inhibitory interneurons that release opioid peptides and stop the transmitter release, closing the neurological gates

Question 33

Function of prostaglandins

Answer 33

release G proteins when stimulated which sensitise the nociceptors to bradykinin

Question 34

Why do NSAIDs work well against pain associated with inflammation?

Answer 34

They are anti-pyretic and anti-inflammatory | They inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins (prostaglandins sensitise nociceptors)

Question 35

Local anaesthetics block

Answer 35

the voltage gated sodium channels from transmitting the action potential and therefore block axonal transmission

Question 36

How does transcutaneous electric nerve stimulation (TENS) work?

Answer 36

Electrically stimulates the nerve fibres to close the gate

Question 37

How do opiates e.g. morphine work?

Answer 37

Reduce sensitivity of nociceptors Block transmitter release in the dorsal horn Activate descending inhibitory pathways

Question 38

What route of opiate administration is most effective and why?

Answer 38

Epidural Allows them to be delivered around the spinal cord where they have best access to the synapses at the top levels of the spinal cord and can block transmission