Nociception

Question 1

What is a nociceptive stimulus?

Answer 1

One that is potentially harmful or unpleasant

Question 2

Whats the difference between pain and nociception?

Answer 2

Nociception is a real thing and felt by receptors, whereas pain is subjective and conjured by the brain in response to nociception

Question 3

What are the only receptors that detect pain?

Answer 3

Nociceptors

Question 4

What does it mean that nociceptors are polymodal?

Answer 4

There are different types of nociceptors that respond to different stimuli

Question 5

How do nociceptors compare to mechanoceptors?

Answer 5

They are much simpler, usually they’re just free axonal endings of sensory neurones
They also have higher thresholds
They are slow adapting

Question 6

What are the two types of sensory neurone that carry nociceptive information?

Answer 6

A delta and C

Question 7

What is the difference between A delta and C?

Answer 7

A delta have larger fibres, they are fast adapting and produce pain fast
C neurones are smaller, produce a dull, aching pain and slow adapting

Question 8

How do receptive fields for nociceptive neurones compare to touch neurones?

Answer 8

They are much larger- don’t need to be able to localise pain as much as touch

Question 9

What happens to pain and temperature information coming from the body?

Answer 9

It will synapse immediately with the second neurone as it enters the spinal cord which then decussates, goes into the white matter and ascends up the spinothalamic tract

Question 10

Which nerve detects nociceptive stimuli in the face?

Answer 10

Trigeminal (CN V)

Question 11

Where does the trigeminal nerve enter the trigeminal ganglion?

Answer 11

At the level of pons

Question 12

What strange event happens after the trigeminal nerve enters the ganglion?

Answer 12

The axon goes downwards in the brainstem alongside the trigeminal nucleus. It eventually synapses with a secondary neurone in the trigeminal nucleus at the level of the medulla.

Question 13

Why does the axon of the trigeminal go downwards in the brain?

Answer 13

Trigeminal nucleus is actually a large column of grey matter that extends from midbrain to medulla

Question 14

The trigeminal nucleus is divided into parts, which modality is each part responsible for?

Answer 14

Touch- Pons

Nociception- Medulla

Question 15

Where does nociceptive information initially go when it reaches the brain and what is the function of this area?

Answer 15

Primary somatosensory cortex- Registration of the localisation of nociceptive stimuli (information will go to relevant part of primary somatosensory cortex based on motor homunculus)

Question 16

Which areas are responsible for actual sensation of pain?

Answer 16

Hypothalamus, cingulate gyrus and insula

Question 17

Where do the collateral branches of the ascending spinothalamic tract go to?

Answer 17

Brainstem, thalamus, hypothalamus and limbic system

Question 18

What does the input from the spinothalamic tract to the brainstem mainly go to?

Answer 18

Reticular formation

Question 19

What does input from spinothalamic to thalamus mainly go to?

Answer 19

Intralaminar nuclei

Question 20

What is the purpose of the collateral branches?

Answer 20

The reticular formation and intralaminar nuclei are parts of your reticular activating system which controls consciousness so the collateral branches ensures that these are stimulated so that you are alert and aware of any potentially harmful situations. The information that passes through hypothalamus and limbic system makes you aware of the unpleasantness of the situation

Question 21

What are the pathways that reduce the amount of pain that you feel?

Answer 21

Central inhibition pathway and peripheral inhibition pathway

Question 22

What location do both of these pathways affect?

Answer 22

The system in the dorsal horn

Question 23

What is the focus of the central inhibition pathway?

Answer 23

Periaqueductal grey matter (grey matter surrounding cerebral aqueduct)- cells in this area have an enormous input from other parts of the brain

Question 24

How does the central inhibition pathway work?

Answer 24

If brain activity gets too high, cells in the periaqueductal grey matter send impulses down various pathways through the brainstem and it eventually gets to the dorsal horn at each level. These descending axons synapse with interneurones and activate it which leads to the synapse between first and second order neurones being affected. The interneurones release enkephalin which is inhibitory- activity feeding into spinothalamic tract is reduced

Question 25

What is enkephalin?

Answer 25

Enkephalin is an opiod which is inhibitory

Question 26

How does peripheral inhibition pathway work?

Answer 26

There is a c-fibre carrying nociceptive information, this enters the dorsal horn and activates a projection neurone which then goes across the midline and enters the spinothalamic tract, there are also non-nociceptive neurones that go straight into the dorsal horn however they also have a collateral branch that is capable of activating an inhibitory interneurone which can reduce the activity of the projection neurone and thus decrease information going up the spinothalamic tract

Question 27

Give an example of the peripheral inhibition pathway?

Answer 27

When you have an insect bite and you rub it, the pain decreases