Neuro 8 - Sensory Pathways - Nociception

Question 1

What are pain receptors called?

Answer 1

Nociceptors

Question 2

Can very high intensity stimulation of mechanoreceptors cause the feeling of pain?

Answer 2

No, only nociceptors can cause pain sensation

Question 3

Describe some features of nociceptors.

Answer 3

• Polymodal - different types that respond to different types of stimuli
• Free nerve endings
• High threshold - higher activation that touch receptors
• slow adapting - constantly reminded of pain

Question 4

What are the two main types of sensory neurone that carries sensory information?

Answer 4

• A fibres - large, fast conduction, fast adapting

- C-fibres - small, dull aching pain, slow conducting

Question 5

Compare the receptive fields of nociception compared to those of touch.

Answer 5

Receptive fields for nociception much larger

don’t need to be able to localise pain as well

Question 6

Describe the method of coding intensity in nociception.

Answer 6

FREQUENCY

Question 7

Describe the passage of the central pathway which carries information about pain and temperature.

Answer 7

First order neurons enters the spinal cord and synapses in dorsal horn with second order neuron

Second order neuron decussates immediately then travels up

Goes to thalamus - synapses with 3rd order neuron and then travels to the primary somatosensory cortex

Question 8

Describe the somatotopic arrangement of the fibres in the spinothalamic tract?

Answer 8

Lower = lateral
Higher = medial

Question 9

Which thalamic nucleus relays sensory information from below the neck?

Answer 9

Ventral Postero-lateral

Question 10

Where does decussation occur in the pain and temperature pathway?

Answer 10

At the same level as the information coming into the spinal cord

Question 11

Which nerve carries nociceptive information from the face?

Answer 11

Trigeminal

Question 12

Where does the Trigeminal nerve enter the brainstem?

Answer 12

Pons

Question 13

Describe the passage of the trigeminal nerve carry nociceptive information from entry into the brainstem?

Answer 13

Enters pons and travels downwards along trigeminal nucleus

synapses with lower part of trigeminal nucleus in the medulla

then decussated and joins at the medial end of the spinothalamic tract

Question 14

Describe the division of the trigeminal nucleus.

Answer 14

column of grey matter that runs from midbrain to medulla

Question 15

Which thalamic nucleus relays pain information from the face?

Answer 15

Ventral Posteromedial

Question 16

Which part of the trigeminal nucleus does the first order nociceptive neurons from the face synapse in?

Answer 16

Spinal Trigeminal nucleus

Question 17

What is the role of the primary somatosensory cortex in processing nociceptive stimulus?

Answer 17

registers location and intensity of the stimulus

Question 18

As the spinothalamic tract projects towards the primary somatosensory cortex it gives off collateral branches. Where do these branches go to?

Answer 18

brainstem - reticular formation
thalamus
hypothalamus
limbic structures

Question 19

What is the point of these collateral connections?

Answer 19

connections to the reticular formation and intralaminar nuclei allow the spinothalamic tract to increase your level of arousal to make sure that you are aware of danger

Question 20

Which CNS structures are involved in signalling the unpleasantness of a stimulus?

Answer 20

Limbic and hypothalamus

Question 21

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

Answer 21

Central and Peripheral Inhibition Pathways

Question 22

What is the focus of the central inhibition pathway?

Answer 22

Periaqueductual grey matter

Question 23

Describe the function of the central inhibition pathway.

Answer 23

increased brain activity will send impulses down the central inhibition pathway and go to the dorsal horn at every level

activates interneurone

interneurone synapses with the 1st and 2nd order neurone and releases enkephalin which is inhibiotry

Question 24

What type of molecule is enkephalin?

Answer 24

Opioid

Question 25

Other than a first order nociceptive neurone, what else has input into the second order nociceptive neurone?

Answer 25

Non-nociceptive neurones
axons of touch neurones will go into the dorsal horns

they are able to activate inhibitory interneurones which can reduce the activity of the projecting neurone

e.g. rubbing head after banging it

Question 26

Describe the arrangement and function of the peripheral inhibition pathway?

Answer 26

stimulation of touch receptors in the same area as the pain sensation will lead to increased activity of the non-nocieptive neurone

so greater inhibition from the internueuron

Question 27

State two examples of loss of pain sensation.

Answer 27

Syringomyelia

Charcot’s joints - peripheral neuropathy

Question 28

How can you get exacerbation of pain?

Answer 28

Wing up in the dorsal horn

chronic pain = nerves carrying high input for a long time
so cells in dorsal horn can lower their sensitivity increasing chronic pain.