Senses, perception and pain

Question 1

What kind of cell is a sensory nerve cell? What is the function?
Hint: Polar

Answer 1

Pseudounipolar cell.

Axon has 2 branches, one projects into the CNS and one is in the peripheral component.

Question 2

What is a receptive field?

Answer 2

The area where a cluster of peripheral nerve branches cover. All branches react to the same stimuli.

Question 3

What are the purposes of receptive fields? (2)

Answer 3

Fields overlap to ensure the skin is sensitive to various stimuli.
2 point discrimination.

Question 4

Describe receptive fields on the finger tips in comparison to the trunk.

Answer 4

Finger tips: Receptive fields are smaller and more densely packed.
Trunk: Larger receptive fields that barely overlap.

Question 5

What ensure 2 point discrimination?

Answer 5

That two separate receptive fields are activated.

Question 6

How is a mechanoreceptor stimulus transduced?

Answer 6

Touch pulls on the cytoskeletal elements in the skin which opens the ion gated channels. Sodium moves in and potassium moves out. Action potential is fired.

Question 7

Name the 2 ways a chemoreceptor stimulus is transduced.

Answer 7

Inotropic.

G protein.

Question 8

How is the inotropic stimulus transduced?

Answer 8

Ligand binds directly to the channel, changes its conformation and allows the passage of ions which triggers the action potential.

Question 9

How is the G protein stimulus transduced?

Answer 9

Ligand binds to a distant receptor protein in the chain. Longer sequence activated until the transmembrane pore is opened and the passage of ions is granted.
(Longer process)

Question 10

What is a slowly adapting response?

Answer 10

Fires rapidly at the start, firing persists yet slows down until it stops.

Question 11

What is a rapidly adapting response?

Answer 11

Rapid firing at the start, stimulus persists yet no firing occurs after the initial wave.

Question 12

Describe the sensory homunculus in relation to the face and hands?

Answer 12

Face and hands section of the homunculus is greater due to the face and hands having smaller and more densely packed receptive fields. Much more sensitive to various stimuli compared to the trunk.

Question 13

Name the 5 cutaneous and subcutaneous mechanoreceptors.

Answer 13

Reissner's corpuscle 
Merkel disk.
Hair follicule.
Pacinian corpuscle.
Ruffini's ending.

Question 14

What afferents are active in innocuous tactile stimulation?

Answer 14

A beta afferents.

Question 15

What is the term for bundles of axons?

Answer 15

Fasciculi

Question 16

What axons are active in proprioreceptors/skeletal muscle?

Answer 16

A alpha afferents.

Question 17

What sensation are A delta axons active in?

Answer 17

Pain, crude touch and temperature.

Question 18

What branch of the trigeminal nerve has both motor and sensory function?

Answer 18

The mandibular branch.

Question 19

Ascending sensory pathways are composed of how many neurons?

Answer 19

3 interconnected neurons

Question 20

What is the pathway for mechanoreceptors (touch)?

Answer 20

Dorsal column medial lemniscal pathway.

Question 21

Mechanoreception: touch.
Dorsal column medial lemniscal pathway:
Where do each of the 3 neurons cover?

Answer 21

Primary neuron: From skin to brainstem on the same side as stimulus.
Secondary neuron: From brainstem to thalamus. Crosses over.
Third neuron: Thalamus to the specific region of the cortex.

Question 22

What is the mechanoreceptor pathway in the face called?

Answer 22

Dorsal trigeminothalamic pathway.

Question 23

What is the pathway for pain called?

Answer 23

Spinothalamic

Question 24

What fibres are in the primary neuron of the spinothalamic pathway?

Answer 24

A delta or C fibres.

Question 25

What is the pathway called for nociception of the face?

Answer 25

Ventral trigeminothalamic tract.

Question 26

What is stereognosis?

Answer 26

Visualise a structure via touch only.

Question 27

Name the 2 classifications of pain.

Answer 27

Nociceptive pain

Clinical Pain

Question 28

What causes clinical pain?

Answer 28

Damage to the CNS or the peripheral nerve.

Question 29

What does maladaptive mean in relation to clinical pain?

Answer 29

No protective function.

Question 30

What is referred pain?

Answer 30

Pain that is felt in one place yet the source is in another.

Question 31

Where is the pain usually felt (referred pain)?

Answer 31

Embryological origin.

Question 32

Where do ascending second order nociceptor neurons run through?

Answer 32

Antero-lateral funiculus.

Question 33

What role do ascending second order neurons have in relieving pain?

Answer 33

Can have surgery to cut the axons to relive pain in terminal illness.

Question 34

Explain the control theory of pain; rubbing the area.

Answer 34

Rubbing activates A beta fibres.
Axon projects into the spinal cord and branches.
One branch enters the dorsal horn and activates the inhibitory interneuron which inhibits the second order neuron and stops the conduction of pain.

Question 35

Name the three stages of the triple response. (after mechanical trauma)

Answer 35

Red reaction: Response to mild mechanical trauma.
Wheal: Area of skin around the trauma site becomes pale and swollen.
Flare: Skin further out from the wheal becomes red and mottled.

Question 36

Explain the stages of the triple response.

Answer 36

Pain felt when K is released (and bradykinin if blood vessels are damaged) causes an ionic change and fires an AP.
CGRP causes dilation of blood vessels (red reaction)
Sub P causes oedema which causes swelling. (Wheal)