Lecture 17 Sensory Systems (including physiology of pain)

Question 1

Receptor that senses light touch

Answer 1

Tactile (Meissner’s) Corpuscle

Question 2

Receptor that senses touch

Answer 2

Tactile (Merkel’s) Corpuscle

Question 3

Receptor that senses pain

Answer 3

Free nerve ending nociceptor

Question 4

Receptor that sense deep pressure

Answer 4

Lamellated (Pacinian_ Corpuscle

Question 5

Receptor that senses warmth

Answer 5

Ruffini corpuscle

Question 6

What encodes the intensity of the stimulus

Answer 6

The frequency of the action potentials

Question 7

What encodes the location of the stimulus

Answer 7

The receptive field

Question 8

Where is the receptor potential integrated at

Answer 8

The trigger zone

Question 9

Cutaneous sensation is mediated by 3 types of primary afferent fibres what are they?

Answer 9

– Aβ = large myelinated (30-70m/s) touch, pressure, vibration
– Aδ = small myelinated (5-30m/s) cold, “fast” pain, pressure
– C = unmyelinated fibres (0.5-2m/s) warmth, “slow” pain

Question 10

Proprioception is mediated by what 2 types of primary afferent fibres

Answer 10

– Aα & Aβ eg muscle spindles, golgi tendon organs etc

Question 11

Afferent fibres of mechanoreceptors

Answer 11

(Aα & Aβ) fibres

Question 12

Describe the path of the Mechanoreceptive (Aα & Aβ) fibres

Answer 12

– 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 13

Name the Thermoreceptive & nociceptive fibres

Answer 13

(Aδ & C)

Question 14

Describe the path of the Thermoreceptive & nociceptive (Aδ & C) fibres

Answer 14

– 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 15

What would be the consequence of damage to the dorsal columns

Answer 15

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

Question 16

What would be the consequence of damage to the anterolateral quadrant

Answer 16

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

Question 17

Define Adaption

Answer 17

gradual decrease over time in the responsiveness of the sensory system to a constant stimulus. Can be rapid or slow

Question 18

Define Lateral Inhibition

Answer 18

– activation of one sensory input causes synaptic inhibition of its neighbours
– gives better definition of boundaries
– cleans up sensory information

Question 19

Singal transduction in Nociceptors are activated by what

Answer 19

low pH, heat (via ASIC, TRPV1 etc)

-local chemical mediators (eg bradykinin, histamine, prostaglandins)