Physiology of Sensation

Question 1

What are the 3 divisions of the somatosensory system?

Answer 1

exteroceptive
proprioceptive
enteroceptive

Question 2

Describe the exteroceptive division?

Answer 2

cutaneous senses - registers information from the surface of the body

Question 3

Describe the proprioceptive division?

Answer 3

monitors posture and movement of the body

Question 4

Describe the enteroceptive division?

Answer 4

reports upon the internal state of the body and closely relates to autonomic function

Question 5

How are stimuli passed on through the nerves?

Answer 5

open a cation selective ion channel in the peripheral terminal of the primary sensory afferent - this elects a depolarising receptor potential
this triggers an action potential
action potentials cause a graded neurotransmitter release

Question 6

What do low threshold receptors respond to?

Answer 6

low intensity non damaging stimuli

Question 7

What do high threshold receptors respond to?

Answer 7

high intensity, potentially damaging stimuli

Question 8

What do thermal nociceptors respond to?

Answer 8

extremes of heat = >45 or <10-15

Question 9

What do chemical nociceptors respond to?

Answer 9

substances in the tissue eg serotonin, histamine, prostaglandin

Question 10

What do polymodal receptors respond to?

Answer 10

two or more different stimuli

Question 11

What is a receptive field?

Answer 11

target area where a sensory unit can be excited

Question 12

How do receptive fields relate to innervation density and sensory acuity?

Answer 12

inversely proportional

i.e. high receptive field = low innervation density and low sensory acuity

Question 13

What is two point discrimination?

Answer 13

minimum distance required between two simultaneous stimuli for them to be registered

Question 14

Do regions with high descriminative capacity have big or small RFs?

Answer 14

small

Question 15

What stimulates messiners corpuscles?

Answer 15

fine touch

Question 16

What stimulates merkels discs?

Answer 16

pressure

Question 17

What stimulates ruffini endings?

Answer 17

stretch

Question 18

What stimulates pacinian capsules?

Answer 18

pressure and vibration

Question 19

What is gray matter divided into?

Answer 19

10 laminae of Rexed

Question 20

What laminae do nociceptors go to?

Answer 20

laminae 1 and 2

Question 21

What laminae do low threshold mechanoreceptors go to?

Answer 21

laminae 3 - 6

Question 22

What laminae do properioceptors go to?

Answer 22

laminae 7 - 9

Question 23

What are the two dorsal columns?

Answer 23

fasciculus gracilis

fasciculus cunate

Question 24

Which is more medial - fasciculus gracilis or fasciculus cunate?

Answer 24

fasciculus gracilis

Question 25

What nerves does the fasciculus gracilis carry through the dorsal column?

Answer 25

sensory input from T6 and downwards | eg FROM THE LEGS

Question 26

What nerves does the fasciculus cunate carry through the dorsal column?

Answer 26

sensory input from T6 upwards | eg FROM THE UPPER BODY

Question 27

What order does information from the spinal section come in? Laterally to medially?

Answer 27

cervical thoracic lumbar sacral

Question 28

What is stereognosis?

Answer 28

the ability to recognise an object just by feeling it

Question 29

What is fine touch?

Answer 29

the ability to recognise the exact location of something just by light touch

Question 30

What is concious proprioception?

Answer 30

awareness of body movements and posture

Question 31

What is contrast enhancement?

Answer 31

when information is conveyed from one neuron to the next, the differences in adjacent neurons is amplified - meaning the main signal is wishy washy

Question 32

How is contrast enhancement combatted?

Answer 32

lateral inhibition

Question 33

What is lateral inhibition?

Answer 33

works via inhibitory interneurons to sharpen stimulus perception

Question 34

Where is the somatosensory cortex located?

Answer 34

post central gyrus of the parietal cortex

Question 35

What makes up the somatosensory cortex?

Answer 35

brodmann areas

Question 36

What makes up 1, 2, 3a and 3b of brodmann areas?

Answer 36

1 - cutaneous and 3a 2 - 3a,3b,joint afferents, deep tissue, golgi tendon organs 3a - proprioceptors 3b - cutaneous and 3a

Question 37

What does S1 stand for?

Answer 37

Brodmann areas

Question 38

What does S2 stand for?

Answer 38

Posterior parietal cortex

Question 39

What would a lesion in brodmann area 1 present as?

Answer 39

loss of texture discrimination

Question 40

What would a lesion in brodmann area 2 present as?

Answer 40

impaired grasping and size and shape discrimination

Question 41

What would a lesion in brodmann area 3a present as?

Answer 41

deficits in texture, shape and discrimination

Question 42

How is the somatosensory cortex arranged?

Answer 42

in columns - each column consisting of neurons with simlar inputs and responses - fast/slow adapting

Question 43

What is the role of the posterior parietal cortex (S2)?

Answer 43

recieves and integrates information from S1, other cortical areas (visual, auditory) and subcorticle areas (thalamus) and deciphers the deeper meaning - i.e. inputs the texture size context etc then tells its a key

Question 44

What can damage to the posterior parietal cortex cause/

Answer 44

neglect syndrome - patients believe that one side of their body doesnt exist