L23 Somatosensory system

Question 1

what 5 different modalities are seen in the somatosensory system

Answer 1

touch
vibration
proprioception

pain
temperature

*most of the somatic sensory modalities refer to sensations of the skin, proprioception refers to sensory receptors originating int he skeleto-musclar system

Question 2

all of the receptors in the somatosensory system are what type (morphology) of neurons?

Answer 2

pseudo-unipolar neurons

Question 3

where are the somatosensory system receptor endings found?

Answer 3

skin
or in (or close to) muscle

Question 4

where do the fibers of somatosensory system receptor run?

Answer 4

in peripheral nerve

Question 5

where are the somatosensory system receptor cell bodies found?

Answer 5

ganglia (DRG)

Question 6

what transduces touch?

Answer 6

Merkel’s disks - discriminative touch

Ruffini’s endings - skin stretch

Question 7

what transduces vibration

Answer 7

Meissner’s corpuscles - high sensitivity, low threshold for freq of 50 Hz
Pacinian corpuscles - high sensitivity, low threshold for freq of 300 Hz

Question 8

how is pain transduced?

Answer 8

rapidly adapting mechno-sensitive or thermo-sensitive receptors - pricking pain

slowly adapting polymodal receptors - burning pain

Question 9

how is temperature transduced?

Answer 9

free nerve endings (cold receptors and warm receptors)

Question 10

how is proprioception transduced?

Answer 10

prorioceptors - muscle spindles, golgi tendon organs

Question 11

what is the primary receptor of a muscle spindle

Answer 11

rapidly adapting receptor with a 1a afferent fiber (info on muscle stretch) = forms afferent limb of myotactic reflex

Question 12

what is the secondary receptor of a muscle spindle

Answer 12

slowly adapting receptor carrying info about muscle length = uses class 2 afferent fiber

Question 13

where are golgi tendon organs located? what fibers do they have

Answer 13

close to the border of muscle and tendon

IIb afferent fibers = form afferent limb of reverse myotactic reflex

Question 14

what are the 4 types of fiber types used by the somatosensory system?

Answer 14

• large myelinated
• medium myelinated
• small myelinated
• small UNmyelinated

Question 15

what are characteristics of large and medium myelinated fibers (diameter, conduction velocity, used by, info carried)

Answer 15

diameter - 20 micrometers
conduction velocity = 120 m/s
used by - cut. mechanoreceptors and proprioceptors
info - carry sensory info of touch, vibration and proprioception

Question 16

what are characteristics of small myelinated fibers (diameter, conduction velocity, used by, info carried)

Answer 16

diameter - 1 micrometer
conduction velocity - 5 m/s
info - pain and temp

Question 17

what are characteristics of small UNmyelinated fibers (diameter, conduction velocity, used by, info carried)

Answer 17

diameter - 0.2-1.5 micrometer
conduction velocity - 0.5-2 m/s
info - pain and temperature

Question 18

how do you calculate conduction velocity?

Answer 18

diameter (micrometers) x 6

Question 19

Where is dermatome C2?

Answer 19

back of the head

Question 20

Where is dermatome C6

Answer 20

thumb

Question 21

Where is dermatome C7

Answer 21

middle finger

Question 22

Where is dermatome C8

Answer 22

pinky!

Question 23

Where is dermatome T4

Answer 23

nipple

Question 24

Where is dermatome T10

Answer 24

umbilicus

Question 25

Where is dermatome L1

Answer 25

groin

Question 26

Where is dermatome L5

Answer 26

big toe

Question 27

Where is dermatome S1

Answer 27

little pinky toe

Question 28

what pathway within the somatosensory system is touch, vibration and proprioception carried?

Answer 28

dorsal column/medial lemniscus system

DCML

Question 29

what pathway within the somatosensory system is pain and temperature carried?

Answer 29

anterolateral system ALS