Somatosensory System I&II

Question 1

what are receptive fields?

Answer 1

sensitive areas that have more sensitive areas with smaller receptor fields
-ex. hands, lips, tongue, face, feet

Question 2

long vs. short axon

Answer 2

• long = depolarization near stimulus –> action potential –> conduction into CNS (ex. somatic, visceral, olfactory)
• short = depolarization near stimulus –> synapse to primary afferent –> conducted into CNS (ex. taste, photo, hair)

Question 3

where are synapses located?

Answer 3

• somatosensory = synapses in the CNS

- hair and photo = synapses on peripheral nerve endings of vestibular cochlear nerve or retinal interneurons

Question 4

special somatosensory receptors

Answer 4

1. meisnner - tactile shape
2. merkel - tactile indentations
3. hair - tactile in hairy skin
4. Ruffini - stretching and shapes
5. pacinian - vibrations
6. muscle spindles - proprioception

Question 5

types of nociceptors

Answer 5

1. Adelta - encapsulated; pinprick

2. C-polymodal - free nerve ending; tissue damage

Question 6

Meissner’s corpuscle

Answer 6

• fingers, palms, soles, toes
• touch and low frequency vibration
• ex. movement across skin

Question 7

merkel receptors

Answer 7

• lips, genitalia

- shape and texture of non-moving objects touching skin

Question 8

pacinian corpuscle

Answer 8

• hands, feet, nipples
• high frequency vibrations
• breast feeding

Question 9

Ruffini corpuscle

Answer 9

wide distribution - skin stretch

Question 10

where are the cell bodies of proprioception and tactile sensation located?**

Answer 10

dorsal root ganglion

Question 11

function of T6

Answer 11

• below T6 - fasciculus gracilis –> innervate legs

- above T6 - fasciculus cuneatus –> innervate arms

Question 12

different positions of neurons

Answer 12

• 1st order - dorsal root ganglion
• 2nd order - in medulla
• 3rd order - VPL of the thalamus

Question 13

afferent vs. efferent myotatic/stretch reflex

Answer 13

• afferent - intrafusal muscle fibers; stretch sensation

- efferent - extrafusal muscle fibers; contract to counteract the stretch

Question 14

posterior spinocerebellar tract

Answer 14

• proprioception from muscle spindles and Golgi tendons

- does NOT cross (decussate)

Question 15

anterior spinocerebellar tract

Answer 15

• proprioception and cutaneous info.

- crosses twice (spinal cord and pons)

Question 16

cerebellar ataxia

Answer 16

uncoordinated gate –> cerebellum not processing proprioceptive stimuli

Question 17

Friedreichs ataxia

Answer 17

neurodegenerative –> affect spinocerebellar tracts

• lack of upper limb coordination
• wide gate; wheel chair early adult
• autosomal recessive - FXN gene

Question 18

what is fast and acute pain conducted by?

Answer 18

carried to CNS by myelinated Adelta fibers

-Adelta also carry cold stimulus

Question 19

what is slow and chronic pain conducted by?

Answer 19

carried to CNS by unmyelinated C fibers

-C fibers also carry heat stimulus

Question 20

neospinothalamic tract

Answer 20

• pain signals to brain

- fibers cross in lateral funiculus

Question 21

anterolateral cordotomy

Answer 21

lesioning spinothalamic tract to interrupt pain transmission

Question 22

periaquaductal gray

Answer 22

surrounds aquaduct and is origin of a descending pain-control pathway
-start of controlling how you feel pain

Question 23

role of enkephalins

Answer 23

inhibit NT release from central process of nociceptive dorsal root ganglion neurons

Question 24

what does stimulation of descending pain pathways result in?

Answer 24

analgesia

Question 25

capsaicin vs. menthol

Answer 25

capsaicin - binds to heat channels priming them

menthol - binds to cold channels priming them

Question 26

neospinothalamic tract injury

Answer 26

injury –> loss of pain and thermal sensation on contralateral side inferior to the level of the lesion

Question 27

primary somatosensory cortex or thalamic lesion - left side lesion

Answer 27

loss of contralateral sensation for vibration, position, sense, touch, pain, temp., on entire right side of body

Question 28

lateral pontine or medullary lesion - left side lesion

Answer 28

• loss of sensation of pain and temp of ipsilateral face

- loss of sensation of pain and temp of contralateral body

Question 29

medial medullary lesion

Answer 29

affects posteromedial column

• no affect on face sensation
• loss of contralateral sensation to body

Question 30

distal symmetrical polyneuropathy

Answer 30

most distal parts of limbs affected

-starts distally works proximally

Question 31

isolated nerve lesion

Answer 31

stabbing most common cause

Question 32

posterior column medial lemniscal pathway

Answer 32

vibration, sense, touch, position

Question 33

anterolateral pathway

Answer 33

pain and temp.

Question 34

hyperalgesia

Answer 34

enhancement of pain sensation from tissue damage and release of endogenous chemicals

• activate or lowers nociceptor threshold
• treat with aspirin/NSAIDs

Question 35

allodynia

Answer 35

pain sensitization, sun burn, sore throat

• caused by thermal, mechanical, chemical
• symptom of fibromyalgia, migraines, neuropathies

Question 36

phantom limb pain

Answer 36

overactive dorsal horn neurons on same side as amputated limb - pain from amputated limb

Question 37

causalgia

Answer 37

sympathetic dystrophy syndrome

-burning sensation from increased sympathetic efferent activity - peripheral nerve injury

Question 38

neuralgia

Answer 38

suicide pain - can be debilitating and severe

-ex. trigeminal neuralgia

Question 39

paresthesia

Answer 39

sensation with no apparent cause

-caused by nerve compression or PVD

Question 40

meralgia paresthetica

Answer 40

numbess/tingling of outside thigh

-compression of pants on lateral cutaneous nerve

Question 41

thalamic pain syndrome aka dejerine-roussy syndrome

Answer 41

lesions of posterior thalamus causing chronic pain

-occurs after stroke

Question 42

referred pain

Answer 42

pain from deep visceral structures felt on surface

• mistake location of pain
• ex. myocardial ischemia radiating to arms/wrists

Question 43

2 point discrimination

Answer 43

help detect early stage neuropathies

-fingertips and toes have small receptor fields