S12 peripheral Nervous System and Spinal Cord

Question 1

what sensation do mechanoreceptors detect

Answer 1

mechanical stimuli

Question 2

What sensation do baroreceptors detect

Answer 2

pressure inside blood vessels

Question 3

what sensation do nociceptors detect

Answer 3

Pain/damage stimuli

Question 4

what sensation do thermoreceptors detect

Answer 4

thermal stimuli

Question 5

what sensation do photoreceptors, chemoreceptors and proprioceptors detect

Answer 5

light blood chemistry joint position

Question 6

what kind of receptors are free nerve endings

Answer 6

nociceptors.

Question 7

what is the free nerve endings relationship with skin biopsy in the study of peripheral neuropathies

Answer 7

look at density of free nerve endings in diseases where these free nerve endings and their density in the skin will diminish.

Question 8

What kind of cutaneous (or somatosensory) sensations do we evaluate clinically? How do we do such evaluation

Answer 8

Light touch; Brush, examiner’s finger tips

pressure; Semmes Weinstein filaments, von Frey Filaments/hairs

pain; pin prick

temperature; temeprature threshold devices

vibration; tuning fork

position sense

Question 9

To localize lesions we rely on three main neural tracts

Answer 9

One motor

two somatosensory (pain/temperature and vibration/propioception)

Question 10

all the main neural tracts are present in the

Answer 10

peripheral nerves, spinal nerves (or spinal root. Spinal nerve= anterior root+ posterior root), spinal cord, brainstem, internal capsule, cerebral cortex.

somatosensory tracts make a relay in the thalamus before reaching the cerebral cortex.

Question 11

Each of the main neural tracks contain both

Answer 11

somatic and visceral information

Question 12

Are the Spinothalamic tract myelinated in the peripheral nerves

Answer 12

Spinothalamic tract conveys pain and termperature, so its fibers are mainly thinly myelinated (Aδ), non-myelinated (C).

Question 13

Where does the spinothalamic tract localize in the spinal column and what name does it receive there.

Answer 13

cell bodies are in the posterior horn in the substantia gelatinosa.

tract fibers decussate and ascend contrallaterally in the lateral Spinothalamic tract

Question 14

where does the spinothalamic tract decussate

Answer 14

decussates in gray commisure either at level where information enters or one to three levels up or down.

Question 15

Where does the spinothalamic tract localize in the pons

Answer 15

in pons: lateral to Medial leminiscus. dorsal to pontine nucleis. in bottom of pons, the S-TT gets displaced more laterally.

Question 16

where is the spinothalamic tract localized in the midbrain

Question 17

where is the spinothalamic tract localized in the medulla

Answer 17

dorsal to the inferior olivary nuclei we have the spinothalamic tract. So basically in the medulla, the inferior olivary nucleus gets in between the spinothalamic tract and the medial lemniscus

Question 18

where in cerebral corext does the information from the spinalthalamic tract originate

Answer 18

VPL neurons somatesthetic cortex of the postcentral gyrus. Intralaminar neurons project to caudatoputamen and to the frontal and parietal cortex.

Question 19

what symptoms would you see in case of damage to spinothalamic tract

Answer 19

damage to pain/temperature tract can give you positive and negative symptoms. how do patients describe each.

contralateral loss of pain and temperature sensation one segment below the level of the lesion

Question 20

what characteristics does neuropathic pain have.

Answer 20

This is pain that is secondary to damage of neuronal structures and it can take two forms

One classical form is a burning or electric pain that runs down the nerve distribution in a superficial manner. intermittent

damage to neuronal structures can also give you a deep, aching pain like if somebody was sticking a knife into their skin. This pain can be continuous and it can have periods of waxing and waning. If the pain is secondary to damage of neural structures it will be confined to the territory covered either by a peripheral nerve or a nerve plexus. Keep in mind that both presentations of neuropathic pain may coexist.

Question 21

pain and temperature positive and negative symptoms

Answer 21

–Negative symptoms: Thermanestesia, analgesia, hypesthesia (numbness – depends on how much the other system compensates)

–Positive symptoms: Paresthesia (pins and needles, limb asleep), hyperalgesia, allodynia, neuropathic pain, dysesthesia

Nervi nervorum?

Damages to the pain and temperature system can give you either negative or positive symptoms. Negative symptoms are those in which sensation is diminished. If the sensation that is diminished is thermal sensation, that is called thermanesthesia. Analgesia is a decrease in the sensation of pain. Hypesthesia is a decrease in the sensation of touch. Remember, touch is carried both by the pain and temperature system and the vibration and proprioception system so you can find hypesthesia in damage of both of those systems depending on how much the other system is compensating. Positive symptoms refer to abnormal sensation. They include paresthesia which is a feeling of pins and needles in a certain region of the body similar to what you feel when your limbs fall asleep. You can have hyperalgesia which is feeling that a painful stimuli is more painful than normal; allodynia in which you interpret non-painful stimuli as painful; dysesthesia in which you interpret a stimulus as a very uncomfortable sensation but not necessarily painful; or neuropathic pain, on which we will expand in a little bit. I just want to mention that you can have positive symptoms also if you damage motor or vibration and proprioception fibers, probably because when you damage a nerve, you are activating the nerve receptors in the nervi nervorum.