Chapter 7: Sensing on Contact

Question 1

the somatosensory system also involves the ___ and ___ systems

Answer 1

gustatory (taste) and vestibular systems

Question 2

nerve endings that act as skin sensors may terminate as ____ nerve endings or ____ nerve endings, or can be wrapped around the base of a hair cell.

Answer 2

can be FREE nerve endings or ENCAPSULATED nerve endings in addition to wrapping around the base of a hair cell

Question 3

3 Main encapsulated nerve endings

Answer 3

1) merkel cells
2) Meissners’s corpuscles
3) Pacinian corpuscles.

Question 4

___ cells are sensitive to indentation of overlying skin. Are these cells slow or fast adapting to stimulation? What are these cells typically used for? How do they modulate the rate of neurotransmitter release?

Answer 4

MERKEL CELLS are sensitive to indentation of overlying skin.

Slow adapting

Seen in touch-sensitive areas (fingers) and can be used to identify the shape and texture of objects in contact with their skin

modulate their transmitter release in response to changes in MEMBRANE TENSION

Question 5

In Meissner corpuscle skin sensors, the free nerve ending is centered within stacks of ____ cells, which filters incoming stimuli and protect the nerve ending from overstimulation.

Answer 5

lamellar cells protect the Meissner’s corpuscles nerve ending

Question 6

discuss the spatial resolution of meissner corpuscle skin sensors. What are these sensors good for? Are they slow or fast adapting?

Answer 6

Meissner corpuscles have lower spatial resolution compared to both merkel and pacinian sensors. They are rapidly adapting. They are good for controlling grip strength because they can detect slipping.

Question 7

in Pacinian corpuscles, numerous ___ cells surround the nerve ending like an onion layer. Are they slow or fast adapting? Where are these skin sensors located?

Answer 7

numerous GLIAL cells surround the nerve ending to protect the sensitive nerve ending, like lamellar cells of the Meissner corpuscles.

They are faster to adapt than merkel cells but they are mores sensitive than meissner corpuscles

They are located deeper in the skin compared to Meissner cells.

Question 8

Meissner cells respond to ___ frequency vibrations

Pacinian Corpuscles respond to ___ frequency vibration.

Answer 8

Meissner cells respond to LOW frequency vibrations (if frequency is too high they adapt)

Pacinian Corpuscles respond to HIGH frequency vibration (more sensitive than Meissner cells)

Question 9

mechanosensory axons (merkel, meissner, pacinian etc) that innervate the skin project into the spinal cord through __ ___

Answer 9

spinal nerves.

8 cranial, 12 sacral, 5 lumbar, 5 thoracic, 1 coccyx

Question 10

skin sensory nerves project to the spinal cord through the ___ ___, and motor neurons leave the spinal cord and innervate muscle through the ____ ___.

Answer 10

skin sensory nerves project to the spinal cord through the DORSAL ROOT, and motor neurons leave the spinal cord and innervate muscle through the VENTRAL ROOT.

Question 11

Merkel, Meissner and Pacinian cells are ____ myelinated and are known as ____ fibers.

Answer 11

Merkel, Meissner and Pacinian cells are THICKLY myelinated and are known as AB fibers.

Question 12

AB fibers respond to __and ___

Answer 12

touch and vibration

Question 13

AS (sigma) fibers respond to ___ ___ and ___. Degree of myelination?

Answer 13

AS fibers respond to sharp pain and temperature. they are thinly myelinated

Question 14

C fibers respond to __ ___. Degree of myelination?

Answer 14

C fibers respond to DULL PAIN. Not myelinated

Question 15

Aalpha fibers project to ___ muscle. Degree of myelination?

Answer 15

alpha fibers project to deep muscle. They are thickly myelinated.

Question 16

AG(gamma) fibers project to ____ muscle fibers. Degree of myelination?

Answer 16

project to SPECIAL muscle fibers (intrafusal), medium myelination.

Question 17

when AB (beta) fibers (touch and vibration) fibers enter the dorsal root of the spinal cord, they can enter two different pathways. what are they?

Answer 17

AB fiber firing –> dorsal column of spinal cord. 2 branches:

1) Ipisilateral white matter dorsal column —> dorsal column nucei in CAUDAL MEDULLA
2) Dorsal horn grey matter —> Rexed Laminae divided into 10 layers, but 1-6 are for sensory projections.

Question 18

AB (beta) touch and vibration fibers branch as they enter the dorsal horn of the psinal cord. One branch ascends to the ____ through a ____ matter tract. The other branch forms terminal branches that synapse on neurons in deeper layers of the dorsal horn known as the ___ ___.

Answer 18

AB (beta) touch and vibration fibers branch as they enter the dorsal horn of the spinal cord. One branch ascends to the MEDULLA through a WHITE matter tract (IPSILATERAL DORSAL COLUMN). The other branch forms terminal branches that synapse on neurons in deeper layers of the dorsal horn known as the REXED LAMINAE.

Question 19

AB(beta) fibers terminate primarily on the __, __, and __ laminae

Answer 19

3, 4, and 5 laminae.

Question 20

Where do AB(beta) fibers on the head project to?

Answer 20

when skin of head is touched, AB vibration fibers convey impulse thorugh trigeminal nerve and the trigeminal nerve projects to the PRINCIPAL NUCLEI of TRIG. NERVE in the PONS.

Question 21

when skin of head is touched, AB vibration fibers convey impulse through ______ ____ and the____ ___ projects to the ___ ____ in the PONS.

Answer 21

when skin of head is touched, AB vibration fibers convey impulse through TRIGEMINAL NERVE and the trigeminal nerve projects to the PRINCIPAL NUCLEI of TRIG. NERVE in the PONS.

Question 22

somatosensory maps on the body and the head are located in 2 separate areas. what are they?

Answer 22

1) dorsal column nuclei in the medulla (where body map projects)
2) principal nuclei of the trigeminal nerve in the caudal pons (where the head map projects)

Question 23

what two fibers typically make up nociceotors?

Answer 23

C fibers and AS(sigma) fibers.

Question 24

nociceptor fibers (C and AS) fibers terminate in which regions of the rexed laminae

Answer 24

1 and 2

Question 25

t/f nociceptor fibers also have two tracts that go either into the rexed laminae or into the dorsal column to the thalamus

Answer 25

false. they only project into the rexed laminae 1 or 2 layers and then ASCEND INTO THE SPINOTHALAMIC TRACT on the CONTRALATERAL SIDe

Question 26

after projecting to the rexed laminae 1 and 2 layers, nociceptor fibers project into the _____ ______ tract.

Answer 26

CONTRALATERAL spinothalamic tract.

Question 27

rexed laminae layers 1 and 2 that recieve nociceptor information (C fiber and AS (sigma) fibers) also also known as the ___ ___ region

Answer 27

substantia gelatinosa region.

Question 28

Brown Sequard Syndrome

Answer 28

if a person incurs damage to one half of the spinal cord (damages the one dorsal side), then that person becomes unable to sense pain on the contralateral side to site of injury, because the pain fibers send info to the spinothalamic tract on the contralateral side.

Question 29

How and where is pain in the head conveyed to?

Answer 29

C and AS (sigma) pain fibers convey impulse through the TRIGEMINAL NERVE (like AB fibers), but they carry the signal to SPINAL NUCLEUS OF TRIGEMINAL NERVE IN THE MEDULLA (not the principle nucleus of the trigeminal nerve in the pons, like AB touch and vibration fibers)

Question 30

Both pain (C or AS) and touch (AB fibers) project axons into the trigeminal nerves, but where do they diverge?

Answer 30

after projecting through the trigeminal nerve, pain fibers project to the spinal nucleus in the medulla region, whereas normal touch and vibration fibers (AB) project to the "principle nucleus of the trigeminal nerve" of the pons

Question 31

Why is visceral pain hard to localize?

Answer 31

because of convergence of nociceptive axons from the skin and from internal organs into a SINGLE NEURON in brain or spinal cord

Question 32

Which sodium channel is prominent in nociceptors (C or AS fibers)

Answer 32

NaV1.7 channel. If you block these channels, you prevent pain detection. linked to congenital sensitivity to pain.

Question 33

How do opioids affect pain modulation?

Answer 33

exogenous and endogenous opioids bind onto GPCR opioid receptors and the activation of opioid receptors causes the CLOSING of Ca2+ channels and OPENING of K+ channels, causing HYPERPOLARIZATION of nociceptors and preventing pain detection.

Question 34

Dermatome

Answer 34

region of skin innervated by a specific spinal sensory nerve.

Question 35

Gate control theory of pain

Answer 35

rubbing activates touch sensitive axons that excite inhibitory neurons in the spinal cord, that in turn reduce the ability of nociceptive axons to transmit signals to higher brain regions.

Question 36

Explain the steps of neurogenic inflammation

Answer 36

1) noxious stimulation activates C and AS fibers and trigger APs that travel toward the spinal cord (through the 1 and 2 layers of rexed laminae and then to the spinothalamic tract) 2) varicosities from the C and AS fibers travel antidromically towards the peripheral axon terminals and site of pain 3) the varicosities release neurotransmitters and neuromodulators (SUBSTANCE P and CGRP) 4) Substance P causes histamine release and white blood cell release into the area 5) histamine causes further stimulation of C fibers and creates a POSITIVE FEEDBACK LOOP; inflammation causes MORE PAIN

Question 37

in addition to histamine and white blood cell release, ____ are released, which reduces inhibition in spinal cord dorsal horn, making it easier for pain signals to reach the brain.

Answer 37

PROSTAGLANDINS

Question 38

Which enzyme is required for prostaglandin synthesis?

Answer 38

COX enzyme. without, prostaglandins cannot be made. COX enzyme is targeted by many analgesic to PREVENT reduction in inhibition in spinal cord dorsal horn.

Question 39

Nociceptive info from spinal cord moves through the spinothalamic tract to the thalamic nuclei. from the spinothalamic tract, where do the projections go?

Answer 39

thalamic nuclei in dorsal region project to the ANTERIOR CINGULATE GYRUS to the PFC thalamic nuclei in the ventral region project to the primary somatosensory cortex and to the INSULA, which then goes to the anterior cingulate gyrus (forms a loop) See notes for Pain in the Brain pathway

Question 40

Where is pain "truly felt"?

Answer 40

when the signal from nociceptors has travelled to the anterior cingulate cortex and PFC.

Question 41

Hypnotic analgesia shows decreased activation of the ___ ___ __, showing a reduced emotional value of pain.

Answer 41

Hypnotic analgesia shows decreased activation of the ANTERIOR CINGULATE GYRUS, showing a reduced emotional value of pain.

Question 42

the descending pathway inhibits an ascending pathway of pain at the level of the ___ ___

Answer 42

spinal cord

Question 43

explain the descending pain pathway

Answer 43

1) periaqueductal grey gets activated by opiates (opiates inhibit the neurons that inhibit PAG) 2) PAG stimulates the NUCLEUS RAPHE MAGNUS in the midbrain, which ACTIVATES the Dorsal horn neurons that INHIBIT NOCICEPTION.