General Sensory Mechanisms II (Lec 4)

Question 1

What does widespread bilateral excision of somatasensory area I cause?

Answer 1

loss of ability to localize discretely the different sensations in the different parts of the body, loss of ability to sense pressure and weight, loss of ability to judge weight, shape, and texture of objects

Question 2

Where does the somatosensory area II receive signals from?

Answer 2

brain stem, secondarily from somatosensory area II, visual/auditory areas

Question 3

True or False?

projections from somatosensory area I are not required for function of somatosensory area II

Answer 3

false, they are required

Question 4

What do layers I and II of the somatosensory cortex receive input signals from?

Answer 4

lower brain centers

Question 5

What do layers II and III of the somatosensory cortex send information through?

Answer 5

corpus callosum to opposite hemisphere

Question 6

What are found in layers V and VI and where do they project to?

Answer 6

large neurons in layer V project to distant areas such as basal nuclei, brain stem, and spinal cord

axons from layer VI project to thalamus

Question 7

How is receptor potential created?

Answer 7

by opening “modality” gated channels such as sodium channels that are opened in response to membrane deformation caused by the touch or pressure

Question 8

Most sensory pathways are made up of how many neurons?

Answer 8

three

Question 9

Where do primary sensory neurons originate from and where do they go?

Answer 9

originate from peripheral receptors such as Merkel’s receptors; enter spinal cord or brain via dorsal roots of cranial nerves and synapse with secondary neurons

note: primary neuron cell bodies are located in the dorsal root ganglia

Question 10

Where do secondary sensory neurons originate from and where do they go?

Answer 10

originate in spinal cord gray matter; travel through spinal cord and synapse in thalamus with tertiary neurons

Question 11

Where do tertiary sensory neurons travel through?

Answer 11

internal capsule: myelinated pathway between thalamus and basal nuclei and synapse in somatosensory cortex

Question 12

What is two-point discrimination touch and where does it travel?

Answer 12

the ability to distinguish two separate points as close as 2 mm apart; travels in the dorsal column-medial lemniscal pathway

Question 13

In the dorsal column-medial lemniscal pathway, where do axons from the lower limbs travel?

Answer 13

in the medial portions of the two dorsal columns

Question 14

In the dorsal column-medial lemniscal pathway, where do axons from the upper limbs travel?

Answer 14

in the lateral portions of the two dorsal columns

Question 15

What are the two subdivisions of the dorsal column that make up the two tracts in the medial lemniscus?

Answer 15

fasciculus gracilis; fasciculus cuneatus

Question 16

What are pain receptors (nociceptors)?

Answer 16

free nerve endings

Question 17

What are some of the characteristics of fast pain?

Answer 17

felt within 0.1 seconds after stimulus is applied; not felt in deep tissue; generally elicited by mechanical and thermal stimuli; is typically carried by pain fibers

Question 18

Where do fast pain fibers terminate?

Answer 18

in lamina I of the dorsal horns of the spinal cord

Question 19

What are some of the characteristics of slow pain?

Answer 19

felt about 1 second after stimulus is applied and increases over several seconds; aching/slow burning/throbbing/nauseous/chronic; elicited by mechanical, thermal, and chemical stimuli; carried by C type fibers

Question 20

Where C type fibers in slow pain terminate?

Answer 20

layers II and III of the dorsal horns of the spinal cord

Question 21

Pain travels through ____ pathways

Answer 21

anterolateral

Question 22

Secondary fibers in pain pathways immediately decussate and make up what pathways?

Answer 22

the anterolateral pathways

Question 23

Fast pain fibers make up what tract? Where do they terminate?

Answer 23

make up neospinothalamic tract; terminate in ventrobasal nuclei of thalamus

Question 24

Slow pain fibers make up what pathway? Where do they terminate?

Answer 24

make up paleospinothalamic pathway; terminate throughout the brainstem

Question 25

What do the fibers of the fast pain path use as their NT?

Answer 25

glutamate

Question 26

What do Type C fibers of the slow path release as NTs?

Answer 26

glutmate instantaneously; substance P which is released more slowly

Question 27

What is Brown-Sequard syndrome?

Answer 27

occurs when there is a hemisection of the spinal cord - all motor functions are blocked, sensations of pain are lost, and two-point discrimination type sensations are lost

Question 28

What does the analgesia system consist of?

Answer 28

periaquaductal gray and periventricular regions of brainstem and third ventricle, raphe magnus nucleus and reticular nuclei in medulla, an drain inhibitory complex in dorsal horns of spinal cord

Question 29

What are the three types of receptors that discriminate thermal gradations?

Answer 29

cold; warmth; pain

Question 30

Warmth is transmitted over what type of fibers?

Answer 30

C-type

Question 31

Cold is transmitted over what type of fibers?

Answer 31

Small type fast (Abomb symbol) myenlinated endings

Question 32

Which receptor is more numerous, cold or warmth?

Answer 32

cold; 3-10 times as numerous

Question 33

What stimulates cold and warmth receptors?

Answer 33

changes in metabolic rates

Question 34

What is referred pain?

Answer 34

occurs when visceral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin

Question 35

Severe referred pain can result from what?

Answer 35

ischemia

Question 36

What causes headaches?

Answer 36

result of pain referred to the surface of the head from deep head structures

Question 37

True or False?

The brain itself is almost completely insensitive to pain

Answer 37

true

Question 38

What is the primary somatosensory area made up of?

Answer 38

Brodman’s areas 1, 2, 3

Question 39

Brodman’s areas 5 & 7 make up what?

Answer 39

The somatosensory association area

Question 40

All visceral referred pain from the thoracic and abdominal cavities is transmitted via what type of fiber?

Answer 40

Type c pain fibers