Lecture 11 And 12

Front 1

Most sensory neurons send information over the ______________ or the ______________.

Back 1

dorsal column pathway, spinothalamic pathway

Front 2

Both ascending pathways have common features:

Back 2

they consist of three neurons in series. they are mostly crossed. they are somatotopically organized. they maintain modality specificity

Front 3

The area of skin supplied by the sensory axons from one single spinal segment (i.e., dorsal root) is called a __________.

Back 3

dermatome

Front 4

A single sensory neuron can influence other neurons in the spinal cord at ___________ through ascending and descending branches.Many of these connections are important for __________

Back 4

multiple segmental levels, spinal reflexes.

Front 5

The central axons of cutaneous mechanoreceptors andproprioceptors are

Back 5

thick and heavily myelinated (A alpha and A beta)

Front 6

Cutaneous mechanoreceptors and proprioceptors enter the spinal cord white matter in a ______________. ________________ of these axons terminate in relatively deep layers of the dorsal horn and in the ventral horn. The major collateral ascends in the ________ to the first synaptic relay in the dorsal column nuclei.

Back 6

medial position, Collateral branches, dorsal column

Front 7

The central axons of nociceptors and thermoreceptors are

Back 7

thin and lightly myelinated or unmyelinated (A delta and C).

Front 8

Nociceptors and thermo receptors enter the spinal white matter in a _______________ before terminating in relatively superficial layers of the _________________________. These _______________ then project across the midline into the spinothalamic pathway.

Back 8

lateral position, dorsal horn (i.e. the first synaptic relay), second order dorsal horn cells

Front 9

Within the dorsal column pathway, sensory nerves from the lower extremities join the column first, assuming a __________. Sensory nerves from the ________________ join the column later and so assume successively more _____________ up to the dorsal column nuclei.

Back 9

medial position, trunk and upper extremities, lateral positions

Front 10

The dorsal columns exhibit a segmental organization,consisting of (1) a ________ from lumbar and sacral segments traveling in the _________ and terminating in the brainstem ___________,

Back 10

medial group, gracile fascicle, gracile nucleus

Front 11

The dorsal columns exhibit a segmental organization, consisting of (2) a ________ from thoracic and cervical segments traveling in the ________ and terminating in the brainstem ____________.

Back 11

lateral group, cuneate fascicle, cuneate nucleus.

Front 12

Second order neurons in the brainstem dorsal column nuclei (gracile and cuneate) __________ and project via the ___________ to third order neurons in the ___________ nucleus of the thalamus.

Back 12

cross the midline, medial lemniscus, ventral posterolateral (VPL)

Front 13

Third order neurons from the VPL thalamus project via the _____________ to the _____________ in the postcentral gyrus (Brodmann's areas 3, 2,1) and to the more ventral _________________.

Back 13

internal capsule, primary somatosensory cortex, secondary somatosensory cortex.

Front 14

A ___________ organization is maintained throughout the ascending trajectory and ultimately mapped onto the somatosensory cortex.

Back 14

somatotopic

Front 15

The sites of termination of the dorsal column pathway are ___________ in the postcentral gyrus, also called the ______________. Within SI, different cytoarchitectonic subdivisions process different stimulus qualities. Other fibers terminate in the secondary somatosensory cortex (SII) in the upper wall of the lateral fissure.

Back 15

Brodmann's areas 3, 1, and 2, primary somatosensory cortex (SI)

Front 16

The ____________ of the dorsal column pathway is manifested as a well-defined _____________ in the thalamus and primary somatosensory cortex.

Back 16

somatotopic organization, "homunculus" (i.e., map)

Front 17

Differences in the ____________ of body parts represented in the homunculus are related to the ____________________ in each region of the body.

Back 17

proportion, density of sensory units

Front 18

Receptive field size is ___________ related to the density of sensory units. Cortical cells have receptive field sizes that are proportional to those in the periphery, though still _______ on average.

Back 18

inversely, larger than the humunculus

Front 19

Discrete ________ of somatosensory cortex or thalamus produce loss of sensation and/or _______________________ in restricted body regions on the side opposite to the brain damage.

Back 19

lesions, motor incoordination (ataxia)

Front 20

Higher order somatosensory processing (e.g., identifying objects based on their feel) occurs in ____________________. In these areas,the large and complex receptive fields of individual neurons imply a significant degree of convergence.

Back 20

posterior parietal association areas (5 and 7)

Front 21

The spinothalamic pathway is also called the ________________________. It relays information from free nociceptors and thermoreceptors on A delta and C fibers.

Back 21

anterolateral pathway or pain pathway

Front 22

The primary A delta and C fibers enter the spinal cord in a _______ position relative to the thicker fibers making up the dorsal column pathway and end in more superficial layers of the ____

Back 22

lateral, dorsal horn.

Front 23

Local projections of A delta and C fibers to other spinal segments travel through a small bundle called _____________.

Back 23

Lissauer’s tract (zone)

Front 24

The most unique features of the spinothalamic tract are:

Back 24

The primary afferents synapse with second order neurons almost immediately upon entering the spinal cord, the second order neurons cross to the opposite side within the spinal cord, and the second order neurons project all the way from the spinal cord to the thalamus.

Front 25

The primary afferents synapse on ___________ within the spinal cord.The axons of these second order neurons cross to the opposite side of the cord and ascend in the __________________

Back 25

second order neurons, spinothalamic tract (anterolateral fascicle).

Front 26

There is both a segmental and a super imposed somatotopic organization to the spinothalamic tract.Fibers entering the tract at the most ______ levels assume the most lateral positions, whereas fibers entering at more ________ levels assume successively more medial positions. Hence...

Back 26

caudal, rostral, segmental organization ofthe anterolateral fascicle (cervicalmedial to sacral lateral) is reversedfrom the dorsal column pathway.

Front 27

The _________________________________ of the spinothalamic and dorsal column pathways are similar and exhibit a comparable _______________. However, different neurons appear to be contacted so that ________________ is maintained.

Back 27

VPL thalamic and SI cortical terminations, somatotopic organization, modality specificity

Front 28

The somatotopic organization of the spinothalamic pathway conveys information regarding the _________________________ . However,some axons traveling in the _________________ in the brainstem reticular formation.

Back 28

location of painful stimuli in the body, anterolateral fascicle terminate

Front 29

Information is then relayed to the _____________, which are considered“non-specific” based on their diffuse projections to large parts of cortex, including limbic (i.e.emotional) regions.

Back 29

intralaminar thalamic nuclei

Front 30

This ________ is probably responsible for general “awareness” of pain and for emotional aspects of the pain experience. In other words,pain has both somatotopic and affective representations.

Back 30

spinoreticular tract

Front 31

______________ neurons, identified by retrograde tract-tracing from the VPL, are found in layers I, V, VII, and VIII of the spinal cord.

Back 31

Spinothalamic

Front 32

_________ fibers terminate in layers I and V, presumably on spinothalamic neurons. However, ____________ terminate in layer II where no spinothalamic neurons are present.

Back 32

A delta, C fibers

Front 33

Thus, _________ innervate _________ that provide polysynaptic connections to spinothalamic neurons.

Back 33

C fibers, interneurons

Front 34

Interneurons in the circuit means __________ and more opportunities for convergence and divergence. This factor, plus the ______________ time in C fibers (as compared to A delta fibers) makes the pain information they carry ________________ and be perceived as more diffuse in nature and more difficult to localize.

Back 34

more synapses, slower conduction, arrive in the cortex more slowly, diffuse

Front 35

Nociceptive information transmitted by ________ is conducted more quickly and has fewer synapses in the circuit, thus creating a _________,well-localized pain sensation at the level of cortex.

Back 35

A delta, sharp

Front 36

_______________ occurs with a hemi-section of the spinal cord, usually from a gunshot wound.

Back 36

Brown-Sequard syndrome

Front 37

In Brown-Sequard, the part of the body below the cut on the _______________ loses fine tactile discrimination sense and proprioception, The ______________________ loses pain and temperature sense below the cut.

Back 37

same side (ipsilateral), opposite side (contralateral)

Front 38

_________________ occurs when a cavity or cyst (syrinx) forms in the center of the spinal cord, often due to trauma, tumor growth, or a congenital defect.

Back 38

Syringomyelia

Front 39

Syringomyelia is accompanied by selective disruption of the spinothalamic tract. ____________ sense are lost on both sides of the body at the level of the lesion (usually cervical or thoracic); ____________________ sense are retained.

Back 39

Pain and temperature, tactile and proprioceptive

Front 40

Pain of visceral origin is often perceived as arising from a somatic source, i.e. within the body structure. Such ___________ results from the fact that visceral nociceptors do not have a dedicated cortical territory. Instead, these cells terminate on the ________________ neurons as used by somatic nociceptors from the same dermatome.

Back 40

referred pain, same spinothalamic

Front 41

Stimulation of large, well myelinated (Aalpha/Abeta) fibers from cutaneous receptors and proprioceptors can sometimes mask pain transmission. This phenomenon, known as )______, is based on activation of interneurons in the spinal cord dorsal horn, although the exact circuit is not known.

Back 41

afferent inhibition

Front 42

The _________________ method for treating chronic pain is based on the idea of afferent inhibition.

Back 42

transcutaneous electrical nerve stimulation (TENS)

Front 43

Inhibitory spinal interneurons are also involved in the ______________. Pathways descending from the brainstem are able to dampen the spinal cord transmission of pain by activating these interneurons and suppressing transmission in the spinothalamic tract.

Back 43

descending control of pain,

Front 44

What is referred pain

Back 44

When the visceral nociceptor synapses on the same spinal neuron that a cutaneous neuron also synapses on so you feel internal organ pain in your outer body.

Front 45

Afferent Inhibition

Back 45

Activation of large myelinated axons from cutaneous receptors and proprioceptors suppresses the transmission of nociceptive information. Most likely A alpha and A beta fibers synapse into inhibitory spinal interneurons that gate transmission of signals from spinothalamic neurons. Less information making it to the anterolateral fascicle.

Front 46

_________________ is the mechanism is invoked b the transcutaneous electrical nerve stimulation (TENS) treatment for chronic pain.

Back 46

Afferent Inhibition

Front 47

Inhibitory spinal interneurons are also involved in the ________________________. Pathwaysdescending from the brainstem are able to dampen the spinal cord transmission of pain byactivating these interneurons and suppressing transmission in the spinothalamic tract.

Back 47

descending control of pain