Somatosensory System Pathways

Front 1

Where are the cell bodies of afferent (sensory) fibers from peripheral nerves to the spinal cord located?

Back 1

In the spinal ganglia (dorsal root ganglia)

Front 2

Where are the cell bodies of afferent (sensory) fibers from cranial nerves to the brainstem located?

Back 2

In the gaglia close to the brainstem (e.g. semilunar ganglion of trigeminal nerve)

Front 3

Where do the two processes travel in primary afferent cells that are pseudo-unipolar?

Back 3

One process goes peripherally to a free ending or receptor, the other process travels to the spinal cord

Front 4

Where do the fibers with the thickest myelination (Ia, Ib, II) enter the spinal cord?

Back 4

On the medial aspect of the dorsal horn

Front 5

Where do the fibers with the thickest myelination (Ia, Ib, II) terminate?

Back 5

In lamina III-VI, VII and IX

Front 6

Where do A-delta fibers enter the spinal cord?

Back 6

On the lateral aspect of the dorsal horn

Front 7

Where do A-delta fibers terminate?

Back 7

In lamina I and V

Front 8

Where do C fibers enter the spinal cord?

Back 8

On the lateral aspect of the dorsal horn

Front 9

Where do C fibers terminate?

Back 9

In lamina II (substantia gelatinosa)

Front 10

What are three neurotransmitters associated with somatosensory pathways?

Back 10

Glutamate (excitatory), GABA (inhibitory), neuropeptides

Front 11

Where are neuropeptides found?

Back 11

In central and peripheral terminals

Front 12

What are three neuropeptides?

Back 12

Substance P (SP), cholecytokinin (CCK), somatostatin

Front 13

Do dermatomes overlap?

Back 13

Yes

Front 14

Every spot on the skin is innervated by sensory fibers from how many dorsal roots?

Back 14

At least two

Front 15

Is there more overlap of pain fibers or touch fibers in dermatomes?

Back 15

More overlap in touch fibers

Front 16

When a nerve root is irritated, what does the patient feel in the associated dermatome?

Back 16

A numb or pricking sensation is found in the territory of the dermatome

Front 17

Most somatosensory system pathways consist of a chain of how many neurons?

Back 17

Three

Front 18

Where are the cell bodies of primary sensory neurons located?

Back 18

In the dorsal root ganglion or cranial nerve ganglion

Front 19

Where do primary sensory neurons travel from and synapse to?

Back 19

They travel from peripheral receptors to synapse in the spinal cord or brainstem

Front 20

Where are the cell bodies of secondary sensory neurons located?

Back 20

In the gray matter (dorsal horn) of the spinal cord or in the brainstem

Front 21

Where do the axons of secondary sensory neurons ascend?

Back 21

In the spinal cord or brainstem

Front 22

Where do the axons of secondary sensory neurons terminate?

Back 22

In the thalamus

Front 23

Where are the cell bodies of third order sensory neurons located?

Back 23

In the thalamus

Front 24

Where do the axons of third order sensory neurons terminate?

Back 24

They terminate in the primary somatosensory cortex

Front 25

What are the two major divisions of somatosensory pathways?

Back 25

The dorsal column medial lemniscus (DCML) and the spinothalamic tract (ST)

Front 26

The DCML pathway carries impulses from what types of receptors?

Back 26

Low-threshold mechanoreceptors

Front 27

The spinothalamic tract carries impulses from what types of receptors?

Back 27

Pain and temperature receptors

Front 28

What are the three major subdivisions of the thalamus?

Back 28

Anterior, medial and lateral (dorsal and ventral)

Front 29

Intralaminal thalamic nuclei are important in the perception of what?

Back 29

Pain

Front 30

Where do fibers enter the spinal cord in the DCML pathway?

Back 30

On the medial aspect of the dorsal horn

Front 31

What is the gracile fasciculus?

Back 31

The medial portion of the dorsal column of the spinal cord

Front 32

The gracile fasciculus carries fibers with information from what part of the body?

Back 32

The lower trunk and lower extremities

Front 33

Where do fibers in the gracile fasciculus synapse?

Back 33

In the gracile nucleus in the medulla

Front 34

What is the cuneate fasciculus?

Back 34

The lateral portion of the dorsal column of the spinal cord

Front 35

The cuneate fasciculus carries fibers with information from what part of the body?

Back 35

The upper trunk and upper extremities

Front 36

Where do fibers in the cuneate fasciculus synapse?

Back 36

In the cuneate nucleus of the medulla

Front 37

The dorsal column nuclei of the medulla receives fibers from what two structures?

Back 37

The gracile fasciculus and the cuneate fasciculus

Front 38

What is the medial lemniscus?

Back 38

A fiber tract carrying second order neurons of the DCML

Front 39

Where do fibers from the medial lemniscus cross over

Back 39

The medulla

Front 40

Where are the cell bodies of second order neurons in the DCML pathway found?

Back 40

In the dorsal column nuclei

Front 41

Where do fibers of the medial lemniscus terminate?

Back 41

In the ventral posterior lateral (VPL) nucleus of the thalamus

Front 42

Fibers mediating information from the face terminate where?

Back 42

In the ventral posterior medial (VPM) nucleus of the thalamus

Front 43

Where are cell bodies of third order neurons in the DCML pathway located?

Back 43

In the VPM and VPL of the thalamus

Front 44

Where do third order neurons of the DCML pathway send axons?

Back 44

To the postcentral gyrus (Brodmann areas 1, 2 and 3)

Front 45

Where do third order neurons of the DCML pathway terminate?

Back 45

In the primary somatosensory cortex

Front 46

How are terminations in the primary somatosensory cortex organized?

Back 46

Somatotopically (sensory homunculus)

Front 47

What body parts have large areas of representation on the sensory homunculus?

Back 47

Lips, tongue and thumb

Front 48

Are fibers in the DCML pathway rapidly or slowly adapting?

Back 48

Rapidly adapting

Front 49

The DCML pathway is designed to mediate what type of information?

Back 49

Fast and precise information about stimulus type, exact site of stimulus and when the stimulus starts and stops

Front 50

Are fibers in the DCML pathway myelinated?

Back 50

Yes

Front 51

Lesions of the DCML pathway result in what kinds of deficits?

Back 51

The inability to discriminate spatial and temporal characteristics of a stimuli

Front 52

Are individuals with DCML pathway lesions able to perceive crude touch?

Back 52

Yes

Front 53

Can lesions of the DCML pathway result in motor deficits?

Back 53

Yes, due to the dependence of accurate voluntary movement on feedback regarding sensory information

Front 54

Syphilis can cause what condition affecting the dorsal column of the spinal cord?

Back 54

Tabes dorsalis-degeneration of the dorsal column

Front 55

Where do fibers from the spinothalamic tract enter the spinal cord?

Back 55

The lateral portion of the dorsal root

Front 56

The tract of Lissauer is made up of what fibers?

Back 56

Type C fibers

Front 57

Where is the tract of Lissauer located?

Back 57

Dorsal to the gray matter of the dorsal horn

Front 58

Where are cell bodies of second order neurons of the spinothalamic tract located?

Back 58

In the dorsal horn

Front 59

Where do fibers of the spinothalamic tract cross over?

Back 59

At the level of the second order neurons

Front 60

List the Six types of chemical agents.

blood, blister, nerve, what are the other three?

Back 60

Blood, Blister, Choking, Nerve, Incapacitating, Military Compound.

Front 61

Where is the spinothalamic tract situated in the pons?

Back 61

Lateral to the medial lemniscus

Front 62

Where is the spinothalamic tract situated in the midbrain?

Back 62

Dorsolateral and adjacent to the medial lemniscus

Front 63

Where do second order neurons of the spinothalamic tract synapse?

Back 63

With cells in the VPM, VPL, posterior complex and intralaminar nuclei of the thalamus

Front 64

Where do third order neurons of the spinothalamic tract send neurons?

Back 64

To the primary somatosensory cortex (areas 1, 2 and 3) and many parts of the ipsilateral cortex

Front 65

What is the function of the spinothalamic tract?

Back 65

It mediates perception of pain and temperature and a relatively crude sense of pressure and touch

Front 66

Lesions of the spinothalamic tract cause what sorts of deficits?

Back 66

Loss of pain and temperature sensation in the contralateral side of the body

Front 67

Where do deficits of the spinothalamic tract of the spinal cord begin to be seen?

Back 67

Two segments below the lesion

Front 68

How is the spinothalamic tract involved with referred pain?

Back 68

The spinothalamic tract receives input from nociceptors in the periphery and in the viscera. It is not possible for higher centers to determine where painful stimulus is coming from.

Front 69

What is reflex sympathetic dystrophy (CRPS) caused by?

Back 69

Spinal reflexes that trigger a release of neuropeptides from the sensory end organs in the skin

Front 70

Are the activation of nociceptors and the conscious experience of pain dependent on one another?

Back 70

No, pain can be perceived without activation of a nociceptor and vice versa

Front 71

What are two examples of pain without activation of a nociceptor?

Back 71

Phantom limb pain and thalamic pain caused by thalamic lesions