Ascending Sensory Spinal Brain Pathways

Question 1

Two main divisions of somatosensory transport are?

Answer 1

Protopathic- Concerns pain, temperature, crude touch

Epicritic- fine touching, texture, body position and vibration

Question 2

Motoneuron cell bodies are located where in the spinal cord?

Answer 2

Ventral Horn

Question 3

How do sensory receptors found in the skin, muscles, joints, and viscera communicate with the CNS?

Answer 3

Via the peripheral processes of “psuedo unipolar sensory neurons”…must know

Question 4

Where are the cell bodies of “psuedo unipolar sensory neurons” located?

Answer 4

Outside of the spinal cord in the dorsal root ganglia

Question 5

What are ganglia?

Answer 5

aggregations of nerve cell bodies outside the CNS….Thi sis in contrast to aggregations of nerve cell bodies inside the CNS which are called nuclei

Question 6

Know the classification of peripheral nerve fibers

Answer 6

pg. 49

Question 7

Pacinian Corpuscle

Answer 7

Large, lamellar, rapidly adapting adapting mechanoreceptor that efficiently detects gross pressure and VIBRATION

Question 8

Meissner’s corpuscle is

Answer 8

rapidly adapting skin mechanoreceptor that is sensitive to light touch and vibrations of less than 50

Question 9

Merkel’s Disks

Answer 9

Slowly adapting mechanoreceptors located in skin and mucosa

Question 10

Ruffini organs are slowly adapting mechanoreceptors found only in deep layers of glabrous skin (finger tips)

Answer 10

ok

Question 11

Sensory receptors transduce the energy contained in whatever stimuli activated them into electrical potentials…action potentials.

Answer 11

realize this

Question 12

What is adaptation

Answer 12

a reduced response to a stimulus in teh face of a constant continued stimulus

Question 13

Protopathic somesthisis travels in what tract?

Answer 13

Spinothalamic Tract/ Anterolateral Pathways

Question 14

Where does epicritic information travel in the spinal cord?

Answer 14

In the posterior columns that become a tract known as the medial lemniscus

Question 15

Pain receptors and temperature receptors are typically what?

Answer 15

unspecialized free nerve endings

Question 16

The axons attached to the free nerve endings are generally what type of axons

Answer 16

small and slowly conducting

Question 17

When nerve fibers decussate they are called?

Answer 17

Internal Arcuate fibers (they arc across the midline)

Question 18

In the Lemniscal pathway, what is the pathway from the VPL to the cortex?

Answer 18

Posterior limb of the internal capsule

Question 19

Collaterals of the proprioceptive afferents go where

Answer 19

Whereas most epicritic signal travel via the lemniscla pathway, some proprioceptive collaterals are sent deep into the dorsal horn and also to the ventral horn, some of which are monosynaptic on motoneurons

Question 20

Why is it that when you have a spinal cord lesion, you lose protopathic inputs from 2-3 levles below the lesion

Answer 20

Because protopathic inputs synapse immediately in the Dorsal horn of the spinal cord and then decussate to the contralateral spinothalamic tract.
Many of them however, travel 2-3 segments through Lissauer’s tract before synapsing in the dorsal horn and decussating. Thus, in a spinal cord lesion, these inputs that are travelling up are also lost.

Question 21

This is tricky, so we know that as we move up the body, proprioceptive inputs are added in a lateral fashion to the posterior/dorsal column. What happens when decussation occurs?

Answer 21

It reverses, whereas legs where medial in the spinal cord, they now travel laterally in the brainstem

Question 22

Substantia gelatinosa is what

Answer 22

Lamina I and Lamina II of the spinal cord gray matter (remember lmina are numbered from dorsal to ventral). This is the site of first modulation of pain and temperature information (Protopathic somesthesis)

Question 23

Lissauer’s tract is what?

Answer 23

composed of sensory fibers carrying pain and temperature that ascend or descend several spinal cord levels before synapsing in the dorsal horn.

Question 24

know spinothalamic, spinoreticular, spinomesencephalic

Answer 24

Spinothalamic: discriminative aspects of pain,
Spinoreticular: characterized by synapses with neurons in the reticular formation of the pons and medulla. Important for emotional aspects of pain
Spinomesencephalic: connections to periaqueductal gray matter…activates descending, efferent pathways that modulate pain.

If you stepped on a nail, the spinothalamic system would report that a sharp object is in your left foot, the spinoreticular system would say “ouch that hurts” and the spinomesencephalic system would initiate pathways to modulate the response to pain decreasing.

HJighest concentration of opiate receptors in the periaqueductal gray matter.

Question 25

In the protopathic system, as afferents are added as you ascend the spinal cord, how are they incoporated into the cervical dorsal horn?

Answer 25

Medially. This is the opposite of the epicritic system

Question 26

Adelta fibers of the protopathic pathways mediate what?

Answer 26

First Pain- a sharp sensation that can be readily localized on the body.

Question 27

A delta fibers first synapse where SPECIFICALLY

Answer 27

Laminae I and II in the Dorsal horn (Substantia Gelatinosa)

Question 28

What are propriospinal fibers?

Answer 28

The propriospinal tract runs between spinal cord segments Interneurons in lamina I and II of the dorsal horn project some fibers via this tract.

Question 29

What is the deepest layer of the dorsal horn?

Answer 29

Layer V

Question 30

Protopahtic fibers that project into layer V do what?

Answer 30

Decussare and ascend

Question 31

C fibers of the protopathic pathway are associated with what?

Answer 31

Second pain- a duller, less localizeable aspect of pain

Question 32

Where do C fibers synapse

Answer 32

Substantia Gelatinosa

Question 33

For the head and face, what system is responsible for somesthesis?

Answer 33

Trigeminal system

Question 34

What are the three divisions of the trigeminal nerve that innervate the face?

Answer 34

Opthalmic, Maxillary, Mandibular

Question 35

What is analogous to the posterior column nucleus (epicritic somesthesis) in the trigeminal nuclei?

Answer 35

Chief Sensory nucleus of V( cell bodies of second order neurons for epicritic system of head and face

Question 36

What is analogous to the DRG?

Answer 36

Mesencephalic nucleus of V

Question 37

What is analogous to the dorsal horn (especially the substantia gelatinosa?

Answer 37

Spinal nucleus

Question 38

Somatosensory afferents for the head/face have their cell bodies where?

Answer 38

In a ganglion outside of the brain know as the Trigeminal Ganglion

Question 39

Instead of the VPL, the trigeminal projects to which part of the Thalamus

Answer 39

VPM

Question 40

Somesthetic information from the body is relayed to primary somatosensory cortex via the

Answer 40

Ventral posterolateral nucleus (VPL) of the Thalamus

Question 41

Somethetic info from the face is relayed to primary somatosensory cortex via the

Answer 41

ventroposteromedial (VPM) of the thalamus

Question 42

C fibers carry what

Answer 42

They are umyelinated nerve fibers and they carry postganglionic autonomic fibers; sensory from free nerve endings for pain and temperature; smell

Question 43

Free Nerve endings sensitive to temperature and pain

Answer 43

ok

Question 44

Lets say you have a Pacinian Corpuscle sensing Epicritic Sensation (like vibration in the leg). The signal is carried by a ABeta afferent axon and travels where in the spinal cord

Answer 44

Would travel ipsilaterally in the dorsal column of the spinal cord and ascend into the ipsilateral brainstem.

Question 45

First synapse in Lemniscal pathway is where

Answer 45

Posterior colmn nuclei in the CAUDAL medulla.

• Gracilis Nucleus (medial) if these are afferents that enter in the lumbar or sacral region.
• Cuneatus nucleus if they are afferents that enter in the thoracic or cervical region

Question 46

WHere does decussation occur in the Lemniscal pathway?

Answer 46

Posterior Column nuclei in the medulla….from here, the secondary neuron runs in the contralateral medial lemniscus to the VPL

Question 47

What is the VPL

Answer 47

Ventralposterolateral nucleus- Thalamus section involved in somesthesis

Question 48

From the VPL what happens?

Answer 48

A third order neuron is sent to the primary somatosensory cortex in the postcentral gyrus. Same side as the VPL.

Question 49

Say we start with a free nerve ending sensing pain in the leg. What type of sensation pathway is this

Answer 49

Protopathic sensation so spinothalamic tract

Question 50

What type of axon is attached to free nerve endings?

Answer 50

Small, unmyelinated or lightly myelinated slowly conducting fibers (Adelta or C fibers for the most part).

Question 51

Where is the first synapse in the spinothalamic tract?

Answer 51

Ipsilateral dorsal horn of Spinal cord

Question 52

Where does the second order neuron of the spinothalamic tract then go?

Answer 52

Decussates, usually at the level of the first synapse. Then ascends in the contralateral anterolateral funiculus through the anterolateral spinal cord and through the brainstem to the VPL.

Question 53

Second synapse of spinothalamic tract

Answer 53

VPL

Question 54

Third order neuron of spinothalamic tract then projects ipsilaterally to the the VPL to the somatosensory cortex

Answer 54

ok

Question 55

Protopathic inputs synapse mostly in what layers of the ipsilateral dorsal horn?

Answer 55

Layers 1 and 5

Question 56

From medial to lateral (Gracilis to cuneatus) how are different parts of the body represented in the posterior columns

Answer 56

Gracilis from medial to lateral- Leg, lower trunk

Cuneatus- uppertrunk, arm, neck, occipitus

Cut off between input to gracilis and cuneatus = T6