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Clinical Neuroscience weeks 1-3 > Ascending Sensory Spinal Brain Pathways > Flashcards

Flashcards in Ascending Sensory Spinal Brain Pathways Deck (56):

Two main divisions of somatosensory transport are?

Protopathic- Concerns pain, temperature, crude touch

Epicritic- fine touching, texture, body position and vibration


Motoneuron cell bodies are located where in the spinal cord?

Ventral Horn


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

Via the peripheral processes of "psuedo unipolar sensory neurons"...must know


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

Outside of the spinal cord in the dorsal root ganglia


What are ganglia?

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


Know the classification of peripheral nerve fibers

pg. 49


Pacinian Corpuscle

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


Meissner's corpuscle is

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


Merkel's Disks

Slowly adapting mechanoreceptors located in skin and mucosa


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



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

realize this


What is adaptation

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


Protopathic somesthisis travels in what tract?

Spinothalamic Tract/ Anterolateral Pathways


Where does epicritic information travel in the spinal cord?

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


Pain receptors and temperature receptors are typically what?

unspecialized free nerve endings


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

small and slowly conducting


When nerve fibers decussate they are called?

Internal Arcuate fibers (they arc across the midline)


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

Posterior limb of the internal capsule


Collaterals of the proprioceptive afferents go where

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


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

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.


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?

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


Substantia gelatinosa is what

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)


Lissauer's tract is what?

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


know spinothalamic, spinoreticular, spinomesencephalic

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.


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

Medially. This is the opposite of the epicritic system


Adelta fibers of the protopathic pathways mediate what?

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


A delta fibers first synapse where SPECIFICALLY

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


What are propriospinal fibers?

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


What is the deepest layer of the dorsal horn?

Layer V


Protopahtic fibers that project into layer V do what?

Decussare and ascend


C fibers of the protopathic pathway are associated with what?

Second pain- a duller, less localizeable aspect of pain


Where do C fibers synapse

Substantia Gelatinosa


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

Trigeminal system


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

Opthalmic, Maxillary, Mandibular


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

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


What is analogous to the DRG?

Mesencephalic nucleus of V


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

Spinal nucleus


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

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


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



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

Ventral posterolateral nucleus (VPL) of the Thalamus


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

ventroposteromedial (VPM) of the thalamus


C fibers carry what

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


Free Nerve endings sensitive to temperature and pain



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

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


First synapse in Lemniscal pathway is where

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


WHere does decussation occur in the Lemniscal pathway?

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


What is the VPL

Ventralposterolateral nucleus- Thalamus section involved in somesthesis


From the VPL what happens?

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


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

Protopathic sensation so spinothalamic tract


What type of axon is attached to free nerve endings?

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


Where is the first synapse in the spinothalamic tract?

Ipsilateral dorsal horn of Spinal cord


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

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.


Second synapse of spinothalamic tract



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



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

Layers 1 and 5


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

Gracilis from medial to lateral- Leg, lower trunk

Cuneatus- uppertrunk, arm, neck, occipitus

Cut off between input to gracilis and cuneatus = T6