Ascending Sensory Spinal Brain Pathways Flashcards
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)
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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
VPM
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
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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
VPL
Third order neuron of spinothalamic tract then projects ipsilaterally to the the VPL to the somatosensory cortex
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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
