Ascending Somatosensory Systems Flashcards
Incoming information at the segmental level is referred to as what?
afferent
Outgoing information at the segmental level is referred to as what?
efferent
Are axons named in the CNS?
NO
Encapsulated nerve endings enter the dorsal root over what fibers?
Ia, Ib, II (muscle, joint)
Free nerve endings enter the dorsal root over what fibers?
A-delta and C fibers (temp, touch, itch, pain)
Ia, Ib, and II fibers enter the dorsal horn more medially or laterally?
medially
A-delta and C fibers enter the dorsal horn more medially or laterally?
laterally
The second order neuron of encapsulated nerve endings travel into the CNS over what pathway?
Dorsal column/medial lemniscus system
The second order neuron of free nerve endings travel into the CNS over what pathway?
Anterolateral system
In the dorsal column/medial lemniscus system, what does the ascending fibers travel through?
Dorsal column
In the dorsal column/medial lemniscus system, as the first order encapsulated axon enters the dorsal column, what does it do?
the axon bifurcates: one branch remains segmental and the other follows the dorsal column pathway
In the dorsal column/medial lemniscus system, the first order encapsulated axon synapses with the second order neuron where?
dorsal column nuclei of the medulla
What 2 subsets does the dorsal column divide into? What segments do they each cover?
- fasciculus cuneatus (T6–>C1)
- fasciculus gracilis (sacral–>T6)
What are the 2 nuclei included in the dorsal column nuclei of the medulla?
- medial - nucleus gracilis
- lateral - nucleus cuneatus
Does the organizational somatotopic map of incoming segmental information remain maintained throughout the pathways?
YES
nucleus gracilis receives information from what spinal segments?
sacral–>T6
nucleus cuneatus receives information from what spinal segments?
T6–>C1
In the dorsal column/medial lemniscus system, after the second order neuron synapses at the medulla, its axon then travels where?
the axon then leaves the neuron cell body and crosses the midline and travel sup the pathway known as the medial lemniscus
Encapsulated nerve endings carry what kind of information?
proprioception, vibration, and discriminative touch
In the dorsal column/medial lemniscus system, what is the end target of the second order axon (where it synapses with the cell body of the third order neuron)?
thalamus - ventralposterolateral thalamic nucleus (VPL)
In the dorsal column/medial lemniscus system, the axon of the third order neuron projects where?
primary somatosensory cortex (areas 3,1,2)
- postcentral gyrus
Once information reaches the primary somatosensory cortex, where does it go next?
association cortex
What does the primary somatosensory cortex do with the sensory information it receives?
takes in the sensory information and perceives it
What does the association cortex do with the information it receives from the primary somatosensory cortex?
the association cortex makes sense of the perceived information from the primary somatosensory cortex
Where do the first order neuron body and axon lie in relation to the initial stimulus?
ipsilateral to the initial stimulus
Where does the second order neuron body and axon lie in relation to the initial stimulus?
body - ipsilateral
axon - contralateral
Where does the third order neuron body and axon lie in relation to the initial stimulus?
contralateral to the initial stimulus
Layout of the homunculus? (in thirds)
- inferior third of postcentral gyrus = face
- middle third = upper extremity
- superior third = trunk
In the dorsal column/medial lemniscus system, what is the role of interneurons?
interneurons can change, manipulate, inhibit the ascending pathway, where the sensory information never reach the cortex
In the dorsal column/medial lemniscus system, where are interneurons found?
dorsal column nuclei synapse point or the VPL synapse point (ONLY these two places)
What sensory information does the anterolateral system (ascending pain pathway) carry?
pain and temperature information
In the anterolateral system, what neurons and fibers are involved?
- free nerve endings
- fibers A-delta and C (unmyelinated)
In the anterolateral system, where does the first order axon synapse with the cell body of the second order neuron?
the dorsal horn close to the segment they enter at
In the anterolateral system, where does the second order neuron axon cross contralaterally?
anterolateral white commissure (through the ventral part of the spinal cord)
In the anterolateral system, once the second order neuron crosses contralaterally, what tract does it ascend through?
ascends up the spinothalamic tract through the brainstem, pons and midbrain
In the anterolateral system, as the second order neuron axon ascends up the spinothalamic tract, where does it then synapse with the cell body of the third order neuron?
VPL (thalamus)
In the anterolateral system, after synapsing at the VPL, where does the third order neuron axon travel to?
primary somatosensory cortex (where the information if perceived and arranged in the homunculus)
How many pathway does the anterolateral system actually contain?
5 pathways
What happens if the pathway does NOT reach the primary somatosensory cortex?
the sensory information does NOT get perceived
Where does pain information travel from and to in the descending pain pathway?
sensory pain information travels back down from the midbrain to the dorsal horn
In the descending pain pathway, where do the interneurons lie?
interneurons are found between the first order and second order neuron
In the descending pain pathway, what does the first order axon synapse with?
interneurons
In the descending pain pathway, what is released by the interneuron after it synapses with the first order axon?
enkephalon
In the descending pain pathway, what does enkephalon do?
hyperpolarizes the second order neuron, inhibiting it, which minimizes the summation of the pain so when it travels back up to the cortex, it is perceived as not as painful as the initial stimulus; ultimately decreasing the transfer of sensory information
What is the neurotransmitter of the midbrain and dorsal horn?
seratonin
What is the neurotransmitter of interneurons?
enkephalon
Nuclei of the midbrain (where the cell body of the first order neuron of the descending pain pathway is found)?
Raphe nuclei (uses serotonin as a neurotransmitter)
What occurs in the cortex during chronic pain?
- chronic pain is a response of the CNS not being able to understand what is going on
- inhibiting the raphe nuclei of the descending pain pathway
- there is no cortex (paralyzed) to make sense of the pain; therefore, it is a constant pain
What sensory information does the trigeminal nerve provide?
nerve for facial sensation
The trigeminal has how many neuronal pathways?
3
Where does the trigeminal nerve enter the brainstem?
at the level of the pons
In the trigeminal nerve pathway for pain and touch, where does the first order axon travel and then synapse with the cell body of the second order neuron?
- the first order axon turn caudally after entering the brainstem at the level of the pons
- synapses with the spinal trigeminal nucleus which extends into the C1 spinal cord level
What are the first order neurons of the trigeminal nerve pathways?
free nerve endings
In the trigeminal nerve pathway for pain and touch, the axon of the second order neuron crosses contralaterally where?
At the spinal cord level
In the trigeminal nerve pathway for pain and touch, the axon of the second order neuron ascends towards the thalamus through what tract?
ventral trigeminothalamic tract (VTT)
In the trigeminal nerve pathway for pain and touch, where does the axon of the second order neuron synapse with the cell body of the third order neuron?
VPM
In the trigeminal nerve pathway for pain and touch, where does the axon of the third order neuron go after leaving the VPM?
primary somatosensory cortex
Incoming information of free nerve endings uses what nerve fibers?
A-delta and C fibers
What is the descending tract of the trigeminal nerve?
spinotrigeminal pathway
What is the ascending tract of the trigeminal nerve?
VTT
Are touch and proprioception represented unilaterally or bilaterally?
bilaterally
Where does the first order neuron of proprioception synapse and at what level?
the mesencephalic nucleus at the level of the mid pons and extends into the midbrain
Where does the first order neuron of discriminative touch synapse and at what level?
at the main sensory nucleus at the mid pon level
All three trigeminal pathways/systems have a second order synapse where?
axon of the second order neuron synapses with the cell body of the third order neuron at the VPM
Sensory information from where passes through fasiculus gracilis?
lower limb
Sensory information from where passes through fasiculus cuneatus?
upper limb
