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What is the purpose of the somatosensory system?
To bring in environmental stimulus to the nervous system for understanding, awareness, and response formation
What are the three types of somatosensory information received at the superficial level?
What is the difference between fine touch and course touch?
- Fine touch: sensitive to light touch and vibration
- Coarse touch: mostly pressure, or sensation of tickle or itch
What is the somatosensory information received by the musculoskeletal system?
Proprioception: sensation of movement and static position
What are the two types of proprioception?
conscious and unconscious
What are 3 different pathways in the brain (in a broad sense)?
- conscious relay pathways: discriminative touch, pain, and temperature, conscious proprioception
- divergent pathways: non-descriptive and temperature (achey and sore)
- unconscious relay pathways: unconscious proprioception
What are the three treacts that carry conscious, disrciminitive info?
- anterolateral (neospinaothalamic) tract
- dorsal column/medial leminiscal tract
- trigeminal tract
What are the two main divergent pathways?
- anterolateral system
- trigeminoreticulothalamic system
What are the three tracts of the non-discriminative anterolateral system?
Where does the first order neuron cell body lie and where does it terminate in the dorsal column/medial leminisus?
- CB location: dorsal root ganglion
- Terminates: nucleus gracilis and nucleus cuneatus
Where does the 3rd order neuron lie and terminate in the dorsal column/medial leminiscus?
- Starts: ventral posterolateral nucleus of the thalamus
- Terminates: post central gyri of the cortex
Which neurons in the conscious pathways lie in the CNS/PNS?
- 1st order neuron: PNS (dorsal root, CN ganglion)
- 2nd order neuron: CNS (SC or brainstem nucleus)
- 3rd order neuron: CNS (thalamus)
Which neurons in the divergent and unconscious pathways are in the CNS/PNS?
- 1st order neuron: PNS (dorsal root, CN ganglion)
- 2nd order neuron: CNS (SC or brainstem nucleus)
- 3rd order neuron: CNS (may or may not exist- brainstem or cerebellum)
Summarize the Dorsal Column/Medial Lemniscus Pathway:
Nuerons start in the dorsal root ganglion and ascend in the ipsilateral dorsal column. The lower limbs axons are occupied in the fasiculus gracilis and the upper limb axons are occupied in the fasiculus cuneatus, then terminate in the nucleus gracilis and nucleus cuneatus. There the 2nd order neuron cross the midline at the level of the pons (= sensory dessication) and ascends to the medial leminiscus through the upper medulla, pons and midbrain to the VPL. The 3rd order neuron arises from VPL to the post central gyri of the cortex.
What are the 3 divisions of the trigeminal nerve that carry sensory information to the face?
Where does the first order nucleus originate and terminate itn the trigeminothalamic pathway that carry sensory info?
- originate: trigeminal ganglion
- terminate: chief sensory nucleus
Where does the third order nucleus originate and terminate itn the trigeminothalamic pathway that carries sensory info?
- Originate: VPM
- Terminate: post central gyri of the cortex
In conscious pathways what will lesions to the first order neurons cause?
problems on ipsilateral side
Where will sensational loss be exhibited if there is a lesion to the second order neuron (or medial leminiscus) of conscious pathways?
loss of sensation to contralateral side
In conscious pathways what happens when a lesion occurs above the pons?
deficit in face on contralateral side
Summarize the trigeminothalamic pathway that carries sensory info from the face in the conscious pathway:
The first order neuron originates in the trigeminal ganglion and enters the pons and terminates in the nucleus of pons, aka the chief sensory nucleus. There the first order neuron terminates and the the 2nd order neuron originates and crosses the midline at the level of the pons and ascends up to the thalamus ending in the VPM where the 3rd order neuron orignates and ascends up to the cerebral cortex to the post central gyri.
What does the Homonculus figure show?
where the different areas of the dorsal column/medial lemniscus pathway and the trigiminothalamic pathway terminate
Is fast pain or slow pain somatopically organized?
fast pain- that's why someone can pinpoint fast pain
What are the names of the fibers that carry fast pain?
A-delta fibers: small diameter, and myelinated
Which pathways carry A-Delta fibers?
- Neospinothalamic Pathway (anterolateral)
- Trigeminothalamic Pathway
(fast pain pathways- they are small in diameter and myelinated)
What is the difference between the axon movement and crossing of the medial lemniscus pathway comopared to the neospinothalamic pathway?
- Medial Lemniscus:
- axons of the primary neurons ascend ipsilaterally
- crosses midline at the level of the brainstem (pons)
- ascending axons are secondary neurons and are ascending contralaterally
- crosses midline at the level of the spinal cord (ventral white commissure) before the axons ascend
Where does the first order neuron originate and terminate in the Neospinothalamic pathway of the conscious system?
- originate: dorsal root ganglion
- termination: dorsal horn
Where does the third order neuron originate and terminate in the Neospinothalamic pathway of the conscious system?
- originate: VPL of thalamus
- termination: post central gyri of cortex
Summarize the Neospinothalamic pathway of the conscious system:
The 1st order neuron orignates in the dorsal root ganglion and enters into Lissauers tract and out into the dorsal horn where it terminates and the 2nd order neuron originates. There is crosses the midline in the ventral white commissure (at the level of the spinal cord) and ascends into the anterolater part of the spinal cord to the VPL of the thalamus. From there the 3rd order neuron travels up to the post central gyri of the cortex.
Where does the first order neuron originate and terminate in the trigeminothalamic pathway that senses fast pain in the face?
- originate: trigeminal ganglion
- terminate: spinal trigeminal nucleus
Where does the third order neuron originate and terminate in the trigeminothalamic pathway that senses fast pain in the face?
- originate: VPM
- terminate: Post central gyri of cortex
Summarize the fast pain pathway of the face (trigeminothalamic pathway):
The first order neuron orginates in the trigeminal ganglion and goes to the pons where is descentes to the nucleus in the upper and lower medulla called the spinal trigeminal nucleus. There the 2nd order neuron orignates and crosses the midline at the level of the medula and ascends to the VPM where the 3rd order neuron arises and ascends into the post central gyri of the cortex.
What pathway uses Lissauer's Tract?
- Neospinothalamic Pathway of the anterolateral system
- (this may or may not be right, i'm still confused about Lissauer's tract)
Which fibers are myelinated A-Delta or C fibers?
A-Delta fibers are myelinated
What do all of the conscious pathways have in common?
they terminate in the post central gyri
What are the three different tracts of the Anterolateral system of the divergent pathway?
What kind of pain does the spinoreticular pathway associate with and where do the 2nd order neurons terminate?
- part of pain that make you feel sick to your stomach- effects BP and HR
- reticular formation
What does the spinomesencephalic pathway associate with in terms of pain and where do the 2nd order neurons terminate?
- helps direct your eyes to your pain
In the pain process where does the paleospinothalamic pathway kick in and where does the 3rd order nucleus terminate?
- "bitchy" center- affective response
- 3rd order neurons go from intralaminar nuclei --> all throughout the cortex (except the post central gyri)
What is Lissauer's Tract continous as in the spinal cord?
spinal trigeminal tract
What is the only tract of the anterolateral system of the divergent pathway that has 3rd order neurons?
Summarize the pathway of the anterolateral system of the divergent system:
The first order neurons begin in the dorsal root ganglion. The second order neurons cross the midline in the ventral white commissure and ascend into the anterolateral part of the spinal cord up to the brain stem. There the neurons terminate in the reticular formation (spinoreticular), midbrain (spinomesencephalic), or the intralaminar nuclei (paleospinothalamic). The 2nd order neurons that terminate in the intralaminar nuclei then have 3rd order neurons that spread throughout the cerebral cortex (except the post central gyri)
What is the key for the anterolateral system?
where the 2nd neuron goes...
- (all lead to different places)
What are the 1st order neurons of the divergent system classified as?
C fiber- smaller diameter, unmyelinated, so have slow, throbbing pain that you can't pinpoint
What does the trigeminoreticulothalamic pathway carry?
- slow pain from the face
- C fibers
Summarize the trigeminoreticulothalamic pathway:
The cell bodies of the first order neurons lie in the trigeminal ganglion they then descend to the spinal trigeminal pathway in the medulla (the same as the discimitive pathway) and then terminate in the spinal trigeminal nucleus. The 2nd order neurons cross the midline at the level of the medulla and ascend as part of the anterolateral part of the spinal cord. The neurons then go to the reticular formation, mesencephalon, or the intralaminar nuclei. If they go to the intralaminar nuclei, 3rd order neurons then spread throughout the cerebral cortex
What are the two high fidelity pathways and which correspond to the upper/lower limbs?
- Dorsal spinocerebellar tract: lower limbs
- cuneocerebellar tract: upper limbs
What are the two internal feedback pathways and which corresspond to the upper/lower limbs?
- Ventral spinocerebellar tract: lower limbs
- Rostral spinocerebellar tract: upper limbs
List what you know about crossing the midline in high fidelity pathways and internal feedback pathways:
- both are ipsilateral pathways, meaning they end on the same side they started
- the dorsal pathways do NOT cross the midline
- the ventral pathways DOUBLE cross the midline
What are the functions of the spinocerebellar tracts?
- unconscious alteration of movement and posture
- compared intended motor output with actual output
- cerebellum acts as comparator
What is the brown sequard syndrome?
- spinal cord hemisection
- affects anterolateral and DC/ML system
In brown sequard syndrome what happens on the ipsilateral and contralateral side of the injury?
- Ipsilateral side of injury: lose conscious proprioception and discriminative touch (because 1st order neurons ascend ipsilaterally)
- Contralateral side of injury: lose pain and temp 1-2 segments below (occur 1-2 segments below because ascend or descent before entering Lissauers (?))
Summarize the dorsal spinocerebellar tract:
First order neuron travels into the dorsal column heading toward the thoracic or upper lumbar spinal cord. It terminates in the dorsal gray matter, Clark's column (C8-L2). It then extends vertically from T1-S2 and the 2nd order neurons form the posterior spinocerebellar tract. It projects through th cerebellum, entering through the inferior cerebellar peduncle.
Summarize the ventral spinocerebellar tract:
Cell bodies start in the lateral and ventral horns (where there is an abundance of interneurons). The axons then cross the midline through the ventral white commissure and ascend to the lateral funiculus in the contralateral anterior spinocerebral tract. The 2nd order neurons then enter the cerebellum through the superior cerebellar peduncle and crosses over before reaching the cerebellum.
What are the two main spinocerebellar tracts?
- Dorsal spinocerebellar tract
- Ventral spinocereberllar tract
(both are for the lower limb)
Which of the spinocerebellar tracts cross the midline?
- The ventral spinocerebellar tract of the internal feedback pathway DOUBLE CROSSES.
- The dorsal spinocerebellar tract does NOT cross the midline.
How do the axons from the ventral spinocerebellar tract enter the cerebellum?
through the superior cerebellar peduncle
How do axons from the dorsal spinocerebellar tract enter the cerebellum?
through the inferior cerebellar peduncle.
What are the two tracts from the high fidelity pathways and the internal feedback system that carry information to from the upper limbs?
- Cuneocerebellar (dorsal)
- Rostral spinocerebellar (ventral)
What fiber types carry nocioceptive and temperature information?
- A-Delta (fast pain)
- C fibers (slow pain)
Where do all the conscious pathways end?
Where do all the unconscious pathways end?
- Conscious: post central gyri of the thalamus
- Unconscious: cerebellum
What tracts relay unconscious proprioceptive information to the cerebellum?
Dorsal spinocerebellar and cuneocerebellar
What tracts provide unconscious info about activity in spinal interneurons and descending motor commands?
Ventral spinocerebellar and rostral spinocerebellar
What pathway delivers discriminitive touch and conscious proprioception information?
dorsal column/medial lemniscus
What pathway delivers discriminitive pain and temperature?
neospinothalamic (fast pain)
What pathways deliver slow-aching, non-discriminitive pain?
What type of touch can the anterolateral conscious pathway transmit?
(which conveys less info than the touch transmitted by the Dorsal column/medial lemniscus system)