4: PNS receptors and spinal cord white matter

Question 1

Where is the origin of the PSCT?

Answer 1

Clarke’s nucleus (aka Posterior thoracic nucleus) in Lamina VII; T1-L2.
p.99 BRS

Question 2

What type of information do all of the spinocerebellar tracts carry? Receptors?

Answer 2

All divisions project information about body position and motion to the cerebellum.
Receptors: Muscle spindles and Golgi tendon organs. 
#39

Question 3

What are the 1st, 2nd, and 3rd order neurons of the ALS? Termination?

Answer 3

1st: DRG
2nd: Dorsal (posterior) horn; then crosses midline in spinal cord (anterior white commissure). Ascending via posterolateral (Lissauer’s) tract.
3rd: VPL nucleus in thalamus.
Terminates in the somatosensory cortex via the internal capsule.
#64, p.106 BRS

Question 4

What does the PCML receive input from (4)?

Answer 4

Pacinian, Meissner, spindles, and Golgi tendon organs.

p.104 BRS

Question 5

At what levels does the anterior spinocerebellar (ASCT) tract exist?

Answer 5

L3 and below
#47

Question 6

Which two parts of CSF circulation are outside of the brain?

Answer 6

Subarachnoid space and arachnoid granulations.

L3a #61

Question 7

What is the upper trunk and limb equivalent of the PSCT?

Answer 7

Cuneocerebellar tract; 
#44

Question 8

Describe (1) the main receptors and (2) fibers of the ALS.

Answer 8

1.) Main receptors are FREE NERVE ENDINGS, i.e. lack specializations or CT capsule; non-specific.
-High threshold receptors (i.e. require strong stimulus for threshold/to elicit pain).
2.) Sensation conveyed via Aδ (thinly myelinated) or C unmyelinated fibers.
#53

Question 9

What is the role of the ASCT?

Answer 9

Concerned with coordinated movement and posture of the entire lower extremity.
p.109 BRS

Question 10

1. ) Where in the ventricular system is most CSF produced?

2. ) Where is it NOT produced?

Answer 10

1.) IV foramen, body and inferior horns of lateral ventricles.
-But also in the 3rd and 4th.
2.) Anterior or posterior horns.
L3a #59

Question 11

What parts of the cerebrum to the following portions of ventricle correspond to?

1. ) Anterior and posterior horn
2. ) Inferior horn

Answer 11

1. ) occipital lobe

2. ) temporal lobe

Question 12

The cuneocerebellar tract is the equivalent of _______ for incoming information _____ ________.

Answer 12

Equivalent of the PSCT for incoming information above T4. 
#45

Question 13

List the four mechanoreceptors, their receptive fields, their stimulus, and their stimulus response (i.e. phasic or tonic). Indicate if capsule or no capsule.

Answer 13

1.) Meissner’s corpuscle: Small, sharp borders. Tap, flutter. Phasic. Encapsulated.
2.) Merkel’s disc: Small, sharp borders. Touch, pressure. Tonic. No capsule.
3.) Pacinian corpuscles: Large, vague borders. Vibration. Phasic. Encapsulated.
4.) Ruffini’s ending: Large, vague borders. Skin stretch. Tonic. Encapsulated.
#9

Question 14

What are the 1st and 2nd order neurons of the ASCT? Termination?

Answer 14

1st: DRG; synapses on spinal border cells (Vidal says dorsal horn???).
2nd: Lateral (accessory) cuneate nucleus in the caudal medulla. Gives rise to axons that project IPSILATERALLY to the cerebellum via the inferior cerebellar peduncle.
#47, p.109 BRS, p238 text

Question 15

What type of fibers carry information in the PCML? What senses are carried (3).

Answer 15

SA fibers —> Stereognosis, proprioception, kinesthesia. 
#4

Question 16

What type of information does the PSCT carry?

Answer 16

Proprioception from the ipsilateral trunk and leg.
#40

Question 17

What are the 1st and 2nd order neurons for the cuneocerebellar tract? Where does it terminate?

Answer 17

1st: DRG
2nd: Lateral (accessory) cuneate nucleus in lower (caudal) medulla) NOT CLARKE’s nucleus, like the PSCT, b/c it doesn’t exist from C2-T4
Termination: Fibers arising from lateral cuneate nucleus proceed into the cerebellum via the inferior cerebellar peduncle.
#44, p.109 BRS

Question 18

Choroid plexus is where ________ is vascularized by ________.

Answer 18

where ependyma is vascularized by capillaries.

L3a #59.

Question 19

What are four methods for improving drugs crossing the BBB?

Answer 19

1.) Nanoparticle
2.) Liposomes
3.) Focused ultrasound increases permeability
4.) Metabolic precursors (e.g. L-Dopa for dopamine for treating Parkinson’s).
L3a #84

Question 20

How are ALS nociceptors different than PCML fibers?

Answer 20

ALS: Crude touch —> Conveys the general feeling of being touched. Larger receptive fields, smaller diameter fibers, slower conductance. 
#52

Question 21

Where are the 1st and 2nd order neurons for the PSCT? Where does it terminate?

Answer 21

1st: DRG
2nd: Cell in Clarke’s nucleus (Lamina VII of intermediate zone; T1-L2).
Termination: Projects ipsilaterally to the cerebellum, entering via the inferior cerebellar peduncle.
#40

Question 22

What is are the first, second, and third order neurons for the PCML? What is its final destination?

Answer 22

1st: DRG
2nd: Cuneate or gracile nuclei
3rd: VPL nuclei in thalamus
Final: 1˚ and 2˚ somatosensory cortex in the post-central gyrus.

Question 23

Where does the PCML decussate? Fibers?

Answer 23

In the lower medulla within internal arcuate fibers (as 2nd order fibers, after synapsing in gracile or cuneate nuclei). Ascends as the medial lemniscus.
p.105 BRS

Question 24

1. ) Choroid plexus is a specialized part of ________.

2. ) How is choroid plexus formed?

Answer 24

1. ) Pia mater.

2. ) Pia fuses with ependyma to form tela choroidia. When tela choroidia is vascularized, it becomes choroid pleuxus.

Question 25

1. ) What are circumventricular organs and where are they? 2.) What is their purpose?
2. ) Interestingly, all circumventricular organs are _______.

Answer 25

1.) Areas of BBB that are weak due to fenestrated capillaries; typically around the 3rd or 4th ventricle.
2.) Provide sensory and effector capabilites —> sensation of circulating substances, and facilitates release of substances of action.
3.) Midline
L3a #86