Neuro Pathways



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Neuro Pathways



Pain/temperature:

Body: Lissauer’s tract  substantia gelatinosa  contralateral spinothalamic tract  VPL  posterior internal capsule  postcentral gyrus
Head: trigeminal n.  spinal trigeminal tract  spinal trigeminal nucleus  contralateral spinothalamic tract  VPM  posterior internal capsule  postcentral gyrus


  • Note: The homunculus of the facial tract has the midline structures in the superior brainstem with lateral in the inferior brainstem; it also has the superior (V1) structures in the anterior tract and the inferior (V3) in the posterior tract.


Touch/position:

Arm: fasciculus cuneatus  nucleus cuneatus  contralateral medial lemniscus  VPL  posterior internal capsule  postcentral gyrus
Leg: fasciculus gracilis  nucleus gracilis  contralateral medial lemniscus  VPL  posterior internal capsule  postcentral gyrus
Face: trigeminal n.  main sensory nucleus  contralateral medial lemniscus  VPL  posterior internal capsule  postcentral gyrus
Visual:

retina  optic n.  optic chiasm  bilateral optic tract  LGN

 retrolenticular/sublenticular internal capsule  occipital lobe

 superior brachium  pretectal area  (posterior commisure)  Edinger-Westphal nucleus  eye muscles


Oculomotor:

Saccades: frontal eye field  (superior colliculus)  contralateral PPRF  abducens nucleus

 abducens n.  lateral rectus (ends contralaterally)

 contralateral MLF  oculomotor nucleus  oculomotor n.  medial rectus (ends ipsilaterally)
Pursuit: frontal eye field and visual association cortex  pontine nucleus  contralateral flocculus  vestibular nuclei  contralateral abducens nucleus

 abducens n.  lateral rectus (ends ipsilaterally)

 contralateral MLF  oculomotor nucleus  oculomotor n.  medial rectus (ends contralaterally)

Olfactory:

olfactory n. bundles  olfactory bulb  uncus/amygdala



  • Note: This pathway doesn’t relay in the thalamus or cross the midline


Gustatory:

taste buds  solitary tract  nucleus of the solitary tract  anterior insula



  • Note: This pathway doesn’t relay in the thalamus or cross the midline


Vestibular:

vestibulocochlear n.  vestibular nuclei

 medial vestibulospinal tract (in MLF)  head posture

 lateral vestibulospinal tract (in MLF)  body posture

 oculomotor pathway

 inferior cerebellar peduncle  flocculonodular lobe

 thalamus  cortex (regions not specified)
Motor output:

precentral gyrus  posterior internal capsule  cerebral peduncle  basal pons  pyramid  pyramidal decussation  contralateral corticospinal tract  lower motor neuron  ventral root  output


Basal ganglia (speed of movement, involuntary and abnormal postures):

(Direct pathway):

cortex  (glutamate +)

compact substantia nigra  (dopamine, D1 receptors +)

striatum (caudate, nucleus accumbens, putamen)(GABA -)

 globus pallidus internal segment
(Indirect pathway):

compact substantia nigra  (dopamine, D2 receptors +)

globus pallidus external segment  (+)

 subthalamic nucleus  (+)

 globus pallidus internal segment
globus pallidus internal segment (also reticular substantia nigra) (GABA -)  ansa lenticularis, lenticular fasciculus  VA/VL  (glutamate +)  posterior internal capsule  precentral gyrus, premotor cortex (voluntary movement planning), supplementary motor areas (complex, self-paced movements)
Cerebellum (uncoordinated ataxia, tremor, dysmetria):

Intermediate: cortex, periphery  interposed nuclei 

 superior cerebellar peduncle  red nucleus  spinal cord

 VA/VL  posterior internal capsule  precentral gyrus, premotor cortex, supplementary motor areas
Lateral: cortex

 inferior olive  inferior cerebellar peduncle

 pons  middle cerebellar peduncle

dentate nucleus

 red nucleus  inferior olive  inferior cerebellar peduncle loop back to dentate nucleus

 superior cerebellar peduncle  VA/VL  posterior internal capsule  precentral gyrus, premotor cortex, supplementary motor areas


Vermis: spinocerebellar input  fastigial nucleus

 vestibular nuclei

 reticular formation
Hypothalamus:

Temperature: preoptic/anterior sensitive to high temperatures  cooling

posterior sensitive to low temperature  heating


Osmotic thirst: preoptic/anterior (OVLT)  anterior pituitary (supraoptic, paraventricular)

Volumetric thirst: serum angiotensin  SFO
Eating: high fat, high glucose

 inhibit LH

 excite VMH (energy regulator)

stop eating

low fat, low glucose

 excite LH

 inhibit VMH

 eat
Hippocampus:



Papez circuit: hippocampus

 fornix  mammilary bodies  mammilothalamic tract → anterior nucleus  cingulate, parahippocampal gyri  loop back to hippocampus

 fornix → hypothalamus  prefrontal cortex  association cortex  loop back to hippocampus

 amygdala  septal areas and loop back to hippocampus



Amygdala:

amygdala

 stria terminalis  hypothalamus, septal area

 amygdalofugal

DM thalamus

 brainstem

 cingulate, parahippocampal gyri
Sleep:

rostral medulla/caudal pons reticular formation  inhibits ARAS  causes sleep

tubermammilary nucleus  (histamine)  REM sleep


  • Note: the preoptic/anterior hypothalamus blocks histamine


Pain modulation:

pain afferent  periaqueductal grey  nucleus Raphe magnus  output


Micturition:

Storage: T11-L2  inhibit parasympathetic  detrusor relaxation

S2 (Onuf’s nucleus)  stimulates sphincter


Elimination: detrusor stretch  pontine micturition center

 S2-S4  stimulates parasympathetic  detrusor constriction

 inhibition of S2 (Onuf’s nucleus)  relaxes sphincter
Neuro Reflex Arcs
Stretch: afferent → dorsal root → spinal cord → ventral root → efferent

Flexor: stretch reflex ascending/descending to multiple levels
Near/light: light on retina → optic n. → optic chiasm → optic tract → LGN → superior brachium  pretectal area  (posterior commisure)  Edinger-Westphal nucleus → MLF → oculomotor n.

→ ciliary ganglion → short ciliary n. → ciliary contraction/papillary sphincter contraction



→ medial recti muscle contraction
Dark: hypothalamus → intermediolateral cell column → superior cervical ganglion → dilator contraction
Blink: cornea touch → spinal trigeminal nucleus → bilateral facial motor nuclei → orbicularis oculi
Vestibuloocular: vestibular n. → vestibular nuclei → abducens nucleus → eye muscles
Vesicovesical: detrusor stretch → S2-S4 → parasympathetic stimulation → detrusor contraction


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