Geniculate Fibers

The geniculate fibers are the fibers in the region of the genu of the internal capsule; they originate in the motor part of the cerebral cortex, and, after passing downward through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the motor nuclei of the cranial nerves of the opposite side.

This article incorporates text from a public domain edition of Gray's Anatomy.

Human brain: forebrain (cerebrum, cerebral cortex, cerebral hemispheres, grey matter) (TA A14.1.09.002–240, 301–320, GA 9.818–826)
Frontal lobe
Superolateral
Prefrontal
  • Superior frontal gyrus
    • 4l
    • 6l
    • 8l
  • Middle frontal gyrus
    • 9l
    • 10l
    • 46
  • Inferior frontal gyrus: 11l
  • 47-Pars orbitalis
  • Broca's area
    • 44-Pars opercularis
    • 45-Pars triangularis
  • Superior frontal sulcus
  • Inferior frontal sulcus
Precentral
  • Precentral gyrus
  • Precentral sulcus
Medial/inferior
Prefrontal
  • Superior frontal gyrus
    • 4m
    • 6m
  • Medial frontal gyrus
    • 8m
    • 9m
  • Paraterminal gyrus/Paraolfactory area
    • 12
  • Straight gyrus
    • 11m
  • Orbital gyri/Orbitofrontal cortex
    • 10m
    • 11m
    • 12
  • Ventromedial prefrontal cortex
    • 10m
  • Subcallosal area
    • 25
  • Olfactory sulcus
  • Orbital sulci
Precentral
  • Paracentral lobule
    • 4
  • Paracentral sulcus
Both
  • Primary motor cortex
    • 4
  • Premotor cortex
    • 6
  • Supplementary motor area
    • 6
  • Frontal eye fields
    • 8
Parietal lobe
Superolateral
  • Superior parietal lobule
    • 5l
    • 7l
  • Inferior parietal lobule
    • 40-Supramarginal gyrus
    • 39-Angular gyrus
  • Parietal operculum
    • 43
  • Intraparietal sulcus
Medial/inferior
  • Paracentral lobule
    • 1m
    • 2m
    • 3m
    • 5m
  • Precuneus
    • 7m
Marginal sulcus
Both
  • Postcentral gyrus/primary somatosensory cortex
    • 1
    • 2
    • 3
  • Secondary somatosensory cortex
    • 5
  • Posterior parietal cortex
    • 7
Occipital lobe
Superolateral
  • Occipital pole of cerebrum
  • Lateral occipital gyrus
    • 18
    • 19
  • Lunate sulcus
  • Transverse occipital sulcus
Medial/inferior
  • Primary visual cortex
    • 17
  • Cuneus
  • Lingual gyrus
  • Calcarine fissure
Temporal lobe
Superolateral
  • Transverse temporal gyrus/Primary auditory cortex
    • 41
    • 42
  • Superior temporal gyrus
    • 38
    • 22/Wernicke's area
  • Middle temporal gyrus
    • 21
  • Inferior temporal gyrus
    • 20
  • Superior temporal sulcus
  • Inferior temporal sulcus
Medial/inferior
  • Fusiform gyrus
    • 37
  • Medial temporal lobe
    • 27
    • 28
    • 34
    • 35
    • 36
  • Inferior temporal sulcus
Interlobar
sulci/fissures
Superolateral
  • Central (frontal+parietal)
  • Lateral (frontal+parietal+temporal)
  • Parieto-occipital
  • Preoccipital notch
Medial/inferior
  • Medial longitudinal
  • Cingulate (frontal+cingulate)
  • Collateral (temporal+occipital)
  • Callosal sulcus
Limbic lobe
Parahippocampal gyrus
  • anterior
    • Entorhinal cortex
    • Perirhinal cortex
  • Posterior parahippocampal gyrus
  • Prepyriform area
Cingulate cortex/gyrus
  • Subgenual area
    • 25
  • Anterior cingulate
    • 24
    • 32
    • 33
  • Posterior cingulate
    • 23
    • 31
  • Isthmus of cingulate gyrus: Retrosplenial cortex
    • 26
    • 29
    • 30
Hippocampal formation
  • Hippocampal sulcus
  • Fimbria of hippocampus
  • Dentate gyrus
  • Rhinal sulcus
Other
  • Supracallosal gyrus
  • Uncus
Insular lobe
  • Long gyrus of insula
  • Short gyri of insula
  • Circular sulcus of insula
General
  • Operculum
  • Poles of cerebral hemispheres
Some categorizations are approximations, and some Brodmann areas span gyri.

M: CNS

anat (n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug (N1A/2AB/C/3/4/7A/B/C/D)
Brain and spinal cord: neural tracts and fasciculi
Sensory/
ascending
PCML

1°: Pacinian corpuscle/Meissner's corpuscle → Gracile fasciculus/Cuneate fasciculus → Gracile nucleus/Cuneate nucleus

2°: → sensory decussation/arcuate fibers (Posterior external arcuate fibers, Internal arcuate fibers) → Medial lemniscus/Trigeminal lemniscus → Thalamus (VPL, VPM)

3°: → Posterior limb of internal capsule → Postcentral gyrus
Anterolateral/
pain
Fast/lateral

1° (Free nerve ending → A delta fiber) → 2° (Anterior white commissure → Lateral and Anterior Spinothalamic tract → Spinal lemniscus → VPL of Thalamus) → 3° (Postcentral gyrus) → 4° (Posterior parietal cortex)

2° (Spinotectal tract → Superior colliculus of Midbrain tectum)
Slow/medial 1° (Group C nerve fiber → Spinoreticular tract → Reticular formation) → 2° (MD of Thalamus) → 3° (Cingulate cortex)
Motor/
descending
Pyramidal flexion: Primary motor cortex → Posterior limb of internal capsule → Decussation of pyramids → Corticospinal tract (Lateral, Anterior) → Neuromuscular junction
Extrapyramidal

flexion: Primary motor cortex → Genu of internal capsule → Corticobulbar tract → Facial motor nucleus → Facial muscles

flexion: Red nucleus → Rubrospinal tract

extension: Vestibulocerebellum → Vestibular nuclei → Vestibulospinal tract

extension: Vestibulocerebellum → Reticular formation → Reticulospinal tract

Midbrain tectum → Tectospinal tract → muscles of neck
Basal ganglia

direct: 1° (Motor cortex → Striatum) → 2° (GPi) → 3° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 4° (Thalamocortical radiations → Supplementary motor area) → 5° (Motor cortex)

indirect: 1° (Motor cortex → Striatum) → 2° (GPe) → 3° (Subthalamic fasciculus → Subthalamic nucleus) → 4° (Subthalamic fasciculus → GPi) → 5° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 6° (Thalamocortical radiations → Supplementary motor area) → 7° (Motor cortex)

nigrostriatal pathway: Pars compacta → Striatum
Cerebellar
Afferent

Vestibular nucleus → Vestibulocerebellar tract → ICP → Cerebellum → Granule cell

Pontine nuclei → Pontocerebellar fibers → MCP → Deep cerebellar nuclei → Granule cell

Inferior olivary nucleus → Olivocerebellar tract → ICP → Hemisphere → Purkinje cell → Deep cerebellar nuclei
Efferent

Dentate nucleus in Lateral hemisphere/pontocerebellum → SCP → Dentatothalamic tract → Thalamus (VL) → Motor cortex

Interposed nucleus in Intermediate hemisphere/spinocerebellum → SCP → Reticular formation, or → Cerebellothalamic tract → Red nucleus → Thalamus (VL) → Motor cortex

Fastigial nucleus in Flocculonodular lobe/vestibulocerebellum → Vestibulocerebellar tract → Vestibular nucleus
Bidirectional:
Spinocerebellar
Unc. prop.

lower limb → 1° (muscle spindles → DRG) → 2° (Posterior thoracic nucleus → Dorsal/posterior spinocerebellar tract → ICP → Cerebellar vermis)

upper limb → 1° (muscle spindles → DRG) → 2° (Accessory cuneate nucleus → Cuneocerebellar tract → ICP → Anterior lobe of cerebellum)
Reflex arc

lower limb → 1° (Golgi tendon organ) → 2° (Ventral/anterior spinocerebellar tract→ SCP → Cerebellar vermis)

upper limb → 1° (Golgi tendon organ) → 2° (Rostral spinocerebellar tract → ICP → Cerebellum)

M: CNS

anat (n/s/m/p/4/e/b/d/c/a/f/l/g)/phys/devp

noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr

proc, drug (N1A/2AB/C/3/4/7A/B/C/D)

M: PNS

anat (h/r/t/c/b/l/s/a)/phys (r)/devp/prot/nttr/nttm/ntrp

noco/auto/cong/tumr, sysi/epon, injr

proc, drug (N1B)