A neural pathway, neural tract, or neural face, connects one part of the nervous system with another via a bundle of axons, the long fibers of neurons. A neural pathway that serves to connect relatively distant areas of the brain or nervous system is usually a bundle of neurons, known collectively as white matter. A neural pathway that spans a shorter distance between structures, such as most of the pathways of the major neurotransmitter systems, is usually called grey matter.
Contents
- 1 Naming of neural pathways
- 2 Functional aspects
- 3 Major neural pathways
- 4 References
Naming of neural pathways
The first named pathways are evident to the naked eye even in a poorly preserved brain, and were named by the great anatomists of the Renaissance using cadaver material. Examples of these include the great commissures of the brain such as the corpus callosum (Latin, "hard body"; not to be confused with the Latin word "colossus" - the "huge" statue), anterior commissure, and posterior commissure. Further examples of this (by no means a complete list) include the pyramidal tract, crus cerebri (Latin, "leg of the brain"), and cerebellar peduncles (Latin, "little foot of the cerebellum"). Note that these names describe the appearance of a structure but give one no information on its function or location.
Later, as neuroanatomical knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination. For example, the nigrostriatal pathway, which is degenerated in Parkinson's disease, runs from the substantia nigra (Latin, "black substance") to the corpus striatum (Latin, "striped body"). This naming can extend to include any number of structures in a pathway, such that the cerebellorubrothalamocortical pathway originates in the cerebellum, synapses in the red nucleus ("ruber" in Latin), on to the thalamus, and finally terminating in the cerebral cortex.
Sometimes, these two naming conventions coexist. For example, the name "pyramidal tract" has been mainly supplanted by lateral corticospinal tract in most texts. Note that the "old" name was primarily descriptive, evoking the pyramids of antiquity, from the appearance of this neural pathway in the medulla oblongata. The "new" name is based primarily on its origin (in the primary motor cortex, Brodmann area 4) and termination (onto the alpha motor neurons of the spinal cord).
Functional aspects
In general, neurons receive information either at their dendrites or cell bodies. The axon of a nerve cell is, in general, responsible for transmitting information over a relatively long distance. Therefore, most neural pathways are made up of axons. the pathway will appear a darker beige color, which is generally called grey (British English, or gray in American English).
Some neurons are responsible for conveying information over long distances. For example, motor neurons, which travel from the spinal cord to the muscle, can have axons up to a meter in length in humans; the longest axon in the human body is almost two meters long in tall individuals and runs from the great toe to the medulla oblongata of the brainstem. These are archetypical examples of neural pathways.
Major neural pathways
- Arcuate fasciculus
- Cerebral peduncle
- Corpus callosum
- Pyramidal or corticospinal tract
Dopamine pathways:
- Mesocortical pathway
- Mesolimbic pathway.
- Nigrostriatal pathway
- Tuberoinfundibular pathway
References
- Haines DE. Neuroanatomy: An Atlas of Structures, Sections, and Systems ISBN 0-7817-3736-2.
Brain and spinal cord: neural tracts and fasciculi
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Sensory/
ascending |
PCML |
1°: |
- Pacinian corpuscle/Meissner's corpuscle → Posterior column (Gracile fasciculus/Cuneate fasciculus) → Gracile nucleus/Cuneate nucleus
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2°: |
- → sensory decussation/arcuate fibers (Posterior external arcuate fibers, Internal arcuate fibers) → Medial lemniscus/Trigeminal lemniscus → Thalamus (VPL, VPM)
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3°: |
- → Posterior limb of internal capsule → Postcentral gyrus
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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° (Spinomesencephalic tract → Superior colliculus of Midbrain tectum)
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Slow/medial |
- 1° (Group C nerve fiber → Spinoreticular tract → Reticular formation) → 2° (MD of Thalamus) → 3° (Cingulate cortex)
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Motor/
descending |
Pyramidal |
- flexion: Primary motor cortex → Posterior limb of internal capsule → Decussation of pyramids → Corticospinal tract (Lateral, Anterior) → Neuromuscular junction
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Extrapyramidal |
flexion: |
- Primary motor cortex → Genu of internal capsule → Corticobulbar tract → Facial motor nucleus → Facial muscles
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flexion: |
- Red nucleus → Rubrospinal tract
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extension: |
- Vestibulocerebellum → Vestibular nuclei → Vestibulospinal tract
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extension: |
- Vestibulocerebellum → Reticular formation → Reticulospinal tract
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- Midbrain tectum → Tectospinal tract → muscles of neck
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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)
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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)
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nigrostriatal pathway: |
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Cerebellar |
Afferent |
- Vestibular nuclei → 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
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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 nuclei
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Bidirectional:
Spinocerebellar |
Unconscious
proprioception |
- 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)
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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)
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Index of the central nervous system
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Description |
- Anatomy
- meninges
- cortex
- association fibers
- commissural fibers
- lateral ventricles
- basal ganglia
- diencephalon
- mesencephalon
- pons
- cerebellum
- medulla
- spinal cord
- Physiology
- Development
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Disease |
- Addiction
- Cerebral palsy
- Meningitis
- Demyelinating diseases
- Seizures and epilepsy
- Headache
- Stroke
- Sleep
- Congenital
- Injury
- Neoplasms and cancer
- Other
- Symptoms and signs
- head and neck
- eponymous
- lesions
- Tests
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Treatment |
- Procedures
- Drugs
- general anesthetics
- analgesics
- dependence
- epilepsy
- cholinergics
- migraine
- Parkinson's
- vertigo
- other
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Neuroanatomy of eye movements
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Visual perception |
- 1° (Retina bipolar cell) → 2° (Ganglionic cell) → 3° (Optic nerve → Optic chiasm → Optic tract → LGN of Thalamus) → 4° (Optic radiation → Cuneus and Lingual gyrus of Visual cortex → Blobs → Globs)
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Muscles of orbit |
Tracking |
Smooth pursuit: |
- Parietal lobe
- Occipital lobe
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Saccade: |
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- Nystagmus → Fixation reflex → PPRF
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Horizontal gaze |
- PPRF → Abducens nucleus → MLF → Oculomotor nucleus → Medial rectus muscle
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Vertical gaze |
- Rostral interstitial nucleus → Oculomotor nucleus, Trochlear nucleus → Muscles of orbit
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Vestibulo–ocular reflex |
- Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Abducens nucleus → MLF (Vestibulo-oculomotor fibers) → Oculomotor nucleus → Medial rectus muscle
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Pupillary reflex |
Pupillary response |
- 1° (Posterior hypothalamus → Ciliospinal center) → 2° (Superior cervical ganglion) → 3° (Sympathetic root of ciliary ganglion → Nasociliary nerve → Long ciliary nerves → Iris dilator muscle)
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Pupillary light reflex
(constriction) |
- 1° (Retina → Optic nerve → Optic chiasm → Optic tract → Pretectal nucleus) → 2° (Edinger–Westphal nucleus) → 3° (Oculomotor nerve → Parasympathetic root of ciliary ganglion → Ciliary ganglion) → (4° Short ciliary nerves → Iris sphincter muscle)
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Accommodation
vergence |
- 1° (Retina → Optic nerve → Optic chiasm → Optic tract → Visual cortex → Brodmann area 19 → Pretectal area) → 2° (Edinger–Westphal nucleus) → 3° (Short ciliary nerves → Ciliary ganglion → Ciliary muscle)
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Circadian rhythm |
- Retina → Retinohypothalamic tract → Hypothalamus (Suprachiasmatic nucleus)
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Index of the eye
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Description |
- Anatomy
- Physiology
- Phenomena
- appearance
- visual
- optical illusions
- proteins
- Development
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Disease |
- Congenital
- Corneal dystrophy
- Neoplasms and cancer
- Other
- Symptoms and signs
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Treatment |
- Procedures
- Drugs
- infection
- glaucoma and miosis
- mydriatics
- vascular
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Physiology of balance and hearing
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Hearing |
General
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- Auditory system
- Bone conduction
- Otoacoustic emission
- Tullio phenomenon
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Pathway
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- inner ear: Hair cells → Spiral ganglion → Cochlear nerve VIII →
- pons: Cochlear nucleus (Anterior, Dorsal) → Trapezoid body → Superior olivary nuclei →
- midbrain: Lateral lemniscus → Inferior colliculi →
- thalamus: Medial geniculate nuclei →
- cerebrum: Acoustic radiation → Primary auditory cortex
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Balance |
General
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Pathway
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- inner ear: Vestibular nerve VIII →
- pons: Vestibular nuclei (Medial vestibular nucleus, Lateral vestibular nucleus)
- cerebellum: Flocculonodular lobe
- spinal cord: Vestibulospinal tract (Medial vestibulospinal tract, Lateral vestibulospinal tract)
- thalamus: Ventral posterolateral nucleus
- cerebrum: Vestibular cortex
- Vestibulo-oculomotor fibers
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Index of the ear
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Description |
- Anatomy
- Physiology
- Development
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Disease |
- Congenital
- Other
- Symptoms and signs
- Tests
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Treatment |
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Papez circuit pathway
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Diencephalon |
- Mammillary body → Mammillothalamic tract → Anterior nuclei of thalamus →
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Telencephalon |
- Anterior limb of internal capsule → Cingulate gyrus → Cingulum → Parahippocampal gyrus → Entorhinal cortex → Perforant path → Hippocampus/Hippocampal formation (CA3 → CA1 → Subiculum) → Fornix →
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Index of the central nervous system
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Description |
- Anatomy
- meninges
- cortex
- association fibers
- commissural fibers
- lateral ventricles
- basal ganglia
- diencephalon
- mesencephalon
- pons
- cerebellum
- medulla
- spinal cord
- Physiology
- Development
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Disease |
- Addiction
- Cerebral palsy
- Meningitis
- Demyelinating diseases
- Seizures and epilepsy
- Headache
- Stroke
- Sleep
- Congenital
- Injury
- Neoplasms and cancer
- Other
- Symptoms and signs
- head and neck
- eponymous
- lesions
- Tests
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|
Treatment |
- Procedures
- Drugs
- general anesthetics
- analgesics
- dependence
- epilepsy
- cholinergics
- migraine
- Parkinson's
- vertigo
- other
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