-
dorsal column-medial lemniscal system
- ascending: fine touch, position sense
- Cell bodies in DRG -> dorsal horn -> dorsal columns
- lower limbs/trunk: gracilis fasciculus
- upper limbs/trunk: cuneate fasciculus
- internal arcuate fibers, cross @ decussation of the medial lemniscus
- synapse @ ventral posterior lateral (VPL) nucleus of thalamus
- fibers go to primary somatosensory cortex of parietal lobe via posterior limb of internal capsule
-
pathway of fine touch, proprioception from face
- processed in brain stem, not spinal cord
- afferents from skin have cell bodies in trigeminal ganglion
- trigeminal nerve -> synapse in sensory/principal nucleus of the trigeminal complex in the pons
- Decussation in pons, join trigeminothalamic tract (adj to medial lemniscus) -> synapse on ventral posterior medial (VPM) nucleus of thalamus
-
anterolateral system
- pain, temperature, coarse touch
- cell bodies in DRG -> dorsal roots -> may ascend/descend 2-3 segments in Lissauer's tract (dorsolateral) before going deeper & synapsing in dorsal horn
- Axons cross midline in anterior white commissure -> spinothalamic/anterolateral tract on contralateral side
- dorsolateral to medial lemniscus
- synapse in ventral posterior lateral (VPL) nucleus of thalamus
- project to primary somatosensory cortex
-
pathway of pain, temp, coarse touch from face
- cell bodies in trigeminal ganglion & ganglia assoc. w/ VII, IX, X
- Run w/those nerves into brainstem
- Descend in spinal trigeminal tract -> synapse in spinal nucleus of the trigeminal complex (pas caudalis) in medulla
- Decussate in medulla, join anterolateral tract
- synapse in ventral posterior medial (VPM) nucleus of the thalamus
-
corticospinal path
- descending motor pathway, lateral
- Primarily area 4 in cerebral cortex -> internal capsule -> central basis pedunculi -> diverge in basis pontis -> converge in pyramid of ventral medulla
- Decussation of pyramids: fibers cross -> more dorsolateral
- @ target level, synapse onto motorneurons or interneurons in ventral horn
- 85% cross, 15% do not
-
corticospinal path function
- necessary for skilled movements of digits
- voluntary, goal-directed movements
- facilitatory effects on flexor muscles
-
upper motor neuron syndrome
- damage of multiple descending paths
- eg - stroke, multiple sclerosis
- paralysis
- hyperreflexia, hypertonia (spasticity)
- minimal/disuse atrophy
- Babinski sign, extensor plantar response
-
lower motor neuron syndrome
- direct damage to alpha motor neurons innervating skeletal muscle
- paralysis
- hyporeflexia, hypotonia
- atrophy
- fibrillations, fasciculations
-
spasticity
- hyperreflexia
- hypertonia: increased resistance to passive stretch, velocity dependent
- clasp-knife lengthening rxn
- clonus: rhythmic, alternating contractions
-
pathway of CSF
- choroid plexus
- out of lateral ventricle thru foramen of Monro (interventricular)
- into third ventricle
- cerebral aqueduct to fourth ventricle
- out midline of 4th ventricle thru foramen of Magendie, out lateral sides thru foramina of Luschka
- eventually reabsorbed thru arachnoid villi
-
cisterns
- cisterna magna: between medulla and cerebellum
- interpedunclar cistern: between cerebral peduncles
- superior or quadrigeminal cistern: surrounds dorsal and lateral surface of midbrain
-
pathway of blood thru brain
- vertebral artery joins basilar artery which gives off:
- posterior inferior cerebellar artery (PICA)
- anterior inferior cerebellar artery (AICA)
- superior cerebellar artery
- 2 posterior cerebral arteries
- internal carotid gives off:
- anterior cerebral artery (into longitudinal fissure), connected by anterior communicating artery
- posterior communicating artery, which connects w/ posterior cerebral artery
-
corticobulbar fibers
- descending inputs into motor cranial nerve nuclei
- upper part of face receives bilateral innervation, lower is contralateral
- contralateral lesions can produce mild/transitory weakness
- fibers cross at level of facial nucleus
-
oculomotor nucleus
ptosis, diplopia
-
trochlear nucleus
diplopia, affected eye appears slightly elevated @ rest
-
abducens (VI) nucleus
- damage to nerve: medial deviation
- damage to nucleus: cannot move contralateral eye medially when the other eye moves laterally, internuclear neurons not able to coordinate
- MLF: medial longitudinal fasciculus, fibers go to oculomotor nucleus on the opposite side
-
hypoglossal XII nucleus
- loss of genioglossus fx on one side
- tongue deviates toward weak side
-
Edinger-Westphal nucleus
- preganglionic neurons of parasympathetic, synapse in ciliary ganglia
- postganglionic neurons innervate pupillary constrictor and ciliary muscles
- travel w/III nerve
- damage = mydriasis
- needed for pupillary light reflex
-
Trigeminal sensory nuclear complex
- mesencephalic nucleus: Ia afferents from muscles of mastication/ mechanoreceptors have ccell bodies here
- main sensory nucleus: tactile & proprioception, homologous to dorsal column nuclei
- spinal nucleus: pain/temp fibers from spinal trigeminal tract
-
special sensory nuclei: auditory (VIII) central pathway
- vestibulocochlear nerve
- enter brainstem near ponto-medullary jx
- go to dorsal cochlear and ventral cochlear nuclei, near inf cerebellar peduncle in rostral medulla
- cross, enter lateral lemniscus
- trapezoid body
- inferior colliculus in midbrain
- medial geniculate
- primary auditory cortex
-
Chemotrigger zone
- area postrema
- emetic: D2-dopamine receptors, mu-opioid receptors, 5-HT3 serotonin receptors, and H1-histamine receptors
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