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  1. Cells in the spinal cord receive inputs from ipsilateral structures. Pathways to the thalamus cross to terminate on the contralateral side.
  2. The major ascending pathways are the dorsal (posterior) columns and the anterolateral system.

For Pain, Temperature, and Tactile sensations

  1. Simple receptors, unmyelinated, or poorly myelinated fibers.
  2. Enter via dorsal root and may ascend or descend a few segments.
  3. Secondary fibers cross the midline in the ventral commissure and ascend in ventral and lateral funiculi (ventral and lateral spinothalamic tracts).
  4. Terminate in ventral posterior lateral nucleus of thalamus.
  5. Tertiary fibers project via the internal capsule to terminate in the post­ central gyrus.
  6. Injury to the spinothalamic tracts results in loss of pain and temperature sensation on the opposite side of the body
  7. Syringomyelia interrupts pain and temperature fibers crossing in the ventral white commissure and thus results in bilateral sensory deficit.

For Proprioception, Tactile Discrimination, and Stereognosisa

  1. Primary fibers arising from more complicated receptors are generally well myelinated.
  2. Afferents enter the spinal cord via the dorsal root and ascend in the dor­sal funiculus. The dorsal funiculus divides into a medial fasciculus gra­cilis (sacral, lumbar, and lower thoracic inputs) and a lateral fasciculus cuneatus (upper thoracic and cervical inputs). Both fasciculi terminate in corresponding nuclei in the medulla.
  3. Secondary fibers from the nucleus gracilis and nucleus cuneatus cross the midline and ascend in the medial lemniscus to terminate in the ven­tral posterior lateral nucleus of the thalamus.
  4. Tertiary fibers terminate in the postcentral gyrus.
  5. Muscle spindle information is sent to the cerebellum via two major pathways. The dorsal spinocerebellar tract originates from Clarke's nucleus in the thoracic cord and enters the cerebellum via the inferior cerebellar peduncle. The ventral spinocerebellar tract originates from spinal cord gray matter and enters the cerebellum via the superior cere­bellar peduncle.
  6. Interruption of primary fibers in the dorsal funiculus will cause loss of proprioception, and so forth, on the same side of the body as the lesion.
  7. Interruption of secondary fibers in the medial lemniscus will give rise to contralateral deficits.
  8. Tabes dorsalis and pernicious anemia attack the dorsal funiculi.

For Trigeminal Pathwaysa

  1. Primary trigeminal fibers enter at the level of the pons.
  2. Primary afferents of the descending root terminate in the spinal trigemi­nal nucleus.
  3. Secondary fibers ascend through the medulla and pons as the trigeminal lemniscus to terminate in the ventral posterior medial (VPM) nucleus of the thalamus.
  4. The ascending root primary tactile afferents terminate in the main sen­sory nucleus of CN V . Secondary fibers ascend in the trigeminal lemniscus to the VPM. The cell bodies of the primary proprioceptive afferents from the muscles of mastication are located in mesencephalic nucleus of V, and thus are "like" dorsal root ganglion cells embedded in the brain. They project to the motor nucleus of V for a monosynaptic jaw jerk reflex.
  5. Lesion of the descending root of V and the adjacent lateral spinothalamic tract on one side of the medulla will result in pain and temperature deficits on the contralateral side of the body and the ipsilateral side of the head.

For Vestibular Pathwaysa

  1. Primary afferents terminate in the vestibular nuclei and in the cerebellum on the same side.
  2. Secondary fibers ascend or descend in the medial longitudinal fasciculus or the ventral funiculus of the spinal cord.
  3. Unilateral lesions of the vestibular system result in movement of the head, body, and eyes (nystagmus) to the affected (ipsilateral) side. Symptoms include vertigo, nausea, and a tendency to fall to the affected side.

For Visceral Afferentsa

  1. Primary general visceral afferents have cell bodies in the dorsal root gan­glia and terminate in the dorsal horn. Ascending secondary neurons make abundant reflex connections with autonomic and somatic pathways and terminate in the reticular formation and .intralaminar thalamic nuclei.
  2. Central processes of primary general visceral afferents associated with cranial nerves VII, IX, and X enter the solitary fasciculus and terminate in the nucleus of the solitary tract. Secondary fibers make reflex connec­tions with visceral motor nuclei. Taste is represented in tamus in a region medial to the nuclei.
  • In the brain, the cell bodies of general somatic efferent neurons are located in columns ventral to the cerebral aqueduct and fourth ventricle and ven­trolateral to the central canal. Special visceral efferents (associated with branchial archderived muscle) are located lateral and ventral to the general somatic efferents. In the spinal cord, they originate in the ventral horn.
  • These are lower motor neurons, or the "final common pathway." Total, or flaccid, paralysis results from destruction of peripheral nerves or motor ~nuclei. Destruction of upper motor neurons (from higher centers) results in spastic paralysis: initially hyporeflexia and later hyperreflexia.

For corticospinal (pyramidal) pathway

  1. Fibers arise from pyramidal neurons in layer 5 of the p Central gyrus and Premo torr areas and descend through the internal capsule and basis pedunculi, cross at the spino medullary junction and form the ~tera corticospinal tract in the lateral funiculus of the spinal cord. They terminate on lower motor neurons in the ventral horn or on interneurons.
  2. Most muscles are represented in the contralateral motor cortex. How­ever, some (such as the muscles of the upper face and the muscles of mastication and muscles of the larynx) are represented bilaterally.
  3. With the noted bilateral exceptions, lesion of the pyramidal tract above the decussation results in spastic paralysis, loss of fine movements, and hyperreflexia on the contralateral side.
  4. Lesion of the corticospinal tract in the cord results in ipsilateral deficits.

For Extrapyramidal (Basal Ganglia) Systema

  1. The basal ganglia (caudate, putamen, globus pallidus) and associated nuclei (e.g., substantia nigra) do not project directly to medullary or spinal lower motor neurons, but to the motor cortex.
  2. The system controls coarse, stereotyped movements. lesions result in altered muscle tone (usually rigidity)paucity of movement, and the appearance of rhythmic tremors and writhing or jerky movements.

For Reticular Pathwaysa

  1. Nuclei of the reticular system send ascending projections to the hypo­ thalamus and thalamus as well as descending projections to the motor nuclei of cranial nerves, and the intermediate gray of the spinal cord.
  2. The reticular formation has reciprocal connections with most other areas of the CNS and produces both facilitatory and inhibitory effects on motor systems, receptors, and sensory conduction pathways.

Cerebellar cortex has 3 layers:

  1. Outermost Molecular layer – 2 cells: Stellate and Basket
  2. Middle layer – Purkinje cells    
  3. Inner (deeper/granular) layer– 2 cells: Granule and Golgi
  • The only output (efferent) fibres of cerebellar cortex are by the Purkinje cells, which use GABA as their neurotransmitter and are inhibitory in nature.

The efferents from cerebellum are from deep nuclei (DEFG)

  1. D – Dentate (lateral most)                     
  2. E – Emboliform
  3. F – Fastigii                                
  4. G - Globose
  1. Ganglion cells are the 'third' order neurons for the optic pathway.
  1. Optic nerve is third order neuron and is constituted by the axons of Ganglion cells of retina. Rods /Cones(I) → Bipolar cells(II) → Ganglion cells(III) → Lateral geniculate body(IV)
  2. Supranuclear lesion of facial nerve affects lower part of the face on opposite side of the lesion.
  3. Trochlear (4th cranial nerve) nerve fibers have a dorsal exit from the brain and decussate in the superior medullary velum (Internal decussation).
  4. Visual area (17) receives its blood supply from the calcarine artery, a branch of the posterior cerebral artery. Anastomosis with the middle cerebral artery may be substantial and leads to macular sparing in the lesions of middle cerebral artery.
  5. Corticospinal tract controls fine and skilled voluntary motor activity. E.g., threading a needle.
  6. Most lateral of deep cerebellar nuclei is dentate nucleus.
  7. Foramen of Magendie drains CSF from the 4th ventricle into the subarachnoid space.
  8. Broca’s motor speech area is located in the inferior frontal gyrus.
  9. Medial geniculate body(MGB) is related to auditory pathway. (MM: MGB – Music)

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