1. Somatic Sensory Pathways
1.1. Dorsal Column
1.1.1. Gracile Fasciculus Tracts
1.1.2. Cuneate Fasciculus Tracts
1.1.3. • Ascend Dorsal White Column • Deep Sensations (conscious proprioception) • Fine (complex) touch
1.1.3.1. 1st Order Neuron- (Dorsal Root Ganglion Cells) • Peripheral Processes (Muscles, Tendons, Joints) • Central Processes (Spinal Cord)- Pseudo-Unipolar • Lower ½ Ascend Medially, Dorsal Column Gracile Tract • Upper ½ Ascend Laterally, Posterior Column Cuneate Tract
1.1.3.2. 2nd order neuron: • Gracile Nucleus Cuneate Nucleus, Both in Medulla Oblongata • Axons cross middle line (sensory decussation), Ascend in brain stem as medial lemniscus. • Some fibers end in accessory cuneate nucleus, which axons form cuneocerebellar pathway reaching cerebellum via inferior cerebellar peduncle.
1.1.3.3. 3rd Order Neuron: * Anterior Group of Thalamic Nuclei (Ventralis Posterolateralis) * Nucleus Axons Pass Posterior Limb of Internal Capsule * Reach Sensory Cerebral Cortex Via Corona Radiata
1.2. Spinocerebellar
1.2.1. Anterior Spinocerebellar Tracts
1.2.2. Posterior Spinocerebellar Tracts
1.2.3. • Ascend Lateral White Column • Unconscious Proprioception to cerebellum
1.2.3.1. 1st Order Neuron: • Dorsal Root Ganglion Cells, Central Processes to Spinal Cord Via Dorsal Root. • End at Ipsilateral Clarke's Nucleus.
1.2.3.2. 2nd order neuron: Clarke's nucleus.
1.2.3.2.1. Anterior Spinocerebellar Tract: Axons Mostly Cross Middle Line, Few Remain Uncrossed. Ascend In Lateral White Column Reach Cerebellum Via Superior Cerebellar Peduncle Cross Again to Reach Ipsilateral Cerebellum (Functional Significance Of 2 Crossing Unknown Why)
1.2.3.2.2. Posterior spinocerebellar tract: ascend ipsilaterally in lateral white column of the spinal cord (posterior to anterior spinocerebellar tract). reach ipsilateral cerebellum via inferior cerebellar peduncle.
1.2.3.2.3. Summary • Anterior SCT (Has Double Cross) Posterior SCT (No Cross) • Anterior SCT (Superior Cerebellar Peduncle) Reach Contralateral Cerebellum • Posterior SCT Inferior Cerebellar Peduncle Reach Ipsilateral Cerebellum
1.2.3.3. No 3rd Order Neurons in Spinocerebellar Pathway
1.3. Spinothalamic
1.3.1. Ventral Spinothalamic Tracts
1.3.1.1. 1st order neuron: • central processes, dorsal root ganglion cells. • end on many grey matter laminae (mainly IV-VII) of spinal cord
1.3.1.2. 2nd order neuron: • neurons of laminae IV- VII. • axons cross middle line in ventral white commissure of spinal cord • ascend in the ventral white column as ventral spinothalamic tract. • Cervical fibers are medial while sacral fibers are lateral. • ascends in brain stem, joins medial lemniscus (of gracile and cuneate tracts) accompanying it end at thalamic nuclei (ventralis posterolateralis).
1.3.1.3. 3rd order neuron: • ventralis posterolateralis of thalamus. • Axons pass posterior limb of internal capsule. • reach sensory area of cerebral cortex via corona radiata.
1.3.2. Lateral Spinothalamic Tracts
1.3.2.1. 1ST order neuron: • central processes, dorsal root ganglion cells • They end on many laminae of grey matter (mainly laminae I and IV-VIII)
1.3.2.2. 2ND order neuron: • neurons of laminae I and IV-VIII (central process of 2nd order neurons). • axons cross the middle line in the ventral white commissure of spinal cord. • ascend in lateral white column as lateral spinothalamic tract. • Cervical fibers are medial, sacral fibers are lateral. • ascends in brain stem as spinal lemniscus • ends at of thalamic nuclei (ventralis posterolateralis).
1.3.2.3. 3rd order neuron: • (ventralis posterolateralis) of thalamus. • Axons pass posterior limb of internal capsule • reach sensory area of the cerebral cortex via the corona radiata.
1.3.3. • Ascend Ventral, Lateral White Columns • Ventral Spinothalamic Tract Carries (Crude Touch, Pressure) from opposite side of body • Lateral Spinothalamic Tract (Pain, Temperature) from opposite side of body
1.4. Others
1.4.1. Spioolivary
1.4.1.1. • End at Contralateral Olivary Nuclei • Then Olivo-Cerebellar Fibers Pass Via Inferior Cerebellar Peduncle • Reach Again Ipsilateral Cerebellum
1.4.2. Spinotectal
1.4.2.1. • Ends At Both Pontine, Medullary Reticular Formation. • Route For Slow Dull Aching Pain Sensation.
1.4.3. Spinoreticalar
1.4.3.1. • Ends At Superior Colliculus of Mid Brain. • Responsible For Spino-Visual Reflexes (Head Turning to The Source of Pain).
1.5. Pain Sensation from The Face
1.5.1. • 1st Order Neuron: Trigeminal Ganglion. • 2nd Order Neuron: Spinal Nucleus of Trigeminal, Axons Cross Middle Line, Ascend as Trigeminal Lemniscus. • 3rd Order Neuron: Ends in Thalamus Ventralis Posteromedialis, Axons Pass Internal Capsule to Sensory Area of Face In Cerebral Cortex Via Corona Raiata.
1.6. -
2. -
3. -
4. Motor (Descending)
4.1. Pyramidal system:
4.1.1. Cortico-Bulbar Tracts:
4.1.1.1. • Motor Cranial Nerves Nuclei in Brain Stem) • Descend In Corona Radiata, Genu of Internal Capsule, Then Brain Stem. • Terminate On Motor Nuclei Of 3rd, 4th, 5th, 6th, 7th, 9th, 11th, And 12th Cranial Nerves • Supplying Head Muscles (Muscles of The Eye, Jaw, Face, And Some Neck Muscles). • Fibers Mainly Terminate on Contralateral Motor Nuclei of Cranial Nerves + on Ipsilateral Nuclei. • 2 Nuclei Lack of Double Control (Receive Contralateral Fibers Only): • 1. Motor Nucleus of Fascial Nerve Controlling Muscles of Lower Half of Face. • 2. Hypoglossal Nucleus Controlling Genioglossus Muscle.
4.1.2. Cortico-Spinal
4.1.2.1. Lateral Cortico-Spinal
4.1.2.1.1. • Descend at Lateral white column • End On Lateral Group of Anterior Horn Cells of The Spinal Cord Controlling Limb Muscles.
4.1.2.2. Anterior Cortico-Spinal
4.1.2.2.1. • Descend in Anterior White Column • End on Medial Group of Anterior Horn Cells of The Spinal Cord of Both Sides Controlling Trunk Muscles. • Only 2% of Fibers Will End at Spinal Accessory Nucleus Controlling Sternomastoid Muscle of Same Side
4.1.2.3. • Axons Cerebral Cortex Descend, Converge in Corona Radiata. • Then Pass in Anterior 2/3 Of Posterior Limb of Internal Capsule (Upper Limb Fibers Are Anterior, While Lower Limb Fibers Are Posterior). • Then Descend in Brain Stem (Midbrain: Middle 3/5 Of Cerebral Peduncles. • Then Pons: In Basis Pontis Separated by Transverse Pontine Fibers. • Then Medulla Oblongata: Forming Pyramid of Medulla • Along The Length of Pyramid, 85% of Fibers Cross Midline Forming (Motor Decussation) • Then Descend in The Spinal Cord As (Lateral Corticospinal Tract). • 15% Of Fibers Remain Uncrossed and Descend in Spinal Cord as (Ventral Corticospinal Tract). • But (Ventral Corticospinal Tract), Will Cross at Lower Level In The Spinal Cord At Target Spinal Cord Segment.
4.2. Extra Pyramidal system
4.2.1. Medial pathway
4.2.1.1. Vestibulospinal tracts
4.2.1.1.1. • Upper Motor Neurons in Vestibular Nuclei. • Receive Information Via Vestibulocochlear Nerve About Changes in Orientation of Head • Tracts Send Motor Commands Adjusting Muscle Tone and Position of Neck, Eyes, Head, And Limbs to Maintain Posture, Balance.
4.2.1.2. Tectospinal tracts
4.2.1.2.1. • Upper Neurons, Superior and Inferior Colliculi That Located at Roof (Tectum) of Midbrain. • Superior Colliculi Receive Visual Stimuli • Inferior Colliculi Receive Auditory Stimuli. • Axons Neurons Descend Forming Tectospinal Tracts, Cross Midline, End on Lower Motor Neurons in Brain Stem or Spinal Cord. • Tracts Adjust Reflex Changes in Position of Muscles in Response to Visual or Auditory Stimuli.
4.2.1.3. Reticulospinal tracts
4.2.1.3.1. • Origin in Reticular Formation (Which Receives Input From Almost All Ascending, Descending Pathways). • Axons of Upper Motor Neurons in Reticular Formation Descend as Reticulospinal Tracts Without Crossing to Opposite Side. • Concerned With Subconscious Regulation of Reflex Activity
4.2.1.4. • controlling movements of trunk and proximal limb muscles
4.2.2. Lateral pathway
4.2.2.1. Rubrospinal tracts
4.2.2.1.1. • Controlling Distal Limb Muscles with Its More Discrete Movements • Upper Motor Neurons in Red Nuclei of Midbrain • Axons of Neurons Cross Midline • Descend in Spinal Cord as Rubrospinal Tract. • Tracts Small Reaching Only Cervical Segments Of Spine • Provide Control on Distal Muscles of Upper Limb (Concerned with Highly Skilled Precise Movements). • Role of Rubrospinal Tracts Insignificant, Weak As Compared to Lateral Corticospinal Tracts. • May Important in Maintaining Tone of Upper Limb Muscles if Lateral Corticospinal Tracts Are Damaged
4.2.3. concerned with subconscious regulation of muscle tone, movement, subconscious control of balance needed for each movement.