ANATOMY OF THE SPINAL CORD, ASCENDING, DESCENDING, AND INTERSEGMENTAL TRACTS (PART 2)

Tracts and shi

TRACTS REVIEW: ASCENDING PATHWAYS

The following slides will ask for everything in the tables of the WS Doc gave us, make sure u studied them before.

Lateral Spinothalamic Tract:

Good luck

Sensation

Pain and temperature
Lab: Pain can be fast pain or general pain

FAST PAIN

• Within 0.1 sec

• Sharp, acute, pricking pain

• Almost confined to skin

Receptor

Free nerve endings

• Chemical substances in damaged tissue (serotonin, histamine, bradykinin, acids like lactic acid and K+) excite nerve endings 

1st order neuron

Ipsilateral Dorsal Root Ganglia

2nd order neuron

Ipsilateral Substantia Gelatinosa

3rd order neuron

Contralateral ventral posterolateral nucleus (VPL) of the thalamus

Lab: can also be ventral posteromedial (VPM)

Termination

Post Central gyrus of the cortex
Lab: Broddman area 312 , 57

Location in SC

Contralateral Lateral White Column

Extent in SC

All levels of the spinal cord

Follow up questions for lateral spinothalamic tract

1. Before synapsing at the 1st order neuron, the stimulus climbs which tract (Lec: 1-2 segments; Lab: 2-3 segments)
2. The Lateral spinothalamic tract is medial and anterior to what tract?
3. Which fibers are more anterior; Fibers carrying pain or Fibers carrying temperature?
4. What is the arrangement of fibers from medial to lateral?
5. At the level of the MEDULLA what is the tract called?

6. What is the sulcus that separates Motor and Sensory gyrus

1. Tract of Lissaur

2. Spinocerebellar tract

3. Fibers carrying pain

4. Cervical, Thoracic, Lumbar, Sacral

5. Spinal Lemniscus

6. Rolandic sulcus

7. Main excitatory Amino acid NT released by A δ  fibers and C fibers; Fast-acting and localized

8. Neuropeptide; Released from C fibers, Slow release and diffuses widely in the posterior horn 

9. Termination for FAST pain

10. Termination for SLOW pain

11. Gyrus for interpretation of pain

12. Gyrus for interpretation of emotional aspect of pain

13. Gyrus for interpretation of pain from internal organs and cause an autonomic response 

7. Glutamate

8. Substance P

9. Cerebral cortex

10. Reticular formation

11. Postcentral Gyrus

12. Cingulate Gyrus

13. Insular Gyrus

Anterior Spinothalamic Tract

Good luck

Sensation

Light/Crude Touch and Pressure

Lab: Slow pain

SLOW PAIN

• Felt 1.0 secs after stimulation

• Burning, aching, throbbing pain

• Produced by tissue destruction

• Occur in any tissue of the body

Receptor

Free nerve endings

1st order neuron

Ipsilateral Dorsal Root Ganglia

2nd Order Neuron

Ipsilateral Substantia Gelatinosa

3rd Order neuron

Contralateral VPL of the Thalamus

Lab: Can also be VPM

Termination

Contralateral Postcentral gyrus

Lab: Broddman area 312, 57

Location in SC

Contralateral Anterolateral White Column

Extent in SC

All levels of the spinal cord

Extra Notes

Also has tract of lissaur

Also turns into spinal lemniscus at level of medulla

Together with lateral spinothalamic:

Level of pons : located at the posterior part of the spinal lemniscus

Level of midbrain : Located at tegmentum lateral to medial lemniscus

POSTERIOR/DORSAL COLUMN MEDIAL LEMNISCUS

Good luck

Sensation

Discriminative touch, Vibration sense, Conscious muscle joint sense
Lab: Spatial proprioception, kinesthesia

Receptors

Meissner Corpuscles, Pacinian Corpuscles, Muscle Spindles and GTO

1st Order neuron

Ipsilateral Dorsal Root Ganglia

2nd Order neuron

Ipsilateral Nucleus Gracilis and Nucleus Cuneatus

3rd Order neuron

Contralateral VPL of the thalamus
Lab: Or VPM

Termination

Postcentral gyrus of cerebral cortex

Lab: Broddman area 312, 57

Location in SC

Posterior white column

Medial = Gracilis

Lateral = Cuneatus

Extent in Spinal Cord

Fasciculus Gracilis = T6 below (meron pa above pero gracilis lng nasa baba)

Fasciculus Cuneatus = T6 above

Follow up questions:

1. At the 2nd order neuron of the DCML tract, what are the axons called?

2. As the tract ascends through the brainstem after decussation what is it called?

3. At the 3rd order neuron, where do the axons pass through?

4. What is the arrangement of the spinal nerves from medial to lateral?

1. Internal Arcuate Fibers

2. Medial Lemniscus

3. Posterior limb of the internal capsule of the corona radiata

4. Sacrum, Lumbar, Thoracic, Cervical.

CUNEOCEREBELLAR TRACT (READ)

Above T6 only

• Originate in nucleus cuneatus and enter cerebellum through the ipsilateral inferior  cerebellar peduncle

• Known as the posterior external arcuate fibers

• To convey information of muscle joint sense to the cerebellum

POSTERIOR and ANTERIOR SPINOCEREBELLAR TRACT

good luck

Sensation

Unconscious muscle joint sense

Receptors

Muscle Spindles, GTO and joint receptors

1st Order neuron

Ipsilateral DRG

2nd Order Neuron

Ipsilateral Nucleus Dorsalis / Clarke Nucleus

3rd Order Neuron

Termination

Ipsilateral Cerebellar Cortex

Location in SC

Posterior : Ipsilateral White Lateral Column

Anterior : Contralateral White Lateral Column

Only Anterior fibers decussate

Some anterior fibers go ipsilaterally

Extent in SC

above L2

Follow up questions:

1. Which cerebellar peduncle does the posterior spinocerebellar tract join?

2. Which cerebellar peduncle does the Anterior spinocerebellar tract join?

3. Since the nucleus dorsalis only extends from C8-L2, where does the axons below L2 pass?

1. Inferior cerebellar peduncle

2. Superior cerebellar peduncle

3. Posterior white column

SPINOTECTAL tract

Good luck

Sensation

Spinovisual reflexes

receptor

free nerve endings

1st order neuron

Ipsilateral DRG

2nd order neuron

Unknown; decussates at the level of the spinal cord

3rd order neuron

N/A

Termination

Contralateral superior colliculus

Location in SC

Anterolateral white column

extent in SC

All levels

SPINORETICULAR tract

Good luck

Sensation

Consciousness

Receptor

Free nerve ending

1st order neuron

Ipsilateral Dorsal Root Ganglia

2nd Order Neuron

Unknown; uncrossed

3rd order neuron

N/A

Termination

Reticular formation of brainstem

Location in SC

Lateral white column

Extent in SC

All levels

SPINO-OLIVARY TRACT (READ)

1st Order Neuron: DRG

• Unknown 2nd order neuron

• Axons cross midline and ascend as spino-olivary tract in junction of anterior and lateral columns 

3rd Order: inferior olivary nuclei in medulla

• Axons decussate and pass through inferior cerebellar peduncle to cerebellum

Conveys information from cutaneous and proprioceptive organs

VISCERAL SENSORY TRACTS (READ)

Receptor: pain and stretch receptor endings in viscera 

1st Order Neuron: DRG

2nd Order Neuron: posterior or lateral gray horn

• Axons join the spinothalamic tracts and ascend

3rd Order Neuron: VPL of thalamus

ASCENDING TRACTS DONE

Take a break and rehydrate

DESCENDING TRACTS REVIEW

The following slides will ask for everything in the tables of the WS Doc gave us, make sure u studied them before.

Anatomical Organization

Lower Motor Neuron (LMN) 

• Anterior horn motor neuron send axon to innervate the skeletal muscle through the anterior roots of spinal nerves

Upper Motor Neuron (UMN)

• Supraspinal neurons and their tracts

Anatomical Organization

1st Order Neuron: cerebral cortex

2nd Order Neuron: anterior horn of spinal cord; axons are short

3rd Order Neuron: LMN; axons innervate the skeletal muscle through anterior root of spinal nerve

LATERAL AND ANTERIOR CORTICOSPINAL TRACT

good luck

Function

Rapid, Skilled, Voluntary movements, especially distal ends of the limbs

Origin

Primary motor cortex (1/3), secondary motor cortex(1/3), Parietal lobe (1/3)

More info:

• ⅓ from primary motor cortex (area 4) cortical layer 5, pyramidal cells

• ⅓ from secondary motor cortex (area 6)

• ⅓ from postcentral gyrus of parietal lobe (area 3,1,2)

Decussation

Lateral Tract : Junction of the spinal cord and medulla

Anterior Tract: Level of termination

Termination

Anterior Horn Cells

Location in spinal cord

Lateral : Descends into the contralateral white columns

Anterior: Descends into the anterior white column

RUBROSPINAL TRACT

Good luck

Function

Facilitates the activity of flexor muscles and inhibits activity of extensors

Origin

Red nucleus of the midbrain

Decussation

Immediately at the level of the red nucleus

Termination

Anterior horn cells

Location in SC

Lateral white column

Additional Notes

Receive afferent impulses with cerebral cortex and cerebellum

Indirect pathway by which the cerebrum and the cerebellum can influence a and y motor neurons

VESTIBULOSPINAL TRACT

Facilitates extensors and inhibits flexors

Lab: responsible for Balance as well

Origin

Vestibular nuclei

Decussation

N/A; uncrossed

Termination

Anterior Horn cells

Location in SC

Anterior column

RETICULOSPINAL TRACT

Good luck

Function

Inhibits or facilitates voluntary movement; hypothalamus controls sympathetic and parasympathetic outflows

Origin

Reticular formation of pons and medulla

Decussation

Some cross at various levels

Termination

α and 𝛾 motor neurons 

Location in SC

Descends in anterior column

TECTOSPINAL TRACT

Good luck

Function

Reflex postural movements concerning sight

Origin

superior colliculus of midbrain

Decussation

Soon after origin

Termination

α and 𝛾 motor neurons or anterior horn cells (idrk)

Location in SC

Anterior white column

DESCENDING AUTONOMIC FIBERS (read)

From cerebral cortex, hypothalamus, amygdaloid complex and reticular formation

Cross midline in brainstem

Descend in lateral column

Synapse with autonomic motor cells in thoracic and upper lumbar levels for sympathetic and mid sacral levels for parasympathetic 

ARRANGEMENT OF NERVE FIBERS IN WHITE MATTER

INTERSEGMENTAL TRACTS (read)

Short ascending and descending tracts that originate and end within the SC

In anterior, lateral and posterior columns

To interconnect neurons of different segmental levels

Important for intersegmental reflex 

Does not go out of the SC

• Tracts that start within the spinal cord and end within the spinal cord only at a different level 

• Connect different segments of the SC