Exam 1 Week 3: Ascending Tracts & Local Tracts Flashcards
Where do the dorsal column tract decussate?
Both dorsal column tracts decussate in the medulla
Fasiculus Gracilis
Fasiculus Cuneatus
Dorsal Spinocerebellar tract
Size
From body area
Path
Decussation
Entry into cerebellum
Size: large caliber & medium caliber axons
From body area: LE
Path:
- Proprioceptive 1st degree neuron enters through dorsal horn
- Synapses in Nucleus Dorsalis
- Rises ipsilaterally in Lateral Funiculus
- Enteres cerebellum through Inferior Cerebellar Peduncle
Decussation: none
Entry into cerebellum: inferior cerebellar peduncle

The two Local (intrinsic) tracts
Spinospinal (propriospinal system) (1)
Lissauer’s Tract (2)

Anterior Spinothalamic tract
Describe 2nd order neuron pathway
Anterior Spinothalamic Tract
- Synapses in Nucleus Proprius
- Transmits crude (non-discrimitive) touch & pressure
- Decussates immediately in ventral white commussure
- Ascends in ventral funiculus
- Ends in thalamus

Function of all the Spinocerebellar tracts
Unconscious proprioception information:
(Convey proprioceptive, touch and pressure info to the cerebellum to use in correction of movment.)
UNLIKE: Conscious proprioception that goes into the cerebral cortex, such as what tells you the location of your joints.
Spinothalamic Tracts: Everything
Also called anterolateral pathway/system
Two Tracts
- Lateral Spinothalamic Tract
- Anterior (ventral) spinothalamic Tract
Describe Pathways:
- 1st order neuron
- (cell body in DRG) enters through dorsal root.
- Descends or Ascends 1-2 segments before synapsing
- in Lissaur’s tract
- 2nd order neuron (tract neuron)
- Lateral Spinothalamic Tract
- Synapses in Substantia Gelatinosa
- Transmits pain & temperature
- Decussates immediately in ventral white commissure
- Ascends in ventrolateral funiculus
- Ends in Thalamus
- Synapses in Substantia Gelatinosa
- Anterior Spinothalamic Tract
- Synapses in Nucleus Proprius
- Transmits crude (non-discrimitive) touch & pressure
- Decussates immediately in ventral white commussure
- Ascends in ventral funiculus
- Ends in thalamus
- Synapses in Nucleus Proprius
- Lateral Spinothalamic Tract
- 3rd order neuron
- Synapse in thalamus
- end in
- primary somatosensory cortex
- cingulate cortex
- insular cortex
Function:
- Lateral Spinothalamic Tracts
- Pain
- Temperature
- Anterior Spinothalamic Tracts
- Crude touch (non-discriminant touch)
- pressure
Somatotopic Relationship:
- LE: lateral
- UE: medial

Dorsal Tract Columns: Describe pathway and other relevant details
Describe pathway and other relavant details:
Primary unipolar afferents with cell bodies in dorsal ganglia. They enter dorsal horn and travel the gracilis and cuneate tracts as primary affernets without synapsing until they reach the Medulla. They are arranged with a Somatotopic relationship. Afferents from LE travel medially in the Fasciculus Gracilis, synapse with secondary neurons in the Nucleus Gracilis (which can be seen as the Gracile Tubercle) in the medulla. Likewise, afferents from the UE travel laterally in the Fasciculus Cuneatus and synapse with secondary neurons in the Nucleus Cuneatus (which can be seen as the Cuneate Tubercle) in the Medulla. Secondary neurons for both tracts synapse with tertiary neruons in the Thalamus. The tertiary neurons end in the Somatosensory Cortex in the Post-Central Gyrus.

Which Ascending Tracts decussate and end contralaterally?
- Fasiculus Gracilis
- Fasiculis Cuneatus
- Lateral Spinothalamic tract
- Medial Spinothalamic Tract

Two Spinothalamic Tracts
- Lateral Spinothalamic Tract
- Anterior (ventral) spinothalamic tract

Which ascending tracts decussate?
Both Dorsal Tracts (in the medulla)
- Fasiculus Gracilis
- Fasiculus Cuneatus
Both Spinothalamic Tracts (in the ventral white commisure of the spinal cord)
- Lateral Spinothalamic tract
- Medial Spinothalamic tract
Lateral spinothalamic tract:
Describe 2nd order neuron pathway
2nd order neuron (tract neuron)
Lateral Spinothalamic Tract
- Synapses in Substantia Gelatinosa
- Transmits pain & temperature
- Decussates immediately in ventral white commissure
- Ascends in ventrolateral funiculus
- Ends in Thalamus

Intrinsic tracts: Where do axons ascend & descend?
Axons Ascend & Descned in:
- Propriospinal bundles which are immediately adjacent to gray matter)
- Dorsal propriospinal bundles
- Lateral propriospinal bundles
- Ventral Propriospinal bundles
- Lissauer’s tract (limited extent
- at dorsal end of tip of dorsal horn

Intrinsic tracts: Functions
- Link spinal segments
- Allow for motor coordination between spinal levels
- produce multi-limb reflexes
- help with coordination of limbs during gait
- Allow for sensory effects to be spread over many spinal segments
Which Ascending Tracts decussate and end ipsilaterally?
Ventral Spinocerebellar tract
Intrinsic tracts: origin
Originate form a varitey of sources, including:
- Posteromarginal nuclei
- Ventral Motor Nuclei
- Inter-nuclear neurons between nuclei of spinal gray

Spinothalamic Tracts:
Describe Pathways
Also called anterolateral pathway/system
Describe Pathways:
1st order neuron
- (cell body in DRG) enters through dorsal root.
- Descends or Ascends 1-2 segments before synapsing
- in Lissaur’s tract
2nd order neuron (tract neuron)
- Lateral Spinothalamic Tract
- Synapses in Substantia Gelatinosa
- Transmits pain & temperature
- Decussates immediately in ventral white commissure
- Ascends in ventrolateral funiculus
- Ends in Thalamus
- Anterior Spinothalamic Tract
- Synapses in Nucleus Proprius
- Transmits crude (non-discrimitive) touch & pressure
- Decussates immediately in ventral white commussure
- Ascends in ventral funiculus
- Ends in thalamus
3rd order neuron
- Synapse in thalamus
- ends in
- primary somatosensory cortex
- cingulate cortex
- insular cortex

Spinothalamic tracts: Function
Function:
Lateral Spinothalamic Tracts
- Pain
- Temperature
Anterior Spinothalamic Tracts
- Crude touch (non-discriminant touch)
- pressure

Dorsal Colum tracts: Everything
There are two:
- Fasciculus Gracilis
- Fasiculus Cuneatus
Describe pathway and othe relavant details:
- Primary unipolar afferents with cell bodies in dorsal ganglia. They enter dorsal horn and travel the gracilis and cuneate tracts as primary affernets without synapsing until they reach the Medulla. They are arranged with a Somatotopic relationship. Afferents from LE travel medially in the Fasciculus Gracilis, synapse with secondary neurons in the Nucleus Gracilis (which can be seen as the Gracile Tubercle) in the medulla. Likewise, afferents from the UE travel laterally in the Fasciculus Cuneatus and synapse with secondary neurons in the Nucleus Cuneatus (which can be seen as the Cuneate Tubercle) in the Medulla. Secondary neurons for both tracts synapse with tertiary neruons in the Thalamus. The tertiary neurons end in the Somatosensory Cortex in the Post-Central Gyrus.
Function:
- Mediates sensory modalities of Fine, discriminative touch and proprioception.

Intrinsic tracts: Types of connections (2)
Ipsilateral
Commissural
Name the two dorsal colum tracts
- Fasciculus Gracilis
- Fasciculus Cuneatus

Where do the spinocerebellar tracts decussate?
The following three don’t dessucate at all:
- Dorsal Spinocerebellar tract
- Rostral Spinocerebellar tract
- Cuneocerebellar tract
They run directly ipsilaterally into the cerebellum.
The Ventral Spinocerebellar tract decussates twice:
- Decussates in spinal cord right after synapsing with 2nd order neuron
- Decussates in midbrain before descending into the cerebellum

What are local (intrinsic) tracts?
Tract axons go from one segment to another over very few segments.
The Spinothalamic tracts are also known as
- anterolateral pathway (used by Dr. Lake when explaining). Also referred to as system.
- ventrolateral system
Rostral Spinocerebellar tract
From body area:
Path:
Decussation:
Entry into cerebellum:
Similar to Dorsal Spinocerebellar tract but for UE
From body area: UE
Path:
- Proprioceptive 1st degree neuron enters through dorsal horn
- Synapses on base of dorsal horn (instead of nucleus dorsalis)
- Rises ipsilaterally in Lateral Funiculus
- Enteres cerebellum through Inferior Cerebellar Peduncle
Decussation: none
Entry into cerebellum: inferior cerebellar peduncle

Ventral Spinocereellar tract
Size:
From body area:
Path:
Decussation:
Entry into cerebellum: i
Size: large caliber & medium caliber axons
From body area: LE
Path:
- Proprioceptive 1st degree neuron enters through dorsal horn
- Synapses at base of dorsal horn
- Decussates
- Rises in contralateral Lateral Funiculus
- Decussates again in midbrain
- Enteres cerebellum through Superior Cerebellar Peduncle
Decussation:
- right after entering spinal cord
- In midbrain
Entry into cerebellum: superior cerebellar peduncle

Dorsal Tract Columns: function
Function:
Mediates sensory modalities of fine, discriminative touch and proprioception.
Where do the spinothalamic tracts decussate?
Both Spinothalamic Tracts decussate in the ventral white commisure of the spinal cord
Lateral Spinothalamic tract
Medial Spinothalamic tract
Name the 8 White Ascending Tracts?
- Dorsal Column/Funiculus
- Fasciculus Gracilis (1)
- Fasciculus Cuneatus (2)
- Lateral Columns
- Spinothalamic Tracts
- Lateral Spinothalamic Tract (3)
- Anterior (Ventral) Spinothalamic Tract (4)
- Spinocerebellar Tracts
- Dorsal Spinocerebellar Tract (5)
- Ventral Spinocerebellar Tract (6)
- Rostral Spinocerebellar Tract (7)
- Cuneo-Spinocerebellar Tract (8)
- Spinothalamic Tracts
Note: Sometimes it is said that there are 7 ascending tracts if the dorsal tracts are counted as one.

Which Ascending Tracts DO NOT decussate and end ipsilaterally?
- Dorsal Spinocerebellar tract
- Rostral Spinocerebellar tract
- Cuneocerebellar tract
Spinothalamic tracts: Somatotopic?
Yes
Somatotopic Relationship:
LE: lateral
UE: medial

Cuneocerebellar tract
From body area:
Path:
Decussation:
Entry into cerebellum:
Similar to Fasiculus Cuneatus, except no decussation, goes to cerebellum, and carries just proprioception
From body area: UE
Path:
Proprioceptive 1st degree neuron enters through dorsal horn
Rises without synapsing in the fasciculus cuneatus
Synapses with 2nd order neuron in Accessory Cuneate Nucleus of caudal Nedulla
Enteres cerebellum through Inferior Cerebellar Peduncle
Decussation: none
Entry into cerebellum: inferior cerebellar peduncle
