Topic map

1. Ascending sensory tracts

1. Dorsal columns
   • Fasciculus gracilis
   • Fasciculus cuneatus
2. Anterolateral system
   • Anterior spinothalamic tract
   • Lateral spinothalamic tract
3. Spinocerebellar pathways
   • Posterior (dorsal) spinocerebellar tract
   • Anterior (ventral) spinocerebellar tract
4. Other ascending pathways
   • Spinotectal tract
   • Spino-olivary tract
   • Spinoreticular tract

2. Descending motor tracts

1. Pyramidal tracts
   • Lateral corticospinal tract
   • Anterior corticospinal tract
2. Extrapyramidal tracts
   • Rubrospinal tract
   • Lateral vestibulospinal tract
   • Medial vestibulospinal tract
   • Reticulospinal tracts

High-yield overview

• Dorsal column-medial lemniscus pathway carries fine touch, vibration, conscious proprioception, and two-point discrimination. It crosses in the caudal medulla.
• Spinothalamic tracts carry pain, temperature, crude touch, and pressure. They cross in the spinal cord, usually within 1-2 segments through the anterior white commissure.
• Spinocerebellar tracts carry unconscious proprioceptive information to the cerebellum for coordination. Posterior spinocerebellar fibers are mainly uncrossed; anterior spinocerebellar fibers characteristically cross twice.
• Corticospinal tracts mediate voluntary skilled movement. Most fibers cross at the pyramidal decussation and form the lateral corticospinal tract.
• Brainstem extrapyramidal tracts regulate posture, balance, muscle tone, automatic movements, and head/neck orientation.

1. Dorsal columns
2. Spinothalamic tracts
3. Spinocerebellar tracts
4. Other ascending tracts
5. Corticospinal tracts
6. Extrapyramidal descending tracts

Spinal Cord Tracts: High-yield Detailed Notes

Orientation diagram: where the major tracts lie

              POSTERIOR / DORSAL

                  Posterior median sulcus
                           │
              ┌────────────────────────┐
              │  Cuneate | Gracile     │  ← Dorsal columns
              │ (T6 up)  | (all cord)  │
              │          │              │
              │ DSCT     │     LCST     │
              │          │ Rubrospinal  │
              │          │              │
              │          │  LSTT        │
              │          │              │
              │          │  ASCT        │
              │                          │
              │     Anterior CST         │
              │ Ant. spinothalamic       │
              └───────────┬────────────┘
                       Anterior

• DCML: dorsal column-medial lemniscus pathway
• LSTT: lateral spinothalamic tract
• ASTT: anterior spinothalamic tract
• DSCT: dorsal/posterior spinocerebellar tract
• ASCT: anterior/ventral spinocerebellar tract
• LCST: lateral corticospinal tract

---

1. Dorsal column-medial lemniscus pathway

Fasciculus gracilis and fasciculus cuneatus

Main function

Position in posterior column

Posterior spinal cord cross-section

            Posterior median sulcus
                     │
        ┌───────────────────────┐
        │     CUNEATUS          │  Lateral
        │   Upper limb/trunk    │
        │───────────────────────│
        │     GRACILIS          │  Medial
        │   Lower limb/trunk    │
        └───────────────────────┘

• Gracilis = lower body = medial
• Cuneatus = upper body = lateral
• Cuneate fasciculus is present only at T6 and above.

Pathway and crossing

Receptor in skin, muscle, joint, tendon
        │
        ▼
1st-order neuron: dorsal root ganglion
        │
        ▼
Enters spinal cord through dorsal root
        │
        └──── Ascends IPSILATERALLY in posterior column ────┐
                                                             │
                     Gracilis: nucleus gracilis, caudal medulla
                     Cuneatus: nucleus cuneatus, caudal medulla
                                                             │
                                                             ▼
2nd-order fibers cross as INTERNAL ARCUATE FIBERS
                 in caudal medulla
                                                             │
                                                             ▼
Contralateral MEDIAL LEMNISCUS
        │
        ▼
Ventral posterolateral nucleus, VPL, of thalamus
        │
        ▼
3rd-order neuron through posterior limb of internal capsule
        │
        ▼
Primary somatosensory cortex, postcentral gyrus

Decussation

• Crosses in the caudal medulla, not in the spinal cord.
• The crossing fibers are called internal arcuate fibers.
• After crossing, they form the medial lemniscus.

Clinical lesion pattern

Important signs of posterior-column damage

• Sensory ataxia
• Positive Romberg sign
• Stamping gait
• Loss of vibration sense, often tested at great toe or malleolus
• Pseudoathetosis due to loss of position sense

---

2. Spinothalamic tracts

Comparison

---

A. Lateral spinothalamic tract

Function

• Fast sharp pain
• Slow aching/burning pain
• Temperature
• Often itch and some crude tactile information

Pathway

Pain / temperature receptor
        │
        ▼
1st-order neuron in dorsal root ganglion
        │
        ▼
Enters dorsolateral spinal cord
        │
        ▼
May ascend or descend 1-2 spinal segments in Lissauer tract
        │
        ▼
Synapse in dorsal horn
  - Substantia gelatinosa: lamina II
  - Nucleus proprius: laminae III-IV
  - Lamina I and V also participate
        │
        ▼
2nd-order neuron crosses in ANTERIOR WHITE COMMISSURE
        │
        ▼
Ascends CONTRALATERALLY in anterolateral funiculus
        │
        ▼
VPL nucleus of thalamus
        │
        ▼
Primary somatosensory cortex

Decussation

• Fibers cross through the anterior white commissure.
• This occurs approximately 1-2 spinal segments above the level at which the sensory fiber entered.

Somatotopy

Lateral spinothalamic tract

More medial                 More lateral
Cervical → Thoracic → Lumbar → Sacral

Clinical relevance

• Contralateral loss of pain and temperature
• Beginning about 1-2 segments below the lesion.

---

B. Anterior spinothalamic tract

Function

• Crude touch
• Light touch
• Pressure

Pathway

Crude touch / pressure receptor
        │
        ▼
Dorsal root ganglion
        │
        ▼
Dorsal horn
        │
        ▼
Crosses in anterior white commissure
        │
        ▼
Ascends contralaterally in anterior funiculus
        │
        ▼
VPL thalamus
        │
        ▼
Primary somatosensory cortex

Clinical point

---

Brown-Sequard syndrome: classic tract pattern

                RIGHT hemicord lesion

RIGHT, below lesion:
- LMN signs at exact level
- UMN weakness below lesion
- Loss of vibration, position, fine touch

LEFT, beginning 1-2 levels below:
- Loss of pain and temperature

• Dorsal columns and corticospinal fibers have not crossed yet at spinal level, so their deficits are ipsilateral.
• Spinothalamic fibers crossed close to entry, so deficits are contralateral.

---

3. Spinocerebellar tracts

Main purpose

---

A. Posterior spinocerebellar tract

Function

• Unconscious proprioception from lower limb and lower trunk
• Input from muscle spindles
• Input from Golgi tendon organs
• Information relevant to posture and coordination

Origin

• Clarke nucleus, also called nucleus dorsalis
• Present mainly from T1 to L2/L3
• Sensory fibers from lower levels can ascend in fasciculus gracilis before synapsing in Clarke nucleus.

Pathway

Muscle spindle / Golgi tendon organ / joint receptor
        │
        ▼
Dorsal root ganglion
        │
        ▼
Clarke nucleus, T1-L2
        │
        ▼
Posterior spinocerebellar tract
        │
        └──── Ascends IPSILATERALLY in lateral funiculus ────┐
                                                              │
                                                              ▼
Inferior cerebellar peduncle
        │
        ▼
Ipsilateral cerebellar cortex
  Mainly vermis and intermediate zone

Crossing

• Does not cross.
• The right side of body is represented in the right cerebellum.

Lesion

• Ipsilateral limb ataxia
• Gait incoordination
• Dysmetria may be present
• Conscious proprioception can remain relatively preserved because dorsal columns are separate.

Upper-limb equivalent: cuneocerebellar tract

• Primary fibers enter cervical cord.
• Ascend in fasciculus cuneatus.
• Synapse in accessory cuneate nucleus in medulla.
• Fibers enter cerebellum via inferior cerebellar peduncle.
• They remain ipsilateral.

---

B. Anterior spinocerebellar tract

Function

• Integrated activity from spinal interneuronal circuits
• Information about lower-limb movement and spinal motor activity
• A type of internal “status report” about what the spinal cord is doing

Origin

• Spinal border cells, mainly in lumbosacral cord, approximately L4-S3.

Double-crossed pathway

Lower-limb sensory and interneuronal input
        │
        ▼
Spinal border cells, lumbosacral cord
        │
        ▼
FIRST CROSSING:
anterior white commissure
        │
        ▼
Ascends on CONTRALATERAL side
in anterior/lateral funiculus
        │
        ▼
Superior cerebellar peduncle
        │
        ▼
SECOND CROSSING:
within or near cerebellum
        │
        ▼
Ends in cerebellum IPSILATERAL to original body side

Key memory point

Anterior spinocerebellar tract:
Crosses in spinal cord → crosses again in/near cerebellum

Two crossings = ends ipsilateral to its body of origin.

Lesion

---

4. Other ascending tracts

---

A. Spinotectal tract

Function

• Orienting eyes, head, and neck toward a stimulus
• Defensive responses to painful stimuli
• Reflexive attention to biologically important sensory events

Pathway

Pain / temperature input
        │
        ▼
Dorsal root ganglion
        │
        ▼
Dorsal horn
        │
        ▼
Crosses in anterior white commissure
        │
        ▼
Ascends in anterolateral system
        │
        ▼
Superior colliculus and other midbrain tectal areas
        │
        ▼
Reflex orientation of head and eyes

Main target

• Superior colliculus, part of the tectum of midbrain.

---

B. Spino-olivary tract

Function

Simplified pathway

Peripheral proprioceptive and cutaneous input
        │
        ▼
Dorsal horn / spinal interneurons
        │
        ▼
Spino-olivary fibers, largely crossed or bilateral
        │
        ▼
Inferior olivary nucleus in medulla
        │
        ▼
Olivocerebellar fibers cross
        │
        ▼
Contralateral cerebellum via inferior cerebellar peduncle

Main point

• Connects spinal sensory activity with the olivocerebellar system.
• Likely contributes to timing, error signaling, motor adaptation, and coordination.
• Details of its precise organization and functional importance are less settled than those of the major tracts.

---

C. Spinoreticular tract

Function

• Arousal and alertness
• Emotional/affective unpleasantness of pain
• Autonomic responses to pain
• Prolonged pain behavior

Pathway

Slow pain / visceral pain / nociceptive input
        │
        ▼
Dorsal horn
        │
        ▼
Bilateral ascent, usually contralateral predominance,
within anterolateral system
        │
        ▼
Reticular formation of medulla and pons
        │
        ▼
Intralaminar thalamic nuclei
        │
        ▼
Widespread cortex, limbic system, autonomic centers

Clinical meaning

• “Where is the pain and how intense is it?” is largely related to lateral spinothalamic processing.
• “How unpleasant, exhausting, alarming, or attention-demanding is it?” involves reticular, thalamic, and limbic connections, including spinoreticular pathways.

---

5. Corticospinal tracts

Common supraspinal course

Motor cortex and related cortical regions
  - Primary motor cortex
  - Premotor cortex
  - Supplementary motor area
  - Somatosensory cortex also contributes
        │
        ▼
Corona radiata
        │
        ▼
Posterior limb of internal capsule
        │
        ▼
Middle three-fifths of cerebral peduncle, midbrain
        │
        ▼
Basis pontis
        │
        ▼
Medullary pyramids
        │
        ├──── 85-90% cross at pyramidal decussation → LCST
        │
        └──── 10-15% remain uncrossed initially → ACST

---

A. Lateral corticospinal tract

Function

• Skilled voluntary movement
• Fine fractionated movement of fingers and hands
• Voluntary distal limb movement
• Especially important for contralateral limb control

Pathway

Motor cortex
        │
        ▼
Internal capsule → midbrain → pons → medullary pyramids
        │
        ▼
PYRAMIDAL DECUSSATION, caudal medulla
        │
        ▼
Descends in lateral funiculus as LCST
        │
        ▼
Synapses mainly on spinal interneurons
and, for some hand muscles, more directly on alpha motor neurons
        │
        ▼
Ventral horn motor neurons
        │
        ▼
Contralateral skeletal muscle

Crossing

• Crosses at pyramidal decussation in the caudal medulla.
• Therefore, the left motor cortex controls the right body, and vice versa.

Somatotopy

• Cervical fibers tend to lie more medially
• Sacral fibers tend to lie more laterally

Lesions

Upper motor neuron signs

• Weakness with pyramidal distribution
• Spasticity
• Hyperreflexia
• Clonus
• Extensor plantar response, Babinski sign
• Reduced fine voluntary movement

---

B. Anterior corticospinal tract

Function

• Axial muscles
• Trunk muscles
• Proximal limb muscles
• Postural adjustments associated with voluntary movement

Pathway

Motor cortex
        │
        ▼
Descends through brainstem pyramids
        │
        ▼
Does NOT cross at pyramidal decussation initially
        │
        ▼
Descends ipsilaterally in anterior funiculus
        │
        ▼
At segmental spinal level:
many fibers cross through anterior white commissure
        │
        ▼
Synapses bilaterally, especially on medial motor neuron pools
        │
        ▼
Axial and proximal muscles

Crossing

• Most fibers do not cross in the medulla.
• Many cross near their spinal termination.
• There is substantial bilateral innervation.

Clinical consequence

---

6. Extrapyramidal descending tracts

• Posture
• Balance
• Muscle tone
• Automatic movement
• Gait
• Head and eye stabilization
• Proximal and axial muscle control

Functional division

Lateral descending system:
- Lateral corticospinal
- Rubrospinal
Mainly distal limb control

Medial/ventromedial descending system:
- Vestibulospinal
- Reticulospinal
- Anterior corticospinal
- Tectospinal
Mainly axial and proximal muscle control, posture and balance

---

A. Rubrospinal tract

Origin

• Red nucleus in the midbrain, mainly magnocellular region.

Function

• Facilitates flexor activity, especially upper-limb flexors
• Contributes to distal limb control
• More important in many nonhuman mammals than in humans
• In humans, the lateral corticospinal tract is the dominant pathway for skilled distal movement

Pathway

Red nucleus, midbrain
        │
        ▼
Crosses immediately in ventral tegmental decussation
        │
        ▼
Descends contralaterally in lateral funiculus
just anterior to LCST
        │
        ▼
Mostly terminates at cervical spinal levels
        │
        ▼
Interneurons and motor neurons supplying upper limb,
especially flexor muscle groups

Crossing

• Crosses in the midbrain, immediately after leaving red nucleus.

Lesion significance

---

B. Lateral vestibulospinal tract

Origin

• Lateral vestibular nucleus, also called Deiters nucleus.

Function

• Maintains upright posture
• Facilitates antigravity extensor muscles
• Helps maintain balance in response to vestibular information
• Influences trunk and limb extensor tone

Pathway

Vestibular apparatus
        │
        ▼
Lateral vestibular nucleus
        │
        ▼
Descends IPSILATERALLY without crossing
in anterior funiculus
        │
        ▼
Terminates at many spinal levels
        │
        ▼
Facilitates ipsilateral extensor motor neurons
and inhibits opposing flexor patterns

Crossing

• No major crossing.
• It acts mainly ipsilaterally.

Memory aid

---

C. Medial vestibulospinal tract

Origin

• Mainly medial vestibular nucleus, with contributions from inferior vestibular nucleus.

Function

• Coordinates head and neck position
• Stabilizes the head during body movement
• Assists vestibulocollic reflexes
• Works with eye movement systems to stabilize gaze

Pathway

Vestibular nuclei
        │
        ▼
Medial longitudinal fasciculus, MLF
        │
        ▼
Descends bilaterally in anterior funiculus
        │
        ▼
Mainly cervical and upper thoracic spinal cord
        │
        ▼
Neck and upper trunk motor neurons

Crossing

• Has bilateral projections.
• Unlike lateral vestibulospinal tract, it primarily reaches cervical and upper thoracic levels rather than the entire spinal cord.

Memory aid

---

D. Reticulospinal tracts

Overall functions

• Automatic postural responses
• Anticipatory postural adjustment before voluntary movement
• Locomotor control
• Muscle tone regulation
• Coordination of axial and proximal muscles
• Integration of cortical, vestibular, visual, and cerebellar input

Pathway diagram

Motor cortex, cerebellum, vestibular system,
sensory inputs and limbic/autonomic centers
        │
        ▼
Reticular formation of pons and medulla
        │
        ├──── Pontine reticulospinal tract
        │       ↓ mainly ipsilateral
        │       ↓ promotes extensor tone/postural support
        │
        └──── Medullary reticulospinal tract
                ↓ bilateral influence
                ↓ modulates extensor tone and locomotion
        │
        ▼
Spinal interneurons and medial motor neuron pools
        │
        ▼
Axial and proximal muscles

Clinical significance

• Why postural control is partly preserved after some corticospinal injuries
• Spasticity after upper motor neuron lesions
• Automatic gait and postural reactions
• Abnormal flexor/extensor posturing in severe CNS injury

---

One-page crossing summary

---

Best mnemonic set

Dorsal columns:
Touch, vibration, position
Cross in medulla

Spinothalamic:
Pain, temperature, crude touch
Cross in spinal cord

Posterior spinocerebellar:
Does not cross

Anterior spinocerebellar:
Crosses twice

Lateral corticospinal:
Cross in pyramids
Controls distal limbs

Anterior corticospinal:
Mostly uncrossed until spinal level
Controls trunk

Lateral vestibulospinal:
Lateral nucleus → ipsilateral limb extensors

Medial vestibulospinal:
MLF → bilateral neck muscles

---

1. Dorsal column-medial lemniscus pathway

Fasciculus gracilis and fasciculus cuneatus

Carries

• Fine/discriminative touch
• Vibration
• Conscious proprioception or joint-position sense
• Two-point discrimination
• Stereognosis, identifying an object by touch

How to read the diagram

1. A receptor in the skin, muscle, tendon, or joint detects the stimulus.
2. The first-order neuron cell body lies in the dorsal root ganglion.
3. It enters the posterior side of the spinal cord and ascends on the same side.
4. From the leg and lower trunk, it ascends in fasciculus gracilis.
5. From the upper trunk and arm, it ascends in fasciculus cuneatus.
6. It synapses in the nucleus gracilis or nucleus cuneatus in the caudal medulla.
7. The second-order neuron now crosses in the medulla as the internal arcuate fibers.
8. After crossing, it ascends as the medial lemniscus.
9. It synapses in the VPL nucleus of thalamus.
10. The third-order neuron passes through the posterior limb of internal capsule to the primary somatosensory cortex.

Crossing

Spinal cord: does NOT cross
Caudal medulla: crosses
Above medulla: information is contralateral

Very important arrangement

Posterior column in spinal cord

Medial                         Lateral
Gracile tract                  Cuneate tract
Lower limb + lower trunk       Upper limb + upper trunk

Lesion

• Lesion of right posterior column in spinal cord:
  • Right-sided loss of vibration, position sense, and fine touch below lesion.
• Lesion above the medullary crossing:
  • Contralateral sensory loss.

---

2. Anterolateral system

Lateral and anterior spinothalamic tracts

A. Lateral spinothalamic tract

Carries

• Pain
• Temperature
• Itch
• Some crude tactile sensation

Route

Pain/temperature receptor
        ↓
Dorsal root ganglion
        ↓
Enters dorsal horn of spinal cord
        ↓
May travel up/down 1-2 levels in Lissauer tract
        ↓
Synapses in dorsal horn
        ↓
Crosses in anterior white commissure
        ↓
Ascends on opposite side in lateral spinothalamic tract
        ↓
VPL thalamus
        ↓
Primary somatosensory cortex

Crossing

• Crosses in the spinal cord, through the anterior white commissure.
• Crossing usually occurs about 1-2 spinal levels above the point where the nerve entered.

Lesion

Left-sided loss of pain and temperature
Beginning 1-2 levels below the lesion

---

B. Anterior spinothalamic tract

Carries

• Crude touch
• Light touch
• Pressure

Route

Skin receptor
        ↓
Dorsal root ganglion
        ↓
Dorsal horn
        ↓
Cross in anterior white commissure
        ↓
Ascend contralaterally in anterior funiculus
        ↓
VPL thalamus
        ↓
Primary somatosensory cortex

Key difference

Lateral spinothalamic = pain + temperature
Anterior spinothalamic = crude touch + pressure

---

3. Spinocerebellar tracts

Posterior and anterior spinocerebellar pathways

---

A. Posterior spinocerebellar tract

Carries

• Unconscious proprioception from lower limb and lower trunk
• Muscle spindle information
• Golgi tendon organ information
• Joint and tendon information needed for coordinated movement

Route

Muscle/joint/tendon receptor
        ↓
Dorsal root ganglion
        ↓
Clarke nucleus, mainly T1-L2
        ↓
Posterior spinocerebellar tract
        ↓
Ascends on SAME side of spinal cord
        ↓
Inferior cerebellar peduncle
        ↓
Ipsilateral cerebellar cortex

Crossing

Does not cross.

Result

Upper-limb equivalent

Upper limb receptor
        ↓
Dorsal root ganglion
        ↓
Fasciculus cuneatus
        ↓
Accessory cuneate nucleus in medulla
        ↓
Inferior cerebellar peduncle
        ↓
Ipsilateral cerebellum

---

B. Anterior spinocerebellar tract

Carries

• Mainly information about spinal interneuronal and motor activity
• “Feedback” about lower-limb movement
• Information important for gait and coordinated lower limb activity

Route and double crossing

Lower-limb sensory/interneuron activity
        ↓
Spinal border cells, lumbosacral spinal cord
        ↓
FIRST CROSSING:
Anterior white commissure
        ↓
Ascends on opposite side
        ↓
Superior cerebellar peduncle
        ↓
SECOND CROSSING:
In or near the cerebellum
        ↓
Ends in cerebellum on original side

Key memory rule

Posterior spinocerebellar = no crossing

Anterior spinocerebellar = crosses twice

---

4. Corticospinal pathways

Lateral and anterior corticospinal tracts

Common route before division

Primary motor cortex
        ↓
Corona radiata
        ↓
Posterior limb of internal capsule
        ↓
Cerebral peduncle, midbrain
        ↓
Pons
        ↓
Medullary pyramids

---

A. Lateral corticospinal tract

Function

• Voluntary movement of limbs
• Skilled movement of fingers and hand
• Fine, fractionated distal movement
• Main pathway for precise motor control

Route

Motor cortex
        ↓
Internal capsule
        ↓
Midbrain → pons → medullary pyramids
        ↓
Pyramidal decussation in caudal medulla
        ↓
Descends in lateral funiculus as LCST
        ↓
Ventral horn motor neurons
        ↓
Contralateral distal limb muscles

Crossing

• Crosses in the pyramidal decussation of the caudal medulla.
• About 85-90% of corticospinal fibers do this.

Clinical rule

Lesion above pyramidal decussation:
Contralateral upper motor neuron weakness

Lesion below pyramidal decussation, in spinal cord:
Ipsilateral upper motor neuron weakness

Upper motor neuron signs

• Spasticity
• Hyperreflexia
• Clonus
• Extensor plantar response, Babinski sign
• Weakness, especially of fine distal movement

---

B. Anterior corticospinal tract

Function

• Voluntary control of axial muscles
• Trunk muscles
• Proximal limb muscles
• Postural adjustments

Route

Motor cortex
        ↓
Brainstem pyramids
        ↓
Does not cross at pyramidal decussation initially
        ↓
Descends in anterior funiculus
        ↓
Many fibers cross at their spinal level of termination
        ↓
Bilateral connections to axial/proximal muscles

Crossing

• Initially uncrossed in the medulla.
• Many fibers cross near the level where they terminate in the spinal cord.
• Many terminate bilaterally.

Why unilateral cortical lesions spare the trunk relatively

---

5. Extrapyramidal descending pathways

Rubrospinal, vestibulospinal, and reticulospinal tracts

• Posture
• Balance
• Muscle tone
• Gait
• Head position
• Automatic postural reactions
• Proximal and axial movement

---

A. Rubrospinal tract

Origin

• Red nucleus of midbrain

Function

• Assists upper-limb flexor activity
• Contributes to distal limb control
• More important in nonhuman mammals than in humans

Route

Red nucleus, midbrain
        ↓
Crosses immediately in ventral tegmental decussation
        ↓
Descends contralaterally in lateral funiculus
        ↓
Mostly terminates at cervical spinal levels
        ↓
Influences upper-limb flexor motor neurons

Crossing

Crosses in the midbrain.

---

B. Lateral vestibulospinal tract

Origin

• Lateral vestibular nucleus, Deiters nucleus

Function

• Maintains balance
• Facilitates antigravity muscles
• Increases extensor tone in limb and trunk muscles
• Helps keep the body upright

Route

Vestibular apparatus
        ↓
Lateral vestibular nucleus
        ↓
Descends ipsilaterally through spinal cord
        ↓
Facilitates ipsilateral extensor muscles

Crossing

Does not cross.

Memory aid

Lateral vestibulospinal tract = lateral vestibular nucleus
                             = limb extensors
                             = balance and antigravity posture

---

C. Medial vestibulospinal tract

Origin

• Mainly medial vestibular nucleus

Function

• Head and neck stabilization
• Vestibulocollic reflexes
• Maintains head position during body movement
• Supports gaze stabilization with vestibulo-ocular reflex circuits

Route

Medial vestibular nucleus
        ↓
Medial longitudinal fasciculus, MLF
        ↓
Bilateral descent to cervical and upper thoracic cord
        ↓
Neck and upper trunk motor neurons

Crossing

• Has bilateral projections.
• Mainly acts at cervical and upper thoracic levels.

Memory aid

Medial vestibulospinal = MLF = neck and head control

---

D. Reticulospinal tracts

Origin

• Reticular formation of pons and medulla

Functions

• Posture
• Gait
• Muscle tone
• Automatic movement
• Anticipatory postural adjustments before voluntary movement

Pontine/medial reticulospinal tract

Pontine reticular formation
        ↓
Mainly ipsilateral descent
        ↓
Facilitates extensor tone
        ↓
Supports posture

Medullary/lateral reticulospinal tract

Medullary reticular formation
        ↓
Bilateral spinal influence
        ↓
Modulates or inhibits excessive extensor tone
        ↓
Contributes to gait and voluntary postural adjustment

---

6. Other ascending pathways

Spinotectal, spino-olivary, and spinoreticular tracts

---

A. Spinotectal tract

Destination

• Superior colliculus in midbrain tectum

Main role

• Reflex orientation of eyes, head, and neck toward a sensory stimulus, especially a painful or unexpected one.

Route

Pain/temperature input
        ↓
Dorsal root ganglion
        ↓
Dorsal horn
        ↓
Crosses in spinal cord
        ↓
Ascends in anterolateral system
        ↓
Superior colliculus
        ↓
Orienting response of head and eyes

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B. Spino-olivary tract

Destination

• Inferior olivary nucleus in medulla
• Then, indirectly, cerebellum

Main role

• Communicates sensory and proprioceptive information to cerebellar circuits.
• Believed to contribute to coordination, timing, motor learning, and error correction.

Simplified route

Peripheral sensory/proprioceptive information
        ↓
Spinal cord neurons
        ↓
Spino-olivary fibers
        ↓
Inferior olivary nucleus
        ↓
Olivocerebellar fibers
        ↓
Cerebellum

Important note

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C. Spinoreticular tract

Destination

• Reticular formation in medulla and pons
• Intralaminar nuclei of thalamus
• Widespread cortical and limbic areas

Main role

• Arousal response to pain
• Emotional unpleasantness of pain
• Autonomic reaction to pain
• Diffuse, slow, persistent pain response

Route

Slow pain / visceral pain input
        ↓
Dorsal horn
        ↓
Bilateral ascent in anterolateral system
        ↓
Reticular formation
        ↓
Intralaminar thalamic nuclei
        ↓
Widespread cortex and limbic areas

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Final rapid-revision chart