Major motor pathway from the cortex. Corticospinal, corticobulbar, corticoreticular tracts. _Originates_ primary motor cortex (main) premotor cortex primary somatosensory cortex posterior parietal area _Terminates_ alpha & gamma motor neurons in _spinal cord_ cranial nerve motor neurons in _brainstem_ Susceptible to major insult including vascular damage.

CNS Pathways & ANS Flashcards by Quynh Tran

Dorsal Columns System

(DC)

Carries afferent epicritic sensation.

Fine touch, vibration sense, proprioception.

Type A𝛼 and A𝛽 (or Ia, Ib, and II)

[Lumbar Spinal Cord]

Primary neuron enters via medial division of dorsal root ganglion (DRG).

Carries lower limb information.

Axons form the gracile fasciculus.

[Cervical Spinal Cord]

Primary neuron enters via medial division of dorsal root ganglion (DRG).

Carries upper limb information.

Axons form the lateral cuneate fasciculus at or above T5.

Somatotopy: cervical fibers located laterally next to gray matter

[Medulla]

Gracile and cuneate fasciculi run ipsolaterally up to medulla.

Axons terminate on secondary neurons in gracile and cuneate nuclei.

Second neurons cross midline as internal arcuate fibers.

Somatotopy: lower limb info ventral; upper limb info dorsal

[Pons and Midbrain]

Axons form the medial lemniscus (ML).

Somatotopy: lower limb info lateral; upper limb info medial

[Thalamus]

Medial lemniscus terminates in the ventral posterior lateral (VPL) nucleus.

Third neurons in VPL thalamus.

Somatotopy: lower limb info lateral; upper limb info medial

[Cortex]

VPL axons terminate in the postcentral gyrus (primary somatosensory cortex)

Somatotopy: lower limb info medial; upper limb info lateral

How well did you know this?

Not at all

Perfectly

Anterolateral System

(ALS)

Carries protopathic sensation.

Includes 3 pathways:

Spinothalamic tract (STT)
Spinoreticular tract
Spinomesecephalic tract

How well did you know this?

Not at all

Perfectly

Spinothalamic Tract

(STT)

Part of the anterolateral system along with spinoreticular and spinotectal fibers.

Carries protopathic sensation from contralateral side of the body.

Pain, temperature, and crude touch.

Type A-𝛿 and C fibers.

[Spinal cord]

Primary neurons in dorsal root ganglion (DRG)

Axons enter via lateral division of DRG

Sends collaterals into Lissauer’s tract

(~ 1 level rostrally and caudally)

Axons terminate in dorsal horn (lamina I, II, and V)

Second neurons in Lamina I and V

Axons decussate immediately in ventral white commissure

Axons form the spinothalamic tract (STT)

Stomatotopy: cervical fibers located ventrally next to gray matter

[Pons, Medulla, Midbrain]

Axons ascend as the STT carrying information from contralateral side of the body.

Somatotopy: cervical ⇒ sacral goes ventral ⇒ dorsal

Medulla: STT is lateral/dorsal to inferior olive

Pons/Midbrain: STT lateral to medial lemniscus

[Thalamus]

STT axons terminate at the ventral posterior lateral nucleus (VPL)

Third neurons in the VPL thalamus.

Somatotopy: lower limb lateral, upper limb medial

[Cortex]

VPL axons terminate in the postcentral gyrus

Somatotopy: lower limb medial, upper limb lateral

How well did you know this?

Not at all

Perfectly

Facial

Epicritic Pathway

Fine touch and proprioception transmitted via the trigeminal nerve (CN V).

[Pons]

Enters at the mid-pons.

Majority of fibers crosses midline.

Travels medially within longitudinal pontine fibers.

Some fibers travel via Dorsal trigeminal tract.

[Midbrain]

Anterior position within medial leminiscus.

Some fibers travel via Dorsal trigeminal tract.

[Thalamus]

Project into the ventral posterior medial (VPM) thalamus.

[Cortex]

Project to lateral somatotopy of post-central gyrus.

How well did you know this?

Not at all

Perfectly

Facial

Protopathic Pathway

Pain and temperature information carried via

Trigeminal nerve (CN V)

[Pons]

Enters spinal cord at the mid-pons.

Descends down to the caudal medulla and crosses midline.

Ascends via the Spinothalamic tract (STT).

[Midbrain]

Anterior position within the STT

[Thalamus]

Fibers terminate within the ventral posterior medial (VPM) thalamus.

Third neuron originates in the VPM.

[Cortex]

VPM fibers terminate laterally within the postcentral gyrus.

How well did you know this?

Not at all

Perfectly

Horner’s Syndrome

Preganglionic sympathetic neurons in the T1 intermediolateral nucleus (aka ciliospinal center of Budge) ⇒ postganglionic neurons in cervical ganglion.

Postganglionic sympathetic neurons ⇒ ipsilateral dilator muscle of pupillae, superior tarsal muscle, and sweat glands of face.

Lesion of this pathway results in Horner’s syndrome.

Characterized by ipsilateral:

miosis (constricted pupil)

ptosis (drooping eyelid)

anhidrosis (lack of sweating) on the face

How well did you know this?

Not at all

Perfectly

Ventral Spinocerebellar Tract

(VSCT)

VSCT sends to cerebellum an efferent copy of spinal cord motor neuron output.

Used for motor control of lower limbs.

Fibers cross twice ending on ipsilateral side to origin.

Lesion of VSCT fibers produces contralateral deficits.

Spinal Cord
- neurons in lamina VII & ventral horn of lumbar spine (spinal border cells)
- 1st crossing:
  ⟾ axons cross in ventral white commissure
  ⟾ forms contralateral VSCT
Rostral Pons:
- VSCT enters superior cerebellar peduncle (SCP)
- 2nd crossing:
  ⟾ axons cross again in decussation of superior cerebellar peduncle to reach ipsilateral cerebellum to origin

How well did you know this?

Not at all

Perfectly

Cuneocerebellar Tract

(CCT)

Carries unconscious proprioception from upper body to cerebellum.

Used for motor control.

Spinal cord
- 1st neuron in DRG
  - enter via medial division of dorsal root
  - travel in cuneate fasciculus
  - send collaterals to lateral (accessory) cuneate nucleus
Caudal medulla
- 2nd neuron in lateral cuneate nucleus
  - axons form cuneocerebellar tract
Rostral medulla
- CCT fibers travel via inferior cerebellar peduncle (ICP)
Cerebellum
- Fibers enter ipsilateral cerebellum
  - tract lesions produces ipsilateral deficits

How well did you know this?

Not at all

Perfectly

Pyramidal System

Major motor pathway from the cortex.

Corticospinal, corticobulbar, corticoreticular tracts.

Originates
- primary motor cortex (main)
- premotor cortex
- primary somatosensory cortex
- posterior parietal area
Terminates
- alpha & gamma motor neurons in spinal cord
- cranial nerve motor neurons in brainstem
Susceptible to major insult including vascular damage.

How well did you know this?

Not at all

Perfectly

Cortical Spinal Tracts

(CST)

Control of voluntary movements.

Suppression of innate reflexes.

[Cortex]

Pyramidal neurons (lamina V of cerebral cortex) mostly in precentral gyrus but also other cortical areas

⇒ corona radiata

⇒ posterior limb of internal capsule

[Midbrain]

Middle 1/3 portion of cerebral peduncle

(Crus cerebri and Basis pedunculi)

[Pons]

Pyramidal tract in basal pons

(Longitudinal pontine fibers)

[Open Medulla]

Pyramid

[Closed Medulla]

85% of fibers cross at the pyramidal decussation

15% of fibers remain on ipsilateral side

[Spinal Cord - starting at cervical]

Decussated fibers form Lateral Cortical Spinal Tract (LCST)

Cervical fibers closer to gray matter

Controls distal motor neurons for fine movements

Runs within lateral funiculus w/ RuST & MRST

Remainder of fibers form the Ventral Cortical Spinal Tract (VCST)

Cross at segmental level

Influences bilateral neurons controlling axial muscles

How well did you know this?

Not at all

Perfectly

Lateral Corticospinal Tract (LCST)

Characteristics

Terminates on LMN in ventral horn for distal muscles
Synapses on spinal interneurons
- Ia & Ib interneurons
- Renshaw cells
Lesions:
- spasticity → d/t mix with corticoreticular and reticulospinal tracts
- Babinski sign ± Grasp reflex
Isolated LVST lesion
- rare
- see w/ lesion in primary motor cortex or pyramids
- get flaccid paralysis & substantial atrophy
- no UMNs

How well did you know this?

Not at all

Perfectly

Ventral Corticospinal Tract (VCST)

Characteristics

Originates in trunk & limb extensors region of contra. motor cortex
Runs in ventral funiculus
Bilaterally innervates:
- axial motor neurons
- interneurons in ventral horn
Functions to maintain posture
Lesion → little deficit if unilateral

How well did you know this?

Not at all

Perfectly

Corticobulbar Tract

(CBT)

Controls cranial nerve motor functions.

Cortex
- originates from pyramidal neurons in lamina V of contralateral motor cortex head region
  ⟾ corona radiata
  ⟾ genu of internal capsule
Midbrain
- axons in medial 1/3 of cerebral peduncle
Pons
- controls bilateral trigeminal motor nucleus
- controls bilateral upper face facial motor neurons
- controls only contralateral lower face facial motor neurons
  - unilateral CBT lesion = contralateral drooping of corner of mouth
Medulla and Spinal Cord
- controls bilateral hypoglossal nucleus
- controls bilateral nucleus ambiguus
- controls bilateral spinal accessory nucleus
  ⟾ nuclei often receive mostly crossed CBT fibers
  ⟾ CBT lesion may cause contralateral weakness

How well did you know this?

Not at all

Perfectly

Extrapyramidal Tracts

Involves multiple UMNs.

Originates primarily in premotor cortex and cerebellum.

Synapses in brainstem before reaching LMN.

How well did you know this?

Not at all

Perfectly

Rubrospinal Tract

(RuST)

Functions to control upper arm flexion.

Specialized for brachiation in primates.

Path:
- Cortex
  - magnocellular neurons of contralateral red nucleus
- Midbrain
  - crosses in ventral tegmental decussation
- Travels with LCST in lateral funiculus
- Terminates in cervical spinal cord
  - synapses with ventral horn LMN & interneurons
Controls upper arm musculature
- flexors > extensors
Lesions → upper arm spasticity
Contributes to decorticate posture

How well did you know this?

Not at all

Perfectly

Rubro-olivary Fibers

Study These Flashcards

Originates from parvocellular neurons in red nucleus
Axons project via central tegmental tract → ipsilateral inferior olive
Functions in motor learning
- regulates cerebellar function

Pontine Reticulospinal Tract

(PRST)

Study These Flashcards

Function:
- Facilitates extensor and inhibits flexors.
- Involved in control of posture and gait-related movements.
- Maintains muslce tone.
- Opposes MRST.
- Controlled by contralateral motor cortex.
- Lesions = spasticity.
Tract:
- Originates from 2 pairs of neurons within pontine reticular formation
  - nucleus reticularis pontis oralis (rostral pons)
  - nucleus reticularis pontis caudalis (caudal pons)
Axons descend ipsilaterally
- travel in ventral funiculus with VCST
Terminate bilaterally in all spinal cord levels

Medullary Reticulospinal Tract

(MRST)

Study These Flashcards

Characteristics:
- Inhibits extensors and facilitates flexors.
- Involved in control of posture and gait-related movements.
- Terminates mostly on gamma MN and interneurons that control proximal extensors.
- Opposes PRST.
- Primarily controlled by contralateral motor cortex.
- Lesion = spasticity
Originates from gigantocellular neurons of ipsilateral medullary reticular formation
Axons descend bilaterally, mostly uncrossed
Terminates in all spinal cord levels
- Travels within lateral funiculus with LCST

Lateral Vestibulospinal Tract

(LVST)

Study These Flashcards

Characteristics:
- Controls ipsi LMN & interneurons innervating extensor antigravitic muscles
- Controls contralateral limb via interneurons
- Maintain muscle tone by exciting extensors
  - Balance at rest and during movement
  - Equilibrium
  - Maintain/adjust posture
- Labyrinthine Reflex
Lesion = balance problems
Path:
- Medulla
  - Originates from ipsilateral lateral vestibular nucleus (Deiter’s nucleus)
  - Fibers pass through inferior vestibular nucleus
  - Axons descend ipsilaterally to all spinal cord levels
Spinal cord
- Travels in ventral funiculus with VCST

Controlled by inhibitory input from Purkinje neurons in cerebellum:

Vermis and flocculonodular lobes.

Medial Vestibulospinal Tract

(MVST)

Study These Flashcards

Characteristics:
- Primarily controls LMNs innervating muscles of the head and neck.
- Role in positioning of head/neck in relation to balance and eye movement.
- Right reflex
- Allows suppression of vestibular ocular reflex (VOR)
  - Synchronize head and eye movements
Path:
- Originates mostly from medial vestibular nuclei
- Axons descend bilaterally to cervical and high thoracic spinal cord
  - Forms the descending branch of MLF
  - Travels in ventral funiculus with VCST

Tectospinal Tract

(TST)

Study These Flashcards

Important in directing head movement towards novel visual, auditory, or somatic stimuli.

Midbrain
- Originates in contralateral superior colliculus
- Axons curve around PAG
- Crosses in dorsal tegmental decussation
- Continues caudally as tectospinal tract
Travels in midbrain, pons, and medulla near midline, ventral to MLF
Travels in ventral funiculus with MLF and PRST
Terminates in high cervical spinal cord

Spasticity

Study These Flashcards

Reticulospinal tracts from PRF & MRF → spinal cord
- both ⊕ and ⊖ interneuronal connections
- both terminate directly & indirectly to MNs in IML
- Act on somatic LMNs to ∆ muscle tone & segmental reflexes
Lesion of reticulospinal tract or corticoreticular fibers ⟾ imbalance of MN ⊕ and ⊖
Spasticity due to net overexcitation of reflex pathways
- clonus
- clasp-knife
- hyperreflexia
Treatment:
- activate reciprocal ⊖ systems via
  - Ia muscle stretch to opposing muscle
  - Ib GTO reflexes with message/vibration
- Deafferentation of DRG to remove afferent limb of stretch reflex
- Intrathecal Baclofen → GABA-B agonist

Loss of Consciousness

Study These Flashcards

Consciousness depends on intact RF
Major insult to brainstem RF → LOC
- Often due to central tegmental tract damage
  - Part of Ascending Reticular Activating System (ARAS)
Severity varies
- Extensive damage to lower medulla RF incompatible with life

Decorticate Posturing

Study These Flashcards

Damage in the brainstem above the level of the red nucleus.

Decortication interrupts cortical fibers providing tonic activation of MRST.

Upper limbs flexed ⟾ d/t red nucleus via rubrospinal tract (RST)

Lower limbs extended ⟾ due to ⊕ influence by PRST and LVST without ⊖ influence from MRST.

Decerebrate Posturing

Damage to brainstem **below or at the level of the red nucleus**. **Both upper and lower limbs extended.** Extension due to ⊕ influence of PRST and LVST without ⊖ influence of MRST. Progression from decorticate → decerebrate life threatening → lesion expanding towards medullary life centers.

Central Regulation of ANS

**Hypothalamus regulates autonomic responses.** Visceral afferents → hypothalamus → autonomic ganglion → ∆ visceral functions. Sensory inputs → amygdala → emotional response → stria terminalis → hypothalamus → ∆ ANS. Hypothalamus ↔ limbic system ↔ neocortex.

Hypothalamus Mechanisms

Hypothalamus influences organisms: 1. **Regulation of ANS** via descending projections to brainstem 2. **Endocrine organ** 3. **Behavior influenced** via ascending projectiosn to forebrain regions

Sympathetic Nervous System

**_Fight or Flight_** **preganglionic neuron (Ach)**: in IML of thoracic and lumbar spinal cord **postganglionic neuron (Norepi)**: sympathetic chain ganglia directly innervates adrenal medulla → epi/norepi except sweat glands which use Ach

Horner's Syndrome

Results from interuption of SNS innervation to eye. * **Miosis** ⟾ pupillary constriction * due to unopposed PNS action on iris * **Ptosis** ⟾ drooping of eyelid * due to loss of SNS to superior tarsal muscle * **Anhydrosis** ⟾ lack of sweating to ipsi face * due to loss of SNS on sweat glands

Parasympathetic Nervous System

**_Rest and Digest_** **preganglionic neuron (Ach)**: in brainstem and sacral spinal cord **postganglionic neuron (Ach)**: in or near targets Outflow mainly to glands, smooth muscles in head and neck & thoracic, abdominal, pelvic viscera. **Activation of PNS → energy conservation:** ↓ HR ↓ BP ↑ peristalsis ↑ salivation pupillary constriction bladder contraction

Pelvic Splanchnic Nerve Functions (PNS)

1. Empty bladder during micturition 2. Stimulate glandular secretions and peristalsis in hindgut 3. Faciliate defication 4. Facilitate erction 5. Stimulate secretory activity of penile glands **Pudendal nerve** in ventral rami of S2-S4. **Somatic innervation** to UG and pelvic diaphragms, external anal and urethral sphincters.

Voiding Reflex

**Bladder emptying under voluntary control.** * Fullness → S2-S4 → sensory cortex * **Frontal micturition center** ⟾ descending pathways ⟾ **voiding reflex** * Regulated by **pontine micturition center** * ⨂ of SNS → **pudendal nerve** → bladder neck → relaxation of external urethral sphincter * ⊕ of PNS → **pelvic splanchnic nerves** → contraction of detrusor → voiding

Infantile Bladder

Loss of conscious control of voiding. Damage to frontal micturition centers ⟾ reflex activation of pontine & spinal centers ⟾ bladder empties when full.

Spastic Bladder

**Hyperreflexic bladder.** Caused by lesion to **pontine micturition center**. **Adequate sphincteric control but with urge incontinence.** Bladder small and contracted. Post-void residual common. May require catheterization.

Atonic Bladder

**Flaccid areflexic bladder** or **significant loss of bladder contractility**. Due to **loss of PNS outflow** to detursor and/or **loss of afferents** from bladder/urethra. **Overflow incontinence common**. Bladder fills to capacity but urine continuously dribbles out.

CNS Pathways & ANS Flashcards

(35 cards)