Ascending Tracts😍

Ascending Tracts

• First-order neurons from muscles and joints
• enter spinal cord
• via dorsal root ganglion (DRG).

• Mnemonic: CTLS → always downwards

Spinothalamic Tract

• MTSL → Manage 3rd stage Labor

Sensory Tract	Carries C/L
Lateral Lemniscus	Hearing sensation
Spinal Lemniscus	Pain and temperature from body
Trigeminal Lemniscus	Pain and temperature from face
Medial Lemniscus (Anterior STT & DCT)	- Pressure & crude touch - Conscious proprioception - Fine touch - Vibration - Stereognosis

• Lesion
• Loss of pain, temperature, crude touch, pressure
• below lesion.
• Brainstem → C/L
• Spinal cord → C/L
• At the level of entry of tract → I/L

Function

• Lateral spinothalamic tract
• Pain & temperature

• Anterior spinothalamic tract
• Crude touch, pressure, tickling, itching, sexual sensation.

• Fiber location:
• Cervical inner, sacral superficial.

Sensations Carried

Pathway

1. First-order neuron
• Cell body in Dorsal Root Ganglion (DRG)
• Enters spinal cord → synapses in Substantia Gelatinosa (Lamina II)

2. Second-order neuron
• Crosses to opposite side (anterior white commissure)
• Ascends in the anterolateral (spinothalamic) tract

3. Third-order neuron
• Synapse in Thalamus (VPL nucleus)
• Projects via thalamic radiations to primary somatosensory cortex (areas 3, 1, 2)

Clinical Relevance

• Highest center for pain perception = Thalamus

4 types of Arnold Chiari malformations

ㅤ	ㅤ
Type 1	• Cerebellar tonsil herniation • +/- syringomyelia (painless burns in hand)
Type 2	• Herniation of medulla • + 4th ventricle + vermis + myelomeningocele ↳ Headache increases on sitting ↳ Valsalva maneuver
Type 3 and 4	• not compatible with life

Cerebellar tonsil herniation

Syringomyelia:

• Causes central canal lesion

• fluid-filled cavity (syrinx) within the spinal cord.

• A/w Chiari malformation Type 1, trauma, or tumors

• damage to spinothalamic tract fibers crossing the anterior commissure

Central canal lesion

• B/L loss of pain & temperature initially
• due to disruption of decussating fibers
• Preserved touch and vibration (Proprioception)

• Cape-like distribution Sensory loss over the nape of the neck

• First affect Cervical spinothalamic

• f/b LMN dysfunction
• due to anterior horn cell compression if large lesion
• features
• muscle wasting,
• weakness
• hyporeflexia in the upper extremities.

• Autonomic dysfunction:
• Bowel and bladder dysfunction in advanced cases

• UL > LL

Anterior canal lesion

• Pain and temperature loss + Motor loss together appears

• Involves anterior 2/3rd of column

• UL = LL

• Preserved touch and vibration (Proprioception)

Dorsal Column - Medial Lemniscus (DCML) Pathway

Mnemonic: CTLS → always downwards

 

• DCT injury
• I/L loss conscious propioception, vibration, stereognosis, fine touch.

Components

• ”Mneumonic: gods Grace (gracilis), Men (medially) can walk (lower limb)“

Fasciculus	Carries Sensations From	Location
Fasciculus gracilis (FG)	Lower limb & lower trunk	Medial
Fasciculus cuneatus (FC)	Upper limb & upper trunk	Lateral

First Order Neuron

• Originates from Dorsal Root Ganglia (DRG)

• Enters spinal cord → ascends ipsilaterally in FG or FC

• Synapses in medulla
• Nucleus gracilis (for FG)
• Nucleus cuneatus (for FC)

Second Order Neuron

• From nucleus gracilis/cuneatus in medulla

• Axons decussate as
• internal arcuate fibers

• Ascend as medial lemniscus

• Synapse in VPL nucleus of thalamus

Third Order Neuron

• From VPL of thalamus to:

• Primary somatosensory cortex (Brodmann areas 3, 1, 2)
• via thalamic radiations

Function

• Localizing pressure

• Fine touch

• Two-point discrimination.

• Vibration sense

• Conscious proprioception

• Stereognosis

• Fiber location:
• Sacral medial
• cervical lateral.

Nucleus Proprius:

• Interneuronal relay in the dorsal horn
• not part of DCML proper
• involved in reflex arcs

• LMN (Lower Motor Neuron):
• Works with nucleus proprius
• to maintain reflex arc

Spinocerebellar Tracts

• Injury to spinocerebellar tract
• I/L
• ataxia,
• loss of unconscious proprioception.

• Superior Cerebellar Peduncle:
• Ventral Spinocerebellar Tract (crosses twice)

• Inferior Cerebellar Peduncle:
• Dorsal Spinocerebellar Tract,
• Cuneocerebellar Tract

Function

• Carry unconscious proprioception
• from muscles, joints, and tendons to the cerebellum.

• Important for coordination and balance.

Lesion Concepts

• Lesion of Fasciculus cuneatus (FC):
• Results in ipsilateral loss of:
• Conscious proprioception & vibration from UL
• Unconscious proprioception (cuneocerebellar) from UL

• Lesion of Fasciculus gracilis (FG):
• Results in ipsilateral loss of:
• Conscious proprioception & vibration from LL

Thalamic Radiations Projecting on Cortex

• Acts as a relay station for sensory information.

Ascending Tract	Part if IC
Anterior thalamic radiation	Anterior Limb
Superior thalamic radiation	Genu
Inferior thalamic radiation	• Sublentiform part • Auditory radiation
Posterior thalamic radiation	• Retrolentiform • Optic radiation

Nuclei & Their Input

• All ventral Together forms Superior thalamic radiation

Nuclei	Destination	Input
ATN	Cingulate gyrus	• Part of limbic system • Anterior Thalamic Radiation • Mammillary bodies → Mammillothalamic tract
Ventroanterior (VA)	Premotor Area (6)	• Globus pallidus → Pallidothalamic tract • VA yil Pallu
Ventrolateral (VL)	Motor cortex (4)	• Dentato-thalamic tract • Dentato-rubrothalamic tract • VL → Villan → Dental doctor
Ventroposterolateral (VPL)	Sensory Cortex (3, 1, 2)	Sensations from limbs • Medial lemniscus → Dorsal + Anterior STT • Spinal lemniscus → Lateral STT • Postero lateral → Posterior coloumn tract and lateral spinothalmic tract • vpL → Limbs
Ventroposteromedial (VPM)	Sensory Cortex (3, 1, 2)	• Trigeminal lemniscus: sensations from mouth & face • Nucleus of tractus solitarius: visceral sensations • vpM → Mouth
MGB	Auditory Cortex	Go below the lentiform nucleus • Sublentiform fibers • Inferior thalamic radiation • Connects Inferior Colliculus • 41, 42 → hear about restaurant • 43 → taste it
LGB	Visual Cortex (17)	Go behind the lentiform nucleus • Retro lentiform fibers • Posterior thalamic radiation • Connects Superior Colliculus • start meeting people → at 17

Applied aspect

Dejerine-Roussy Syndrome (Thalamic Pain Syndrome)

• Thalamus
• Function: Sensory relay station.
• 3rd order neurons present.
• Nucleus involved:
• Ventroposterolateral (VPL)
• carries touch, pain, temperature.

• Pathology
• Stroke (infarction) → Irritable VPL nerve fibres → ↑ Neuronal signalling.

• Symptom
• Excruciating pain

Laws in Sensory Physiology

Bell–Magendie Law

• Dorsal root → Sensory

• Ventral root → Motor

• Mnemonic: Door (Dorsal) bell (Bell megendie) is ventrally (Ventral)

Law of Specific Nerve Energies (Müller’s Doctrine)

• Each receptor detects a specific sensation

• Examples:
• Pain receptor → Pain
• Touch receptor → Touch
• Cold receptor → Cold

• Mnemonic: Kayyil mulli → athoru specific sensation ayirunnu

Law of Projection

• Stimulation of a receptor
• Cortex projects sensation back to the lowest receptor level
• where the sensation originated

Cortical Plasticity

• Cortical reorganization by adjacent areas following injury.

• Example: Hand amputation → Hand area in cortex taken over by arm area → Arm pain felt as hand pain (Phantom limb pain)
• Primary somatosensory area = 4

• Mnemonic: Plastic prosthesis → Hand amputation

Weber–Fechner Law

• Magnitude of sensation ∝ log of initial stimulus intensity

• Mnemonic: SpiderWeb to skin → no intensity → no sensation