Ascending and Descending Pathways ☺️

Question 1

Spinothalamic tract

• functions
• pathway

Answer 1

Lateral - pain, temperature
Anterior - crude touch, pressure

Sensory neurone synapses in DH of SC
Decussates ventrally in SC
Ascends via STT
2ndary neurone synapses in VPL nucleus of  thalamus
3ary neurone ascends via TCT
Synapses in somatosensory cortex

Question 2

Effects of lesions in spinal cord affecting the

• STT
• MLT

Answer 2

STT - Contralateral sensory loss

MLT - Ipsilateral sensory loss

Question 3

Medial leminiscal tract

• functions
• pathway

Answer 3

Proprioceptive
Fine touch
Vibration

Upper limb (T6 upwards) => fasciculus cuneatus (lateral dorsal column)
Lower limb (T6 downwards) => fasciculus gracilis (medial dorsal column)
Synapse with nucleus cuneatus of medulla oblongata
Decussates ventrally in MO
2ndary neurone synapses in VPL nucleus of thalamus
3ary neurone ascends via TCT
Synapses in somatosensory cortex

Question 4

Corticospinal tract

• functions
• pathway

Answer 4

Motor function of body from

• primary motor cortex
• premotor cortex
• supplementary motor area
• somatosensory area

Cortex => internal capsule => medulla
DIVIDES INTO 2
Lateral decussates in medulla => ventral horn in SC => supply muscles of the body

Anterior descends into SC => decussates => ventral horn in cervical, upper thoracic SC

Question 5

Corticobulbar tract

• functions
• pathway

Answer 5

Same inputs as CST

Cortex => internal capsule => brainstem => motor nuclei of CN
-bilateral innervation of UMN
EXCEPT
-contralateral for UMN VII
(LMN that supplies upper face gets innervation from both sides)
(LMN that supplies lower face gets innervation from contralateral side only)

Question 6

Effects of lesions in the SC affecting the

• CST
• CBT
• EPT

Answer 6

Lateral => ipsilateral motor loss
Anterior above lesion => contralateral motor loss

Increased muscle tone
Increased reflexes, +ve Babinski
Increased fasciculations
Muscle weakness

CNVII => spastic paralysis of contralateral lower face

Often in encephalitis, tumours, degenerative conditions
-dyskinesias

Question 7

Extrapyramidal tracts

Answer 7

Brainstem - involuntary, automatic control of muscle

IPSILATERAL - vestibulospinal, reticulospinal
CONTRALATERAL - rubrospinal, tectospinal

Vestibulospinal - inputs from balance nuclei

• innervate arm flexors, leg extensors
• balance and posture

Reticulospinal

• MRS from pons => voluntary mv, increased tone
• LRS from medulla => inhibits voluntary mv, reduced tone

Rubrospinal - inputs from red nucleus in midbrain
-decussate in midbrain => SC => fine hand mv control

Tectospinal - inputs from sup colliculus (visual inputs)
-decussate in midbrain => cervical SC => head mv in response to visual stimuli