Exam 2- Tracts Simplified

Corticospinal tract function

Voluntary, fine, dexterous movements

CST origin

Primary motor cortex, premotor cortex, supplementary motor area

CST decussation?

Lateral- 90% of the UMN axon decussate in the medulla pyramids

Medial- 10% continue down the SC without crossing

Lateral CST function

Principal motor control pathway

Lateral CST destination

Neurons that innervate the muscles of the distal limbs (hands, fingers)

Injury to Lateral CST would cause

loss of fractionated movements (inability to move digits independently)

Medial CST function

Provides bilateral supply of the postural muscles and axial skeleton

Medial CST destination

Neurons that innervate the muscles of the trunk and shoulders (axial and girdle muscles)

Corticobulbar tract function

Controls the muscles of the face, neck, tongue, jaw, larynx, pharynx

Corticobulbar tract origin

Cerebral cortex

Corticobulbar tract destination

Cranial nerve nuclei in the brainstem

Corticobulbar tract lesion would cause

Contralateral weakness

Extrapyramidal motor pathways decussation

Do NOT decussate in the pyramids

Rubrospinal Tract function

Helps with arm control, NOT leg control

Rubrospinal Tract decussation

Crosses immediately within the midbrain

Reticulospinal tract function

Controls the proximal muscles of the limbs for automatic movements like walking and reaching

Reticulospinal tract origin

Reticular formations of the pons and medulla

Reticulospinal tract (pontine/ medial)

Facilitates extensors, inhibits flexors

Reticulospinal tract (Medullary/ Lateral)

Inhibits extensors, facilitates flexors

Tectospinal tract function

Flinch reflex in response to auditory or visual stimuli

Tectospinal tract decussation

Crosses descending the cervical spinal cord

Vestibulospinal tract function

Helps with balance and posture

Medial Vestibulospinal tract function

Coordinates head and eye input

Lateral Vestibulospinal tract function

Controls axial and proximal muscles (fine adjustments to maintain balance)

DCML function

Highly detailed, precisely localized information

Discriminative (fine) touch, vibration, conscious proprioception

DCML origin

First-order sensory neurons enter the SC and ascend ipsilaterally in the dorsal columns

DCML Fasciculus Gracilis function

Sensory information from the LE and worse (T6 and below)

DCML Fasciculus Cuneatus function

Sensory information from the UE and torso (T5 and above)

DCML Decussation

Medulla

DCML destination

Thalamus via medial lemniscus

DCML lesion

ipsilateral loss of discriminative touch sensation and conscious proprioception below the level of lesion

Spinothalamic tract function

Pain, temperature, course touch

Spinothalamic tract decussation

Immediately in the SC in the dorsal horn

Spinothalamic tract destination

Thalamus

Spinothalamic tract pain fibers

A-delta and C fibers

Spinothalamic tract A-delta fibers

Lightly myelinated, transmit signals quickly, causing a sharp, localized "first pain"

Spinothalamic tract C Fibers

Unmyelinated, they transmit signals slowly, causing a dull, throbbing, and diffuse "second pain"

Spinothalamic tract lesion

Loss of pain and temperature sensation on the contralateral side

Spinocerebellar tract function

Continuous, unconscious information to the cerebellum to help with fine-tuning movement and posture (proprioception)

Spinocerebellar tract destination

Cerebellum

Spinocerebellar tract (Dorsal) decussation

Uncrossed

Spinocerebellar tract (Ventral) decussation

Crosses twice-- Once in SC and another in the Brainstem (superior cerebellar peduncle)

Spinocerebellar tract lesion

Ataxia (lack of coordinated movements), tremors, atrophy