Ascending/Descending Pathways (B)

Lateral Pathways

Control voluntary movement + stimulate flexor muscles

(class of pathways)

Medial Pathways

Control posture and balance + stimulate axial extensor muscles

(class of pathways)

lateral corticospinal tract, rubrospinal tract

Lateral pathways - (2)

ventral corticospinal tract, vestibulospinal tract, reticulospinal tract, tectospinal tract

Medial pathways - (4)

Corticospinal pathways

Function of pathway is primarily synapse onto inhibitory interneurons

Corticospinal Tracts

• Run from motor cortex

• Cross at Medullary Pyramids

• Up lateral or ventral divisions of pathway

• Anterior horn of spinal cord

• Descending pathway

Motor, brainstem, never, bi, uni, contra

Corticobulbar pathway DESCENDING PATHWAY

• Location - Originates in __ cortex; descends to the __

• Corticobulbar tract __ (usually/never) enters spinal cord

• Most synapses are __lateral

• Some synapses are __lateral on the __lateral side from origin (i.e. lower division of facial nerve)

Corticobulbar pathway

Synapses on cranial motor neurons and interneurons that control muscles of head and neck

Uni, corticobulbar, both

In patients who experience a stroke, why is lower portion of the face more susceptible to paralysis than upper portion of the face?

• Lower portion of face is innervated __laterally by the __ pathway

• Unlike most head/neck muscles controlled by __ hemisphere(s) of motor cortex

Extrapyramidal, red, inter, cerebral, cerebellum

Rubrospinal pathway

• Is an __ pathway

• Location - Originates in __ nucleus of midbrain

• Synapses on __neurons that communicate with alpha motor neurons

• Modulated by input from - __ cortex and __

Rubrospinal pathway

Extrapyramidal pathway that is major system of voluntary/fine motor control AND excites flexors

Extrapyramidal, vestibular, cerebellum, NOT

Vestibulospinal pathway

• Is an __ pathway

• Receives input from __ organ and __

• __ (does/not) receive input from cerebral cortex

Vestibulospinal pathway

Extrapyramidal pathway that regulates balance and posture AND excites extensors in trunk and proximal limbs

Extrapyramidal, posture, tone, intrafusal

Reticulospinal pathway

• Is an __ pathway

• Composed of 2 antagonistic pathways regulating fine control of __ and muscle __

• Influence muscle spindles via communication with __ fibers

Reticulospinal pathway

Extrapyramidal pathway that ONLY modulates activity of extensor muscles

Tectospinal pathway

Extrapyramidal pathway that modulates head and eye movement in response to auditory and visual cues

Corticospinal, vestibulospinal, rubrospinal

Communication disruption between cerebral cortex and brainstem associated with “posturing” leads to:

• *Losing function of __ pathways

• *__ pathway remains intact

• __ pathway may or may not be disrupted

Decorticate, decerebrate

• __ Posturing = Upper limb flexion, arms folded in

• __ Posturing = Upper limb extension, arms parallel

Dorsal column pathway

Pathway

Spinothalamic pathway

Pathway

Fine touch, vibration, proprioception, ascending

Dorsal Column Pathway Senses + ascending or descending

Ipsilateral, contralateral (ipsi, contra)

Dorsal column pathway injury

• Sx from spinal cord lesion below medulla will be loss of __ sensation

• Sx from spinal cord lesion at/above medulla will be loss of __ sensation

Ipsilateral, white, medulla, thalamus, somatosensory

Dorsal Column Pathway - Crosses over!

• First Order neuron

  • Sensory neuron with cell body in dorsal root

  • Axon ascends via __ (ipsilateral/contralateral) dorsal column __ (grey/white) matter to medulla

• Second Order neuron

  • Originates and immediately decussates in __

  • Ascends via medial lemniscus tract to __

• Third Order neuron

  • Originates in thalamus and ascends to __ cortex

Crude touch, pain, temperature, ascending

Spinothalamic Pathway Senses + ascending or descending

2, tract of lissauer, ipsilateral, grey, immediately, thalamus, somatosensory

Spinothalamic Pathway - Crosses over!

• First Order neuron

  • Sensory neuron with cell body in dorsal root

  • Ascends about _ spinal segments in the __ __ __

  • Terminates in __ (ipsilateral/contralateral) dorsal horn __ (grey/white) matter

• Second Order neuron

  • Originates in dorsal horn gray matter and __ (immediately/later) decussates

  • Ascends via anterolateral spinothalamic tract to __

• Third Order neuron

  • Originates in thalamus and ascends to __ cortex

above, contra, below

Spinothalamic pathway

• Site of decussation is 2 spinal segments __ (above/below) level where sensory afferent neurons enter spinal cord

• Damage to second order neuron results in __lateral sensation loss beginning about 2 spinal segments __ site of lesion

Brown Sequard Syndrome

Unilateral spinal cord hemisection

Spinothalamic, 2, below, spinothalamic, at, ipsi, corticospinal, at, ipsi, dorsal column, at

Brown-Sequard Syndrome

• Contralateral loss of pain and temp sensation from __ tract, _ levels __ site of injury and all dermatomes distally

• Ipsilateral loss of pain and temp sensation from __ tract, __ level of injury and 2 distal dermatomes

• __lateral loss of motor control from __ tract, __ level of injury and all distal dermatomes

• __lateral loss of vibration and fine touch from __ __ tract, __ level of injury and all distal dermatomes

(contra/ipsi AND — pathway AND at/below)

Precentral Gyrus

Controls motor output in motor cortex

Postcentral Gyrus

Receives sensory input in somatosensory cortex

Disc herniation

Spinal discs push outward and infringe on spinal nerve root(s) // Always an ipsilateral effect!

Motor homunculus

Sensory homunculus

Deceberate, rubrospinal disrupted, vestibulospinal intact

Posturing and pathway effects

Decerebrate posturing

Decorticate posturing