descendingSC

• descending projection pathways
• -motor neurons & interneurons
• -basal ganglia
• -cerebellum
• (during movements of the leg and the trunk by regulating skeletal muscles

skeletal muscle

• for muscles of hte limbs and trunk
• -motor neurons and interneurons

ventral horn and hte internal zone fo the spinal cord

cranial nerve motor nuclei and reticular formation in the brainstem

to serve as the spinal cord for the head

basal ganglia and cerebellum

does not project directly to motor neurons, but synapse on descending pathways and an important influence

seeing a cup; higher order in post parietal lobe (for id object)

• "get the idea"
• for maturation and cognition

"plan of action"

feedback control and movement intention

1. motor control pathways

• 2. regulate somatic sensory processing: somatic sensory relay nuclei (brainstem) and dorsal horn neurons (spinal cord)
• eg. pain suppression triggering of motor reflexes damage -> spasticity
• 3. regulate ANS
• cortex, amygdala, hypothalamas, brainstem --> preganglionic autonomic nerves of brainsteam and sc

• lateral corticospinal tract
• -ventral corticospinal tract
• corticobulbar tract (cranial n. motor nuclei)
• rubrospinal tract
• reticulospinal tract
• -vestibulospinal tract
• -tectospinal tract

• from FRONTAL CORTEX
• lateral corticospinal tract,
• ventral corticospinal tract
• corticobulbar tract
• FROM BRAINSTEM NUCLEI:
• rubrospinal tract
• reticulospinal tract
• vestibulospinal tract
• tectospinal tract

sometimes an intermediary before motor neurons

• segmental interneurons
• propiospinal neurons

short branches within single spinal cord segment

• projects for multiple spinal segments before synapsing onto motor n.
• long projections coordinating movements of upper and lower limbs; may transmit control signals lower, for some paths ending in cervical areas

• from lateral descending paths...
• lateral: limbs
• Medial: axial

lateral corticospinal tract

start in primary motor cortex, decussation zone and lateral motor nuclei of cervical and lumbrosacral cord

limbs

red nucleus (magnocellular) to midbrain decussation to lateral intermediate zone and ventral horn

• provides additional (residual) motor control
• -connection with the cerebellum

Ipsilateral ventral column to bilateral projections to medial grey matter

• Axial and girdle muscles
• -controls espeically for head, should, and upper trunk muscles

Rubrospinal tract and the lateral corticospinal tract

• terminate in cervical cord
• but...secondary projections to propiospinal neurons may influence lower aixal muscles

• Pontine to ventral column
• Medullary reticular formation to the lateral column (ventrolateral)

autonomoic movements: posture and repetitve movements

• superior collulus (deep)
• -coordinate head and eye movements

• lateral vestibular n. to lateral vestibulospinal tract (to all spinal limbs)
• -medial n. - med tracts for control of head position (cervical only)
• -maintains balance

• planning movement
• -integration of info from diverse cortex
• a. bg à VA (thal) à

• supplementary motor area (bimanual
• coordination) ß
• prefrontal cortex

• b.
• cerebellum à
• VL (thal) à premotor cortex à reticulospinal tracts (control of girdle muscles).

• c. Cingulate motor areas (part of limbic system) –
• rhythmical movements (e.g., pedaling a bike).

• - may
• be important in triggering movements initiated by emotions and drives.

• through Internal capsule and corticospinal fibers
• -posterior limb of the IC contains corticospinal tract
• -somatotropic: organization is maintained

• corticospinal tract courses in base of midbrain (basis pedunculi)
• -somatotopic organization is retained here
• -origin of tectospinal tract (superior colliculus) and rubrospinal tract (red nucleus) - these tracts cross close to their origins in midbrain

descending cortical fibres are no longer on ventral surface --> dive deeper within the pons (and also branch up into fasciculi) among pointe and pontocerebellar fibres

• nuclei of dorsal pons and medulla: start of vestibulospinal and reticulospinal tracts
• functions: reticular formation has mutliple projections, which makes this system highly integrative (ex. between motor and sensory)
• -analogous to intermediate zone of spinal cord

• fibres from cortex collect on ventral surface, forming pyramids
• -decussations occurs in medulla -specifically of lateral corticospinal tract axons

• motor pathways synapse on motor neurons of ventral horn and interneurons (segmental, propiospinal) of intermediate zone
• -generalized organization of grey and white matter
• -ventral horn: Rexed's laminae (VIII, IX)
• Intermediate zone: (Laminae VII)

• medially descending and terminating pathways ->girdle and axial muscles
• - cross-overs and bilateral connectivities: coordinates contaction during postural adjustments

• distal limb muscles
• terminations only evident in cervial and lumbrosacral segments (sensory limbs)
• medial input=continuous
• lateral input = interrupted

• lesions of posterior limb of internal capsule, ventral brainstem
• on 1 side produce a sequential series of symptoms (focus primarily on limb muscles)
• 1. flaccid paralysis (immed)
• 2. spasticity (a few weeks later)

-> decrease strength + muscle tone due to corticospinal interruption

increase muscle tone + exaggerated reflexe (Babinski sign) due to reticulospinal and sensory input damage (decrease feedback)