Higher level motor control

Pyramidal system
- originates from where? UMN or LMN? structure names (in descending order)?

UMNs that originate from layer V of the cerebral cortex (mainly the primary motor cortex) and travel in corona radiata, internal capsule, cerebral peduncles (midbrain), longitudinal fibers of the pons, and pyramids (medulla) where partial decussation occurs to form lateral corticospinal tracts (80%, innervate limbs) and anterior corticospinal tract (20%, bilaterally innervates trunk muscles)

Extrapyramidal system

UMNs originating in the brainstem (outside the cortex) and travel in the tegmentum

Rubrospinal tracts (originates from where and involved in what)

UMNs originate from the red nucleus (midbrain) and are involved in upper arm flexion (e,g, baby crawling, arm swing, posturing in TBIs).

Tectospinal tract (originates from where and involved in what?)

originates from the tectum (superior and inferior colliculi - midbrain) and coordinates head and eye movement in response to visual and auditory stimuli

reticulospinal tract (originates from where and involved in what?)

originate from the pontine and medullary reticular formation and is involved in upright posture, patterned movement, and the stretch reflex

vestibulospinal tract (originates from where and involved in what?)

originates from vestibular nuclei (afferents from CN VIII) and is involved in maintaining head and body posture and “righting” movements

Components of the vestibular system, their location, and their function

(In the inner ear)

1) Semicircular canal - detects angular acceleration of head

2) Otolith organs (Utricle and saccules)- detects gravity and linear acceleration

3) Macula (contains hair cells- mechanoreceptors).

What stimulates hair cells in the semicircular canals?

The movement of endolymph fluid (bending of stereocilia toward the kinocilium increases action potentials)

What stimulates hair cells in the otolith organs?

Sliding of the calcium carbonate crystals (otoliths) on the otolithic membrane due to vertical/horizontal acceleration that anchor the hair cells

Pathways into the cerebellum?

• corticopontocerebellar pathway through MCP (from contralateral pontine nuclei) to relay cortical plan.

• ipsilateral vestibular system through ICP&MCP (information from vestibular organs about the whole body position in space)

• contralateral inferior olivary nucleus through ICP (motor learning loops)

• ipsilateral dorsal spinal cerebellar tract (proprioceptive information about position of individual body parts)

pathways out of the cerebellum?

• contralateral red nucleus

• contralateral VA/VL thalamus (to primary motor cortex)

• the brainstem (vestibular nucleus and reticular formation)

3 zones of the cerebellum (medial to lateral)

1. vestibulocerebellum

   • cortical area = vermis

   • deep nucleus = fastigial

   • function = balance/posture regulation of trunk and proximal limbs - outputs to brainstem

2. spinocerebellum

   • cortical area = paravermis

   • deep nucleus = interposed

   • precise control of voluntary movements of distal limbs

3. pontocerebellum

   • cortical area = lateral hemispheres

   • deep nucleus = dentate

   • function = motor planning, learning, cognition

cerebellar efferent to the thalamus and red nucleus leave from where and are excitatory or inhibitory?

from the deep nuclei

all outputs are excitatory

cerebellar efferent to the vestibular system leave from where?

the flocculus and nodule (flocculonodular lobe)

what are the 3 layers of the cerebellar cortex and their cell types?

1. molecular layer

2. Purkinje cell layer

   • excitatory inputs from climbing fibers (olive)

   • inhibitory output to deep nuclei

3. granule cell layer

   • excitatory inputs from mossy fibers (cerebllum) that excite purkinje cells

climbing fibers

from the inferior olive, excitatory, synapse onto the cell body of and directly excites Purkinje cells. one climbing fiber activates only a few purkinje cells.

mossy fibers

come from pontine nuclei, vestibular nuclei, and DSCT, indirectly innervate Purkinje cells by first synapsing on granule cells. one mossy giber can activate many purkinje cells (parallel fibers)