W5.1 - Motor Systems part 2

neuroscience spring '26

where are UMN cell bodies located (2)

brainstem and cerebral cortex

where do UMNs synapse (2)

local circuit interneurons or LMNs

what are the brainstem UMN centers (5)

postural control, balance, orientation to sensory stimuli, locomotion, orofacial behavior

what are the cortical UMN centers

initiation and execution of voluntary skilled movement

UMN centers work (in sequence/simultaneously), with (cortical/brainstem) centers stabilizing posture and (cortical/brainstem) centers directing the skilled component

simultaneously, brainstem, cortical

the lateral corticospinal tract is in charge of what

the skilled movements of distal limb muscles

UMNs in the (cortex/brainstem) project bilaterally

brainstem

UMNs in the (cortex/brainstem) decussate to affect the contralateral side

cortex

the axial and proximal limb muscles are controlled by UMNs in the ____

brainstem

LMNs located in the ventral horn of the spinal cord are organized in what fashion

somatotopic

what 3 motor pathways originate in the cortex?

lateral corticospinal, corticobulbar, anterior corticospinal

what 4 motor pathways originate in the brainstem?

rubrospinal, vestibulospinal, reticulospinal, tectospinal

where does the LCST start, decussate, and end?

M1, medullary pyramids, motor pools of rexed 9 of the whole SC

what is the function of the LCST

contralateral limb fractionated movement

everything above the ____ in the LSCT is ipsalateral, and everything below is contralateral

pyramids

where does the CBT start, decussate, and end?

M1, medullary pyramids, CN nuclei

where does the ACST start, decussate, and end?

M1, bifurcates at cervicomedullary junction, ends in cervical/upper thoracic SC

what is the function of the ACST

bilateral axial and girdle muscle control

how is the primary motor cortex organized

somatotopy

which map is more precise: primary motor cortex or primary sensory cortex?

primary sensory cortex

one UMN stimulates ___ LMN

>1

stimulation of M1 produces:

functional movement patterns to accomplish action goals

M1 produces ___ ____, not ___ ___ ___

motor behaviors, individual muscle contractions

what is a motor behavior

coordination of muscle actions to accomplish a behavior

the primary motor cortex (M1) is responsible for:

motor execution

the premotor cortex (PMC) is responsible for:

planning and execution of motor plans

what information does the premotor cortex receive and where does it come from? (2)

multisensory input from parietal lobules and motivational/intentional input from the prefrontal lobe

how do PMC UMNs directly influence motor behavior

through corticospinal pathways onto local circuits to organize LMNs

how do PMC UMNs indirectly influence motor behavior

through connections with M1

what percentage of axons in corticospinal tracts come from the PMC

30%

action goals encoded by M1 tend to be oriented to ____

personal space (within arm’s length)

action goals encoded by the PMC tend to be oriented to ____

extrapersonal space (beyond arm’s length)

the PMC likely uses information from __ __ __ to select movements appropriate to ____ and ____ of the action

other cortical regions, context, goal

which motor center is in charge of precise movements of distal UEs? why?

M1, it’s within arm’s reach

when a movement is associated with a signal, where in the brain do neurons fire?

lateral premotor cortex

what happens in the lateral premotor cortex in anticipation of a signal for a movement

increase of firing rate so the body is ready to react upon receipt of the signal

the lateral premotor cortex is ___, using ___________________________

reflexive, prepared/learned motor plans to respond to the environment

mirror neurons are a (medial/lateral) premotor cortex response

lateral

what is the purpose of mirror neurons? (2)

to help us understand the purposes of other people’s movements and to help us learn by watching

the (medial/lateral) premotor cortex plays a role in encoding the observed actions of others

lateral

the medial division of the premotor cortex is specialized for:

initiating movements specified by internal cues

the lateral division of the premotor cortex is specialized for:

initiating movements specified by external cues

when is the medial premotor cortex active

in performing a task from memory without an external cue

what region involved in ocular movement is located in the medial premotor cortex? what does it do here?

frontal eye fields; directs our eyes to an area of interest

if the medial premotor cortex is damaged, what happens?

reduces the number of self-initated movements

where does the RST start, decussate, and end?

magnocellular red nucleus, ventral tegmentum of midbrain, lateral column of cervical SC

what is the function of the rubrospinal tract (RST)

uncertain, may help with contralateral UE movement

where does the LVST start, decussate, and end?

lateral vestibular nucleus, no decussation, rexed 7 of full SC

what is the function of the LVST

balance

where does the MVST start, decussate, and end?

medial and inferior vestibular nuclei, bifurcates at cervicomedullary junction, cervical SC

what is the function of the MVST

positioning of the head and neck

where does the TST start, decussate, and end?

superior colliculus, medullary central tegmentum, rexed 7 of cervical SC

what is the function of the tectospinal tract (TST)?

coordination of hand and eye movementts

where does the PRST start, decussate, and end?

pontine reticular formation, no decussation, rexed 7&8 of full SC

where does the MRST start, decussate, and end?

medullary reticular formation, no decussation, rexed 7&8 of full SC

what is the function of the PRST and MRST

autonomic posture and gait related movements

what is feedforward control

creating a motor plan from start to finish in anticipation of a movement

what can feedback control do that feedforward control cannot

adjust for unexpected events

what does feedforward control receive input from

PMC, RF, sensory afferents

what does feedforward control do to our neurons

upregulates alpha and gamma motor neurons

what is feedback control

using information from the environment to adjust the motor plan

what input does feedback control receive (3)

vestibular, visual, proprioceptive

feedforward ___ the motor plan, feedback ___ the motor plan

initiates, fine-tunes

when you have inactivation at the ___ ____, you see a lack of ___ responses prior to initiation of a motor plan

reticular formation, postural

UMN syndrome is about loss of:

descending control and regulation

LMN syndrome is about loss of:

peripheral function

UMN syndrome presents with (hypertonicity/hypotonicity) with impairment of __ __ __, while LMN syndrome presents with (hypertonicity/hypotonicity) with impairment of __, ___, __ __ ____.

hypertonicity; fine voluntary movements; hypotonicity; reflexive, gross, and fine movements