1.7 Motor System: Upper Motor Neurons

what is movement driven by?

peripheral nerves, the spinal cord, the brainstem, the cerebellum, and the forebrain

how is movement shaped?

context, intention, motivation, sensation

movement is driven by both ______ and _______ systems

motor;sensory

what must coordinate to determine the output signal of LMN (in brainstem or spinal cord)?

somatosensory and UMNs from cerebral cortex

UMN communicate with somatosensory pathways and send signals to ____ to intiate action

LMN

UMN are either (3 broad categories)...

•Postural/gross movement tracts (limb/postural movements)

•Selective motor control tracts (isolated, fine movements)

•Nonspecific tracts

role of cerebellum and motor basal ganglia in central motor system

- modulate signal of descending motor tracts (excite/inhibit)

- help make movements smooth

UMNs provide all motor signals from the _____ to the ______ ________

brain; spinal cord

where do UMN come from?

cerebral cortex or brainstem

where do UMN project?

LMN and/or interneurons of SC

how are UMN classified?

where they synapse to relative to ventral horn

medial UMN innervate

broad postural and gross limb muscles

lateral UMN innervate

specific, all muscles but are the only UMN for distal muscles

these are the only UMN responsible for distal control of muscles

lateral UMN

nonspecific LMN (throughout) have what functions? examples?

background excitation, facilitate local reflexes

(examples: muscle tone, coordinate movements, enhance reflex response)

UMN medial tracts innervate muscles of the

include what they do not innervate

neck, trunk, limbs

NOT: wrist/finger extensors, dorsiflexors, toe extensors, hand/foot intrinsic muscles

movements due to innervations of UMN medial tracts often occur without

conscious effort---> most triggered by brainstem

ex. turning towards a loud noise, balance adjustments, tripping response

where do UMN medial tracts originate?

brainstem (x3)

cerebral cortex (x1)

what are axons?

medial white matter of spinal cord

what do axons synapse with? what is their role?

medial LMN pools

role: supply postural and axial muscles

medial tracts CANNOT....

isolate specific muscle activation because axons branch widley to multiple LMN and multiple muscles

what are the 4 main medial tracts? general function?

1.Reticulospinal

2.Medial vestibulospinal

3.Lateral vestibulospinal

4.Medial corticospinal

function: postural and gross limb movements

where does the reticulospinal tract start?

reticular formation of brainstem

role of reticulospinal tract

- bilateral posture (go to both sides), gross limb movements

- coordinate simultaneous contraction of different muscle groups via propriospinal interneurons (allow is to hit different LMN)

Propriospinal interneurons help provide:

•Anticipatory postural adjustments

•Muscle synergies

what are muscle synergies?

agonist muscles contracted at the same time to accomplish broader task

what are anticipatory postural adjustments?

ex?

signals to other muscle groups that prepare them for movement

reaching arms forward ---> moves COM forward

what are muscle synergies?

ex?

Activation of multiple muscle groups to achieve a specific task

ex.

•Reaching up to grab something off the top shelf

•Walking

reticulospinal tract UMN receive ilfunce from what 3 areas

•Cerebral cortex

•Cerebellum

•Sensory input to reticular formation

*help contextualize info to make motion smooth

where does the medial vestibulospinal tract start?

medial vestibular nuclei in the brainstem

where does the medial vestibulospinal tract receive afferent information?

vestibular apparatus in inner ear which relates to head movement and position info

what structure is responsible for sending info to the vestibular apparatus in inner ear?

vestibulocochlear nerve

where does the medial vestibulospinal tract project?

projects bilaterally cervical and thoracic spinal cord

primary role of medial vestibulospinal tract

control neck and upper back muscles

where does the lateral vestibulospinal tract start?

lateral vestibular nuclei in brainstem

where does the lateral vestibulospinal tract recieve info from?

vestibular apparatus in inner ear which relates to gravity information

where does the lateral vestibulospinal tract project?

projects ipsilaterally to all spinal cord regions

*projects to side signal originated from*

primary role of lateral vestibulospinal tract

excitatory to ipsi. extensors, inhibitory to ipsi. flexors

where does the medial corticospinal tract start and end?

cerebral cortex and ends in medial side of SC

in what situations is the lateral vestibulospinal tract constantly active?

during standing to maintain CoM over BoS

UMN of the medial corticospinal tract are directly connected to the

cerebral cortex

what type of muscle control does the medial corticospinal tract take part in?

voluntary muscle control

where do axons of the medial corticospinal tract project (include how)? why?

both ipsilateral and contralateral spinal cord by having some axons decussate at the spinal level they exit

this is important for bilateral control

primary role of medial corticospinal tract?

gross motor control over neck, shoulder, and trunk muscles

what is the primary pathway for controlling voluntary movement?

lateral corticospinal tract

what is the primary role of the lateral corticospinal tract?

- selective motor control

- innervate all skeletal muscle

- can activate individual muscles independent of others (also dampen activation of other muscles)

- coordinates with reticulospinal tract to control muscle synergies

where does the lateral corticospinal tract travel?

- ipsilateral and contralateral limbs

(ipsilateral and contralateral UE, contralateral LE)

what does the lateral corticospinal tract synapse with to perform selective motor control?

- LMN for single muscle

- interneurons that inhibit other muscles

the lateral corticospinal tract is solely responsible for

- wrist/hand extension

- ankle dorsiflexion

- toe extension

- hand/foot intrinsics

where does the lateral corticospinal tract start?

primary motor cortex and premotor cortex (motor planning area)

what is the pathway of the lateral corticospinal tract?

starts in primary motor cortex and premotor cortex and travels down the internal capsule goes through cerebral peduncles (midbrain) then goes though anterior pons where it reaches the medullary pyramids and lateral spinal cord

where do majority of the axons dessucate from the lateral corticospinal tract?

medullary pyramids and lateral spinal cord

primary role of nonspecific upper motor neurons

enhance interneuron, LMN activity

what are the 2 nonspecific upper motor neuron tracts from the brainstem?

1. Ceruleospinal tract

2. Raphespinal tract

where does the Ceruleospinal tract start and what does it release?

job?

• Starts at locus coeruleus (midbrain/pons)

• Releases norepinephrine

• background activity; downregulates pain signals

where does the Raphespinal tract start and what does it release?

• Starts at raphe nuclei (medulla)

• Releases serotonin

• can excite and tamp down pain signals

when are nonspecific upper motor neurosn active?

during intense emotional states via the emotional motor system

do nonspecific upper motor neurons provide specific motor input? what is the significance of this?

no it provides broad motor input. this is why during high stress moments we tend to have poor performance

ex. keys in door when getting chased , missing a wide open shot

primary role of corticobrainstem tracts

voluntary control of

muscles of the head and most muscles of the neck

where does the corticobrainstem tract start and end?

primary motor, premotor cortices and ends at brainstem

what do the corticobrainstem tracts synapse with? function?

CN 3-12 to control muscles of face, head, and neck

*DOES NOT SYNAPSE WITH CN 1,2,8)

what lobe, sulcus, and gyrus is the primary motor cortex found?

frontal lobe; central sulcus, pre-central gyrus

what is the primary motor cortex responsible for?

responsible for precise, (mostly) contralateral control of movement

the cell bodies for what 3 main tracts are found in the cortical motor area?

1. medial corticospinal tract

2. lateral corticospinal tract

3. corticobrainstem tract

homunculus represents

joint motions (not muscles)

what 2 areas anterior to the PMC are responsible for preparing for movement?

1. premotor cortex/area

2. supplementary motor cortex/area

what surface is the premotor cortex/area found? function?

- lateral surface

- planning/coordination of gross movements (ex. reaching for an object, taking a step)

what surface is the supplementary motor cortex/area found? function?

- superior, medial surface

- planning/coordination of sequential and bilateral movements, especially fine motor (ex. putting on socks, buttoning a button)

potential causes of UMN lesions

stroke, cerebral palsy, spinal cord injury, traumatic brain injury, developmental disorders

where can UMN lesions occur?

cerebral cortex, brainstem, spinal regions and

damage can be classified as loss of function or gain of function

loss of function due to UMN lesions

loss: absence of normal feature (paralysis, hypotonia, impaired motor control)

gain of function due to UMN lesions

gain: extra feature (hypertonia/spasticity, abnormal reflexes, cocontraction)