Motor Pathways Flashcards
Brainstem internal anatomy: what is the white matter?
Composed mostly of axons in fasciculi, tracts, leminisci, and peduncles
What color does the white matter stain in a myelin stain?
Grey
The rostral and caudal midbrain contain the ____ pathway
Descending
What tracts do the rostral and caudal midbrain contain?
Corticospinal tract
Corticonuclear tract
What is the function of the corticospinal and corticonuclear tract?
Aid with voluntary movement
Where does the corticospinal tract lead to?
Axons run down to the spinal cord
Where does the corticonuclear tract lead to?
Axons travel down to nuclei, go down to brainstem
Brainstem internal anatomy: what is the grey matter?
Composed of cell bodies and dendrites in the posterior and anterior horns
What color does the grey matter stain in a myelin stain?
White
Features of the spinal cord cross-sections while going down?
Greatest diameter and largest horns at cervical and lumbosacral levels
White matter decreases from superior to inferior
The descending pathway goes through the …
Rostral midbrain, caudal midbrain, middle pons, caudal pons, rostral medulla, and caudal medulla
In the cervical spinal cord, the descending pathway becomes the
Lateral corticospinal tract
LMNs innervate …. originate at …. terminate at …..
Innervate: skeletal muscle
Originate: brainstem and spinal cord
Terminate: skeletal muscle
What are signs of LMN damage?
Flaccid paralysis (paralysis with hypotonia)
Hyporeflexia (reflexes diminished)
Atrophy of muscle after weeks or months
Fasciculations (twitches)
What does one motor unit consist of?
One LMN, all of the skeletal muscle fibers it innervates
Brainstem LMNs lead to ….
Muscles contracting
LMNs for head and neck muscles, cell bodies are located….. axons are located in ……
Cell bodies in brainstem nuclei or accessory nucleus of cervical spinal cord
Axons in cranial nerves
The cell bodies for LMNs for limb muscles are located in
Spinal cord anterior horn
C5 to T1 for upper limb
L2 to S4 for lower limb
Spinal cord LMNs: axons in the limb plexus and peripheral nerves innervate
Brachial plexus innervates upper limb
Lumbosacral plexus for lower limb
Spinal cord LMNs: axons from medial part of the anterior horn innervate
Proximal muscles
Spinal cord LMNs: axons from lateral part of the anterior horn innverate
Distal muscles
Most muscles receive innervation from _____ spinal cord levels
Multiple
Need damage at multiple levels for paralysis
The function of UMNs is to …..
Activate LMNs
UMNs originate at ….. and terminate at…..
Originate: cerebral cortex and brainstem
Terminate: brainstem and spinal cord
What are signs of UMN damage?
Spastic paralysis with hypertonia
Clonus (rapid series of rhythmic contractions)
Hyperreflexia
Positive Babinski signs (extend large during plantar felxor response)
Where is the origin of the corticospinal system (pyramidal system)?
Medial and superior portion of precentral gyrus to spinal cord
What is the course of the corticospinal system?
Corona radiata, posterior limb of internal capsule, cerebral crus, descending fibers in pons, pyramid, pyramidal decussation (crossing to contralateral side), lateral corticospinal tract
Where does the corticospinal system terminate?
Contralateral spinal cord anterior horn
Area for precise and detailed movements
What is the function of the corticospinal system?
Activate LMNs which innervate flexor muscles of upper and lower limbs
Important for distal flexor muscles of wrist and fingers)
What part of the internal capsule is part of the corticospinal system?
Posterior limb
Contains axons from primary somatomotor cortex to spinal cord genu
What are the vascular territories of the corticospinal system?
Spinal cord: anterior spinal artery
Medulla: anterior spinal artery
Pons: basilar artery
Midbrain: posterior cerebral artery
Where is the origin of the corticonuclear system (corticobulbar system)?
Lateral portion of the precentral gyrus to brainstem and spinal cord
What is the course of the corticonuclear system?
Corona radiata, genu of internal capsule, cerebral crus, descending fibers in pons
Where is the termination of the corticonuclear system?
Contralateral projections to nuclei of CN X and XII
Ipsilateral projections to CN XI nucleus
Bilateral projections to CN V nucleus
No projection to nuclei of CN II, IV, and VI
What is the function of the corticonuclear system?
Activate LMNs which control
V: mastication
VII: facial expression
X: swallowing and vocalization
Xi: shrugging shoulders and turning head to contralateral side
XII: tongue movements
What are the targets of the corticonuclear system in the face and neck?
Facial motor nucleus CN VII: facial expression muscles
Nucleus ambiguus CN X: uvula, soft palate muscles, larynx
Hypoglossal nucleus CN XII: tongue muscles
What is the primary UMN lesion sign for the corticonuclear system?
Contralateral spastic paralysis
What are some clinical signs for lesions of the corticonuclear system?
Spastic paralysis of contralateral face (CN VII)
Uvula deviates contralateral to paralysis, dysarthria, difficulty swallowing, loss of gag reflex (CN X)
Tongue deviates to ipsilateral side of paralysis, dysarthria (weak or hoarse voice, slurred speech) (CN XII)
What areas is the motor cortex influenced by?
Supplementary motor cortex
Premotor cortex
Ordering of firing in the motor association cortex?
- Ready (supplementary motor cortex)
- Set (premotor cortex)
- Go (primary motor cortex)
Damage in the motor association cortex leads to
Apraxia
What is apraxia?
Inability to produce voluntary movement despite normal muscle power and tone and normal reflexes
Review of blood supply of the cerebrum:
MCA supplies ….
ACA supplies ….
PCA supplies ….
MCA: lateral cerebral hemispheres
ACA: medial frontal and parietal lobes
PCA: medical temporal and occipital lobes
UMNs activate …. originate …. terminate ….
Activate LMNs
Originate in the cerebral cortex and brainstem
Terminate in the spinal cord
What is the sequence of events of a tendon (stretch) reflex?
Muscle is stretched
Muscle spindles excite sensory neurons
Sensory neurons excite LMNs to stretched muscles
LMNs stimulate stretched muscles to contract
What are muscle spindles?
Located in skeletal muscles
Continuously monitor length and changes in the length of muscle
What is the jaw jerk reflex?
Stretch reflex that is used to rest the status of UMNs that activate trigeminal motor nucleus
Mandible is tapped at a downward angle just below the lips at the chin while the mouth is held slightly open
What would the jaw jerk reflex look like with UMN damage? What is the normal reflex?
Abnormal: Masseter will contract and jerk the mandible superiorly, exaggerated
Normal: reflex is light or absent
The tendon reflex is used to … usually tested on …
Test integrity of spinal cord segments
Biceps, triceps, patellar, achilles
Where is the origin of the vestibulospinal tract?
Vestibular nuclei
What is the function of the vestibulospinal tract?
Activates ipsilateral spinal cord LMNs which innervates trunk and proximal limb and extensor muscles related to balance and posture
What does the vestibulospinal tract activate in response to?
Postural instability
Feedback pathway
Vestibulospinal tract is activated to reestablish or maintain stable posture
Where is the origin of the reticulospinal tract?
Reticular formation
What is the function of the reticulospinal tract?
Activates ipsilateral spinal cord LMNs which innervate trunk and limb extensor muscles
Related to postural support of limb movements
When is the reticulospinal tract activated …..
Prior to limb movement
When is the reticulospinal tract activated …..
Prior to limb movement
The feedforward pathway of the reticulospinal tract activates
The reticulospinal tract to establish appropriate posture to support limb movement
LMNs connected to flexor muscles are activated by ______ tract
Corticospinal tract
LMNs connected to extensor muscles are activated by ____ tract and ____ tract
Vestibulospinal tract
Reticulospinal tract
UMN systems: corticospinal tract general functions
Neurons of motor cortex activate contralateral spinal cord LMNs
Control of individual muscles or groups of muscles for purposeful movement
Mainly flexor muscles, especially those related to dexterous movement
UMN systems: corticonuclear tract general functions
Neurons of motor cortex activate the brainstem LMNs of cranial nerves
Does not activate LMNs associated with CN III, IV, and VI
UMN systems: vestibulospinal tract general functions
Neurons of vestibular nuclei activate ipsilateral spinal cord LMNs
Control of trunk and proximal limb extensor muscles related to posture and balance in response to postural instability feedback pathway activating the vestibulospinal tract to reestablish or maintain posture
