Lab 10: Upper And Lower Motor Systems Flashcards
Lateral Prefrontal Cortex
An area in the anterolateral frontal lobe that processes sensory and memory information for analysis and decision making
Premotor Area (PMA)
A vertical strip of cortex rostral to the precentral gyrus (in the middle and inferior frontal gyri). It’s part of the circuitry for motor planning for voluntary actions
Supplementary Motor Area (SMA)
Area anterior to the upper precentral gyrus and paracentral lobule. It’s also part of the circuitry for motor planning
Areas of Primary Motor Cortex that contain upper motor neurons that deliver orders to lower motor neurons for movement
Precentral Gyrus
Anterior paracentral lobule
Anterior cingulate cortex: used in emotion and culture-driven movements
Frontal Eye Field
This cortical motor center sends axons for voluntary eyeball movements through the anterior limb of the internal capsule and the reticular formation to reach premotor centers for synchronized eye movements
-because FEF fibers travel separately from other cortical UMN and terminate on premotor centers rather than LMNs, they’re not considered a formal part of the cortical UMN system. But they ARE a part of the cortical system for voluntary movements
Lateral Prefrontal cortex (hierarchy)
Area for thinking, planning and decision making. This cortex is often referred to as the “executive” Cortex for the highest level of command (the CEO of voluntary movements)
PMA and SMA (hierarchy)
Cortical areas involved in circuits with the basal ganglion, sensory association cortex and cerebellum in order to select specific motor sequences that match the actions decided by the cortical CEO to environment and body conditions. These areas of cortex are considered the “motor planning” areas for voluntary movement
Primary Motor Cortex (hierarchy)
Receives movement-sequence decisions from the motor planning cortex and translates them into orders for muscle contractions needed for the desired action. The primary motor cortex transmits these orders mainly to lower motor centers and local area networks of interneurons, although a small percentage send terminals directly to lower motor neurons. The neurons in the primary cortex that influence lower motor neurons are described clinically as upper motor neurons. They use glutamate as their neurotransmitter and they have cell bodies in Layer V of the cortex.
Anterior Limb of the Internal Capsule
Contains fibers passing to and from the anterior part of the frontal lobe including the frontal eye field
Genu
Contains fibers from the lower area of the precentral gyrus, including corticobulbar fibers that descend to the GSE and BE lower motor neurons of the brainstem for voluntary movement of head muscles
Posterior Limb
Contains many axons, including descending fibers from the upper precentral gyrus and paracentral lobule, for voluntary movement of the trunk and limbs
Anterior limb of internal capsule (location)
Between lentiform nucleus laterally and head of caudate nucleus medially
-contains fibers from the frontal eye fields and descending fibers that send info to the cerebellum
Genu of internal capsule (location)
- between the lentiform nucleus and Interventricular foramen
- contains corticobulbar fibers en route to motor nuclei for striated muscles of the head
Posterior Limb of the internal capsule (location)
-between lentiform nucleus and thalamas
-contains:
Descending corticospinal fibers to motor nuclei in the spinal cord
Ascending thalamocortical fibers to primary somatosensory cortex
descending fibers that send info to the cerebellum
thalamus (location)
Each half is located between the posterior limb capsule and the III ventricle
Corticospinal/Corticobulbar Tracts (path overview)
-travel in the ventral brainstem, ipsilateral to their cell bodies in the motor cortex. Most corticospinal fibers cross in the medulla and travel in the lateral column of the spinal cord, contralateral to their cells of origin and ipsilateral to their targets
Red nucleus (tegmentum of rostral midbrain)
- a brainstem upper motor neuron center that is embedded in the reticular formation. It receives input from descending fibers form the primary motor cortex
- the red nucleus sends axons across the midline at this level. Its fibers then descend in the brainstem reticular formation and lateral white matter of the spinal cord. In humans, this Nucleus functions with the motor cortex mainly in initiating flexor movements of the proximal upper arm
Oculomotor Nucleus (tegmentum of rostral midbrain)
- a GSE motor nucleus to most extraocular muscles; is embedded in the PAG near the midline. It doesn’t receive direct corticobulbar fibers but it’s supplied by premotor nuclei, including saccade centers like the PPRF for voluntary eye movements as well as the vestibular nuclei for reflex eye movements
- fibers from the FEF travel through the reticular formation, not with the corticobulbar system
Location of descending Corticospinal and corticobulbar fibers in the caudal midbrain
Eternally, in the transition from the crus cerebri to the basilar pons
Trochlear Nucleus (caudal midbrain)
Located in the lower PAG of the midbrain. It receives input from
- The FEF via brainstem saccade centers for voluntary eye movements
- The vestibular nuclei for reflex eye movements
- this nucleus sends its fibers dorsally and across the midline caudal to the inferior colliculus
MLF (caudal midbrain)
Located immediately ventral to the trochlear Nucleus; brings input to this nucleus from the vestibular nuclei and saccade center
Corticospinal/Corticobulbar location in the Mid Pons
-ventral area of the base of the pons
Pontine reticular formation
Contains scattered cells of the reticular nuclei with UMNs that contribute to changes in postural set associated with movements of the body; also contains descending rubrospinal fibers
Motor Nucleus of V (mid pons)
Located in the lateral periventricular zone; receives corticobulbar fibers bilaterally from both left and right motor cortex; receives input from afferent fibers in the jaw muscles for the jaw jerk reflex
Trigeminal Nerve (mid pons)
Passes anteriorly from the middle cerebellar peduncle toward the posterior area of the cavernous sinus
Corticospinal/corticobulbar fibers (caudal pons)
- in the base of the pons
- the corticobulbar system sends branches to the facial motor Nucleus bilaterally for LMN that supply upper facial muscles like the orbicularis oris and contralaterally only to the LMN supplying the lower or perioral facial muscles
Facial Nucleus (VII) (Caudal Pons)
In ventrolateral pontine tegmentum; receives input from the corticobulbar system for voluntary facial movements
Facial Nerve Roots (caudal Pons)
Travel dorsomedially from the nucleus, then bend around the abducens nucleus and travel ventrolaterally to exit the brainstem lateral to the base of the pons, near the cerebellar flocculus
NOTE: cranial nerves with BE fibers exit the brainstem lateral to cranial nerves with GSE fibers
Abducens Nucleus (caudal pons)
Receives info from the premotor Nuclei, including the PPRF and the vestibular Nuclei via the MLF. This nucleus supplies the ipsilateral lateral rectus muscle
Abducens Nerve Roots (caudal Pons)
Travel ventrally from the abducens nucleus, lateral to the medial lemniscus, and exit the brainstem at the pontomedullary junction, medial to the exit of facial nerve fibers.
NOTE: abducens nerve roots and descending Corticospinal/corticobulbar fibers could be affected in a single vascular insult
Pontine Reticular Formation (caudal)
Contains he PPRF (premotor nuclei for horizontal saccades) and cells of the pontine part of the reticular motor nuclei (upper motor neurons involved in adjustments for postural changes), as well as descending rubrospinal fibers
Vascular Note about the Abducens Nerve Roots
Descending corticospinal/corticobulbar fibers are often in the same paramedian vascular zone as abducens nerve roots passing thru the base of the pons. A one-sided stroke in this zone could result in ALTERNATING hemiplegia: weakness on the contralateral side of the body and the ipsilateral lateral rectus muscle
Pyramidal Tracts (rostral Medulla)
Corticospinal fibers (almost all corticobulbar fibers have branched off to reach the medullary motor nuclei)
Medullary Reticular Formation
Contains the medullary reticular nuclei, brainstem upper motor neurons that receive input from the motor cortex and mechanoreceptors and contribute to postural adjustments
Vestibular Nuclei (rostral medulla)
A multifunctional group of nuclei in the lateral periventricular gray that:
- contain brainstem UMNs that send descending fibers in the vestibulospinal tracts to spinal lower motor neurons to maintain body balance in space
- contain premotor neurons that adjust contraction of eyeball muscles to keep object son the fovea of the eye during head movements via MLF
- contain neurons that stimulate LMN for resting muscle tone
- receive major input form the vestibular nerve and cerebellum, with NO direct input from the primary motor cortex
Hypoglossal Nucleus
Supplied by corticobulbar fibers (usually bilaterally, but often asymmetrically)
-is a GSE nucleus that supplies tongue musclesa
Hypoglossal Nerve Roots
Travel between the pyramidal tract and the inferior olivary nucleus
-are located in the paramedian vascular zone, along with the pyramidal tracts
Nucleus Ambiguus
Located general position in the central area of the reticular formation
-a BE Nucleus that sends fibers laterally into CN X (and IX) to supply swallowing and breathing muscles of the pharynx, larynx and palate; usually receives bilateral cortical supply via corticobulbar fibers
General Path of the Rubrospinal, Vestibulospinal, and Reticulospinal tracts
In the reticular formation of the Brainstem
Decussation of the Pyramids
Lateral corticospinal tract
Ventral Corticospinal tract
Uncrossed fibers of the pyramidal tracts descend on the same side as their motor cortex
-these fibers branch nearer their termination to supply trunk LMN bilaterally
Lateral Funiculus
- lateral corticospinal tract: located lateral to the dorsal horn; supplies Motor Nuclei of ipsilateral limb muscles
- rubrospinal tract: this tract is near the lateral corticospinal tract and influences mainly flexor LMNs of the proximal upper limb muscles in humans. These fibers are ipsilateral to the muscles they supply
Ventral Funiculus
Vestibulospinal and reticulospinal tracts from the brainstem
Ventral corticospinal fibers from the motor cortex
Ventral Horn
- lateral motor nuclei: are found in the cervical and lumbar enlargements only. Contain: LMNs for lower and upper limb muscles and receive fibers from the adjacent lateral corticospinal and rubrospinal tracts
- medial motor nuclei: contain LMNs for muscles of the trunk and proximal limbs (shoulders and hips). Receive bilateral cortical input from the ventral corticospinal tracts and bilateral fibers from the vestibulospinal and reticulospinal tracts
