Mkgrady8 Neuro 3 Higher Control

integration centers= pontine and medullar reticular formation; major sensory inputs detecting postural instability; integration of sensory inputs= integration of proprioceptive input to maintain balance and posture

integration centers= deeper layers of superior colliculi; major sensory inputs detecting postural instability= eyes and ears; integration of sensory inputs= integration of visual and auditory stimuli for involuntary orientation of the head and eyes

integration centers: vestibular complex; major sensory inputs detecting postural instability= vestibular system; integration of sensory inputs= integration of vestibular input to maintain balance and posture

ventromedial tract; IPSILATERAL cortical input; DECUSSATES in posterior (dorsal) tegmental decussation; TERMINATES CONTRALATERAL TO ORIGIN in upper cervical levels

ventromedial tract; pontine (medial)= BILATERAL cortical input, does not decussate, TERMINATES IPSILATERAL TO ORIGIN; medullary (lateral)= BILATERAL cortical input, BILATERAL termination

ventromedial tract; lateral= somatotopically organized, does not decussate, TERMINATES IPSILATERAL TO ORIGIN AND TERMINATION IS IN THE CERVICAL REGION OF THE SPINAL CORD; medial= BILATERAL termination limited to cervical spinal cord segments

dorsolateral tract; IPSILATERAL cortical input; DECUSSATES in the ANTERIOR (VENTRAL) TEGMENTUM; TERMINATES CONTRALATRAL TO ORIGIN

axial, flexor, and extensor musculature

facilitates upper limb flexor and inhibits extensor alpha and gamma motor neurons to the upper extremities; BIAS FOR UPPER LIMB FLEXORS

orienting movements of head and eyes

inhibits extensors and neurons innervating muscles of the back and neck

supplements the excitatory function of the pontine (medial) reticulospinal system by integrating vestibular info; EXTENSOR BIAS

excites upper and lower proximal limb extensor and inhibits flexor alpha and gamma motor neurons, excites antigravity muscles; facilitates extensor spinal reflexes, increases muscle tones of axial and proximal muscle; EXTENSOR BIAS

inhibits extensor and excites flexor alpha and gamma motor neurons, inhibits antigravity muscles; suppresses extensor spinal reflex activity; decreases muscle tone and axial and proximal muscle

essentially never see isolated lesions of ONLY rubrospinal, vestibulospinal, tectospinal, and reticulospinal fibers; lesions of corticospinal tract (indirect pathways) to brainstem motor nuclei --> POSTURING appears --> DECORTICATE (upper limb flexion with lower limb extension) and DECEREBRATE POSTURING (upper and lower limb extension)

generally descending cortical tracts projecting to motor brainstem sites impose an INHIBITORY TONE on the 'bias' action of motor brainstem tracts; therefore lesions of these descending cortical tracts can lead to DISINHIBITION of descending brainstem motor tracts; POSTURING is a sign of this disinhibition following brain injury (so expression of the usually repressed bias); since posturing is an important indicator of the amount of damage that has occurred to the brain it is used to assess the severity of head injury on the GLASGOW COMA SCALE

severe= 8 or less; moderate= 9-12; mild= 13-15

lesion above the red nucleus (midbrain); an upper motor neuron syndrome posturing that involves rigidity, flexion of the arms, clenched fists, and extended legs; tonic neck reflexes can occur= aka fencing reflex observed in infants, when the child's head is turned to the site the arm on that side will straighten and the opposite arm will bend, if the reflex is observed in adults or in the infant past 6 months of age a disorder of the upper motor neuron may be present

lesion below the red nucleus (midbrain); occurs when the posterior part of the brain stem and spinal cord are isolated from the rest of the brain by injury at the superior border of the pons; the extensor muscles in all of the limbs and those of the trunk and neck have increased tone; when the brain stem is transected inhibitory influences from the cortex and basal ganglia can no longer reach the spinal cord and facilitatory influences which descend in the vestibulospinal and reticulospinal tracts dominate; this results in increased activity of alpha motor neurons innervating extensor muscles which can be due to increased gamma motor nueron discharge for these muscles

decerebrate posture can occur on one site, on both sides, or in just the arms; it may alternate with decorticate posture (abnormal posturing due to corticospinal tract injury) or a person can have decorticate posture on one side and decerebrate posture on the other

in the diffuse hemisphere region; trauma, ischemia, hypoglycemia/other metabolic disorders, infection, drugs

in the bilateral thalamic region, brainstem compression; hemorrhage, infarction, supra or infra tentorial mass lesions; ischemia, hemorrhage, drugs

normally corticospinal input tonically inhibits brainstem motor centers and associated POSTURAL REFLEXES; lesion of corticospinal tract results in DISINHIBITION of brainstem motor centers resulting in the UMN sign of POSTURING= a lesion above the red nucleus results in DECORTICATE POSTURING OR FLEXOR SPASTICITY, a lesion that extends to include the red nucleus results in DECEREBRATE POSTURING OR EXTENSOR SPASTICITY; coma= pathological state of unconciousness from which a person cannot be aroused to make purposeful responses, as a rule LIGHT coma is present when reflex motor response (i.e. decorticate and decerebrate posturing) can be elicited by NOXIOUS stimulation, in DEEP coma there is no response

PRIMARY MOTOR CORTEX brodman's area 4, MI lowest current threshold elicits contralateral movement= BETZ cells have largest somas in CNS and are a subset (5%) of primary motor cortex pyramidal neurons in area 4, MIRROR cells respond to performance of action/observation of action in others; MEDIAL AND LATERAL PROMOTOR CORTEX= immediately rostral to precentral gyrus, medial supplemental motor area (SMA), lateral premotor cortex (PMC), brodman's area 6, MII higher threshold often elicits bilateral limb movement; PRIMARY SOMATIC SENSORY CORTEX= also called S1, areas 3, 1, 2 especially 3z that receives input from muscle spindles

primary motor cortex neurons fire 5-100 msec before the onset of a movement; organizes voluntary and fine control of distal musculature via DIRECT PATHWAY; primate evolution= an increase in the overall size of the corticospinal tract especially to the musculature of the digits, one hypothesis is foveate retina/fine motor control; primary motor cortex encodes for= force of a movement, direction of movement, extent (distance) of movement, speed of movement

lateral corticospinal tract= 90% of fibers, notable for synaptic contacts DIRECTLY onto alpha motor neurons, damage results in a permanent loss of the fine control of the digits; anterior cotricospinal tract= 10% of fibers, responsible for the voluntary control of the proximal limb and axial musculature, terminates bilaterally

convergence of all ascending and descending white matter tracts to and from the cortex; the descending motor fibers for the face, arm, and leg run medially to laterally in the posterior limb of the IC; blood supply to posterior limb of IC= lenticulostiate branches of MCA, anterior choroidal artery of internal carotid artery; clinical note= LACUNAR INFARCTS arise from blocked blood flow to small, deep, penetrating vessels, one common location is the internal capsule white matter

cerebral motor cortical output is mostly inhibitory to spinal cord reflexes via indirect pathways; for this reason interruption of corticospinal results in HYPERREFLEXIA

lamina VII, intermediate zone= presynaptic inhibition of primary afferent fibers such as I1 afferents from stretch receptors, inhibition of reflexes during normal gait probably by presynaptic inhibition of Ia afferents; lamina IX motor nuclei= in primates substantial direct corticospinal projections to alpha and gamma motor neurons in lamina IX, also synaptic contact mainly with short interneurons that synapse upon alpha and gamma motor neurons

the PRIMARY MOTOR CORTEX or M1 is located on the PRECENTRAL GYRUS and on the ANTERIOR PARACENTRAL LOBULE on the medial surface of the brain; paracentral lobule refers to the junction of the precentral gyrus and postcentral gyrus on the medial surface of the cerebral cortex and contains the sensorimotor representation of the distal lower extremities

primary motor cortex= comparatively low threshold, monosynaptic connections to a few spinal motor neurons, projects to contralateral side

stimulation of premotor areas= high threshold, coordinated contractions at more than one joint; medial (dorsal) premotor cortex= supplemental motor area (SMA), active with initiation of movement from internal cues; lateral (ventral) premotor cortex= active at appearance of external cue

the external cue; the LATERALIZED PREMOTOR POTENTIAL OR READINESS POTENTIAL is a measure of electrical activity that precedes voluntary muscle movement; the readiness potential precedes voluntary acts by about half a second; voluntary acts are nonconsciously initiated

memory of motor activity; more complex finger PERFORMANCE; finger REHEARSAL or motor imagery; SUPPLEMENTARY MOTOR AREA (SMA) is heavily activated while the primary motor cortex and somatosensory cortex are not because the fingers weren't actually moving

HIERARCHICAL ORGANIZATION of DIRECT AND INDIRECT motor pathways; FEEDBACK and FEEDFORWARD (anticipatory) mechanisms; feedforward mechanisms= LEARNED ADAPTIVE POSTURAL CONTROL, FEEDFORWARD PREACTIVATION of muscle groups; HE RAN OUT OF TIME HERE

feedback response= a muscle activation pattern that is a response to the sensory signals resulting from postural instability; feedforward (anticipatory) response= activity of trunk and limb muscles that occurs before voluntary movement to prepare the body for any disturbance to posture, feedforward responses can originate from motor cortex

flexor/extensor muscle tone and reflexes; for intact walking ventral CST projects to reticulospinal neurons to the medullary (lateral reticulospinal tract (activates flexor reflexes, inhibits extensor reflexes) and the pontine (medial) reticulospinal tract (activates extensor reflexes, inhibits flexor reflexes)

HE MADE A POINT OF STILL DOING THIS ONE; stretch reflex sensitivity can be increased or decreased; initially feedback then feedforward postural adjustment; modulation of stretch reflex by central descending mechanisms; adaptive postural control requires intact cerebellum= atrophy of anterior cerebellar lobe prevents appropriate SCALING of correcting postural response, all levels of CNS are involved in postural control (integrity of brainstem centers is necessary for generation of compensatory postural adjustments, integrity of highest levels of the CNS including the motor areas of the cerebral cortex is necessary for anticipatory postural adjustments, adaptive postural control requires an intact cerebellum)

motor cortex -- direct pathways corticospinal tract --> contract bicep; indirect pathway --corticoreticular tract--> brain stem reticular formation --reticulospinal tracts (postural set automatic postural adjustment)--> preactivated contraction of gastrocnemius; POSTURAL SET is a task specific feedforward motor readiness to respond as would occur with a runner getting set on their mark

a set of neural circuit capable of producing repetitive activity in the absence of any sensory input; CPGs possess rhythmic predetermined neural activation for activities such as breathing, chewing, and walking; they free up your conscious mind sot hat you don't have to send down a voluntary command every time you want to put one foot in front of the other

CPG activity for rudimentary walking can be elicited from an isolated human spinal cord; electrical stimulation of the lumbar spinal cord in paraplegics can induce rhythmic, alternating stance and swing phases; in intact human direct and indirect pathways converge on CPGs

any disease that disrupts blood flow to a focal region of the brain; 80% ischemic= thrombosis which is a blood clot at the site of origin and most common or Embolism which is a blood clot that Enters from a distant site; 20% hemorrhagic

three medial brainstem syndromes (oculomotor, abducens, and hypoglossal) (the alternating hemiplegias) and locking in syndrome

NTD

aka superior alternating hemiplegia; midbrain= base cerebral peduncle (crus cerebri); paramedian branches of posterior cerebral artery (PCA); presentation= pyramidal tract contralateral hemiparesis of the limb and facial muscles, CN III (oculomotor) ipsilateral oculomotor palsy, eyes deviate laterally due to medial rectus muscle weakness (diplopia), ptosis (low eyelid), parasympathetic branch of CH III ispilateral failure of pupil constriction in response to light pupil is dilated and fixed

aka middle alternating hemiplegia; pons basis pontis; paramedian branches of basilar artery; presentation= pyramidal tract contralateral hemiparesis upper and lower extremity, CN 6 abducens ipsilateral lateral rectus palsy and diplopia

aka inferior alternating hemiplegia; penetrating branches of the vertebral or anterior spinal artery; presentation= pyramidal tract contralateral hemiparesis upper and lower extremity, CN 12 ipsilateral tongue weakness +/- atrophy tongue points to side of lesion, medial lemniscus vibration and proprioception

medial inferior midbrain= weber's sundrome, superior alternating hemiplegia (contralateral hemiparesis, ipsilateral oculomotor (CNIII) palsy); medial inferior pontine syndrome= foville's syndrome, middle alternating hemiplegia (contralateral hemiparesis, ipsilateral abducens (CN4) palsy; medial medullary syndrome= dejerine syndrome, interior alternating hemiplegia (contralateral hemiparsis, ipsilateral hypoglossal (CN12) palsy

ventral pontine syndrome; pons bilateral ventral medial pons; basilar artery; pyramidal tract= corticospinal tract complete paralysis from head to toe, corticobulbar tract complete paralysis of entire face aphonia, spares the oculomotor and trochlear nerves so pt is only able to communicate with eye movements, pt is awake and aware

anterior cerebral artery (ACA) supplies the medial cortex (lower extremity of homonuculus); middle cerebral artery (MCA) supplies the lateral aspect

NTD

posterior limb of internal capsule, subcortical structures are fed by: MCA --> lenticulostriate artery, internal carotid artery --> anterior choroidal artery; HX chronic HTN in 80-90% of cases; lacunar strokes; lacunar syndrome= pure motor hemiplegia, face, arm, and leg, no cortical signs or sensory deficits; anatomical location= posterior limb of internal capsule, corona radiate, pons (basis postis)

most common presentation= contralateral weakness, contralateral hemisensory loss; foot/leg>trunk, mild or no involvement of upper extremity

NTD

a pt who presents with arm and leg weakness may have either a small internal capsule stoke or a large ACA+MCA cortical stoke; the presence of these cortical signs exclude an internal capsule stroke= gaze preference or gaze deviation, expressive or receptive aphasia, visual field deficits, visual or spacial neglect

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