Block 4 Flashcards
corticospinal tract
- important for movements requiring conscious, voluntary movement and for spontaneous acts of will
- also known as pyramidal tract
60% of fibers from corticospinal tract originate from ___ and project to ___, __, and ____
- motor cortical areas anterior to the central sulcus
- collateral to rubrospinal and reticulspinal tract and terminate in ventral horn
40% of fibers from corticospinal tract originate from___ and terminate _____
- somatosensory cortex posterior to the central sulcus
- in the dorsal horn
where do corticospinal tract fibers from frontal lobe originate?
primary motor cortex (Brodman’s area 4) and premotor cortex (BRODMAN’s area 6)
supplementary motor area (SMA)
-the superior and medial part of the premotor cortex
corticospinal tract fibers from parietal lobe originate from
primary somatosensory cortex, Brodman’s areas 3,1,and 2 and some from 5
course of the corticospinal tract
fibers leaving cortex–> corona radiata–> internal capsule (most travel in posterior limb)–> cerebral peduncle (occupy middle 2/3)–> split into longitudinal bundles as they course through pontine gray matter–> reunite in medulla to form pyramids
corticospinal fibers maintain a topography
-fibers destined for upper body parts are medial, nd fibers destined for lower body parts run laterally
corticobulbar pathways
-travel near corticospinal axons in the internal capsule and innervate cranial nerve nuclei controlling: movements of face, tongue, pharynx, and larynx
spinomedullary junction
area where most corticospinal fibers cross to opposite side in pyramidal decussation
the crossed corticospinal tract travels through the
lateral column
** it innervates neurons that control distal muscles
uncrossed corticospinal fibers travel in
ventral column
lesions to the corticospinal tract lead to
- sensory as well as motor deficits
- inability to RAPIDLY match tactile sensation to motor output
Most corticospinal tract fibers influence
Aa and Agamma motor neurons indirectly via interneurons, but some fibers from primary motor cortex end monosynaptically on Aa motor neurons of the hand!!!
lesions of the corticospinal tract would lead to loss of
irreversible loss of independent (fractionated) finger movements as well as ability to oppose thumb and fingers*** but they can still move hand as a whole
Parallel to the corticospinal tract, the corticoreticular fibers…
-modify reticulospinal projections and provide an alternative route for voluntary motor control
red nucleus
- caudal magnocellular division of this structure is the origin of the rubrospinal tract
- makes corticorubrospinal tract
do rubrospinal fibers cross midline? Travel in pyramids?
- rubrospinal efferents cross the midline
- rubrospinal efferents do not travel in the pyramids, they travel in the lateral column in the spinal cord
describe the sequence of voluntary movement steps
- a decision must be made that a movement is desired
- the starting position of the body and target must be determined from proprioceptive, vestibular, and visual or auditory signals
- movement must be planned and organized
- motor plan has to be initiated and executed
- mid-course corrections must be made
Integration of sensory information into a motor plan occurs via
-intracortical and thalamocortical circuitry
Intracortical connections: area 4
area 4 is innervated by primary somatosensory cortex according to homotopic organization
Intracortical connections: Area 6
is innervated by parietal association areas, directly and indirectly from prefrontal cortex:
Area 5 relays vestibular and proprioceptive info
Area 7 relays visual information from dorsal stream
parietal-temporal-occipital association cortex relays integrated somatosensory, visual, and auditory information
Thalamocortical information involves
-feedback from basal ganglia and cerebellum that the cortex uses to assist in planning
Initiation and execution of movement is commanded by
-primary motor cortex
electrical stimulation of area 6 evokes
-coordinated contractions of muscles at multiple joints
area 6 lesions produce
-apraxia: difficulty in executing complex movements
where are mirror neurons found?
- premotor areas
- they fire either when complex movements are performed or witnessed
Name the evidence that execution of movement occurs in the primary motor cortex
- increased blood flows to area 4 only when movement is actually performed
- neurons in area 4 begin to fire before contraction of the relevant muscle begins
- frequency of neuronal firing codes for the amount of force that is needed in the muscle
the net effect of supraspinal pathways on motor neurons is
inhibitory
the basal ganglia receives input from the _____ and feeds back through the
- receives input from entire cortical mantle
- feeds back through the ventral anterior and ventral lateral thalamic nuclei to the prefrontal/premotor cortices
the principle function of the basal ganglia is to
-provide a mechanism for the selection of adaptive motor programs for planning and initiating movement
corpus striatum
-caudate+ putamen+pallidum
striatum
caudate + putamen
palidum
-globus pallidus, GPi and GPe segments
substantia niagra
-zona compacta, zona reticulata
Globus Pallidus internal (GPi) regulates movement of
-trunk and limbs
Substantia Niagra (SNr) regulates movement of
-head and eye movement
principle function of the basal ganglia
-provide a mechanism for the selection of adaptive motor programs for planning and initiating movement
sensorimotor projections from frontal/parietal cortex to the ____
-project to putamen to operate in fine motor control
associative: from prefrontal cortex and other association areas to the ___
-caudate to operate in cognitive functions
limbic: from frontal/temporal lobes to the ___
ventral striatum (nucleus accumbens) to contribute to motivated behaviors
are striatal neurons spontaneously active?
no; striatal neurons lack spontaneous activity unless they receive excitatory drive from the cortex or thalamus
Are pallidal neurons typically spontaneously active?
-yes, pallidal neurons are typically spontanously active and tonically inhibit the thalamus
direct pathway provides circuitry for
-disinhibiting winning competitors
Dopamine affects on Direct Pathway
-facilitates corticostriatal transmission in the direct pathway via D1 receptor
Dopamine effects on Indirect Pathway
-attenuates corticostriatal transmission in the indirect pathway via a D2 receptor
So whats the net effect of dopamine on basal ganglia
-facilitate thalamocortical drive through direct pathway
What structures are targeted in Parkinson’s Disease
-loss of neurons in brainstem, specifically the pigmented dopamine neurons in the midbrain
What environmental factors can cause Parkinson’s?
-head trauma, viral encephalitis, MPTP, methamphetamines
Parkinson’s patients symptoms
- hypokinesia, resting tremor, rigidity
- many suffer cognitive effects
The principal defect in Huntington’s Disease is
-loss of striatal GABA neurons in the indirect Pathway
the Huntington’s mutation is on the short arm of chromosome __ and codes for
4 and codes for huntingtin
what two descending pathways are modified by the vermis of the cerebellum?
-reticulospinal and vestibulospinal
what are the two descending pathways that are modified by the intermediate cerebellum?
rubrospinal and corticospinal
cerebellar lesions lead to
- ataxia: uncoordinated movements of the limbs, trunk, and eyes
- impaired balance, loss of muscle tone, and inability to update motor programs
describe how afferent information is processed in the cerebellum
-all afferents to the cerebellar cortex also gives collaterals to the deep cerebellar nuclei to prime the deep nuclei to later deal with the more processed info coming from cortex
cerebellar hemispheres coordinates movements on the ___ side
-ipsilateral
which cerebellar system receives sensory information mainly from sensorimotor cortices and projects back to the premotor areas
- cerebrocerebellum
- this is a parallel system to the basal ganglia for motor planning and programming
through the ___ circuit, the spinocerebellum receives
- corticopontine circuit
- motor input regarding the intended movement (efference copy) and receives peripheral sensory information regarding the evolving movement and then mediates errror correction
the main function of the cerebrocerebellum is
-forms a parallel system to the basal ganglia for motor planning and programming
main function of spinocerebellum
-mediates error correction
what is meant by the efference copy
- the intended movement
- the spinocerebellum receives motor input regarding the intended movement via the corticopontine circuit
the ____ is the only cerebellar division to receive direct inputs from primary sensory afferents
-vestibulocerebellum
what symptoms appear with damage to the flocculonodular lobe ?
-nystagmus, truncal ataxia, and wide-based standing position
the output of the vermis via the ___ nucleus is relayed primarily to the descending ___ and ____ pathways to adjust movements of the proximal musculature
- fastigial nucleus
- vestibulospinal and the reticulospinal
lesions of the anterior lobe of the vermis produce
-unsteadiness of walking (gait ataxia)
Wernicke’s encephalopathy
-alcohol induced cerebellar damage and permament nystagmus, ataxia, and other neurological disorders
damage to the intermediate zone of the cerebellum leads to
-limb ataxia and dysmetria
intention tremor
-the inability to target an object at the end of a reach, with constant over and under shooting
lesions of interposed or fastigial nuclei lead to
-hypotonia
dysdiadochokinesia
- the inability to perform a series of rapid alternating movements
name the 3 layers of the cerebellar cortex
- molecular layer
- Purkinje layer
- granaular layer
what cells are in the molecular layer
-basket cells and stellate cells
what cells are in the Purkinje layer?
-Purkinje cells
what cells are in th granule layer?
-granule cells and some Golgi cells
vergence
- when the eyes move inward to view a target near the face
- ciliary muscles contract making lens more convex
saccades
- conjugate eye movements that can be generated reflexively or voluntarily
- goal is to fixate new targets for optimal visual processing by the fovea
smooth pursuit eye movements
- slower, conjugate mevements that keep a moving stimulus on the fovea
- voluntary movements
- requires the presence of a moving target
optokinetic reflexes
- reflexive eye movements to a slow-moving broad visual field
- *does not require processig of visual signals by visual cortex
vestibulo-ocular reflexes
- the SCC and otilith organs trigger eye movements in opposite directions to head movements
- eye velocity/head velocity= gain of vestibulo-ocular reflex
- does not require any visual inputs
Gaze
-combined movement of head and eyes
the output of the cerebrocerebellum is directed to the ___ nucleus which relays info to the ___ cortex via the __ thalamus
- dendate nucleus
- premotor cortex
- VL thalamus
dysmetria
- term for errors in smoothness and direction of targeting movements
- over or undershoot targets
- lesions to cerebrocerebellum or dendate nucleus
Functional Divison: vestibulocerebellum
name the: anatomical region, principle input, deep nucleus, principle output, function, and effect of lesion
anatomical region: flocculonodular lobe
principle input: vestibular
deep nucleus: vestibular nuclei
principle output: vestibular nuclei
Function: vestibular reflexes for balance and eye movement
effect of lesion: nystagmus, trunkal ataxia
Functional Divison: Spinocerebellum (Vermis)
name the: anatomical region, principle input, deep nucleus, principle output, function, and effect of lesion
anatomical region: vermis
principle input: spinal cord and trigeminal, visual, auditory, and vestibular
Deep nucleus: Fastigial
Principle Output: medial descending systems for proximal muscles
Principle output: medial descending systems (vestibular and reticular) for proximal muscles
Function: error correction for proximal muscles
Effect of lesions: gait ataxia, dysarthia, hypotonia (fastigial nucleus lesion)
Functional Divison: spinocerebellum (intermediate hemisphere)
name the: anatomical region, principle input, deep nucleus, principle output, function, and effect of lesion
anatomical region: Intermediate hemisphere
Principle input: spinal cord and trigeminal, motor cortex via pontine nucleus
Deep nucleus: interposed
Principle Output: Lateral descending systems: rubrospinal and corticospinal by way of VL thalamus for distal muscles
Function: error correction for distal muscles
Effects of lesions: limb ataxia, dymetria, intention tremor, hypotonia, if lession of interposed nuclei
Functional Divison: cerebrocerebellum
name the: anatomical region, principle input, deep nucleus, principle output, function, and effect of lesion
ANatomical region: lateral hemisphere
Principle input: pontine nucleus, relays info from cortical areas 1-10 and 45-46
Deep nucleus: dendate nucleus
Principle output: premotor cortex by way of VL thalamus
Functions: planning and programming, initiation, timing, precision, fine dexterity
Effect of lesions: delayed initiation and termination, dysdiadochokinesia, dysmetria
