Exam 3 Flashcards by Mallory Fredricks

Corticobulbar

Cortex&raquo_space; brainstem

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Corticobulbar function

Fine fractionated movements of the face/head/neck

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Rubrospinal pathway

Originate: Red nucleus
Pathway: cross almost immediately in pons
Function: Gross motor movements, primarily upper limb flexion

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Medial Vestibulospinal Pathway

originate: Medial and inferior vestibular nuclei
pathway: Project bilaterally and terminate in ventral horn of cervical and upper thoracic
function: Controls head and back muscles to stabilize head; posture

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Lateral Vestibulospinal Pathway

originate: Lateral vestibular nuclei
pathway: Projects ipsilaterally to all levels
function: Activates extensor LMN to maintain upright and balanced posture

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Tectospinal Pathway

originate: Superior colliculus and Inferior colliculus
pathway: Crosses midline and terminates in medial part of ventral horn in cervical spinal cord
function: Reflexive turning of head

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Function of Lateral Pathways

goal-directed limb movements; voluntary

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Function of Medial Pathways

postural control system; involuntary

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Which pathways are the lateral motor pathways?

corticospinal tract; rubrospinal tracts; corticorubrospinal tracts

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Which pathways are ventromedial motor pathways?

vestibulospinal pathways; pontine reticulospinal tracts; medullary reticulospinal tracts

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Functions of Basil Ganglia

Preparation for movement
Initiation for movement
Regulate stereotypic movement
Learning of new motor tasks

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Internal Motor Circuit (basal ganglia)

PMC/M1 – “planning” (input to BG) –> caudate/Putamen – initiate –> Globus Pallidus – “magnitude” (output from BG) –> thalamus (ventral anterior nucleus / ventral lateral nucleus) – convey preparation parameters for movement to cortex –> PMC/M1

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Input Modulation (basal ganglia)

PMC/M1 – input –> caudate / Putamen – initiate –> Globus Pallidus –> thalamus (ventral anterior / ventral lateral) –> PMC/M1

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Output Modulation (basal ganglia)

PMC/M1 –> caudate / Putamen –> globus pallidus – output –> Thalamus (ventral anterior / ventral lateral) –> PMC/M1

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Direct Motor Pathway (purpose)

facilitates movement
goes through internal segment of globus pallidus
VL thalamus is released from inhibition = more excitation of PMC and M1
Net result: Activity in PMC/M1 is boosted by this positive feedback loop

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Indirect Motor Pathway (purpose)

inhibits movement
goes through external segment of globus pallidus
More inhibition of thalamus = less excitation of PMC and M1
Net Result: Activity of indirect loop provides negative feedback

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Dorsolateral Prefrontal Circuit

Role: executive functions; organizing behavioral responses; problem solving

Dorsolateral Prefrontal Cortex –> caudate –> globus pallidus / substantia nigra –> thalamus (ventral lateral / dorsomedial) –> dorsolateral prefrontal cortex

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Lateral Orbitofrontal Circuit

Role: Mediates empathy and socially appropriate responses (disorders include OCD and schizophrenia)

Lateral Orbitofrontal Cortex –> caudate –> globus pallidus / substantia nigra –> thalamus (ventral anterior / dorsomedial) –> lateral orbitofrontal cortex

Anterior Cingulate Circuit

Role: Motivated behavior; procedural learning

Anterior Cingulate Cortex –> putamen –> globus pallidus / substantia nigra –> thalamus (dorsomedial) –> anterior cingulate cortex

Basal Ganglia Disorders

Increased BG inhibition of the thalamus = reduced excitation of motor cortex = hypokinesia (poverty of movement)
- When putamen cannot be activated due to loss of dopamine input from the substantia nigra (Parkinson Disease)
- When there is damage to putamen or globus pallidus (Parkinsonism)
Decreased BG inhibition of the thalamus = increased excitation of motor cortex = hyperkinesia (excess movement)
- When connections with subthalamic nuclei are lost (ballisms)
- When striatal neurons of indirect pathway are lost (Huntington’s chorea). This disinhibits (“releases”) the direct pathway

Functions of the Thalamus

General arousal: from reticular connections to cortex generally
Sensory connections: from spinal cord and brain stem to the sensory cortex
Motor connections: from basal ganglia and cerebellum to motor cortex, but not UMN pathways
Emotional tone and affect: connections between limbic system and prefrontal lobe

Increased swelling in ________ could significantly interfere with thalamic function

ventricles

4 Regional Zones of the Thalamus

Anterior = Affect
Medial = Arousal
Lateral = Motor
Posterior = Sensory

What does the Anterior Nucleus of the thalamus do?

The Anterior Nucleus relays information from subcortical limbic structures to cortical limbic structures (cingulate gyrus) to contribute to emotional tone.

What does the Dorsomedial Nucleus of the thalamus do?

The Dorsomedial Nucleus relays information to and from the prefrontal lobe, to contribute to judgment and reasoning

What does the Ventral Anterior Nucleus of the thalamus do?

The Ventral Anterior Nucleus relays information from globus pallidus of basal ganglia & from cerebellum to SMA, to PMC, and to M1; important for motor planning & regulation

What does the Ventral Lateral Nucleus of the thalamus do?

The Ventral Lateral Nucleus relays information from cerebellum and globus pallidus of basal ganglia to M1 (primarily from cerebellum) and to PMC (primarily from BG); important for motor output regulation

What does the Ventral Posterior Nucleus of the thalamus do? (Ventral Posterior Medial; Ventral Posterior Intermediate; and Ventral Posterior Lateral)

VPM & VPL relay somatosensory information to the cortex. | VPI relays vestibular information to the somatosensory cortex.

What does the Pulvinar Nucleus of the thalamus do?

The Pulvinar Nucleus interfaces with 2°sensory cortex areas, including areas 5 & 7 (parietal lobe), areas 18 & 19 (occipital lobe), and both the angular gyrus & supermarginal gyrus

What does the Lateral Geniculate Nucleus of the thalamus do?

The Lateral Geniculate Nucleus relays visual information to primary visual cortex (area 17 of the occipital lobe).

What does the Medial Geniculate Nucleus of the thalamus do?

The Medial Geniculate Nucleus relays auditory information to primary auditory cortex (area 41 of the temporal lobe).

What does the Anterior zone of the Internal Capsule do?

Affective information to prefrontal & cingulate cortex

What does Genu zone of the Internal Capsule do?

Motor output (UMNs) from motor cortex

What does the Posterior zone of the Internal Capsule do?

- BG & cerebellar input to motor cortex (via thalamus) - Motor output (UMNs) from motor cortex - Sensory input to sensory cortex

Fiber Tracts of the Internal Capsule

1. Frontopontine 2. Corticorubral 3. Corticobulbar 4. Ascending sensory 5. Corticospinal 6. Auditory radiation 7. Optic radiation

Cerebellar Function

1. Balance 2. Feedback information 3. Feed-forward information (anticipation) 4. Sensory information integrated into movements 5. Timing & sequencing 6. Motor learning

3 Cerebellar Lobes

Anterior Posterior Flocculonodular

Cerebellar Cellular Anatomy: Summary

- Primary cell = purkinje fibers (the output from cerebellum) - Each purkinje cell receives weak input from many parallel fibers - Each purkinje cell receives strong input strong from one climbing fiber - Climbing fibers strongly influence the function of the purkinje fiber; “teaches” purkinje cells - This arrangement allows the cerebellum to modify its output in response to previously produced errors

Decreasing tract of cerebellum: Lateral hemisphere (cerebrocerebellum)

- Input: via pontine n. from widespread areas of cerebral cortex - Output: via dentate and VL (VA secondary) to premotor and motor cortex - Involved in planning and programming of voluntary, learned, skillful movement via influencing output of motor cortex

Descending tract of cerebellum: Paravermal section (medial hemisphere) of spinocerebellum primarily influence limb movement

- Input: projections from motor cortex and spinal cord - Output: via interposed n. through VL/VA to M1 and red n. - Compares commands from motor cortex with actual position and velocity of moving part and can issue correcting signals - Adjusts limb movements as they take place

Damage of vestibulocerebellum and vermis:

- Balance disorders - Ataxia - But these patients maintain full control of limbs when supine (so influence of gravity on posture removed)

Damage of vestibulocerebellum only:

- Control of eye movements is degraded or lost - Difficulty with pursuit eye movements or making accurate voluntary eye movements (e.g., problems reading, catching a ball, etc.)

Cerebellum - Feedforward

- Feedforward operations of the cerebellum allow precisely timed behaviors - Particularly important for multi-joint movements - Cerebellum predicts and adjusts movement on-line - Controls relative timing (while eating, fork in mouth not eye!)

Cerebrocerebellum two loops

1. To thalamus to premotor and primary motor areas 2. To red nucleus to inferior olivary n. and back to contralateral cerebellum forming feedback loop These feedback loop pathways may support mental rehearsal of movements and motor learning