Control of Movement: Basal Ganglia and the Cerebellum

Basal Ganglia and Cerebellum – can be considered part of the ________ system

extrapyramidal

essential function of extrapyramidal system?

maintaining posture and regulating involuntary motor functions

•Postural tone adjustment

•Performing movements that make voluntary movements more natural and correct

•Control of automatic modifications of tone and movements

•Control of the reflexes that accompany the responses to affective and attentive situations (reactions)

•Control of the movements that are originally voluntary but then become automatic through exercise and learning (e.g., in writing)

•Inhibition of involuntary movements (hyperkinesias), which are particularly evident in extrapyramidal diseases

the basal ganglia is a group of …?

subcortical nuclei

what is the main component of the basal ganglia?

striatum with several subpartswhat ar

what are the subparts of the striatum of basal ganglia?

caudate nucleus, putamen, substantia nigra, globus pallidus, and nucleus accumbens

the basal ganglia is important in action selection. what does this mean?

deciding which of several possible behaviors to execute at a given time and regulating them so that motor movements are performed smoothly

specific areas of the basal ganglia called substantia nigra are involved in

dopamine release and brains reward system

what is the Primary region of the brain for controlling movement?

primary motor cortex

describe the corticopsinal pathway

1. Upper motor neurons in layer V of the primary motor cortex (precentral gyrus), send long axons that will decussate in the medullary pyramids

2. axons travel down the spinal cord via the lateral corticospinal tract

3. synapse directly onto the alpha (lower) motor neurons in the ventral horn and also onto the interneuron circuitry of the spinal cord

why do we think the basal ganglia and cerebellum are involved in movement?

Neurodegenerative movement disorders where there is damage to the basal ganglia or cerebellum demonstrates their role in controlling movement

damage to the basal ganglia can cause what neurodegenerative movement disorders?

Huntington’s Disease

Parkinsons’s Disease

Tourette’s Syndrome

damage to the cerebellum can cause what neurodegenerative movement disorders?

Ataxia - Can initiate movements but they are not accurate

The Basal Ganglia consist of # paired structures deep in the center of the brain that are involved primarily in …?

five

the control and initiation of movement

what are the 5 paired structures deep in the center of brain that the basal ganglia consists of?

1) The Caudate

2) The Putamen

3) The Globus Pallidus

4) The Subthalamic nucleus

5) The Substantia Nigra

These structures are not visible externally but are prominent in coronal and axial sections

The basal ganglia (caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra) are considered part of the_________ system

extrapyramidal

The basal ganglia direct their output mainly through the

thalamus to the cerebral cortex

Most neural lesions that cause movement disorders occur in the _________ system

extrapyramidal system; thus, these movement disorders are sometimes called extrapyramidal disorders

what is the function of basal ganglia?

• basal ganglia makes a loop with thalamus and cortex to release appropriate movements from premotor and motor areas

• release appropriate behaviors from prefrontal association areas.

• select a particular movement or sequence of movements, or behaviors, while suppressing others, Ex) Tourette’s syndrome

what are the 2 pathways within the basal ganglia? and what do they each do?

• direct pathway → stimulates appropriate movements through disinhibition

• indirect pathway → inhibits specific inappropriate movements (further suppress competing movements)

how do the basal ganglia stimulate appropriate movements via the direct and indirect pathways?

• basal ganglia normally exert a constant inhibitory influence on thalamic regions that excite premotor and motor cortex

  • prevent them from becoming active at inappropriate times.

• To initiate a movement, Direct Pathway removes brakes from thalamus releasing selected movements and behaviors from the cortex, so it stimulates appropriate movements.

• The indirect pathway inhibits specific inappropriate movements and suppresses competing movements

the substantia nigra projects to the _____

putamen (nigrostrial pathway)

describe the nigrostrial pathway

• dopamine is the neurotransmitter

• has activating effect on direct pathway

• has inhibitory effect on indirect pathway

what is dopamine thumb?

involved in reward system and also in searching/seeking/arousal system which creates a loop when you’re scrolling on your phone

Loss of dopamanergic neurons in the Substantia results in what disease?

Parkinson's Disease, which is characterized by a difficulty in initiating movements

epidemilogy of Parkinson’s disease?

• Mean age of onset 55-60 years of age

• 1-3% of population above age of 60

• Slight male preponderance

• Vast majority are idiopathic (of unknown origin)

main symptoms of Parkinson’s disease?

• Bradykinesia (abnormal slowness of movement)

• Resting Tremor (rhythmic motion in fingers)

• Rigidity

• Postural Instability (shuffling gait)

(bradykinesia +1 is diagnostic of Parkinson’s)

there are ___ per 100,000 in US with Huntington’s disease.

2-10 (prevalence worldwide is variable)

what are genetic causes of Huntington’s disease?

• Chromosome 4, AD

• “Huntingtin” mutant form creates aggregates in striatum

  • Likely several independent mutations

  • unknown function

  • ubiquitous (not just CNS)

• CAG repeat

  • # correlates with severity, inversely to age of onset

  • < 36 normal, 36-39 intermediate, 40+ HD

signs of Huntington’s disease

-Involuntary jerking or writhing movements (chorea)

-Muscle problems, such as rigidity or muscle contracture (dystonia)

-Slow or abnormal eye movements

-Impaired gait, posture and balance

-Difficulty with speech or swallowing

black dots are aggregates of huntington proteins

Spinocerebellar Pathways terminate in the ______

cerebellum

Dorsal Spinocerebellar/Cuneocerebellar (DSC): function

Conveys muscle sense information which is used by the cerebellum to coordinate movement and posture. It collects information about individual muscles

Dorsal Spinocerebellar/Cuneocerebellar (DSC): receptors and afferents

• Muscle spindles and golgi tendon organs

• Thick and highly myelinated afferents

Dorsal Spinocerebellar/Cuneocerebellar (DSC): first order sensory neurons

Located at the dorsal root ganglia (DRG), afferent fibers enter the spinal cord and stay in the same side in the lateral part of the lateral funiculus

Dorsal Spinocerebellar/Cuneocerebellar (DSC): decussation

Fibers do not cross the midline and stay always in the same side

The bulk of the structure of the cerebellum is made up of a very tightly folded layer of gray matter called?

the cerebellar cortex (but also contains white matter tracts and 4 deep nuclei)

t/f: the cerebellum contains more neurons than the rest of the brain put together, but it only takes up 10% of total brain volume

true

how many layers does the cerebellar cortex have?

3

what is the major goal of the cerebrella cortex?

regulate the gain and timing of motor actions (movements), i.e., coordination

The cerebellar cortex has a great amount of synaptic plasticity. What does this allow?

allows continuous adjustment and fine tuning – learning how to do movements

Synapses in the cerebellar cortex are very sensitive to what substance?

alcohol

what are these?

cerebella peduncles

which cerebellar peduncle receives input? output?

output → superior

input → middle + inferior

Cerebellar input travels through the ___ to the _________ from ____ to integrate motor function and proprioceptive sensation

pons; cerebellum; cortex and spinal cord

cerebellar input is important in coordinating…?

amount of force used when doing an action

Think about lifting a box that was much lighter than you thought it was going to be..

Cerebellar output is through # deep nuclei of the cerebellum

4

which cerebellar deep nucelus is responsible for planning, initiation and control of voluntary movements and also contains output channels involved in motor function through the thalamus?

dentate nucleus

which cerebellar deep nucleus is responsibel for regulating saccadic eye movements and estimating movement of the body through space?

fastigial nucleus

In humans, Emboliform and globose nuclei make up the _______ nucleus.

interposed

the interposed nucleus is involved in what functions?

coordinating agonist/antagonist muscle pairs.

lesions in the area of interposed nucleus can result in what clinical presentation?

tremors

which portion of the cerebellar cortex is involved in posture, movement of the trunk, walking, eye movements?

vermis (inner strip of spinocerebellum)

which portion of the cerebellar cortex is involved in coordinating movement of limbs?

cerebrocerebellum (lateral)

which portion of the cerebellar cortex is involved in receiving limb position information from the spinal cord?

Spinocerebellum (Medial)

• Based on proprioceptive inputs thought to anticipate future position of limbs

which portion of the cerebellar cortex uses information about head movement to influence eye movement and balance?

floculonodular lobe (anterior inferior surface)

Cerebellar dysfunction results in uncoordinated:

• walking (vermis)

• limb movements (cerebrocerebellum)

• muscles of speech (many parts)

• Eye movement (floculonodular lobe - Nystagmus –rapid, uncoordinated eye movements)

Cerebellar Syndromes – archetypal is

ataxia (inaccurate movements)