L-4 Contributions of Cerebellum and Basal Nuclei to Motor Function II

Question 1

what does the basal nuclei help do?

Answer 1

helps plan and control complex patterns of muscle movement, controlling relative intensities of the separate movements, directions of movements, and sequencing of multiple successive and parallel movements.

Question 2

where does the basal nuclei get its input from?

Answer 2

the cerebral cortex and returns most of their output to the cerebral cortex

Question 3

what is the principal role of the basal nuclei?

Answer 3

to work with the corticospinal system to modulate thalamic output to the motor cortex to plan and execute smooth movements.

Question 4

what does the basal nuclei consist of?

Answer 4

paired nuclei:

• striatum: (caudate nucleus and putamen)
• globus pallidus
• substantia nigra
• subthalamic nucleus

Question 5

what are the two major basal nuclei circuits? what are their general functions

Answer 5

• putamen circuit (direct)
  &laquo_space;function not clear; inhibitis athetosis or non-volatile movements; suppresses rigidity»
• caudate nucleus circuit (indirect)
  &laquo_space;motor planning: activating muscles in sequence for motor patterns 5 seconds ahead or more»

Question 6

what are two things about the putamen circuit?

Answer 6

• for subconscious execution of learned patterns of movements
• overall excitatory - tends to increase motor activity

Question 7

describe the direct pathway itself

Answer 7

1) cerebral cortex (premotor, supplementary motor, somatosensory); +/acetylcholine
2) putamen (-/GABA)

Question 8

T/F: the putamen circuit bypasses caudate nucleus

Answer 8

True

Question 9

what neurotransmitter is used between the connections of the striatum and the substantia nigra?

Answer 9

dopamine

Question 10

what direct/indirect receptors id dopamine inhibitory/excitatory on?

Answer 10

• dopamine is INhibitory in the INdirect way (D2 receptors)
• dopamine is Excitatory in Direct pathway: (D1)
• action of dopamine is overall excitatory

Question 11

describe the IGP/SubNigRet

Answer 11

the IGP/SubNigRet is normally active and sends inhibitory signals to the thalamus

exciting the putamen inhibits the IGP/SubNigRet and allows the thalamus to send excitatory signals to the motor cortex

Question 12

whats to note about this system?

Answer 12

IGP/SNR is normally active and sends inhibitory signals to the thalamus

exciting the putamen inhibits the IGP/SNR and allows the thalamus to send excitatory signals to the motor cortex

Question 13

describe lesions in globus pallidus:

Answer 13

• results in inability to maintain postural support

- results in continuous spontaneous writhing movements of a hand, arm, neck or face = athetosis

Question 14

describe lesions in subthalamic nuclei

Answer 14

• results in the release of inhibition on the contralateral side
• results in sudden, flailing movements of an entire limb = hemiballismus

Question 15

describe lesions in striatum

Answer 15

• results in the release of inhibition
• results in flicking movements in hands, face, or elsewhere = chorea
• occur in patients w Huntington Disease

Question 16

describe lesions in substantia nigra

Answer 16

• caused by destruction of dopaminergic neurons
• occur in patients with Parkinsons Disease
• results in rigidity, akinesia, and tremors
• since dopamine inhibits the indirect (inhibitory) pathway and excites the direct (excitatory) pathway, destruction of the dopaminergic neurons results in an overall inhibitory effect

Question 17

describe the purpose of caudate circuit

Answer 17

• indirect pathway
• for cognitive planning of sequential and parallel motor patterns
• plays major role in cognitive control of motor activity
• overall inhibitory– tends to decrease motor activity

Question 18

delineate the caudate circuit

Answer 18

1) cerebral cortex (pre-m, supplementary-motor, somatosensory) (+/acetylcholine) –>
2) caudate nucleus (-/GABA)
3) globus pallidus (external –(-/GABA)–> globus pallidus (internal) –(-/GABA)–> 4) thalamic relay nuclei (+/glutamate) —> 5) premotor and supplementary motor cortex

*substantia nigra compacta –(-/dopamine d2)–> caudate nucleus

Question 19

neurotransmitter for substantia nigra –> caudate nucleus and putamen:

Answer 19

dopamine (inhibitory)

Question 20

caudate nucleus and putamen –> globus pallidus and substantia nigra:

Answer 20

GABA (inh)

Question 21

cortex –> caudate nucleus and putamen

Answer 21

Acetylcholine (exc)

Question 22

multiple pathways from brain stem

Answer 22

norepinephrine, serotonin (inh), enkephalin

Question 23

mutliple glutamate pathways

Answer 23

provide most of the excitatory signals

Question 24

• in huntintons disease, which neurons are destroyed?

Answer 24

• /GABA

- indirect pathway no longer has inhibitory influence on direct pathway and motor activity is increased

Question 25

describe parkinsons disease

Answer 25

• aka: paralysis agitas
• results from widespread destruction of pars compacta of substantia nigra that sends dopaminergic fibers to caudate nucleus and putamen
• dopaminergic pathways to direct and indirect pathways are lost. the direct pathway loses some of its excitatory input and the indirect pathway loses some of its inhibitory input. in both cases there is decreased motor activity

Question 26

what are the characteristics of parkinsons?

Answer 26

• rigidity of much of body musculature
• involuntary tremors; fixed rate
• akinesia (difficulty in initiating movement)
• postural instability
• dysphagia, speech disorders, gait disturbances, fatigue

Question 27

describe Huntington disease characteristics

Answer 27

• usually becomes symptomatic around 30-40 years of age
• flicking movements of individual muscles
• progressive severe distortional movements of entire body
• severe dementia
• motor dysfunctions

Question 28

what are the abnormal movements probably caused by?

Answer 28

probably by loss of most of cell bodies of GABA-secreting neurons of caudate nucleus and putamen of Ach neurons in other parts of the brain

• indirect pathway no longer has inh influence on direct pathway and motor activity is increased
• GABA neurons normally inhibit parrts of the globus pallidus and substantia nigra

Question 29

what gene is the huntington mutated in?

Answer 29

- HTT gene, which produces the huntingtin protein
function is unknown but appears to play important role in CNS neuron health

Question 30

describe DNA changes

Answer 30

• causes DNA segment known CAG repeats (cytosine, adenine, and guanine) that appear multiple times in a row

normally, CAG segment is repeated 10-35 times within the gene.

in huntington disease, CAG repeated 36-120+ times

Question 31

describe the spectrum

Answer 31

• people with 36-39 CAG repeats may or may not develop the signs and symptoms of Huntington, while people with 40 or more repeats almost always develop the disorder

Question 32

how?

Answer 32

an increase in the size of the CAG segment leads to the production of an abnormally long version of the huntingtin protein. the elongated protein is cut into smaller, toxic fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells.