Lecture 12 - Basal Nuclei Control of Motor Function

Question 1

Basal Nuclei

Answer 1

•Plan and execute motor commands in concert with cerebral cortex; help cortex execute subconscious but learned pattern •Help plan multiple parallel sequential patterns •Control complex patterns of motor activity

Question 2

Basal Nuclei receive most of their input from __ and return most of their output to __.

Answer 2

cerebral cortex and cerebral cortex

Question 3

The principal role of the basal nuclei is

Answer 3

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

Question 4

Two major basal nuclei circuits

Answer 4

Putamen circuit (direct)

Caudate nucleus circuit (indirect)

Question 5

Putamen Circuit

Answer 5

Direct
Function: not clear
inhibits athetosis or non-volitional movements
suppresses rigidity

•For subconscious execution of learned patterns of movement
•Overall excitatory –tends to increase motor activity
BYPASSES CAUDATE

Question 6

caudate nucleus circuit

Answer 6

indirect
motor planning: activating muscle in sequence for motor patterns 5 seconds ahead or more

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 7

Dopamine is __ on the direct pathway and __ on the indirect pathway.

Answer 7

excitatory (D1 receptors)

inhibitory (D2 receptors)

Question 8

Dopamine’s function overall is __

Answer 8

excitatory

Question 9

Exciting the putamen ___ the IGP/SbNigRet and allows the thalamus to send ___ signals to the motor cortex. IGP/SubNigRet is otherwise active and sends __ signals to the thalamus.

Answer 9

inhibits

excitatory

inhibitory

Question 10

Lesions in Globus Pallidus

Answer 10

• Result in inability to maintain postural support.

* Result in continuous spontaneous writhing movements of a hand, arm, neck or face = athetosis

Question 11

Lesions in subthalamic nuclei

Answer 11

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

Question 12

Lesions in striatum

Answer 12

• Results in the release of inhibition
• Results in flicking movements in hands, face, or elsewhere = chorea.
• Occur in patients with Huntington disease.

Question 13

Lesions in substantia nigra

Answer 13

• Caused by destruction of dopaminergic neurons.
• Occur in patients with Parkinson’s 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 14

Neurotransmitters

Substantianigra→ caudate nucleus and putamen

Answer 14

Dopamine (inhibitory)

Question 15

Neurotransmitters

Caudate nucleus and putamen →globuspallidus and substantianigra

Answer 15

GABA (inhibitory)

Question 16

Neurotransmitters

Cortex →caudate nucleus and putamen

Answer 16

Acetylcholine (excitatory)

Question 17

Neurotransmitters

Multiple pathways from brain stem

Answer 17

Norepinephrine, serotonin (inhibitory), enkephalin

Question 18

Neurotransmitters

Multiple glutamate pathways

Answer 18

Provide most of the excitatory signals

Question 19

Parkinson’s

Answer 19

AKA: Paralysis agitans
•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.
•Characteristics: Rigidity of much of body musculature Involuntary tremors of involved areas even at rest at a fixed rate Serious difficulty in initiating movement (akinesia) Postural instability Dysphagia, speech disorders, gait disturbances, fatigue

Question 20

Huntington’s

Answer 20

• Usually becomes symptomatic around 30-40 years of age
• Characteristics:
• Flicking movements of individual muscles
• Progressive severe distortional movements of entire body
• Severe dementia
• Motor dysfunctions
• Abnormal movements probably caused by loss of most of cell bodies of GABA-secreting neurons of caudate nucleus and putamen and of Ach neurons in other parts of the brain.
• Indirect pathway no longer has inhibitory influence on direct pathway and motor activity is increased.
• GABA neurons normally inhibit parts of the globuspallidus and substantia nigra.

Question 21

Huntington Mutation

Answer 21

• Mutations in the HTT gene, produces protein -huntingtin
• Function unknown, it appears to play an important role in CNS neuron health
• Causes DNA segment known CAG repeats (cytosine, adenine, and guanine) that appear multiple times in a row.
• Normally, the CAG segment is repeated 10 to 35 times within the gene.
• In people with Huntington disease, the CAG segment is repeated 36 to more than 120 times.
• People with 36 to 39 CAG repeats may or may not develop the signs and symptoms of Huntington disease, while people with 40 or more repeats almost always develop the disorder.
• 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.