Basal Ganglia Flashcards
Describe function of following connections of basal ganglia:
1. Cortical
2. Between nuclei
3. Brain sten
- Inhibits excessive activity of motor cortical area (4&6), inform basal ganglia about program & intention of movement
- Control intrinsic activity
- Regulation of muscle tone & body posture
Describe caudate circuit & its function
Sensory & motor association areas —caudate nucleus—globus pallidus—thalamus—supplementary motor, premotor & prefrontal areas
F, cognitive control of sequences of motor movements. This subconciously determines within seconds patterns of movement which will be used together to achieve a goal.
Describe putamen circuit & its function
Premotor, supplementary motor & somatosensory areas —putamen—globus pallidus—thalamus—primary motor & premotor areas
Execute learned patterns of movement
Enumerate connections of basal ganglia to brain stem
Reticular formation, red nucleus, vestibular nucleus
Mention neurotransmitters in basal ganglia
Cerebral cortex release glutamate on corpus striatum
Intrastriatal interneurons release Ach
Substantia nigra release dopamine on corpus striatum
Coprus striatum release GABA on substantia nigra
Basal ganglia release NE, ecephalin & Serotonin on brain stem
Describe effect of stimulatiry & inhibitory circuits
Stimulatory, facilitate muscle activity especially at beginning if voluntary movement like rising from sitting or beginning to walk
Inhibitory, inhibit unwanted muscle activity
Describe the direct pathway
Cortical fibers stimulates striatum by glutamate, striatum inhibits to GPi (GABA, inhibitory), which disihibits the thalamus & thalamic projections excite motor neurons.
This functions to maintain ongoing motor activity
Describe the indirect pathway
Cortical input to stiatum in excitatory (glutatmate), striatum inhibits GPe (GABA, inhibitory) thus the subthalamic nuclei are released from GPe inhibition thus cause increased GPi activity which inhibitsvthe thalamus & the net effect is cortical inhibition & suppression of muscle activity.
Effects of dopamine & acetylcholine
- Dopamine in nigrostriatal fibers activates direct pathway (D1) & inactivates indirect pathway (D2) thus facilitatory to movement.
- Acetycholine is present in balance with dopamine to facilitate the movement
What happens with degeneration in the dopamine releasing neurons?
Decreased activity of direct pathway & increased activity of indirect pathway, thus hypokinesia & slow voluntary movements take place, known as parkinsonism.
Mention functions of basal ganglia
- Regulation of muscle tone
- Role in voluntary movements
- Automatic associated movements
- In lower animals, BG is highest motor center
Describe role of BG in muscle tone
Caudate is stimulatory, lentiform is inhibitory there is net inhibition.
It decreases the activity of alpha motor neurons through decreasing the activity of motor cortex
It decreases the activity of gamma motor neurons through stimulation of inhibitory reticular formation
Describe role of BG in voluntary movements
There are no direct descending tracts from basal ganglia, but it affects voluntary movements by extra-pyramidal tracts
1. Storage of programs of some learned voluntary movements in putamen circuit, lesion results in motor apraxia
2. Planning of motor activity through caudate circuit
3. Provision of postural background for the fine voluntary movements, adjust muscle tone of proximal muscles via ventro-medial pathways to facilitate more regulated fine skilled actions
Causes of chorea
Lesion in the caudate nucleus & degenrenation of GABA releaseing striatal fibers to GPe leading to decreased activity of indirect pathway:
1. As a complication of rheumatic fever, but no dementia
2. Congenital (Huntington’s chorea) = progressive dementia
C/P of chorea
- Hypotonia & pendular knee jerk
- Involuntary movements: sudden semipurposeful movements
- Dancing movements of arms, legs, face, head & trunk, increase by emotions decrease by sleep