Basal Ganglia

Question 0

Components of the basal ganglia

Answer 0

GREY MATTER
Caudate nucleus + Lentiform nucleus-> corpus striatum
Caudate nucleus + putamen-> striatum
Caudate nucleus+ putamen+ nuclues accumbens-> neostriatium
Lentiform nucleus-> putamen and globus pallidus
Substantia nigra-> in crus cerebri
Sub thalamic nucleus
Motor nuclei of the thalamus-> VA,VL, DM

Question 1

Functions of the basal ganglia

Answer 1

Control and regulate motor acts as they are evolving
Activity occurs before movement has began-> idea of movement then motor expression of that idea
Lesions cause disturbance of initiation
-> dyskinesias
-> hyperkinesia-> involuntary spontaneous movements
-> hypokinesia/bradykinesis-> inability to initiate voluntary movements

Question 2

Telencephalic ganglia

Answer 2

Striatum separated during development by corona radiata
-> caudate nucleus-> nuclus accumbens-> putamen medial to lateral
Caudate and putamen-> dorsal striatum-> sensorimotor
Nucleus accumbens and olfactory tubercle-> ventral striatum-> emotional and motivational function
Putamen joins with palidium-> Lentiform nucleus-> retain differing functions

Question 3

Other ganglia

Answer 3

Ventral pallidium-> with ventral striatum functionally
Dorsal pallidium-> globus pallidus->
-> external/lateral segment-> GPe important regulator
-> internal/medial segment-> GPi output nucleus

Question 4

Substantial nigra

Answer 4

Ventral pars reticularis-> output nuclues

Dorsal pars compacts-> functional input to the striatum -> affected in Parkinson’s

Question 5

Basal ganglia circuits

Answer 5

Originate in cortex
Pass through BG 
Project back on to cortex via thalamus
Motor loop-> learned movements
Cognitive loop-> motor intentions
Limbic loop-> emotional aspects of movement 
Occult motor loop-> voluntary saccades

Question 6

Motor loop direct pathway

Answer 6

Direct-> facilitates and smooths out movement
1) starts in cortex-> makes original movement plan
2) sends plan to striatum first (putamen and caudate)-> positive glutamate neurone-> striatum on
3) negative GABA neurone to medial globus pallidus, the medium spiny neurone, goes wrong in huntingtons-> GPM off
4)GPM Has a negative neurone going to the thalamus (VA and VL)in the thalamic fasciculus -> switched off so thalamus is dis inhibited-> thalamus on
5) two positive neurones to supplementary motor area and the cortex -> on .
Sub thalamic nucleus-> activates GPM -> turns off thamalus-> stops movement
Substantial nigra compacta-> activation of D1 r’s in the striatum-> tonically activated striatum-> lowers threshold for movement

Question 7

Motor loop indirect pathway

Answer 7

Indirect-> inhibits muscles opposing movement wanted and stops over movement
1) cortex activates striatum via an activatory neurone in the internal capsule
2) striatum inhibits globus pallidus lateral via medium spiny neurone
3) GPL inhibits subthalamic nucleus -> when striatum is on subthalamic nucleus is dis inhibited
4) subthalamic nucleus activates GPM
5) GPM inhibits thalamus
6) no cortex stimulation
Substantia nigra-> activates D2 receptors-> inhibit indirect pathway
Motor cortex can directly stimulate the substantial nigra

Question 8

Cognitive loop

Answer 8

Learning new functions
Active at same time as motor loop during new tasks
Dorsolateral prefrontal cortex-> head of caudate-> GPi SNr-> medico dorsal and VA thalamus-> cortex
Execuative function
Plan for movements next time

Question 9

Limbic loop

Answer 9

Emotional movements-> smiling! gesturing! aggressive and submissive, posture
Amygdala, cingulate gyrus-> pre frontal cortex-> nuclues accumbens-> ventral pallidium-> medial dorsal thalamus-> premotor area
Involves a lot of dopamine

Question 10

Occulomotor loop

Answer 10

Saccades-> rapid eye movements
Superior colliculus -> automatic movement of eyes to a point where there is movement -> topically inhibited by the substantia nigra
For rapid eye movement the substantia nigra has to be inhibited by
Posterior parietal cortex-> body of caudate-> GPi SNr-> ventroanteriour nucleus of thalamus-> eye fields