Basal Ganglia

Question 1

what are the 5 overall functions of the basal ganglia

Answer 1

1. normal movement patterns
2. planning/execution complex motor tasks
3. fast (saccadic) eye movements
4. motor memories
5. psychological well being (emotional responses)

Question 2

input/receptive areas

Answer 2

(striatum)

• nucleus accumbens (ventral striatum, limbic circuit)
• caudate nucleus (dorsal striatum, oculomotor circuit, executive/association circuit)
• putamen (dorsal striatum, motor circuit)

Question 3

output/projection areas

Answer 3

(pallidum)

• ventral pallidum (limbic circuit)
• globus pallidus (internal segment) (motor association and oculomotor circuits)
• substantia nigra reticulata (motor, oculomotor, and association circuits)

Question 4

modulators

Answer 4

• globus pallidus (external segment)
• substantia nigra (midbrain)
  SN pars compacta (SNC)
• subthalamic nuclei (projection modulation, underneath thalamus)

Question 5

4 functional loops within the basal ganglia

Answer 5

Motor
Oculomotor
Executive/associative
Limbic

Question 6

motor circuit afferents/receptive/projection

Answer 6

Afferents: somatic sensory cortex, primary motor cortex, premotor and supplementary motor areas
Receptive = Putamen
Projection = Globus pallidus (GB) internus and substantia nigra (SN) reticulata, through thalamus, and back to cortex

Question 7

oculomotor circuit afferents/receptive/projection

Answer 7

Afferents = frontal eye fields and other cortical areas
Receptive = caudate nucleus
Projection = GB internus and SN reticulata,  through thalamus, and back to frontal eye fields

Question 8

executive/associative circuit circuit afferents/receptive/projection

Answer 8

Afferents = prefrontal association cortex
Receptive = caudate nucleus
Projection = GP internus and SN reticulata, through thalamus,  and back to prefrontal cortex

Question 9

limbic circuit afferents/receptive/projection

Answer 9

Afferent = limbic cortex
Receptive = nucleus accumbens
Projection = ventral pallidum, through thalamus, and back to limbic cortex

Question 10

which motor circuit cells are active (excited) at rest

Answer 10

GP and SN are active at rest

Question 11

which motor circuit cells are inactive (inhibited) at rest

Answer 11

Ventral lateral and ventral anterior nuclei of thalamus are inactive at rest

Question 12

cortical activation between a command to move with modulation present

Answer 12

• modulation pathway serves to facilitate tonic high activity of neurons in projection portion of motor circuit
• the end result will be to dampen or inhibit excessive movement
• how much inhibition is removed will depend on modulation circuit

Question 13

cortical activation between a command to move without modulation present

Answer 13

• motor-related regions of cortex become active
• neurons in receptive portion of basal ganglia are stimulated by cortical neurons
• removal of inhibition of motor cortex normally produced by neurons in projection portion of basal ganglia allows movement
• without modulation, movements produced will be excessive

Question 14

function of modulation pathway in the motor circuit that modulates the projection areas

Answer 14

it decreases excessive movement

Question 15

how does a lesion in the sub thalamic nucleus change modulation and what are the clinical signs

Answer 15

• modulation becomes impaired
• clinically, this results in a ballismus:
  severe involuntary motor disturbance
  characterized by uncontrolled, excessive, and involuntary movements
  not present at rest

Question 16

how does a lesion in the putamen that destroys cells projecting to the globus pallidus change modulation

what are the clinical signs

Answer 16

• interrupts the circuit responsible for dampening excessive activity
• this causes chorea:
  characterized by involuntary movements (often called tics) that look much like fragments of purposeful goal-directed movements
  this is somewhat different from Huntington’s Chorea, which is a hereditary and progressively degenerative disorder that can cause chorea, severe cognitive and personality changes, and movement disorders

Question 17

role of modulation produced by the substantia nigeria’s release of dopamine

Answer 17

dopamine will stimulate motor-related cortical areas to facilitate movement

Question 18

which cells release dopamine and are implicated in parkinson’s disease and where are they located

Answer 18

dopaminergic neurons located in the substantia nigra pars compacta portion of the midbrain

Question 19

when dopamine is decreased in Parkinson’s, what is the effect on the motor related cortex

Answer 19

• decreased dopamine means that the motor related cortical regions that facilitate movement are not stimulated as much
• decrease in activation of motor-related cortex in basal ganglia
• supplementary motor cortex is involved with this circuit, so patients have the most difficulty planning and executing movement to command or that are internally guided
  this is why pt’s with Parkinson’s are able to produce better movement when prompted by sensory stimuli

Question 20

s/s of Parkinson’s

Answer 20

bradykinesia – slow movement
akinesia – impairment of voluntary movement (freezing)
flat affect  or mask like expression
resting tremors
shuffling gait
dysarthria and dysphagia
rigidity
flexed, stooped posture
decreased balance reactions
dementia
depression