3: Basal Ganglia Flashcards
What is the general function of the basal ganglia? (2)
Planning and initiating movement
Regulating muscle tone and posture
Four broad generalities about the basal ganglia:
- -Where does most input come from?
- -Where does most output go to?
- -How does the basal ganglia modulate cortical activity?
- -What results form damage to the basal ganglia?
Input from CEREBRAL CORTEX
Output back to CEREBRAL CORTEX topographically
Modulation: intrinsic circuits and NT systems, esp. dopamine
Damage -> disorders of movement, also damage to other cortical functions
(OBJ) List the anatomical components of the extrapyramidal system (3 major components, 5 subdivisions).
Extrapyramidal system:
- Basal ganglia
- -Caudate and putamen nuclei (striatum)
- -Globus pallidus (with lateral and medial divisions) - Substantia nigra of midbrain
- -Pars reticulata
- -Pars compacta - Subthalamic nucleus
(OBJ) Describe the relative locations of the anatomical components of the extrapyramidal system: basal ganglia (caudate, putamen, globus pallidus), substantia nigra (pars reticulata and pars compacta), and the subthalamic nucleus.
Basal ganglia:
- -Caudate located on lateral wall of lateral ventricle
- —Long body and tail, extending from the putamen
- -Putamen lateral, separated from caudate by internal capsule
- —Putamen = body of tadpole, caudate = tail of tadpole, merged anteriorly (nucleus accumbens), then extending medially and superior, then inferior to putamen
- -Globus pallidus located directly lateral to thalamus (separated by internal capsule) and immediately medial to putamen
- —Has lateral (external) and medial (internal) divisions
Substantia nigra located in rostral midbrain
Subthalamic nucleus in caudal diencephalon, ventral to thalamus
Very briefly, what is the claustrum? (2)
A Y-shaped gray matter tract located between the putamen and the insular cortex
Possibly helps modulate rhythmic cortical activity
(OBJ) Diagram the direct pathway for information transmission through the basal ganglia and discuss its physiological role.
DIRECT = FACILITATING movement and cortical excitability
–Terminates narrowly, facilitates only those motor programs that are appropriate
- Cerebral cortex -> excitatory input to caudate/putamen
- -Substantia nigra pars compacta also -> caudate/putamen through D1 dopamine receptors - Caudate/putamen inhibit tonically active/inhibitory neurons of INTERNAL segment of globus pallidus
- Disinhibition of VA/VL of thalamus by globus pallidus -> activation of VA/VL
- VA/VL -> excitatory thalamic feedback to frontal cortex
[SUMMARY: cortex/SN -!-> C/P -x-> IS of GP -x!x-> VA/VL -!-> cortex]
What is disinhibition?
Inhibition of an inhibitory part of a circuit
Net result = facilitation
(OBJ) Diagram the indirect pathway for information transmission through the basal ganglia and discuss its physiological role.
INDIRECT = INHIBITING movement and cortical excitability
–Terminates broadly, provides an inhibitory background
- Cerebral cortex -> excitatory input to caudate/putamen
- -Substantia nigra pars compacta INHIBITS caudate/putamen through D2 dopamine receptors (OPPOSITE) - Caudate/putamen inhibit tonically active/inhibitory neurons of EXTERNAL segment of globus pallidus
- Disinhibition of subthalamic nucleus by globus pallidus -> excitement of subthalamic nucleus
- Subthalamic nucleus -> excitatory input to internal segment of globus pallidus -> inhibition of VA/VL
[SUMMARY: cortex -!-> C/P -x-> ES of GP -x!x-> subthalamic nucleus -!-> IS of GP -x-> VA/VL -x-> cortex]
(OBJ) Explain the effects of dopamine in the striatum and the implications of excess or deficiency of dopamine transmission.
Inhibits indirect pathway, facilitates direct pathway -> facilitates cortical activity
- -Loss of dopamine = inhibitory; difficulty initiating movements, slowness in performance of movements
- -Excess dopamine = excitatory; too much movement
What are the only two areas that do not make input to the striatum?
Primary visual and primary auditory cortices
Briefly, describe evidence for segregation of circuits within the basal ganglia.
Segregation: parallel circuits feedback to specific, functionally distinct areas of cortex
- -Mapping motor, premotor, supplementary motor cortices onto putamen, GP, SN, and VA/VL -> very specific/targeted regions on each
- -Each area feeds back to the same cortical region that gave it input
Briefly, describe evidence for convergence of circuits within the basal ganglia.
Massive number of cerebral cortical cells -> smaller numbers (75 mil) of striatal neurons -> even smaller numbers (0.7 mil) of globus pallidus neurons
(OBJ) Describe the MOTOR LOOP in terms of functional organization: cortical input, striatum, pallidum, thalamus, and output.
MOTOR LOOP: controls body movement
- -Input: motor, premotor, somatosensory cortex
- -Striatum: putamen
- -Pallidum: internal segment of GP
- -Thalamus: VL/VA nuclei
- -Output: primary motor, premotor, supplementary motor cortex
(OBJ) Describe the OCULOMOTOR LOOP in terms of functional organization: cortical input, striatum, pallidum, thalamus, and output.
OCULOMOTOR LOOP: controls eye movement
- -Input: posterior partietal, prefrontal cortex
- -Striatum: caudate
- -Pallidum: internal segment of GP; substantia nigra pars reticulata (-> superior colliculus)
- -Thalamus: mediodorsal, VA nuclei
- -Output: frontal eye field, supplementary eye field
(OBJ) Describe the PREFRONTAL CORTICAL LOOP in terms of functional organization: cortical input, striatum, pallidum, thalamus, and output.
PREFRONTAL CORTICAL LOOP: involved in executive functions of the brain
- -Input: dorsolateral prefrontal cortex
- -Striatum: anterior caudate
- -Pallidum: internal segment of GP; substantia nigra pars reticulata
- -Thalamus: mediodorsal, VA nuclei
- -Output: dorsolateral prefrontal cortex